Update contrib/restricted/abseil-cpp-tstring to 20220623.0

135 files changed, 4826 insertions, 2605 deletions

diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/algorithm/container.h b/contrib/restricted/abseil-cpp-tstring/y_absl/algorithm/container.h
index 3abb26f1b3..b34b4f498b 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/algorithm/container.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/algorithm/container.h
@@ -166,7 +166,7 @@ container_algorithm_internal::ContainerDifferenceType<const C> c_distance(
 // c_all_of()
 //
 // Container-based version of the <algorithm> `std::all_of()` function to
-// test a condition on all elements within a container.
+// test if all elements within a container satisfy a condition.
 template <typename C, typename Pred>
 bool c_all_of(const C& c, Pred&& pred) {
   return std::all_of(container_algorithm_internal::c_begin(c),
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/attributes.h b/contrib/restricted/abseil-cpp-tstring/y_absl/base/attributes.h
index 66751eaddf..21e64f43b3 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/attributes.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/attributes.h
@@ -136,9 +136,10 @@
 // for further information.
 // The MinGW compiler doesn't complain about the weak attribute until the link
 // step, presumably because Windows doesn't use ELF binaries.
-#if (Y_ABSL_HAVE_ATTRIBUTE(weak) ||                   \
-     (defined(__GNUC__) && !defined(__clang__))) && \
-    (!defined(_WIN32) || __clang_major__ < 9) && !defined(__MINGW32__)
+#if (Y_ABSL_HAVE_ATTRIBUTE(weak) ||                                         \
+     (defined(__GNUC__) && !defined(__clang__))) &&                       \
+    (!defined(_WIN32) || (defined(__clang__) && __clang_major__ >= 9)) && \
+    !defined(__MINGW32__)
 #undef Y_ABSL_ATTRIBUTE_WEAK
 #define Y_ABSL_ATTRIBUTE_WEAK __attribute__((weak))
 #define Y_ABSL_HAVE_ATTRIBUTE_WEAK 1
@@ -212,6 +213,9 @@
 // https://gcc.gnu.org/gcc-4.8/changes.html
 #if Y_ABSL_HAVE_ATTRIBUTE(no_sanitize_address)
 #define Y_ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS __attribute__((no_sanitize_address))
+#elif defined(_MSC_VER) && _MSC_VER >= 1928
+// https://docs.microsoft.com/en-us/cpp/cpp/no-sanitize-address
+#define Y_ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS __declspec(no_sanitize_address)
 #else
 #define Y_ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS
 #endif
@@ -311,7 +315,6 @@
   __attribute__((section(#name))) __attribute__((noinline))
 #endif
 
-
 // Y_ABSL_ATTRIBUTE_SECTION_VARIABLE
 //
 // Tells the compiler/linker to put a given variable into a section and define
@@ -338,8 +341,8 @@
 // a no-op on ELF but not on Mach-O.
 //
 #ifndef Y_ABSL_DECLARE_ATTRIBUTE_SECTION_VARS
-#define Y_ABSL_DECLARE_ATTRIBUTE_SECTION_VARS(name) \
-  extern char __start_##name[] Y_ABSL_ATTRIBUTE_WEAK;    \
+#define Y_ABSL_DECLARE_ATTRIBUTE_SECTION_VARS(name)   \
+  extern char __start_##name[] Y_ABSL_ATTRIBUTE_WEAK; \
   extern char __stop_##name[] Y_ABSL_ATTRIBUTE_WEAK
 #endif
 #ifndef Y_ABSL_DEFINE_ATTRIBUTE_SECTION_VARS
@@ -400,6 +403,9 @@
 //
 // Tells the compiler to warn about unused results.
 //
+// For code or headers that are assured to only build with C++17 and up, prefer
+// just using the standard `[[nodiscard]]` directly over this macro.
+//
 // When annotating a function, it must appear as the first part of the
 // declaration or definition. The compiler will warn if the return value from
 // such a function is unused:
@@ -426,9 +432,10 @@
 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66425
 //
 // Note: past advice was to place the macro after the argument list.
-#if Y_ABSL_HAVE_ATTRIBUTE(nodiscard)
-#define Y_ABSL_MUST_USE_RESULT [[nodiscard]]
-#elif defined(__clang__) && Y_ABSL_HAVE_ATTRIBUTE(warn_unused_result)
+//
+// TODO(b/176172494): Use Y_ABSL_HAVE_CPP_ATTRIBUTE(nodiscard) when all code is
+// compliant with the stricter [[nodiscard]].
+#if defined(__clang__) && Y_ABSL_HAVE_ATTRIBUTE(warn_unused_result)
 #define Y_ABSL_MUST_USE_RESULT __attribute__((warn_unused_result))
 #else
 #define Y_ABSL_MUST_USE_RESULT
@@ -498,7 +505,7 @@
 #define Y_ABSL_XRAY_NEVER_INSTRUMENT [[clang::xray_never_instrument]]
 #if Y_ABSL_HAVE_CPP_ATTRIBUTE(clang::xray_log_args)
 #define Y_ABSL_XRAY_LOG_ARGS(N) \
-    [[clang::xray_always_instrument, clang::xray_log_args(N)]]
+  [[clang::xray_always_instrument, clang::xray_log_args(N)]]
 #else
 #define Y_ABSL_XRAY_LOG_ARGS(N) [[clang::xray_always_instrument]]
 #endif
@@ -642,6 +649,9 @@
 // declarations. The macro argument is used as a custom diagnostic message (e.g.
 // suggestion of a better alternative).
 //
+// For code or headers that are assured to only build with C++14 and up, prefer
+// just using the standard `[[deprecated("message")]]` directly over this macro.
+//
 // Examples:
 //
 //   class Y_ABSL_DEPRECATED("Use Bar instead") Foo {...};
@@ -652,14 +662,17 @@
 //   Y_ABSL_DEPRECATED("Use DoThat() instead")
 //   void DoThis();
 //
+//   enum FooEnum {
+//     kBar Y_ABSL_DEPRECATED("Use kBaz instead"),
+//   };
+//
 // Every usage of a deprecated entity will trigger a warning when compiled with
-// clang's `-Wdeprecated-declarations` option. This option is turned off by
-// default, but the warnings will be reported by clang-tidy.
-#if defined(__clang__) && defined(__cplusplus) && __cplusplus >= 201103L
+// GCC/Clang's `-Wdeprecated-declarations` option. Google's production toolchain
+// turns this warning off by default, instead relying on clang-tidy to report
+// new uses of deprecated code.
+#if Y_ABSL_HAVE_ATTRIBUTE(deprecated)
 #define Y_ABSL_DEPRECATED(message) __attribute__((deprecated(message)))
-#endif
-
-#ifndef Y_ABSL_DEPRECATED
+#else
 #define Y_ABSL_DEPRECATED(message)
 #endif
 
@@ -669,9 +682,18 @@
 // not compile (on supported platforms) unless the variable has a constant
 // initializer. This is useful for variables with static and thread storage
 // duration, because it guarantees that they will not suffer from the so-called
-// "static init order fiasco".  Prefer to put this attribute on the most visible
-// declaration of the variable, if there's more than one, because code that
-// accesses the variable can then use the attribute for optimization.
+// "static init order fiasco".
+//
+// This attribute must be placed on the initializing declaration of the
+// variable. Some compilers will give a -Wmissing-constinit warning when this
+// attribute is placed on some other declaration but missing from the
+// initializing declaration.
+//
+// In some cases (notably with thread_local variables), `Y_ABSL_CONST_INIT` can
+// also be used in a non-initializing declaration to tell the compiler that a
+// variable is already initialized, reducing overhead that would otherwise be
+// incurred by a hidden guard variable. Thus annotating all declarations with
+// this attribute is recommended to potentially enhance optimization.
 //
 // Example:
 //
@@ -680,14 +702,19 @@
 //     Y_ABSL_CONST_INIT static MyType my_var;
 //   };
 //
-//   MyType MyClass::my_var = MakeMyType(...);
+//   Y_ABSL_CONST_INIT MyType MyClass::my_var = MakeMyType(...);
+//
+// For code or headers that are assured to only build with C++20 and up, prefer
+// just using the standard `constinit` keyword directly over this macro.
 //
 // Note that this attribute is redundant if the variable is declared constexpr.
-#if Y_ABSL_HAVE_CPP_ATTRIBUTE(clang::require_constant_initialization)
+#if defined(__cpp_constinit) && __cpp_constinit >= 201907L
+#define Y_ABSL_CONST_INIT constinit
+#elif Y_ABSL_HAVE_CPP_ATTRIBUTE(clang::require_constant_initialization)
 #define Y_ABSL_CONST_INIT [[clang::require_constant_initialization]]
 #else
 #define Y_ABSL_CONST_INIT
-#endif  // Y_ABSL_HAVE_CPP_ATTRIBUTE(clang::require_constant_initialization)
+#endif
 
 // Y_ABSL_ATTRIBUTE_PURE_FUNCTION
 //
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/casts.h b/contrib/restricted/abseil-cpp-tstring/y_absl/base/casts.h
index 4ea832f441..e78b28c53b 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/casts.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/casts.h
@@ -29,6 +29,10 @@
 #include <type_traits>
 #include <utility>
 
+#if defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L
+#include <bit>  // For std::bit_cast.
+#endif  // defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L
+
 #include "y_absl/base/internal/identity.h"
 #include "y_absl/base/macros.h"
 #include "y_absl/meta/type_traits.h"
@@ -36,19 +40,6 @@
 namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
 
-namespace internal_casts {
-
-template <class Dest, class Source>
-struct is_bitcastable
-    : std::integral_constant<
-          bool,
-          sizeof(Dest) == sizeof(Source) &&
-              type_traits_internal::is_trivially_copyable<Source>::value &&
-              type_traits_internal::is_trivially_copyable<Dest>::value &&
-              std::is_default_constructible<Dest>::value> {};
-
-}  // namespace internal_casts
-
 // implicit_cast()
 //
 // Performs an implicit conversion between types following the language
@@ -105,81 +96,83 @@ constexpr To implicit_cast(typename y_absl::internal::identity_t<To> to) {
 
 // bit_cast()
 //
-// Performs a bitwise cast on a type without changing the underlying bit
-// representation of that type's value. The two types must be of the same size
-// and both types must be trivially copyable. As with most casts, use with
-// caution. A `bit_cast()` might be needed when you need to temporarily treat a
-// type as some other type, such as in the following cases:
+// Creates a value of the new type `Dest` whose representation is the same as
+// that of the argument, which is of (deduced) type `Source` (a "bitwise cast";
+// every bit in the value representation of the result is equal to the
+// corresponding bit in the object representation of the source). Source and
+// destination types must be of the same size, and both types must be trivially
+// copyable.
 //
-//    * Serialization (casting temporarily to `char *` for those purposes is
-//      always allowed by the C++ standard)
-//    * Managing the individual bits of a type within mathematical operations
-//      that are not normally accessible through that type
-//    * Casting non-pointer types to pointer types (casting the other way is
-//      allowed by `reinterpret_cast()` but round-trips cannot occur the other
-//      way).
-//
-// Example:
+// As with most casts, use with caution. A `bit_cast()` might be needed when you
+// need to treat a value as the value of some other type, for example, to access
+// the individual bits of an object which are not normally accessible through
+// the object's type, such as for working with the binary representation of a
+// floating point value:
 //
 //   float f = 3.14159265358979;
-//   int i = bit_cast<int32_t>(f);
+//   int i = bit_cast<int>(f);
 //   // i = 0x40490fdb
 //
-// Casting non-pointer types to pointer types and then dereferencing them
-// traditionally produces undefined behavior.
+// Reinterpreting and accessing a value directly as a different type (as shown
+// below) usually results in undefined behavior.
 //
 // Example:
 //
 //   // WRONG
-//   float f = 3.14159265358979;            // WRONG
-//   int i = * reinterpret_cast<int*>(&f);  // WRONG
+//   float f = 3.14159265358979;
+//   int i = reinterpret_cast<int&>(f);    // Wrong
+//   int j = *reinterpret_cast<int*>(&f);  // Equally wrong
+//   int k = *bit_cast<int*>(&f);          // Equally wrong
 //
-// The address-casting method produces undefined behavior according to the ISO
-// C++ specification section [basic.lval]. Roughly, this section says: if an
-// object in memory has one type, and a program accesses it with a different
-// type, the result is undefined behavior for most values of "different type".
+// Reinterpret-casting results in undefined behavior according to the ISO C++
+// specification, section [basic.lval]. Roughly, this section says: if an object
+// in memory has one type, and a program accesses it with a different type, the
+// result is undefined behavior for most "different type".
+//
+// Using bit_cast on a pointer and then dereferencing it is no better than using
+// reinterpret_cast. You should only use bit_cast on the value itself.
 //
 // Such casting results in type punning: holding an object in memory of one type
 // and reading its bits back using a different type. A `bit_cast()` avoids this
-// issue by implementing its casts using `memcpy()`, which avoids introducing
-// this undefined behavior.
-//
-// NOTE: The requirements here are more strict than the bit_cast of standard
-// proposal p0476 due to the need for workarounds and lack of intrinsics.
-// Specifically, this implementation also requires `Dest` to be
-// default-constructible.
-template <
-    typename Dest, typename Source,
-    typename std::enable_if<internal_casts::is_bitcastable<Dest, Source>::value,
-                            int>::type = 0>
+// issue by copying the object representation to a new value, which avoids
+// introducing this undefined behavior (since the original value is never
+// accessed in the wrong way).
+//
+// The requirements of `y_absl::bit_cast` are more strict than that of
+// `std::bit_cast` unless compiler support is available. Specifically, without
+// compiler support, this implementation also requires `Dest` to be
+// default-constructible. In C++20, `y_absl::bit_cast` is replaced by
+// `std::bit_cast`.
+#if defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L
+
+using std::bit_cast;
+
+#else  // defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L
+
+template <typename Dest, typename Source,
+          typename std::enable_if<
+              sizeof(Dest) == sizeof(Source) &&
+                  type_traits_internal::is_trivially_copyable<Source>::value &&
+                  type_traits_internal::is_trivially_copyable<Dest>::value
+#if !Y_ABSL_HAVE_BUILTIN(__builtin_bit_cast)
+                  && std::is_default_constructible<Dest>::value
+#endif  // !Y_ABSL_HAVE_BUILTIN(__builtin_bit_cast)
+              ,
+              int>::type = 0>
+#if Y_ABSL_HAVE_BUILTIN(__builtin_bit_cast) && (!defined(__CUDACC__) || CUDA_VERSION >= 11010)
+inline constexpr Dest bit_cast(const Source& source) {
+  return __builtin_bit_cast(Dest, source);
+}
+#else  // Y_ABSL_HAVE_BUILTIN(__builtin_bit_cast)
 inline Dest bit_cast(const Source& source) {
   Dest dest;
   memcpy(static_cast<void*>(std::addressof(dest)),
          static_cast<const void*>(std::addressof(source)), sizeof(dest));
   return dest;
 }
+#endif  // Y_ABSL_HAVE_BUILTIN(__builtin_bit_cast)
 
-// NOTE: This overload is only picked if the requirements of bit_cast are
-// not met. It is therefore UB, but is provided temporarily as previous
-// versions of this function template were unchecked. Do not use this in
-// new code.
-template <
-    typename Dest, typename Source,
-    typename std::enable_if<
-        !internal_casts::is_bitcastable<Dest, Source>::value,
-        int>::type = 0>
-Y_ABSL_DEPRECATED(
-    "y_absl::bit_cast type requirements were violated. Update the types "
-    "being used such that they are the same size and are both "
-    "TriviallyCopyable.")
-inline Dest bit_cast(const Source& source) {
-  static_assert(sizeof(Dest) == sizeof(Source),
-                "Source and destination types should have equal sizes.");
-
-  Dest dest;
-  memcpy(&dest, &source, sizeof(dest));
-  return dest;
-}
+#endif  // defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L
 
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/config.h b/contrib/restricted/abseil-cpp-tstring/y_absl/base/config.h
index cb0bf305c9..334555260a 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/config.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/config.h
@@ -56,6 +56,25 @@
 #include <cstddef>
 #endif  // __cplusplus
 
+// Y_ABSL_INTERNAL_CPLUSPLUS_LANG
+//
+// MSVC does not set the value of __cplusplus correctly, but instead uses
+// _MSVC_LANG as a stand-in.
+// https://docs.microsoft.com/en-us/cpp/preprocessor/predefined-macros
+//
+// However, there are reports that MSVC even sets _MSVC_LANG incorrectly at
+// times, for example:
+// https://github.com/microsoft/vscode-cpptools/issues/1770
+// https://reviews.llvm.org/D70996
+//
+// For this reason, this symbol is considered INTERNAL and code outside of
+// Abseil must not use it.
+#if defined(_MSVC_LANG)
+#define Y_ABSL_INTERNAL_CPLUSPLUS_LANG _MSVC_LANG
+#elif defined(__cplusplus)
+#define Y_ABSL_INTERNAL_CPLUSPLUS_LANG __cplusplus
+#endif
+
 #if defined(__APPLE__)
 // Included for TARGET_OS_IPHONE, __IPHONE_OS_VERSION_MIN_REQUIRED,
 // __IPHONE_8_0.
@@ -92,7 +111,7 @@
 //
 // LTS releases can be obtained from
 // https://github.com/abseil/abseil-cpp/releases.
-#define Y_ABSL_LTS_RELEASE_VERSION 20211102
+#define Y_ABSL_LTS_RELEASE_VERSION 20220623
 #define Y_ABSL_LTS_RELEASE_PATCH_LEVEL 0
 
 // Helper macro to convert a CPP variable to a string literal.
@@ -183,12 +202,6 @@ static_assert(Y_ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
 #define Y_ABSL_HAVE_BUILTIN(x) 0
 #endif
 
-#if defined(__is_identifier)
-#define Y_ABSL_INTERNAL_HAS_KEYWORD(x) !(__is_identifier(x))
-#else
-#define Y_ABSL_INTERNAL_HAS_KEYWORD(x) 0
-#endif
-
 #ifdef __has_feature
 #define Y_ABSL_HAVE_FEATURE(f) __has_feature(f)
 #else
@@ -212,11 +225,12 @@ static_assert(Y_ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
 #endif
 
 // Y_ABSL_HAVE_TLS is defined to 1 when __thread should be supported.
-// We assume __thread is supported on Linux when compiled with Clang or compiled
-// against libstdc++ with _GLIBCXX_HAVE_TLS defined.
+// We assume __thread is supported on Linux or Asylo when compiled with Clang or
+// compiled against libstdc++ with _GLIBCXX_HAVE_TLS defined.
 #ifdef Y_ABSL_HAVE_TLS
 #error Y_ABSL_HAVE_TLS cannot be directly set
-#elif defined(__linux__) && (defined(__clang__) || defined(_GLIBCXX_HAVE_TLS))
+#elif (defined(__linux__) || defined(__ASYLO__)) && \
+    (defined(__clang__) || defined(_GLIBCXX_HAVE_TLS))
 #define Y_ABSL_HAVE_TLS 1
 #endif
 
@@ -259,19 +273,6 @@ static_assert(Y_ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
 #define Y_ABSL_HAVE_STD_IS_TRIVIALLY_ASSIGNABLE 1
 #endif
 
-// Y_ABSL_HAVE_SOURCE_LOCATION_CURRENT
-//
-// Indicates whether `y_absl::SourceLocation::current()` will return useful
-// information in some contexts.
-#ifndef Y_ABSL_HAVE_SOURCE_LOCATION_CURRENT
-#if Y_ABSL_INTERNAL_HAS_KEYWORD(__builtin_LINE) && \
-    Y_ABSL_INTERNAL_HAS_KEYWORD(__builtin_FILE)
-#define Y_ABSL_HAVE_SOURCE_LOCATION_CURRENT 1
-#elif Y_ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(5, 0)
-#define Y_ABSL_HAVE_SOURCE_LOCATION_CURRENT 1
-#endif
-#endif
-
 // Y_ABSL_HAVE_THREAD_LOCAL
 //
 // Checks whether C++11's `thread_local` storage duration specifier is
@@ -414,7 +415,8 @@ static_assert(Y_ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
     defined(_AIX) || defined(__ros__) || defined(__native_client__) ||    \
     defined(__asmjs__) || defined(__wasm__) || defined(__Fuchsia__) ||    \
     defined(__sun) || defined(__ASYLO__) || defined(__myriad2__) ||       \
-    defined(__HAIKU__)
+    defined(__HAIKU__) || defined(__OpenBSD__) || defined(__NetBSD__) ||  \
+    defined(__QNX__)
 #define Y_ABSL_HAVE_MMAP 1
 #endif
 
@@ -425,7 +427,8 @@ static_assert(Y_ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
 #ifdef Y_ABSL_HAVE_PTHREAD_GETSCHEDPARAM
 #error Y_ABSL_HAVE_PTHREAD_GETSCHEDPARAM cannot be directly set
 #elif defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__) || \
-    defined(_AIX) || defined(__ros__)
+    defined(_AIX) || defined(__ros__) || defined(__OpenBSD__) ||          \
+    defined(__NetBSD__)
 #define Y_ABSL_HAVE_PTHREAD_GETSCHEDPARAM 1
 #endif
 
@@ -520,22 +523,41 @@ static_assert(Y_ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
 #error "y_absl endian detection needs to be set up for your compiler"
 #endif
 
-// macOS 10.13 and iOS 10.11 don't let you use <any>, <optional>, or <variant>
-// even though the headers exist and are publicly noted to work.  See
-// https://github.com/abseil/abseil-cpp/issues/207 and
+// macOS < 10.13 and iOS < 11 don't let you use <any>, <optional>, or <variant>
+// even though the headers exist and are publicly noted to work, because the
+// libc++ shared library shipped on the system doesn't have the requisite
+// exported symbols.  See https://github.com/abseil/abseil-cpp/issues/207 and
 // https://developer.apple.com/documentation/xcode_release_notes/xcode_10_release_notes
+//
 // libc++ spells out the availability requirements in the file
 // llvm-project/libcxx/include/__config via the #define
 // _LIBCPP_AVAILABILITY_BAD_OPTIONAL_ACCESS.
-#if defined(__APPLE__) && defined(_LIBCPP_VERSION) && \
-  ((defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) && \
-   __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101400) || \
-  (defined(__ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__) && \
-   __ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__ < 120000) || \
-  (defined(__ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__) && \
-   __ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__ < 50000) || \
-  (defined(__ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__) && \
-   __ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__ < 120000))
+//
+// Unfortunately, Apple initially mis-stated the requirements as macOS < 10.14
+// and iOS < 12 in the libc++ headers. This was corrected by
+// https://github.com/llvm/llvm-project/commit/7fb40e1569dd66292b647f4501b85517e9247953
+// which subsequently made it into the XCode 12.5 release. We need to match the
+// old (incorrect) conditions when built with old XCode, but can use the
+// corrected earlier versions with new XCode.
+#if defined(__APPLE__) && defined(_LIBCPP_VERSION) &&               \
+    ((_LIBCPP_VERSION >= 11000 && /* XCode 12.5 or later: */        \
+      ((defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) &&   \
+        __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101300) ||  \
+       (defined(__ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__) &&  \
+        __ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__ < 110000) || \
+       (defined(__ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__) &&   \
+        __ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__ < 40000) ||   \
+       (defined(__ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__) &&      \
+        __ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__ < 110000))) ||   \
+     (_LIBCPP_VERSION < 11000 && /* Pre-XCode 12.5: */              \
+      ((defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) &&   \
+        __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101400) ||  \
+       (defined(__ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__) &&  \
+        __ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__ < 120000) || \
+       (defined(__ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__) &&   \
+        __ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__ < 50000) ||   \
+       (defined(__ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__) &&      \
+        __ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__ < 120000))))
 #define Y_ABSL_INTERNAL_APPLE_CXX17_TYPES_UNAVAILABLE 1
 #else
 #define Y_ABSL_INTERNAL_APPLE_CXX17_TYPES_UNAVAILABLE 0
@@ -700,8 +722,6 @@ static_assert(Y_ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
 #endif
 #endif
 
-#undef Y_ABSL_INTERNAL_HAS_KEYWORD
-
 // Y_ABSL_DLL
 //
 // When building Abseil as a DLL, this macro expands to `__declspec(dllexport)`
@@ -727,8 +747,6 @@ static_assert(Y_ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
 // a compiler instrumentation module and a run-time library.
 #ifdef Y_ABSL_HAVE_MEMORY_SANITIZER
 #error "Y_ABSL_HAVE_MEMORY_SANITIZER cannot be directly set."
-#elif defined(__SANITIZE_MEMORY__)
-#define Y_ABSL_HAVE_MEMORY_SANITIZER 1
 #elif !defined(__native_client__) && Y_ABSL_HAVE_FEATURE(memory_sanitizer)
 #define Y_ABSL_HAVE_MEMORY_SANITIZER 1
 #endif
@@ -755,6 +773,45 @@ static_assert(Y_ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
 #define Y_ABSL_HAVE_ADDRESS_SANITIZER 1
 #endif
 
+// Y_ABSL_HAVE_HWADDRESS_SANITIZER
+//
+// Hardware-Assisted AddressSanitizer (or HWASAN) is even faster than asan
+// memory error detector which can use CPU features like ARM TBI, Intel LAM or
+// AMD UAI.
+#ifdef Y_ABSL_HAVE_HWADDRESS_SANITIZER
+#error "Y_ABSL_HAVE_HWADDRESS_SANITIZER cannot be directly set."
+#elif defined(__SANITIZE_HWADDRESS__)
+#define Y_ABSL_HAVE_HWADDRESS_SANITIZER 1
+#elif Y_ABSL_HAVE_FEATURE(hwaddress_sanitizer)
+#define Y_ABSL_HAVE_HWADDRESS_SANITIZER 1
+#endif
+
+// Y_ABSL_HAVE_LEAK_SANITIZER
+//
+// LeakSanitizer (or lsan) is a detector of memory leaks.
+// https://clang.llvm.org/docs/LeakSanitizer.html
+// https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer
+//
+// The macro Y_ABSL_HAVE_LEAK_SANITIZER can be used to detect at compile-time
+// whether the LeakSanitizer is potentially available. However, just because the
+// LeakSanitizer is available does not mean it is active. Use the
+// always-available run-time interface in //y_absl/debugging/leak_check.h for
+// interacting with LeakSanitizer.
+#ifdef Y_ABSL_HAVE_LEAK_SANITIZER
+#error "Y_ABSL_HAVE_LEAK_SANITIZER cannot be directly set."
+#elif defined(LEAK_SANITIZER)
+// GCC provides no method for detecting the presense of the standalone
+// LeakSanitizer (-fsanitize=leak), so GCC users of -fsanitize=leak should also
+// use -DLEAK_SANITIZER.
+#define Y_ABSL_HAVE_LEAK_SANITIZER 1
+// Clang standalone LeakSanitizer (-fsanitize=leak)
+#elif Y_ABSL_HAVE_FEATURE(leak_sanitizer)
+#define Y_ABSL_HAVE_LEAK_SANITIZER 1
+#elif defined(Y_ABSL_HAVE_ADDRESS_SANITIZER)
+// GCC or Clang using the LeakSanitizer integrated into AddressSanitizer.
+#define Y_ABSL_HAVE_LEAK_SANITIZER 1
+#endif
+
 // Y_ABSL_HAVE_CLASS_TEMPLATE_ARGUMENT_DEDUCTION
 //
 // Class template argument deduction is a language feature added in C++17.
@@ -764,4 +821,88 @@ static_assert(Y_ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
 #define Y_ABSL_HAVE_CLASS_TEMPLATE_ARGUMENT_DEDUCTION 1
 #endif
 
+// Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+//
+// Prior to C++17, static constexpr variables defined in classes required a
+// separate definition outside of the class body, for example:
+//
+// class Foo {
+//   static constexpr int kBar = 0;
+// };
+// constexpr int Foo::kBar;
+//
+// In C++17, these variables defined in classes are considered inline variables,
+// and the extra declaration is redundant. Since some compilers warn on the
+// extra declarations, Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL can be used
+// conditionally ignore them:
+//
+// #ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+// constexpr int Foo::kBar;
+// #endif
+#if defined(Y_ABSL_INTERNAL_CPLUSPLUS_LANG) && \
+    Y_ABSL_INTERNAL_CPLUSPLUS_LANG < 201703L
+#define Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL 1
+#endif
+
+// `Y_ABSL_INTERNAL_HAS_RTTI` determines whether abseil is being compiled with
+// RTTI support.
+#ifdef Y_ABSL_INTERNAL_HAS_RTTI
+#error Y_ABSL_INTERNAL_HAS_RTTI cannot be directly set
+#elif !defined(__GNUC__) || defined(__GXX_RTTI)
+#define Y_ABSL_INTERNAL_HAS_RTTI 1
+#endif  // !defined(__GNUC__) || defined(__GXX_RTTI)
+
+// Y_ABSL_INTERNAL_HAVE_SSE is used for compile-time detection of SSE support.
+// See https://gcc.gnu.org/onlinedocs/gcc/x86-Options.html for an overview of
+// which architectures support the various x86 instruction sets.
+#ifdef Y_ABSL_INTERNAL_HAVE_SSE
+#error Y_ABSL_INTERNAL_HAVE_SSE cannot be directly set
+#elif defined(__SSE__)
+#define Y_ABSL_INTERNAL_HAVE_SSE 1
+#elif defined(_M_X64) || (defined(_M_IX86_FP) && _M_IX86_FP >= 1)
+// MSVC only defines _M_IX86_FP for x86 32-bit code, and _M_IX86_FP >= 1
+// indicates that at least SSE was targeted with the /arch:SSE option.
+// All x86-64 processors support SSE, so support can be assumed.
+// https://docs.microsoft.com/en-us/cpp/preprocessor/predefined-macros
+#define Y_ABSL_INTERNAL_HAVE_SSE 1
+#endif
+
+// Y_ABSL_INTERNAL_HAVE_SSE2 is used for compile-time detection of SSE2 support.
+// See https://gcc.gnu.org/onlinedocs/gcc/x86-Options.html for an overview of
+// which architectures support the various x86 instruction sets.
+#ifdef Y_ABSL_INTERNAL_HAVE_SSE2
+#error Y_ABSL_INTERNAL_HAVE_SSE2 cannot be directly set
+#elif defined(__SSE2__)
+#define Y_ABSL_INTERNAL_HAVE_SSE2 1
+#elif defined(_M_X64) || (defined(_M_IX86_FP) && _M_IX86_FP >= 2)
+// MSVC only defines _M_IX86_FP for x86 32-bit code, and _M_IX86_FP >= 2
+// indicates that at least SSE2 was targeted with the /arch:SSE2 option.
+// All x86-64 processors support SSE2, so support can be assumed.
+// https://docs.microsoft.com/en-us/cpp/preprocessor/predefined-macros
+#define Y_ABSL_INTERNAL_HAVE_SSE2 1
+#endif
+
+// Y_ABSL_INTERNAL_HAVE_SSSE3 is used for compile-time detection of SSSE3 support.
+// See https://gcc.gnu.org/onlinedocs/gcc/x86-Options.html for an overview of
+// which architectures support the various x86 instruction sets.
+//
+// MSVC does not have a mode that targets SSSE3 at compile-time. To use SSSE3
+// with MSVC requires either assuming that the code will only every run on CPUs
+// that support SSSE3, otherwise __cpuid() can be used to detect support at
+// runtime and fallback to a non-SSSE3 implementation when SSSE3 is unsupported
+// by the CPU.
+#ifdef Y_ABSL_INTERNAL_HAVE_SSSE3
+#error Y_ABSL_INTERNAL_HAVE_SSSE3 cannot be directly set
+#elif defined(__SSSE3__)
+#define Y_ABSL_INTERNAL_HAVE_SSSE3 1
+#endif
+
+// Y_ABSL_INTERNAL_HAVE_ARM_NEON is used for compile-time detection of NEON (ARM
+// SIMD).
+#ifdef Y_ABSL_INTERNAL_HAVE_ARM_NEON
+#error Y_ABSL_INTERNAL_HAVE_ARM_NEON cannot be directly set
+#elif defined(__ARM_NEON)
+#define Y_ABSL_INTERNAL_HAVE_ARM_NEON 1
+#endif
+
 #endif  // Y_ABSL_BASE_CONFIG_H_
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/cycleclock.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/cycleclock.cc
index f12104f9e4..86bceda4d4 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/cycleclock.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/cycleclock.cc
@@ -25,6 +25,8 @@
 #include <atomic>
 #include <chrono>  // NOLINT(build/c++11)
 
+#include "y_absl/base/attributes.h"
+#include "y_absl/base/config.h"
 #include "y_absl/base/internal/unscaledcycleclock.h"
 
 namespace y_absl {
@@ -33,44 +35,20 @@ namespace base_internal {
 
 #if Y_ABSL_USE_UNSCALED_CYCLECLOCK
 
-namespace {
-
-#ifdef NDEBUG
-#ifdef Y_ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY
-// Not debug mode and the UnscaledCycleClock frequency is the CPU
-// frequency.  Scale the CycleClock to prevent overflow if someone
-// tries to represent the time as cycles since the Unix epoch.
-static constexpr int32_t kShift = 1;
-#else
-// Not debug mode and the UnscaledCycleClock isn't operating at the
-// raw CPU frequency. There is no need to do any scaling, so don't
-// needlessly sacrifice precision.
-static constexpr int32_t kShift = 0;
-#endif
-#else
-// In debug mode use a different shift to discourage depending on a
-// particular shift value.
-static constexpr int32_t kShift = 2;
+#ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+constexpr int32_t CycleClock::kShift;
+constexpr double CycleClock::kFrequencyScale;
 #endif
 
-static constexpr double kFrequencyScale = 1.0 / (1 << kShift);
-static std::atomic<CycleClockSourceFunc> cycle_clock_source;
+Y_ABSL_CONST_INIT std::atomic<CycleClockSourceFunc>
+    CycleClock::cycle_clock_source_{nullptr};
 
-CycleClockSourceFunc LoadCycleClockSource() {
-  // Optimize for the common case (no callback) by first doing a relaxed load;
-  // this is significantly faster on non-x86 platforms.
-  if (cycle_clock_source.load(std::memory_order_relaxed) == nullptr) {
-    return nullptr;
-  }
-  // This corresponds to the store(std::memory_order_release) in
-  // CycleClockSource::Register, and makes sure that any updates made prior to
-  // registering the callback are visible to this thread before the callback is
-  // invoked.
-  return cycle_clock_source.load(std::memory_order_acquire);
+void CycleClockSource::Register(CycleClockSourceFunc source) {
+  // Corresponds to the load(std::memory_order_acquire) in LoadCycleClockSource.
+  CycleClock::cycle_clock_source_.store(source, std::memory_order_release);
 }
 
-}  // namespace
-
+#ifdef _WIN32
 int64_t CycleClock::Now() {
   auto fn = LoadCycleClockSource();
   if (fn == nullptr) {
@@ -78,15 +56,7 @@ int64_t CycleClock::Now() {
   }
   return fn() >> kShift;
 }
-
-double CycleClock::Frequency() {
-  return kFrequencyScale * base_internal::UnscaledCycleClock::Frequency();
-}
-
-void CycleClockSource::Register(CycleClockSourceFunc source) {
-  // Corresponds to the load(std::memory_order_acquire) in LoadCycleClockSource.
-  cycle_clock_source.store(source, std::memory_order_release);
-}
+#endif
 
 #else
 
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/cycleclock.h b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/cycleclock.h
index 9777d214da..e75b28d1ad 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/cycleclock.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/cycleclock.h
@@ -42,14 +42,19 @@
 #ifndef Y_ABSL_BASE_INTERNAL_CYCLECLOCK_H_
 #define Y_ABSL_BASE_INTERNAL_CYCLECLOCK_H_
 
+#include <atomic>
 #include <cstdint>
 
+#include "y_absl/base/attributes.h"
 #include "y_absl/base/config.h"
+#include "y_absl/base/internal/unscaledcycleclock.h"
 
 namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
 namespace base_internal {
 
+using CycleClockSourceFunc = int64_t (*)();
+
 // -----------------------------------------------------------------------------
 // CycleClock
 // -----------------------------------------------------------------------------
@@ -68,12 +73,37 @@ class CycleClock {
   static double Frequency();
 
  private:
+#if Y_ABSL_USE_UNSCALED_CYCLECLOCK
+  static CycleClockSourceFunc LoadCycleClockSource();
+
+#ifdef NDEBUG
+#ifdef Y_ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY
+  // Not debug mode and the UnscaledCycleClock frequency is the CPU
+  // frequency.  Scale the CycleClock to prevent overflow if someone
+  // tries to represent the time as cycles since the Unix epoch.
+  static constexpr int32_t kShift = 1;
+#else
+  // Not debug mode and the UnscaledCycleClock isn't operating at the
+  // raw CPU frequency. There is no need to do any scaling, so don't
+  // needlessly sacrifice precision.
+  static constexpr int32_t kShift = 0;
+#endif
+#else   // NDEBUG
+  // In debug mode use a different shift to discourage depending on a
+  // particular shift value.
+  static constexpr int32_t kShift = 2;
+#endif  // NDEBUG
+
+  static constexpr double kFrequencyScale = 1.0 / (1 << kShift);
+  Y_ABSL_CONST_INIT static std::atomic<CycleClockSourceFunc> cycle_clock_source_;
+#endif  //  Y_ABSL_USE_UNSCALED_CYCLECLOC
+
   CycleClock() = delete;  // no instances
   CycleClock(const CycleClock&) = delete;
   CycleClock& operator=(const CycleClock&) = delete;
-};
 
-using CycleClockSourceFunc = int64_t (*)();
+  friend class CycleClockSource;
+};
 
 class CycleClockSource {
  private:
@@ -87,6 +117,41 @@ class CycleClockSource {
   static void Register(CycleClockSourceFunc source);
 };
 
+#if Y_ABSL_USE_UNSCALED_CYCLECLOCK
+
+inline CycleClockSourceFunc CycleClock::LoadCycleClockSource() {
+#if !defined(__x86_64__)
+  // Optimize for the common case (no callback) by first doing a relaxed load;
+  // this is significantly faster on non-x86 platforms.
+  if (cycle_clock_source_.load(std::memory_order_relaxed) == nullptr) {
+    return nullptr;
+  }
+#endif  // !defined(__x86_64__)
+
+  // This corresponds to the store(std::memory_order_release) in
+  // CycleClockSource::Register, and makes sure that any updates made prior to
+  // registering the callback are visible to this thread before the callback
+  // is invoked.
+  return cycle_clock_source_.load(std::memory_order_acquire);
+}
+
+// Accessing globals in inlined code in Window DLLs is problematic.
+#ifndef _WIN32
+inline int64_t CycleClock::Now() {
+  auto fn = LoadCycleClockSource();
+  if (fn == nullptr) {
+    return base_internal::UnscaledCycleClock::Now() >> kShift;
+  }
+  return fn() >> kShift;
+}
+#endif
+
+inline double CycleClock::Frequency() {
+  return kFrequencyScale * base_internal::UnscaledCycleClock::Frequency();
+}
+
+#endif  // Y_ABSL_USE_UNSCALED_CYCLECLOCK
+
 }  // namespace base_internal
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/direct_mmap.h b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/direct_mmap.h
index 805ae82873..5b7750628a 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/direct_mmap.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/direct_mmap.h
@@ -20,7 +20,7 @@
 
 #include "y_absl/base/config.h"
 
-#if Y_ABSL_HAVE_MMAP
+#ifdef Y_ABSL_HAVE_MMAP
 
 #include <sys/mman.h>
 
@@ -41,13 +41,13 @@
 
 #ifdef __mips__
 // Include definitions of the ABI currently in use.
-#ifdef __BIONIC__
+#if defined(__BIONIC__) || !defined(__GLIBC__)
 // Android doesn't have sgidefs.h, but does have asm/sgidefs.h, which has the
 // definitions we need.
 #include <asm/sgidefs.h>
 #else
 #include <sgidefs.h>
-#endif  // __BIONIC__
+#endif  // __BIONIC__ || !__GLIBC__
 #endif  // __mips__
 
 // SYS_mmap and SYS_munmap are not defined in Android.
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/endian.h b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/endian.h
index d450704225..e8ac2d6c3d 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/endian.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/endian.h
@@ -16,16 +16,9 @@
 #ifndef Y_ABSL_BASE_INTERNAL_ENDIAN_H_
 #define Y_ABSL_BASE_INTERNAL_ENDIAN_H_
 
-// The following guarantees declaration of the byte swap functions
-#ifdef _MSC_VER
-#include <stdlib.h>  // NOLINT(build/include)
-#elif defined(__FreeBSD__)
-#include <sys/endian.h>
-#elif defined(__GLIBC__)
-#include <byteswap.h>  // IWYU pragma: export
-#endif
-
 #include <cstdint>
+#include <cstdlib>
+
 #include "y_absl/base/casts.h"
 #include "y_absl/base/config.h"
 #include "y_absl/base/internal/unaligned_access.h"
@@ -34,47 +27,11 @@
 namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
 
-// Use compiler byte-swapping intrinsics if they are available.  32-bit
-// and 64-bit versions are available in Clang and GCC as of GCC 4.3.0.
-// The 16-bit version is available in Clang and GCC only as of GCC 4.8.0.
-// For simplicity, we enable them all only for GCC 4.8.0 or later.
-#if defined(__clang__) || \
-    (defined(__GNUC__) && \
-     ((__GNUC__ == 4 && __GNUC_MINOR__ >= 8) || __GNUC__ >= 5))
 inline uint64_t gbswap_64(uint64_t host_int) {
+#if Y_ABSL_HAVE_BUILTIN(__builtin_bswap64) || defined(__GNUC__)
   return __builtin_bswap64(host_int);
-}
-inline uint32_t gbswap_32(uint32_t host_int) {
-  return __builtin_bswap32(host_int);
-}
-inline uint16_t gbswap_16(uint16_t host_int) {
-  return __builtin_bswap16(host_int);
-}
-
 #elif defined(_MSC_VER)
-inline uint64_t gbswap_64(uint64_t host_int) {
   return _byteswap_uint64(host_int);
-}
-inline uint32_t gbswap_32(uint32_t host_int) {
-  return _byteswap_ulong(host_int);
-}
-inline uint16_t gbswap_16(uint16_t host_int) {
-  return _byteswap_ushort(host_int);
-}
-
-#else
-inline uint64_t gbswap_64(uint64_t host_int) {
-#if defined(__GNUC__) && defined(__x86_64__) && !defined(__APPLE__)
-  // Adapted from /usr/include/byteswap.h.  Not available on Mac.
-  if (__builtin_constant_p(host_int)) {
-    return __bswap_constant_64(host_int);
-  } else {
-    uint64_t result;
-    __asm__("bswap %0" : "=r"(result) : "0"(host_int));
-    return result;
-  }
-#elif defined(__GLIBC__)
-  return bswap_64(host_int);
 #else
   return (((host_int & uint64_t{0xFF}) << 56) |
           ((host_int & uint64_t{0xFF00}) << 40) |
@@ -84,12 +41,14 @@ inline uint64_t gbswap_64(uint64_t host_int) {
           ((host_int & uint64_t{0xFF0000000000}) >> 24) |
           ((host_int & uint64_t{0xFF000000000000}) >> 40) |
           ((host_int & uint64_t{0xFF00000000000000}) >> 56));
-#endif  // bswap_64
+#endif
 }
 
 inline uint32_t gbswap_32(uint32_t host_int) {
-#if defined(__GLIBC__)
-  return bswap_32(host_int);
+#if Y_ABSL_HAVE_BUILTIN(__builtin_bswap32) || defined(__GNUC__)
+  return __builtin_bswap32(host_int);
+#elif defined(_MSC_VER)
+  return _byteswap_ulong(host_int);
 #else
   return (((host_int & uint32_t{0xFF}) << 24) |
           ((host_int & uint32_t{0xFF00}) << 8) |
@@ -99,33 +58,29 @@ inline uint32_t gbswap_32(uint32_t host_int) {
 }
 
 inline uint16_t gbswap_16(uint16_t host_int) {
-#if defined(__GLIBC__)
-  return bswap_16(host_int);
+#if Y_ABSL_HAVE_BUILTIN(__builtin_bswap16) || defined(__GNUC__)
+  return __builtin_bswap16(host_int);
+#elif defined(_MSC_VER)
+  return _byteswap_ushort(host_int);
 #else
   return (((host_int & uint16_t{0xFF}) << 8) |
           ((host_int & uint16_t{0xFF00}) >> 8));
 #endif
 }
 
-#endif  // intrinsics available
-
 #ifdef Y_ABSL_IS_LITTLE_ENDIAN
 
-// Definitions for ntohl etc. that don't require us to include
-// netinet/in.h. We wrap gbswap_32 and gbswap_16 in functions rather
-// than just #defining them because in debug mode, gcc doesn't
-// correctly handle the (rather involved) definitions of bswap_32.
-// gcc guarantees that inline functions are as fast as macros, so
-// this isn't a performance hit.
+// Portable definitions for htonl (host-to-network) and friends on little-endian
+// architectures.
 inline uint16_t ghtons(uint16_t x) { return gbswap_16(x); }
 inline uint32_t ghtonl(uint32_t x) { return gbswap_32(x); }
 inline uint64_t ghtonll(uint64_t x) { return gbswap_64(x); }
 
 #elif defined Y_ABSL_IS_BIG_ENDIAN
 
-// These definitions are simpler on big-endian machines
-// These are functions instead of macros to avoid self-assignment warnings
-// on calls such as "i = ghtnol(i);".  This also provides type checking.
+// Portable definitions for htonl (host-to-network) etc on big-endian
+// architectures. These definitions are simpler since the host byte order is the
+// same as network byte order.
 inline uint16_t ghtons(uint16_t x) { return x; }
 inline uint32_t ghtonl(uint32_t x) { return x; }
 inline uint64_t ghtonll(uint64_t x) { return x; }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/fast_type_id.h b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/fast_type_id.h
index 4fa0cf8ea6..a99371c091 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/fast_type_id.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/fast_type_id.h
@@ -28,8 +28,10 @@ struct FastTypeTag {
   constexpr static char dummy_var = 0;
 };
 
+#ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 template <typename Type>
 constexpr char FastTypeTag<Type>::dummy_var;
+#endif
 
 // FastTypeId<Type>() evaluates at compile/link-time to a unique pointer for the
 // passed-in type. These are meant to be good match for keys into maps or
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/invoke.h b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/invoke.h
index 5d5348c377..16a222ce5c 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/invoke.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/invoke.h
@@ -14,6 +14,8 @@
 //
 // y_absl::base_internal::invoke(f, args...) is an implementation of
 // INVOKE(f, args...) from section [func.require] of the C++ standard.
+// When compiled as C++17 and later versions, it is implemented as an alias of
+// std::invoke.
 //
 // [func.require]
 // Define INVOKE (f, t1, t2, ..., tN) as follows:
@@ -35,6 +37,26 @@
 #ifndef Y_ABSL_BASE_INTERNAL_INVOKE_H_
 #define Y_ABSL_BASE_INTERNAL_INVOKE_H_
 
+#include "y_absl/base/config.h"
+
+#if Y_ABSL_INTERNAL_CPLUSPLUS_LANG >= 201703L
+
+#include <functional>
+
+namespace y_absl {
+Y_ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+using std::invoke;
+using std::invoke_result_t;
+using std::is_invocable_r;
+
+}  // namespace base_internal
+Y_ABSL_NAMESPACE_END
+}  // namespace y_absl
+
+#else  // Y_ABSL_INTERNAL_CPLUSPLUS_LANG >= 201703L
+
 #include <algorithm>
 #include <type_traits>
 #include <utility>
@@ -80,8 +102,18 @@ struct MemFunAndRef : StrippedAccept<MemFunAndRef> {
   static decltype((std::declval<Obj>().*
                    std::declval<MemFun>())(std::declval<Args>()...))
   Invoke(MemFun&& mem_fun, Obj&& obj, Args&&... args) {
+// Ignore bogus GCC warnings on this line.
+// See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101436 for similar example.
+#if Y_ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(11, 0)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Warray-bounds"
+#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
     return (std::forward<Obj>(obj).*
             std::forward<MemFun>(mem_fun))(std::forward<Args>(args)...);
+#if Y_ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(11, 0)
+#pragma GCC diagnostic pop
+#endif
   }
 };
 
@@ -180,8 +212,30 @@ invoke_result_t<F, Args...> invoke(F&& f, Args&&... args) {
   return Invoker<F, Args...>::type::Invoke(std::forward<F>(f),
                                            std::forward<Args>(args)...);
 }
+
+template <typename AlwaysVoid, typename, typename, typename...>
+struct IsInvocableRImpl : std::false_type {};
+
+template <typename R, typename F, typename... Args>
+struct IsInvocableRImpl<
+    y_absl::void_t<y_absl::base_internal::invoke_result_t<F, Args...> >, R, F,
+    Args...>
+    : std::integral_constant<
+          bool,
+          std::is_convertible<y_absl::base_internal::invoke_result_t<F, Args...>,
+                              R>::value ||
+              std::is_void<R>::value> {};
+
+// Type trait whose member `value` is true if invoking `F` with `Args` is valid,
+// and either the return type is convertible to `R`, or `R` is void.
+// C++11-compatible version of `std::is_invocable_r`.
+template <typename R, typename F, typename... Args>
+using is_invocable_r = IsInvocableRImpl<void, R, F, Args...>;
+
 }  // namespace base_internal
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
 
+#endif  // Y_ABSL_INTERNAL_CPLUSPLUS_LANG >= 201703L
+
 #endif  // Y_ABSL_BASE_INTERNAL_INVOKE_H_
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/prefetch.h b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/prefetch.h
new file mode 100644
index 0000000000..0c9c358570
--- /dev/null
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/prefetch.h
@@ -0,0 +1,138 @@
+// Copyright 2022 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef Y_ABSL_BASE_INTERNAL_PREFETCH_H_
+#define Y_ABSL_BASE_INTERNAL_PREFETCH_H_
+
+#include "y_absl/base/config.h"
+
+#ifdef __SSE__
+#include <xmmintrin.h>
+#endif
+
+#if defined(_MSC_VER) && defined(Y_ABSL_INTERNAL_HAVE_SSE)
+#include <intrin.h>
+#pragma intrinsic(_mm_prefetch)
+#endif
+
+// Compatibility wrappers around __builtin_prefetch, to prefetch data
+// for read if supported by the toolchain.
+
+// Move data into the cache before it is read, or "prefetch" it.
+//
+// The value of `addr` is the address of the memory to prefetch. If
+// the target and compiler support it, data prefetch instructions are
+// generated. If the prefetch is done some time before the memory is
+// read, it may be in the cache by the time the read occurs.
+//
+// The function names specify the temporal locality heuristic applied,
+// using the names of Intel prefetch instructions:
+//
+//   T0 - high degree of temporal locality; data should be left in as
+//        many levels of the cache possible
+//   T1 - moderate degree of temporal locality
+//   T2 - low degree of temporal locality
+//   Nta - no temporal locality, data need not be left in the cache
+//         after the read
+//
+// Incorrect or gratuitous use of these functions can degrade
+// performance, so use them only when representative benchmarks show
+// an improvement.
+//
+// Example usage:
+//
+//   y_absl::base_internal::PrefetchT0(addr);
+//
+// Currently, the different prefetch calls behave on some Intel
+// architectures as follows:
+//
+//                 SNB..SKL   SKX
+// PrefetchT0()   L1/L2/L3  L1/L2
+// PrefetchT1()      L2/L3     L2
+// PrefetchT2()      L2/L3     L2
+// PrefetchNta()  L1/--/L3  L1*
+//
+// * On SKX PrefetchNta() will bring the line into L1 but will evict
+//   from L3 cache. This might result in surprising behavior.
+//
+// SNB = Sandy Bridge, SKL = Skylake, SKX = Skylake Xeon.
+//
+namespace y_absl {
+Y_ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+void PrefetchT0(const void* addr);
+void PrefetchT1(const void* addr);
+void PrefetchT2(const void* addr);
+void PrefetchNta(const void* addr);
+
+// Implementation details follow.
+
+#if Y_ABSL_HAVE_BUILTIN(__builtin_prefetch) || defined(__GNUC__)
+
+#define Y_ABSL_INTERNAL_HAVE_PREFETCH 1
+
+// See __builtin_prefetch:
+// https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html.
+//
+// These functions speculatively load for read only. This is
+// safe for all currently supported platforms. However, prefetch for
+// store may have problems depending on the target platform.
+//
+inline void PrefetchT0(const void* addr) {
+  // Note: this uses prefetcht0 on Intel.
+  __builtin_prefetch(addr, 0, 3);
+}
+inline void PrefetchT1(const void* addr) {
+  // Note: this uses prefetcht1 on Intel.
+  __builtin_prefetch(addr, 0, 2);
+}
+inline void PrefetchT2(const void* addr) {
+  // Note: this uses prefetcht2 on Intel.
+  __builtin_prefetch(addr, 0, 1);
+}
+inline void PrefetchNta(const void* addr) {
+  // Note: this uses prefetchtnta on Intel.
+  __builtin_prefetch(addr, 0, 0);
+}
+
+#elif defined(Y_ABSL_INTERNAL_HAVE_SSE)
+
+#define Y_ABSL_INTERNAL_HAVE_PREFETCH 1
+
+inline void PrefetchT0(const void* addr) {
+  _mm_prefetch(reinterpret_cast<const char*>(addr), _MM_HINT_T0);
+}
+inline void PrefetchT1(const void* addr) {
+  _mm_prefetch(reinterpret_cast<const char*>(addr), _MM_HINT_T1);
+}
+inline void PrefetchT2(const void* addr) {
+  _mm_prefetch(reinterpret_cast<const char*>(addr), _MM_HINT_T2);
+}
+inline void PrefetchNta(const void* addr) {
+  _mm_prefetch(reinterpret_cast<const char*>(addr), _MM_HINT_NTA);
+}
+
+#else
+inline void PrefetchT0(const void*) {}
+inline void PrefetchT1(const void*) {}
+inline void PrefetchT2(const void*) {}
+inline void PrefetchNta(const void*) {}
+#endif
+
+}  // namespace base_internal
+Y_ABSL_NAMESPACE_END
+}  // namespace y_absl
+
+#endif  // Y_ABSL_BASE_INTERNAL_PREFETCH_H_
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/raw_logging.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/raw_logging.cc
index 75af4543d5..1a5a18f804 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/raw_logging.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/raw_logging.cc
@@ -14,15 +14,17 @@
 
 #include "y_absl/base/internal/raw_logging.h"
 
-#include <stddef.h>
 #include <cstdarg>
+#include <cstddef>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
+#include <util/generic/string.h>
 
 #include "y_absl/base/attributes.h"
 #include "y_absl/base/config.h"
 #include "y_absl/base/internal/atomic_hook.h"
+#include "y_absl/base/internal/errno_saver.h"
 #include "y_absl/base/log_severity.h"
 
 // We know how to perform low-level writes to stderr in POSIX and Windows.  For
@@ -36,8 +38,8 @@
 // This preprocessor token is also defined in raw_io.cc.  If you need to copy
 // this, consider moving both to config.h instead.
 #if defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__) || \
-    defined(__Fuchsia__) || defined(__native_client__) || \
-    defined(__EMSCRIPTEN__) || defined(__ASYLO__)
+    defined(__Fuchsia__) || defined(__native_client__) ||               \
+    defined(__OpenBSD__) || defined(__EMSCRIPTEN__) || defined(__ASYLO__)
 
 #include <unistd.h>
 
@@ -50,7 +52,8 @@
 // Y_ABSL_HAVE_SYSCALL_WRITE is defined when the platform provides the syscall
 //   syscall(SYS_write, /*int*/ fd, /*char* */ buf, /*size_t*/ len);
 // for low level operations that want to avoid libc.
-#if (defined(__linux__) || defined(__FreeBSD__)) && !defined(__ANDROID__)
+#if (defined(__linux__) || defined(__FreeBSD__) || defined(__OpenBSD__)) && \
+    !defined(__ANDROID__)
 #include <sys/syscall.h>
 #define Y_ABSL_HAVE_SYSCALL_WRITE 1
 #define Y_ABSL_LOW_LEVEL_WRITE_SUPPORTED 1
@@ -76,13 +79,6 @@ namespace {
 // Explicitly `#error` out when not `Y_ABSL_LOW_LEVEL_WRITE_SUPPORTED`, except for
 // a selected set of platforms for which we expect not to be able to raw log.
 
-Y_ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES
-    y_absl::base_internal::AtomicHook<LogPrefixHook>
-        log_prefix_hook;
-Y_ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES
-    y_absl::base_internal::AtomicHook<AbortHook>
-        abort_hook;
-
 #ifdef Y_ABSL_LOW_LEVEL_WRITE_SUPPORTED
 constexpr char kTruncated[] = " ... (message truncated)\n";
 
@@ -130,6 +126,18 @@ bool DoRawLog(char** buf, int* size, const char* format, ...) {
   return true;
 }
 
+bool DefaultLogFilterAndPrefix(y_absl::LogSeverity, const char* file, int line,
+                               char** buf, int* buf_size) {
+  DoRawLog(buf, buf_size, "[%s : %d] RAW: ", file, line);
+  return true;
+}
+
+Y_ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES
+y_absl::base_internal::AtomicHook<LogFilterAndPrefixHook>
+    log_filter_and_prefix_hook(DefaultLogFilterAndPrefix);
+Y_ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES
+y_absl::base_internal::AtomicHook<AbortHook> abort_hook;
+
 void RawLogVA(y_absl::LogSeverity severity, const char* file, int line,
               const char* format, va_list ap) Y_ABSL_PRINTF_ATTRIBUTE(4, 0);
 void RawLogVA(y_absl::LogSeverity severity, const char* file, int line,
@@ -150,14 +158,7 @@ void RawLogVA(y_absl::LogSeverity severity, const char* file, int line,
   }
 #endif
 
-  auto log_prefix_hook_ptr = log_prefix_hook.Load();
-  if (log_prefix_hook_ptr) {
-    enabled = log_prefix_hook_ptr(severity, file, line, &buf, &size);
-  } else {
-    if (enabled) {
-      DoRawLog(&buf, &size, "[%s : %d] RAW: ", file, line);
-    }
-  }
+  enabled = log_filter_and_prefix_hook(severity, file, line, &buf, &size);
   const char* const prefix_end = buf;
 
 #ifdef Y_ABSL_LOW_LEVEL_WRITE_SUPPORTED
@@ -168,11 +169,12 @@ void RawLogVA(y_absl::LogSeverity severity, const char* file, int line,
     } else {
       DoRawLog(&buf, &size, "%s", kTruncated);
     }
-    SafeWriteToStderr(buffer, strlen(buffer));
+    AsyncSignalSafeWriteToStderr(buffer, strlen(buffer));
   }
 #else
   static_cast<void>(format);
   static_cast<void>(ap);
+  static_cast<void>(enabled);
 #endif
 
   // Abort the process after logging a FATAL message, even if the output itself
@@ -195,8 +197,11 @@ void DefaultInternalLog(y_absl::LogSeverity severity, const char* file, int line
 
 }  // namespace
 
-void SafeWriteToStderr(const char *s, size_t len) {
+void AsyncSignalSafeWriteToStderr(const char* s, size_t len) {
+  y_absl::base_internal::ErrnoSaver errno_saver;
 #if defined(Y_ABSL_HAVE_SYSCALL_WRITE)
+  // We prefer calling write via `syscall` to minimize the risk of libc doing
+  // something "helpful".
   syscall(SYS_write, STDERR_FILENO, s, len);
 #elif defined(Y_ABSL_HAVE_POSIX_WRITE)
   write(STDERR_FILENO, s, len);
@@ -229,7 +234,9 @@ Y_ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES Y_ABSL_DLL
     y_absl::base_internal::AtomicHook<InternalLogFunction>
         internal_log_function(DefaultInternalLog);
 
-void RegisterLogPrefixHook(LogPrefixHook func) { log_prefix_hook.Store(func); }
+void RegisterLogFilterAndPrefixHook(LogFilterAndPrefixHook func) {
+  log_filter_and_prefix_hook.Store(func);
+}
 
 void RegisterAbortHook(AbortHook func) { abort_hook.Store(func); }
 
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/raw_logging.h b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/raw_logging.h
index 8febc13fc3..56cb5dc363 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/raw_logging.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/raw_logging.h
@@ -109,12 +109,9 @@ namespace raw_logging_internal {
 void RawLog(y_absl::LogSeverity severity, const char* file, int line,
             const char* format, ...) Y_ABSL_PRINTF_ATTRIBUTE(4, 5);
 
-// Writes the provided buffer directly to stderr, in a safe, low-level manner.
-//
-// In POSIX this means calling write(), which is async-signal safe and does
-// not malloc.  If the platform supports the SYS_write syscall, we invoke that
-// directly to side-step any libc interception.
-void SafeWriteToStderr(const char *s, size_t len);
+// Writes the provided buffer directly to stderr, in a signal-safe, low-level
+// manner.
+void AsyncSignalSafeWriteToStderr(const char* s, size_t len);
 
 // compile-time function to get the "base" filename, that is, the part of
 // a filename after the last "/" or "\" path separator.  The search starts at
@@ -148,11 +145,12 @@ bool RawLoggingFullySupported();
 // 'severity' is the severity level of the message being written.
 // 'file' and 'line' are the file and line number where the Y_ABSL_RAW_LOG macro
 // was located.
-// 'buffer' and 'buf_size' are pointers to the buffer and buffer size.  If the
-// hook writes a prefix, it must increment *buffer and decrement *buf_size
+// 'buf' and 'buf_size' are pointers to the buffer and buffer size.  If the
+// hook writes a prefix, it must increment *buf and decrement *buf_size
 // accordingly.
-using LogPrefixHook = bool (*)(y_absl::LogSeverity severity, const char* file,
-                               int line, char** buffer, int* buf_size);
+using LogFilterAndPrefixHook = bool (*)(y_absl::LogSeverity severity,
+                                        const char* file, int line, char** buf,
+                                        int* buf_size);
 
 // Function type for a raw_logging customization hook called to abort a process
 // when a FATAL message is logged.  If the provided AbortHook() returns, the
@@ -162,7 +160,10 @@ using LogPrefixHook = bool (*)(y_absl::LogSeverity severity, const char* file,
 // was located.
 // The NUL-terminated logged message lives in the buffer between 'buf_start'
 // and 'buf_end'.  'prefix_end' points to the first non-prefix character of the
-// buffer (as written by the LogPrefixHook.)
+// buffer (as written by the LogFilterAndPrefixHook.)
+//
+// The lifetime of the filename and message buffers will not end while the
+// process remains alive.
 using AbortHook = void (*)(const char* file, int line, const char* buf_start,
                            const char* prefix_end, const char* buf_end);
 
@@ -184,7 +185,7 @@ Y_ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES Y_ABSL_DLL extern base_internal::AtomicHo
 //
 // These functions are safe to call at any point during initialization; they do
 // not block or malloc, and are async-signal safe.
-void RegisterLogPrefixHook(LogPrefixHook func);
+void RegisterLogFilterAndPrefixHook(LogFilterAndPrefixHook func);
 void RegisterAbortHook(AbortHook func);
 void RegisterInternalLogFunction(InternalLogFunction func);
 
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/spinlock.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/spinlock.cc
index efffecdb7e..aaa8b3c156 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/spinlock.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/spinlock.cc
@@ -19,6 +19,7 @@
 #include <limits>
 
 #include "y_absl/base/attributes.h"
+#include "y_absl/base/config.h"
 #include "y_absl/base/internal/atomic_hook.h"
 #include "y_absl/base/internal/cycleclock.h"
 #include "y_absl/base/internal/spinlock_wait.h"
@@ -66,12 +67,14 @@ void RegisterSpinLockProfiler(void (*fn)(const void *contendedlock,
   submit_profile_data.Store(fn);
 }
 
+#ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 // Static member variable definitions.
 constexpr uint32_t SpinLock::kSpinLockHeld;
 constexpr uint32_t SpinLock::kSpinLockCooperative;
 constexpr uint32_t SpinLock::kSpinLockDisabledScheduling;
 constexpr uint32_t SpinLock::kSpinLockSleeper;
 constexpr uint32_t SpinLock::kWaitTimeMask;
+#endif
 
 // Uncommon constructors.
 SpinLock::SpinLock(base_internal::SchedulingMode mode)
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/spinlock.h b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/spinlock.h
index a570699d68..67bbbabdca 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/spinlock.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/spinlock.h
@@ -120,6 +120,14 @@ class Y_ABSL_LOCKABLE SpinLock {
     return (lockword_.load(std::memory_order_relaxed) & kSpinLockHeld) != 0;
   }
 
+  // Return immediately if this thread holds the SpinLock exclusively.
+  // Otherwise, report an error by crashing with a diagnostic.
+  inline void AssertHeld() const Y_ABSL_ASSERT_EXCLUSIVE_LOCK() {
+    if (!IsHeld()) {
+      Y_ABSL_RAW_LOG(FATAL, "thread should hold the lock on SpinLock");
+    }
+  }
+
  protected:
   // These should not be exported except for testing.
 
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/spinlock_linux.inc b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/spinlock_linux.inc
index 5d2bbbcd15..dc654ab6e1 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/spinlock_linux.inc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/spinlock_linux.inc
@@ -57,13 +57,10 @@ static_assert(sizeof(std::atomic<uint32_t>) == sizeof(int),
 extern "C" {
 
 Y_ABSL_ATTRIBUTE_WEAK void Y_ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay)(
-    std::atomic<uint32_t> *w, uint32_t value, int loop,
+    std::atomic<uint32_t> *w, uint32_t value, int,
     y_absl::base_internal::SchedulingMode) {
   y_absl::base_internal::ErrnoSaver errno_saver;
-  struct timespec tm;
-  tm.tv_sec = 0;
-  tm.tv_nsec = y_absl::base_internal::SpinLockSuggestedDelayNS(loop);
-  syscall(SYS_futex, w, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, value, &tm);
+  syscall(SYS_futex, w, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, value, nullptr);
 }
 
 Y_ABSL_ATTRIBUTE_WEAK void Y_ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockWake)(
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/sysinfo.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/sysinfo.cc
index 6a1ef60711..25b6a005bb 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/sysinfo.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/sysinfo.cc
@@ -124,7 +124,6 @@ int Win32NumCPUs() {
 
 }  // namespace
 
-
 static int GetNumCPUs() {
 #if defined(__myriad2__)
   return 1;
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/thread_identity.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/thread_identity.cc
index 9e67f0b964..7f5c39a7d1 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/thread_identity.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/thread_identity.cc
@@ -14,7 +14,7 @@
 
 #include "y_absl/base/internal/thread_identity.h"
 
-#ifndef _WIN32
+#if !defined(_WIN32) || defined(__MINGW32__)
 #include <pthread.h>
 #include <signal.h>
 #endif
@@ -56,6 +56,7 @@ void AllocateThreadIdentityKey(ThreadIdentityReclaimerFunction reclaimer) {
 // *different* instances of this ptr.
 // Apple platforms have the visibility attribute, but issue a compile warning
 // that protected visibility is unsupported.
+Y_ABSL_CONST_INIT  // Must come before __attribute__((visibility("protected")))
 #if Y_ABSL_HAVE_ATTRIBUTE(visibility) && !defined(__APPLE__)
 __attribute__((visibility("protected")))
 #endif  // Y_ABSL_HAVE_ATTRIBUTE(visibility) && !defined(__APPLE__)
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/unscaledcycleclock.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/unscaledcycleclock.cc
index dcbcb0c24d..4f959fadef 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/unscaledcycleclock.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/unscaledcycleclock.cc
@@ -24,8 +24,13 @@
 #ifdef __GLIBC__
 #include <sys/platform/ppc.h>
 #elif defined(__FreeBSD__)
-#include <sys/sysctl.h>
+// clang-format off
+// This order does actually matter =(.
 #include <sys/types.h>
+#include <sys/sysctl.h>
+// clang-format on
+
+#include "y_absl/base/call_once.h"
 #endif
 #endif
 
@@ -49,12 +54,6 @@ double UnscaledCycleClock::Frequency() {
 
 #elif defined(__x86_64__)
 
-int64_t UnscaledCycleClock::Now() {
-  uint64_t low, high;
-  __asm__ volatile("rdtsc" : "=a"(low), "=d"(high));
-  return (high << 32) | low;
-}
-
 double UnscaledCycleClock::Frequency() {
   return base_internal::NominalCPUFrequency();
 }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/unscaledcycleclock.h b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/unscaledcycleclock.h
index fd82752f78..15ee5e4434 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/unscaledcycleclock.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/internal/unscaledcycleclock.h
@@ -47,7 +47,7 @@
 // The following platforms have an implementation of a hardware counter.
 #if defined(__i386__) || defined(__x86_64__) || defined(__aarch64__) || \
     defined(__powerpc__) || defined(__ppc__) || defined(__riscv) ||     \
-    defined(_M_IX86) || defined(_M_X64)
+    defined(_M_IX86) || (defined(_M_X64) && !defined(_M_ARM64EC))
 #define Y_ABSL_HAVE_UNSCALED_CYCLECLOCK_IMPLEMENTATION 1
 #else
 #define Y_ABSL_HAVE_UNSCALED_CYCLECLOCK_IMPLEMENTATION 0
@@ -59,8 +59,7 @@
 // CycleClock that runs at atleast 1 MHz. We've found some Android
 // ARM64 devices where this is not the case, so we disable it by
 // default on Android ARM64.
-#if defined(__native_client__) ||                      \
-    (defined(TARGET_OS_IPHONE) && TARGET_OS_IPHONE) || \
+#if defined(__native_client__) || (defined(__APPLE__)) || \
     (defined(__ANDROID__) && defined(__aarch64__))
 #define Y_ABSL_USE_UNSCALED_CYCLECLOCK_DEFAULT 0
 #else
@@ -115,6 +114,16 @@ class UnscaledCycleClock {
   friend class base_internal::UnscaledCycleClockWrapperForInitializeFrequency;
 };
 
+#if defined(__x86_64__)
+
+inline int64_t UnscaledCycleClock::Now() {
+  uint64_t low, high;
+  __asm__ volatile("rdtsc" : "=a"(low), "=d"(high));
+  return (high << 32) | low;
+}
+
+#endif
+
 }  // namespace base_internal
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/log_severity.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/base/log_severity.cc
index 3212ba04c9..890fa4eb6a 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/log_severity.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/log_severity.cc
@@ -16,6 +16,8 @@
 
 #include <ostream>
 
+#include "y_absl/base/attributes.h"
+
 namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
 
@@ -23,5 +25,31 @@ std::ostream& operator<<(std::ostream& os, y_absl::LogSeverity s) {
   if (s == y_absl::NormalizeLogSeverity(s)) return os << y_absl::LogSeverityName(s);
   return os << "y_absl::LogSeverity(" << static_cast<int>(s) << ")";
 }
+
+std::ostream& operator<<(std::ostream& os, y_absl::LogSeverityAtLeast s) {
+  switch (s) {
+    case y_absl::LogSeverityAtLeast::kInfo:
+    case y_absl::LogSeverityAtLeast::kWarning:
+    case y_absl::LogSeverityAtLeast::kError:
+    case y_absl::LogSeverityAtLeast::kFatal:
+      return os << ">=" << static_cast<y_absl::LogSeverity>(s);
+    case y_absl::LogSeverityAtLeast::kInfinity:
+      return os << "INFINITY";
+  }
+  return os;
+}
+
+std::ostream& operator<<(std::ostream& os, y_absl::LogSeverityAtMost s) {
+  switch (s) {
+    case y_absl::LogSeverityAtMost::kInfo:
+    case y_absl::LogSeverityAtMost::kWarning:
+    case y_absl::LogSeverityAtMost::kError:
+    case y_absl::LogSeverityAtMost::kFatal:
+      return os << "<=" << static_cast<y_absl::LogSeverity>(s);
+    case y_absl::LogSeverityAtMost::kNegativeInfinity:
+      return os << "NEGATIVE_INFINITY";
+  }
+  return os;
+}
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/log_severity.h b/contrib/restricted/abseil-cpp-tstring/y_absl/base/log_severity.h
index 07ee164f45..1fc55e8223 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/log_severity.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/log_severity.h
@@ -115,6 +115,57 @@ constexpr y_absl::LogSeverity NormalizeLogSeverity(int s) {
 // unspecified; do not rely on it.
 std::ostream& operator<<(std::ostream& os, y_absl::LogSeverity s);
 
+// Enums representing a lower bound for LogSeverity. APIs that only operate on
+// messages of at least a certain level (for example, `SetMinLogLevel()`) use
+// this type to specify that level. y_absl::LogSeverityAtLeast::kInfinity is
+// a level above all threshold levels and therefore no log message will
+// ever meet this threshold.
+enum class LogSeverityAtLeast : int {
+  kInfo = static_cast<int>(y_absl::LogSeverity::kInfo),
+  kWarning = static_cast<int>(y_absl::LogSeverity::kWarning),
+  kError = static_cast<int>(y_absl::LogSeverity::kError),
+  kFatal = static_cast<int>(y_absl::LogSeverity::kFatal),
+  kInfinity = 1000,
+};
+
+std::ostream& operator<<(std::ostream& os, y_absl::LogSeverityAtLeast s);
+
+// Enums representing an upper bound for LogSeverity. APIs that only operate on
+// messages of at most a certain level (for example, buffer all messages at or
+// below a certain level) use this type to specify that level.
+// y_absl::LogSeverityAtMost::kNegativeInfinity is a level below all threshold
+// levels and therefore will exclude all log messages.
+enum class LogSeverityAtMost : int {
+  kNegativeInfinity = -1000,
+  kInfo = static_cast<int>(y_absl::LogSeverity::kInfo),
+  kWarning = static_cast<int>(y_absl::LogSeverity::kWarning),
+  kError = static_cast<int>(y_absl::LogSeverity::kError),
+  kFatal = static_cast<int>(y_absl::LogSeverity::kFatal),
+};
+
+std::ostream& operator<<(std::ostream& os, y_absl::LogSeverityAtMost s);
+
+#define COMPOP(op1, op2, T)                                         \
+  constexpr bool operator op1(y_absl::T lhs, y_absl::LogSeverity rhs) { \
+    return static_cast<y_absl::LogSeverity>(lhs) op1 rhs;             \
+  }                                                                 \
+  constexpr bool operator op2(y_absl::LogSeverity lhs, y_absl::T rhs) { \
+    return lhs op2 static_cast<y_absl::LogSeverity>(rhs);             \
+  }
+
+// Comparisons between `LogSeverity` and `LogSeverityAtLeast`/
+// `LogSeverityAtMost` are only supported in one direction.
+// Valid checks are:
+//   LogSeverity >= LogSeverityAtLeast
+//   LogSeverity < LogSeverityAtLeast
+//   LogSeverity <= LogSeverityAtMost
+//   LogSeverity > LogSeverityAtMost
+COMPOP(>, <, LogSeverityAtLeast)
+COMPOP(<=, >=, LogSeverityAtLeast)
+COMPOP(<, >, LogSeverityAtMost)
+COMPOP(>=, <=, LogSeverityAtMost)
+#undef COMPOP
+
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
 
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/optimization.h b/contrib/restricted/abseil-cpp-tstring/y_absl/base/optimization.h
index 72cf6ef8a2..024b5c163c 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/optimization.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/optimization.h
@@ -181,35 +181,43 @@
 #define Y_ABSL_PREDICT_TRUE(x) (x)
 #endif
 
-// Y_ABSL_INTERNAL_ASSUME(cond)
+// Y_ABSL_ASSUME(cond)
+//
 // Informs the compiler that a condition is always true and that it can assume
-// it to be true for optimization purposes. The call has undefined behavior if
-// the condition is false.
+// it to be true for optimization purposes.
+//
+// WARNING: If the condition is false, the program can produce undefined and
+// potentially dangerous behavior.
+//
 // In !NDEBUG mode, the condition is checked with an assert().
-// NOTE: The expression must not have side effects, as it will only be evaluated
-// in some compilation modes and not others.
+//
+// NOTE: The expression must not have side effects, as it may only be evaluated
+// in some compilation modes and not others. Some compilers may issue a warning
+// if the compiler cannot prove the expression has no side effects. For example,
+// the expression should not use a function call since the compiler cannot prove
+// that a function call does not have side effects.
 //
 // Example:
 //
 //   int x = ...;
-//   Y_ABSL_INTERNAL_ASSUME(x >= 0);
+//   Y_ABSL_ASSUME(x >= 0);
 //   // The compiler can optimize the division to a simple right shift using the
 //   // assumption specified above.
 //   int y = x / 16;
 //
 #if !defined(NDEBUG)
-#define Y_ABSL_INTERNAL_ASSUME(cond) assert(cond)
+#define Y_ABSL_ASSUME(cond) assert(cond)
 #elif Y_ABSL_HAVE_BUILTIN(__builtin_assume)
-#define Y_ABSL_INTERNAL_ASSUME(cond) __builtin_assume(cond)
+#define Y_ABSL_ASSUME(cond) __builtin_assume(cond)
 #elif defined(__GNUC__) || Y_ABSL_HAVE_BUILTIN(__builtin_unreachable)
-#define Y_ABSL_INTERNAL_ASSUME(cond)        \
+#define Y_ABSL_ASSUME(cond)                 \
   do {                                    \
     if (!(cond)) __builtin_unreachable(); \
   } while (0)
 #elif defined(_MSC_VER)
-#define Y_ABSL_INTERNAL_ASSUME(cond) __assume(cond)
+#define Y_ABSL_ASSUME(cond) __assume(cond)
 #else
-#define Y_ABSL_INTERNAL_ASSUME(cond)      \
+#define Y_ABSL_ASSUME(cond)               \
   do {                                  \
     static_cast<void>(false && (cond)); \
   } while (0)
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/options.h b/contrib/restricted/abseil-cpp-tstring/y_absl/base/options.h
index 05f05f9410..40601c2bee 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/options.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/options.h
@@ -206,7 +206,7 @@
 // allowed.
 
 #define Y_ABSL_OPTION_USE_INLINE_NAMESPACE 1
-#define Y_ABSL_OPTION_INLINE_NAMESPACE_NAME lts_y_20211102
+#define Y_ABSL_OPTION_INLINE_NAMESPACE_NAME lts_y_20220623
 
 // Y_ABSL_OPTION_HARDENED
 //
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/base/thread_annotations.h b/contrib/restricted/abseil-cpp-tstring/y_absl/base/thread_annotations.h
index 25427b419a..864784143c 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/base/thread_annotations.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/base/thread_annotations.h
@@ -154,8 +154,8 @@
 
 // Y_ABSL_LOCKS_EXCLUDED()
 //
-// Documents the locks acquired in the body of the function. These locks
-// cannot be held when calling this function (as Abseil's `Mutex` locks are
+// Documents the locks that cannot be held by callers of this function, as they
+// might be acquired by this function (Abseil's `Mutex` locks are
 // non-reentrant).
 #if Y_ABSL_HAVE_ATTRIBUTE(locks_excluded)
 #define Y_ABSL_LOCKS_EXCLUDED(...) __attribute__((locks_excluded(__VA_ARGS__)))
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/container/fixed_array.h b/contrib/restricted/abseil-cpp-tstring/y_absl/container/fixed_array.h
index 8fb4c679dc..94c69145fa 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/container/fixed_array.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/container/fixed_array.h
@@ -489,12 +489,14 @@ class FixedArray {
   Storage storage_;
 };
 
+#ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 template <typename T, size_t N, typename A>
 constexpr size_t FixedArray<T, N, A>::kInlineBytesDefault;
 
 template <typename T, size_t N, typename A>
 constexpr typename FixedArray<T, N, A>::size_type
     FixedArray<T, N, A>::inline_elements;
+#endif
 
 template <typename T, size_t N, typename A>
 void FixedArray<T, N, A>::NonEmptyInlinedStorage::AnnotateConstruct(
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/container/flat_hash_map.h b/contrib/restricted/abseil-cpp-tstring/y_absl/container/flat_hash_map.h
index 71f49b0bbe..e3d24a077e 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/container/flat_hash_map.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/container/flat_hash_map.h
@@ -36,6 +36,7 @@
 #include <utility>
 
 #include "y_absl/algorithm/container.h"
+#include "y_absl/base/macros.h"
 #include "y_absl/container/internal/container_memory.h"
 #include "y_absl/container/internal/hash_function_defaults.h"  // IWYU pragma: export
 #include "y_absl/container/internal/raw_hash_map.h"  // IWYU pragma: export
@@ -75,6 +76,10 @@ struct FlatHashMapPolicy;
 // y_absl/hash/hash.h for information on extending Abseil hashing to user-defined
 // types.
 //
+// Using `y_absl::flat_hash_map` at interface boundaries in dynamically loaded
+// libraries (e.g. .dll, .so) is unsupported due to way `y_absl::Hash` values may
+// be randomized across dynamically loaded libraries.
+//
 // NOTE: A `flat_hash_map` stores its value types directly inside its
 // implementation array to avoid memory indirection. Because a `flat_hash_map`
 // is designed to move data when rehashed, map values will not retain pointer
@@ -356,8 +361,8 @@ class flat_hash_map : public y_absl::container_internal::raw_hash_map<
   // `flat_hash_map`.
   //
   //   iterator try_emplace(const_iterator hint,
-  //                        const init_type& k, Args&&... args):
-  //   iterator try_emplace(const_iterator hint, init_type&& k, Args&&... args):
+  //                        const key_type& k, Args&&... args):
+  //   iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args):
   //
   // Inserts (via copy or move) the element of the specified key into the
   // `flat_hash_map` using the position of `hint` as a non-binding suggestion
@@ -541,10 +546,12 @@ class flat_hash_map : public y_absl::container_internal::raw_hash_map<
 // erase_if(flat_hash_map<>, Pred)
 //
 // Erases all elements that satisfy the predicate `pred` from the container `c`.
+// Returns the number of erased elements.
 template <typename K, typename V, typename H, typename E, typename A,
           typename Predicate>
-void erase_if(flat_hash_map<K, V, H, E, A>& c, Predicate pred) {
-  container_internal::EraseIf(pred, &c);
+typename flat_hash_map<K, V, H, E, A>::size_type erase_if(
+    flat_hash_map<K, V, H, E, A>& c, Predicate pred) {
+  return container_internal::EraseIf(pred, &c);
 }
 
 namespace container_internal {
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/container/inlined_vector.h b/contrib/restricted/abseil-cpp-tstring/y_absl/container/inlined_vector.h
index b91b1fb11d..fd5d07019a 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/container/inlined_vector.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/container/inlined_vector.h
@@ -36,7 +36,6 @@
 #define Y_ABSL_CONTAINER_INLINED_VECTOR_H_
 
 #include <algorithm>
-#include <cassert>
 #include <cstddef>
 #include <cstdlib>
 #include <cstring>
@@ -152,7 +151,7 @@ class InlinedVector {
                 const allocator_type& allocator = allocator_type())
       : storage_(allocator) {
     storage_.Initialize(IteratorValueAdapter<A, ForwardIterator>(first),
-                        std::distance(first, last));
+                        static_cast<size_t>(std::distance(first, last)));
   }
 
   // Creates an inlined vector with elements constructed from the provided input
@@ -233,8 +232,8 @@ class InlinedVector {
   // specified allocator is also `noexcept`.
   InlinedVector(
       InlinedVector&& other,
-      const allocator_type& allocator)
-      noexcept(y_absl::allocator_is_nothrow<allocator_type>::value)
+      const allocator_type&
+          allocator) noexcept(y_absl::allocator_is_nothrow<allocator_type>::value)
       : storage_(allocator) {
     if (IsMemcpyOk<A>::value) {
       storage_.MemcpyFrom(other.storage_);
@@ -486,8 +485,8 @@ class InlinedVector {
   InlinedVector& operator=(InlinedVector&& other) {
     if (Y_ABSL_PREDICT_TRUE(this != std::addressof(other))) {
       if (IsMemcpyOk<A>::value || other.storage_.GetIsAllocated()) {
-        inlined_vector_internal::DestroyElements<A>(storage_.GetAllocator(),
-                                                    data(), size());
+        inlined_vector_internal::DestroyAdapter<A>::DestroyElements(
+            storage_.GetAllocator(), data(), size());
         storage_.DeallocateIfAllocated();
         storage_.MemcpyFrom(other.storage_);
 
@@ -523,7 +522,7 @@ class InlinedVector {
             EnableIfAtLeastForwardIterator<ForwardIterator> = 0>
   void assign(ForwardIterator first, ForwardIterator last) {
     storage_.Assign(IteratorValueAdapter<A, ForwardIterator>(first),
-                    std::distance(first, last));
+                    static_cast<size_t>(std::distance(first, last)));
   }
 
   // Overload of `InlinedVector::assign(...)` to replace the contents of the
@@ -586,8 +585,20 @@ class InlinedVector {
 
     if (Y_ABSL_PREDICT_TRUE(n != 0)) {
       value_type dealias = v;
+      // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102329#c2
+      // It appears that GCC thinks that since `pos` is a const pointer and may
+      // point to uninitialized memory at this point, a warning should be
+      // issued. But `pos` is actually only used to compute an array index to
+      // write to.
+#if !defined(__clang__) && defined(__GNUC__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
       return storage_.Insert(pos, CopyValueAdapter<A>(std::addressof(dealias)),
                              n);
+#if !defined(__clang__) && defined(__GNUC__)
+#pragma GCC diagnostic pop
+#endif
     } else {
       return const_cast<iterator>(pos);
     }
@@ -721,8 +732,8 @@ class InlinedVector {
   // Destroys all elements in the inlined vector, setting the size to `0` and
   // deallocating any held memory.
   void clear() noexcept {
-    inlined_vector_internal::DestroyElements<A>(storage_.GetAllocator(), data(),
-                                                size());
+    inlined_vector_internal::DestroyAdapter<A>::DestroyElements(
+        storage_.GetAllocator(), data(), size());
     storage_.DeallocateIfAllocated();
 
     storage_.SetInlinedSize(0);
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/common.h b/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/common.h
index 6c7369e67b..c32dbd8179 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/common.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/common.h
@@ -84,10 +84,11 @@ class node_handle_base {
     PolicyTraits::transfer(alloc(), slot(), s);
   }
 
-  struct move_tag_t {};
-  node_handle_base(move_tag_t, const allocator_type& a, slot_type* s)
+  struct construct_tag_t {};
+  template <typename... Args>
+  node_handle_base(construct_tag_t, const allocator_type& a, Args&&... args)
       : alloc_(a) {
-    PolicyTraits::construct(alloc(), slot(), s);
+    PolicyTraits::construct(alloc(), slot(), std::forward<Args>(args)...);
   }
 
   void destroy() {
@@ -186,8 +187,8 @@ struct CommonAccess {
   }
 
   template <typename T, typename... Args>
-  static T Move(Args&&... args) {
-    return T(typename T::move_tag_t{}, std::forward<Args>(args)...);
+  static T Construct(Args&&... args) {
+    return T(typename T::construct_tag_t{}, std::forward<Args>(args)...);
   }
 };
 
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/container_memory.h b/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/container_memory.h
index 90d35184ab..d40cf7531c 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/container_memory.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/container_memory.h
@@ -174,7 +174,7 @@ decltype(std::declval<F>()(std::declval<T>())) WithConstructed(
 //
 // 2. auto a = PairArgs(args...);
 //    std::pair<F, S> p(std::piecewise_construct,
-//                      std::move(p.first), std::move(p.second));
+//                      std::move(a.first), std::move(a.second));
 inline std::pair<std::tuple<>, std::tuple<>> PairArgs() { return {}; }
 template <class F, class S>
 std::pair<std::tuple<F&&>, std::tuple<S&&>> PairArgs(F&& f, S&& s) {
@@ -402,6 +402,15 @@ struct map_slot_policy {
     }
   }
 
+  // Construct this slot by copying from another slot.
+  template <class Allocator>
+  static void construct(Allocator* alloc, slot_type* slot,
+                        const slot_type* other) {
+    emplace(slot);
+    y_absl::allocator_traits<Allocator>::construct(*alloc, &slot->value,
+                                                 other->value);
+  }
+
   template <class Allocator>
   static void destroy(Allocator* alloc, slot_type* slot) {
     if (kMutableKeys::value) {
@@ -424,33 +433,6 @@ struct map_slot_policy {
     }
     destroy(alloc, old_slot);
   }
-
-  template <class Allocator>
-  static void swap(Allocator* alloc, slot_type* a, slot_type* b) {
-    if (kMutableKeys::value) {
-      using std::swap;
-      swap(a->mutable_value, b->mutable_value);
-    } else {
-      value_type tmp = std::move(a->value);
-      y_absl::allocator_traits<Allocator>::destroy(*alloc, &a->value);
-      y_absl::allocator_traits<Allocator>::construct(*alloc, &a->value,
-                                                   std::move(b->value));
-      y_absl::allocator_traits<Allocator>::destroy(*alloc, &b->value);
-      y_absl::allocator_traits<Allocator>::construct(*alloc, &b->value,
-                                                   std::move(tmp));
-    }
-  }
-
-  template <class Allocator>
-  static void move(Allocator* alloc, slot_type* src, slot_type* dest) {
-    if (kMutableKeys::value) {
-      dest->mutable_value = std::move(src->mutable_value);
-    } else {
-      y_absl::allocator_traits<Allocator>::destroy(*alloc, &dest->value);
-      y_absl::allocator_traits<Allocator>::construct(*alloc, &dest->value,
-                                                   std::move(src->value));
-    }
-  }
 };
 
 }  // namespace container_internal
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/hashtablez_sampler.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/hashtablez_sampler.cc
index 51235fd9be..36816872fd 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/hashtablez_sampler.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/hashtablez_sampler.cc
@@ -21,33 +21,43 @@
 #include <limits>
 
 #include "y_absl/base/attributes.h"
-#include "y_absl/container/internal/have_sse.h"
+#include "y_absl/base/config.h"
 #include "y_absl/debugging/stacktrace.h"
 #include "y_absl/memory/memory.h"
 #include "y_absl/profiling/internal/exponential_biased.h"
 #include "y_absl/profiling/internal/sample_recorder.h"
 #include "y_absl/synchronization/mutex.h"
+#include "y_absl/utility/utility.h"
 
 namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
 namespace container_internal {
+
+#ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 constexpr int HashtablezInfo::kMaxStackDepth;
+#endif
 
 namespace {
 Y_ABSL_CONST_INIT std::atomic<bool> g_hashtablez_enabled{
     false
 };
 Y_ABSL_CONST_INIT std::atomic<int32_t> g_hashtablez_sample_parameter{1 << 10};
+std::atomic<HashtablezConfigListener> g_hashtablez_config_listener{nullptr};
 
 #if defined(Y_ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
 Y_ABSL_PER_THREAD_TLS_KEYWORD y_absl::profiling_internal::ExponentialBiased
     g_exponential_biased_generator;
 #endif
 
+void TriggerHashtablezConfigListener() {
+  auto* listener = g_hashtablez_config_listener.load(std::memory_order_acquire);
+  if (listener != nullptr) listener();
+}
+
 }  // namespace
 
 #if defined(Y_ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
-Y_ABSL_PER_THREAD_TLS_KEYWORD int64_t global_next_sample = 0;
+Y_ABSL_PER_THREAD_TLS_KEYWORD SamplingState global_next_sample = {0, 0};
 #endif  // defined(Y_ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
 
 HashtablezSampler& GlobalHashtablezSampler() {
@@ -55,13 +65,11 @@ HashtablezSampler& GlobalHashtablezSampler() {
   return *sampler;
 }
 
-// TODO(bradleybear): The comments at this constructors declaration say that the
-// fields are not initialized, but this definition does initialize the fields.
-// Something needs to be cleaned up.
-HashtablezInfo::HashtablezInfo() { PrepareForSampling(); }
+HashtablezInfo::HashtablezInfo() = default;
 HashtablezInfo::~HashtablezInfo() = default;
 
-void HashtablezInfo::PrepareForSampling() {
+void HashtablezInfo::PrepareForSampling(int64_t stride,
+                                        size_t inline_element_size_value) {
   capacity.store(0, std::memory_order_relaxed);
   size.store(0, std::memory_order_relaxed);
   num_erases.store(0, std::memory_order_relaxed);
@@ -74,11 +82,13 @@ void HashtablezInfo::PrepareForSampling() {
   max_reserve.store(0, std::memory_order_relaxed);
 
   create_time = y_absl::Now();
+  weight = stride;
   // The inliner makes hardcoded skip_count difficult (especially when combined
   // with LTO).  We use the ability to exclude stacks by regex when encoding
   // instead.
   depth = y_absl::GetStackTrace(stack, HashtablezInfo::kMaxStackDepth,
                               /* skip_count= */ 0);
+  inline_element_size = inline_element_size_value;
 }
 
 static bool ShouldForceSampling() {
@@ -101,23 +111,32 @@ static bool ShouldForceSampling() {
   return state == kForce;
 }
 
-HashtablezInfo* SampleSlow(int64_t* next_sample, size_t inline_element_size) {
+HashtablezInfo* SampleSlow(SamplingState& next_sample,
+                           size_t inline_element_size) {
   if (Y_ABSL_PREDICT_FALSE(ShouldForceSampling())) {
-    *next_sample = 1;
-    HashtablezInfo* result = GlobalHashtablezSampler().Register();
-    result->inline_element_size = inline_element_size;
+    next_sample.next_sample = 1;
+    const int64_t old_stride = exchange(next_sample.sample_stride, 1);
+    HashtablezInfo* result =
+        GlobalHashtablezSampler().Register(old_stride, inline_element_size);
     return result;
   }
 
 #if !defined(Y_ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
-  *next_sample = std::numeric_limits<int64_t>::max();
+  next_sample = {
+      std::numeric_limits<int64_t>::max(),
+      std::numeric_limits<int64_t>::max(),
+  };
   return nullptr;
 #else
-  bool first = *next_sample < 0;
-  *next_sample = g_exponential_biased_generator.GetStride(
+  bool first = next_sample.next_sample < 0;
+
+  const int64_t next_stride = g_exponential_biased_generator.GetStride(
       g_hashtablez_sample_parameter.load(std::memory_order_relaxed));
+
+  next_sample.next_sample = next_stride;
+  const int64_t old_stride = exchange(next_sample.sample_stride, next_stride);
   // Small values of interval are equivalent to just sampling next time.
-  Y_ABSL_ASSERT(*next_sample >= 1);
+  Y_ABSL_ASSERT(next_stride >= 1);
 
   // g_hashtablez_enabled can be dynamically flipped, we need to set a threshold
   // low enough that we will start sampling in a reasonable time, so we just use
@@ -127,13 +146,11 @@ HashtablezInfo* SampleSlow(int64_t* next_sample, size_t inline_element_size) {
   // We will only be negative on our first count, so we should just retry in
   // that case.
   if (first) {
-    if (Y_ABSL_PREDICT_TRUE(--*next_sample > 0)) return nullptr;
+    if (Y_ABSL_PREDICT_TRUE(--next_sample.next_sample > 0)) return nullptr;
     return SampleSlow(next_sample, inline_element_size);
   }
 
-  HashtablezInfo* result = GlobalHashtablezSampler().Register();
-  result->inline_element_size = inline_element_size;
-  return result;
+  return GlobalHashtablezSampler().Register(old_stride, inline_element_size);
 #endif
 }
 
@@ -146,7 +163,7 @@ void RecordInsertSlow(HashtablezInfo* info, size_t hash,
   // SwissTables probe in groups of 16, so scale this to count items probes and
   // not offset from desired.
   size_t probe_length = distance_from_desired;
-#if Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
+#ifdef Y_ABSL_INTERNAL_HAVE_SSE2
   probe_length /= 16;
 #else
   probe_length /= 8;
@@ -163,11 +180,33 @@ void RecordInsertSlow(HashtablezInfo* info, size_t hash,
   info->size.fetch_add(1, std::memory_order_relaxed);
 }
 
+void SetHashtablezConfigListener(HashtablezConfigListener l) {
+  g_hashtablez_config_listener.store(l, std::memory_order_release);
+}
+
+bool IsHashtablezEnabled() {
+  return g_hashtablez_enabled.load(std::memory_order_acquire);
+}
+
 void SetHashtablezEnabled(bool enabled) {
+  SetHashtablezEnabledInternal(enabled);
+  TriggerHashtablezConfigListener();
+}
+
+void SetHashtablezEnabledInternal(bool enabled) {
   g_hashtablez_enabled.store(enabled, std::memory_order_release);
 }
 
+int32_t GetHashtablezSampleParameter() {
+  return g_hashtablez_sample_parameter.load(std::memory_order_acquire);
+}
+
 void SetHashtablezSampleParameter(int32_t rate) {
+  SetHashtablezSampleParameterInternal(rate);
+  TriggerHashtablezConfigListener();
+}
+
+void SetHashtablezSampleParameterInternal(int32_t rate) {
   if (rate > 0) {
     g_hashtablez_sample_parameter.store(rate, std::memory_order_release);
   } else {
@@ -176,7 +215,16 @@ void SetHashtablezSampleParameter(int32_t rate) {
   }
 }
 
+int32_t GetHashtablezMaxSamples() {
+  return GlobalHashtablezSampler().GetMaxSamples();
+}
+
 void SetHashtablezMaxSamples(int32_t max) {
+  SetHashtablezMaxSamplesInternal(max);
+  TriggerHashtablezConfigListener();
+}
+
+void SetHashtablezMaxSamplesInternal(int32_t max) {
   if (max > 0) {
     GlobalHashtablezSampler().SetMaxSamples(max);
   } else {
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/hashtablez_sampler.h b/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/hashtablez_sampler.h
index 3f600deea0..fefa2bb9f0 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/hashtablez_sampler.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/hashtablez_sampler.h
@@ -44,9 +44,9 @@
 #include <memory>
 #include <vector>
 
+#include "y_absl/base/config.h"
 #include "y_absl/base/internal/per_thread_tls.h"
 #include "y_absl/base/optimization.h"
-#include "y_absl/container/internal/have_sse.h"
 #include "y_absl/profiling/internal/sample_recorder.h"
 #include "y_absl/synchronization/mutex.h"
 #include "y_absl/utility/utility.h"
@@ -67,7 +67,8 @@ struct HashtablezInfo : public profiling_internal::Sample<HashtablezInfo> {
 
   // Puts the object into a clean state, fills in the logically `const` members,
   // blocking for any readers that are currently sampling the object.
-  void PrepareForSampling() Y_ABSL_EXCLUSIVE_LOCKS_REQUIRED(init_mu);
+  void PrepareForSampling(int64_t stride, size_t inline_element_size_value)
+      Y_ABSL_EXCLUSIVE_LOCKS_REQUIRED(init_mu);
 
   // These fields are mutated by the various Record* APIs and need to be
   // thread-safe.
@@ -84,18 +85,18 @@ struct HashtablezInfo : public profiling_internal::Sample<HashtablezInfo> {
 
   // All of the fields below are set by `PrepareForSampling`, they must not be
   // mutated in `Record*` functions.  They are logically `const` in that sense.
-  // These are guarded by init_mu, but that is not externalized to clients, who
-  // can only read them during `HashtablezSampler::Iterate` which will hold the
-  // lock.
+  // These are guarded by init_mu, but that is not externalized to clients,
+  // which can read them only during `SampleRecorder::Iterate` which will hold
+  // the lock.
   static constexpr int kMaxStackDepth = 64;
   y_absl::Time create_time;
   int32_t depth;
   void* stack[kMaxStackDepth];
-  size_t inline_element_size;
+  size_t inline_element_size;  // How big is the slot?
 };
 
 inline void RecordRehashSlow(HashtablezInfo* info, size_t total_probe_length) {
-#if Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
+#ifdef Y_ABSL_INTERNAL_HAVE_SSE2
   total_probe_length /= 16;
 #else
   total_probe_length /= 8;
@@ -144,7 +145,15 @@ inline void RecordEraseSlow(HashtablezInfo* info) {
       std::memory_order_relaxed);
 }
 
-HashtablezInfo* SampleSlow(int64_t* next_sample, size_t inline_element_size);
+struct SamplingState {
+  int64_t next_sample;
+  // When we make a sampling decision, we record that distance so we can weight
+  // each sample.
+  int64_t sample_stride;
+};
+
+HashtablezInfo* SampleSlow(SamplingState& next_sample,
+                           size_t inline_element_size);
 void UnsampleSlow(HashtablezInfo* info);
 
 #if defined(Y_ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
@@ -234,7 +243,7 @@ class HashtablezInfoHandle {
 #endif  // defined(Y_ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
 
 #if defined(Y_ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
-extern Y_ABSL_PER_THREAD_TLS_KEYWORD int64_t global_next_sample;
+extern Y_ABSL_PER_THREAD_TLS_KEYWORD SamplingState global_next_sample;
 #endif  // defined(Y_ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
 
 // Returns an RAII sampling handle that manages registration and unregistation
@@ -242,11 +251,11 @@ extern Y_ABSL_PER_THREAD_TLS_KEYWORD int64_t global_next_sample;
 inline HashtablezInfoHandle Sample(
     size_t inline_element_size Y_ABSL_ATTRIBUTE_UNUSED) {
 #if defined(Y_ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
-  if (Y_ABSL_PREDICT_TRUE(--global_next_sample > 0)) {
+  if (Y_ABSL_PREDICT_TRUE(--global_next_sample.next_sample > 0)) {
     return HashtablezInfoHandle(nullptr);
   }
   return HashtablezInfoHandle(
-      SampleSlow(&global_next_sample, inline_element_size));
+      SampleSlow(global_next_sample, inline_element_size));
 #else
   return HashtablezInfoHandle(nullptr);
 #endif  // !Y_ABSL_PER_THREAD_TLS
@@ -258,14 +267,23 @@ using HashtablezSampler =
 // Returns a global Sampler.
 HashtablezSampler& GlobalHashtablezSampler();
 
+using HashtablezConfigListener = void (*)();
+void SetHashtablezConfigListener(HashtablezConfigListener l);
+
 // Enables or disables sampling for Swiss tables.
+bool IsHashtablezEnabled();
 void SetHashtablezEnabled(bool enabled);
+void SetHashtablezEnabledInternal(bool enabled);
 
 // Sets the rate at which Swiss tables will be sampled.
+int32_t GetHashtablezSampleParameter();
 void SetHashtablezSampleParameter(int32_t rate);
+void SetHashtablezSampleParameterInternal(int32_t rate);
 
 // Sets a soft max for the number of samples that will be kept.
+int32_t GetHashtablezMaxSamples();
 void SetHashtablezMaxSamples(int32_t max);
+void SetHashtablezMaxSamplesInternal(int32_t max);
 
 // Configuration override.
 // This allows process-wide sampling without depending on order of
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/have_sse.h b/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/have_sse.h
deleted file mode 100644
index d89f632a45..0000000000
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/have_sse.h
+++ /dev/null
@@ -1,50 +0,0 @@
-// Copyright 2018 The Abseil Authors.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//      https://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-//
-// Shared config probing for SSE instructions used in Swiss tables.
-#ifndef Y_ABSL_CONTAINER_INTERNAL_HAVE_SSE_H_
-#define Y_ABSL_CONTAINER_INTERNAL_HAVE_SSE_H_
-
-#ifndef Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
-#if defined(__SSE2__) ||  \
-    (defined(_MSC_VER) && \
-     (defined(_M_X64) || (defined(_M_IX86) && _M_IX86_FP >= 2)))
-#define Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2 1
-#else
-#define Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2 0
-#endif
-#endif
-
-#ifndef Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSSE3
-#ifdef __SSSE3__
-#define Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSSE3 1
-#else
-#define Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSSE3 0
-#endif
-#endif
-
-#if Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSSE3 && \
-    !Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
-#error "Bad configuration!"
-#endif
-
-#if Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
-#include <emmintrin.h>
-#endif
-
-#if Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSSE3
-#include <tmmintrin.h>
-#endif
-
-#endif  // Y_ABSL_CONTAINER_INTERNAL_HAVE_SSE_H_
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/inlined_vector.h b/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/inlined_vector.h
index 9c8b3858af..047dd99882 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/inlined_vector.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/inlined_vector.h
@@ -40,7 +40,6 @@ namespace inlined_vector_internal {
 #if !defined(__clang__) && defined(__GNUC__)
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Warray-bounds"
-#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
 #endif
 
 template <typename A>
@@ -94,16 +93,30 @@ struct TypeIdentity {
 template <typename T>
 using NoTypeDeduction = typename TypeIdentity<T>::type;
 
+template <typename A, bool IsTriviallyDestructible =
+                          y_absl::is_trivially_destructible<ValueType<A>>::value>
+struct DestroyAdapter;
+
 template <typename A>
-void DestroyElements(NoTypeDeduction<A>& allocator, Pointer<A> destroy_first,
-                     SizeType<A> destroy_size) {
-  if (destroy_first != nullptr) {
+struct DestroyAdapter<A, /* IsTriviallyDestructible */ false> {
+  static void DestroyElements(A& allocator, Pointer<A> destroy_first,
+                              SizeType<A> destroy_size) {
     for (SizeType<A> i = destroy_size; i != 0;) {
       --i;
       AllocatorTraits<A>::destroy(allocator, destroy_first + i);
     }
   }
-}
+};
+
+template <typename A>
+struct DestroyAdapter<A, /* IsTriviallyDestructible */ true> {
+  static void DestroyElements(A& allocator, Pointer<A> destroy_first,
+                              SizeType<A> destroy_size) {
+    static_cast<void>(allocator);
+    static_cast<void>(destroy_first);
+    static_cast<void>(destroy_size);
+  }
+};
 
 template <typename A>
 struct Allocation {
@@ -133,7 +146,7 @@ void ConstructElements(NoTypeDeduction<A>& allocator,
   for (SizeType<A> i = 0; i < construct_size; ++i) {
     Y_ABSL_INTERNAL_TRY { values.ConstructNext(allocator, construct_first + i); }
     Y_ABSL_INTERNAL_CATCH_ANY {
-      DestroyElements<A>(allocator, construct_first, i);
+      DestroyAdapter<A>::DestroyElements(allocator, construct_first, i);
       Y_ABSL_INTERNAL_RETHROW;
     }
   }
@@ -253,7 +266,7 @@ class ConstructionTransaction {
 
   ~ConstructionTransaction() {
     if (DidConstruct()) {
-      DestroyElements<A>(GetAllocator(), GetData(), GetSize());
+      DestroyAdapter<A>::DestroyElements(GetAllocator(), GetData(), GetSize());
     }
   }
 
@@ -297,10 +310,10 @@ class Storage {
   // Storage Constructors and Destructor
   // ---------------------------------------------------------------------------
 
-  Storage() : metadata_(A(), /* size and is_allocated */ 0) {}
+  Storage() : metadata_(A(), /* size and is_allocated */ 0u) {}
 
   explicit Storage(const A& allocator)
-      : metadata_(allocator, /* size and is_allocated */ 0) {}
+      : metadata_(allocator, /* size and is_allocated */ 0u) {}
 
   ~Storage() {
     if (GetSizeAndIsAllocated() == 0) {
@@ -416,7 +429,7 @@ class Storage {
   }
 
   void SubtractSize(SizeType<A> count) {
-    assert(count <= GetSize());
+    Y_ABSL_HARDENING_ASSERT(count <= GetSize());
 
     GetSizeAndIsAllocated() -= count << static_cast<SizeType<A>>(1);
   }
@@ -427,7 +440,8 @@ class Storage {
   }
 
   void MemcpyFrom(const Storage& other_storage) {
-    assert(IsMemcpyOk<A>::value || other_storage.GetIsAllocated());
+    Y_ABSL_HARDENING_ASSERT(IsMemcpyOk<A>::value ||
+                          other_storage.GetIsAllocated());
 
     GetSizeAndIsAllocated() = other_storage.GetSizeAndIsAllocated();
     data_ = other_storage.data_;
@@ -469,14 +483,14 @@ class Storage {
 template <typename T, size_t N, typename A>
 void Storage<T, N, A>::DestroyContents() {
   Pointer<A> data = GetIsAllocated() ? GetAllocatedData() : GetInlinedData();
-  DestroyElements<A>(GetAllocator(), data, GetSize());
+  DestroyAdapter<A>::DestroyElements(GetAllocator(), data, GetSize());
   DeallocateIfAllocated();
 }
 
 template <typename T, size_t N, typename A>
 void Storage<T, N, A>::InitFrom(const Storage& other) {
   const SizeType<A> n = other.GetSize();
-  assert(n > 0);  // Empty sources handled handled in caller.
+  Y_ABSL_HARDENING_ASSERT(n > 0);  // Empty sources handled handled in caller.
   ConstPointer<A> src;
   Pointer<A> dst;
   if (!other.GetIsAllocated()) {
@@ -508,8 +522,8 @@ template <typename ValueAdapter>
 auto Storage<T, N, A>::Initialize(ValueAdapter values, SizeType<A> new_size)
     -> void {
   // Only callable from constructors!
-  assert(!GetIsAllocated());
-  assert(GetSize() == 0);
+  Y_ABSL_HARDENING_ASSERT(!GetIsAllocated());
+  Y_ABSL_HARDENING_ASSERT(GetSize() == 0);
 
   Pointer<A> construct_data;
   if (new_size > GetInlinedCapacity()) {
@@ -566,7 +580,8 @@ auto Storage<T, N, A>::Assign(ValueAdapter values, SizeType<A> new_size)
   ConstructElements<A>(GetAllocator(), construct_loop.data(), values,
                        construct_loop.size());
 
-  DestroyElements<A>(GetAllocator(), destroy_loop.data(), destroy_loop.size());
+  DestroyAdapter<A>::DestroyElements(GetAllocator(), destroy_loop.data(),
+                                     destroy_loop.size());
 
   if (allocation_tx.DidAllocate()) {
     DeallocateIfAllocated();
@@ -587,7 +602,7 @@ auto Storage<T, N, A>::Resize(ValueAdapter values, SizeType<A> new_size)
   A& alloc = GetAllocator();
   if (new_size <= size) {
     // Destroy extra old elements.
-    DestroyElements<A>(alloc, base + new_size, size - new_size);
+    DestroyAdapter<A>::DestroyElements(alloc, base + new_size, size - new_size);
   } else if (new_size <= storage_view.capacity) {
     // Construct new elements in place.
     ConstructElements<A>(alloc, base + size, values, new_size - size);
@@ -595,7 +610,7 @@ auto Storage<T, N, A>::Resize(ValueAdapter values, SizeType<A> new_size)
     // Steps:
     //  a. Allocate new backing store.
     //  b. Construct new elements in new backing store.
-    //  c. Move existing elements from old backing store to now.
+    //  c. Move existing elements from old backing store to new backing store.
     //  d. Destroy all elements in old backing store.
     // Use transactional wrappers for the first two steps so we can roll
     // back if necessary due to exceptions.
@@ -611,7 +626,7 @@ auto Storage<T, N, A>::Resize(ValueAdapter values, SizeType<A> new_size)
         (MoveIterator<A>(base)));
     ConstructElements<A>(alloc, new_data, move_values, size);
 
-    DestroyElements<A>(alloc, base, size);
+    DestroyAdapter<A>::DestroyElements(alloc, base, size);
     std::move(construction_tx).Commit();
     DeallocateIfAllocated();
     SetAllocation(std::move(allocation_tx).Release());
@@ -650,7 +665,8 @@ auto Storage<T, N, A>::Insert(ConstIterator<A> pos, ValueAdapter values,
     ConstructElements<A>(GetAllocator(), new_data + insert_end_index,
                          move_values, storage_view.size - insert_index);
 
-    DestroyElements<A>(GetAllocator(), storage_view.data, storage_view.size);
+    DestroyAdapter<A>::DestroyElements(GetAllocator(), storage_view.data,
+                                       storage_view.size);
 
     std::move(construction_tx).Commit();
     std::move(move_construction_tx).Commit();
@@ -753,7 +769,8 @@ auto Storage<T, N, A>::EmplaceBackSlow(Args&&... args) -> Reference<A> {
     Y_ABSL_INTERNAL_RETHROW;
   }
   // Destroy elements in old backing store.
-  DestroyElements<A>(GetAllocator(), storage_view.data, storage_view.size);
+  DestroyAdapter<A>::DestroyElements(GetAllocator(), storage_view.data,
+                                     storage_view.size);
 
   DeallocateIfAllocated();
   SetAllocation(std::move(allocation_tx).Release());
@@ -778,9 +795,9 @@ auto Storage<T, N, A>::Erase(ConstIterator<A> from, ConstIterator<A> to)
   AssignElements<A>(storage_view.data + erase_index, move_values,
                     storage_view.size - erase_end_index);
 
-  DestroyElements<A>(GetAllocator(),
-                     storage_view.data + (storage_view.size - erase_size),
-                     erase_size);
+  DestroyAdapter<A>::DestroyElements(
+      GetAllocator(), storage_view.data + (storage_view.size - erase_size),
+      erase_size);
 
   SubtractSize(erase_size);
   return Iterator<A>(storage_view.data + erase_index);
@@ -804,7 +821,8 @@ auto Storage<T, N, A>::Reserve(SizeType<A> requested_capacity) -> void {
   ConstructElements<A>(GetAllocator(), new_data, move_values,
                        storage_view.size);
 
-  DestroyElements<A>(GetAllocator(), storage_view.data, storage_view.size);
+  DestroyAdapter<A>::DestroyElements(GetAllocator(), storage_view.data,
+                                     storage_view.size);
 
   DeallocateIfAllocated();
   SetAllocation(std::move(allocation_tx).Release());
@@ -814,7 +832,7 @@ auto Storage<T, N, A>::Reserve(SizeType<A> requested_capacity) -> void {
 template <typename T, size_t N, typename A>
 auto Storage<T, N, A>::ShrinkToFit() -> void {
   // May only be called on allocated instances!
-  assert(GetIsAllocated());
+  Y_ABSL_HARDENING_ASSERT(GetIsAllocated());
 
   StorageView<A> storage_view{GetAllocatedData(), GetSize(),
                               GetAllocatedCapacity()};
@@ -847,7 +865,8 @@ auto Storage<T, N, A>::ShrinkToFit() -> void {
     Y_ABSL_INTERNAL_RETHROW;
   }
 
-  DestroyElements<A>(GetAllocator(), storage_view.data, storage_view.size);
+  DestroyAdapter<A>::DestroyElements(GetAllocator(), storage_view.data,
+                                     storage_view.size);
 
   MallocAdapter<A>::Deallocate(GetAllocator(), storage_view.data,
                                storage_view.capacity);
@@ -862,7 +881,7 @@ auto Storage<T, N, A>::ShrinkToFit() -> void {
 template <typename T, size_t N, typename A>
 auto Storage<T, N, A>::Swap(Storage* other_storage_ptr) -> void {
   using std::swap;
-  assert(this != other_storage_ptr);
+  Y_ABSL_HARDENING_ASSERT(this != other_storage_ptr);
 
   if (GetIsAllocated() && other_storage_ptr->GetIsAllocated()) {
     swap(data_.allocated, other_storage_ptr->data_.allocated);
@@ -883,9 +902,10 @@ auto Storage<T, N, A>::Swap(Storage* other_storage_ptr) -> void {
                          move_values,
                          large_ptr->GetSize() - small_ptr->GetSize());
 
-    DestroyElements<A>(large_ptr->GetAllocator(),
-                       large_ptr->GetInlinedData() + small_ptr->GetSize(),
-                       large_ptr->GetSize() - small_ptr->GetSize());
+    DestroyAdapter<A>::DestroyElements(
+        large_ptr->GetAllocator(),
+        large_ptr->GetInlinedData() + small_ptr->GetSize(),
+        large_ptr->GetSize() - small_ptr->GetSize());
   } else {
     Storage* allocated_ptr = this;
     Storage* inlined_ptr = other_storage_ptr;
@@ -904,23 +924,24 @@ auto Storage<T, N, A>::Swap(Storage* other_storage_ptr) -> void {
                            inlined_ptr->GetSize());
     }
     Y_ABSL_INTERNAL_CATCH_ANY {
-      allocated_ptr->SetAllocation(
-          Allocation<A>{allocated_storage_view.data, allocated_storage_view.capacity});
+      allocated_ptr->SetAllocation(Allocation<A>{
+          allocated_storage_view.data, allocated_storage_view.capacity});
       Y_ABSL_INTERNAL_RETHROW;
     }
 
-    DestroyElements<A>(inlined_ptr->GetAllocator(),
-                       inlined_ptr->GetInlinedData(), inlined_ptr->GetSize());
+    DestroyAdapter<A>::DestroyElements(inlined_ptr->GetAllocator(),
+                                       inlined_ptr->GetInlinedData(),
+                                       inlined_ptr->GetSize());
 
-    inlined_ptr->SetAllocation(
-        Allocation<A>{allocated_storage_view.data, allocated_storage_view.capacity});
+    inlined_ptr->SetAllocation(Allocation<A>{allocated_storage_view.data,
+                                             allocated_storage_view.capacity});
   }
 
   swap(GetSizeAndIsAllocated(), other_storage_ptr->GetSizeAndIsAllocated());
   swap(GetAllocator(), other_storage_ptr->GetAllocator());
 }
 
-// End ignore "array-bounds" and "maybe-uninitialized"
+// End ignore "array-bounds"
 #if !defined(__clang__) && defined(__GNUC__)
 #pragma GCC diagnostic pop
 #endif
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/raw_hash_set.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/raw_hash_set.cc
index a3291e681e..d18535fcbb 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/raw_hash_set.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/raw_hash_set.cc
@@ -23,13 +23,17 @@ namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
 namespace container_internal {
 
+// A single block of empty control bytes for tables without any slots allocated.
+// This enables removing a branch in the hot path of find().
 alignas(16) Y_ABSL_CONST_INIT Y_ABSL_DLL const ctrl_t kEmptyGroup[16] = {
     ctrl_t::kSentinel, ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty,
     ctrl_t::kEmpty,    ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty,
     ctrl_t::kEmpty,    ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty,
     ctrl_t::kEmpty,    ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty};
 
+#ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 constexpr size_t Group::kWidth;
+#endif
 
 // Returns "random" seed.
 inline size_t RandomSeed() {
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/raw_hash_set.h b/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/raw_hash_set.h
index d264d85eef..e24a2bb813 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/raw_hash_set.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/container/internal/raw_hash_set.h
@@ -53,51 +53,121 @@
 //
 // IMPLEMENTATION DETAILS
 //
-// The table stores elements inline in a slot array. In addition to the slot
-// array the table maintains some control state per slot. The extra state is one
-// byte per slot and stores empty or deleted marks, or alternatively 7 bits from
-// the hash of an occupied slot. The table is split into logical groups of
-// slots, like so:
+// # Table Layout
+//
+// A raw_hash_set's backing array consists of control bytes followed by slots
+// that may or may not contain objects.
+//
+// The layout of the backing array, for `capacity` slots, is thus, as a
+// pseudo-struct:
+//
+//   struct BackingArray {
+//     // Control bytes for the "real" slots.
+//     ctrl_t ctrl[capacity];
+//     // Always `ctrl_t::kSentinel`. This is used by iterators to find when to
+//     // stop and serves no other purpose.
+//     ctrl_t sentinel;
+//     // A copy of the first `kWidth - 1` elements of `ctrl`. This is used so
+//     // that if a probe sequence picks a value near the end of `ctrl`,
+//     // `Group` will have valid control bytes to look at.
+//     ctrl_t clones[kWidth - 1];
+//     // The actual slot data.
+//     slot_type slots[capacity];
+//   };
+//
+// The length of this array is computed by `AllocSize()` below.
+//
+// Control bytes (`ctrl_t`) are bytes (collected into groups of a
+// platform-specific size) that define the state of the corresponding slot in
+// the slot array. Group manipulation is tightly optimized to be as efficient
+// as possible: SSE and friends on x86, clever bit operations on other arches.
 //
 //      Group 1         Group 2        Group 3
 // +---------------+---------------+---------------+
 // | | | | | | | | | | | | | | | | | | | | | | | | |
 // +---------------+---------------+---------------+
 //
-// On lookup the hash is split into two parts:
-// - H2: 7 bits (those stored in the control bytes)
-// - H1: the rest of the bits
-// The groups are probed using H1. For each group the slots are matched to H2 in
-// parallel. Because H2 is 7 bits (128 states) and the number of slots per group
-// is low (8 or 16) in almost all cases a match in H2 is also a lookup hit.
+// Each control byte is either a special value for empty slots, deleted slots
+// (sometimes called *tombstones*), and a special end-of-table marker used by
+// iterators, or, if occupied, seven bits (H2) from the hash of the value in the
+// corresponding slot.
+//
+// Storing control bytes in a separate array also has beneficial cache effects,
+// since more logical slots will fit into a cache line.
+//
+// # Hashing
+//
+// We compute two separate hashes, `H1` and `H2`, from the hash of an object.
+// `H1(hash(x))` is an index into `slots`, and essentially the starting point
+// for the probe sequence. `H2(hash(x))` is a 7-bit value used to filter out
+// objects that cannot possibly be the one we are looking for.
+//
+// # Table operations.
 //
-// On insert, once the right group is found (as in lookup), its slots are
-// filled in order.
+// The key operations are `insert`, `find`, and `erase`.
 //
-// On erase a slot is cleared. In case the group did not have any empty slots
-// before the erase, the erased slot is marked as deleted.
+// Since `insert` and `erase` are implemented in terms of `find`, we describe
+// `find` first. To `find` a value `x`, we compute `hash(x)`. From
+// `H1(hash(x))` and the capacity, we construct a `probe_seq` that visits every
+// group of slots in some interesting order.
 //
-// Groups without empty slots (but maybe with deleted slots) extend the probe
-// sequence. The probing algorithm is quadratic. Given N the number of groups,
-// the probing function for the i'th probe is:
+// We now walk through these indices. At each index, we select the entire group
+// starting with that index and extract potential candidates: occupied slots
+// with a control byte equal to `H2(hash(x))`. If we find an empty slot in the
+// group, we stop and return an error. Each candidate slot `y` is compared with
+// `x`; if `x == y`, we are done and return `&y`; otherwise we contine to the
+// next probe index. Tombstones effectively behave like full slots that never
+// match the value we're looking for.
 //
-//   P(0) = H1 % N
+// The `H2` bits ensure when we compare a slot to an object with `==`, we are
+// likely to have actually found the object.  That is, the chance is low that
+// `==` is called and returns `false`.  Thus, when we search for an object, we
+// are unlikely to call `==` many times.  This likelyhood can be analyzed as
+// follows (assuming that H2 is a random enough hash function).
 //
-//   P(i) = (P(i - 1) + i) % N
+// Let's assume that there are `k` "wrong" objects that must be examined in a
+// probe sequence.  For example, when doing a `find` on an object that is in the
+// table, `k` is the number of objects between the start of the probe sequence
+// and the final found object (not including the final found object).  The
+// expected number of objects with an H2 match is then `k/128`.  Measurements
+// and analysis indicate that even at high load factors, `k` is less than 32,
+// meaning that the number of "false positive" comparisons we must perform is
+// less than 1/8 per `find`.
+
+// `insert` is implemented in terms of `unchecked_insert`, which inserts a
+// value presumed to not be in the table (violating this requirement will cause
+// the table to behave erratically). Given `x` and its hash `hash(x)`, to insert
+// it, we construct a `probe_seq` once again, and use it to find the first
+// group with an unoccupied (empty *or* deleted) slot. We place `x` into the
+// first such slot in the group and mark it as full with `x`'s H2.
 //
-// This probing function guarantees that after N probes, all the groups of the
-// table will be probed exactly once.
+// To `insert`, we compose `unchecked_insert` with `find`. We compute `h(x)` and
+// perform a `find` to see if it's already present; if it is, we're done. If
+// it's not, we may decide the table is getting overcrowded (i.e. the load
+// factor is greater than 7/8 for big tables; `is_small()` tables use a max load
+// factor of 1); in this case, we allocate a bigger array, `unchecked_insert`
+// each element of the table into the new array (we know that no insertion here
+// will insert an already-present value), and discard the old backing array. At
+// this point, we may `unchecked_insert` the value `x`.
 //
-// The control state and slot array are stored contiguously in a shared heap
-// allocation. The layout of this allocation is: `capacity()` control bytes,
-// one sentinel control byte, `Group::kWidth - 1` cloned control bytes,
-// <possible padding>, `capacity()` slots. The sentinel control byte is used in
-// iteration so we know when we reach the end of the table. The cloned control
-// bytes at the end of the table are cloned from the beginning of the table so
-// groups that begin near the end of the table can see a full group. In cases in
-// which there are more than `capacity()` cloned control bytes, the extra bytes
-// are `kEmpty`, and these ensure that we always see at least one empty slot and
-// can stop an unsuccessful search.
+// Below, `unchecked_insert` is partly implemented by `prepare_insert`, which
+// presents a viable, initialized slot pointee to the caller.
+//
+// `erase` is implemented in terms of `erase_at`, which takes an index to a
+// slot. Given an offset, we simply create a tombstone and destroy its contents.
+// If we can prove that the slot would not appear in a probe sequence, we can
+// make the slot as empty, instead. We can prove this by observing that if a
+// group has any empty slots, it has never been full (assuming we never create
+// an empty slot in a group with no empties, which this heuristic guarantees we
+// never do) and find would stop at this group anyways (since it does not probe
+// beyond groups with empties).
+//
+// `erase` is `erase_at` composed with `find`: if we
+// have a value `x`, we can perform a `find`, and then `erase_at` the resulting
+// slot.
+//
+// To iterate, we simply traverse the array, skipping empty and deleted slots
+// and stopping when we hit a `kSentinel`.
 
 #ifndef Y_ABSL_CONTAINER_INTERNAL_RAW_HASH_SET_H_
 #define Y_ABSL_CONTAINER_INTERNAL_RAW_HASH_SET_H_
@@ -113,7 +183,9 @@
 #include <type_traits>
 #include <utility>
 
+#include "y_absl/base/config.h"
 #include "y_absl/base/internal/endian.h"
+#include "y_absl/base/internal/prefetch.h"
 #include "y_absl/base/optimization.h"
 #include "y_absl/base/port.h"
 #include "y_absl/container/internal/common.h"
@@ -122,12 +194,27 @@
 #include "y_absl/container/internal/hash_policy_traits.h"
 #include "y_absl/container/internal/hashtable_debug_hooks.h"
 #include "y_absl/container/internal/hashtablez_sampler.h"
-#include "y_absl/container/internal/have_sse.h"
 #include "y_absl/memory/memory.h"
 #include "y_absl/meta/type_traits.h"
 #include "y_absl/numeric/bits.h"
 #include "y_absl/utility/utility.h"
 
+#ifdef Y_ABSL_INTERNAL_HAVE_SSE2
+#include <emmintrin.h>
+#endif
+
+#ifdef Y_ABSL_INTERNAL_HAVE_SSSE3
+#include <tmmintrin.h>
+#endif
+
+#ifdef _MSC_VER
+#include <intrin.h>
+#endif
+
+#ifdef Y_ABSL_INTERNAL_HAVE_ARM_NEON
+#include <arm_neon.h>
+#endif
+
 namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
 namespace container_internal {
@@ -142,14 +229,40 @@ template <typename AllocType>
 void SwapAlloc(AllocType& /*lhs*/, AllocType& /*rhs*/,
                std::false_type /* propagate_on_container_swap */) {}
 
+// The state for a probe sequence.
+//
+// Currently, the sequence is a triangular progression of the form
+//
+//   p(i) := Width * (i^2 + i)/2 + hash (mod mask + 1)
+//
+// The use of `Width` ensures that each probe step does not overlap groups;
+// the sequence effectively outputs the addresses of *groups* (although not
+// necessarily aligned to any boundary). The `Group` machinery allows us
+// to check an entire group with minimal branching.
+//
+// Wrapping around at `mask + 1` is important, but not for the obvious reason.
+// As described above, the first few entries of the control byte array
+// are mirrored at the end of the array, which `Group` will find and use
+// for selecting candidates. However, when those candidates' slots are
+// actually inspected, there are no corresponding slots for the cloned bytes,
+// so we need to make sure we've treated those offsets as "wrapping around".
+//
+// It turns out that this probe sequence visits every group exactly once if the
+// number of groups is a power of two, since (i^2+i)/2 is a bijection in
+// Z/(2^m). See https://en.wikipedia.org/wiki/Quadratic_probing
 template <size_t Width>
 class probe_seq {
  public:
+  // Creates a new probe sequence using `hash` as the initial value of the
+  // sequence and `mask` (usually the capacity of the table) as the mask to
+  // apply to each value in the progression.
   probe_seq(size_t hash, size_t mask) {
     assert(((mask + 1) & mask) == 0 && "not a mask");
     mask_ = mask;
     offset_ = hash & mask_;
   }
+
+  // The offset within the table, i.e., the value `p(i)` above.
   size_t offset() const { return offset_; }
   size_t offset(size_t i) const { return (offset_ + i) & mask_; }
 
@@ -158,7 +271,7 @@ class probe_seq {
     offset_ += index_;
     offset_ &= mask_;
   }
-  // 0-based probe index. The i-th probe in the probe sequence.
+  // 0-based probe index, a multiple of `Width`.
   size_t index() const { return index_; }
 
  private:
@@ -182,9 +295,9 @@ struct IsDecomposable : std::false_type {};
 
 template <class Policy, class Hash, class Eq, class... Ts>
 struct IsDecomposable<
-    y_absl::void_t<decltype(
-        Policy::apply(RequireUsableKey<typename Policy::key_type, Hash, Eq>(),
-                      std::declval<Ts>()...))>,
+    y_absl::void_t<decltype(Policy::apply(
+        RequireUsableKey<typename Policy::key_type, Hash, Eq>(),
+        std::declval<Ts>()...))>,
     Policy, Hash, Eq, Ts...> : std::true_type {};
 
 // TODO(alkis): Switch to std::is_nothrow_swappable when gcc/clang supports it.
@@ -200,57 +313,84 @@ constexpr bool IsNoThrowSwappable(std::false_type /* is_swappable */) {
 
 template <typename T>
 uint32_t TrailingZeros(T x) {
-  Y_ABSL_INTERNAL_ASSUME(x != 0);
-  return countr_zero(x);
+  Y_ABSL_ASSUME(x != 0);
+  return static_cast<uint32_t>(countr_zero(x));
 }
 
-// An abstraction over a bitmask. It provides an easy way to iterate through the
-// indexes of the set bits of a bitmask.  When Shift=0 (platforms with SSE),
-// this is a true bitmask.  On non-SSE, platforms the arithematic used to
-// emulate the SSE behavior works in bytes (Shift=3) and leaves each bytes as
-// either 0x00 or 0x80.
+// An abstract bitmask, such as that emitted by a SIMD instruction.
 //
-// For example:
-//   for (int i : BitMask<uint32_t, 16>(0x5)) -> yields 0, 2
-//   for (int i : BitMask<uint64_t, 8, 3>(0x0000000080800000)) -> yields 2, 3
+// Specifically, this type implements a simple bitset whose representation is
+// controlled by `SignificantBits` and `Shift`. `SignificantBits` is the number
+// of abstract bits in the bitset, while `Shift` is the log-base-two of the
+// width of an abstract bit in the representation.
+// This mask provides operations for any number of real bits set in an abstract
+// bit. To add iteration on top of that, implementation must guarantee no more
+// than one real bit is set in an abstract bit.
 template <class T, int SignificantBits, int Shift = 0>
-class BitMask {
-  static_assert(std::is_unsigned<T>::value, "");
-  static_assert(Shift == 0 || Shift == 3, "");
-
+class NonIterableBitMask {
  public:
-  // These are useful for unit tests (gunit).
-  using value_type = int;
-  using iterator = BitMask;
-  using const_iterator = BitMask;
+  explicit NonIterableBitMask(T mask) : mask_(mask) {}
 
-  explicit BitMask(T mask) : mask_(mask) {}
-  BitMask& operator++() {
-    mask_ &= (mask_ - 1);
-    return *this;
-  }
-  explicit operator bool() const { return mask_ != 0; }
-  int operator*() const { return LowestBitSet(); }
+  explicit operator bool() const { return this->mask_ != 0; }
+
+  // Returns the index of the lowest *abstract* bit set in `self`.
   uint32_t LowestBitSet() const {
     return container_internal::TrailingZeros(mask_) >> Shift;
   }
+
+  // Returns the index of the highest *abstract* bit set in `self`.
   uint32_t HighestBitSet() const {
     return static_cast<uint32_t>((bit_width(mask_) - 1) >> Shift);
   }
 
-  BitMask begin() const { return *this; }
-  BitMask end() const { return BitMask(0); }
-
+  // Return the number of trailing zero *abstract* bits.
   uint32_t TrailingZeros() const {
     return container_internal::TrailingZeros(mask_) >> Shift;
   }
 
+  // Return the number of leading zero *abstract* bits.
   uint32_t LeadingZeros() const {
     constexpr int total_significant_bits = SignificantBits << Shift;
     constexpr int extra_bits = sizeof(T) * 8 - total_significant_bits;
-    return countl_zero(mask_ << extra_bits) >> Shift;
+    return static_cast<uint32_t>(countl_zero(mask_ << extra_bits)) >> Shift;
   }
 
+  T mask_;
+};
+
+// Mask that can be iterable
+//
+// For example, when `SignificantBits` is 16 and `Shift` is zero, this is just
+// an ordinary 16-bit bitset occupying the low 16 bits of `mask`. When
+// `SignificantBits` is 8 and `Shift` is 3, abstract bits are represented as
+// the bytes `0x00` and `0x80`, and it occupies all 64 bits of the bitmask.
+//
+// For example:
+//   for (int i : BitMask<uint32_t, 16>(0b101)) -> yields 0, 2
+//   for (int i : BitMask<uint64_t, 8, 3>(0x0000000080800000)) -> yields 2, 3
+template <class T, int SignificantBits, int Shift = 0>
+class BitMask : public NonIterableBitMask<T, SignificantBits, Shift> {
+  using Base = NonIterableBitMask<T, SignificantBits, Shift>;
+  static_assert(std::is_unsigned<T>::value, "");
+  static_assert(Shift == 0 || Shift == 3, "");
+
+ public:
+  explicit BitMask(T mask) : Base(mask) {}
+  // BitMask is an iterator over the indices of its abstract bits.
+  using value_type = int;
+  using iterator = BitMask;
+  using const_iterator = BitMask;
+
+  BitMask& operator++() {
+    this->mask_ &= (this->mask_ - 1);
+    return *this;
+  }
+
+  uint32_t operator*() const { return Base::LowestBitSet(); }
+
+  BitMask begin() const { return *this; }
+  BitMask end() const { return BitMask(0); }
+
  private:
   friend bool operator==(const BitMask& a, const BitMask& b) {
     return a.mask_ == b.mask_;
@@ -258,15 +398,27 @@ class BitMask {
   friend bool operator!=(const BitMask& a, const BitMask& b) {
     return a.mask_ != b.mask_;
   }
-
-  T mask_;
 };
 
 using h2_t = uint8_t;
 
 // The values here are selected for maximum performance. See the static asserts
-// below for details. We use an enum class so that when strict aliasing is
-// enabled, the compiler knows ctrl_t doesn't alias other types.
+// below for details.
+
+// A `ctrl_t` is a single control byte, which can have one of four
+// states: empty, deleted, full (which has an associated seven-bit h2_t value)
+// and the sentinel. They have the following bit patterns:
+//
+//      empty: 1 0 0 0 0 0 0 0
+//    deleted: 1 1 1 1 1 1 1 0
+//       full: 0 h h h h h h h  // h represents the hash bits.
+//   sentinel: 1 1 1 1 1 1 1 1
+//
+// These values are specifically tuned for SSE-flavored SIMD.
+// The static_asserts below detail the source of these choices.
+//
+// We use an enum class so that when strict aliasing is enabled, the compiler
+// knows ctrl_t doesn't alias other types.
 enum class ctrl_t : int8_t {
   kEmpty = -128,   // 0b10000000
   kDeleted = -2,   // 0b11111110
@@ -294,15 +446,17 @@ static_assert(
      static_cast<int8_t>(ctrl_t::kSentinel) & 0x7F) != 0,
     "ctrl_t::kEmpty and ctrl_t::kDeleted must share an unset bit that is not "
     "shared by ctrl_t::kSentinel to make the scalar test for "
-    "MatchEmptyOrDeleted() efficient");
+    "MaskEmptyOrDeleted() efficient");
 static_assert(ctrl_t::kDeleted == static_cast<ctrl_t>(-2),
               "ctrl_t::kDeleted must be -2 to make the implementation of "
               "ConvertSpecialToEmptyAndFullToDeleted efficient");
 
-// A single block of empty control bytes for tables without any slots allocated.
-// This enables removing a branch in the hot path of find().
 Y_ABSL_DLL extern const ctrl_t kEmptyGroup[16];
+
+// Returns a pointer to a control byte group that can be used by empty tables.
 inline ctrl_t* EmptyGroup() {
+  // Const must be cast away here; no uses of this function will actually write
+  // to it, because it is only used for empty tables.
   return const_cast<ctrl_t*>(kEmptyGroup);
 }
 
@@ -310,28 +464,61 @@ inline ctrl_t* EmptyGroup() {
 // randomize insertion order within groups.
 bool ShouldInsertBackwards(size_t hash, const ctrl_t* ctrl);
 
-// Returns a hash seed.
+// Returns a per-table, hash salt, which changes on resize. This gets mixed into
+// H1 to randomize iteration order per-table.
 //
 // The seed consists of the ctrl_ pointer, which adds enough entropy to ensure
 // non-determinism of iteration order in most cases.
-inline size_t HashSeed(const ctrl_t* ctrl) {
+inline size_t PerTableSalt(const ctrl_t* ctrl) {
   // The low bits of the pointer have little or no entropy because of
   // alignment. We shift the pointer to try to use higher entropy bits. A
   // good number seems to be 12 bits, because that aligns with page size.
   return reinterpret_cast<uintptr_t>(ctrl) >> 12;
 }
-
+// Extracts the H1 portion of a hash: 57 bits mixed with a per-table salt.
 inline size_t H1(size_t hash, const ctrl_t* ctrl) {
-  return (hash >> 7) ^ HashSeed(ctrl);
+  return (hash >> 7) ^ PerTableSalt(ctrl);
 }
+
+// Extracts the H2 portion of a hash: the 7 bits not used for H1.
+//
+// These are used as an occupied control byte.
 inline h2_t H2(size_t hash) { return hash & 0x7F; }
 
+// Helpers for checking the state of a control byte.
 inline bool IsEmpty(ctrl_t c) { return c == ctrl_t::kEmpty; }
 inline bool IsFull(ctrl_t c) { return c >= static_cast<ctrl_t>(0); }
 inline bool IsDeleted(ctrl_t c) { return c == ctrl_t::kDeleted; }
 inline bool IsEmptyOrDeleted(ctrl_t c) { return c < ctrl_t::kSentinel; }
 
-#if Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
+#ifdef Y_ABSL_INTERNAL_HAVE_SSE2
+// Quick reference guide for intrinsics used below:
+//
+// * __m128i: An XMM (128-bit) word.
+//
+// * _mm_setzero_si128: Returns a zero vector.
+// * _mm_set1_epi8:     Returns a vector with the same i8 in each lane.
+//
+// * _mm_subs_epi8:    Saturating-subtracts two i8 vectors.
+// * _mm_and_si128:    Ands two i128s together.
+// * _mm_or_si128:     Ors two i128s together.
+// * _mm_andnot_si128: And-nots two i128s together.
+//
+// * _mm_cmpeq_epi8: Component-wise compares two i8 vectors for equality,
+//                   filling each lane with 0x00 or 0xff.
+// * _mm_cmpgt_epi8: Same as above, but using > rather than ==.
+//
+// * _mm_loadu_si128:  Performs an unaligned load of an i128.
+// * _mm_storeu_si128: Performs an unaligned store of an i128.
+//
+// * _mm_sign_epi8:     Retains, negates, or zeroes each i8 lane of the first
+//                      argument if the corresponding lane of the second
+//                      argument is positive, negative, or zero, respectively.
+// * _mm_movemask_epi8: Selects the sign bit out of each i8 lane and produces a
+//                      bitmask consisting of those bits.
+// * _mm_shuffle_epi8:  Selects i8s from the first argument, using the low
+//                      four bits of each i8 lane in the second argument as
+//                      indices.
 
 // https://github.com/abseil/abseil-cpp/issues/209
 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87853
@@ -360,30 +547,32 @@ struct GroupSse2Impl {
   BitMask<uint32_t, kWidth> Match(h2_t hash) const {
     auto match = _mm_set1_epi8(hash);
     return BitMask<uint32_t, kWidth>(
-        _mm_movemask_epi8(_mm_cmpeq_epi8(match, ctrl)));
+        static_cast<uint32_t>(_mm_movemask_epi8(_mm_cmpeq_epi8(match, ctrl))));
   }
 
   // Returns a bitmask representing the positions of empty slots.
-  BitMask<uint32_t, kWidth> MatchEmpty() const {
-#if Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSSE3
+  NonIterableBitMask<uint32_t, kWidth> MaskEmpty() const {
+#ifdef Y_ABSL_INTERNAL_HAVE_SSSE3
     // This only works because ctrl_t::kEmpty is -128.
-    return BitMask<uint32_t, kWidth>(
-        _mm_movemask_epi8(_mm_sign_epi8(ctrl, ctrl)));
+    return NonIterableBitMask<uint32_t, kWidth>(
+        static_cast<uint32_t>(_mm_movemask_epi8(_mm_sign_epi8(ctrl, ctrl))));
 #else
-    return Match(static_cast<h2_t>(ctrl_t::kEmpty));
+    auto match = _mm_set1_epi8(static_cast<h2_t>(ctrl_t::kEmpty));
+    return NonIterableBitMask<uint32_t, kWidth>(
+        static_cast<uint32_t>(_mm_movemask_epi8(_mm_cmpeq_epi8(match, ctrl))));
 #endif
   }
 
   // Returns a bitmask representing the positions of empty or deleted slots.
-  BitMask<uint32_t, kWidth> MatchEmptyOrDeleted() const {
-    auto special = _mm_set1_epi8(static_cast<int8_t>(ctrl_t::kSentinel));
-    return BitMask<uint32_t, kWidth>(
-        _mm_movemask_epi8(_mm_cmpgt_epi8_fixed(special, ctrl)));
+  NonIterableBitMask<uint32_t, kWidth> MaskEmptyOrDeleted() const {
+    auto special = _mm_set1_epi8(static_cast<uint8_t>(ctrl_t::kSentinel));
+    return NonIterableBitMask<uint32_t, kWidth>(static_cast<uint32_t>(
+        _mm_movemask_epi8(_mm_cmpgt_epi8_fixed(special, ctrl))));
   }
 
   // Returns the number of trailing empty or deleted elements in the group.
   uint32_t CountLeadingEmptyOrDeleted() const {
-    auto special = _mm_set1_epi8(static_cast<int8_t>(ctrl_t::kSentinel));
+    auto special = _mm_set1_epi8(static_cast<uint8_t>(ctrl_t::kSentinel));
     return TrailingZeros(static_cast<uint32_t>(
         _mm_movemask_epi8(_mm_cmpgt_epi8_fixed(special, ctrl)) + 1));
   }
@@ -391,7 +580,7 @@ struct GroupSse2Impl {
   void ConvertSpecialToEmptyAndFullToDeleted(ctrl_t* dst) const {
     auto msbs = _mm_set1_epi8(static_cast<char>(-128));
     auto x126 = _mm_set1_epi8(126);
-#if Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSSE3
+#ifdef Y_ABSL_INTERNAL_HAVE_SSSE3
     auto res = _mm_or_si128(_mm_shuffle_epi8(x126, ctrl), msbs);
 #else
     auto zero = _mm_setzero_si128();
@@ -405,6 +594,63 @@ struct GroupSse2Impl {
 };
 #endif  // Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
 
+#if defined(Y_ABSL_INTERNAL_HAVE_ARM_NEON) && defined(Y_ABSL_IS_LITTLE_ENDIAN)
+struct GroupAArch64Impl {
+  static constexpr size_t kWidth = 8;
+
+  explicit GroupAArch64Impl(const ctrl_t* pos) {
+    ctrl = vld1_u8(reinterpret_cast<const uint8_t*>(pos));
+  }
+
+  BitMask<uint64_t, kWidth, 3> Match(h2_t hash) const {
+    uint8x8_t dup = vdup_n_u8(hash);
+    auto mask = vceq_u8(ctrl, dup);
+    constexpr uint64_t msbs = 0x8080808080808080ULL;
+    return BitMask<uint64_t, kWidth, 3>(
+        vget_lane_u64(vreinterpret_u64_u8(mask), 0) & msbs);
+  }
+
+  NonIterableBitMask<uint64_t, kWidth, 3> MaskEmpty() const {
+    uint64_t mask =
+        vget_lane_u64(vreinterpret_u64_u8(
+                          vceq_s8(vdup_n_s8(static_cast<h2_t>(ctrl_t::kEmpty)),
+                                  vreinterpret_s8_u8(ctrl))),
+                      0);
+    return NonIterableBitMask<uint64_t, kWidth, 3>(mask);
+  }
+
+  NonIterableBitMask<uint64_t, kWidth, 3> MaskEmptyOrDeleted() const {
+    uint64_t mask =
+        vget_lane_u64(vreinterpret_u64_u8(vcgt_s8(
+                          vdup_n_s8(static_cast<int8_t>(ctrl_t::kSentinel)),
+                          vreinterpret_s8_u8(ctrl))),
+                      0);
+    return NonIterableBitMask<uint64_t, kWidth, 3>(mask);
+  }
+
+  uint32_t CountLeadingEmptyOrDeleted() const {
+    uint64_t mask = vget_lane_u64(vreinterpret_u64_u8(ctrl), 0);
+    // ctrl | ~(ctrl >> 7) will have the lowest bit set to zero for kEmpty and
+    // kDeleted. We lower all other bits and count number of trailing zeros.
+    // Clang and GCC optimize countr_zero to rbit+clz without any check for 0,
+    // so we should be fine.
+    constexpr uint64_t bits = 0x0101010101010101ULL;
+    return countr_zero((mask | ~(mask >> 7)) & bits) >> 3;
+  }
+
+  void ConvertSpecialToEmptyAndFullToDeleted(ctrl_t* dst) const {
+    uint64_t mask = vget_lane_u64(vreinterpret_u64_u8(ctrl), 0);
+    constexpr uint64_t msbs = 0x8080808080808080ULL;
+    constexpr uint64_t lsbs = 0x0101010101010101ULL;
+    auto x = mask & msbs;
+    auto res = (~x + (x >> 7)) & ~lsbs;
+    little_endian::Store64(dst, res);
+  }
+
+  uint8x8_t ctrl;
+};
+#endif  // Y_ABSL_INTERNAL_HAVE_ARM_NEON && Y_ABSL_IS_LITTLE_ENDIAN
+
 struct GroupPortableImpl {
   static constexpr size_t kWidth = 8;
 
@@ -431,19 +677,23 @@ struct GroupPortableImpl {
     return BitMask<uint64_t, kWidth, 3>((x - lsbs) & ~x & msbs);
   }
 
-  BitMask<uint64_t, kWidth, 3> MatchEmpty() const {
+  NonIterableBitMask<uint64_t, kWidth, 3> MaskEmpty() const {
     constexpr uint64_t msbs = 0x8080808080808080ULL;
-    return BitMask<uint64_t, kWidth, 3>((ctrl & (~ctrl << 6)) & msbs);
+    return NonIterableBitMask<uint64_t, kWidth, 3>((ctrl & (~ctrl << 6)) &
+                                                   msbs);
   }
 
-  BitMask<uint64_t, kWidth, 3> MatchEmptyOrDeleted() const {
+  NonIterableBitMask<uint64_t, kWidth, 3> MaskEmptyOrDeleted() const {
     constexpr uint64_t msbs = 0x8080808080808080ULL;
-    return BitMask<uint64_t, kWidth, 3>((ctrl & (~ctrl << 7)) & msbs);
+    return NonIterableBitMask<uint64_t, kWidth, 3>((ctrl & (~ctrl << 7)) &
+                                                   msbs);
   }
 
   uint32_t CountLeadingEmptyOrDeleted() const {
-    constexpr uint64_t gaps = 0x00FEFEFEFEFEFEFEULL;
-    return (TrailingZeros(((~ctrl & (ctrl >> 7)) | gaps) + 1) + 7) >> 3;
+    // ctrl | ~(ctrl >> 7) will have the lowest bit set to zero for kEmpty and
+    // kDeleted. We lower all other bits and count number of trailing zeros.
+    constexpr uint64_t bits = 0x0101010101010101ULL;
+    return countr_zero((ctrl | ~(ctrl >> 7)) & bits) >> 3;
   }
 
   void ConvertSpecialToEmptyAndFullToDeleted(ctrl_t* dst) const {
@@ -457,32 +707,40 @@ struct GroupPortableImpl {
   uint64_t ctrl;
 };
 
-#if Y_ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
+#ifdef Y_ABSL_INTERNAL_HAVE_SSE2
 using Group = GroupSse2Impl;
+#elif defined(Y_ABSL_INTERNAL_HAVE_ARM_NEON) && defined(Y_ABSL_IS_LITTLE_ENDIAN)
+using Group = GroupAArch64Impl;
 #else
 using Group = GroupPortableImpl;
 #endif
 
-// The number of cloned control bytes that we copy from the beginning to the
-// end of the control bytes array.
+// Returns he number of "cloned control bytes".
+//
+// This is the number of control bytes that are present both at the beginning
+// of the control byte array and at the end, such that we can create a
+// `Group::kWidth`-width probe window starting from any control byte.
 constexpr size_t NumClonedBytes() { return Group::kWidth - 1; }
 
 template <class Policy, class Hash, class Eq, class Alloc>
 class raw_hash_set;
 
+// Returns whether `n` is a valid capacity (i.e., number of slots).
+//
+// A valid capacity is a non-zero integer `2^m - 1`.
 inline bool IsValidCapacity(size_t n) { return ((n + 1) & n) == 0 && n > 0; }
 
+// Applies the following mapping to every byte in the control array:
+//   * kDeleted -> kEmpty
+//   * kEmpty -> kEmpty
+//   * _ -> kDeleted
 // PRECONDITION:
 //   IsValidCapacity(capacity)
 //   ctrl[capacity] == ctrl_t::kSentinel
 //   ctrl[i] != ctrl_t::kSentinel for all i < capacity
-// Applies mapping for every byte in ctrl:
-//   DELETED -> EMPTY
-//   EMPTY -> EMPTY
-//   FULL -> DELETED
 void ConvertDeletedToEmptyAndFullToDeleted(ctrl_t* ctrl, size_t capacity);
 
-// Rounds up the capacity to the next power of 2 minus 1, with a minimum of 1.
+// Converts `n` into the next valid capacity, per `IsValidCapacity`.
 inline size_t NormalizeCapacity(size_t n) {
   return n ? ~size_t{} >> countl_zero(n) : 1;
 }
@@ -495,8 +753,8 @@ inline size_t NormalizeCapacity(size_t n) {
 //   never need to probe (the whole table fits in one group) so we don't need a
 //   load factor less than 1.
 
-// Given `capacity` of the table, returns the size (i.e. number of full slots)
-// at which we should grow the capacity.
+// Given `capacity`, applies the load factor; i.e., it returns the maximum
+// number of values we should put into the table before a resizing rehash.
 inline size_t CapacityToGrowth(size_t capacity) {
   assert(IsValidCapacity(capacity));
   // `capacity*7/8`
@@ -506,8 +764,12 @@ inline size_t CapacityToGrowth(size_t capacity) {
   }
   return capacity - capacity / 8;
 }
-// From desired "growth" to a lowerbound of the necessary capacity.
-// Might not be a valid one and requires NormalizeCapacity().
+
+// Given `growth`, "unapplies" the load factor to find how large the capacity
+// should be to stay within the load factor.
+//
+// This might not be a valid capacity and `NormalizeCapacity()` should be
+// called on this.
 inline size_t GrowthToLowerboundCapacity(size_t growth) {
   // `growth*8/7`
   if (Group::kWidth == 8 && growth == 7) {
@@ -533,16 +795,15 @@ size_t SelectBucketCountForIterRange(InputIter first, InputIter last,
   return 0;
 }
 
-inline void AssertIsFull(ctrl_t* ctrl) {
-  Y_ABSL_HARDENING_ASSERT((ctrl != nullptr && IsFull(*ctrl)) &&
-                        "Invalid operation on iterator. The element might have "
-                        "been erased, or the table might have rehashed.");
-}
+#define Y_ABSL_INTERNAL_ASSERT_IS_FULL(ctrl, msg) \
+  Y_ABSL_HARDENING_ASSERT((ctrl != nullptr && IsFull(*ctrl)) && msg)
 
 inline void AssertIsValid(ctrl_t* ctrl) {
-  Y_ABSL_HARDENING_ASSERT((ctrl == nullptr || IsFull(*ctrl)) &&
-                        "Invalid operation on iterator. The element might have "
-                        "been erased, or the table might have rehashed.");
+  Y_ABSL_HARDENING_ASSERT(
+      (ctrl == nullptr || IsFull(*ctrl)) &&
+      "Invalid operation on iterator. The element might have "
+      "been erased, the table might have rehashed, or this may "
+      "be an end() iterator.");
 }
 
 struct FindInfo {
@@ -550,44 +811,40 @@ struct FindInfo {
   size_t probe_length;
 };
 
-// The representation of the object has two modes:
-//  - small: For capacities < kWidth-1
-//  - large: For the rest.
+// Whether a table is "small". A small table fits entirely into a probing
+// group, i.e., has a capacity < `Group::kWidth`.
 //
-// Differences:
-//  - In small mode we are able to use the whole capacity. The extra control
-//  bytes give us at least one "empty" control byte to stop the iteration.
-//  This is important to make 1 a valid capacity.
+// In small mode we are able to use the whole capacity. The extra control
+// bytes give us at least one "empty" control byte to stop the iteration.
+// This is important to make 1 a valid capacity.
 //
-//  - In small mode only the first `capacity()` control bytes after the
-//  sentinel are valid. The rest contain dummy ctrl_t::kEmpty values that do not
-//  represent a real slot. This is important to take into account on
-//  find_first_non_full(), where we never try ShouldInsertBackwards() for
-//  small tables.
+// In small mode only the first `capacity` control bytes after the sentinel
+// are valid. The rest contain dummy ctrl_t::kEmpty values that do not
+// represent a real slot. This is important to take into account on
+// `find_first_non_full()`, where we never try
+// `ShouldInsertBackwards()` for small tables.
 inline bool is_small(size_t capacity) { return capacity < Group::kWidth - 1; }
 
+// Begins a probing operation on `ctrl`, using `hash`.
 inline probe_seq<Group::kWidth> probe(const ctrl_t* ctrl, size_t hash,
                                       size_t capacity) {
   return probe_seq<Group::kWidth>(H1(hash, ctrl), capacity);
 }
 
-// Probes the raw_hash_set with the probe sequence for hash and returns the
-// pointer to the first empty or deleted slot.
-// NOTE: this function must work with tables having both ctrl_t::kEmpty and
-// ctrl_t::kDeleted in one group. Such tables appears during
-// drop_deletes_without_resize.
+// Probes an array of control bits using a probe sequence derived from `hash`,
+// and returns the offset corresponding to the first deleted or empty slot.
 //
-// This function is very useful when insertions happen and:
-// - the input is already a set
-// - there are enough slots
-// - the element with the hash is not in the table
+// Behavior when the entire table is full is undefined.
+//
+// NOTE: this function must work with tables having both empty and deleted
+// slots in the same group. Such tables appear during `erase()`.
 template <typename = void>
 inline FindInfo find_first_non_full(const ctrl_t* ctrl, size_t hash,
                                     size_t capacity) {
   auto seq = probe(ctrl, hash, capacity);
   while (true) {
     Group g{ctrl + seq.offset()};
-    auto mask = g.MatchEmptyOrDeleted();
+    auto mask = g.MaskEmptyOrDeleted();
     if (mask) {
 #if !defined(NDEBUG)
       // We want to add entropy even when ASLR is not enabled.
@@ -610,7 +867,8 @@ inline FindInfo find_first_non_full(const ctrl_t* ctrl, size_t hash,
 // corresponding translation unit.
 extern template FindInfo find_first_non_full(const ctrl_t*, size_t, size_t);
 
-// Reset all ctrl bytes back to ctrl_t::kEmpty, except the sentinel.
+// Sets `ctrl` to `{kEmpty, kSentinel, ..., kEmpty}`, marking the entire
+// array as marked as empty.
 inline void ResetCtrl(size_t capacity, ctrl_t* ctrl, const void* slot,
                       size_t slot_size) {
   std::memset(ctrl, static_cast<int8_t>(ctrl_t::kEmpty),
@@ -619,8 +877,10 @@ inline void ResetCtrl(size_t capacity, ctrl_t* ctrl, const void* slot,
   SanitizerPoisonMemoryRegion(slot, slot_size * capacity);
 }
 
-// Sets the control byte, and if `i < NumClonedBytes()`, set the cloned byte
-// at the end too.
+// Sets `ctrl[i]` to `h`.
+//
+// Unlike setting it directly, this function will perform bounds checks and
+// mirror the value to the cloned tail if necessary.
 inline void SetCtrl(size_t i, ctrl_t h, size_t capacity, ctrl_t* ctrl,
                     const void* slot, size_t slot_size) {
   assert(i < capacity);
@@ -636,25 +896,28 @@ inline void SetCtrl(size_t i, ctrl_t h, size_t capacity, ctrl_t* ctrl,
   ctrl[((i - NumClonedBytes()) & capacity) + (NumClonedBytes() & capacity)] = h;
 }
 
+// Overload for setting to an occupied `h2_t` rather than a special `ctrl_t`.
 inline void SetCtrl(size_t i, h2_t h, size_t capacity, ctrl_t* ctrl,
                     const void* slot, size_t slot_size) {
   SetCtrl(i, static_cast<ctrl_t>(h), capacity, ctrl, slot, slot_size);
 }
 
-// The allocated block consists of `capacity + 1 + NumClonedBytes()` control
-// bytes followed by `capacity` slots, which must be aligned to `slot_align`.
-// SlotOffset returns the offset of the slots into the allocated block.
+// Given the capacity of a table, computes the offset (from the start of the
+// backing allocation) at which the slots begin.
 inline size_t SlotOffset(size_t capacity, size_t slot_align) {
   assert(IsValidCapacity(capacity));
   const size_t num_control_bytes = capacity + 1 + NumClonedBytes();
   return (num_control_bytes + slot_align - 1) & (~slot_align + 1);
 }
 
-// Returns the size of the allocated block. See also above comment.
+// Given the capacity of a table, computes the total size of the backing
+// array.
 inline size_t AllocSize(size_t capacity, size_t slot_size, size_t slot_align) {
   return SlotOffset(capacity, slot_align) + capacity * slot_size;
 }
 
+// A SwissTable.
+//
 // Policy: a policy defines how to perform different operations on
 // the slots of the hashtable (see hash_policy_traits.h for the full interface
 // of policy).
@@ -769,16 +1032,22 @@ class raw_hash_set {
 
     // PRECONDITION: not an end() iterator.
     reference operator*() const {
-      AssertIsFull(ctrl_);
+      Y_ABSL_INTERNAL_ASSERT_IS_FULL(ctrl_,
+                                   "operator*() called on invalid iterator.");
       return PolicyTraits::element(slot_);
     }
 
     // PRECONDITION: not an end() iterator.
-    pointer operator->() const { return &operator*(); }
+    pointer operator->() const {
+      Y_ABSL_INTERNAL_ASSERT_IS_FULL(ctrl_,
+                                   "operator-> called on invalid iterator.");
+      return &operator*();
+    }
 
     // PRECONDITION: not an end() iterator.
     iterator& operator++() {
-      AssertIsFull(ctrl_);
+      Y_ABSL_INTERNAL_ASSERT_IS_FULL(ctrl_,
+                                   "operator++ called on invalid iterator.");
       ++ctrl_;
       ++slot_;
       skip_empty_or_deleted();
@@ -804,9 +1073,13 @@ class raw_hash_set {
     iterator(ctrl_t* ctrl, slot_type* slot) : ctrl_(ctrl), slot_(slot) {
       // This assumption helps the compiler know that any non-end iterator is
       // not equal to any end iterator.
-      Y_ABSL_INTERNAL_ASSUME(ctrl != nullptr);
+      Y_ABSL_ASSUME(ctrl != nullptr);
     }
 
+    // Fixes up `ctrl_` to point to a full by advancing it and `slot_` until
+    // they reach one.
+    //
+    // If a sentinel is reached, we null both of them out instead.
     void skip_empty_or_deleted() {
       while (IsEmptyOrDeleted(*ctrl_)) {
         uint32_t shift = Group{ctrl_}.CountLeadingEmptyOrDeleted();
@@ -1103,8 +1376,7 @@ class raw_hash_set {
   //   m.insert(std::make_pair("abc", 42));
   // TODO(cheshire): A type alias T2 is introduced as a workaround for the nvcc
   // bug.
-  template <class T, RequiresInsertable<T> = 0,
-            class T2 = T,
+  template <class T, RequiresInsertable<T> = 0, class T2 = T,
             typename std::enable_if<IsDecomposable<T2>::value, int>::type = 0,
             T* = nullptr>
   std::pair<iterator, bool> insert(T&& value) {
@@ -1324,7 +1596,8 @@ class raw_hash_set {
   // This overload is necessary because otherwise erase<K>(const K&) would be
   // a better match if non-const iterator is passed as an argument.
   void erase(iterator it) {
-    AssertIsFull(it.ctrl_);
+    Y_ABSL_INTERNAL_ASSERT_IS_FULL(it.ctrl_,
+                                 "erase() called on invalid iterator.");
     PolicyTraits::destroy(&alloc_ref(), it.slot_);
     erase_meta_only(it);
   }
@@ -1358,7 +1631,8 @@ class raw_hash_set {
   }
 
   node_type extract(const_iterator position) {
-    AssertIsFull(position.inner_.ctrl_);
+    Y_ABSL_INTERNAL_ASSERT_IS_FULL(position.inner_.ctrl_,
+                                 "extract() called on invalid iterator.");
     auto node =
         CommonAccess::Transfer<node_type>(alloc_ref(), position.inner_.slot_);
     erase_meta_only(position);
@@ -1445,12 +1719,13 @@ class raw_hash_set {
   template <class K = key_type>
   void prefetch(const key_arg<K>& key) const {
     (void)key;
-#if defined(__GNUC__)
+    // Avoid probing if we won't be able to prefetch the addresses received.
+#ifdef Y_ABSL_INTERNAL_HAVE_PREFETCH
     prefetch_heap_block();
     auto seq = probe(ctrl_, hash_ref()(key), capacity_);
-    __builtin_prefetch(static_cast<const void*>(ctrl_ + seq.offset()));
-    __builtin_prefetch(static_cast<const void*>(slots_ + seq.offset()));
-#endif  // __GNUC__
+    base_internal::PrefetchT0(ctrl_ + seq.offset());
+    base_internal::PrefetchT0(slots_ + seq.offset());
+#endif  // Y_ABSL_INTERNAL_HAVE_PREFETCH
   }
 
   // The API of find() has two extensions.
@@ -1465,13 +1740,13 @@ class raw_hash_set {
     auto seq = probe(ctrl_, hash, capacity_);
     while (true) {
       Group g{ctrl_ + seq.offset()};
-      for (int i : g.Match(H2(hash))) {
+      for (uint32_t i : g.Match(H2(hash))) {
         if (Y_ABSL_PREDICT_TRUE(PolicyTraits::apply(
                 EqualElement<K>{key, eq_ref()},
                 PolicyTraits::element(slots_ + seq.offset(i)))))
           return iterator_at(seq.offset(i));
       }
-      if (Y_ABSL_PREDICT_TRUE(g.MatchEmpty())) return end();
+      if (Y_ABSL_PREDICT_TRUE(g.MaskEmpty())) return end();
       seq.next();
       assert(seq.index() <= capacity_ && "full table!");
     }
@@ -1538,6 +1813,14 @@ class raw_hash_set {
     return !(a == b);
   }
 
+  template <typename H>
+  friend typename std::enable_if<H::template is_hashable<value_type>::value,
+                                 H>::type
+  AbslHashValue(H h, const raw_hash_set& s) {
+    return H::combine(H::combine_unordered(std::move(h), s.begin(), s.end()),
+                      s.size());
+  }
+
   friend void swap(raw_hash_set& a,
                    raw_hash_set& b) noexcept(noexcept(a.swap(b))) {
     a.swap(b);
@@ -1603,17 +1886,17 @@ class raw_hash_set {
     slot_type&& slot;
   };
 
-  // "erases" the object from the container, except that it doesn't actually
-  // destroy the object. It only updates all the metadata of the class.
-  // This can be used in conjunction with Policy::transfer to move the object to
-  // another place.
+  // Erases, but does not destroy, the value pointed to by `it`.
+  //
+  // This merely updates the pertinent control byte. This can be used in
+  // conjunction with Policy::transfer to move the object to another place.
   void erase_meta_only(const_iterator it) {
     assert(IsFull(*it.inner_.ctrl_) && "erasing a dangling iterator");
     --size_;
-    const size_t index = it.inner_.ctrl_ - ctrl_;
+    const size_t index = static_cast<size_t>(it.inner_.ctrl_ - ctrl_);
     const size_t index_before = (index - Group::kWidth) & capacity_;
-    const auto empty_after = Group(it.inner_.ctrl_).MatchEmpty();
-    const auto empty_before = Group(ctrl_ + index_before).MatchEmpty();
+    const auto empty_after = Group(it.inner_.ctrl_).MaskEmpty();
+    const auto empty_before = Group(ctrl_ + index_before).MaskEmpty();
 
     // We count how many consecutive non empties we have to the right and to the
     // left of `it`. If the sum is >= kWidth then there is at least one probe
@@ -1629,6 +1912,11 @@ class raw_hash_set {
     infoz().RecordErase();
   }
 
+  // Allocates a backing array for `self` and initializes its control bytes.
+  // This reads `capacity_` and updates all other fields based on the result of
+  // the allocation.
+  //
+  // This does not free the currently held array; `capacity_` must be nonzero.
   void initialize_slots() {
     assert(capacity_);
     // Folks with custom allocators often make unwarranted assumptions about the
@@ -1657,6 +1945,10 @@ class raw_hash_set {
     infoz().RecordStorageChanged(size_, capacity_);
   }
 
+  // Destroys all slots in the backing array, frees the backing array, and
+  // clears all top-level book-keeping data.
+  //
+  // This essentially implements `map = raw_hash_set();`.
   void destroy_slots() {
     if (!capacity_) return;
     for (size_t i = 0; i != capacity_; ++i) {
@@ -1707,6 +1999,9 @@ class raw_hash_set {
     infoz().RecordRehash(total_probe_length);
   }
 
+  // Prunes control bytes to remove as many tombstones as possible.
+  //
+  // See the comment on `rehash_and_grow_if_necessary()`.
   void drop_deletes_without_resize() Y_ABSL_ATTRIBUTE_NOINLINE {
     assert(IsValidCapacity(capacity_));
     assert(!is_small(capacity_));
@@ -1773,6 +2068,11 @@ class raw_hash_set {
     infoz().RecordRehash(total_probe_length);
   }
 
+  // Called whenever the table *might* need to conditionally grow.
+  //
+  // This function is an optimization opportunity to perform a rehash even when
+  // growth is unnecessary, because vacating tombstones is beneficial for
+  // performance in the long-run.
   void rehash_and_grow_if_necessary() {
     if (capacity_ == 0) {
       resize(1);
@@ -1832,12 +2132,12 @@ class raw_hash_set {
     auto seq = probe(ctrl_, hash, capacity_);
     while (true) {
       Group g{ctrl_ + seq.offset()};
-      for (int i : g.Match(H2(hash))) {
+      for (uint32_t i : g.Match(H2(hash))) {
         if (Y_ABSL_PREDICT_TRUE(PolicyTraits::element(slots_ + seq.offset(i)) ==
                               elem))
           return true;
       }
-      if (Y_ABSL_PREDICT_TRUE(g.MatchEmpty())) return false;
+      if (Y_ABSL_PREDICT_TRUE(g.MaskEmpty())) return false;
       seq.next();
       assert(seq.index() <= capacity_ && "full table!");
     }
@@ -1857,6 +2157,9 @@ class raw_hash_set {
   }
 
  protected:
+  // Attempts to find `key` in the table; if it isn't found, returns a slot that
+  // the value can be inserted into, with the control byte already set to
+  // `key`'s H2.
   template <class K>
   std::pair<size_t, bool> find_or_prepare_insert(const K& key) {
     prefetch_heap_block();
@@ -1864,19 +2167,23 @@ class raw_hash_set {
     auto seq = probe(ctrl_, hash, capacity_);
     while (true) {
       Group g{ctrl_ + seq.offset()};
-      for (int i : g.Match(H2(hash))) {
+      for (uint32_t i : g.Match(H2(hash))) {
         if (Y_ABSL_PREDICT_TRUE(PolicyTraits::apply(
                 EqualElement<K>{key, eq_ref()},
                 PolicyTraits::element(slots_ + seq.offset(i)))))
           return {seq.offset(i), false};
       }
-      if (Y_ABSL_PREDICT_TRUE(g.MatchEmpty())) break;
+      if (Y_ABSL_PREDICT_TRUE(g.MaskEmpty())) break;
       seq.next();
       assert(seq.index() <= capacity_ && "full table!");
     }
     return {prepare_insert(hash), true};
   }
 
+  // Given the hash of a value not currently in the table, finds the next
+  // viable slot index to insert it at.
+  //
+  // REQUIRES: At least one non-full slot available.
   size_t prepare_insert(size_t hash) Y_ABSL_ATTRIBUTE_NOINLINE {
     auto target = find_first_non_full(ctrl_, hash, capacity_);
     if (Y_ABSL_PREDICT_FALSE(growth_left() == 0 &&
@@ -1920,15 +2227,23 @@ class raw_hash_set {
     growth_left() = CapacityToGrowth(capacity()) - size_;
   }
 
+  // The number of slots we can still fill without needing to rehash.
+  //
+  // This is stored separately due to tombstones: we do not include tombstones
+  // in the growth capacity, because we'd like to rehash when the table is
+  // otherwise filled with tombstones: otherwise, probe sequences might get
+  // unacceptably long without triggering a rehash. Callers can also force a
+  // rehash via the standard `rehash(0)`, which will recompute this value as a
+  // side-effect.
+  //
+  // See `CapacityToGrowth()`.
   size_t& growth_left() { return settings_.template get<0>(); }
 
+  // Prefetch the heap-allocated memory region to resolve potential TLB misses.
+  // This is intended to overlap with execution of calculating the hash for a
+  // key.
   void prefetch_heap_block() const {
-    // Prefetch the heap-allocated memory region to resolve potential TLB
-    // misses.  This is intended to overlap with execution of calculating the
-    // hash for a key.
-#if defined(__GNUC__)
-    __builtin_prefetch(static_cast<const void*>(ctrl_), 0, 1);
-#endif  // __GNUC__
+    base_internal::PrefetchT2(ctrl_);
   }
 
   HashtablezInfoHandle& infoz() { return settings_.template get<1>(); }
@@ -1945,20 +2260,33 @@ class raw_hash_set {
   // TODO(alkis): Investigate removing some of these fields:
   // - ctrl/slots can be derived from each other
   // - size can be moved into the slot array
-  ctrl_t* ctrl_ = EmptyGroup();  // [(capacity + 1 + NumClonedBytes()) * ctrl_t]
-  slot_type* slots_ = nullptr;   // [capacity * slot_type]
-  size_t size_ = 0;              // number of full slots
-  size_t capacity_ = 0;          // total number of slots
+
+  // The control bytes (and, also, a pointer to the base of the backing array).
+  //
+  // This contains `capacity_ + 1 + NumClonedBytes()` entries, even
+  // when the table is empty (hence EmptyGroup).
+  ctrl_t* ctrl_ = EmptyGroup();
+  // The beginning of the slots, located at `SlotOffset()` bytes after
+  // `ctrl_`. May be null for empty tables.
+  slot_type* slots_ = nullptr;
+
+  // The number of filled slots.
+  size_t size_ = 0;
+
+  // The total number of available slots.
+  size_t capacity_ = 0;
   y_absl::container_internal::CompressedTuple<size_t /* growth_left */,
                                             HashtablezInfoHandle, hasher,
                                             key_equal, allocator_type>
-      settings_{0, HashtablezInfoHandle{}, hasher{}, key_equal{},
+      settings_{0u, HashtablezInfoHandle{}, hasher{}, key_equal{},
                 allocator_type{}};
 };
 
 // Erases all elements that satisfy the predicate `pred` from the container `c`.
 template <typename P, typename H, typename E, typename A, typename Predicate>
-void EraseIf(Predicate& pred, raw_hash_set<P, H, E, A>* c) {
+typename raw_hash_set<P, H, E, A>::size_type EraseIf(
+    Predicate& pred, raw_hash_set<P, H, E, A>* c) {
+  const auto initial_size = c->size();
   for (auto it = c->begin(), last = c->end(); it != last;) {
     if (pred(*it)) {
       c->erase(it++);
@@ -1966,6 +2294,7 @@ void EraseIf(Predicate& pred, raw_hash_set<P, H, E, A>* c) {
       ++it;
     }
   }
+  return initial_size - c->size();
 }
 
 namespace hashtable_debug_internal {
@@ -1981,7 +2310,7 @@ struct HashtableDebugAccess<Set, y_absl::void_t<typename Set::raw_hash_set>> {
     auto seq = probe(set.ctrl_, hash, set.capacity_);
     while (true) {
       container_internal::Group g{set.ctrl_ + seq.offset()};
-      for (int i : g.Match(container_internal::H2(hash))) {
+      for (uint32_t i : g.Match(container_internal::H2(hash))) {
         if (Traits::apply(
                 typename Set::template EqualElement<typename Set::key_type>{
                     key, set.eq_ref()},
@@ -1989,7 +2318,7 @@ struct HashtableDebugAccess<Set, y_absl::void_t<typename Set::raw_hash_set>> {
           return num_probes;
         ++num_probes;
       }
-      if (g.MatchEmpty()) return num_probes;
+      if (g.MaskEmpty()) return num_probes;
       seq.next();
       ++num_probes;
     }
@@ -2031,4 +2360,6 @@ struct HashtableDebugAccess<Set, y_absl::void_t<typename Set::raw_hash_set>> {
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
 
+#undef Y_ABSL_INTERNAL_ASSERT_IS_FULL
+
 #endif  // Y_ABSL_CONTAINER_INTERNAL_RAW_HASH_SET_H_
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/CMakeLists.txt b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/CMakeLists.txt
index 941146d1d1..a862043d46 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/CMakeLists.txt
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/CMakeLists.txt
@@ -26,7 +26,6 @@ target_sources(abseil-cpp-tstring-y_absl-debugging PRIVATE
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/examine_stack.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/vdso_support.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/leak_check.cc
-  ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/leak_check_disable.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/stacktrace.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/symbolize.cc
 )
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/failure_signal_handler.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/failure_signal_handler.cc
index a79d902623..9e35a345d9 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/failure_signal_handler.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/failure_signal_handler.cc
@@ -42,7 +42,6 @@
 #include <ctime>
 
 #include "y_absl/base/attributes.h"
-#include "y_absl/base/internal/errno_saver.h"
 #include "y_absl/base/internal/raw_logging.h"
 #include "y_absl/base/internal/sysinfo.h"
 #include "y_absl/debugging/internal/examine_stack.h"
@@ -52,7 +51,7 @@
 #define Y_ABSL_HAVE_SIGACTION
 // Apple WatchOS and TVOS don't allow sigaltstack
 #if !(defined(TARGET_OS_WATCH) && TARGET_OS_WATCH) && \
-    !(defined(TARGET_OS_TV) && TARGET_OS_TV)
+    !(defined(TARGET_OS_TV) && TARGET_OS_TV) && !defined(__QNX__)
 #define Y_ABSL_HAVE_SIGALTSTACK
 #endif
 #endif
@@ -217,8 +216,7 @@ static void InstallOneFailureHandler(FailureSignalData* data,
 #endif
 
 static void WriteToStderr(const char* data) {
-  y_absl::base_internal::ErrnoSaver errno_saver;
-  y_absl::raw_logging_internal::SafeWriteToStderr(data, strlen(data));
+  y_absl::raw_logging_internal::AsyncSignalSafeWriteToStderr(data, strlen(data));
 }
 
 static void WriteSignalMessage(int signo, int cpu,
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/address_is_readable.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/address_is_readable.cc
index 669d81f878..ccfed8bc42 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/address_is_readable.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/address_is_readable.cc
@@ -30,16 +30,12 @@ bool AddressIsReadable(const void* /* addr */) { return true; }
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
 
-#else
+#else  // __linux__ && !__ANDROID__
 
-#include <fcntl.h>
-#include <sys/syscall.h>
+#include <stdint.h>
+#include <syscall.h>
 #include <unistd.h>
 
-#include <atomic>
-#include <cerrno>
-#include <cstdint>
-
 #include "y_absl/base/internal/errno_saver.h"
 #include "y_absl/base/internal/raw_logging.h"
 
@@ -47,93 +43,54 @@ namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
 namespace debugging_internal {
 
-// Pack a pid and two file descriptors into a 64-bit word,
-// using 16, 24, and 24 bits for each respectively.
-static uint64_t Pack(uint64_t pid, uint64_t read_fd, uint64_t write_fd) {
-  Y_ABSL_RAW_CHECK((read_fd >> 24) == 0 && (write_fd >> 24) == 0,
-                 "fd out of range");
-  return (pid << 48) | ((read_fd & 0xffffff) << 24) | (write_fd & 0xffffff);
-}
-
-// Unpack x into a pid and two file descriptors, where x was created with
-// Pack().
-static void Unpack(uint64_t x, int *pid, int *read_fd, int *write_fd) {
-  *pid = x >> 48;
-  *read_fd = (x >> 24) & 0xffffff;
-  *write_fd = x & 0xffffff;
-}
+// NOTE: be extra careful about adding any interposable function calls here
+// (such as open(), read(), etc.). These symbols may be interposed and will get
+// invoked in contexts they don't expect.
+//
+// NOTE: any new system calls here may also require sandbox reconfiguration.
+//
+bool AddressIsReadable(const void *addr) {
+  // Align address on 8-byte boundary. On aarch64, checking last
+  // byte before inaccessible page returned unexpected EFAULT.
+  const uintptr_t u_addr = reinterpret_cast<uintptr_t>(addr) & ~7;
+  addr = reinterpret_cast<const void *>(u_addr);
 
-// Return whether the byte at *addr is readable, without faulting.
-// Save and restores errno.   Returns true on systems where
-// unimplemented.
-// This is a namespace-scoped variable for correct zero-initialization.
-static std::atomic<uint64_t> pid_and_fds;  // initially 0, an invalid pid.
+  // rt_sigprocmask below will succeed for this input.
+  if (addr == nullptr) return false;
 
-bool AddressIsReadable(const void *addr) {
   y_absl::base_internal::ErrnoSaver errno_saver;
-  // We test whether a byte is readable by using write().  Normally, this would
-  // be done via a cached file descriptor to /dev/null, but linux fails to
-  // check whether the byte is readable when the destination is /dev/null, so
-  // we use a cached pipe.  We store the pid of the process that created the
-  // pipe to handle the case where a process forks, and the child closes all
-  // the file descriptors and then calls this routine.  This is not perfect:
-  // the child could use the routine, then close all file descriptors and then
-  // use this routine again.  But the likely use of this routine is when
-  // crashing, to test the validity of pages when dumping the stack.  Beware
-  // that we may leak file descriptors, but we're unlikely to leak many.
-  int bytes_written;
-  int current_pid = getpid() & 0xffff;   // we use only the low order 16 bits
-  do {  // until we do not get EBADF trying to use file descriptors
-    int pid;
-    int read_fd;
-    int write_fd;
-    uint64_t local_pid_and_fds = pid_and_fds.load(std::memory_order_acquire);
-    Unpack(local_pid_and_fds, &pid, &read_fd, &write_fd);
-    while (current_pid != pid) {
-      int p[2];
-      // new pipe
-      if (pipe(p) != 0) {
-        Y_ABSL_RAW_LOG(FATAL, "Failed to create pipe, errno=%d", errno);
-      }
-      fcntl(p[0], F_SETFD, FD_CLOEXEC);
-      fcntl(p[1], F_SETFD, FD_CLOEXEC);
-      uint64_t new_pid_and_fds = Pack(current_pid, p[0], p[1]);
-      if (pid_and_fds.compare_exchange_strong(
-              local_pid_and_fds, new_pid_and_fds, std::memory_order_release,
-              std::memory_order_relaxed)) {
-        local_pid_and_fds = new_pid_and_fds;  // fds exposed to other threads
-      } else {  // fds not exposed to other threads; we can close them.
-        close(p[0]);
-        close(p[1]);
-        local_pid_and_fds = pid_and_fds.load(std::memory_order_acquire);
-      }
-      Unpack(local_pid_and_fds, &pid, &read_fd, &write_fd);
-    }
-    errno = 0;
-    // Use syscall(SYS_write, ...) instead of write() to prevent ASAN
-    // and other checkers from complaining about accesses to arbitrary
-    // memory.
-    do {
-      bytes_written = syscall(SYS_write, write_fd, addr, 1);
-    } while (bytes_written == -1 && errno == EINTR);
-    if (bytes_written == 1) {   // remove the byte from the pipe
-      char c;
-      while (read(read_fd, &c, 1) == -1 && errno == EINTR) {
-      }
-    }
-    if (errno == EBADF) {  // Descriptors invalid.
-      // If pid_and_fds contains the problematic file descriptors we just used,
-      // this call will forget them, and the loop will try again.
-      pid_and_fds.compare_exchange_strong(local_pid_and_fds, 0,
-                                          std::memory_order_release,
-                                          std::memory_order_relaxed);
-    }
-  } while (errno == EBADF);
-  return bytes_written == 1;
+
+  // Here we probe with some syscall which
+  // - accepts an 8-byte region of user memory as input
+  // - tests for EFAULT before other validation
+  // - has no problematic side-effects
+  //
+  // rt_sigprocmask(2) works for this.  It copies sizeof(kernel_sigset_t)==8
+  // bytes from the address into the kernel memory before any validation.
+  //
+  // The call can never succeed, since the `how` parameter is not one of
+  // SIG_BLOCK, SIG_UNBLOCK, SIG_SETMASK.
+  //
+  // This strategy depends on Linux implementation details,
+  // so we rely on the test to alert us if it stops working.
+  //
+  // Some discarded past approaches:
+  // - msync() doesn't reject PROT_NONE regions
+  // - write() on /dev/null doesn't return EFAULT
+  // - write() on a pipe requires creating it and draining the writes
+  // - connect() works but is problematic for sandboxes and needs a valid
+  //   file descriptor
+  //
+  // This can never succeed (invalid first argument to sigprocmask).
+  Y_ABSL_RAW_CHECK(syscall(SYS_rt_sigprocmask, ~0, addr, nullptr,
+                         /*sizeof(kernel_sigset_t)*/ 8) == -1,
+                 "unexpected success");
+  Y_ABSL_RAW_CHECK(errno == EFAULT || errno == EINVAL, "unexpected errno");
+  return errno != EFAULT;
 }
 
 }  // namespace debugging_internal
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
 
-#endif
+#endif  // __linux__ && !__ANDROID__
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/elf_mem_image.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/elf_mem_image.cc
index 1df9cca1b6..0a82359e27 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/elf_mem_image.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/elf_mem_image.cc
@@ -351,7 +351,11 @@ void ElfMemImage::SymbolIterator::Update(int increment) {
   const ElfW(Versym) *version_symbol = image->GetVersym(index_);
   Y_ABSL_RAW_CHECK(symbol && version_symbol, "");
   const char *const symbol_name = image->GetDynstr(symbol->st_name);
+#if defined(__NetBSD__)
+  const int version_index = version_symbol->vs_vers & VERSYM_VERSION;
+#else
   const ElfW(Versym) version_index = version_symbol[0] & VERSYM_VERSION;
+#endif
   const ElfW(Verdef) *version_definition = nullptr;
   const char *version_name = "";
   if (symbol->st_shndx == SHN_UNDEF) {
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/elf_mem_image.h b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/elf_mem_image.h
index c19c0e9f8e..a7dde97206 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/elf_mem_image.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/elf_mem_image.h
@@ -31,8 +31,9 @@
 #error Y_ABSL_HAVE_ELF_MEM_IMAGE cannot be directly set
 #endif
 
-#if defined(__ELF__) && !defined(__native_client__) && !defined(__asmjs__) && \
-    !defined(__wasm__)
+#if defined(__ELF__) && !defined(__OpenBSD__) && !defined(__QNX__) && \
+    !defined(__native_client__) && !defined(__asmjs__) &&             \
+    !defined(__wasm__) && !defined(__HAIKU__)
 #define Y_ABSL_HAVE_ELF_MEM_IMAGE 1
 #endif
 
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/examine_stack.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/examine_stack.cc
index edc926cafd..3f1c0b8b79 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/examine_stack.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/examine_stack.cc
@@ -20,7 +20,13 @@
 #include <unistd.h>
 #endif
 
-#ifdef __APPLE__
+#include "y_absl/base/config.h"
+
+#ifdef Y_ABSL_HAVE_MMAP
+#include <sys/mman.h>
+#endif
+
+#if defined(__linux__) || defined(__APPLE__)
 #include <sys/ucontext.h>
 #endif
 
@@ -37,10 +43,115 @@ namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
 namespace debugging_internal {
 
+namespace {
+constexpr int kDefaultDumpStackFramesLimit = 64;
+// The %p field width for printf() functions is two characters per byte,
+// and two extra for the leading "0x".
+constexpr int kPrintfPointerFieldWidth = 2 + 2 * sizeof(void*);
+
+Y_ABSL_CONST_INIT SymbolizeUrlEmitter debug_stack_trace_hook = nullptr;
+
+// Async-signal safe mmap allocator.
+void* Allocate(size_t num_bytes) {
+#ifdef Y_ABSL_HAVE_MMAP
+  void* p = ::mmap(nullptr, num_bytes, PROT_READ | PROT_WRITE,
+                   MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  return p == MAP_FAILED ? nullptr : p;
+#else
+  (void)num_bytes;
+  return nullptr;
+#endif  // Y_ABSL_HAVE_MMAP
+}
+
+void Deallocate(void* p, size_t size) {
+#ifdef Y_ABSL_HAVE_MMAP
+  ::munmap(p, size);
+#else
+  (void)p;
+  (void)size;
+#endif  // Y_ABSL_HAVE_MMAP
+}
+
+// Print a program counter only.
+void DumpPC(OutputWriter* writer, void* writer_arg, void* const pc,
+            const char* const prefix) {
+  char buf[100];
+  snprintf(buf, sizeof(buf), "%s@ %*p\n", prefix, kPrintfPointerFieldWidth, pc);
+  writer(buf, writer_arg);
+}
+
+// Print a program counter and the corresponding stack frame size.
+void DumpPCAndFrameSize(OutputWriter* writer, void* writer_arg, void* const pc,
+                        int framesize, const char* const prefix) {
+  char buf[100];
+  if (framesize <= 0) {
+    snprintf(buf, sizeof(buf), "%s@ %*p  (unknown)\n", prefix,
+             kPrintfPointerFieldWidth, pc);
+  } else {
+    snprintf(buf, sizeof(buf), "%s@ %*p  %9d\n", prefix,
+             kPrintfPointerFieldWidth, pc, framesize);
+  }
+  writer(buf, writer_arg);
+}
+
+// Print a program counter and the corresponding symbol.
+void DumpPCAndSymbol(OutputWriter* writer, void* writer_arg, void* const pc,
+                     const char* const prefix) {
+  char tmp[1024];
+  const char* symbol = "(unknown)";
+  // Symbolizes the previous address of pc because pc may be in the
+  // next function.  The overrun happens when the function ends with
+  // a call to a function annotated noreturn (e.g. CHECK).
+  // If symbolization of pc-1 fails, also try pc on the off-chance
+  // that we crashed on the first instruction of a function (that
+  // actually happens very often for e.g. __restore_rt).
+  const uintptr_t prev_pc = reinterpret_cast<uintptr_t>(pc) - 1;
+  if (y_absl::Symbolize(reinterpret_cast<const char*>(prev_pc), tmp,
+                      sizeof(tmp)) ||
+      y_absl::Symbolize(pc, tmp, sizeof(tmp))) {
+    symbol = tmp;
+  }
+  char buf[1024];
+  snprintf(buf, sizeof(buf), "%s@ %*p  %s\n", prefix, kPrintfPointerFieldWidth,
+           pc, symbol);
+  writer(buf, writer_arg);
+}
+
+// Print a program counter, its stack frame size, and its symbol name.
+// Note that there is a separate symbolize_pc argument. Return addresses may be
+// at the end of the function, and this allows the caller to back up from pc if
+// appropriate.
+void DumpPCAndFrameSizeAndSymbol(OutputWriter* writer, void* writer_arg,
+                                 void* const pc, void* const symbolize_pc,
+                                 int framesize, const char* const prefix) {
+  char tmp[1024];
+  const char* symbol = "(unknown)";
+  if (y_absl::Symbolize(symbolize_pc, tmp, sizeof(tmp))) {
+    symbol = tmp;
+  }
+  char buf[1024];
+  if (framesize <= 0) {
+    snprintf(buf, sizeof(buf), "%s@ %*p  (unknown)  %s\n", prefix,
+             kPrintfPointerFieldWidth, pc, symbol);
+  } else {
+    snprintf(buf, sizeof(buf), "%s@ %*p  %9d  %s\n", prefix,
+             kPrintfPointerFieldWidth, pc, framesize, symbol);
+  }
+  writer(buf, writer_arg);
+}
+
+}  // namespace
+
+void RegisterDebugStackTraceHook(SymbolizeUrlEmitter hook) {
+  debug_stack_trace_hook = hook;
+}
+
+SymbolizeUrlEmitter GetDebugStackTraceHook() { return debug_stack_trace_hook; }
+
 // Returns the program counter from signal context, nullptr if
 // unknown. vuc is a ucontext_t*. We use void* to avoid the use of
 // ucontext_t on non-POSIX systems.
-void* GetProgramCounter(void* vuc) {
+void* GetProgramCounter(void* const vuc) {
 #ifdef __linux__
   if (vuc != nullptr) {
     ucontext_t* context = reinterpret_cast<ucontext_t*>(vuc);
@@ -82,6 +193,8 @@ void* GetProgramCounter(void* vuc) {
       return reinterpret_cast<void*>(context->uc_mcontext.gregs[16]);
 #elif defined(__e2k__)
     return reinterpret_cast<void*>(context->uc_mcontext.cr0_hi);
+#elif defined(__loongarch__)
+    return reinterpret_cast<void*>(context->uc_mcontext.__pc);
 #else
 #error "Undefined Architecture."
 #endif
@@ -120,59 +233,17 @@ void* GetProgramCounter(void* vuc) {
   return nullptr;
 }
 
-// The %p field width for printf() functions is two characters per byte,
-// and two extra for the leading "0x".
-static constexpr int kPrintfPointerFieldWidth = 2 + 2 * sizeof(void*);
-
-// Print a program counter, its stack frame size, and its symbol name.
-// Note that there is a separate symbolize_pc argument. Return addresses may be
-// at the end of the function, and this allows the caller to back up from pc if
-// appropriate.
-static void DumpPCAndFrameSizeAndSymbol(void (*writerfn)(const char*, void*),
-                                        void* writerfn_arg, void* pc,
-                                        void* symbolize_pc, int framesize,
-                                        const char* const prefix) {
-  char tmp[1024];
-  const char* symbol = "(unknown)";
-  if (y_absl::Symbolize(symbolize_pc, tmp, sizeof(tmp))) {
-    symbol = tmp;
-  }
-  char buf[1024];
-  if (framesize <= 0) {
-    snprintf(buf, sizeof(buf), "%s@ %*p  (unknown)  %s\n", prefix,
-             kPrintfPointerFieldWidth, pc, symbol);
-  } else {
-    snprintf(buf, sizeof(buf), "%s@ %*p  %9d  %s\n", prefix,
-             kPrintfPointerFieldWidth, pc, framesize, symbol);
-  }
-  writerfn(buf, writerfn_arg);
-}
-
-// Print a program counter and the corresponding stack frame size.
-static void DumpPCAndFrameSize(void (*writerfn)(const char*, void*),
-                               void* writerfn_arg, void* pc, int framesize,
-                               const char* const prefix) {
-  char buf[100];
-  if (framesize <= 0) {
-    snprintf(buf, sizeof(buf), "%s@ %*p  (unknown)\n", prefix,
-             kPrintfPointerFieldWidth, pc);
-  } else {
-    snprintf(buf, sizeof(buf), "%s@ %*p  %9d\n", prefix,
-             kPrintfPointerFieldWidth, pc, framesize);
-  }
-  writerfn(buf, writerfn_arg);
-}
-
-void DumpPCAndFrameSizesAndStackTrace(
-    void* pc, void* const stack[], int frame_sizes[], int depth,
-    int min_dropped_frames, bool symbolize_stacktrace,
-    void (*writerfn)(const char*, void*), void* writerfn_arg) {
+void DumpPCAndFrameSizesAndStackTrace(void* const pc, void* const stack[],
+                                      int frame_sizes[], int depth,
+                                      int min_dropped_frames,
+                                      bool symbolize_stacktrace,
+                                      OutputWriter* writer, void* writer_arg) {
   if (pc != nullptr) {
     // We don't know the stack frame size for PC, use 0.
     if (symbolize_stacktrace) {
-      DumpPCAndFrameSizeAndSymbol(writerfn, writerfn_arg, pc, pc, 0, "PC: ");
+      DumpPCAndFrameSizeAndSymbol(writer, writer_arg, pc, pc, 0, "PC: ");
     } else {
-      DumpPCAndFrameSize(writerfn, writerfn_arg, pc, 0, "PC: ");
+      DumpPCAndFrameSize(writer, writer_arg, pc, 0, "PC: ");
     }
   }
   for (int i = 0; i < depth; i++) {
@@ -182,20 +253,61 @@ void DumpPCAndFrameSizesAndStackTrace(
       // call to a function annotated noreturn (e.g. CHECK). Note that we don't
       // do this for pc above, as the adjustment is only correct for return
       // addresses.
-      DumpPCAndFrameSizeAndSymbol(writerfn, writerfn_arg, stack[i],
+      DumpPCAndFrameSizeAndSymbol(writer, writer_arg, stack[i],
                                   reinterpret_cast<char*>(stack[i]) - 1,
                                   frame_sizes[i], "    ");
     } else {
-      DumpPCAndFrameSize(writerfn, writerfn_arg, stack[i], frame_sizes[i],
-                         "    ");
+      DumpPCAndFrameSize(writer, writer_arg, stack[i], frame_sizes[i], "    ");
     }
   }
   if (min_dropped_frames > 0) {
     char buf[100];
     snprintf(buf, sizeof(buf), "    @ ... and at least %d more frames\n",
              min_dropped_frames);
-    writerfn(buf, writerfn_arg);
+    writer(buf, writer_arg);
+  }
+}
+
+// Dump current stack trace as directed by writer.
+// Make sure this function is not inlined to avoid skipping too many top frames.
+Y_ABSL_ATTRIBUTE_NOINLINE
+void DumpStackTrace(int min_dropped_frames, int max_num_frames,
+                    bool symbolize_stacktrace, OutputWriter* writer,
+                    void* writer_arg) {
+  // Print stack trace
+  void* stack_buf[kDefaultDumpStackFramesLimit];
+  void** stack = stack_buf;
+  int num_stack = kDefaultDumpStackFramesLimit;
+  int allocated_bytes = 0;
+
+  if (num_stack >= max_num_frames) {
+    // User requested fewer frames than we already have space for.
+    num_stack = max_num_frames;
+  } else {
+    const size_t needed_bytes = max_num_frames * sizeof(stack[0]);
+    void* p = Allocate(needed_bytes);
+    if (p != nullptr) {  // We got the space.
+      num_stack = max_num_frames;
+      stack = reinterpret_cast<void**>(p);
+      allocated_bytes = needed_bytes;
+    }
   }
+
+  size_t depth = y_absl::GetStackTrace(stack, num_stack, min_dropped_frames + 1);
+  for (size_t i = 0; i < depth; i++) {
+    if (symbolize_stacktrace) {
+      DumpPCAndSymbol(writer, writer_arg, stack[i], "    ");
+    } else {
+      DumpPC(writer, writer_arg, stack[i], "    ");
+    }
+  }
+
+  auto hook = GetDebugStackTraceHook();
+  if (hook != nullptr) {
+    (*hook)(stack, depth, writer, writer_arg);
+  }
+
+  if (allocated_bytes != 0) Deallocate(stack, allocated_bytes);
 }
 
 }  // namespace debugging_internal
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/examine_stack.h b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/examine_stack.h
index 4ac2c8358a..25d9da3e1e 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/examine_stack.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/examine_stack.h
@@ -23,17 +23,39 @@ namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
 namespace debugging_internal {
 
+// Type of function used for printing in stack trace dumping, etc.
+// We avoid closures to keep things simple.
+typedef void OutputWriter(const char*, void*);
+
+// RegisterDebugStackTraceHook() allows to register a single routine
+// `hook` that is called each time DumpStackTrace() is called.
+// `hook` may be called from a signal handler.
+typedef void (*SymbolizeUrlEmitter)(void* const stack[], int depth,
+                                    OutputWriter* writer, void* writer_arg);
+
+// Registration of SymbolizeUrlEmitter for use inside of a signal handler.
+// This is inherently unsafe and must be signal safe code.
+void RegisterDebugStackTraceHook(SymbolizeUrlEmitter hook);
+SymbolizeUrlEmitter GetDebugStackTraceHook();
+
 // Returns the program counter from signal context, or nullptr if
 // unknown. `vuc` is a ucontext_t*. We use void* to avoid the use of
 // ucontext_t on non-POSIX systems.
-void* GetProgramCounter(void* vuc);
+void* GetProgramCounter(void* const vuc);
 
-// Uses `writerfn` to dump the program counter, stack trace, and stack
+// Uses `writer` to dump the program counter, stack trace, and stack
 // frame sizes.
-void DumpPCAndFrameSizesAndStackTrace(
-    void* pc, void* const stack[], int frame_sizes[], int depth,
-    int min_dropped_frames, bool symbolize_stacktrace,
-    void (*writerfn)(const char*, void*), void* writerfn_arg);
+void DumpPCAndFrameSizesAndStackTrace(void* const pc, void* const stack[],
+                                      int frame_sizes[], int depth,
+                                      int min_dropped_frames,
+                                      bool symbolize_stacktrace,
+                                      OutputWriter* writer, void* writer_arg);
+
+// Dump current stack trace omitting the topmost `min_dropped_frames` stack
+// frames.
+void DumpStackTrace(int min_dropped_frames, int max_num_frames,
+                    bool symbolize_stacktrace, OutputWriter* writer,
+                    void* writer_arg);
 
 }  // namespace debugging_internal
 Y_ABSL_NAMESPACE_END
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_aarch64-inl.inc b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_aarch64-inl.inc
index e225b4dd18..d33f47e1cd 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_aarch64-inl.inc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_aarch64-inl.inc
@@ -176,12 +176,17 @@ static int UnwindImpl(void** result, int* sizes, int max_depth, int skip_count,
     // Implementation detail: we clamp the max of frames we are willing to
     // count, so as not to spend too much time in the loop below.
     const int kMaxUnwind = 200;
-    int j = 0;
-    for (; frame_pointer != nullptr && j < kMaxUnwind; j++) {
+    int num_dropped_frames = 0;
+    for (int j = 0; frame_pointer != nullptr && j < kMaxUnwind; j++) {
+      if (skip_count > 0) {
+        skip_count--;
+      } else {
+        num_dropped_frames++;
+      }
       frame_pointer =
           NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(frame_pointer, ucp);
     }
-    *min_dropped_frames = j;
+    *min_dropped_frames = num_dropped_frames;
   }
   return n;
 }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_arm-inl.inc b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_arm-inl.inc
index d735d1f933..bccf1174b7 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_arm-inl.inc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_arm-inl.inc
@@ -112,11 +112,16 @@ static int UnwindImpl(void** result, int* sizes, int max_depth, int skip_count,
     // Implementation detail: we clamp the max of frames we are willing to
     // count, so as not to spend too much time in the loop below.
     const int kMaxUnwind = 200;
-    int j = 0;
-    for (; sp != nullptr && j < kMaxUnwind; j++) {
+    int num_dropped_frames = 0;
+    for (int j = 0; sp != nullptr && j < kMaxUnwind; j++) {
+      if (skip_count > 0) {
+        skip_count--;
+      } else {
+        num_dropped_frames++;
+      }
       sp = NextStackFrame<!IS_STACK_FRAMES>(sp);
     }
-    *min_dropped_frames = j;
+    *min_dropped_frames = num_dropped_frames;
   }
   return n;
 }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_config.h b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_config.h
index d93c3f1dd9..6a13b5f24a 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_config.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_config.h
@@ -37,7 +37,8 @@
   "y_absl/debugging/internal/stacktrace_generic-inl.inc"
 #endif  // defined(Y_ABSL_HAVE_THREAD_LOCAL)
 
-#elif defined(__EMSCRIPTEN__)
+// Emscripten stacktraces rely on JS. Do not use them in standalone mode.
+#elif defined(__EMSCRIPTEN__) && !defined(STANDALONE_WASM)
 #define Y_ABSL_STACKTRACE_INL_HEADER \
   "y_absl/debugging/internal/stacktrace_emscripten-inl.inc"
 
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_powerpc-inl.inc b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_powerpc-inl.inc
index 635c3dd2a6..56dcd40c67 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_powerpc-inl.inc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_powerpc-inl.inc
@@ -231,11 +231,16 @@ static int UnwindImpl(void** result, int* sizes, int max_depth, int skip_count,
     // Implementation detail: we clamp the max of frames we are willing to
     // count, so as not to spend too much time in the loop below.
     const int kMaxUnwind = 1000;
-    int j = 0;
-    for (; next_sp != nullptr && j < kMaxUnwind; j++) {
+    int num_dropped_frames = 0;
+    for (int j = 0; next_sp != nullptr && j < kMaxUnwind; j++) {
+      if (skip_count > 0) {
+        skip_count--;
+      } else {
+        num_dropped_frames++;
+      }
       next_sp = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(next_sp, ucp);
     }
-    *min_dropped_frames = j;
+    *min_dropped_frames = num_dropped_frames;
   }
   return n;
 }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_riscv-inl.inc b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_riscv-inl.inc
index 4072ecc116..39a1fb2408 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_riscv-inl.inc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_riscv-inl.inc
@@ -56,7 +56,7 @@ static const unsigned char *GetKernelRtSigreturnAddress() {
     y_absl::debugging_internal::VDSOSupport::SymbolInfo symbol_info;
     // Symbol versioning pulled from arch/riscv/kernel/vdso/vdso.lds at v5.10.
     auto lookup = [&](int type) {
-      return vdso.LookupSymbol("__kernel_rt_sigreturn", "LINUX_4.15", type,
+      return vdso.LookupSymbol("__vdso_rt_sigreturn", "LINUX_4.15", type,
                                &symbol_info);
     };
     if ((!lookup(STT_FUNC) && !lookup(STT_NOTYPE)) ||
@@ -171,26 +171,21 @@ Y_ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS  // May read random elements from stack.
 Y_ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY   // May read random elements from stack.
 static int UnwindImpl(void **result, int *sizes, int max_depth, int skip_count,
                       const void *ucp, int *min_dropped_frames) {
+  // The `frame_pointer` that is computed here points to the top of the frame.
+  // The two words preceding the address are the return address and the previous
+  // frame pointer.
 #if defined(__GNUC__)
   void **frame_pointer = reinterpret_cast<void **>(__builtin_frame_address(0));
 #else
 #error reading stack pointer not yet supported on this platform
 #endif
 
-  skip_count++;  // Skip the frame for this function.
   int n = 0;
-
-  // The `frame_pointer` that is computed here points to the top of the frame.
-  // The two words preceding the address are the return address and the previous
-  // frame pointer.  To find a PC value associated with the current frame, we
-  // need to go down a level in the call chain.  So we remember the return
-  // address of the last frame seen.  This does not work for the first stack
-  // frame, which belongs to `UnwindImp()` but we skip the frame for
-  // `UnwindImp()` anyway.
-  void *prev_return_address = nullptr;
-
+  void *return_address = nullptr;
   while (frame_pointer && n < max_depth) {
-    // The y_absl::GetStackFrames routine si called when we are in some
+    return_address = frame_pointer[-1];
+
+    // The y_absl::GetStackFrames routine is called when we are in some
     // informational context (the failure signal handler for example).  Use the
     // non-strict unwinding rules to produce a stack trace that is as complete
     // as possible (even if it contains a few bogus entries in some rare cases).
@@ -200,26 +195,33 @@ static int UnwindImpl(void **result, int *sizes, int max_depth, int skip_count,
     if (skip_count > 0) {
       skip_count--;
     } else {
-      result[n] = prev_return_address;
+      result[n] = return_address;
       if (IS_STACK_FRAMES) {
         sizes[n] = ComputeStackFrameSize(frame_pointer, next_frame_pointer);
       }
       n++;
     }
-    prev_return_address = frame_pointer[-1];
+
     frame_pointer = next_frame_pointer;
   }
+
   if (min_dropped_frames != nullptr) {
     // Implementation detail: we clamp the max of frames we are willing to
     // count, so as not to spend too much time in the loop below.
     const int kMaxUnwind = 200;
-    int j = 0;
-    for (; frame_pointer != nullptr && j < kMaxUnwind; j++) {
+    int num_dropped_frames = 0;
+    for (int j = 0; frame_pointer != nullptr && j < kMaxUnwind; j++) {
+      if (skip_count > 0) {
+        skip_count--;
+      } else {
+        num_dropped_frames++;
+      }
       frame_pointer =
           NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(frame_pointer, ucp);
     }
-    *min_dropped_frames = j;
+    *min_dropped_frames = num_dropped_frames;
   }
+
   return n;
 }
 
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_x86-inl.inc b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_x86-inl.inc
index 6e598bc359..bd5dc13d99 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_x86-inl.inc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/stacktrace_x86-inl.inc
@@ -341,12 +341,17 @@ static int UnwindImpl(void **result, int *sizes, int max_depth, int skip_count,
     // Implementation detail: we clamp the max of frames we are willing to
     // count, so as not to spend too much time in the loop below.
     const int kMaxUnwind = 1000;
-    int j = 0;
-    for (; fp != nullptr && j < kMaxUnwind; j++) {
+    int num_dropped_frames = 0;
+    for (int j = 0; fp != nullptr && j < kMaxUnwind; j++) {
+      if (skip_count > 0) {
+        skip_count--;
+      } else {
+        num_dropped_frames++;
+      }
       fp = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(fp, ucp, stack_low,
                                                              stack_high);
     }
-    *min_dropped_frames = j;
+    *min_dropped_frames = num_dropped_frames;
   }
   return n;
 }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/vdso_support.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/vdso_support.cc
index ff28d04d57..282b406bb7 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/vdso_support.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/internal/vdso_support.cc
@@ -33,7 +33,7 @@
 #endif
 #include <unistd.h>
 
-#if defined(__GLIBC__) && \
+#if !defined(__UCLIBC__) && defined(__GLIBC__) && \
     (__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 16))
 #define Y_ABSL_HAVE_GETAUXVAL
 #endif
@@ -50,8 +50,14 @@
 #define AT_SYSINFO_EHDR 33  // for crosstoolv10
 #endif
 
+#if defined(__NetBSD__)
+using Elf32_auxv_t = Aux32Info;
+using Elf64_auxv_t = Aux64Info;
+#endif
 #if defined(__FreeBSD__)
+#if defined(__ELF_WORD_SIZE) && __ELF_WORD_SIZE == 64
 using Elf64_auxv_t = Elf64_Auxinfo;
+#endif
 using Elf32_auxv_t = Elf32_Auxinfo;
 #endif
 
@@ -63,7 +69,9 @@ Y_ABSL_CONST_INIT
 std::atomic<const void *> VDSOSupport::vdso_base_(
     debugging_internal::ElfMemImage::kInvalidBase);
 
-std::atomic<VDSOSupport::GetCpuFn> VDSOSupport::getcpu_fn_(&InitAndGetCPU);
+Y_ABSL_CONST_INIT std::atomic<VDSOSupport::GetCpuFn> VDSOSupport::getcpu_fn_(
+    &InitAndGetCPU);
+
 VDSOSupport::VDSOSupport()
     // If vdso_base_ is still set to kInvalidBase, we got here
     // before VDSOSupport::Init has been called. Call it now.
@@ -104,8 +112,13 @@ const void *VDSOSupport::Init() {
     ElfW(auxv_t) aux;
     while (read(fd, &aux, sizeof(aux)) == sizeof(aux)) {
       if (aux.a_type == AT_SYSINFO_EHDR) {
+#if defined(__NetBSD__)
+        vdso_base_.store(reinterpret_cast<void *>(aux.a_v),
+                         std::memory_order_relaxed);
+#else
         vdso_base_.store(reinterpret_cast<void *>(aux.a_un.a_val),
                          std::memory_order_relaxed);
+#endif
         break;
       }
     }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/leak_check.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/leak_check.cc
index 0ac471b986..1cddc78cc8 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/leak_check.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/leak_check.cc
@@ -11,29 +11,19 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
-
+//
 // Wrappers around lsan_interface functions.
-// When lsan is not linked in, these functions are not available,
-// therefore Abseil code which depends on these functions is conditioned on the
-// definition of LEAK_SANITIZER.
-#include "y_absl/base/attributes.h"
-#include "y_absl/debugging/leak_check.h"
+//
+// These are always-available run-time functions manipulating the LeakSanitizer,
+// even when the lsan_interface (and LeakSanitizer) is not available. When
+// LeakSanitizer is not linked in, these functions become no-op stubs.
 
-#ifndef LEAK_SANITIZER
+#include "y_absl/debugging/leak_check.h"
 
-namespace y_absl {
-Y_ABSL_NAMESPACE_BEGIN
-bool HaveLeakSanitizer() { return false; }
-bool LeakCheckerIsActive() { return false; }
-void DoIgnoreLeak(const void*) { }
-void RegisterLivePointers(const void*, size_t) { }
-void UnRegisterLivePointers(const void*, size_t) { }
-LeakCheckDisabler::LeakCheckDisabler() { }
-LeakCheckDisabler::~LeakCheckDisabler() { }
-Y_ABSL_NAMESPACE_END
-}  // namespace y_absl
+#include "y_absl/base/attributes.h"
+#include "y_absl/base/config.h"
 
-#else
+#if defined(Y_ABSL_HAVE_LEAK_SANITIZER)
 
 #include <sanitizer/lsan_interface.h>
 
@@ -66,4 +56,18 @@ LeakCheckDisabler::~LeakCheckDisabler() { __lsan_enable(); }
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
 
-#endif  // LEAK_SANITIZER
+#else  // defined(Y_ABSL_HAVE_LEAK_SANITIZER)
+
+namespace y_absl {
+Y_ABSL_NAMESPACE_BEGIN
+bool HaveLeakSanitizer() { return false; }
+bool LeakCheckerIsActive() { return false; }
+void DoIgnoreLeak(const void*) { }
+void RegisterLivePointers(const void*, size_t) { }
+void UnRegisterLivePointers(const void*, size_t) { }
+LeakCheckDisabler::LeakCheckDisabler() { }
+LeakCheckDisabler::~LeakCheckDisabler() { }
+Y_ABSL_NAMESPACE_END
+}  // namespace y_absl
+
+#endif  // defined(Y_ABSL_HAVE_LEAK_SANITIZER)
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/leak_check.h b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/leak_check.h
index 154fe4805d..17256e0c03 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/leak_check.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/leak_check.h
@@ -24,7 +24,24 @@
 // Note: this leak checking API is not yet supported in MSVC.
 // Leak checking is enabled by default in all ASan builds.
 //
-// See https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer
+// https://clang.llvm.org/docs/LeakSanitizer.html
+// https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer
+//
+// GCC and Clang both automatically enable LeakSanitizer when AddressSanitizer
+// is enabled. To use the mode, simply pass `-fsanitize=address` to both the
+// compiler and linker. An example Bazel command could be
+//
+//   $ bazel test --copt=-fsanitize=address --linkopt=-fsanitize=address ...
+//
+// GCC and Clang auto support a standalone LeakSanitizer mode (a mode which does
+// not also use AddressSanitizer). To use the mode, simply pass
+// `-fsanitize=leak` to both the compiler and linker. Since GCC does not
+// currently provide a way of detecting this mode at compile-time, GCC users
+// must also pass -DLEAK_SANIITIZER to the compiler. An example Bazel command
+// could be
+//
+//   $ bazel test --copt=-DLEAK_SANITIZER --copt=-fsanitize=leak
+//     --linkopt=-fsanitize=leak ...
 //
 // -----------------------------------------------------------------------------
 #ifndef Y_ABSL_DEBUGGING_LEAK_CHECK_H_
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/symbolize.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/symbolize.cc
index 43363339cd..57dff31090 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/symbolize.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/symbolize.cc
@@ -23,6 +23,11 @@
 #endif
 #endif
 
+// Emscripten symbolization relies on JS. Do not use them in standalone mode.
+#if defined(__EMSCRIPTEN__) && !defined(STANDALONE_WASM)
+#define Y_ABSL_INTERNAL_HAVE_SYMBOLIZE_WASM
+#endif
+
 #if defined(Y_ABSL_INTERNAL_HAVE_ELF_SYMBOLIZE)
 #include "y_absl/debugging/symbolize_elf.inc"
 #elif defined(Y_ABSL_INTERNAL_HAVE_SYMBOLIZE_WIN32)
@@ -31,7 +36,7 @@
 #include "y_absl/debugging/symbolize_win32.inc"
 #elif defined(__APPLE__)
 #include "y_absl/debugging/symbolize_darwin.inc"
-#elif defined(__EMSCRIPTEN__)
+#elif defined(Y_ABSL_INTERNAL_HAVE_SYMBOLIZE_WASM)
 #include "y_absl/debugging/symbolize_emscripten.inc"
 #else
 #include "y_absl/debugging/symbolize_unimplemented.inc"
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/symbolize_elf.inc b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/symbolize_elf.inc
index 343be4f91b..0640bfc76f 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/symbolize_elf.inc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/symbolize_elf.inc
@@ -323,6 +323,7 @@ class Symbolizer {
                                            const ptrdiff_t relocation,
                                            char *out, int out_size,
                                            char *tmp_buf, int tmp_buf_size);
+  const char *GetUncachedSymbol(const void *pc);
 
   enum {
     SYMBOL_BUF_SIZE = 3072,
@@ -1145,6 +1146,14 @@ bool Symbolizer::RegisterObjFile(const char *filename,
                      reinterpret_cast<uintptr_t>(old->end_addr), old->filename);
       }
       return true;
+    } else if (old->end_addr == start_addr &&
+               reinterpret_cast<uintptr_t>(old->start_addr) - old->offset ==
+                   reinterpret_cast<uintptr_t>(start_addr) - offset &&
+               strcmp(old->filename, filename) == 0) {
+      // Two contiguous map entries that span a contiguous region of the file,
+      // perhaps because some part of the file was mlock()ed. Combine them.
+      old->end_addr = end_addr;
+      return true;
     }
   }
   ObjFile *obj = impl->addr_map_.Add();
@@ -1333,13 +1342,7 @@ static bool MaybeInitializeObjFile(ObjFile *obj) {
 // they are called here as well.
 // To keep stack consumption low, we would like this function to not
 // get inlined.
-const char *Symbolizer::GetSymbol(const void *const pc) {
-  const char *entry = FindSymbolInCache(pc);
-  if (entry != nullptr) {
-    return entry;
-  }
-  symbol_buf_[0] = '\0';
-
+const char *Symbolizer::GetUncachedSymbol(const void *pc) {
   ObjFile *const obj = FindObjFile(pc, 1);
   ptrdiff_t relocation = 0;
   int fd = -1;
@@ -1427,6 +1430,42 @@ const char *Symbolizer::GetSymbol(const void *const pc) {
   return InsertSymbolInCache(pc, symbol_buf_);
 }
 
+const char *Symbolizer::GetSymbol(const void *pc) {
+  const char *entry = FindSymbolInCache(pc);
+  if (entry != nullptr) {
+    return entry;
+  }
+  symbol_buf_[0] = '\0';
+
+#ifdef __hppa__
+  {
+    // In some contexts (e.g., return addresses), PA-RISC uses the lowest two
+    // bits of the address to indicate the privilege level. Clear those bits
+    // before trying to symbolize.
+    const auto pc_bits = reinterpret_cast<uintptr_t>(pc);
+    const auto address = pc_bits & ~0x3;
+    entry = GetUncachedSymbol(reinterpret_cast<const void *>(address));
+    if (entry != nullptr) {
+      return entry;
+    }
+
+    // In some contexts, PA-RISC also uses bit 1 of the address to indicate that
+    // this is a cross-DSO function pointer. Such function pointers actually
+    // point to a procedure label, a struct whose first 32-bit (pointer) element
+    // actually points to the function text. With no symbol found for this
+    // address so far, try interpreting it as a cross-DSO function pointer and
+    // see how that goes.
+    if (pc_bits & 0x2) {
+      return GetUncachedSymbol(*reinterpret_cast<const void *const *>(address));
+    }
+
+    return nullptr;
+  }
+#else
+  return GetUncachedSymbol(pc);
+#endif
+}
+
 bool RemoveAllSymbolDecorators(void) {
   if (!g_decorators_mu.TryLock()) {
     // Someone else is using decorators. Get out.
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/flags/config.h b/contrib/restricted/abseil-cpp-tstring/y_absl/flags/config.h
index c6d4488c51..08de490eb1 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/flags/config.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/flags/config.h
@@ -45,14 +45,6 @@
 #define Y_ABSL_FLAGS_STRIP_HELP Y_ABSL_FLAGS_STRIP_NAMES
 #endif
 
-// Y_ABSL_FLAGS_INTERNAL_HAS_RTTI macro is used for selecting if we can use RTTI
-// for flag type identification.
-#ifdef Y_ABSL_FLAGS_INTERNAL_HAS_RTTI
-#error Y_ABSL_FLAGS_INTERNAL_HAS_RTTI cannot be directly set
-#elif !defined(__GNUC__) || defined(__GXX_RTTI)
-#define Y_ABSL_FLAGS_INTERNAL_HAS_RTTI 1
-#endif  // !defined(__GNUC__) || defined(__GXX_RTTI)
-
 // These macros represent the "source of truth" for the list of supported
 // built-in types.
 #define Y_ABSL_FLAGS_INTERNAL_BUILTIN_TYPES(A) \
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/flags/declare.h b/contrib/restricted/abseil-cpp-tstring/y_absl/flags/declare.h
index f7455d0873..0b36402496 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/flags/declare.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/flags/declare.h
@@ -60,6 +60,14 @@ Y_ABSL_NAMESPACE_END
 // The Y_ABSL_DECLARE_FLAG(type, name) macro expands to:
 //
 //   extern y_absl::Flag<type> FLAGS_name;
-#define Y_ABSL_DECLARE_FLAG(type, name) extern ::y_absl::Flag<type> FLAGS_##name
+#define Y_ABSL_DECLARE_FLAG(type, name) Y_ABSL_DECLARE_FLAG_INTERNAL(type, name)
+
+// Internal implementation of Y_ABSL_DECLARE_FLAG to allow macro expansion of its
+// arguments. Clients must use Y_ABSL_DECLARE_FLAG instead.
+#define Y_ABSL_DECLARE_FLAG_INTERNAL(type, name)               \
+  extern y_absl::Flag<type> FLAGS_##name;                      \
+  namespace y_absl /* block flags in namespaces */ {}          \
+  /* second redeclaration is to allow applying attributes */ \
+  extern y_absl::Flag<type> FLAGS_##name
 
 #endif  // Y_ABSL_FLAGS_DECLARE_H_
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/flags/flag.h b/contrib/restricted/abseil-cpp-tstring/y_absl/flags/flag.h
index edfbff9c30..65448650d3 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/flags/flag.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/flags/flag.h
@@ -67,6 +67,10 @@ Y_ABSL_NAMESPACE_BEGIN
 //      Y_ABSL_FLAG(int, count, 0, "Count of items to process");
 //
 // No public methods of `y_absl::Flag<T>` are part of the Abseil Flags API.
+//
+// For type support of Abseil Flags, see the marshalling.h header file, which
+// discusses supported standard types, optional flags, and additional Abseil
+// type support.
 #if !defined(_MSC_VER) || defined(__clang__)
 template <typename T>
 using Flag = flags_internal::Flag<T>;
@@ -265,6 +269,7 @@ Y_ABSL_NAMESPACE_END
 // global name for FLAGS_no<flag_name> symbol, thus preventing the possibility
 // of defining two flags with names foo and nofoo.
 #define Y_ABSL_FLAG_IMPL(Type, name, default_value, help)                       \
+  extern ::y_absl::Flag<Type> FLAGS_##name;                                     \
   namespace y_absl /* block flags in namespaces */ {}                           \
   Y_ABSL_FLAG_IMPL_DECLARE_DEF_VAL_WRAPPER(name, Type, default_value)           \
   Y_ABSL_FLAG_IMPL_DECLARE_HELP_WRAPPER(name, help)                             \
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/flags/internal/flag.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/flags/internal/flag.cc
index 55950b52d1..d3047ee045 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/flags/internal/flag.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/flags/internal/flag.cc
@@ -30,6 +30,7 @@
 #include "y_absl/base/call_once.h"
 #include "y_absl/base/casts.h"
 #include "y_absl/base/config.h"
+#include "y_absl/base/dynamic_annotations.h"
 #include "y_absl/base/optimization.h"
 #include "y_absl/flags/config.h"
 #include "y_absl/flags/internal/commandlineflag.h"
@@ -160,6 +161,8 @@ void FlagImpl::Init() {
         std::memcpy(buf.data() + Sizeof(op_), &initialized,
                     sizeof(initialized));
       }
+      // Type can contain valid uninitialized bits, e.g. padding.
+      Y_ABSL_ANNOTATE_MEMORY_IS_INITIALIZED(buf.data(), buf.size());
       OneWordValue().store(y_absl::bit_cast<int64_t>(buf),
                            std::memory_order_release);
       break;
@@ -205,7 +208,7 @@ void FlagImpl::AssertValidType(FlagFastTypeId rhs_type_id,
 
   if (lhs_runtime_type_id == rhs_runtime_type_id) return;
 
-#if defined(Y_ABSL_FLAGS_INTERNAL_HAS_RTTI)
+#ifdef Y_ABSL_INTERNAL_HAS_RTTI
   if (*lhs_runtime_type_id == *rhs_runtime_type_id) return;
 #endif
 
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/flags/internal/flag.h b/contrib/restricted/abseil-cpp-tstring/y_absl/flags/internal/flag.h
index c5d52f9993..bce5e32656 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/flags/internal/flag.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/flags/internal/flag.h
@@ -163,7 +163,7 @@ inline ptrdiff_t ValueOffset(FlagOpFn op) {
 // Returns an address of RTTI's typeid(T).
 template <typename T>
 inline const std::type_info* GenRuntimeTypeId() {
-#if defined(Y_ABSL_FLAGS_INTERNAL_HAS_RTTI)
+#ifdef Y_ABSL_INTERNAL_HAS_RTTI
   return &typeid(T);
 #else
   return nullptr;
@@ -303,7 +303,9 @@ constexpr FlagDefaultArg DefaultArg(char) {
 ///////////////////////////////////////////////////////////////////////////////
 // Flag current value auxiliary structs.
 
-constexpr int64_t UninitializedFlagValue() { return 0xababababababababll; }
+constexpr int64_t UninitializedFlagValue() {
+  return static_cast<int64_t>(0xababababababababll);
+}
 
 template <typename T>
 using FlagUseValueAndInitBitStorage = std::integral_constant<
@@ -755,8 +757,8 @@ void* FlagOps(FlagOp op, const void* v1, void* v2, void* v3) {
     case FlagOp::kValueOffset: {
       // Round sizeof(FlagImp) to a multiple of alignof(FlagValue<T>) to get the
       // offset of the data.
-      ptrdiff_t round_to = alignof(FlagValue<T>);
-      ptrdiff_t offset =
+      size_t round_to = alignof(FlagValue<T>);
+      size_t offset =
           (sizeof(FlagImpl) + round_to - 1) / round_to * round_to;
       return reinterpret_cast<void*>(offset);
     }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/flags/marshalling.h b/contrib/restricted/abseil-cpp-tstring/y_absl/flags/marshalling.h
index 35f6a5b7c6..be84b1ea72 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/flags/marshalling.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/flags/marshalling.h
@@ -33,6 +33,7 @@
 // * `double`
 // * `TString`
 // * `std::vector<TString>`
+// * `std::optional<T>`
 // * `y_absl::LogSeverity` (provided natively for layering reasons)
 //
 // Note that support for integral types is implemented using overloads for
@@ -65,6 +66,42 @@
 // below.)
 //
 // -----------------------------------------------------------------------------
+// Optional Flags
+// -----------------------------------------------------------------------------
+//
+// The Abseil flags library supports flags of type `std::optional<T>` where
+// `T` is a type of one of the supported flags. We refer to this flag type as
+// an "optional flag." An optional flag is either "valueless", holding no value
+// of type `T` (indicating that the flag has not been set) or a value of type
+// `T`. The valueless state in C++ code is represented by a value of
+// `std::nullopt` for the optional flag.
+//
+// Using `std::nullopt` as an optional flag's default value allows you to check
+// whether such a flag was ever specified on the command line:
+//
+//   if (y_absl::GetFlag(FLAGS_foo).has_value()) {
+//     // flag was set on command line
+//   } else {
+//     // flag was not passed on command line
+//   }
+//
+// Using an optional flag in this manner avoids common workarounds for
+// indicating such an unset flag (such as using sentinal values to indicate this
+// state).
+//
+// An optional flag also allows a developer to pass a flag in an "unset"
+// valueless state on the command line, allowing the flag to later be set in
+// binary logic. An optional flag's valueless state is indicated by the special
+// notation of passing the value as an empty string through the syntax `--flag=`
+// or `--flag ""`.
+//
+//   $ binary_with_optional --flag_in_unset_state=
+//   $ binary_with_optional --flag_in_unset_state ""
+//
+// Note: as a result of the above syntax requirements, an optional flag cannot
+// be set to a `T` of any value which unparses to the empty string.
+//
+// -----------------------------------------------------------------------------
 // Adding Type Support for Abseil Flags
 // -----------------------------------------------------------------------------
 //
@@ -162,14 +199,27 @@
 #ifndef Y_ABSL_FLAGS_MARSHALLING_H_
 #define Y_ABSL_FLAGS_MARSHALLING_H_
 
+#include "y_absl/base/config.h"
+
+#if defined(Y_ABSL_HAVE_STD_OPTIONAL) && !defined(Y_ABSL_USES_STD_OPTIONAL)
+#include <optional>
+#endif
 #include <util/generic/string.h>
 #include <vector>
 
-#include "y_absl/base/config.h"
 #include "y_absl/strings/string_view.h"
+#include "y_absl/types/optional.h"
 
 namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
+
+// Forward declaration to be used inside composable flag parse/unparse
+// implementations
+template <typename T>
+inline bool ParseFlag(y_absl::string_view input, T* dst, TString* error);
+template <typename T>
+inline TString UnparseFlag(const T& v);
+
 namespace flags_internal {
 
 // Overloads of `AbslParseFlag()` and `AbslUnparseFlag()` for fundamental types.
@@ -189,6 +239,36 @@ bool AbslParseFlag(y_absl::string_view, TString*, TString*);
 bool AbslParseFlag(y_absl::string_view, std::vector<TString>*, TString*);
 
 template <typename T>
+bool AbslParseFlag(y_absl::string_view text, y_absl::optional<T>* f,
+                   TString* err) {
+  if (text.empty()) {
+    *f = y_absl::nullopt;
+    return true;
+  }
+  T value;
+  if (!y_absl::ParseFlag(text, &value, err)) return false;
+
+  *f = std::move(value);
+  return true;
+}
+
+#if defined(Y_ABSL_HAVE_STD_OPTIONAL) && !defined(Y_ABSL_USES_STD_OPTIONAL)
+template <typename T>
+bool AbslParseFlag(y_absl::string_view text, std::optional<T>* f,
+                   TString* err) {
+  if (text.empty()) {
+    *f = std::nullopt;
+    return true;
+  }
+  T value;
+  if (!y_absl::ParseFlag(text, &value, err)) return false;
+
+  *f = std::move(value);
+  return true;
+}
+#endif
+
+template <typename T>
 bool InvokeParseFlag(y_absl::string_view input, T* dst, TString* err) {
   // Comment on next line provides a good compiler error message if T
   // does not have AbslParseFlag(y_absl::string_view, T*, TString*).
@@ -202,6 +282,18 @@ TString AbslUnparseFlag(y_absl::string_view v);
 TString AbslUnparseFlag(const std::vector<TString>&);
 
 template <typename T>
+TString AbslUnparseFlag(const y_absl::optional<T>& f) {
+  return f.has_value() ? y_absl::UnparseFlag(*f) : "";
+}
+
+#if defined(Y_ABSL_HAVE_STD_OPTIONAL) && !defined(Y_ABSL_USES_STD_OPTIONAL)
+template <typename T>
+TString AbslUnparseFlag(const std::optional<T>& f) {
+  return f.has_value() ? y_absl::UnparseFlag(*f) : "";
+}
+#endif
+
+template <typename T>
 TString Unparse(const T& v) {
   // Comment on next line provides a good compiler error message if T does not
   // have UnparseFlag.
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/functional/bind_front.h b/contrib/restricted/abseil-cpp-tstring/y_absl/functional/bind_front.h
index bf3b367b93..e828c79aa7 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/functional/bind_front.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/functional/bind_front.h
@@ -30,6 +30,10 @@
 #ifndef Y_ABSL_FUNCTIONAL_BIND_FRONT_H_
 #define Y_ABSL_FUNCTIONAL_BIND_FRONT_H_
 
+#if defined(__cpp_lib_bind_front) && __cpp_lib_bind_front >= 201907L
+#include <functional>  // For std::bind_front.
+#endif  // defined(__cpp_lib_bind_front) && __cpp_lib_bind_front >= 201907L
+
 #include "y_absl/functional/internal/front_binder.h"
 #include "y_absl/utility/utility.h"
 
@@ -46,7 +50,8 @@ Y_ABSL_NAMESPACE_BEGIN
 // specified. More importantly, it provides more reliable correctness guarantees
 // than `std::bind()`; while `std::bind()` will silently ignore passing more
 // parameters than expected, for example, `y_absl::bind_front()` will report such
-// mis-uses as errors.
+// mis-uses as errors. In C++20, `y_absl::bind_front` is replaced by
+// `std::bind_front`.
 //
 // y_absl::bind_front(a...) can be seen as storing the results of
 // std::make_tuple(a...).
@@ -170,6 +175,9 @@ Y_ABSL_NAMESPACE_BEGIN
 //   // Doesn't copy "hi".
 //   y_absl::bind_front(Print, y_absl::string_view(hi))("Chuk");
 //
+#if 0
+using std::bind_front;
+#else   // defined(__cpp_lib_bind_front) && __cpp_lib_bind_front >= 201907L
 template <class F, class... BoundArgs>
 constexpr functional_internal::bind_front_t<F, BoundArgs...> bind_front(
     F&& func, BoundArgs&&... args) {
@@ -177,6 +185,7 @@ constexpr functional_internal::bind_front_t<F, BoundArgs...> bind_front(
       y_absl::in_place, y_absl::forward<F>(func),
       y_absl::forward<BoundArgs>(args)...);
 }
+#endif  // defined(__cpp_lib_bind_front) && __cpp_lib_bind_front >= 201907L
 
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/functional/function_ref.h b/contrib/restricted/abseil-cpp-tstring/y_absl/functional/function_ref.h
index 09fec40c7f..78814e8960 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/functional/function_ref.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/functional/function_ref.h
@@ -69,7 +69,8 @@ class FunctionRef;
 // An `y_absl::FunctionRef` is a lightweight wrapper to any invokable object with
 // a compatible signature. Generally, an `y_absl::FunctionRef` should only be used
 // as an argument type and should be preferred as an argument over a const
-// reference to a `std::function`.
+// reference to a `std::function`. `y_absl::FunctionRef` itself does not allocate,
+// although the wrapped invokable may.
 //
 // Example:
 //
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/hash/hash.h b/contrib/restricted/abseil-cpp-tstring/y_absl/hash/hash.h
index f876d11dbd..00a359d224 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/hash/hash.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/hash/hash.h
@@ -26,9 +26,9 @@
 //     support Abseil hashing without requiring you to define a hashing
 //     algorithm.
 //   * `HashState`, a type-erased class which implements the manipulation of the
-//     hash state (H) itself, contains member functions `combine()` and
-//     `combine_contiguous()`, which you can use to contribute to an existing
-//     hash state when hashing your types.
+//     hash state (H) itself; contains member functions `combine()`,
+//     `combine_contiguous()`, and `combine_unordered()`; and which you can use
+//     to contribute to an existing hash state when hashing your types.
 //
 // Unlike `std::hash` or other hashing frameworks, the Abseil hashing framework
 // provides most of its utility by abstracting away the hash algorithm (and its
@@ -40,6 +40,11 @@
 // each process.  E.g., `y_absl::Hash<int>{}(9)` in one process and
 // `y_absl::Hash<int>{}(9)` in another process are likely to differ.
 //
+// `y_absl::Hash` may also produce different values from different dynamically
+// loaded libraries. For this reason, `y_absl::Hash` values must never cross
+// boundries in dynamically loaded libraries (including when used in types like
+// hash containers.)
+//
 // `y_absl::Hash` is intended to strongly mix input bits with a target of passing
 // an [Avalanche Test](https://en.wikipedia.org/wiki/Avalanche_effect).
 //
@@ -74,7 +79,9 @@
 #define Y_ABSL_HASH_HASH_H_
 
 #include <tuple>
+#include <utility>
 
+#include "y_absl/functional/function_ref.h"
 #include "y_absl/hash/internal/hash.h"
 
 namespace y_absl {
@@ -107,14 +114,27 @@ Y_ABSL_NAMESPACE_BEGIN
 //     * std::string_view (as well as any instance of std::basic_string that
 //       uses char and std::char_traits)
 //  * All the standard sequence containers (provided the elements are hashable)
-//  * All the standard ordered associative containers (provided the elements are
+//  * All the standard associative containers (provided the elements are
 //    hashable)
 //  * y_absl types such as the following:
 //    * y_absl::string_view
-//    * y_absl::InlinedVector
-//    * y_absl::FixedArray
 //    * y_absl::uint128
 //    * y_absl::Time, y_absl::Duration, and y_absl::TimeZone
+//  * y_absl containers (provided the elements are hashable) such as the
+//    following:
+//    * y_absl::flat_hash_set, y_absl::node_hash_set, y_absl::btree_set
+//    * y_absl::flat_hash_map, y_absl::node_hash_map, y_absl::btree_map
+//    * y_absl::btree_multiset, y_absl::btree_multimap
+//    * y_absl::InlinedVector
+//    * y_absl::FixedArray
+//
+// When y_absl::Hash is used to hash an unordered container with a custom hash
+// functor, the elements are hashed using default y_absl::Hash semantics, not
+// the custom hash functor.  This is consistent with the behavior of
+// operator==() on unordered containers, which compares elements pairwise with
+// operator==() rather than the custom equality functor.  It is usually a
+// mistake to use either operator==() or y_absl::Hash on unordered collections
+// that use functors incompatible with operator==() equality.
 //
 // Note: the list above is not meant to be exhaustive. Additional type support
 // may be added, in which case the above list will be updated.
@@ -153,7 +173,8 @@ Y_ABSL_NAMESPACE_BEGIN
 //   that are otherwise difficult to extend using `AbslHashValue()`. (See the
 //   `HashState` class below.)
 //
-// The "hash state" concept contains two member functions for mixing hash state:
+// The "hash state" concept contains three member functions for mixing hash
+// state:
 //
 // * `H::combine(state, values...)`
 //
@@ -187,6 +208,15 @@ Y_ABSL_NAMESPACE_BEGIN
 //    (it may perform internal optimizations). If you need this guarantee, use a
 //    loop instead.
 //
+// * `H::combine_unordered(state, begin, end)`
+//
+//    Combines a set of elements denoted by an iterator pair into a hash
+//    state, returning the updated state.  Note that the existing hash
+//    state is move-only and must be passed by value.
+//
+//    Unlike the other two methods, the hashing is order-independent.
+//    This can be used to hash unordered collections.
+//
 // -----------------------------------------------------------------------------
 // Adding Type Support to `y_absl::Hash`
 // -----------------------------------------------------------------------------
@@ -243,8 +273,9 @@ size_t HashOf(const Types&... values) {
 // classes, virtual functions, etc.). The type erasure adds overhead so it
 // should be avoided unless necessary.
 //
-// Note: This wrapper will only erase calls to:
+// Note: This wrapper will only erase calls to
 //     combine_contiguous(H, const unsigned char*, size_t)
+//     RunCombineUnordered(H, CombinerF)
 //
 // All other calls will be handled internally and will not invoke overloads
 // provided by the wrapped class.
@@ -318,6 +349,8 @@ class HashState : public hash_internal::HashStateBase<HashState> {
  private:
   HashState() = default;
 
+  friend class HashState::HashStateBase;
+
   template <typename T>
   static void CombineContiguousImpl(void* p, const unsigned char* first,
                                     size_t size) {
@@ -329,16 +362,57 @@ class HashState : public hash_internal::HashStateBase<HashState> {
   void Init(T* state) {
     state_ = state;
     combine_contiguous_ = &CombineContiguousImpl<T>;
+    run_combine_unordered_ = &RunCombineUnorderedImpl<T>;
+  }
+
+  template <typename HS>
+  struct CombineUnorderedInvoker {
+    template <typename T, typename ConsumerT>
+    void operator()(T inner_state, ConsumerT inner_cb) {
+      f(HashState::Create(&inner_state),
+        [&](HashState& inner_erased) { inner_cb(inner_erased.Real<T>()); });
+    }
+
+    y_absl::FunctionRef<void(HS, y_absl::FunctionRef<void(HS&)>)> f;
+  };
+
+  template <typename T>
+  static HashState RunCombineUnorderedImpl(
+      HashState state,
+      y_absl::FunctionRef<void(HashState, y_absl::FunctionRef<void(HashState&)>)>
+          f) {
+    // Note that this implementation assumes that inner_state and outer_state
+    // are the same type.  This isn't true in the SpyHash case, but SpyHash
+    // types are move-convertible to each other, so this still works.
+    T& real_state = state.Real<T>();
+    real_state = T::RunCombineUnordered(
+        std::move(real_state), CombineUnorderedInvoker<HashState>{f});
+    return state;
+  }
+
+  template <typename CombinerT>
+  static HashState RunCombineUnordered(HashState state, CombinerT combiner) {
+    auto* run = state.run_combine_unordered_;
+    return run(std::move(state), std::ref(combiner));
   }
 
   // Do not erase an already erased state.
   void Init(HashState* state) {
     state_ = state->state_;
     combine_contiguous_ = state->combine_contiguous_;
+    run_combine_unordered_ = state->run_combine_unordered_;
+  }
+
+  template <typename T>
+  T& Real() {
+    return *static_cast<T*>(state_);
   }
 
   void* state_;
   void (*combine_contiguous_)(void*, const unsigned char*, size_t);
+  HashState (*run_combine_unordered_)(
+      HashState state,
+      y_absl::FunctionRef<void(HashState, y_absl::FunctionRef<void(HashState&)>)>);
 };
 
 Y_ABSL_NAMESPACE_END
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/hash/internal/hash.h b/contrib/restricted/abseil-cpp-tstring/y_absl/hash/internal/hash.h
index a14b74ed74..f295ea6018 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/hash/internal/hash.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/hash/internal/hash.h
@@ -23,6 +23,7 @@
 #include <array>
 #include <bitset>
 #include <cmath>
+#include <cstddef>
 #include <cstring>
 #include <deque>
 #include <forward_list>
@@ -36,6 +37,8 @@
 #include <util/generic/string.h>
 #include <tuple>
 #include <type_traits>
+#include <unordered_map>
+#include <unordered_set>
 #include <utility>
 #include <vector>
 
@@ -54,6 +57,9 @@
 
 namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
+
+class HashState;
+
 namespace hash_internal {
 
 // Internal detail: Large buffers are hashed in smaller chunks.  This function
@@ -115,24 +121,66 @@ class PiecewiseCombiner {
   size_t position_;
 };
 
+// is_hashable()
+//
+// Trait class which returns true if T is hashable by the y_absl::Hash framework.
+// Used for the AbslHashValue implementations for composite types below.
+template <typename T>
+struct is_hashable;
+
 // HashStateBase
 //
-// A hash state object represents an intermediate state in the computation
-// of an unspecified hash algorithm. `HashStateBase` provides a CRTP style
-// base class for hash state implementations. Developers adding type support
-// for `y_absl::Hash` should not rely on any parts of the state object other than
-// the following member functions:
+// An internal implementation detail that contains common implementation details
+// for all of the "hash state objects" objects generated by Abseil.  This is not
+// a public API; users should not create classes that inherit from this.
+//
+// A hash state object is the template argument `H` passed to `AbslHashValue`.
+// It represents an intermediate state in the computation of an unspecified hash
+// algorithm. `HashStateBase` provides a CRTP style base class for hash state
+// implementations. Developers adding type support for `y_absl::Hash` should not
+// rely on any parts of the state object other than the following member
+// functions:
 //
 //   * HashStateBase::combine()
 //   * HashStateBase::combine_contiguous()
+//   * HashStateBase::combine_unordered()
 //
-// A derived hash state class of type `H` must provide a static member function
+// A derived hash state class of type `H` must provide a public member function
 // with a signature similar to the following:
 //
 //    `static H combine_contiguous(H state, const unsigned char*, size_t)`.
 //
+// It must also provide a private template method named RunCombineUnordered.
+//
+// A "consumer" is a 1-arg functor returning void.  Its argument is a reference
+// to an inner hash state object, and it may be called multiple times.  When
+// called, the functor consumes the entropy from the provided state object,
+// and resets that object to its empty state.
+//
+// A "combiner" is a stateless 2-arg functor returning void.  Its arguments are
+// an inner hash state object and an ElementStateConsumer functor.  A combiner
+// uses the provided inner hash state object to hash each element of the
+// container, passing the inner hash state object to the consumer after hashing
+// each element.
+//
+// Given these definitions, a derived hash state class of type H
+// must provide a private template method with a signature similar to the
+// following:
+//
+//    `template <typename CombinerT>`
+//    `static H RunCombineUnordered(H outer_state, CombinerT combiner)`
+//
+// This function is responsible for constructing the inner state object and
+// providing a consumer to the combiner.  It uses side effects of the consumer
+// and combiner to mix the state of each element in an order-independent manner,
+// and uses this to return an updated value of `outer_state`.
+//
+// This inside-out approach generates efficient object code in the normal case,
+// but allows us to use stack storage to implement the y_absl::HashState type
+// erasure mechanism (avoiding heap allocations while hashing).
+//
 // `HashStateBase` will provide a complete implementation for a hash state
-// object in terms of this method.
+// object in terms of these two methods.
 //
 // Example:
 //
@@ -141,6 +189,10 @@ class PiecewiseCombiner {
 //       static H combine_contiguous(H state, const unsigned char*, size_t);
 //       using MyHashState::HashStateBase::combine;
 //       using MyHashState::HashStateBase::combine_contiguous;
+//       using MyHashState::HashStateBase::combine_unordered;
+//     private:
+//       template <typename CombinerT>
+//       static H RunCombineUnordered(H state, CombinerT combiner);
 //   };
 template <typename H>
 class HashStateBase {
@@ -181,7 +233,30 @@ class HashStateBase {
   template <typename T>
   static H combine_contiguous(H state, const T* data, size_t size);
 
+  template <typename I>
+  static H combine_unordered(H state, I begin, I end);
+
   using AbslInternalPiecewiseCombiner = PiecewiseCombiner;
+
+  template <typename T>
+  using is_hashable = y_absl::hash_internal::is_hashable<T>;
+
+ private:
+  // Common implementation of the iteration step of a "combiner", as described
+  // above.
+  template <typename I>
+  struct CombineUnorderedCallback {
+    I begin;
+    I end;
+
+    template <typename InnerH, typename ElementStateConsumer>
+    void operator()(InnerH inner_state, ElementStateConsumer cb) {
+      for (; begin != end; ++begin) {
+        inner_state = H::combine(std::move(inner_state), *begin);
+        cb(inner_state);
+      }
+    }
+  };
 };
 
 // is_uniquely_represented
@@ -346,17 +421,43 @@ H AbslHashValue(H hash_state, std::nullptr_t) {
   return H::combine(std::move(hash_state), static_cast<void*>(nullptr));
 }
 
+// AbslHashValue() for hashing pointers-to-member
+template <typename H, typename T, typename C>
+H AbslHashValue(H hash_state, T C::* ptr) {
+  auto salient_ptm_size = [](std::size_t n) -> std::size_t {
+#if defined(_MSC_VER)
+    // Pointers-to-member-function on MSVC consist of one pointer plus 0, 1, 2,
+    // or 3 ints. In 64-bit mode, they are 8-byte aligned and thus can contain
+    // padding (namely when they have 1 or 3 ints). The value below is a lower
+    // bound on the number of salient, non-padding bytes that we use for
+    // hashing.
+    if (alignof(T C::*) == alignof(int)) {
+      // No padding when all subobjects have the same size as the total
+      // alignment. This happens in 32-bit mode.
+      return n;
+    } else {
+      // Padding for 1 int (size 16) or 3 ints (size 24).
+      // With 2 ints, the size is 16 with no padding, which we pessimize.
+      return n == 24 ? 20 : n == 16 ? 12 : n;
+    }
+#else
+    // On other platforms, we assume that pointers-to-members do not have
+    // padding.
+#ifdef __cpp_lib_has_unique_object_representations
+    static_assert(std::has_unique_object_representations_v<T C::*>);
+#endif  // __cpp_lib_has_unique_object_representations
+    return n;
+#endif
+  };
+  return H::combine_contiguous(std::move(hash_state),
+                               reinterpret_cast<unsigned char*>(&ptr),
+                               salient_ptm_size(sizeof ptr));
+}
+
 // -----------------------------------------------------------------------------
 // AbslHashValue for Composite Types
 // -----------------------------------------------------------------------------
 
-// is_hashable()
-//
-// Trait class which returns true if T is hashable by the y_absl::Hash framework.
-// Used for the AbslHashValue implementations for composite types below.
-template <typename T>
-struct is_hashable;
-
 // AbslHashValue() for hashing pairs
 template <typename H, typename T1, typename T2>
 typename std::enable_if<is_hashable<T1>::value && is_hashable<T2>::value,
@@ -502,10 +603,11 @@ AbslHashValue(H hash_state, const std::vector<T, Allocator>& vector) {
                     vector.size());
 }
 
+// AbslHashValue special cases for hashing std::vector<bool>
+
 #if defined(Y_ABSL_IS_BIG_ENDIAN) && \
     (defined(__GLIBCXX__) || defined(__GLIBCPP__))
-// AbslHashValue for hashing std::vector<bool>
-//
+
 // std::hash in libstdc++ does not work correctly with vector<bool> on Big
 // Endian platforms therefore we need to implement a custom AbslHashValue for
 // it. More details on the bug:
@@ -521,6 +623,22 @@ AbslHashValue(H hash_state, const std::vector<T, Allocator>& vector) {
   }
   return H::combine(combiner.finalize(std::move(hash_state)), vector.size());
 }
+#else
+// When not working around the libstdc++ bug above, we still have to contend
+// with the fact that std::hash<vector<bool>> is often poor quality, hashing
+// directly on the internal words and on no other state.  On these platforms,
+// vector<bool>{1, 1} and vector<bool>{1, 1, 0} hash to the same value.
+//
+// Mixing in the size (as we do in our other vector<> implementations) on top
+// of the library-provided hash implementation avoids this QOI issue.
+template <typename H, typename T, typename Allocator>
+typename std::enable_if<is_hashable<T>::value && std::is_same<T, bool>::value,
+                        H>::type
+AbslHashValue(H hash_state, const std::vector<T, Allocator>& vector) {
+  return H::combine(std::move(hash_state),
+                    std::hash<std::vector<T, Allocator>>{}(vector),
+                    vector.size());
+}
 #endif
 
 // -----------------------------------------------------------------------------
@@ -573,6 +691,55 @@ typename std::enable_if<is_hashable<Key>::value, H>::type AbslHashValue(
 }
 
 // -----------------------------------------------------------------------------
+// AbslHashValue for Unordered Associative Containers
+// -----------------------------------------------------------------------------
+
+// AbslHashValue for hashing std::unordered_set
+template <typename H, typename Key, typename Hash, typename KeyEqual,
+          typename Alloc>
+typename std::enable_if<is_hashable<Key>::value, H>::type AbslHashValue(
+    H hash_state, const std::unordered_set<Key, Hash, KeyEqual, Alloc>& s) {
+  return H::combine(
+      H::combine_unordered(std::move(hash_state), s.begin(), s.end()),
+      s.size());
+}
+
+// AbslHashValue for hashing std::unordered_multiset
+template <typename H, typename Key, typename Hash, typename KeyEqual,
+          typename Alloc>
+typename std::enable_if<is_hashable<Key>::value, H>::type AbslHashValue(
+    H hash_state,
+    const std::unordered_multiset<Key, Hash, KeyEqual, Alloc>& s) {
+  return H::combine(
+      H::combine_unordered(std::move(hash_state), s.begin(), s.end()),
+      s.size());
+}
+
+// AbslHashValue for hashing std::unordered_set
+template <typename H, typename Key, typename T, typename Hash,
+          typename KeyEqual, typename Alloc>
+typename std::enable_if<is_hashable<Key>::value && is_hashable<T>::value,
+                        H>::type
+AbslHashValue(H hash_state,
+              const std::unordered_map<Key, T, Hash, KeyEqual, Alloc>& s) {
+  return H::combine(
+      H::combine_unordered(std::move(hash_state), s.begin(), s.end()),
+      s.size());
+}
+
+// AbslHashValue for hashing std::unordered_multiset
+template <typename H, typename Key, typename T, typename Hash,
+          typename KeyEqual, typename Alloc>
+typename std::enable_if<is_hashable<Key>::value && is_hashable<T>::value,
+                        H>::type
+AbslHashValue(H hash_state,
+              const std::unordered_multimap<Key, T, Hash, KeyEqual, Alloc>& s) {
+  return H::combine(
+      H::combine_unordered(std::move(hash_state), s.begin(), s.end()),
+      s.size());
+}
+
+// -----------------------------------------------------------------------------
 // AbslHashValue for Wrapper Types
 // -----------------------------------------------------------------------------
 
@@ -815,6 +982,31 @@ class Y_ABSL_DLL MixingHashState : public HashStateBase<MixingHashState> {
   // move-only ensures that there is only one non-moved-from object.
   MixingHashState() : state_(Seed()) {}
 
+  friend class MixingHashState::HashStateBase;
+
+  template <typename CombinerT>
+  static MixingHashState RunCombineUnordered(MixingHashState state,
+                                             CombinerT combiner) {
+    uint64_t unordered_state = 0;
+    combiner(MixingHashState{}, [&](MixingHashState& inner_state) {
+      // Add the hash state of the element to the running total, but mix the
+      // carry bit back into the low bit.  This in intended to avoid losing
+      // entropy to overflow, especially when unordered_multisets contain
+      // multiple copies of the same value.
+      auto element_state = inner_state.state_;
+      unordered_state += element_state;
+      if (unordered_state < element_state) {
+        ++unordered_state;
+      }
+      inner_state = MixingHashState{};
+    });
+    return MixingHashState::combine(std::move(state), unordered_state);
+  }
+
+  // Allow the HashState type-erasure implementation to invoke
+  // RunCombinedUnordered() directly.
+  friend class y_absl::HashState;
+
   // Workaround for MSVC bug.
   // We make the type copyable to fix the calling convention, even though we
   // never actually copy it. Keep it private to not affect the public API of the
@@ -898,15 +1090,10 @@ class Y_ABSL_DLL MixingHashState : public HashStateBase<MixingHashState> {
   }
 
   Y_ABSL_ATTRIBUTE_ALWAYS_INLINE static uint64_t Mix(uint64_t state, uint64_t v) {
-#if defined(__aarch64__)
-    // On AArch64, calculating a 128-bit product is inefficient, because it
-    // requires a sequence of two instructions to calculate the upper and lower
-    // halves of the result.
-    using MultType = uint64_t;
-#else
+    // Though the 128-bit product on AArch64 needs two instructions, it is
+    // still a good balance between speed and hash quality.
     using MultType =
         y_absl::conditional_t<sizeof(size_t) == 4, uint64_t, uint128>;
-#endif
     // We do the addition in 64-bit space to make sure the 128-bit
     // multiplication is fast. If we were to do it as MultType the compiler has
     // to assume that the high word is non-zero and needs to perform 2
@@ -1049,6 +1236,14 @@ H HashStateBase<H>::combine_contiguous(H state, const T* data, size_t size) {
   return hash_internal::hash_range_or_bytes(std::move(state), data, size);
 }
 
+// HashStateBase::combine_unordered()
+template <typename H>
+template <typename I>
+H HashStateBase<H>::combine_unordered(H state, I begin, I end) {
+  return H::RunCombineUnordered(std::move(state),
+                                CombineUnorderedCallback<I>{begin, end});
+}
+
 // HashStateBase::PiecewiseCombiner::add_buffer()
 template <typename H>
 H PiecewiseCombiner::add_buffer(H state, const unsigned char* data,
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/numeric/bits.h b/contrib/restricted/abseil-cpp-tstring/y_absl/numeric/bits.h
index a4dcd71f7a..75cd272d77 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/numeric/bits.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/numeric/bits.h
@@ -133,7 +133,8 @@ template <class T>
 Y_ABSL_INTERNAL_CONSTEXPR_CLZ inline
     typename std::enable_if<std::is_unsigned<T>::value, T>::type
     bit_width(T x) noexcept {
-  return std::numeric_limits<T>::digits - countl_zero(x);
+  return std::numeric_limits<T>::digits -
+         static_cast<unsigned int>(countl_zero(x));
 }
 
 // Returns: If x == 0, 0; otherwise the maximal value y such that
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/numeric/int128.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/numeric/int128.cc
index 90b7181c7b..fe9d65cc63 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/numeric/int128.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/numeric/int128.cc
@@ -42,11 +42,11 @@ namespace {
 //   Returns: 2
 inline Y_ABSL_ATTRIBUTE_ALWAYS_INLINE int Fls128(uint128 n) {
   if (uint64_t hi = Uint128High64(n)) {
-    Y_ABSL_INTERNAL_ASSUME(hi != 0);
+    Y_ABSL_ASSUME(hi != 0);
     return 127 - countl_zero(hi);
   }
   const uint64_t low = Uint128Low64(n);
-  Y_ABSL_INTERNAL_ASSUME(low != 0);
+  Y_ABSL_ASSUME(low != 0);
   return 63 - countl_zero(low);
 }
 
@@ -332,6 +332,7 @@ std::ostream& operator<<(std::ostream& os, int128 v) {
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
 
+#ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 namespace std {
 constexpr bool numeric_limits<y_absl::uint128>::is_specialized;
 constexpr bool numeric_limits<y_absl::uint128>::is_signed;
@@ -381,3 +382,4 @@ constexpr int numeric_limits<y_absl::int128>::max_exponent10;
 constexpr bool numeric_limits<y_absl::int128>::traps;
 constexpr bool numeric_limits<y_absl::int128>::tinyness_before;
 }  // namespace std
+#endif
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/numeric/int128.h b/contrib/restricted/abseil-cpp-tstring/y_absl/numeric/int128.h
index ef5ff99c78..34c920a032 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/numeric/int128.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/numeric/int128.h
@@ -44,7 +44,7 @@
 // builtin type.  We need to make sure not to define operator wchar_t()
 // alongside operator unsigned short() in these instances.
 #define Y_ABSL_INTERNAL_WCHAR_T __wchar_t
-#if defined(_M_X64)
+#if defined(_M_X64) && !defined(_M_ARM64EC)
 #include <intrin.h>
 #pragma intrinsic(_umul128)
 #endif  // defined(_M_X64)
@@ -980,7 +980,7 @@ inline uint128 operator*(uint128 lhs, uint128 rhs) {
   // can be used for uint128 storage.
   return static_cast<unsigned __int128>(lhs) *
          static_cast<unsigned __int128>(rhs);
-#elif defined(_MSC_VER) && defined(_M_X64)
+#elif defined(_MSC_VER) && defined(_M_X64) && !defined(_M_ARM64EC)
   uint64_t carry;
   uint64_t low = _umul128(Uint128Low64(lhs), Uint128Low64(rhs), &carry);
   return MakeUint128(Uint128Low64(lhs) * Uint128High64(rhs) +
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/profiling/internal/sample_recorder.h b/contrib/restricted/abseil-cpp-tstring/y_absl/profiling/internal/sample_recorder.h
index 9330aae739..f820d567c9 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/profiling/internal/sample_recorder.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/profiling/internal/sample_recorder.h
@@ -46,6 +46,7 @@ struct Sample {
   y_absl::Mutex init_mu;
   T* next = nullptr;
   T* dead Y_ABSL_GUARDED_BY(init_mu) = nullptr;
+  int64_t weight;  // How many sampling events were required to sample this one.
 };
 
 // Holds samples and their associated stack traces with a soft limit of
@@ -59,7 +60,8 @@ class SampleRecorder {
   ~SampleRecorder();
 
   // Registers for sampling.  Returns an opaque registration info.
-  T* Register();
+  template <typename... Targs>
+  T* Register(Targs&&... args);
 
   // Unregisters the sample.
   void Unregister(T* sample);
@@ -75,12 +77,14 @@ class SampleRecorder {
   // samples that have been dropped.
   int64_t Iterate(const std::function<void(const T& stack)>& f);
 
+  int32_t GetMaxSamples() const;
   void SetMaxSamples(int32_t max);
 
  private:
   void PushNew(T* sample);
   void PushDead(T* sample);
-  T* PopDead();
+  template <typename... Targs>
+  T* PopDead(Targs... args);
 
   std::atomic<size_t> dropped_samples_;
   std::atomic<size_t> size_estimate_;
@@ -162,7 +166,8 @@ void SampleRecorder<T>::PushDead(T* sample) {
 }
 
 template <typename T>
-T* SampleRecorder<T>::PopDead() {
+template <typename... Targs>
+T* SampleRecorder<T>::PopDead(Targs... args) {
   y_absl::MutexLock graveyard_lock(&graveyard_.init_mu);
 
   // The list is circular, so eventually it collapses down to
@@ -174,12 +179,13 @@ T* SampleRecorder<T>::PopDead() {
   y_absl::MutexLock sample_lock(&sample->init_mu);
   graveyard_.dead = sample->dead;
   sample->dead = nullptr;
-  sample->PrepareForSampling();
+  sample->PrepareForSampling(std::forward<Targs>(args)...);
   return sample;
 }
 
 template <typename T>
-T* SampleRecorder<T>::Register() {
+template <typename... Targs>
+T* SampleRecorder<T>::Register(Targs&&... args) {
   int64_t size = size_estimate_.fetch_add(1, std::memory_order_relaxed);
   if (size > max_samples_.load(std::memory_order_relaxed)) {
     size_estimate_.fetch_sub(1, std::memory_order_relaxed);
@@ -187,10 +193,14 @@ T* SampleRecorder<T>::Register() {
     return nullptr;
   }
 
-  T* sample = PopDead();
+  T* sample = PopDead(args...);
   if (sample == nullptr) {
     // Resurrection failed.  Hire a new warlock.
     sample = new T();
+    {
+      y_absl::MutexLock sample_lock(&sample->init_mu);
+      sample->PrepareForSampling(std::forward<Targs>(args)...);
+    }
     PushNew(sample);
   }
 
@@ -223,6 +233,11 @@ void SampleRecorder<T>::SetMaxSamples(int32_t max) {
   max_samples_.store(max, std::memory_order_release);
 }
 
+template <typename T>
+int32_t SampleRecorder<T>::GetMaxSamples() const {
+  return max_samples_.load(std::memory_order_acquire);
+}
+
 }  // namespace profiling_internal
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/status/internal/status_internal.h b/contrib/restricted/abseil-cpp-tstring/y_absl/status/internal/status_internal.h
index 3195a6eb4f..87259b1fc4 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/status/internal/status_internal.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/status/internal/status_internal.h
@@ -15,7 +15,9 @@
 #define Y_ABSL_STATUS_INTERNAL_STATUS_INTERNAL_H_
 
 #include <util/generic/string.h>
+#include <utility>
 
+#include "y_absl/base/attributes.h"
 #include "y_absl/container/inlined_vector.h"
 #include "y_absl/strings/cord.h"
 
@@ -25,7 +27,14 @@ namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
 // Returned Status objects may not be ignored. Codesearch doesn't handle ifdefs
 // as part of a class definitions (b/6995610), so we use a forward declaration.
+//
+// TODO(b/176172494): Y_ABSL_MUST_USE_RESULT should expand to the more strict
+// [[nodiscard]]. For now, just use [[nodiscard]] directly when it is available.
+#if Y_ABSL_HAVE_CPP_ATTRIBUTE(nodiscard)
+class [[nodiscard]] Status;
+#else
 class Y_ABSL_MUST_USE_RESULT Status;
+#endif
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
 #endif  // !SWIG
@@ -61,6 +70,14 @@ struct StatusRep {
 };
 
 y_absl::StatusCode MapToLocalCode(int value);
+
+// Returns a pointer to a newly-allocated string with the given `prefix`,
+// suitable for output as an error message in assertion/`CHECK()` failures.
+//
+// This is an internal implementation detail for Abseil logging.
+TString* MakeCheckFailString(const y_absl::Status* status,
+                                 const char* prefix);
+
 }  // namespace status_internal
 
 Y_ABSL_NAMESPACE_END
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/status/status.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/status/status.cc
index 2bfa4be70a..3bcf02dbbd 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/status/status.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/status/status.cc
@@ -13,9 +13,12 @@
 // limitations under the License.
 #include "y_absl/status/status.h"
 
+#include <errno.h>
+
 #include <cassert>
 
 #include "y_absl/base/internal/raw_logging.h"
+#include "y_absl/base/internal/strerror.h"
 #include "y_absl/debugging/stacktrace.h"
 #include "y_absl/debugging/symbolize.h"
 #include "y_absl/status/status_payload_printer.h"
@@ -185,11 +188,16 @@ void Status::ForEachPayload(
 }
 
 const TString* Status::EmptyString() {
-  static TString* empty_string = new TString();
-  return empty_string;
+  static union EmptyString {
+    TString str;
+    ~EmptyString() {}
+  } empty = {{}};
+  return &empty.str;
 }
 
+#ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 constexpr const char Status::kMovedFromString[];
+#endif
 
 const TString* Status::MovedFromString() {
   static TString* moved_from_string = new TString(kMovedFromString);
@@ -440,5 +448,169 @@ bool IsUnknown(const Status& status) {
   return status.code() == y_absl::StatusCode::kUnknown;
 }
 
+StatusCode ErrnoToStatusCode(int error_number) {
+  switch (error_number) {
+    case 0:
+      return StatusCode::kOk;
+    case EINVAL:        // Invalid argument
+    case ENAMETOOLONG:  // Filename too long
+    case E2BIG:         // Argument list too long
+    case EDESTADDRREQ:  // Destination address required
+    case EDOM:          // Mathematics argument out of domain of function
+    case EFAULT:        // Bad address
+    case EILSEQ:        // Illegal byte sequence
+    case ENOPROTOOPT:   // Protocol not available
+    case ENOSTR:        // Not a STREAM
+    case ENOTSOCK:      // Not a socket
+    case ENOTTY:        // Inappropriate I/O control operation
+    case EPROTOTYPE:    // Protocol wrong type for socket
+    case ESPIPE:        // Invalid seek
+      return StatusCode::kInvalidArgument;
+    case ETIMEDOUT:  // Connection timed out
+    case ETIME:      // Timer expired
+      return StatusCode::kDeadlineExceeded;
+    case ENODEV:  // No such device
+    case ENOENT:  // No such file or directory
+#ifdef ENOMEDIUM
+    case ENOMEDIUM:  // No medium found
+#endif
+    case ENXIO:  // No such device or address
+    case ESRCH:  // No such process
+      return StatusCode::kNotFound;
+    case EEXIST:         // File exists
+    case EADDRNOTAVAIL:  // Address not available
+    case EALREADY:       // Connection already in progress
+#ifdef ENOTUNIQ
+    case ENOTUNIQ:  // Name not unique on network
+#endif
+      return StatusCode::kAlreadyExists;
+    case EPERM:   // Operation not permitted
+    case EACCES:  // Permission denied
+#ifdef ENOKEY
+    case ENOKEY:  // Required key not available
+#endif
+    case EROFS:  // Read only file system
+      return StatusCode::kPermissionDenied;
+    case ENOTEMPTY:   // Directory not empty
+    case EISDIR:      // Is a directory
+    case ENOTDIR:     // Not a directory
+    case EADDRINUSE:  // Address already in use
+    case EBADF:       // Invalid file descriptor
+#ifdef EBADFD
+    case EBADFD:  // File descriptor in bad state
+#endif
+    case EBUSY:    // Device or resource busy
+    case ECHILD:   // No child processes
+    case EISCONN:  // Socket is connected
+#ifdef EISNAM
+    case EISNAM:  // Is a named type file
+#endif
+#ifdef ENOTBLK
+    case ENOTBLK:  // Block device required
+#endif
+    case ENOTCONN:  // The socket is not connected
+    case EPIPE:     // Broken pipe
+#ifdef ESHUTDOWN
+    case ESHUTDOWN:  // Cannot send after transport endpoint shutdown
+#endif
+    case ETXTBSY:  // Text file busy
+#ifdef EUNATCH
+    case EUNATCH:  // Protocol driver not attached
+#endif
+      return StatusCode::kFailedPrecondition;
+    case ENOSPC:  // No space left on device
+#ifdef EDQUOT
+    case EDQUOT:  // Disk quota exceeded
+#endif
+    case EMFILE:   // Too many open files
+    case EMLINK:   // Too many links
+    case ENFILE:   // Too many open files in system
+    case ENOBUFS:  // No buffer space available
+    case ENODATA:  // No message is available on the STREAM read queue
+    case ENOMEM:   // Not enough space
+    case ENOSR:    // No STREAM resources
+#ifdef EUSERS
+    case EUSERS:  // Too many users
+#endif
+      return StatusCode::kResourceExhausted;
+#ifdef ECHRNG
+    case ECHRNG:  // Channel number out of range
+#endif
+    case EFBIG:      // File too large
+    case EOVERFLOW:  // Value too large to be stored in data type
+    case ERANGE:     // Result too large
+      return StatusCode::kOutOfRange;
+#ifdef ENOPKG
+    case ENOPKG:  // Package not installed
+#endif
+    case ENOSYS:        // Function not implemented
+    case ENOTSUP:       // Operation not supported
+    case EAFNOSUPPORT:  // Address family not supported
+#ifdef EPFNOSUPPORT
+    case EPFNOSUPPORT:  // Protocol family not supported
+#endif
+    case EPROTONOSUPPORT:  // Protocol not supported
+#ifdef ESOCKTNOSUPPORT
+    case ESOCKTNOSUPPORT:  // Socket type not supported
+#endif
+    case EXDEV:  // Improper link
+      return StatusCode::kUnimplemented;
+    case EAGAIN:  // Resource temporarily unavailable
+#ifdef ECOMM
+    case ECOMM:  // Communication error on send
+#endif
+    case ECONNREFUSED:  // Connection refused
+    case ECONNABORTED:  // Connection aborted
+    case ECONNRESET:    // Connection reset
+    case EINTR:         // Interrupted function call
+#ifdef EHOSTDOWN
+    case EHOSTDOWN:  // Host is down
+#endif
+    case EHOSTUNREACH:  // Host is unreachable
+    case ENETDOWN:      // Network is down
+    case ENETRESET:     // Connection aborted by network
+    case ENETUNREACH:   // Network unreachable
+    case ENOLCK:        // No locks available
+    case ENOLINK:       // Link has been severed
+#ifdef ENONET
+    case ENONET:  // Machine is not on the network
+#endif
+      return StatusCode::kUnavailable;
+    case EDEADLK:  // Resource deadlock avoided
+#ifdef ESTALE
+    case ESTALE:  // Stale file handle
+#endif
+      return StatusCode::kAborted;
+    case ECANCELED:  // Operation cancelled
+      return StatusCode::kCancelled;
+    default:
+      return StatusCode::kUnknown;
+  }
+}
+
+namespace {
+TString MessageForErrnoToStatus(int error_number,
+                                    y_absl::string_view message) {
+  return y_absl::StrCat(message, ": ",
+                      y_absl::base_internal::StrError(error_number));
+}
+}  // namespace
+
+Status ErrnoToStatus(int error_number, y_absl::string_view message) {
+  return Status(ErrnoToStatusCode(error_number),
+                MessageForErrnoToStatus(error_number, message));
+}
+
+namespace status_internal {
+
+TString* MakeCheckFailString(const y_absl::Status* status,
+                                 const char* prefix) {
+  return new TString(
+      y_absl::StrCat(prefix, " (",
+                   status->ToString(StatusToStringMode::kWithEverything), ")"));
+}
+
+}  // namespace status_internal
+
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/status/status.h b/contrib/restricted/abseil-cpp-tstring/y_absl/status/status.h
index b2acacc709..a5705cec46 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/status/status.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/status/status.h
@@ -24,11 +24,11 @@
 //   * A set of helper functions for creating status codes and checking their
 //     values
 //
-// Within Google, `y_absl::Status` is the primary mechanism for gracefully
-// handling errors across API boundaries (and in particular across RPC
-// boundaries). Some of these errors may be recoverable, but others may not.
-// Most functions that can produce a recoverable error should be designed to
-// return an `y_absl::Status` (or `y_absl::StatusOr`).
+// Within Google, `y_absl::Status` is the primary mechanism for communicating
+// errors in C++, and is used to represent error state in both in-process
+// library calls as well as RPC calls. Some of these errors may be recoverable,
+// but others may not. Most functions that can produce a recoverable error
+// should be designed to return an `y_absl::Status` (or `y_absl::StatusOr`).
 //
 // Example:
 //
@@ -469,8 +469,9 @@ class Status final {
 
   // Status::ok()
   //
-  // Returns `true` if `this->ok()`. Prefer checking for an OK status using this
-  // member function.
+  // Returns `true` if `this->code()` == `y_absl::StatusCode::kOk`,
+  // indicating the absence of an error.
+  // Prefer checking for an OK status using this member function.
   Y_ABSL_MUST_USE_RESULT bool ok() const;
 
   // Status::code()
@@ -532,7 +533,7 @@ class Status final {
   //----------------------------------------------------------------------------
 
   // A payload may be attached to a status to provide additional context to an
-  // error that may not be satisifed by an existing `y_absl::StatusCode`.
+  // error that may not be satisfied by an existing `y_absl::StatusCode`.
   // Typically, this payload serves one of several purposes:
   //
   //   * It may provide more fine-grained semantic information about the error
@@ -612,10 +613,6 @@ class Status final {
   const status_internal::Payloads* GetPayloads() const;
   status_internal::Payloads* GetPayloads();
 
-  // Takes ownership of payload.
-  static uintptr_t NewRep(
-      y_absl::StatusCode code, y_absl::string_view msg,
-      std::unique_ptr<status_internal::Payloads> payload);
   static bool EqualsSlow(const y_absl::Status& a, const y_absl::Status& b);
 
   // MSVC 14.0 limitation requires the const.
@@ -741,6 +738,19 @@ Status UnavailableError(y_absl::string_view message);
 Status UnimplementedError(y_absl::string_view message);
 Status UnknownError(y_absl::string_view message);
 
+// ErrnoToStatusCode()
+//
+// Returns the StatusCode for `error_number`, which should be an `errno` value.
+// See https://en.cppreference.com/w/cpp/error/errno_macros and similar
+// references.
+y_absl::StatusCode ErrnoToStatusCode(int error_number);
+
+// ErrnoToStatus()
+//
+// Convenience function that creates a `y_absl::Status` using an `error_number`,
+// which should be an `errno` value.
+Status ErrnoToStatus(int error_number, y_absl::string_view message);
+
 //------------------------------------------------------------------------------
 // Implementation details follow
 //------------------------------------------------------------------------------
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/status/statusor.h b/contrib/restricted/abseil-cpp-tstring/y_absl/status/statusor.h
index 6fd14e9819..428ca28a3b 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/status/statusor.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/status/statusor.h
@@ -106,7 +106,13 @@ class BadStatusOrAccess : public std::exception {
 
 // Returned StatusOr objects may not be ignored.
 template <typename T>
+#if Y_ABSL_HAVE_CPP_ATTRIBUTE(nodiscard)
+// TODO(b/176172494): Y_ABSL_MUST_USE_RESULT should expand to the more strict
+// [[nodiscard]]. For now, just use [[nodiscard]] directly when it is available.
+class [[nodiscard]] StatusOr;
+#else
 class Y_ABSL_MUST_USE_RESULT StatusOr;
+#endif  // Y_ABSL_HAVE_CPP_ATTRIBUTE(nodiscard)
 
 // y_absl::StatusOr<T>
 //
@@ -156,8 +162,8 @@ class Y_ABSL_MUST_USE_RESULT StatusOr;
 // A `y_absl::StatusOr<T*>` can be constructed from a null pointer like any other
 // pointer value, and the result will be that `ok()` returns `true` and
 // `value()` returns `nullptr`. Checking the value of pointer in an
-// `y_absl::StatusOr<T>` generally requires a bit more care, to ensure both that a
-// value is present and that value is not null:
+// `y_absl::StatusOr<T*>` generally requires a bit more care, to ensure both that
+// a value is present and that value is not null:
 //
 //  StatusOr<std::unique_ptr<Foo>> result = FooFactory::MakeNewFoo(arg);
 //  if (!result.ok()) {
@@ -471,7 +477,7 @@ class StatusOr : private internal_statusor::StatusOrData<T>,
   // StatusOr<T>::ok()
   //
   // Returns whether or not this `y_absl::StatusOr<T>` holds a `T` value. This
-  // member function is analagous to `y_absl::Status::ok()` and should be used
+  // member function is analogous to `y_absl::Status::ok()` and should be used
   // similarly to check the status of return values.
   //
   // Example:
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/CMakeLists.txt b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/CMakeLists.txt
index c14b657da5..c855380674 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/CMakeLists.txt
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/CMakeLists.txt
@@ -25,6 +25,8 @@ target_sources(abseil-cpp-tstring-y_absl-strings PRIVATE
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/strings/ascii.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/strings/charconv.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord.cc
+  ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord_analysis.cc
+  ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord_buffer.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/strings/escaping.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/charconv_bigint.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/charconv_parse.cc
@@ -33,6 +35,7 @@ target_sources(abseil-cpp-tstring-y_absl-strings PRIVATE
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_navigator.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_reader.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_consume.cc
+  ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_crc.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_ring.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cordz_functions.cc
   ${CMAKE_SOURCE_DIR}/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cordz_handle.cc
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/ascii.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/ascii.h
index 2050f8f1a9..02a6185ae6 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/ascii.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/ascii.h
@@ -133,7 +133,7 @@ inline bool ascii_isdigit(unsigned char c) { return c >= '0' && c <= '9'; }
 
 // ascii_isprint()
 //
-// Determines whether the given character is printable, including whitespace.
+// Determines whether the given character is printable, including spaces.
 inline bool ascii_isprint(unsigned char c) { return c >= 32 && c < 127; }
 
 // ascii_isgraph()
@@ -197,7 +197,7 @@ Y_ABSL_MUST_USE_RESULT inline TString AsciiStrToUpper(y_absl::string_view s) {
 Y_ABSL_MUST_USE_RESULT inline y_absl::string_view StripLeadingAsciiWhitespace(
     y_absl::string_view str) {
   auto it = std::find_if_not(str.begin(), str.end(), y_absl::ascii_isspace);
-  return str.substr(it - str.begin());
+  return str.substr(static_cast<size_t>(it - str.begin()));
 }
 
 // Strips in place whitespace from the beginning of the given string.
@@ -211,13 +211,13 @@ inline void StripLeadingAsciiWhitespace(TString* str) {
 Y_ABSL_MUST_USE_RESULT inline y_absl::string_view StripTrailingAsciiWhitespace(
     y_absl::string_view str) {
   auto it = std::find_if_not(str.rbegin(), str.rend(), y_absl::ascii_isspace);
-  return str.substr(0, str.rend() - it);
+  return str.substr(0, static_cast<size_t>(str.rend() - it));
 }
 
 // Strips in place whitespace from the end of the given string
 inline void StripTrailingAsciiWhitespace(TString* str) {
   auto it = std::find_if_not(str->rbegin(), str->rend(), y_absl::ascii_isspace);
-  str->erase(str->rend() - it);
+  str->erase(static_cast<size_t>(str->rend() - it));
 }
 
 // Returns y_absl::string_view with whitespace stripped from both ends of the
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord.cc
index 262a84036b..8559893616 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord.cc
@@ -34,9 +34,12 @@
 #include "y_absl/base/port.h"
 #include "y_absl/container/fixed_array.h"
 #include "y_absl/container/inlined_vector.h"
+#include "y_absl/strings/cord_buffer.h"
 #include "y_absl/strings/escaping.h"
+#include "y_absl/strings/internal/cord_data_edge.h"
 #include "y_absl/strings/internal/cord_internal.h"
 #include "y_absl/strings/internal/cord_rep_btree.h"
+#include "y_absl/strings/internal/cord_rep_crc.h"
 #include "y_absl/strings/internal/cord_rep_flat.h"
 #include "y_absl/strings/internal/cordz_statistics.h"
 #include "y_absl/strings/internal/cordz_update_scope.h"
@@ -52,7 +55,7 @@ Y_ABSL_NAMESPACE_BEGIN
 
 using ::y_absl::cord_internal::CordRep;
 using ::y_absl::cord_internal::CordRepBtree;
-using ::y_absl::cord_internal::CordRepConcat;
+using ::y_absl::cord_internal::CordRepCrc;
 using ::y_absl::cord_internal::CordRepExternal;
 using ::y_absl::cord_internal::CordRepFlat;
 using ::y_absl::cord_internal::CordRepSubstring;
@@ -64,56 +67,6 @@ using ::y_absl::cord_internal::kMinFlatLength;
 using ::y_absl::cord_internal::kInlinedVectorSize;
 using ::y_absl::cord_internal::kMaxBytesToCopy;
 
-constexpr uint64_t Fibonacci(unsigned char n, uint64_t a = 0, uint64_t b = 1) {
-  return n == 0 ? a : Fibonacci(n - 1, b, a + b);
-}
-
-static_assert(Fibonacci(63) == 6557470319842,
-              "Fibonacci values computed incorrectly");
-
-// Minimum length required for a given depth tree -- a tree is considered
-// balanced if
-//      length(t) >= min_length[depth(t)]
-// The root node depth is allowed to become twice as large to reduce rebalancing
-// for larger strings (see IsRootBalanced).
-static constexpr uint64_t min_length[] = {
-    Fibonacci(2),          Fibonacci(3),  Fibonacci(4),  Fibonacci(5),
-    Fibonacci(6),          Fibonacci(7),  Fibonacci(8),  Fibonacci(9),
-    Fibonacci(10),         Fibonacci(11), Fibonacci(12), Fibonacci(13),
-    Fibonacci(14),         Fibonacci(15), Fibonacci(16), Fibonacci(17),
-    Fibonacci(18),         Fibonacci(19), Fibonacci(20), Fibonacci(21),
-    Fibonacci(22),         Fibonacci(23), Fibonacci(24), Fibonacci(25),
-    Fibonacci(26),         Fibonacci(27), Fibonacci(28), Fibonacci(29),
-    Fibonacci(30),         Fibonacci(31), Fibonacci(32), Fibonacci(33),
-    Fibonacci(34),         Fibonacci(35), Fibonacci(36), Fibonacci(37),
-    Fibonacci(38),         Fibonacci(39), Fibonacci(40), Fibonacci(41),
-    Fibonacci(42),         Fibonacci(43), Fibonacci(44), Fibonacci(45),
-    Fibonacci(46),         Fibonacci(47),
-    0xffffffffffffffffull,  // Avoid overflow
-};
-
-static const int kMinLengthSize = Y_ABSL_ARRAYSIZE(min_length);
-
-static inline bool btree_enabled() {
-  return cord_internal::cord_btree_enabled.load(
-      std::memory_order_relaxed);
-}
-
-static inline bool IsRootBalanced(CordRep* node) {
-  if (!node->IsConcat()) {
-    return true;
-  } else if (node->concat()->depth() <= 15) {
-    return true;
-  } else if (node->concat()->depth() > kMinLengthSize) {
-    return false;
-  } else {
-    // Allow depth to become twice as large as implied by fibonacci rule to
-    // reduce rebalancing for larger strings.
-    return (node->length >= min_length[node->concat()->depth() / 2]);
-  }
-}
-
-static CordRep* Rebalance(CordRep* node);
 static void DumpNode(CordRep* rep, bool include_data, std::ostream* os,
                      int indent = 0);
 static bool VerifyNode(CordRep* root, CordRep* start_node,
@@ -135,75 +88,6 @@ static inline CordRep* VerifyTree(CordRep* node) {
   return node;
 }
 
-// Return the depth of a node
-static int Depth(const CordRep* rep) {
-  if (rep->IsConcat()) {
-    return rep->concat()->depth();
-  } else {
-    return 0;
-  }
-}
-
-static void SetConcatChildren(CordRepConcat* concat, CordRep* left,
-                              CordRep* right) {
-  concat->left = left;
-  concat->right = right;
-
-  concat->length = left->length + right->length;
-  concat->set_depth(1 + std::max(Depth(left), Depth(right)));
-}
-
-// Create a concatenation of the specified nodes.
-// Does not change the refcounts of "left" and "right".
-// The returned node has a refcount of 1.
-static CordRep* RawConcat(CordRep* left, CordRep* right) {
-  // Avoid making degenerate concat nodes (one child is empty)
-  if (left == nullptr) return right;
-  if (right == nullptr) return left;
-  if (left->length == 0) {
-    CordRep::Unref(left);
-    return right;
-  }
-  if (right->length == 0) {
-    CordRep::Unref(right);
-    return left;
-  }
-
-  CordRepConcat* rep = new CordRepConcat();
-  rep->tag = cord_internal::CONCAT;
-  SetConcatChildren(rep, left, right);
-
-  return rep;
-}
-
-static CordRep* Concat(CordRep* left, CordRep* right) {
-  CordRep* rep = RawConcat(left, right);
-  if (rep != nullptr && !IsRootBalanced(rep)) {
-    rep = Rebalance(rep);
-  }
-  return VerifyTree(rep);
-}
-
-// Make a balanced tree out of an array of leaf nodes.
-static CordRep* MakeBalancedTree(CordRep** reps, size_t n) {
-  // Make repeated passes over the array, merging adjacent pairs
-  // until we are left with just a single node.
-  while (n > 1) {
-    size_t dst = 0;
-    for (size_t src = 0; src < n; src += 2) {
-      if (src + 1 < n) {
-        reps[dst] = Concat(reps[src], reps[src + 1]);
-      } else {
-        reps[dst] = reps[src];
-      }
-      dst++;
-    }
-    n = dst;
-  }
-
-  return reps[0];
-}
-
 static CordRepFlat* CreateFlat(const char* data, size_t length,
                                size_t alloc_hint) {
   CordRepFlat* flat = CordRepFlat::New(length + alloc_hint);
@@ -229,21 +113,7 @@ static CordRep* NewBtree(const char* data, size_t length, size_t alloc_hint) {
 // The returned node has a refcount of 1.
 static CordRep* NewTree(const char* data, size_t length, size_t alloc_hint) {
   if (length == 0) return nullptr;
-  if (btree_enabled()) {
-    return NewBtree(data, length, alloc_hint);
-  }
-  y_absl::FixedArray<CordRep*> reps((length - 1) / kMaxFlatLength + 1);
-  size_t n = 0;
-  do {
-    const size_t len = std::min(length, kMaxFlatLength);
-    CordRepFlat* rep = CordRepFlat::New(len + alloc_hint);
-    rep->length = len;
-    memcpy(rep->Data(), data, len);
-    reps[n++] = VerifyTree(rep);
-    data += len;
-    length -= len;
-  } while (length != 0);
-  return MakeBalancedTree(reps.data(), n);
+  return NewBtree(data, length, alloc_hint);
 }
 
 namespace cord_internal {
@@ -258,22 +128,6 @@ void InitializeCordRepExternal(y_absl::string_view data, CordRepExternal* rep) {
 
 }  // namespace cord_internal
 
-static CordRep* NewSubstring(CordRep* child, size_t offset, size_t length) {
-  // Never create empty substring nodes
-  if (length == 0) {
-    CordRep::Unref(child);
-    return nullptr;
-  } else {
-    CordRepSubstring* rep = new CordRepSubstring();
-    assert((offset + length) <= child->length);
-    rep->length = length;
-    rep->tag = cord_internal::SUBSTRING;
-    rep->start = offset;
-    rep->child = child;
-    return VerifyTree(rep);
-  }
-}
-
 // Creates a CordRep from the provided string. If the string is large enough,
 // and not wasteful, we move the string into an external cord rep, preserving
 // the already allocated string contents.
@@ -306,13 +160,14 @@ static CordRep* CordRepFromString(TString&& src) {
 // --------------------------------------------------------------------
 // Cord::InlineRep functions
 
+#ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 constexpr unsigned char Cord::InlineRep::kMaxInline;
+#endif
 
-inline void Cord::InlineRep::set_data(const char* data, size_t n,
-                                      bool nullify_tail) {
+inline void Cord::InlineRep::set_data(const char* data, size_t n) {
   static_assert(kMaxInline == 15, "set_data is hard-coded for a length of 15");
 
-  cord_internal::SmallMemmove(data_.as_chars(), data, n, nullify_tail);
+  cord_internal::SmallMemmove<true>(data_.as_chars(), data, n);
   set_inline_size(n);
 }
 
@@ -341,7 +196,9 @@ inline void Cord::InlineRep::remove_prefix(size_t n) {
 // Returns `rep` converted into a CordRepBtree.
 // Directly returns `rep` if `rep` is already a CordRepBtree.
 static CordRepBtree* ForceBtree(CordRep* rep) {
-  return rep->IsBtree() ? rep->btree() : CordRepBtree::Create(rep);
+  return rep->IsBtree()
+             ? rep->btree()
+             : CordRepBtree::Create(cord_internal::RemoveCrcNode(rep));
 }
 
 void Cord::InlineRep::AppendTreeToInlined(CordRep* tree,
@@ -349,11 +206,7 @@ void Cord::InlineRep::AppendTreeToInlined(CordRep* tree,
   assert(!is_tree());
   if (!data_.is_empty()) {
     CordRepFlat* flat = MakeFlatWithExtraCapacity(0);
-    if (btree_enabled()) {
-      tree = CordRepBtree::Append(CordRepBtree::Create(flat), tree);
-    } else {
-      tree = Concat(flat, tree);
-    }
+    tree = CordRepBtree::Append(CordRepBtree::Create(flat), tree);
   }
   EmplaceTree(tree, method);
 }
@@ -361,16 +214,14 @@ void Cord::InlineRep::AppendTreeToInlined(CordRep* tree,
 void Cord::InlineRep::AppendTreeToTree(CordRep* tree, MethodIdentifier method) {
   assert(is_tree());
   const CordzUpdateScope scope(data_.cordz_info(), method);
-  if (btree_enabled()) {
-    tree = CordRepBtree::Append(ForceBtree(data_.as_tree()), tree);
-  } else {
-    tree = Concat(data_.as_tree(), tree);
-  }
+  tree = CordRepBtree::Append(ForceBtree(data_.as_tree()), tree);
   SetTree(tree, scope);
 }
 
 void Cord::InlineRep::AppendTree(CordRep* tree, MethodIdentifier method) {
-  if (tree == nullptr) return;
+  assert(tree != nullptr);
+  assert(tree->length != 0);
+  assert(!tree->IsCrc());
   if (data_.is_tree()) {
     AppendTreeToTree(tree, method);
   } else {
@@ -383,11 +234,7 @@ void Cord::InlineRep::PrependTreeToInlined(CordRep* tree,
   assert(!is_tree());
   if (!data_.is_empty()) {
     CordRepFlat* flat = MakeFlatWithExtraCapacity(0);
-    if (btree_enabled()) {
-      tree = CordRepBtree::Prepend(CordRepBtree::Create(flat), tree);
-    } else {
-      tree = Concat(tree, flat);
-    }
+    tree = CordRepBtree::Prepend(CordRepBtree::Create(flat), tree);
   }
   EmplaceTree(tree, method);
 }
@@ -396,16 +243,14 @@ void Cord::InlineRep::PrependTreeToTree(CordRep* tree,
                                         MethodIdentifier method) {
   assert(is_tree());
   const CordzUpdateScope scope(data_.cordz_info(), method);
-  if (btree_enabled()) {
-    tree = CordRepBtree::Prepend(ForceBtree(data_.as_tree()), tree);
-  } else {
-    tree = Concat(tree, data_.as_tree());
-  }
+  tree = CordRepBtree::Prepend(ForceBtree(data_.as_tree()), tree);
   SetTree(tree, scope);
 }
 
 void Cord::InlineRep::PrependTree(CordRep* tree, MethodIdentifier method) {
   assert(tree != nullptr);
+  assert(tree->length != 0);
+  assert(!tree->IsCrc());
   if (data_.is_tree()) {
     PrependTreeToTree(tree, method);
   } else {
@@ -419,7 +264,7 @@ void Cord::InlineRep::PrependTree(CordRep* tree, MethodIdentifier method) {
 // written to region and the actual size increase will be written to size.
 static inline bool PrepareAppendRegion(CordRep* root, char** region,
                                        size_t* size, size_t max_length) {
-  if (root->IsBtree() && root->refcount.IsMutable()) {
+  if (root->IsBtree() && root->refcount.IsOne()) {
     Span<char> span = root->btree()->GetAppendBuffer(max_length);
     if (!span.empty()) {
       *region = span.data();
@@ -428,13 +273,8 @@ static inline bool PrepareAppendRegion(CordRep* root, char** region,
     }
   }
 
-  // Search down the right-hand path for a non-full FLAT node.
   CordRep* dst = root;
-  while (dst->IsConcat() && dst->refcount.IsMutable()) {
-    dst = dst->concat()->right;
-  }
-
-  if (!dst->IsFlat() || !dst->refcount.IsMutable()) {
+  if (!dst->IsFlat() || !dst->refcount.IsOne()) {
     *region = nullptr;
     *size = 0;
     return false;
@@ -448,12 +288,7 @@ static inline bool PrepareAppendRegion(CordRep* root, char** region,
     return false;
   }
 
-  size_t size_increase = std::min(capacity - in_use, max_length);
-
-  // We need to update the length fields for all nodes, including the leaf node.
-  for (CordRep* rep = root; rep != dst; rep = rep->concat()->right) {
-    rep->length += size_increase;
-  }
+  const size_t size_increase = std::min(capacity - in_use, max_length);
   dst->length += size_increase;
 
   *region = dst->flat()->Data() + in_use;
@@ -461,90 +296,6 @@ static inline bool PrepareAppendRegion(CordRep* root, char** region,
   return true;
 }
 
-template <bool has_length>
-void Cord::InlineRep::GetAppendRegion(char** region, size_t* size,
-                                      size_t length) {
-  auto constexpr method = CordzUpdateTracker::kGetAppendRegion;
-
-  CordRep* root = tree();
-  size_t sz = root ? root->length : inline_size();
-  if (root == nullptr) {
-    size_t available = kMaxInline - sz;
-    if (available >= (has_length ? length : 1)) {
-      *region = data_.as_chars() + sz;
-      *size = has_length ? length : available;
-      set_inline_size(has_length ? sz + length : kMaxInline);
-      return;
-    }
-  }
-
-  size_t extra = has_length ? length : (std::max)(sz, kMinFlatLength);
-  CordRep* rep = root ? root : MakeFlatWithExtraCapacity(extra);
-  CordzUpdateScope scope(root ? data_.cordz_info() : nullptr, method);
-  if (PrepareAppendRegion(rep, region, size, length)) {
-    CommitTree(root, rep, scope, method);
-    return;
-  }
-
-  // Allocate new node.
-  CordRepFlat* new_node = CordRepFlat::New(extra);
-  new_node->length = std::min(new_node->Capacity(), length);
-  *region = new_node->Data();
-  *size = new_node->length;
-
-  if (btree_enabled()) {
-    rep = CordRepBtree::Append(ForceBtree(rep), new_node);
-  } else {
-    rep = Concat(rep, new_node);
-  }
-  CommitTree(root, rep, scope, method);
-}
-
-// Computes the memory side of the provided edge which must be a valid data edge
-// for a btrtee, i.e., a FLAT, EXTERNAL or SUBSTRING of a FLAT or EXTERNAL node.
-static bool RepMemoryUsageDataEdge(const CordRep* rep,
-                                   size_t* total_mem_usage) {
-  size_t maybe_sub_size = 0;
-  if (Y_ABSL_PREDICT_FALSE(rep->IsSubstring())) {
-    maybe_sub_size = sizeof(cord_internal::CordRepSubstring);
-    rep = rep->substring()->child;
-  }
-  if (rep->IsFlat()) {
-    *total_mem_usage += maybe_sub_size + rep->flat()->AllocatedSize();
-    return true;
-  }
-  if (rep->IsExternal()) {
-    // We don't know anything about the embedded / bound data, but we can safely
-    // assume it is 'at least' a word / pointer to data. In the future we may
-    // choose to use the 'data' byte as a tag to identify the types of some
-    // well-known externals, such as a TString instance.
-    *total_mem_usage += maybe_sub_size +
-                        sizeof(cord_internal::CordRepExternalImpl<intptr_t>) +
-                        rep->length;
-    return true;
-  }
-  return false;
-}
-
-// If the rep is a leaf, this will increment the value at total_mem_usage and
-// will return true.
-static bool RepMemoryUsageLeaf(const CordRep* rep, size_t* total_mem_usage) {
-  if (rep->IsFlat()) {
-    *total_mem_usage += rep->flat()->AllocatedSize();
-    return true;
-  }
-  if (rep->IsExternal()) {
-    // We don't know anything about the embedded / bound data, but we can safely
-    // assume it is 'at least' a word / pointer to data. In the future we may
-    // choose to use the 'data' byte as a tag to identify the types of some
-    // well-known externals, such as a TString instance.
-    *total_mem_usage +=
-        sizeof(cord_internal::CordRepExternalImpl<intptr_t>) + rep->length;
-    return true;
-  }
-  return false;
-}
-
 void Cord::InlineRep::AssignSlow(const Cord::InlineRep& src) {
   assert(&src != this);
   assert(is_tree() || src.is_tree());
@@ -581,7 +332,7 @@ Cord::Cord(y_absl::string_view src, MethodIdentifier method)
     : contents_(InlineData::kDefaultInit) {
   const size_t n = src.size();
   if (n <= InlineRep::kMaxInline) {
-    contents_.set_data(src.data(), n, true);
+    contents_.set_data(src.data(), n);
   } else {
     CordRep* rep = NewTree(src.data(), n, 0);
     contents_.EmplaceTree(rep, method);
@@ -591,7 +342,7 @@ Cord::Cord(y_absl::string_view src, MethodIdentifier method)
 template <typename T, Cord::EnableIfString<T>>
 Cord::Cord(T&& src) : contents_(InlineData::kDefaultInit) {
   if (src.size() <= InlineRep::kMaxInline) {
-    contents_.set_data(src.data(), src.size(), true);
+    contents_.set_data(src.data(), src.size());
   } else {
     CordRep* rep = CordRepFromString(std::forward<T>(src));
     contents_.EmplaceTree(rep, CordzUpdateTracker::kConstructorString);
@@ -642,14 +393,14 @@ Cord& Cord::operator=(y_absl::string_view src) {
     // - MaybeUntrackCord must be called before set_data() clobbers cordz_info.
     // - set_data() must be called before Unref(tree) as it may reference tree.
     if (tree != nullptr) CordzInfo::MaybeUntrackCord(contents_.cordz_info());
-    contents_.set_data(data, length, true);
+    contents_.set_data(data, length);
     if (tree != nullptr) CordRep::Unref(tree);
     return *this;
   }
   if (tree != nullptr) {
     CordzUpdateScope scope(contents_.cordz_info(), method);
     if (tree->IsFlat() && tree->flat()->Capacity() >= length &&
-        tree->refcount.IsMutable()) {
+        tree->refcount.IsOne()) {
       // Copy in place if the existing FLAT node is reusable.
       memmove(tree->flat()->Data(), data, length);
       tree->length = length;
@@ -675,6 +426,7 @@ void Cord::InlineRep::AppendArray(y_absl::string_view src,
   const CordRep* const root = rep;
   CordzUpdateScope scope(root ? cordz_info() : nullptr, method);
   if (root != nullptr) {
+    rep = cord_internal::RemoveCrcNode(rep);
     char* region;
     if (PrepareAppendRegion(rep, &region, &appended, src.size())) {
       memcpy(region, src.data(), appended);
@@ -705,27 +457,11 @@ void Cord::InlineRep::AppendArray(y_absl::string_view src,
     return;
   }
 
-  if (btree_enabled()) {
-    // TODO(b/192061034): keep legacy 10% growth rate: consider other rates.
-    rep = ForceBtree(rep);
-    const size_t min_growth = std::max<size_t>(rep->length / 10, src.size());
-    rep = CordRepBtree::Append(rep->btree(), src, min_growth - src.size());
-  } else {
-    // Use new block(s) for any remaining bytes that were not handled above.
-    // Alloc extra memory only if the right child of the root of the new tree
-    // is going to be a FLAT node, which will permit further inplace appends.
-    size_t length = src.size();
-    if (src.size() < kMaxFlatLength) {
-      // The new length is either
-      // - old size + 10%
-      // - old_size + src.size()
-      // This will cause a reasonable conservative step-up in size that is
-      // still large enough to avoid excessive amounts of small fragments
-      // being added.
-      length = std::max<size_t>(rep->length / 10, src.size());
-    }
-    rep = Concat(rep, NewTree(src.data(), src.size(), length - src.size()));
-  }
+  // TODO(b/192061034): keep legacy 10% growth rate: consider other rates.
+  rep = ForceBtree(rep);
+  const size_t min_growth = std::max<size_t>(rep->length / 10, src.size());
+  rep = CordRepBtree::Append(rep->btree(), src, min_growth - src.size());
+
   CommitTree(root, rep, scope, method);
 }
 
@@ -746,7 +482,8 @@ inline void Cord::AppendImpl(C&& src) {
     // Since destination is empty, we can avoid allocating a node,
     if (src.contents_.is_tree()) {
       // by taking the tree directly
-      CordRep* rep = std::forward<C>(src).TakeRep();
+      CordRep* rep =
+          cord_internal::RemoveCrcNode(std::forward<C>(src).TakeRep());
       contents_.EmplaceTree(rep, method);
     } else {
       // or copying over inline data
@@ -782,10 +519,50 @@ inline void Cord::AppendImpl(C&& src) {
   }
 
   // Guaranteed to be a tree (kMaxBytesToCopy > kInlinedSize)
-  CordRep* rep = std::forward<C>(src).TakeRep();
+  CordRep* rep = cord_internal::RemoveCrcNode(std::forward<C>(src).TakeRep());
   contents_.AppendTree(rep, CordzUpdateTracker::kAppendCord);
 }
 
+static CordRep::ExtractResult ExtractAppendBuffer(CordRep* rep,
+                                                  size_t min_capacity) {
+  switch (rep->tag) {
+    case cord_internal::BTREE:
+      return CordRepBtree::ExtractAppendBuffer(rep->btree(), min_capacity);
+    default:
+      if (rep->IsFlat() && rep->refcount.IsOne() &&
+          rep->flat()->Capacity() - rep->length >= min_capacity) {
+        return {nullptr, rep};
+      }
+      return {rep, nullptr};
+  }
+}
+
+static CordBuffer CreateAppendBuffer(InlineData& data, size_t capacity) {
+  // Watch out for overflow, people can ask for size_t::max().
+  const size_t size = data.inline_size();
+  capacity = (std::min)(std::numeric_limits<size_t>::max() - size, capacity);
+  CordBuffer buffer = CordBuffer::CreateWithDefaultLimit(size + capacity);
+  cord_internal::SmallMemmove(buffer.data(), data.as_chars(), size);
+  buffer.SetLength(size);
+  data = {};
+  return buffer;
+}
+
+CordBuffer Cord::GetAppendBufferSlowPath(size_t capacity, size_t min_capacity) {
+  auto constexpr method = CordzUpdateTracker::kGetAppendBuffer;
+  CordRep* tree = contents_.tree();
+  if (tree != nullptr) {
+    CordzUpdateScope scope(contents_.cordz_info(), method);
+    CordRep::ExtractResult result = ExtractAppendBuffer(tree, min_capacity);
+    if (result.extracted != nullptr) {
+      contents_.SetTreeOrEmpty(result.tree, scope);
+      return CordBuffer(result.extracted->flat());
+    }
+    return CordBuffer::CreateWithDefaultLimit(capacity);
+  }
+  return CreateAppendBuffer(contents_.data_, capacity);
+}
+
 void Cord::Append(const Cord& src) {
   AppendImpl(src);
 }
@@ -810,7 +587,8 @@ void Cord::Prepend(const Cord& src) {
   CordRep* src_tree = src.contents_.tree();
   if (src_tree != nullptr) {
     CordRep::Ref(src_tree);
-    contents_.PrependTree(src_tree, CordzUpdateTracker::kPrependCord);
+    contents_.PrependTree(cord_internal::RemoveCrcNode(src_tree),
+                          CordzUpdateTracker::kPrependCord);
     return;
   }
 
@@ -837,103 +615,45 @@ void Cord::PrependArray(y_absl::string_view src, MethodIdentifier method) {
   contents_.PrependTree(rep, method);
 }
 
-template <typename T, Cord::EnableIfString<T>>
-inline void Cord::Prepend(T&& src) {
-  if (src.size() <= kMaxBytesToCopy) {
-    Prepend(y_absl::string_view(src));
+void Cord::AppendPrecise(y_absl::string_view src, MethodIdentifier method) {
+  assert(!src.empty());
+  assert(src.size() <= cord_internal::kMaxFlatLength);
+  if (contents_.remaining_inline_capacity() >= src.size()) {
+    const size_t inline_length = contents_.inline_size();
+    memcpy(contents_.data_.as_chars() + inline_length, src.data(), src.size());
+    contents_.set_inline_size(inline_length + src.size());
   } else {
-    CordRep* rep = CordRepFromString(std::forward<T>(src));
-    contents_.PrependTree(rep, CordzUpdateTracker::kPrependString);
+    contents_.AppendTree(CordRepFlat::Create(src), method);
   }
 }
 
-template void Cord::Prepend(TString&& src);
-
-static CordRep* RemovePrefixFrom(CordRep* node, size_t n) {
-  if (n >= node->length) return nullptr;
-  if (n == 0) return CordRep::Ref(node);
-  y_absl::InlinedVector<CordRep*, kInlinedVectorSize> rhs_stack;
-
-  while (node->IsConcat()) {
-    assert(n <= node->length);
-    if (n < node->concat()->left->length) {
-      // Push right to stack, descend left.
-      rhs_stack.push_back(node->concat()->right);
-      node = node->concat()->left;
-    } else {
-      // Drop left, descend right.
-      n -= node->concat()->left->length;
-      node = node->concat()->right;
-    }
-  }
-  assert(n <= node->length);
-
-  if (n == 0) {
-    CordRep::Ref(node);
+void Cord::PrependPrecise(y_absl::string_view src, MethodIdentifier method) {
+  assert(!src.empty());
+  assert(src.size() <= cord_internal::kMaxFlatLength);
+  if (contents_.remaining_inline_capacity() >= src.size()) {
+    const size_t inline_length = contents_.inline_size();
+    char data[InlineRep::kMaxInline + 1] = {0};
+    memcpy(data, src.data(), src.size());
+    memcpy(data + src.size(), contents_.data(), inline_length);
+    memcpy(contents_.data_.as_chars(), data, InlineRep::kMaxInline + 1);
+    contents_.set_inline_size(inline_length + src.size());
   } else {
-    size_t start = n;
-    size_t len = node->length - n;
-    if (node->IsSubstring()) {
-      // Consider in-place update of node, similar to in RemoveSuffixFrom().
-      start += node->substring()->start;
-      node = node->substring()->child;
-    }
-    node = NewSubstring(CordRep::Ref(node), start, len);
-  }
-  while (!rhs_stack.empty()) {
-    node = Concat(node, CordRep::Ref(rhs_stack.back()));
-    rhs_stack.pop_back();
+    contents_.PrependTree(CordRepFlat::Create(src), method);
   }
-  return node;
 }
 
-// RemoveSuffixFrom() is very similar to RemovePrefixFrom(), with the
-// exception that removing a suffix has an optimization where a node may be
-// edited in place iff that node and all its ancestors have a refcount of 1.
-static CordRep* RemoveSuffixFrom(CordRep* node, size_t n) {
-  if (n >= node->length) return nullptr;
-  if (n == 0) return CordRep::Ref(node);
-  y_absl::InlinedVector<CordRep*, kInlinedVectorSize> lhs_stack;
-  bool inplace_ok = node->refcount.IsMutable();
-
-  while (node->IsConcat()) {
-    assert(n <= node->length);
-    if (n < node->concat()->right->length) {
-      // Push left to stack, descend right.
-      lhs_stack.push_back(node->concat()->left);
-      node = node->concat()->right;
-    } else {
-      // Drop right, descend left.
-      n -= node->concat()->right->length;
-      node = node->concat()->left;
-    }
-    inplace_ok = inplace_ok && node->refcount.IsMutable();
-  }
-  assert(n <= node->length);
-
-  if (n == 0) {
-    CordRep::Ref(node);
-  } else if (inplace_ok && !node->IsExternal()) {
-    // Consider making a new buffer if the current node capacity is much
-    // larger than the new length.
-    CordRep::Ref(node);
-    node->length -= n;
+template <typename T, Cord::EnableIfString<T>>
+inline void Cord::Prepend(T&& src) {
+  if (src.size() <= kMaxBytesToCopy) {
+    Prepend(y_absl::string_view(src));
   } else {
-    size_t start = 0;
-    size_t len = node->length - n;
-    if (node->IsSubstring()) {
-      start = node->substring()->start;
-      node = node->substring()->child;
-    }
-    node = NewSubstring(CordRep::Ref(node), start, len);
-  }
-  while (!lhs_stack.empty()) {
-    node = Concat(CordRep::Ref(lhs_stack.back()), node);
-    lhs_stack.pop_back();
+    CordRep* rep = CordRepFromString(std::forward<T>(src));
+    contents_.PrependTree(rep, CordzUpdateTracker::kPrependString);
   }
-  return node;
 }
 
+template void Cord::Prepend(TString&& src);
+
 void Cord::RemovePrefix(size_t n) {
   Y_ABSL_INTERNAL_CHECK(n <= size(),
                       y_absl::StrCat("Requested prefix size ", n,
@@ -944,14 +664,21 @@ void Cord::RemovePrefix(size_t n) {
   } else {
     auto constexpr method = CordzUpdateTracker::kRemovePrefix;
     CordzUpdateScope scope(contents_.cordz_info(), method);
-    if (tree->IsBtree()) {
+    tree = cord_internal::RemoveCrcNode(tree);
+    if (n >= tree->length) {
+      CordRep::Unref(tree);
+      tree = nullptr;
+    } else if (tree->IsBtree()) {
       CordRep* old = tree;
       tree = tree->btree()->SubTree(n, tree->length - n);
       CordRep::Unref(old);
+    } else if (tree->IsSubstring() && tree->refcount.IsOne()) {
+      tree->substring()->start += n;
+      tree->length -= n;
     } else {
-      CordRep* newrep = RemovePrefixFrom(tree, n);
+      CordRep* rep = CordRepSubstring::Substring(tree, n, tree->length - n);
       CordRep::Unref(tree);
-      tree = VerifyTree(newrep);
+      tree = rep;
     }
     contents_.SetTreeOrEmpty(tree, scope);
   }
@@ -967,68 +694,24 @@ void Cord::RemoveSuffix(size_t n) {
   } else {
     auto constexpr method = CordzUpdateTracker::kRemoveSuffix;
     CordzUpdateScope scope(contents_.cordz_info(), method);
-    if (tree->IsBtree()) {
+    tree = cord_internal::RemoveCrcNode(tree);
+    if (n >= tree->length) {
+      CordRep::Unref(tree);
+      tree = nullptr;
+    } else if (tree->IsBtree()) {
       tree = CordRepBtree::RemoveSuffix(tree->btree(), n);
+    } else if (!tree->IsExternal() && tree->refcount.IsOne()) {
+      assert(tree->IsFlat() || tree->IsSubstring());
+      tree->length -= n;
     } else {
-      CordRep* newrep = RemoveSuffixFrom(tree, n);
+      CordRep* rep = CordRepSubstring::Substring(tree, 0, tree->length - n);
       CordRep::Unref(tree);
-      tree = VerifyTree(newrep);
+      tree = rep;
     }
     contents_.SetTreeOrEmpty(tree, scope);
   }
 }
 
-// Work item for NewSubRange().
-struct SubRange {
-  SubRange(CordRep* a_node, size_t a_pos, size_t a_n)
-      : node(a_node), pos(a_pos), n(a_n) {}
-  CordRep* node;  // nullptr means concat last 2 results.
-  size_t pos;
-  size_t n;
-};
-
-static CordRep* NewSubRange(CordRep* node, size_t pos, size_t n) {
-  y_absl::InlinedVector<CordRep*, kInlinedVectorSize> results;
-  y_absl::InlinedVector<SubRange, kInlinedVectorSize> todo;
-  todo.push_back(SubRange(node, pos, n));
-  do {
-    const SubRange& sr = todo.back();
-    node = sr.node;
-    pos = sr.pos;
-    n = sr.n;
-    todo.pop_back();
-
-    if (node == nullptr) {
-      assert(results.size() >= 2);
-      CordRep* right = results.back();
-      results.pop_back();
-      CordRep* left = results.back();
-      results.pop_back();
-      results.push_back(Concat(left, right));
-    } else if (pos == 0 && n == node->length) {
-      results.push_back(CordRep::Ref(node));
-    } else if (!node->IsConcat()) {
-      if (node->IsSubstring()) {
-        pos += node->substring()->start;
-        node = node->substring()->child;
-      }
-      results.push_back(NewSubstring(CordRep::Ref(node), pos, n));
-    } else if (pos + n <= node->concat()->left->length) {
-      todo.push_back(SubRange(node->concat()->left, pos, n));
-    } else if (pos >= node->concat()->left->length) {
-      pos -= node->concat()->left->length;
-      todo.push_back(SubRange(node->concat()->right, pos, n));
-    } else {
-      size_t left_n = node->concat()->left->length - pos;
-      todo.push_back(SubRange(nullptr, 0, 0));  // Concat()
-      todo.push_back(SubRange(node->concat()->right, 0, n - left_n));
-      todo.push_back(SubRange(node->concat()->left, pos, left_n));
-    }
-  } while (!todo.empty());
-  assert(results.size() == 1);
-  return results[0];
-}
-
 Cord Cord::Subcord(size_t pos, size_t new_size) const {
   Cord sub_cord;
   size_t length = size();
@@ -1038,9 +721,7 @@ Cord Cord::Subcord(size_t pos, size_t new_size) const {
 
   CordRep* tree = contents_.tree();
   if (tree == nullptr) {
-    // sub_cord is newly constructed, no need to re-zero-out the tail of
-    // contents_ memory.
-    sub_cord.contents_.set_data(contents_.data() + pos, new_size, false);
+    sub_cord.contents_.set_data(contents_.data() + pos, new_size);
     return sub_cord;
   }
 
@@ -1060,10 +741,11 @@ Cord Cord::Subcord(size_t pos, size_t new_size) const {
     return sub_cord;
   }
 
+  tree = cord_internal::SkipCrcNode(tree);
   if (tree->IsBtree()) {
     tree = tree->btree()->SubTree(pos, new_size);
   } else {
-    tree = NewSubRange(tree, pos, new_size);
+    tree = CordRepSubstring::Substring(tree, pos, new_size);
   }
   sub_cord.contents_.EmplaceTree(tree, contents_.data_,
                                  CordzUpdateTracker::kSubCord);
@@ -1071,146 +753,6 @@ Cord Cord::Subcord(size_t pos, size_t new_size) const {
 }
 
 // --------------------------------------------------------------------
-// Balancing
-
-class CordForest {
- public:
-  explicit CordForest(size_t length)
-      : root_length_(length), trees_(kMinLengthSize, nullptr) {}
-
-  void Build(CordRep* cord_root) {
-    std::vector<CordRep*> pending = {cord_root};
-
-    while (!pending.empty()) {
-      CordRep* node = pending.back();
-      pending.pop_back();
-      CheckNode(node);
-      if (Y_ABSL_PREDICT_FALSE(!node->IsConcat())) {
-        AddNode(node);
-        continue;
-      }
-
-      CordRepConcat* concat_node = node->concat();
-      if (concat_node->depth() >= kMinLengthSize ||
-          concat_node->length < min_length[concat_node->depth()]) {
-        pending.push_back(concat_node->right);
-        pending.push_back(concat_node->left);
-
-        if (concat_node->refcount.IsOne()) {
-          concat_node->left = concat_freelist_;
-          concat_freelist_ = concat_node;
-        } else {
-          CordRep::Ref(concat_node->right);
-          CordRep::Ref(concat_node->left);
-          CordRep::Unref(concat_node);
-        }
-      } else {
-        AddNode(node);
-      }
-    }
-  }
-
-  CordRep* ConcatNodes() {
-    CordRep* sum = nullptr;
-    for (auto* node : trees_) {
-      if (node == nullptr) continue;
-
-      sum = PrependNode(node, sum);
-      root_length_ -= node->length;
-      if (root_length_ == 0) break;
-    }
-    Y_ABSL_INTERNAL_CHECK(sum != nullptr, "Failed to locate sum node");
-    return VerifyTree(sum);
-  }
-
- private:
-  CordRep* AppendNode(CordRep* node, CordRep* sum) {
-    return (sum == nullptr) ? node : MakeConcat(sum, node);
-  }
-
-  CordRep* PrependNode(CordRep* node, CordRep* sum) {
-    return (sum == nullptr) ? node : MakeConcat(node, sum);
-  }
-
-  void AddNode(CordRep* node) {
-    CordRep* sum = nullptr;
-
-    // Collect together everything with which we will merge with node
-    int i = 0;
-    for (; node->length > min_length[i + 1]; ++i) {
-      auto& tree_at_i = trees_[i];
-
-      if (tree_at_i == nullptr) continue;
-      sum = PrependNode(tree_at_i, sum);
-      tree_at_i = nullptr;
-    }
-
-    sum = AppendNode(node, sum);
-
-    // Insert sum into appropriate place in the forest
-    for (; sum->length >= min_length[i]; ++i) {
-      auto& tree_at_i = trees_[i];
-      if (tree_at_i == nullptr) continue;
-
-      sum = MakeConcat(tree_at_i, sum);
-      tree_at_i = nullptr;
-    }
-
-    // min_length[0] == 1, which means sum->length >= min_length[0]
-    assert(i > 0);
-    trees_[i - 1] = sum;
-  }
-
-  // Make concat node trying to resue existing CordRepConcat nodes we
-  // already collected in the concat_freelist_.
-  CordRep* MakeConcat(CordRep* left, CordRep* right) {
-    if (concat_freelist_ == nullptr) return RawConcat(left, right);
-
-    CordRepConcat* rep = concat_freelist_;
-    if (concat_freelist_->left == nullptr) {
-      concat_freelist_ = nullptr;
-    } else {
-      concat_freelist_ = concat_freelist_->left->concat();
-    }
-    SetConcatChildren(rep, left, right);
-
-    return rep;
-  }
-
-  static void CheckNode(CordRep* node) {
-    Y_ABSL_INTERNAL_CHECK(node->length != 0u, "");
-    if (node->IsConcat()) {
-      Y_ABSL_INTERNAL_CHECK(node->concat()->left != nullptr, "");
-      Y_ABSL_INTERNAL_CHECK(node->concat()->right != nullptr, "");
-      Y_ABSL_INTERNAL_CHECK(node->length == (node->concat()->left->length +
-                                           node->concat()->right->length),
-                          "");
-    }
-  }
-
-  size_t root_length_;
-
-  // use an inlined vector instead of a flat array to get bounds checking
-  y_absl::InlinedVector<CordRep*, kInlinedVectorSize> trees_;
-
-  // List of concat nodes we can re-use for Cord balancing.
-  CordRepConcat* concat_freelist_ = nullptr;
-};
-
-static CordRep* Rebalance(CordRep* node) {
-  VerifyTree(node);
-  assert(node->IsConcat());
-
-  if (node->length == 0) {
-    return nullptr;
-  }
-
-  CordForest forest(node->length);
-  forest.Build(node);
-  return forest.ConcatNodes();
-}
-
-// --------------------------------------------------------------------
 // Comparators
 
 namespace {
@@ -1256,7 +798,7 @@ inline y_absl::string_view Cord::InlineRep::FindFlatStartPiece() const {
     return y_absl::string_view(data_.as_chars(), data_.inline_size());
   }
 
-  CordRep* node = tree();
+  CordRep* node = cord_internal::SkipCrcNode(tree());
   if (node->IsFlat()) {
     return y_absl::string_view(node->flat()->Data(), node->length);
   }
@@ -1274,11 +816,6 @@ inline y_absl::string_view Cord::InlineRep::FindFlatStartPiece() const {
     return tree->Data(tree->begin());
   }
 
-  // Walk down the left branches until we hit a non-CONCAT node.
-  while (node->IsConcat()) {
-    node = node->concat()->left;
-  }
-
   // Get the child node if we encounter a SUBSTRING.
   size_t offset = 0;
   size_t length = node->length;
@@ -1298,6 +835,28 @@ inline y_absl::string_view Cord::InlineRep::FindFlatStartPiece() const {
   return y_absl::string_view(node->external()->base + offset, length);
 }
 
+void Cord::SetExpectedChecksum(uint32_t crc) {
+  auto constexpr method = CordzUpdateTracker::kSetExpectedChecksum;
+  if (empty()) return;
+
+  if (!contents_.is_tree()) {
+    CordRep* rep = contents_.MakeFlatWithExtraCapacity(0);
+    rep = CordRepCrc::New(rep, crc);
+    contents_.EmplaceTree(rep, method);
+  } else {
+    const CordzUpdateScope scope(contents_.data_.cordz_info(), method);
+    CordRep* rep = CordRepCrc::New(contents_.data_.as_tree(), crc);
+    contents_.SetTree(rep, scope);
+  }
+}
+
+y_absl::optional<uint32_t> Cord::ExpectedChecksum() const {
+  if (!contents_.is_tree() || !contents_.tree()->IsCrc()) {
+    return y_absl::nullopt;
+  }
+  return contents_.tree()->crc()->crc;
+}
+
 inline int Cord::CompareSlowPath(y_absl::string_view rhs, size_t compared_size,
                                  size_t size_to_compare) const {
   auto advance = [](Cord::ChunkIterator* it, y_absl::string_view* chunk) {
@@ -1473,42 +1032,6 @@ void Cord::CopyToArraySlowPath(char* dst) const {
   }
 }
 
-Cord::ChunkIterator& Cord::ChunkIterator::AdvanceStack() {
-  auto& stack_of_right_children = stack_of_right_children_;
-  if (stack_of_right_children.empty()) {
-    assert(!current_chunk_.empty());  // Called on invalid iterator.
-    // We have reached the end of the Cord.
-    return *this;
-  }
-
-  // Process the next node on the stack.
-  CordRep* node = stack_of_right_children.back();
-  stack_of_right_children.pop_back();
-
-  // Walk down the left branches until we hit a non-CONCAT node. Save the
-  // right children to the stack for subsequent traversal.
-  while (node->IsConcat()) {
-    stack_of_right_children.push_back(node->concat()->right);
-    node = node->concat()->left;
-  }
-
-  // Get the child node if we encounter a SUBSTRING.
-  size_t offset = 0;
-  size_t length = node->length;
-  if (node->IsSubstring()) {
-    offset = node->substring()->start;
-    node = node->substring()->child;
-  }
-
-  assert(node->IsExternal() || node->IsFlat());
-  assert(length != 0);
-  const char* data =
-      node->IsExternal() ? node->external()->base : node->flat()->Data();
-  current_chunk_ = y_absl::string_view(data + offset, length);
-  current_leaf_ = node;
-  return *this;
-}
-
 Cord Cord::ChunkIterator::AdvanceAndReadBytes(size_t n) {
   Y_ABSL_HARDENING_ASSERT(bytes_remaining_ >= n &&
                         "Attempted to iterate past `end()`");
@@ -1551,166 +1074,33 @@ Cord Cord::ChunkIterator::AdvanceAndReadBytes(size_t n) {
     return subcord;
   }
 
-  auto& stack_of_right_children = stack_of_right_children_;
-  if (n < current_chunk_.size()) {
-    // Range to read is a proper subrange of the current chunk.
-    assert(current_leaf_ != nullptr);
-    CordRep* subnode = CordRep::Ref(current_leaf_);
-    const char* data = subnode->IsExternal() ? subnode->external()->base
-                                             : subnode->flat()->Data();
-    subnode = NewSubstring(subnode, current_chunk_.data() - data, n);
-    subcord.contents_.EmplaceTree(VerifyTree(subnode), method);
-    RemoveChunkPrefix(n);
-    return subcord;
-  }
-
-  // Range to read begins with a proper subrange of the current chunk.
-  assert(!current_chunk_.empty());
+  // Short circuit if reading the entire data edge.
   assert(current_leaf_ != nullptr);
-  CordRep* subnode = CordRep::Ref(current_leaf_);
-  if (current_chunk_.size() < subnode->length) {
-    const char* data = subnode->IsExternal() ? subnode->external()->base
-                                             : subnode->flat()->Data();
-    subnode = NewSubstring(subnode, current_chunk_.data() - data,
-                           current_chunk_.size());
-  }
-  n -= current_chunk_.size();
-  bytes_remaining_ -= current_chunk_.size();
-
-  // Process the next node(s) on the stack, reading whole subtrees depending on
-  // their length and how many bytes we are advancing.
-  CordRep* node = nullptr;
-  while (!stack_of_right_children.empty()) {
-    node = stack_of_right_children.back();
-    stack_of_right_children.pop_back();
-    if (node->length > n) break;
-    // TODO(qrczak): This might unnecessarily recreate existing concat nodes.
-    // Avoiding that would need pretty complicated logic (instead of
-    // current_leaf, keep current_subtree_ which points to the highest node
-    // such that the current leaf can be found on the path of left children
-    // starting from current_subtree_; delay creating subnode while node is
-    // below current_subtree_; find the proper node along the path of left
-    // children starting from current_subtree_ if this loop exits while staying
-    // below current_subtree_; etc.; alternatively, push parents instead of
-    // right children on the stack).
-    subnode = Concat(subnode, CordRep::Ref(node));
-    n -= node->length;
-    bytes_remaining_ -= node->length;
-    node = nullptr;
-  }
-
-  if (node == nullptr) {
-    // We have reached the end of the Cord.
-    assert(bytes_remaining_ == 0);
-    subcord.contents_.EmplaceTree(VerifyTree(subnode), method);
+  if (n == current_leaf_->length) {
+    bytes_remaining_ = 0;
+    current_chunk_ = {};
+    CordRep* tree = CordRep::Ref(current_leaf_);
+    subcord.contents_.EmplaceTree(VerifyTree(tree), method);
     return subcord;
   }
 
-  // Walk down the appropriate branches until we hit a non-CONCAT node. Save the
-  // right children to the stack for subsequent traversal.
-  while (node->IsConcat()) {
-    if (node->concat()->left->length > n) {
-      // Push right, descend left.
-      stack_of_right_children.push_back(node->concat()->right);
-      node = node->concat()->left;
-    } else {
-      // Read left, descend right.
-      subnode = Concat(subnode, CordRep::Ref(node->concat()->left));
-      n -= node->concat()->left->length;
-      bytes_remaining_ -= node->concat()->left->length;
-      node = node->concat()->right;
-    }
-  }
-
-  // Get the child node if we encounter a SUBSTRING.
-  size_t offset = 0;
-  size_t length = node->length;
-  if (node->IsSubstring()) {
-    offset = node->substring()->start;
-    node = node->substring()->child;
-  }
+  // From this point on, we need a partial substring node.
+  // Get pointer to the underlying flat or external data payload and
+  // compute data pointer and offset into current flat or external.
+  CordRep* payload = current_leaf_->IsSubstring()
+                         ? current_leaf_->substring()->child
+                         : current_leaf_;
+  const char* data = payload->IsExternal() ? payload->external()->base
+                                           : payload->flat()->Data();
+  const size_t offset = current_chunk_.data() - data;
 
-  // Range to read ends with a proper (possibly empty) subrange of the current
-  // chunk.
-  assert(node->IsExternal() || node->IsFlat());
-  assert(length > n);
-  if (n > 0) {
-    subnode = Concat(subnode, NewSubstring(CordRep::Ref(node), offset, n));
-  }
-  const char* data =
-      node->IsExternal() ? node->external()->base : node->flat()->Data();
-  current_chunk_ = y_absl::string_view(data + offset + n, length - n);
-  current_leaf_ = node;
+  auto* tree = CordRepSubstring::Substring(payload, offset, n);
+  subcord.contents_.EmplaceTree(VerifyTree(tree), method);
   bytes_remaining_ -= n;
-  subcord.contents_.EmplaceTree(VerifyTree(subnode), method);
+  current_chunk_.remove_prefix(n);
   return subcord;
 }
 
-void Cord::ChunkIterator::AdvanceBytesSlowPath(size_t n) {
-  assert(bytes_remaining_ >= n && "Attempted to iterate past `end()`");
-  assert(n >= current_chunk_.size());  // This should only be called when
-                                       // iterating to a new node.
-
-  n -= current_chunk_.size();
-  bytes_remaining_ -= current_chunk_.size();
-
-  if (stack_of_right_children_.empty()) {
-    // We have reached the end of the Cord.
-    assert(bytes_remaining_ == 0);
-    return;
-  }
-
-  // Process the next node(s) on the stack, skipping whole subtrees depending on
-  // their length and how many bytes we are advancing.
-  CordRep* node = nullptr;
-  auto& stack_of_right_children = stack_of_right_children_;
-  while (!stack_of_right_children.empty()) {
-    node = stack_of_right_children.back();
-    stack_of_right_children.pop_back();
-    if (node->length > n) break;
-    n -= node->length;
-    bytes_remaining_ -= node->length;
-    node = nullptr;
-  }
-
-  if (node == nullptr) {
-    // We have reached the end of the Cord.
-    assert(bytes_remaining_ == 0);
-    return;
-  }
-
-  // Walk down the appropriate branches until we hit a non-CONCAT node. Save the
-  // right children to the stack for subsequent traversal.
-  while (node->IsConcat()) {
-    if (node->concat()->left->length > n) {
-      // Push right, descend left.
-      stack_of_right_children.push_back(node->concat()->right);
-      node = node->concat()->left;
-    } else {
-      // Skip left, descend right.
-      n -= node->concat()->left->length;
-      bytes_remaining_ -= node->concat()->left->length;
-      node = node->concat()->right;
-    }
-  }
-
-  // Get the child node if we encounter a SUBSTRING.
-  size_t offset = 0;
-  size_t length = node->length;
-  if (node->IsSubstring()) {
-    offset = node->substring()->start;
-    node = node->substring()->child;
-  }
-
-  assert(node->IsExternal() || node->IsFlat());
-  assert(length > n);
-  const char* data =
-      node->IsExternal() ? node->external()->base : node->flat()->Data();
-  current_chunk_ = y_absl::string_view(data + offset + n, length - n);
-  current_leaf_ = node;
-  bytes_remaining_ -= n;
-}
-
 char Cord::operator[](size_t i) const {
   Y_ABSL_HARDENING_ASSERT(i < size());
   size_t offset = i;
@@ -1718,6 +1108,7 @@ char Cord::operator[](size_t i) const {
   if (rep == nullptr) {
     return contents_.data()[i];
   }
+  rep = cord_internal::SkipCrcNode(rep);
   while (true) {
     assert(rep != nullptr);
     assert(offset < rep->length);
@@ -1729,16 +1120,6 @@ char Cord::operator[](size_t i) const {
     } else if (rep->IsExternal()) {
       // Get the "i"th character from the external array.
       return rep->external()->base[offset];
-    } else if (rep->IsConcat()) {
-      // Recursively branch to the side of the concatenation that the "i"th
-      // character is on.
-      size_t left_length = rep->concat()->left->length;
-      if (offset < left_length) {
-        rep = rep->concat()->left;
-      } else {
-        offset -= left_length;
-        rep = rep->concat()->right;
-      }
     } else {
       // This must be a substring a node, so bypass it to get to the child.
       assert(rep->IsSubstring());
@@ -1778,6 +1159,7 @@ y_absl::string_view Cord::FlattenSlowPath() {
 
 /* static */ bool Cord::GetFlatAux(CordRep* rep, y_absl::string_view* fragment) {
   assert(rep != nullptr);
+  rep = cord_internal::SkipCrcNode(rep);
   if (rep->IsFlat()) {
     *fragment = y_absl::string_view(rep->flat()->Data(), rep->length);
     return true;
@@ -1807,6 +1189,9 @@ y_absl::string_view Cord::FlattenSlowPath() {
 /* static */ void Cord::ForEachChunkAux(
     y_absl::cord_internal::CordRep* rep,
     y_absl::FunctionRef<void(y_absl::string_view)> callback) {
+  assert(rep != nullptr);
+  rep = cord_internal::SkipCrcNode(rep);
+
   if (rep->IsBtree()) {
     ChunkIterator it(rep), end;
     while (it != end) {
@@ -1816,44 +1201,13 @@ y_absl::string_view Cord::FlattenSlowPath() {
     return;
   }
 
-  assert(rep != nullptr);
-  int stack_pos = 0;
-  constexpr int stack_max = 128;
-  // Stack of right branches for tree traversal
-  y_absl::cord_internal::CordRep* stack[stack_max];
-  y_absl::cord_internal::CordRep* current_node = rep;
-  while (true) {
-    if (current_node->IsConcat()) {
-      if (stack_pos == stack_max) {
-        // There's no more room on our stack array to add another right branch,
-        // and the idea is to avoid allocations, so call this function
-        // recursively to navigate this subtree further.  (This is not something
-        // we expect to happen in practice).
-        ForEachChunkAux(current_node, callback);
-
-        // Pop the next right branch and iterate.
-        current_node = stack[--stack_pos];
-        continue;
-      } else {
-        // Save the right branch for later traversal and continue down the left
-        // branch.
-        stack[stack_pos++] = current_node->concat()->right;
-        current_node = current_node->concat()->left;
-        continue;
-      }
-    }
-    // This is a leaf node, so invoke our callback.
-    y_absl::string_view chunk;
-    bool success = GetFlatAux(current_node, &chunk);
-    assert(success);
-    if (success) {
-      callback(chunk);
-    }
-    if (stack_pos == 0) {
-      // end of traversal
-      return;
-    }
-    current_node = stack[--stack_pos];
+  // This is a leaf node, so invoke our callback.
+  y_absl::cord_internal::CordRep* current_node = cord_internal::SkipCrcNode(rep);
+  y_absl::string_view chunk;
+  bool success = GetFlatAux(current_node, &chunk);
+  assert(success);
+  if (success) {
+    callback(chunk);
   }
 }
 
@@ -1868,14 +1222,11 @@ static void DumpNode(CordRep* rep, bool include_data, std::ostream* os,
     *os << " [";
     if (include_data) *os << static_cast<void*>(rep);
     *os << "]";
-    *os << " " << (IsRootBalanced(rep) ? 'b' : 'u');
     *os << " " << std::setw(indent) << "";
-    if (rep->IsConcat()) {
-      *os << "CONCAT depth=" << Depth(rep) << "\n";
+    if (rep->IsCrc()) {
+      *os << "CRC crc=" << rep->crc()->crc << "\n";
       indent += kIndentStep;
-      indents.push_back(indent);
-      stack.push_back(rep->concat()->right);
-      rep = rep->concat()->left;
+      rep = rep->crc()->child;
     } else if (rep->IsSubstring()) {
       *os << "SUBSTRING @ " << rep->substring()->start << "\n";
       indent += kIndentStep;
@@ -1912,7 +1263,7 @@ static TString ReportError(CordRep* root, CordRep* node) {
 }
 
 static bool VerifyNode(CordRep* root, CordRep* start_node,
-                       bool full_validation) {
+                       bool /* full_validation */) {
   y_absl::InlinedVector<CordRep*, 2> worklist;
   worklist.push_back(start_node);
   do {
@@ -1922,21 +1273,10 @@ static bool VerifyNode(CordRep* root, CordRep* start_node,
     Y_ABSL_INTERNAL_CHECK(node != nullptr, ReportError(root, node));
     if (node != root) {
       Y_ABSL_INTERNAL_CHECK(node->length != 0, ReportError(root, node));
+      Y_ABSL_INTERNAL_CHECK(!node->IsCrc(), ReportError(root, node));
     }
 
-    if (node->IsConcat()) {
-      Y_ABSL_INTERNAL_CHECK(node->concat()->left != nullptr,
-                          ReportError(root, node));
-      Y_ABSL_INTERNAL_CHECK(node->concat()->right != nullptr,
-                          ReportError(root, node));
-      Y_ABSL_INTERNAL_CHECK((node->length == node->concat()->left->length +
-                                               node->concat()->right->length),
-                          ReportError(root, node));
-      if (full_validation) {
-        worklist.push_back(node->concat()->right);
-        worklist.push_back(node->concat()->left);
-      }
-    } else if (node->IsFlat()) {
+    if (node->IsFlat()) {
       Y_ABSL_INTERNAL_CHECK(node->length <= node->flat()->Capacity(),
                           ReportError(root, node));
     } else if (node->IsExternal()) {
@@ -1949,75 +1289,17 @@ static bool VerifyNode(CordRep* root, CordRep* start_node,
       Y_ABSL_INTERNAL_CHECK(node->substring()->start + node->length <=
                               node->substring()->child->length,
                           ReportError(root, node));
+    } else if (node->IsCrc()) {
+      Y_ABSL_INTERNAL_CHECK(node->crc()->child != nullptr,
+                          ReportError(root, node));
+      Y_ABSL_INTERNAL_CHECK(node->crc()->length == node->crc()->child->length,
+                          ReportError(root, node));
+      worklist.push_back(node->crc()->child);
     }
   } while (!worklist.empty());
   return true;
 }
 
-// Traverses the tree and computes the total memory allocated.
-/* static */ size_t Cord::MemoryUsageAux(const CordRep* rep) {
-  size_t total_mem_usage = 0;
-
-  // Allow a quick exit for the common case that the root is a leaf.
-  if (RepMemoryUsageLeaf(rep, &total_mem_usage)) {
-    return total_mem_usage;
-  }
-
-  // Iterate over the tree. cur_node is never a leaf node and leaf nodes will
-  // never be appended to tree_stack. This reduces overhead from manipulating
-  // tree_stack.
-  y_absl::InlinedVector<const CordRep*, kInlinedVectorSize> tree_stack;
-  const CordRep* cur_node = rep;
-  while (true) {
-    const CordRep* next_node = nullptr;
-
-    if (cur_node->IsConcat()) {
-      total_mem_usage += sizeof(CordRepConcat);
-      const CordRep* left = cur_node->concat()->left;
-      if (!RepMemoryUsageLeaf(left, &total_mem_usage)) {
-        next_node = left;
-      }
-
-      const CordRep* right = cur_node->concat()->right;
-      if (!RepMemoryUsageLeaf(right, &total_mem_usage)) {
-        if (next_node) {
-          tree_stack.push_back(next_node);
-        }
-        next_node = right;
-      }
-    } else if (cur_node->IsBtree()) {
-      total_mem_usage += sizeof(CordRepBtree);
-      const CordRepBtree* node = cur_node->btree();
-      if (node->height() == 0) {
-        for (const CordRep* edge : node->Edges()) {
-          RepMemoryUsageDataEdge(edge, &total_mem_usage);
-        }
-      } else {
-        for (const CordRep* edge : node->Edges()) {
-          tree_stack.push_back(edge);
-        }
-      }
-    } else {
-      // Since cur_node is not a leaf or a concat node it must be a substring.
-      assert(cur_node->IsSubstring());
-      total_mem_usage += sizeof(CordRepSubstring);
-      next_node = cur_node->substring()->child;
-      if (RepMemoryUsageLeaf(next_node, &total_mem_usage)) {
-        next_node = nullptr;
-      }
-    }
-
-    if (!next_node) {
-      if (tree_stack.empty()) {
-        return total_mem_usage;
-      }
-      next_node = tree_stack.back();
-      tree_stack.pop_back();
-    }
-    cur_node = next_node;
-  }
-}
-
 std::ostream& operator<<(std::ostream& out, const Cord& cord) {
   for (y_absl::string_view chunk : cord.Chunks()) {
     out.write(chunk.data(), chunk.size());
@@ -2035,7 +1317,6 @@ uint8_t CordTestAccess::LengthToTag(size_t s) {
   Y_ABSL_INTERNAL_CHECK(s <= kMaxFlatLength, y_absl::StrCat("Invalid length ", s));
   return cord_internal::AllocatedSizeToTag(s + cord_internal::kFlatOverhead);
 }
-size_t CordTestAccess::SizeofCordRepConcat() { return sizeof(CordRepConcat); }
 size_t CordTestAccess::SizeofCordRepExternal() {
   return sizeof(CordRepExternal);
 }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord.h
index 8f14bb6f8c..a30c7b2a19 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord.h
@@ -70,6 +70,7 @@
 #include <util/generic/string.h>
 #include <type_traits>
 
+#include "y_absl/base/attributes.h"
 #include "y_absl/base/config.h"
 #include "y_absl/base/internal/endian.h"
 #include "y_absl/base/internal/per_thread_tls.h"
@@ -78,9 +79,13 @@
 #include "y_absl/container/inlined_vector.h"
 #include "y_absl/functional/function_ref.h"
 #include "y_absl/meta/type_traits.h"
+#include "y_absl/strings/cord_analysis.h"
+#include "y_absl/strings/cord_buffer.h"
+#include "y_absl/strings/internal/cord_data_edge.h"
 #include "y_absl/strings/internal/cord_internal.h"
 #include "y_absl/strings/internal/cord_rep_btree.h"
 #include "y_absl/strings/internal/cord_rep_btree_reader.h"
+#include "y_absl/strings/internal/cord_rep_crc.h"
 #include "y_absl/strings/internal/cord_rep_ring.h"
 #include "y_absl/strings/internal/cordz_functions.h"
 #include "y_absl/strings/internal/cordz_info.h"
@@ -100,6 +105,20 @@ template <typename Releaser>
 Cord MakeCordFromExternal(y_absl::string_view, Releaser&&);
 void CopyCordToString(const Cord& src, TString* dst);
 
+// Cord memory accounting modes
+enum class CordMemoryAccounting {
+  // Counts the *approximate* number of bytes held in full or in part by this
+  // Cord (which may not remain the same between invocations). Cords that share
+  // memory could each be "charged" independently for the same shared memory.
+  kTotal,
+
+  // Counts the *approximate* number of bytes held in full or in part by this
+  // Cord weighted by the sharing ratio of that data. For example, if some data
+  // edge is shared by 4 different Cords, then each cord is attributed 1/4th of
+  // the total memory usage as a 'fair share' of the total memory usage.
+  kFairShare,
+};
+
 // Cord
 //
 // A Cord is a sequence of characters, designed to be more efficient than a
@@ -214,7 +233,7 @@ class Cord {
   //
   // Releases the Cord data. Any nodes that share data with other Cords, if
   // applicable, will have their reference counts reduced by 1.
-  void Clear();
+  Y_ABSL_ATTRIBUTE_REINITIALIZES void Clear();
 
   // Cord::Append()
   //
@@ -226,6 +245,45 @@ class Cord {
   template <typename T, EnableIfString<T> = 0>
   void Append(T&& src);
 
+  // Appends `buffer` to this cord, unless `buffer` has a zero length in which
+  // case this method has no effect on this cord instance.
+  // This method is guaranteed to consume `buffer`.
+  void Append(CordBuffer buffer);
+
+  // Returns a CordBuffer, re-using potential existing capacity in this cord.
+  //
+  // Cord instances may have additional unused capacity in the last (or first)
+  // nodes of the underlying tree to facilitate amortized growth. This method
+  // allows applications to explicitly use this spare capacity if available,
+  // or create a new CordBuffer instance otherwise.
+  // If this cord has a final non-shared node with at least `min_capacity`
+  // available, then this method will return that buffer including its data
+  // contents. I.e.; the returned buffer will have a non-zero length, and
+  // a capacity of at least `buffer.length + min_capacity`. Otherwise, this
+  // method will return `CordBuffer::CreateWithDefaultLimit(capacity)`.
+  //
+  // Below an example of using GetAppendBuffer. Notice that in this example we
+  // use `GetAppendBuffer()` only on the first iteration. As we know nothing
+  // about any initial extra capacity in `cord`, we may be able to use the extra
+  // capacity. But as we add new buffers with fully utilized contents after that
+  // we avoid calling `GetAppendBuffer()` on subsequent iterations: while this
+  // works fine, it results in an unnecessary inspection of cord contents:
+  //
+  //   void AppendRandomDataToCord(y_absl::Cord &cord, size_t n) {
+  //     bool first = true;
+  //     while (n > 0) {
+  //       CordBuffer buffer = first ? cord.GetAppendBuffer(n)
+  //                                 : CordBuffer::CreateWithDefaultLimit(n);
+  //       y_absl::Span<char> data = buffer.available_up_to(n);
+  //       FillRandomValues(data.data(), data.size());
+  //       buffer.IncreaseLengthBy(data.size());
+  //       cord.Append(std::move(buffer));
+  //       n -= data.size();
+  //       first = false;
+  //     }
+  //   }
+  CordBuffer GetAppendBuffer(size_t capacity, size_t min_capacity = 16);
+
   // Cord::Prepend()
   //
   // Prepends data to the Cord, which may come from another Cord or other string
@@ -235,6 +293,11 @@ class Cord {
   template <typename T, EnableIfString<T> = 0>
   void Prepend(T&& src);
 
+  // Prepends `buffer` to this cord, unless `buffer` has a zero length in which
+  // case this method has no effect on this cord instance.
+  // This method is guaranteed to consume `buffer`.
+  void Prepend(CordBuffer buffer);
+
   // Cord::RemovePrefix()
   //
   // Removes the first `n` bytes of a Cord.
@@ -270,11 +333,10 @@ class Cord {
 
   // Cord::EstimatedMemoryUsage()
   //
-  // Returns the *approximate* number of bytes held in full or in part by this
-  // Cord (which may not remain the same between invocations).  Note that Cords
-  // that share memory could each be "charged" independently for the same shared
-  // memory.
-  size_t EstimatedMemoryUsage() const;
+  // Returns the *approximate* number of bytes held by this cord.
+  // See CordMemoryAccounting for more information on the accounting method.
+  size_t EstimatedMemoryUsage(CordMemoryAccounting accounting_method =
+                                  CordMemoryAccounting::kTotal) const;
 
   // Cord::Compare()
   //
@@ -324,7 +386,7 @@ class Cord {
   //----------------------------------------------------------------------------
   //
   // A `Cord::ChunkIterator` allows iteration over the constituent chunks of its
-  // Cord. Such iteration allows you to perform non-const operatons on the data
+  // Cord. Such iteration allows you to perform non-const operations on the data
   // of a Cord without modifying it.
   //
   // Generally, you do not instantiate a `Cord::ChunkIterator` directly;
@@ -372,12 +434,6 @@ class Cord {
     using CordRepBtree = y_absl::cord_internal::CordRepBtree;
     using CordRepBtreeReader = y_absl::cord_internal::CordRepBtreeReader;
 
-    // Stack of right children of concat nodes that we have to visit.
-    // Keep this at the end of the structure to avoid cache-thrashing.
-    // TODO(jgm): Benchmark to see if there's a more optimal value than 47 for
-    // the inlined vector size (47 exists for backward compatibility).
-    using Stack = y_absl::InlinedVector<y_absl::cord_internal::CordRep*, 47>;
-
     // Constructs a `begin()` iterator from `tree`. `tree` must not be null.
     explicit ChunkIterator(cord_internal::CordRep* tree);
 
@@ -393,17 +449,10 @@ class Cord {
     Cord AdvanceAndReadBytes(size_t n);
     void AdvanceBytes(size_t n);
 
-    // Stack specific operator++
-    ChunkIterator& AdvanceStack();
-
     // Btree specific operator++
     ChunkIterator& AdvanceBtree();
     void AdvanceBytesBtree(size_t n);
 
-    // Iterates `n` bytes, where `n` is expected to be greater than or equal to
-    // `current_chunk_.size()`.
-    void AdvanceBytesSlowPath(size_t n);
-
     // A view into bytes of the current `CordRep`. It may only be a view to a
     // suffix of bytes if this is being used by `CharIterator`.
     y_absl::string_view current_chunk_;
@@ -416,12 +465,9 @@ class Cord {
 
     // Cord reader for cord btrees. Empty if not traversing a btree.
     CordRepBtreeReader btree_reader_;
-
-    // See 'Stack' alias definition.
-    Stack stack_of_right_children_;
   };
 
-  // Cord::ChunkIterator::chunk_begin()
+  // Cord::chunk_begin()
   //
   // Returns an iterator to the first chunk of the `Cord`.
   //
@@ -437,7 +483,7 @@ class Cord {
   //   }
   ChunkIterator chunk_begin() const;
 
-  // Cord::ChunkItertator::chunk_end()
+  // Cord::chunk_end()
   //
   // Returns an iterator one increment past the last chunk of the `Cord`.
   //
@@ -447,7 +493,7 @@ class Cord {
   ChunkIterator chunk_end() const;
 
   //----------------------------------------------------------------------------
-  // Cord::ChunkIterator::ChunkRange
+  // Cord::ChunkRange
   //----------------------------------------------------------------------------
   //
   // `ChunkRange` is a helper class for iterating over the chunks of the `Cord`,
@@ -461,7 +507,7 @@ class Cord {
   class ChunkRange {
    public:
     // Fulfill minimum c++ container requirements [container.requirements]
-    // Theses (partial) container type definitions allow ChunkRange to be used
+    // These (partial) container type definitions allow ChunkRange to be used
     // in various utilities expecting a subset of [container.requirements].
     // For example, the below enables using `::testing::ElementsAre(...)`
     using value_type = y_absl::string_view;
@@ -481,9 +527,9 @@ class Cord {
 
   // Cord::Chunks()
   //
-  // Returns a `Cord::ChunkIterator::ChunkRange` for iterating over the chunks
-  // of a `Cord` with a range-based for-loop. For most iteration tasks on a
-  // Cord, use `Cord::Chunks()` to retrieve this iterator.
+  // Returns a `Cord::ChunkRange` for iterating over the chunks of a `Cord` with
+  // a range-based for-loop. For most iteration tasks on a Cord, use
+  // `Cord::Chunks()` to retrieve this iterator.
   //
   // Example:
   //
@@ -549,7 +595,7 @@ class Cord {
     ChunkIterator chunk_iterator_;
   };
 
-  // Cord::CharIterator::AdvanceAndRead()
+  // Cord::AdvanceAndRead()
   //
   // Advances the `Cord::CharIterator` by `n_bytes` and returns the bytes
   // advanced as a separate `Cord`. `n_bytes` must be less than or equal to the
@@ -557,21 +603,21 @@ class Cord {
   // valid to pass `char_end()` and `0`.
   static Cord AdvanceAndRead(CharIterator* it, size_t n_bytes);
 
-  // Cord::CharIterator::Advance()
+  // Cord::Advance()
   //
   // Advances the `Cord::CharIterator` by `n_bytes`. `n_bytes` must be less than
   // or equal to the number of bytes remaining within the Cord; otherwise,
   // behavior is undefined. It is valid to pass `char_end()` and `0`.
   static void Advance(CharIterator* it, size_t n_bytes);
 
-  // Cord::CharIterator::ChunkRemaining()
+  // Cord::ChunkRemaining()
   //
   // Returns the longest contiguous view starting at the iterator's position.
   //
   // `it` must be dereferenceable.
   static y_absl::string_view ChunkRemaining(const CharIterator& it);
 
-  // Cord::CharIterator::char_begin()
+  // Cord::char_begin()
   //
   // Returns an iterator to the first character of the `Cord`.
   //
@@ -580,7 +626,7 @@ class Cord {
   // a `CharIterator` where range-based for-loops may not be available.
   CharIterator char_begin() const;
 
-  // Cord::CharIterator::char_end()
+  // Cord::char_end()
   //
   // Returns an iterator to one past the last character of the `Cord`.
   //
@@ -589,13 +635,13 @@ class Cord {
   // a `CharIterator` where range-based for-loops are not useful.
   CharIterator char_end() const;
 
-  // Cord::CharIterator::CharRange
+  // Cord::CharRange
   //
   // `CharRange` is a helper class for iterating over the characters of a
   // producing an iterator which can be used within a range-based for loop.
   // Construction of a `CharRange` will return an iterator pointing to the first
   // character of the Cord. Generally, do not construct a `CharRange` directly;
-  // instead, prefer to use the `Cord::Chars()` method show below.
+  // instead, prefer to use the `Cord::Chars()` method shown below.
   //
   // Implementation note: `CharRange` is simply a convenience wrapper over
   // `Cord::char_begin()` and `Cord::char_end()`.
@@ -620,11 +666,11 @@ class Cord {
     const Cord* cord_;
   };
 
-  // Cord::CharIterator::Chars()
+  // Cord::Chars()
   //
-  // Returns a `Cord::CharIterator` for iterating over the characters of a
-  // `Cord` with a range-based for-loop. For most character-based iteration
-  // tasks on a Cord, use `Cord::Chars()` to retrieve this iterator.
+  // Returns a `Cord::CharRange` for iterating over the characters of a `Cord`
+  // with a range-based for-loop. For most character-based iteration tasks on a
+  // Cord, use `Cord::Chars()` to retrieve this iterator.
   //
   // Example:
   //
@@ -671,6 +717,29 @@ class Cord {
     cord->Append(part);
   }
 
+  // Cord::SetExpectedChecksum()
+  //
+  // Stores a checksum value with this non-empty cord instance, for later
+  // retrieval.
+  //
+  // The expected checksum is a number stored out-of-band, alongside the data.
+  // It is preserved across copies and assignments, but any mutations to a cord
+  // will cause it to lose its expected checksum.
+  //
+  // The expected checksum is not part of a Cord's value, and does not affect
+  // operations such as equality or hashing.
+  //
+  // This field is intended to store a CRC32C checksum for later validation, to
+  // help support end-to-end checksum workflows.  However, the Cord API itself
+  // does no CRC validation, and assigns no meaning to this number.
+  //
+  // This call has no effect if this cord is empty.
+  void SetExpectedChecksum(uint32_t crc);
+
+  // Returns this cord's expected checksum, if it has one.  Otherwise, returns
+  // nullopt.
+  y_absl::optional<uint32_t> ExpectedChecksum() const;
+
   template <typename H>
   friend H AbslHashValue(H hash_state, const y_absl::Cord& c) {
     y_absl::optional<y_absl::string_view> maybe_flat = c.TryFlat();
@@ -686,7 +755,8 @@ class Cord {
   // be used by spelling y_absl::strings_internal::MakeStringConstant, which is
   // also an internal API.
   template <typename T>
-  explicit constexpr Cord(strings_internal::StringConstant<T>);
+  // NOLINTNEXTLINE(google-explicit-constructor)
+  constexpr Cord(strings_internal::StringConstant<T>);
 
  private:
   using CordRep = y_absl::cord_internal::CordRep;
@@ -738,12 +808,12 @@ class Cord {
     bool empty() const;
     size_t size() const;
     const char* data() const;  // Returns nullptr if holding pointer
-    void set_data(const char* data, size_t n,
-                  bool nullify_tail);  // Discards pointer, if any
-    char* set_data(size_t n);          // Write data to the result
+    void set_data(const char* data, size_t n);  // Discards pointer, if any
+    char* set_data(size_t n);                   // Write data to the result
     // Returns nullptr if holding bytes
     y_absl::cord_internal::CordRep* tree() const;
     y_absl::cord_internal::CordRep* as_tree() const;
+    const char* as_chars() const;
     // Returns non-null iff was holding a pointer
     y_absl::cord_internal::CordRep* clear();
     // Converts to pointer if necessary.
@@ -831,6 +901,11 @@ class Cord {
     // Returns true if the Cord is being profiled by cordz.
     bool is_profiled() const { return data_.is_tree() && data_.is_profiled(); }
 
+    // Returns the available inlined capacity, or 0 if is_tree() == true.
+    size_t remaining_inline_capacity() const {
+      return data_.is_tree() ? 0 : kMaxInline - data_.inline_size();
+    }
+
     // Returns the profiled CordzInfo, or nullptr if not sampled.
     y_absl::cord_internal::CordzInfo* cordz_info() const {
       return data_.cordz_info();
@@ -861,9 +936,6 @@ class Cord {
   };
   InlineRep contents_;
 
-  // Helper for MemoryUsage().
-  static size_t MemoryUsageAux(const y_absl::cord_internal::CordRep* rep);
-
   // Helper for GetFlat() and TryFlat().
   static bool GetFlatAux(y_absl::cord_internal::CordRep* rep,
                          y_absl::string_view* fragment);
@@ -901,6 +973,15 @@ class Cord {
   template <typename C>
   void AppendImpl(C&& src);
 
+  // Appends / Prepends `src` to this instance, using precise sizing.
+  // This method does explicitly not attempt to use any spare capacity
+  // in any pending last added private owned flat.
+  // Requires `src` to be <= kMaxFlatLength.
+  void AppendPrecise(y_absl::string_view src, MethodIdentifier method);
+  void PrependPrecise(y_absl::string_view src, MethodIdentifier method);
+
+  CordBuffer GetAppendBufferSlowPath(size_t capacity, size_t min_capacity);
+
   // Prepends the provided data to this instance. `method` contains the public
   // API method for this action which is tracked for Cordz sampling purposes.
   void PrependArray(y_absl::string_view src, MethodIdentifier method);
@@ -938,8 +1019,8 @@ namespace cord_internal {
 // Fast implementation of memmove for up to 15 bytes. This implementation is
 // safe for overlapping regions. If nullify_tail is true, the destination is
 // padded with '\0' up to 16 bytes.
-inline void SmallMemmove(char* dst, const char* src, size_t n,
-                         bool nullify_tail = false) {
+template <bool nullify_tail = false>
+inline void SmallMemmove(char* dst, const char* src, size_t n) {
   if (n >= 8) {
     assert(n <= 16);
     uint64_t buf1;
@@ -976,22 +1057,16 @@ inline void SmallMemmove(char* dst, const char* src, size_t n,
 }
 
 // Does non-template-specific `CordRepExternal` initialization.
-// Expects `data` to be non-empty.
+// Requires `data` to be non-empty.
 void InitializeCordRepExternal(y_absl::string_view data, CordRepExternal* rep);
 
 // Creates a new `CordRep` that owns `data` and `releaser` and returns a pointer
-// to it, or `nullptr` if `data` was empty.
+// to it. Requires `data` to be non-empty.
 template <typename Releaser>
 // NOLINTNEXTLINE - suppress clang-tidy raw pointer return.
 CordRep* NewExternalRep(y_absl::string_view data, Releaser&& releaser) {
+  assert(!data.empty());
   using ReleaserType = y_absl::decay_t<Releaser>;
-  if (data.empty()) {
-    // Never create empty external nodes.
-    InvokeReleaser(Rank0{}, ReleaserType(std::forward<Releaser>(releaser)),
-                   data);
-    return nullptr;
-  }
-
   CordRepExternal* rep = new CordRepExternalImpl<ReleaserType>(
       std::forward<Releaser>(releaser), 0);
   InitializeCordRepExternal(data, rep);
@@ -1011,10 +1086,15 @@ inline CordRep* NewExternalRep(y_absl::string_view data,
 template <typename Releaser>
 Cord MakeCordFromExternal(y_absl::string_view data, Releaser&& releaser) {
   Cord cord;
-  if (auto* rep = ::y_absl::cord_internal::NewExternalRep(
-          data, std::forward<Releaser>(releaser))) {
-    cord.contents_.EmplaceTree(rep,
+  if (Y_ABSL_PREDICT_TRUE(!data.empty())) {
+    cord.contents_.EmplaceTree(::y_absl::cord_internal::NewExternalRep(
+                                   data, std::forward<Releaser>(releaser)),
                                Cord::MethodIdentifier::kMakeCordFromExternal);
+  } else {
+    using ReleaserType = y_absl::decay_t<Releaser>;
+    cord_internal::InvokeReleaser(
+        cord_internal::Rank0{}, ReleaserType(std::forward<Releaser>(releaser)),
+        data);
   }
   return cord;
 }
@@ -1069,6 +1149,11 @@ inline const char* Cord::InlineRep::data() const {
   return is_tree() ? nullptr : data_.as_chars();
 }
 
+inline const char* Cord::InlineRep::as_chars() const {
+  assert(!data_.is_tree());
+  return data_.as_chars();
+}
+
 inline y_absl::cord_internal::CordRep* Cord::InlineRep::as_tree() const {
   assert(data_.is_tree());
   return data_.as_tree();
@@ -1207,10 +1292,15 @@ inline size_t Cord::size() const {
 
 inline bool Cord::empty() const { return contents_.empty(); }
 
-inline size_t Cord::EstimatedMemoryUsage() const {
+inline size_t Cord::EstimatedMemoryUsage(
+    CordMemoryAccounting accounting_method) const {
   size_t result = sizeof(Cord);
   if (const y_absl::cord_internal::CordRep* rep = contents_.tree()) {
-    result += MemoryUsageAux(rep);
+    if (accounting_method == CordMemoryAccounting::kFairShare) {
+      result += cord_internal::GetEstimatedFairShareMemoryUsage(rep);
+    } else {
+      result += cord_internal::GetEstimatedMemoryUsage(rep);
+    }
   }
   return result;
 }
@@ -1248,6 +1338,31 @@ inline void Cord::Prepend(y_absl::string_view src) {
   PrependArray(src, CordzUpdateTracker::kPrependString);
 }
 
+inline void Cord::Append(CordBuffer buffer) {
+  if (Y_ABSL_PREDICT_FALSE(buffer.length() == 0)) return;
+  y_absl::string_view short_value;
+  if (CordRep* rep = buffer.ConsumeValue(short_value)) {
+    contents_.AppendTree(rep, CordzUpdateTracker::kAppendCordBuffer);
+  } else {
+    AppendPrecise(short_value, CordzUpdateTracker::kAppendCordBuffer);
+  }
+}
+
+inline void Cord::Prepend(CordBuffer buffer) {
+  if (Y_ABSL_PREDICT_FALSE(buffer.length() == 0)) return;
+  y_absl::string_view short_value;
+  if (CordRep* rep = buffer.ConsumeValue(short_value)) {
+    contents_.PrependTree(rep, CordzUpdateTracker::kPrependCordBuffer);
+  } else {
+    PrependPrecise(short_value, CordzUpdateTracker::kPrependCordBuffer);
+  }
+}
+
+inline CordBuffer Cord::GetAppendBuffer(size_t capacity, size_t min_capacity) {
+  if (empty()) return CordBuffer::CreateWithDefaultLimit(capacity);
+  return GetAppendBufferSlowPath(capacity, min_capacity);
+}
+
 extern template void Cord::Append(TString&& src);
 extern template void Cord::Prepend(TString&& src);
 
@@ -1274,27 +1389,27 @@ inline bool Cord::StartsWith(y_absl::string_view rhs) const {
 }
 
 inline void Cord::ChunkIterator::InitTree(cord_internal::CordRep* tree) {
+  tree = cord_internal::SkipCrcNode(tree);
   if (tree->tag == cord_internal::BTREE) {
     current_chunk_ = btree_reader_.Init(tree->btree());
-    return;
+  } else {
+    current_leaf_ = tree;
+    current_chunk_ = cord_internal::EdgeData(tree);
   }
-
-  stack_of_right_children_.push_back(tree);
-  operator++();
 }
 
-inline Cord::ChunkIterator::ChunkIterator(cord_internal::CordRep* tree)
-    : bytes_remaining_(tree->length) {
+inline Cord::ChunkIterator::ChunkIterator(cord_internal::CordRep* tree) {
+  bytes_remaining_ = tree->length;
   InitTree(tree);
 }
 
-inline Cord::ChunkIterator::ChunkIterator(const Cord* cord)
-    : bytes_remaining_(cord->size()) {
-  if (cord->contents_.is_tree()) {
-    InitTree(cord->contents_.as_tree());
+inline Cord::ChunkIterator::ChunkIterator(const Cord* cord) {
+  if (CordRep* tree = cord->contents_.tree()) {
+    bytes_remaining_ = tree->length;
+    InitTree(tree);
   } else {
-    current_chunk_ =
-        y_absl::string_view(cord->contents_.data(), bytes_remaining_);
+    bytes_remaining_ = cord->contents_.inline_size();
+    current_chunk_ = {cord->contents_.data(), bytes_remaining_};
   }
 }
 
@@ -1324,8 +1439,11 @@ inline Cord::ChunkIterator& Cord::ChunkIterator::operator++() {
   assert(bytes_remaining_ >= current_chunk_.size());
   bytes_remaining_ -= current_chunk_.size();
   if (bytes_remaining_ > 0) {
-    return btree_reader_ ? AdvanceBtree() : AdvanceStack();
-  } else {
+    if (btree_reader_) {
+      return AdvanceBtree();
+    } else {
+      assert(!current_chunk_.empty());  // Called on invalid iterator.
+    }
     current_chunk_ = {};
   }
   return *this;
@@ -1366,7 +1484,11 @@ inline void Cord::ChunkIterator::AdvanceBytes(size_t n) {
   if (Y_ABSL_PREDICT_TRUE(n < current_chunk_.size())) {
     RemoveChunkPrefix(n);
   } else if (n != 0) {
-    btree_reader_ ? AdvanceBytesBtree(n) : AdvanceBytesSlowPath(n);
+    if (btree_reader_) {
+      AdvanceBytesBtree(n);
+    } else {
+      bytes_remaining_ = 0;
+    }
   }
 }
 
@@ -1457,7 +1579,7 @@ inline void Cord::ForEachChunk(
   }
 }
 
-// Nonmember Cord-to-Cord relational operarators.
+// Nonmember Cord-to-Cord relational operators.
 inline bool operator==(const Cord& lhs, const Cord& rhs) {
   if (lhs.contents_.IsSame(rhs.contents_)) return true;
   size_t rhs_size = rhs.size();
@@ -1508,7 +1630,6 @@ class CordTestAccess {
  public:
   static size_t FlatOverhead();
   static size_t MaxFlatLength();
-  static size_t SizeofCordRepConcat();
   static size_t SizeofCordRepExternal();
   static size_t SizeofCordRepSubstring();
   static size_t FlatTagToLength(uint8_t tag);
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord_analysis.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord_analysis.cc
new file mode 100644
index 0000000000..9c925510cc
--- /dev/null
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord_analysis.cc
@@ -0,0 +1,188 @@
+// Copyright 2021 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "y_absl/strings/cord_analysis.h"
+
+#include <cstddef>
+#include <cstdint>
+
+#include "y_absl/base/attributes.h"
+#include "y_absl/base/config.h"
+#include "y_absl/container/inlined_vector.h"
+#include "y_absl/strings/internal/cord_data_edge.h"
+#include "y_absl/strings/internal/cord_internal.h"
+#include "y_absl/strings/internal/cord_rep_btree.h"
+#include "y_absl/strings/internal/cord_rep_crc.h"
+#include "y_absl/strings/internal/cord_rep_flat.h"
+#include "y_absl/strings/internal/cord_rep_ring.h"
+//
+#include "y_absl/base/macros.h"
+#include "y_absl/base/port.h"
+#include "y_absl/functional/function_ref.h"
+
+namespace y_absl {
+Y_ABSL_NAMESPACE_BEGIN
+namespace cord_internal {
+namespace {
+
+// Accounting mode for analyzing memory usage.
+enum class Mode { kTotal, kFairShare };
+
+// CordRepRef holds a `const CordRep*` reference in rep, and depending on mode,
+// holds a 'fraction' representing a cumulative inverse refcount weight.
+template <Mode mode>
+struct CordRepRef {
+  // Instantiates a CordRepRef instance.
+  explicit CordRepRef(const CordRep* r) : rep(r) {}
+
+  // Creates a child reference holding the provided child.
+  // Overloaded to add cumulative reference count for kFairShare.
+  CordRepRef Child(const CordRep* child) const { return CordRepRef(child); }
+
+  const CordRep* rep;
+};
+
+// RawUsage holds the computed total number of bytes.
+template <Mode mode>
+struct RawUsage {
+  size_t total = 0;
+
+  // Add 'size' to total, ignoring the CordRepRef argument.
+  void Add(size_t size, CordRepRef<mode>) { total += size; }
+};
+
+// Returns n / refcount avoiding a div for the common refcount == 1.
+template <typename refcount_t>
+double MaybeDiv(double d, refcount_t refcount) {
+  return refcount == 1 ? d : d / refcount;
+}
+
+// Overloaded 'kFairShare' specialization for CordRepRef. This class holds a
+// `fraction` value which represents a cumulative inverse refcount weight.
+// For example, a top node with a reference count of 2 will have a fraction
+// value of 1/2 = 0.5, representing the 'fair share' of memory it references.
+// A node below such a node with a reference count of 5 then has a fraction of
+// 0.5 / 5 = 0.1 representing the fair share of memory below that node, etc.
+template <>
+struct CordRepRef<Mode::kFairShare> {
+  // Creates a CordRepRef with the provided rep and top (parent) fraction.
+  explicit CordRepRef(const CordRep* r, double frac = 1.0)
+      : rep(r), fraction(MaybeDiv(frac, r->refcount.Get())) {}
+
+  // Returns a CordRepRef with a fraction of `this->fraction / child.refcount`
+  CordRepRef Child(const CordRep* child) const {
+    return CordRepRef(child, fraction);
+  }
+
+  const CordRep* rep;
+  double fraction;
+};
+
+// Overloaded 'kFairShare' specialization for RawUsage
+template <>
+struct RawUsage<Mode::kFairShare> {
+  double total = 0;
+
+  // Adds `size` multiplied by `rep.fraction` to the total size.
+  void Add(size_t size, CordRepRef<Mode::kFairShare> rep) {
+    total += static_cast<double>(size) * rep.fraction;
+  }
+};
+
+// Computes the estimated memory size of the provided data edge.
+// External reps are assumed 'heap allocated at their exact size'.
+template <Mode mode>
+void AnalyzeDataEdge(CordRepRef<mode> rep, RawUsage<mode>& raw_usage) {
+  assert(IsDataEdge(rep.rep));
+
+  // Consume all substrings
+  if (rep.rep->tag == SUBSTRING) {
+    raw_usage.Add(sizeof(CordRepSubstring), rep);
+    rep = rep.Child(rep.rep->substring()->child);
+  }
+
+  // Consume FLAT / EXTERNAL
+  const size_t size =
+      rep.rep->tag >= FLAT
+          ? rep.rep->flat()->AllocatedSize()
+          : rep.rep->length + sizeof(CordRepExternalImpl<intptr_t>);
+  raw_usage.Add(size, rep);
+}
+
+// Computes the memory size of the provided Ring tree.
+template <Mode mode>
+void AnalyzeRing(CordRepRef<mode> rep, RawUsage<mode>& raw_usage) {
+  const CordRepRing* ring = rep.rep->ring();
+  raw_usage.Add(CordRepRing::AllocSize(ring->capacity()), rep);
+  ring->ForEach([&](CordRepRing::index_type pos) {
+    AnalyzeDataEdge(rep.Child(ring->entry_child(pos)), raw_usage);
+  });
+}
+
+// Computes the memory size of the provided Btree tree.
+template <Mode mode>
+void AnalyzeBtree(CordRepRef<mode> rep, RawUsage<mode>& raw_usage) {
+  raw_usage.Add(sizeof(CordRepBtree), rep);
+  const CordRepBtree* tree = rep.rep->btree();
+  if (tree->height() > 0) {
+    for (CordRep* edge : tree->Edges()) {
+      AnalyzeBtree(rep.Child(edge), raw_usage);
+    }
+  } else {
+    for (CordRep* edge : tree->Edges()) {
+      AnalyzeDataEdge(rep.Child(edge), raw_usage);
+    }
+  }
+}
+
+template <Mode mode>
+size_t GetEstimatedUsage(const CordRep* rep) {
+  // Zero initialized memory usage totals.
+  RawUsage<mode> raw_usage;
+
+  // Capture top level node and refcount into a CordRepRef.
+  CordRepRef<mode> repref(rep);
+
+  // Consume the top level CRC node if present.
+  if (repref.rep->tag == CRC) {
+    raw_usage.Add(sizeof(CordRepCrc), repref);
+    repref = repref.Child(repref.rep->crc()->child);
+  }
+
+  if (IsDataEdge(repref.rep)) {
+    AnalyzeDataEdge(repref, raw_usage);
+  } else if (repref.rep->tag == BTREE) {
+    AnalyzeBtree(repref, raw_usage);
+  } else if (repref.rep->tag == RING) {
+    AnalyzeRing(repref, raw_usage);
+  } else {
+    assert(false);
+  }
+
+  return static_cast<size_t>(raw_usage.total);
+}
+
+}  // namespace
+
+size_t GetEstimatedMemoryUsage(const CordRep* rep) {
+  return GetEstimatedUsage<Mode::kTotal>(rep);
+}
+
+size_t GetEstimatedFairShareMemoryUsage(const CordRep* rep) {
+  return GetEstimatedUsage<Mode::kFairShare>(rep);
+}
+
+}  // namespace cord_internal
+Y_ABSL_NAMESPACE_END
+}  // namespace y_absl
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord_analysis.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord_analysis.h
new file mode 100644
index 0000000000..75f9216ae3
--- /dev/null
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord_analysis.h
@@ -0,0 +1,44 @@
+// Copyright 2021 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef Y_ABSL_STRINGS_CORD_ANALYSIS_H_
+#define Y_ABSL_STRINGS_CORD_ANALYSIS_H_
+
+#include <cstddef>
+#include <cstdint>
+
+#include "y_absl/base/config.h"
+#include "y_absl/strings/internal/cord_internal.h"
+
+namespace y_absl {
+Y_ABSL_NAMESPACE_BEGIN
+namespace cord_internal {
+
+// Returns the *approximate* number of bytes held in full or in part by this
+// Cord (which may not remain the same between invocations). Cords that share
+// memory could each be "charged" independently for the same shared memory.
+size_t GetEstimatedMemoryUsage(const CordRep* rep);
+
+// Returns the *approximate* number of bytes held in full or in part by this
+// CordRep weighted by the sharing ratio of that data. For example, if some data
+// edge is shared by 4 different Cords, then each cord is attribute 1/4th of
+// the total memory usage as a 'fair share' of the total memory usage.
+size_t GetEstimatedFairShareMemoryUsage(const CordRep* rep);
+
+}  // namespace cord_internal
+Y_ABSL_NAMESPACE_END
+}  // namespace y_absl
+
+
+#endif  // Y_ABSL_STRINGS_CORD_ANALYSIS_H_
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/leak_check_disable.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord_buffer.cc
index 924d6e3d54..f7fc02fe39 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/debugging/leak_check_disable.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord_buffer.cc
@@ -1,10 +1,10 @@
-// Copyright 2017 The Abseil Authors.
+// Copyright 2022 The Abseil Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//      https://www.apache.org/licenses/LICENSE-2.0
+//     https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ -12,9 +12,19 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// Disable LeakSanitizer when this file is linked in.
-// This function overrides __lsan_is_turned_off from sanitizer/lsan_interface.h
-extern "C" int __lsan_is_turned_off();
-extern "C" int __lsan_is_turned_off() {
-  return 1;
-}
+#include "y_absl/strings/cord_buffer.h"
+
+#include <cstddef>
+
+#include "y_absl/base/config.h"
+
+namespace y_absl {
+Y_ABSL_NAMESPACE_BEGIN
+
+#ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+constexpr size_t CordBuffer::kDefaultLimit;
+constexpr size_t CordBuffer::kCustomLimit;
+#endif
+
+Y_ABSL_NAMESPACE_END
+}  // namespace y_absl
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord_buffer.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord_buffer.h
new file mode 100644
index 0000000000..cbe4287b07
--- /dev/null
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/cord_buffer.h
@@ -0,0 +1,572 @@
+// Copyright 2021 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: cord_buffer.h
+// -----------------------------------------------------------------------------
+//
+// This file defines an `y_absl::CordBuffer` data structure to hold data for
+// eventual inclusion within an existing `Cord` data structure. Cord buffers are
+// useful for building large Cords that may require custom allocation of its
+// associated memory.
+//
+#ifndef Y_ABSL_STRINGS_CORD_BUFFER_H_
+#define Y_ABSL_STRINGS_CORD_BUFFER_H_
+
+#include <algorithm>
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+#include <memory>
+#include <utility>
+
+#include "y_absl/base/config.h"
+#include "y_absl/base/macros.h"
+#include "y_absl/numeric/bits.h"
+#include "y_absl/strings/internal/cord_internal.h"
+#include "y_absl/strings/internal/cord_rep_flat.h"
+#include "y_absl/types/span.h"
+
+namespace y_absl {
+Y_ABSL_NAMESPACE_BEGIN
+
+class Cord;
+class CordBufferTestPeer;
+
+// CordBuffer
+//
+// CordBuffer manages memory buffers for purposes such as zero-copy APIs as well
+// as applications building cords with large data requiring granular control
+// over the allocation and size of cord data. For example, a function creating
+// a cord of random data could use a CordBuffer as follows:
+//
+//   y_absl::Cord CreateRandomCord(size_t length) {
+//     y_absl::Cord cord;
+//     while (length > 0) {
+//       CordBuffer buffer = CordBuffer::CreateWithDefaultLimit(length);
+//       y_absl::Span<char> data = buffer.available_up_to(length);
+//       FillRandomValues(data.data(), data.size());
+//       buffer.IncreaseLengthBy(data.size());
+//       cord.Append(std::move(buffer));
+//       length -= data.size();
+//     }
+//     return cord;
+//   }
+//
+// CordBuffer instances are by default limited to a capacity of `kDefaultLimit`
+// bytes. `kDefaultLimit` is currently just under 4KiB, but this default may
+// change in the future and/or for specific architectures. The default limit is
+// aimed to provide a good trade-off between performance and memory overhead.
+// Smaller buffers typically incur more compute cost while larger buffers are
+// more CPU efficient but create significant memory overhead because of such
+// allocations being less granular. Using larger buffers may also increase the
+// risk of memory fragmentation.
+//
+// Applications create a buffer using one of the `CreateWithDefaultLimit()` or
+// `CreateWithCustomLimit()` methods. The returned instance will have a non-zero
+// capacity and a zero length. Applications use the `data()` method to set the
+// contents of the managed memory, and once done filling the buffer, use the
+// `IncreaseLengthBy()` or 'SetLength()' method to specify the length of the
+// initialized data before adding the buffer to a Cord.
+//
+// The `CreateWithCustomLimit()` method is intended for applications needing
+// larger buffers than the default memory limit, allowing the allocation of up
+// to a capacity of `kCustomLimit` bytes minus some minimum internal overhead.
+// The usage of `CreateWithCustomLimit()` should be limited to only those use
+// cases where the distribution of the input is relatively well known, and/or
+// where the trade-off between the efficiency gains outweigh the risk of memory
+// fragmentation. See the documentation for `CreateWithCustomLimit()` for more
+// information on using larger custom limits.
+//
+// The capacity of a `CordBuffer` returned by one of the `Create` methods may
+// be larger than the requested capacity due to rounding, alignment and
+// granularity of the memory allocator. Applications should use the `capacity`
+// method to obtain the effective capacity of the returned instance as
+// demonstrated in the provided example above.
+//
+// CordBuffer is a move-only class. All references into the managed memory are
+// invalidated when an instance is moved into either another CordBuffer instance
+// or a Cord. Writing to a location obtained by a previous call to `data()`
+// after an instance was moved will lead to undefined behavior.
+//
+// A `moved from` CordBuffer instance will have a valid, but empty state.
+// CordBuffer is thread compatible.
+class CordBuffer {
+ public:
+  // kDefaultLimit
+  //
+  // Default capacity limits of allocated CordBuffers.
+  // See the class comments for more information on allocation limits.
+  static constexpr size_t kDefaultLimit = cord_internal::kMaxFlatLength;
+
+  // kCustomLimit
+  //
+  // Maximum size for CreateWithCustomLimit() allocated buffers.
+  // Note that the effective capacity may be slightly less
+  // because of internal overhead of internal cord buffers.
+  static constexpr size_t kCustomLimit = 64U << 10;
+
+  // Constructors, Destructors and Assignment Operators
+
+  // Creates an empty CordBuffer.
+  CordBuffer() = default;
+
+  // Destroys this CordBuffer instance and, if not empty, releases any memory
+  // managed by this instance, invalidating previously returned references.
+  ~CordBuffer();
+
+  // CordBuffer is move-only
+  CordBuffer(CordBuffer&& rhs) noexcept;
+  CordBuffer& operator=(CordBuffer&&) noexcept;
+  CordBuffer(const CordBuffer&) = delete;
+  CordBuffer& operator=(const CordBuffer&) = delete;
+
+  // CordBuffer::MaximumPayload()
+  //
+  // Returns the guaranteed maximum payload for a CordBuffer returned by the
+  // `CreateWithDefaultLimit()` method. While small, each internal buffer inside
+  // a Cord incurs an overhead to manage the length, type and reference count
+  // for the buffer managed inside the cord tree. Applications can use this
+  // method to get approximate number of buffers required for a given byte
+  // size, etc.
+  //
+  // For example:
+  //   const size_t payload = y_absl::CordBuffer::MaximumPayload();
+  //   const size_t buffer_count = (total_size + payload - 1) / payload;
+  //   buffers.reserve(buffer_count);
+  static constexpr size_t MaximumPayload();
+
+  // Overload to the above `MaximumPayload()` except that it returns the
+  // maximum payload for a CordBuffer returned by the `CreateWithCustomLimit()`
+  // method given the provided `block_size`.
+  static constexpr size_t MaximumPayload(size_t block_size);
+
+  // CordBuffer::CreateWithDefaultLimit()
+  //
+  // Creates a CordBuffer instance of the desired `capacity`, capped at the
+  // default limit `kDefaultLimit`. The returned buffer has a guaranteed
+  // capacity of at least `min(kDefaultLimit, capacity)`. See the class comments
+  // for more information on buffer capacities and intended usage.
+  static CordBuffer CreateWithDefaultLimit(size_t capacity);
+
+
+  // CordBuffer::CreateWithCustomLimit()
+  //
+  // Creates a CordBuffer instance of the desired `capacity` rounded to an
+  // appropriate power of 2 size less than, or equal to `block_size`.
+  // Requires `block_size` to be a power of 2.
+  //
+  // If `capacity` is less than or equal to `kDefaultLimit`, then this method
+  // behaves identical to `CreateWithDefaultLimit`, which means that the caller
+  // is guaranteed to get a buffer of at least the requested capacity.
+  //
+  // If `capacity` is greater than or equal to `block_size`, then this method
+  // returns a buffer with an `allocated size` of `block_size` bytes. Otherwise,
+  // this methods returns a buffer with a suitable smaller power of 2 block size
+  // to satisfy the request. The actual size depends on a number of factors, and
+  // is typically (but not necessarily) the highest or second highest power of 2
+  // value less than or equal to `capacity`.
+  //
+  // The 'allocated size' includes a small amount of overhead required for
+  // internal state, which is currently 13 bytes on 64-bit platforms. For
+  // example: a buffer created with `block_size` and `capacity' set to 8KiB
+  // will have an allocated size of 8KiB, and an effective internal `capacity`
+  // of 8KiB - 13 = 8179 bytes.
+  //
+  // To demonstrate this in practice, let's assume we want to read data from
+  // somewhat larger files using approximately 64KiB buffers:
+  //
+  //   y_absl::Cord ReadFromFile(int fd, size_t n) {
+  //     y_absl::Cord cord;
+  //     while (n > 0) {
+  //       CordBuffer buffer = CordBuffer::CreateWithCustomLimit(64 << 10, n);
+  //       y_absl::Span<char> data = buffer.available_up_to(n);
+  //       ReadFileDataOrDie(fd, data.data(), data.size());
+  //       buffer.IncreaseLengthBy(data.size());
+  //       cord.Append(std::move(buffer));
+  //       n -= data.size();
+  //     }
+  //     return cord;
+  //   }
+  //
+  // If we'd use this function to read a file of 659KiB, we may get the
+  // following pattern of allocated cord buffer sizes:
+  //
+  //   CreateWithCustomLimit(64KiB, 674816) --> ~64KiB (65523)
+  //   CreateWithCustomLimit(64KiB, 674816) --> ~64KiB (65523)
+  //   ...
+  //   CreateWithCustomLimit(64KiB,  19586) --> ~16KiB (16371)
+  //   CreateWithCustomLimit(64KiB,   3215) -->   3215 (at least 3215)
+  //
+  // The reason the method returns a 16K buffer instead of a roughly 19K buffer
+  // is to reduce memory overhead and fragmentation risks. Using carefully
+  // chosen power of 2 values reduces the entropy of allocated memory sizes.
+  //
+  // Additionally, let's assume we'd use the above function on files that are
+  // generally smaller than 64K. If we'd use 'precise' sized buffers for such
+  // files, than we'd get a very wide distribution of allocated memory sizes
+  // rounded to 4K page sizes, and we'd end up with a lot of unused capacity.
+  //
+  // In general, application should only use custom sizes if the data they are
+  // consuming or storing is expected to be many times the chosen block size,
+  // and be based on objective data and performance metrics. For example, a
+  // compress function may work faster and consume less CPU when using larger
+  // buffers. Such an application should pick a size offering a reasonable
+  // trade-off between expected data size, compute savings with larger buffers,
+  // and the cost or fragmentation effect of larger buffers.
+  // Applications must pick a reasonable spot on that curve, and make sure their
+  // data meets their expectations in size distributions such as "mostly large".
+  static CordBuffer CreateWithCustomLimit(size_t block_size, size_t capacity);
+
+  // CordBuffer::available()
+  //
+  // Returns the span delineating the available capacity in this buffer
+  // which is defined as `{ data() + length(), capacity() - length() }`.
+  y_absl::Span<char> available();
+
+  // CordBuffer::available_up_to()
+  //
+  // Returns the span delineating the available capacity in this buffer limited
+  // to `size` bytes. This is equivalent to `available().subspan(0, size)`.
+  y_absl::Span<char> available_up_to(size_t size);
+
+  // CordBuffer::data()
+  //
+  // Returns a non-null reference to the data managed by this instance.
+  // Applications are allowed to write up to `capacity` bytes of instance data.
+  // CordBuffer data is uninitialized by default. Reading data from an instance
+  // that has not yet been initialized will lead to undefined behavior.
+  char* data();
+  const char* data() const;
+
+  // CordBuffer::length()
+  //
+  // Returns the length of this instance. The default length of a CordBuffer is
+  // 0, indicating an 'empty' CordBuffer. Applications must specify the length
+  // of the data in a CordBuffer before adding it to a Cord.
+  size_t length() const;
+
+  // CordBuffer::capacity()
+  //
+  // Returns the capacity of this instance. All instances have a non-zero
+  // capacity: default and `moved from` instances have a small internal buffer.
+  size_t capacity() const;
+
+  // CordBuffer::IncreaseLengthBy()
+  //
+  // Increases the length of this buffer by the specified 'n' bytes.
+  // Applications must make sure all data in this buffer up to the new length
+  // has been initialized before adding a CordBuffer to a Cord: failure to do so
+  // will lead to undefined behavior.  Requires `length() + n <= capacity()`.
+  // Typically, applications will use 'available_up_to()` to get a span of the
+  // desired capacity, and use `span.size()` to increase the length as in:
+  //   y_absl::Span<char> span = buffer.available_up_to(desired);
+  //   buffer.IncreaseLengthBy(span.size());
+  //   memcpy(span.data(), src, span.size());
+  //   etc...
+  void IncreaseLengthBy(size_t n);
+
+  // CordBuffer::SetLength()
+  //
+  // Sets the data length of this instance. Applications must make sure all data
+  // of the specified length has been initialized before adding a CordBuffer to
+  // a Cord: failure to do so will lead to undefined behavior.
+  // Setting the length to a small value or zero does not release any memory
+  // held by this CordBuffer instance. Requires `length <= capacity()`.
+  // Applications should preferably use the `IncreaseLengthBy()` method above
+  // in combination with the 'available()` or `available_up_to()` methods.
+  void SetLength(size_t length);
+
+ private:
+  // Make sure we don't accidentally over promise.
+  static_assert(kCustomLimit <= cord_internal::kMaxLargeFlatSize, "");
+
+  // Assume the cost of an 'uprounded' allocation to CeilPow2(size) versus
+  // the cost of allocating at least 1 extra flat <= 4KB:
+  // - Flat overhead = 13 bytes
+  // - Btree amortized cost / node =~ 13 bytes
+  // - 64 byte granularity of tcmalloc at 4K =~ 32 byte average
+  // CPU cost and efficiency requires we should at least 'save' something by
+  // splitting, as a poor man's measure, we say the slop needs to be
+  // at least double the cost offset to make it worth splitting: ~128 bytes.
+  static constexpr size_t kMaxPageSlop = 128;
+
+  // Overhead for allocation a flat.
+  static constexpr size_t kOverhead = cord_internal::kFlatOverhead;
+
+  using CordRepFlat = cord_internal::CordRepFlat;
+
+  // `Rep` is the internal data representation of a CordBuffer. The internal
+  // representation has an internal small size optimization similar to
+  // TString (SSO).
+  struct Rep {
+    // Inline SSO size of a CordBuffer
+    static constexpr size_t kInlineCapacity = sizeof(intptr_t) * 2 - 1;
+
+    // Creates a default instance with kInlineCapacity.
+    Rep() : short_rep{} {}
+
+    // Creates an instance managing an allocated non zero CordRep.
+    explicit Rep(cord_internal::CordRepFlat* rep) : long_rep{rep} {
+      assert(rep != nullptr);
+    }
+
+    // Returns true if this instance manages the SSO internal buffer.
+    bool is_short() const {
+      constexpr size_t offset = offsetof(Short, raw_size);
+      return (reinterpret_cast<const char*>(this)[offset] & 1) != 0;
+    }
+
+    // Returns the available area of the internal SSO data
+    y_absl::Span<char> short_available() {
+      assert(is_short());
+      const size_t length = (short_rep.raw_size >> 1);
+      return y_absl::Span<char>(short_rep.data + length,
+                              kInlineCapacity - length);
+    }
+
+    // Returns the available area of the internal SSO data
+    y_absl::Span<char> long_available() {
+      assert(!is_short());
+      const size_t length = long_rep.rep->length;
+      return y_absl::Span<char>(long_rep.rep->Data() + length,
+                              long_rep.rep->Capacity() - length);
+    }
+
+    // Returns the length of the internal SSO data.
+    size_t short_length() const {
+      assert(is_short());
+      return short_rep.raw_size >> 1;
+    }
+
+    // Sets the length of the internal SSO data.
+    // Disregards any previously set CordRep instance.
+    void set_short_length(size_t length) {
+      short_rep.raw_size = static_cast<char>((length << 1) + 1);
+    }
+
+    // Adds `n` to the current short length.
+    void add_short_length(size_t n) {
+      assert(is_short());
+      short_rep.raw_size += static_cast<char>(n << 1);
+    }
+
+    // Returns reference to the internal SSO data buffer.
+    char* data() {
+      assert(is_short());
+      return short_rep.data;
+    }
+    const char* data() const {
+      assert(is_short());
+      return short_rep.data;
+    }
+
+    // Returns a pointer the external CordRep managed by this instance.
+    cord_internal::CordRepFlat* rep() const {
+      assert(!is_short());
+      return long_rep.rep;
+    }
+
+    // The internal representation takes advantage of the fact that allocated
+    // memory is always on an even address, and uses the least significant bit
+    // of the first or last byte (depending on endianness) as the inline size
+    // indicator overlapping with the least significant byte of the CordRep*.
+#if defined(Y_ABSL_IS_BIG_ENDIAN)
+    struct Long {
+      explicit Long(cord_internal::CordRepFlat* rep_arg) : rep(rep_arg) {}
+      void* padding;
+      cord_internal::CordRepFlat* rep;
+    };
+    struct Short {
+      char data[sizeof(Long) - 1];
+      char raw_size = 1;
+    };
+#else
+    struct Long {
+      explicit Long(cord_internal::CordRepFlat* rep_arg) : rep(rep_arg) {}
+      cord_internal::CordRepFlat* rep;
+      void* padding;
+    };
+    struct Short {
+      char raw_size = 1;
+      char data[sizeof(Long) - 1];
+    };
+#endif
+
+    union {
+      Long long_rep;
+      Short short_rep;
+    };
+  };
+
+  // Power2 functions
+  static bool IsPow2(size_t size) { return y_absl::has_single_bit(size); }
+  static size_t Log2Floor(size_t size) { return y_absl::bit_width(size) - 1; }
+  static size_t Log2Ceil(size_t size) { return y_absl::bit_width(size - 1); }
+
+  // Implementation of `CreateWithCustomLimit()`.
+  // This implementation allows for future memory allocation hints to
+  // be passed down into the CordRepFlat allocation function.
+  template <typename... AllocationHints>
+  static CordBuffer CreateWithCustomLimitImpl(size_t block_size,
+                                              size_t capacity,
+                                              AllocationHints... hints);
+
+  // Consumes the value contained in this instance and resets the instance.
+  // This method returns a non-null Cordrep* if the current instances manages a
+  // CordRep*, and resets the instance to an empty SSO instance. If the current
+  // instance is an SSO instance, then this method returns nullptr and sets
+  // `short_value` to the inlined data value. In either case, the current
+  // instance length is reset to zero.
+  // This method is intended to be used by Cord internal functions only.
+  cord_internal::CordRep* ConsumeValue(y_absl::string_view& short_value) {
+    cord_internal::CordRep* rep = nullptr;
+    if (rep_.is_short()) {
+      short_value = y_absl::string_view(rep_.data(), rep_.short_length());
+    } else {
+      rep = rep_.rep();
+    }
+    rep_.set_short_length(0);
+    return rep;
+  }
+
+  // Internal constructor.
+  explicit CordBuffer(cord_internal::CordRepFlat* rep) : rep_(rep) {
+    assert(rep != nullptr);
+  }
+
+  Rep rep_;
+
+  friend class Cord;
+  friend class CordBufferTestPeer;
+};
+
+inline constexpr size_t CordBuffer::MaximumPayload() {
+  return cord_internal::kMaxFlatLength;
+}
+
+inline constexpr size_t CordBuffer::MaximumPayload(size_t block_size) {
+  // TODO(y_absl-team): Use std::min when C++11 support is dropped.
+  return (kCustomLimit < block_size ? kCustomLimit : block_size) -
+         cord_internal::kFlatOverhead;
+}
+
+inline CordBuffer CordBuffer::CreateWithDefaultLimit(size_t capacity) {
+  if (capacity > Rep::kInlineCapacity) {
+    auto* rep = cord_internal::CordRepFlat::New(capacity);
+    rep->length = 0;
+    return CordBuffer(rep);
+  }
+  return CordBuffer();
+}
+
+template <typename... AllocationHints>
+inline CordBuffer CordBuffer::CreateWithCustomLimitImpl(
+    size_t block_size, size_t capacity, AllocationHints... hints) {
+  assert(IsPow2(block_size));
+  capacity = (std::min)(capacity, kCustomLimit);
+  block_size = (std::min)(block_size, kCustomLimit);
+  if (capacity + kOverhead >= block_size) {
+    capacity = block_size;
+  } else if (capacity <= kDefaultLimit) {
+    capacity = capacity + kOverhead;
+  } else if (!IsPow2(capacity)) {
+    // Check if rounded up to next power 2 is a good enough fit
+    // with limited waste making it an acceptable direct fit.
+    const size_t rounded_up = size_t{1} << Log2Ceil(capacity);
+    const size_t slop = rounded_up - capacity;
+    if (slop >= kOverhead && slop <= kMaxPageSlop + kOverhead) {
+      capacity = rounded_up;
+    } else {
+      // Round down to highest power of 2 <= capacity.
+      // Consider a more aggressive step down if that may reduce the
+      // risk of fragmentation where 'people are holding it wrong'.
+      const size_t rounded_down = size_t{1} << Log2Floor(capacity);
+      capacity = rounded_down;
+    }
+  }
+  const size_t length = capacity - kOverhead;
+  auto* rep = CordRepFlat::New(CordRepFlat::Large(), length, hints...);
+  rep->length = 0;
+  return CordBuffer(rep);
+}
+
+inline CordBuffer CordBuffer::CreateWithCustomLimit(size_t block_size,
+                                                    size_t capacity) {
+  return CreateWithCustomLimitImpl(block_size, capacity);
+}
+
+inline CordBuffer::~CordBuffer() {
+  if (!rep_.is_short()) {
+    cord_internal::CordRepFlat::Delete(rep_.rep());
+  }
+}
+
+inline CordBuffer::CordBuffer(CordBuffer&& rhs) noexcept : rep_(rhs.rep_) {
+  rhs.rep_.set_short_length(0);
+}
+
+inline CordBuffer& CordBuffer::operator=(CordBuffer&& rhs) noexcept {
+  if (!rep_.is_short()) cord_internal::CordRepFlat::Delete(rep_.rep());
+  rep_ = rhs.rep_;
+  rhs.rep_.set_short_length(0);
+  return *this;
+}
+
+inline y_absl::Span<char> CordBuffer::available() {
+  return rep_.is_short() ? rep_.short_available() : rep_.long_available();
+}
+
+inline y_absl::Span<char> CordBuffer::available_up_to(size_t size) {
+  return available().subspan(0, size);
+}
+
+inline char* CordBuffer::data() {
+  return rep_.is_short() ? rep_.data() : rep_.rep()->Data();
+}
+
+inline const char* CordBuffer::data() const {
+  return rep_.is_short() ? rep_.data() : rep_.rep()->Data();
+}
+
+inline size_t CordBuffer::capacity() const {
+  return rep_.is_short() ? Rep::kInlineCapacity : rep_.rep()->Capacity();
+}
+
+inline size_t CordBuffer::length() const {
+  return rep_.is_short() ? rep_.short_length() : rep_.rep()->length;
+}
+
+inline void CordBuffer::SetLength(size_t length) {
+  Y_ABSL_HARDENING_ASSERT(length <= capacity());
+  if (rep_.is_short()) {
+    rep_.set_short_length(length);
+  } else {
+    rep_.rep()->length = length;
+  }
+}
+
+inline void CordBuffer::IncreaseLengthBy(size_t n) {
+  Y_ABSL_HARDENING_ASSERT(n <= capacity() && length() + n <= capacity());
+  if (rep_.is_short()) {
+    rep_.add_short_length(n);
+  } else {
+    rep_.rep()->length += n;
+  }
+}
+
+Y_ABSL_NAMESPACE_END
+}  // namespace y_absl
+
+#endif  // Y_ABSL_STRINGS_CORD_BUFFER_H_
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_data_edge.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_data_edge.h
new file mode 100644
index 0000000000..afdaa3c8c3
--- /dev/null
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_data_edge.h
@@ -0,0 +1,63 @@
+// Copyright 2022 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef Y_ABSL_STRINGS_INTERNAL_CORD_DATA_EDGE_H_
+#define Y_ABSL_STRINGS_INTERNAL_CORD_DATA_EDGE_H_
+
+#include <cassert>
+#include <cstddef>
+
+#include "y_absl/base/config.h"
+#include "y_absl/strings/internal/cord_internal.h"
+#include "y_absl/strings/internal/cord_rep_flat.h"
+#include "y_absl/strings/string_view.h"
+
+namespace y_absl {
+Y_ABSL_NAMESPACE_BEGIN
+namespace cord_internal {
+
+// Returns true if the provided rep is a FLAT, EXTERNAL or a SUBSTRING node
+// holding a FLAT or EXTERNAL child rep. Requires `rep != nullptr`.
+inline bool IsDataEdge(const CordRep* edge) {
+  assert(edge != nullptr);
+
+  // The fast path is that `edge` is an EXTERNAL or FLAT node, making the below
+  // if a single, well predicted branch. We then repeat the FLAT or EXTERNAL
+  // check in the slow path of the SUBSTRING check to optimize for the hot path.
+  if (edge->tag == EXTERNAL || edge->tag >= FLAT) return true;
+  if (edge->tag == SUBSTRING) edge = edge->substring()->child;
+  return edge->tag == EXTERNAL || edge->tag >= FLAT;
+}
+
+// Returns the `y_absl::string_view` data reference for the provided data edge.
+// Requires 'IsDataEdge(edge) == true`.
+inline y_absl::string_view EdgeData(const CordRep* edge) {
+  assert(IsDataEdge(edge));
+
+  size_t offset = 0;
+  const size_t length = edge->length;
+  if (edge->IsSubstring()) {
+    offset = edge->substring()->start;
+    edge = edge->substring()->child;
+  }
+  return edge->tag >= FLAT
+             ? y_absl::string_view{edge->flat()->Data() + offset, length}
+             : y_absl::string_view{edge->external()->base + offset, length};
+}
+
+}  // namespace cord_internal
+Y_ABSL_NAMESPACE_END
+}  // namespace y_absl
+
+#endif  // Y_ABSL_STRINGS_INTERNAL_CORD_DATA_EDGE_H_
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_internal.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_internal.cc
index 75cd0c044e..22a890c232 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_internal.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_internal.cc
@@ -17,69 +17,57 @@
 #include <cassert>
 #include <memory>
 
+#include "y_absl/base/internal/raw_logging.h"
 #include "y_absl/container/inlined_vector.h"
 #include "y_absl/strings/internal/cord_rep_btree.h"
+#include "y_absl/strings/internal/cord_rep_crc.h"
 #include "y_absl/strings/internal/cord_rep_flat.h"
 #include "y_absl/strings/internal/cord_rep_ring.h"
+#include "y_absl/strings/str_cat.h"
 
 namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
 namespace cord_internal {
 
-Y_ABSL_CONST_INIT std::atomic<bool> cord_btree_enabled(kCordEnableBtreeDefault);
 Y_ABSL_CONST_INIT std::atomic<bool> cord_ring_buffer_enabled(
     kCordEnableRingBufferDefault);
 Y_ABSL_CONST_INIT std::atomic<bool> shallow_subcords_enabled(
     kCordShallowSubcordsDefault);
 Y_ABSL_CONST_INIT std::atomic<bool> cord_btree_exhaustive_validation(false);
 
+void LogFatalNodeType(CordRep* rep) {
+  Y_ABSL_INTERNAL_LOG(FATAL, y_absl::StrCat("Unexpected node type: ",
+                                        static_cast<int>(rep->tag)));
+}
+
 void CordRep::Destroy(CordRep* rep) {
   assert(rep != nullptr);
 
-  y_absl::InlinedVector<CordRep*, Constants::kInlinedVectorSize> pending;
   while (true) {
     assert(!rep->refcount.IsImmortal());
-    if (rep->tag == CONCAT) {
-      CordRepConcat* rep_concat = rep->concat();
-      CordRep* right = rep_concat->right;
-      if (!right->refcount.Decrement()) {
-        pending.push_back(right);
-      }
-      CordRep* left = rep_concat->left;
-      delete rep_concat;
-      rep = nullptr;
-      if (!left->refcount.Decrement()) {
-        rep = left;
-        continue;
-      }
-    } else if (rep->tag == BTREE) {
+    if (rep->tag == BTREE) {
       CordRepBtree::Destroy(rep->btree());
-      rep = nullptr;
+      return;
     } else if (rep->tag == RING) {
       CordRepRing::Destroy(rep->ring());
-      rep = nullptr;
+      return;
     } else if (rep->tag == EXTERNAL) {
       CordRepExternal::Delete(rep);
-      rep = nullptr;
+      return;
     } else if (rep->tag == SUBSTRING) {
       CordRepSubstring* rep_substring = rep->substring();
-      CordRep* child = rep_substring->child;
+      rep = rep_substring->child;
       delete rep_substring;
-      rep = nullptr;
-      if (!child->refcount.Decrement()) {
-        rep = child;
-        continue;
+      if (rep->refcount.Decrement()) {
+        return;
       }
+    } else if (rep->tag == CRC) {
+      CordRepCrc::Destroy(rep->crc());
+      return;
     } else {
+      assert(rep->IsFlat());
       CordRepFlat::Delete(rep);
-      rep = nullptr;
-    }
-
-    if (!pending.empty()) {
-      rep = pending.back();
-      pending.pop_back();
-    } else {
-      break;
+      return;
     }
   }
 }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_internal.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_internal.h
index 80d02395f8..87201b7fb0 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_internal.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_internal.h
@@ -21,6 +21,7 @@
 #include <cstdint>
 #include <type_traits>
 
+#include "y_absl/base/attributes.h"
 #include "y_absl/base/config.h"
 #include "y_absl/base/internal/endian.h"
 #include "y_absl/base/internal/invoke.h"
@@ -33,16 +34,27 @@ namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
 namespace cord_internal {
 
+// The overhead of a vtable is too much for Cord, so we roll our own subclasses
+// using only a single byte to differentiate classes from each other - the "tag"
+// byte.  Define the subclasses first so we can provide downcasting helper
+// functions in the base class.
+struct CordRep;
+struct CordRepConcat;
+struct CordRepExternal;
+struct CordRepFlat;
+struct CordRepSubstring;
+struct CordRepCrc;
+class CordRepRing;
+class CordRepBtree;
+
 class CordzInfo;
 
 // Default feature enable states for cord ring buffers
 enum CordFeatureDefaults {
-  kCordEnableBtreeDefault = true,
   kCordEnableRingBufferDefault = false,
   kCordShallowSubcordsDefault = false
 };
 
-extern std::atomic<bool> cord_btree_enabled;
 extern std::atomic<bool> cord_ring_buffer_enabled;
 extern std::atomic<bool> shallow_subcords_enabled;
 
@@ -52,10 +64,6 @@ extern std::atomic<bool> shallow_subcords_enabled;
 // O(n^2) complexity as recursive / full tree validation is O(n).
 extern std::atomic<bool> cord_btree_exhaustive_validation;
 
-inline void enable_cord_btree(bool enable) {
-  cord_btree_enabled.store(enable, std::memory_order_relaxed);
-}
-
 inline void enable_cord_ring_buffer(bool enable) {
   cord_ring_buffer_enabled.store(enable, std::memory_order_relaxed);
 }
@@ -80,6 +88,9 @@ enum Constants {
   kMaxBytesToCopy = 511
 };
 
+// Emits a fatal error "Unexpected node type: xyz" and aborts the program.
+Y_ABSL_ATTRIBUTE_NORETURN void LogFatalNodeType(CordRep* rep);
+
 // Compact class for tracking the reference count and state flags for CordRep
 // instances.  Data is stored in an atomic int32_t for compactness and speed.
 class RefcountAndFlags {
@@ -87,9 +98,6 @@ class RefcountAndFlags {
   constexpr RefcountAndFlags() : count_{kRefIncrement} {}
   struct Immortal {};
   explicit constexpr RefcountAndFlags(Immortal) : count_(kImmortalFlag) {}
-  struct WithCrc {};
-  explicit constexpr RefcountAndFlags(WithCrc)
-      : count_(kCrcFlag | kRefIncrement) {}
 
   // Increments the reference count. Imposes no memory ordering.
   inline void Increment() {
@@ -125,32 +133,14 @@ class RefcountAndFlags {
     return count_.load(std::memory_order_acquire) >> kNumFlags;
   }
 
-  // Returns true if the referenced object carries a CRC value.
-  bool HasCrc() const {
-    return (count_.load(std::memory_order_relaxed) & kCrcFlag) != 0;
-  }
-
-  // Returns true iff the atomic integer is 1 and this node does not store
-  // a CRC.  When both these conditions are met, the current thread owns
-  // the reference and no other thread shares it, so its contents may be
-  // safely mutated.
-  //
-  // If the referenced item is shared, carries a CRC, or is immortal,
-  // it should not be modified in-place, and this function returns false.
-  //
-  // This call performs the memory barrier needed for the owning thread
-  // to act on the object, so that if it returns true, it may safely
-  // assume exclusive access to the object.
-  inline bool IsMutable() {
-    return (count_.load(std::memory_order_acquire)) == kRefIncrement;
-  }
-
-  // Returns whether the atomic integer is 1.  Similar to IsMutable(),
-  // but does not check for a stored CRC.  (An unshared node with a CRC is not
-  // mutable, because changing its data would invalidate the CRC.)
-  //
-  // When this returns true, there are no other references, and data sinks
-  // may safely adopt the children of the CordRep.
+  // Returns whether the atomic integer is 1.
+  // If the reference count is used in the conventional way, a
+  // reference count of 1 implies that the current thread owns the
+  // reference and no other thread shares it.
+  // This call performs the test for a reference count of one, and
+  // performs the memory barrier needed for the owning thread
+  // to act on the object, knowing that it has exclusive access to the
+  // object.  Always returns false when the immortal bit is set.
   inline bool IsOne() {
     return (count_.load(std::memory_order_acquire) & kRefcountMask) ==
            kRefIncrement;
@@ -166,51 +156,43 @@ class RefcountAndFlags {
   // used for the StringConstant constructor to avoid collecting immutable
   // constant cords.
   // kReservedFlag is reserved for future use.
-  enum {
+  enum Flags {
     kNumFlags = 2,
 
     kImmortalFlag = 0x1,
-    kCrcFlag = 0x2,
+    kReservedFlag = 0x2,
     kRefIncrement = (1 << kNumFlags),
 
     // Bitmask to use when checking refcount by equality.  This masks out
     // all flags except kImmortalFlag, which is part of the refcount for
     // purposes of equality.  (A refcount of 0 or 1 does not count as 0 or 1
     // if the immortal bit is set.)
-    kRefcountMask = ~kCrcFlag,
+    kRefcountMask = ~kReservedFlag,
   };
 
   std::atomic<int32_t> count_;
 };
 
-// The overhead of a vtable is too much for Cord, so we roll our own subclasses
-// using only a single byte to differentiate classes from each other - the "tag"
-// byte.  Define the subclasses first so we can provide downcasting helper
-// functions in the base class.
-
-struct CordRepConcat;
-struct CordRepExternal;
-struct CordRepFlat;
-struct CordRepSubstring;
-class CordRepRing;
-class CordRepBtree;
-
 // Various representations that we allow
 enum CordRepKind {
-  CONCAT = 0,
+  UNUSED_0 = 0,
   SUBSTRING = 1,
-  BTREE = 2,
-  RING = 3,
-  EXTERNAL = 4,
+  CRC = 2,
+  BTREE = 3,
+  RING = 4,
+  EXTERNAL = 5,
 
   // We have different tags for different sized flat arrays,
-  // starting with FLAT, and limited to MAX_FLAT_TAG. The 225 value is based on
-  // the current 'size to tag' encoding of 8 / 32 bytes. If a new tag is needed
-  // in the future, then 'FLAT' and 'MAX_FLAT_TAG' should be adjusted as well
-  // as the Tag <---> Size logic so that FLAT stil represents the minimum flat
-  // allocation size. (32 bytes as of now).
-  FLAT = 5,
-  MAX_FLAT_TAG = 225
+  // starting with FLAT, and limited to MAX_FLAT_TAG. The below values map to an
+  // allocated range of 32 bytes to 256 KB. The current granularity is:
+  // - 8 byte granularity for flat sizes in [32 - 512]
+  // - 64 byte granularity for flat sizes in (512 - 8KiB]
+  // - 4KiB byte granularity for flat sizes in (8KiB, 256 KiB]
+  // If a new tag is needed in the future, then 'FLAT' and 'MAX_FLAT_TAG' should
+  // be adjusted as well as the Tag <---> Size mapping logic so that FLAT still
+  // represents the minimum flat allocation size. (32 bytes as of now).
+  FLAT = 6,
+  MAX_FLAT_TAG = 248
 };
 
 // There are various locations where we want to check if some rep is a 'plain'
@@ -225,6 +207,18 @@ static_assert(EXTERNAL == RING + 1, "BTREE and EXTERNAL not consecutive");
 static_assert(FLAT == EXTERNAL + 1, "EXTERNAL and FLAT not consecutive");
 
 struct CordRep {
+  // Result from an `extract edge` operation. Contains the (possibly changed)
+  // tree node as well as the extracted edge, or {tree, nullptr} if no edge
+  // could be extracted.
+  // On success, the returned `tree` value is null if `extracted` was the only
+  // data edge inside the tree, a data edge if there were only two data edges in
+  // the tree, or the (possibly new / smaller) remaining tree with the extracted
+  // data edge removed.
+  struct ExtractResult {
+    CordRep* tree;
+    CordRep* extracted;
+  };
+
   CordRep() = default;
   constexpr CordRep(RefcountAndFlags::Immortal immortal, size_t l)
       : length(l), refcount(immortal), tag(EXTERNAL), storage{} {}
@@ -249,18 +243,18 @@ struct CordRep {
 
   // Returns true if this instance's tag matches the requested type.
   constexpr bool IsRing() const { return tag == RING; }
-  constexpr bool IsConcat() const { return tag == CONCAT; }
   constexpr bool IsSubstring() const { return tag == SUBSTRING; }
+  constexpr bool IsCrc() const { return tag == CRC; }
   constexpr bool IsExternal() const { return tag == EXTERNAL; }
   constexpr bool IsFlat() const { return tag >= FLAT; }
   constexpr bool IsBtree() const { return tag == BTREE; }
 
   inline CordRepRing* ring();
   inline const CordRepRing* ring() const;
-  inline CordRepConcat* concat();
-  inline const CordRepConcat* concat() const;
   inline CordRepSubstring* substring();
   inline const CordRepSubstring* substring() const;
+  inline CordRepCrc* crc();
+  inline const CordRepCrc* crc() const;
   inline CordRepExternal* external();
   inline const CordRepExternal* external() const;
   inline CordRepFlat* flat();
@@ -283,17 +277,23 @@ struct CordRep {
   static inline void Unref(CordRep* rep);
 };
 
-struct CordRepConcat : public CordRep {
-  CordRep* left;
-  CordRep* right;
-
-  uint8_t depth() const { return storage[0]; }
-  void set_depth(uint8_t depth) { storage[0] = depth; }
-};
-
 struct CordRepSubstring : public CordRep {
   size_t start;  // Starting offset of substring in child
   CordRep* child;
+
+  // Creates a substring on `child`, adopting a reference on `child`.
+  // Requires `child` to be either a flat or external node, and `pos` and `n` to
+  // form a non-empty partial sub range of `'child`, i.e.:
+  // `n > 0 && n < length && n + pos <= length`
+  static inline CordRepSubstring* Create(CordRep* child, size_t pos, size_t n);
+
+  // Creates a substring of `rep`. Does not adopt a reference on `rep`.
+  // Requires `IsDataEdge(rep) && n > 0 && pos + n <= rep->length`.
+  // If `n == rep->length` then this method returns `CordRep::Ref(rep)`
+  // If `rep` is a substring of a flat or external node, then this method will
+  // return a new substring of that flat or external node with `pos` adjusted
+  // with the original `start` position.
+  static inline CordRep* Substring(CordRep* rep, size_t pos, size_t n);
 };
 
 // Type for function pointer that will invoke the releaser function and also
@@ -357,6 +357,47 @@ struct CordRepExternalImpl
   }
 };
 
+inline CordRepSubstring* CordRepSubstring::Create(CordRep* child, size_t pos,
+                                                  size_t n) {
+  assert(child != nullptr);
+  assert(n > 0);
+  assert(n < child->length);
+  assert(pos < child->length);
+  assert(n <= child->length - pos);
+
+  // TODO(b/217376272): Harden internal logic.
+  // Move to strategical places inside the Cord logic and make this an assert.
+  if (Y_ABSL_PREDICT_FALSE(!(child->IsExternal() || child->IsFlat()))) {
+    LogFatalNodeType(child);
+  }
+
+  CordRepSubstring* rep = new CordRepSubstring();
+  rep->length = n;
+  rep->tag = SUBSTRING;
+  rep->start = pos;
+  rep->child = child;
+  return rep;
+}
+
+inline CordRep* CordRepSubstring::Substring(CordRep* rep, size_t pos,
+                                            size_t n) {
+  assert(rep != nullptr);
+  assert(n != 0);
+  assert(pos < rep->length);
+  assert(n <= rep->length - pos);
+  if (n == rep->length) return CordRep::Ref(rep);
+  if (rep->IsSubstring()) {
+    pos += rep->substring()->start;
+    rep = rep->substring()->child;
+  }
+  CordRepSubstring* substr = new CordRepSubstring();
+  substr->length = n;
+  substr->tag = SUBSTRING;
+  substr->start = pos;
+  substr->child = CordRep::Ref(rep);
+  return substr;
+}
+
 inline void CordRepExternal::Delete(CordRep* rep) {
   assert(rep != nullptr && rep->IsExternal());
   auto* rep_external = static_cast<CordRepExternal*>(rep);
@@ -370,7 +411,8 @@ struct ConstInitExternalStorage {
 };
 
 template <typename Str>
-CordRepExternal ConstInitExternalStorage<Str>::value(Str::value);
+Y_ABSL_CONST_INIT CordRepExternal
+    ConstInitExternalStorage<Str>::value(Str::value);
 
 enum {
   kMaxInline = 15,
@@ -456,8 +498,8 @@ class InlineData {
   // Requires the current instance to hold a tree value.
   CordzInfo* cordz_info() const {
     assert(is_tree());
-    intptr_t info =
-        static_cast<intptr_t>(y_absl::big_endian::ToHost64(as_tree_.cordz_info));
+    intptr_t info = static_cast<intptr_t>(
+        y_absl::big_endian::ToHost64(static_cast<uint64_t>(as_tree_.cordz_info)));
     assert(info & 1);
     return reinterpret_cast<CordzInfo*>(info - 1);
   }
@@ -467,8 +509,9 @@ class InlineData {
   // Requires the current instance to hold a tree value.
   void set_cordz_info(CordzInfo* cordz_info) {
     assert(is_tree());
-    intptr_t info = reinterpret_cast<intptr_t>(cordz_info) | 1;
-    as_tree_.cordz_info = y_absl::big_endian::FromHost64(info);
+    uintptr_t info = reinterpret_cast<uintptr_t>(cordz_info) | 1;
+    as_tree_.cordz_info =
+        static_cast<cordz_info_t>(y_absl::big_endian::FromHost64(info));
   }
 
   // Resets the current cordz_info to null / empty.
@@ -568,16 +611,6 @@ class InlineData {
 
 static_assert(sizeof(InlineData) == kMaxInline + 1, "");
 
-inline CordRepConcat* CordRep::concat() {
-  assert(IsConcat());
-  return static_cast<CordRepConcat*>(this);
-}
-
-inline const CordRepConcat* CordRep::concat() const {
-  assert(IsConcat());
-  return static_cast<const CordRepConcat*>(this);
-}
-
 inline CordRepSubstring* CordRep::substring() {
   assert(IsSubstring());
   return static_cast<CordRepSubstring*>(this);
@@ -599,7 +632,9 @@ inline const CordRepExternal* CordRep::external() const {
 }
 
 inline CordRep* CordRep::Ref(CordRep* rep) {
-  assert(rep != nullptr);
+  // Y_ABSL_ASSUME is a workaround for
+  // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105585
+  Y_ABSL_ASSUME(rep != nullptr);
   rep->refcount.Increment();
   return rep;
 }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree.cc
index 5dcdab9cc5..e073876f8c 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree.cc
@@ -22,6 +22,7 @@
 #include "y_absl/base/attributes.h"
 #include "y_absl/base/config.h"
 #include "y_absl/base/internal/raw_logging.h"
+#include "y_absl/strings/internal/cord_data_edge.h"
 #include "y_absl/strings/internal/cord_internal.h"
 #include "y_absl/strings/internal/cord_rep_consume.h"
 #include "y_absl/strings/internal/cord_rep_flat.h"
@@ -32,7 +33,9 @@ namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
 namespace cord_internal {
 
-constexpr size_t CordRepBtree::kMaxCapacity;  // NOLINT: needed for c++ < c++17
+#ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+constexpr size_t CordRepBtree::kMaxCapacity;
+#endif
 
 namespace {
 
@@ -69,7 +72,7 @@ void DumpAll(const CordRep* rep, bool include_contents, std::ostream& stream,
       // indentation and prefix / labels keeps us within roughly 80-100 wide.
       constexpr size_t kMaxDataLength = 60;
       stream << ", data = \""
-             << CordRepBtree::EdgeData(r).substr(0, kMaxDataLength)
+             << EdgeData(r).substr(0, kMaxDataLength)
              << (r->length > kMaxDataLength ? "\"..." : "\"");
     }
     stream << '\n';
@@ -119,6 +122,7 @@ CordRepSubstring* CreateSubstring(CordRep* rep, size_t offset, size_t n) {
     rep = CordRep::Ref(substring->child);
     CordRep::Unref(substring);
   }
+  assert(rep->IsExternal() || rep->IsFlat());
   CordRepSubstring* substring = new CordRepSubstring();
   substring->length = n;
   substring->tag = SUBSTRING;
@@ -149,7 +153,7 @@ inline CordRep* MakeSubstring(CordRep* rep, size_t offset) {
 CordRep* ResizeEdge(CordRep* edge, size_t length, bool is_mutable) {
   assert(length > 0);
   assert(length <= edge->length);
-  assert(CordRepBtree::IsDataEdge(edge));
+  assert(IsDataEdge(edge));
   if (length >= edge->length) return edge;
 
   if (is_mutable && (edge->tag >= FLAT || edge->tag == SUBSTRING)) {
@@ -190,24 +194,29 @@ inline void FastUnref(R* r, Fn&& fn) {
   }
 }
 
-// Deletes a leaf node data edge. Requires `rep` to be an EXTERNAL or FLAT
-// node, or a SUBSTRING of an EXTERNAL or FLAT node.
-void DeleteLeafEdge(CordRep* rep) {
-  for (;;) {
+
+void DeleteSubstring(CordRepSubstring* substring) {
+  CordRep* rep = substring->child;
+  if (!rep->refcount.Decrement()) {
     if (rep->tag >= FLAT) {
       CordRepFlat::Delete(rep->flat());
-      return;
-    }
-    if (rep->tag == EXTERNAL) {
+    } else {
+      assert(rep->tag == EXTERNAL);
       CordRepExternal::Delete(rep->external());
-      return;
     }
-    assert(rep->tag == SUBSTRING);
-    CordRepSubstring* substring = rep->substring();
-    rep = substring->child;
-    assert(rep->tag == EXTERNAL || rep->tag >= FLAT);
-    delete substring;
-    if (rep->refcount.Decrement()) return;
+  }
+  delete substring;
+}
+
+// Deletes a leaf node data edge. Requires `IsDataEdge(rep)`.
+void DeleteLeafEdge(CordRep* rep) {
+  assert(IsDataEdge(rep));
+  if (rep->tag >= FLAT) {
+    CordRepFlat::Delete(rep->flat());
+  } else if (rep->tag == EXTERNAL) {
+    CordRepExternal::Delete(rep->external());
+  } else {
+    DeleteSubstring(rep->substring());
   }
 }
 
@@ -216,8 +225,8 @@ void DeleteLeafEdge(CordRep* rep) {
 // propagate node changes up the stack.
 template <EdgeType edge_type>
 struct StackOperations {
-  // Returns true if the node at 'depth' is mutable, i.e. has a refcount
-  // of one, carries no CRC, and all of its parent nodes have a refcount of one.
+  // Returns true if the node at 'depth' is not shared, i.e. has a refcount
+  // of one and all of its parent nodes have a refcount of one.
   inline bool owned(int depth) const { return depth < share_depth; }
 
   // Returns the node at 'depth'.
@@ -228,11 +237,11 @@ struct StackOperations {
   inline CordRepBtree* BuildStack(CordRepBtree* tree, int depth) {
     assert(depth <= tree->height());
     int current_depth = 0;
-    while (current_depth < depth && tree->refcount.IsMutable()) {
+    while (current_depth < depth && tree->refcount.IsOne()) {
       stack[current_depth++] = tree;
       tree = tree->Edge(edge_type)->btree();
     }
-    share_depth = current_depth + (tree->refcount.IsMutable() ? 1 : 0);
+    share_depth = current_depth + (tree->refcount.IsOne() ? 1 : 0);
     while (current_depth < depth) {
       stack[current_depth++] = tree;
       tree = tree->Edge(edge_type)->btree();
@@ -241,17 +250,17 @@ struct StackOperations {
   }
 
   // Builds a stack with the invariant that all nodes are private owned / not
-  // shared and carry no CRC data. This is used in iterative updates where a
-  // previous propagation guaranteed all nodes have this property.
+  // shared. This is used in iterative updates where a previous propagation
+  // guaranteed all nodes are owned / private.
   inline void BuildOwnedStack(CordRepBtree* tree, int height) {
     assert(height <= CordRepBtree::kMaxHeight);
     int depth = 0;
     while (depth < height) {
-      assert(tree->refcount.IsMutable());
+      assert(tree->refcount.IsOne());
       stack[depth++] = tree;
       tree = tree->Edge(edge_type)->btree();
     }
-    assert(tree->refcount.IsMutable());
+    assert(tree->refcount.IsOne());
     share_depth = depth + 1;
   }
 
@@ -336,12 +345,12 @@ struct StackOperations {
     return Unwind</*propagate=*/true>(tree, depth, length, result);
   }
 
-  // `share_depth` contains the depth at which the nodes in the stack cannot
-  // be mutated. I.e., if the top most level is shared (i.e.:
-  // `!refcount.IsMutable()`), then `share_depth` is 0. If the 2nd node
-  // is shared (and implicitly all nodes below that) then `share_depth` is 1,
-  // etc. A `share_depth` greater than the depth of the stack indicates that
-  // none of the nodes in the stack are shared.
+  // `share_depth` contains the depth at which the nodes in the stack become
+  // shared. I.e., if the top most level is shared (i.e.: `!refcount.IsOne()`),
+  // then `share_depth` is 0. If the 2nd node is shared (and implicitly all
+  // nodes below that) then `share_depth` is 1, etc. A `share_depth` greater
+  // than the depth of the stack indicates that none of the nodes in the stack
+  // are shared.
   int share_depth;
 
   NodeStack stack;
@@ -372,19 +381,37 @@ void CordRepBtree::Dump(const CordRep* rep, std::ostream& stream) {
   Dump(rep, y_absl::string_view(), false, stream);
 }
 
-void CordRepBtree::DestroyLeaf(CordRepBtree* tree, size_t begin, size_t end) {
-  for (CordRep* edge : tree->Edges(begin, end)) {
-    FastUnref(edge, DeleteLeafEdge);
+template <size_t size>
+static void DestroyTree(CordRepBtree* tree) {
+  for (CordRep* node : tree->Edges()) {
+    if (node->refcount.Decrement()) continue;
+    for (CordRep* edge : node->btree()->Edges()) {
+      if (edge->refcount.Decrement()) continue;
+      if (size == 1) {
+        DeleteLeafEdge(edge);
+      } else {
+        CordRepBtree::Destroy(edge->btree());
+      }
+    }
+    CordRepBtree::Delete(node->btree());
   }
-  Delete(tree);
+  CordRepBtree::Delete(tree);
 }
 
-void CordRepBtree::DestroyNonLeaf(CordRepBtree* tree, size_t begin,
-                                  size_t end) {
-  for (CordRep* edge : tree->Edges(begin, end)) {
-    FastUnref(edge->btree(), Destroy);
+void CordRepBtree::Destroy(CordRepBtree* tree) {
+  switch (tree->height()) {
+    case 0:
+      for (CordRep* edge : tree->Edges()) {
+        if (!edge->refcount.Decrement()) {
+          DeleteLeafEdge(edge);
+        }
+      }
+      return CordRepBtree::Delete(tree);
+    case 1:
+      return DestroyTree<1>(tree);
+    default:
+      return DestroyTree<2>(tree);
   }
-  Delete(tree);
 }
 
 bool CordRepBtree::IsValid(const CordRepBtree* tree, bool shallow) {
@@ -773,7 +800,7 @@ CopyResult CordRepBtree::CopyPrefix(size_t n, bool allow_folding) {
 
 CordRep* CordRepBtree::ExtractFront(CordRepBtree* tree) {
   CordRep* front = tree->Edge(tree->begin());
-  if (tree->refcount.IsMutable()) {
+  if (tree->refcount.IsOne()) {
     Unref(tree->Edges(tree->begin() + 1, tree->end()));
     CordRepBtree::Delete(tree);
   } else {
@@ -786,7 +813,7 @@ CordRep* CordRepBtree::ExtractFront(CordRepBtree* tree) {
 CordRepBtree* CordRepBtree::ConsumeBeginTo(CordRepBtree* tree, size_t end,
                                            size_t new_length) {
   assert(end <= tree->end());
-  if (tree->refcount.IsMutable()) {
+  if (tree->refcount.IsOne()) {
     Unref(tree->Edges(end, tree->end()));
     tree->set_end(end);
     tree->length = new_length;
@@ -813,13 +840,13 @@ CordRep* CordRepBtree::RemoveSuffix(CordRepBtree* tree, size_t n) {
 
   size_t length = len - n;
   int height = tree->height();
-  bool is_mutable = tree->refcount.IsMutable();
+  bool is_mutable = tree->refcount.IsOne();
 
   // Extract all top nodes which are reduced to size = 1
   Position pos = tree->IndexOfLength(length);
   while (pos.index == tree->begin()) {
     CordRep* edge = ExtractFront(tree);
-    is_mutable &= edge->refcount.IsMutable();
+    is_mutable &= edge->refcount.IsOne();
     if (height-- == 0) return ResizeEdge(edge, length, is_mutable);
     tree = edge->btree();
     pos = tree->IndexOfLength(length);
@@ -835,8 +862,8 @@ CordRep* CordRepBtree::RemoveSuffix(CordRepBtree* tree, size_t n) {
   length = pos.n;
   while (length != edge->length) {
     // ConsumeBeginTo guarantees `tree` is a clean, privately owned copy.
-    assert(tree->refcount.IsMutable());
-    const bool edge_is_mutable = edge->refcount.IsMutable();
+    assert(tree->refcount.IsOne());
+    const bool edge_is_mutable = edge->refcount.IsOne();
 
     if (height-- == 0) {
       tree->edges_[pos.index] = ResizeEdge(edge, length, edge_is_mutable);
@@ -973,7 +1000,7 @@ char CordRepBtree::GetCharacter(size_t offset) const {
 Span<char> CordRepBtree::GetAppendBufferSlow(size_t size) {
   // The inlined version in `GetAppendBuffer()` deals with all heights <= 3.
   assert(height() >= 4);
-  assert(refcount.IsMutable());
+  assert(refcount.IsOne());
 
   // Build a stack of nodes we may potentially need to update if we find a
   // non-shared FLAT with capacity at the leaf level.
@@ -982,13 +1009,13 @@ Span<char> CordRepBtree::GetAppendBufferSlow(size_t size) {
   CordRepBtree* stack[kMaxDepth];
   for (int i = 0; i < depth; ++i) {
     node = node->Edge(kBack)->btree();
-    if (!node->refcount.IsMutable()) return {};
+    if (!node->refcount.IsOne()) return {};
     stack[i] = node;
   }
 
   // Must be a privately owned, mutable flat.
   CordRep* const edge = node->Edge(kBack);
-  if (!edge->refcount.IsMutable() || edge->tag < FLAT) return {};
+  if (!edge->refcount.IsOne() || edge->tag < FLAT) return {};
 
   // Must have capacity.
   const size_t avail = edge->flat()->Capacity() - edge->length;
@@ -1123,6 +1150,79 @@ CordRepBtree* CordRepBtree::Rebuild(CordRepBtree* tree) {
   return nullptr;
 }
 
+CordRepBtree::ExtractResult CordRepBtree::ExtractAppendBuffer(
+    CordRepBtree* tree, size_t extra_capacity) {
+  int depth = 0;
+  NodeStack stack;
+
+  // Set up default 'no success' result which is {tree, nullptr}.
+  ExtractResult result;
+  result.tree = tree;
+  result.extracted = nullptr;
+
+  // Dive down the right side of the tree, making sure no edges are shared.
+  while (tree->height() > 0) {
+    if (!tree->refcount.IsOne()) return result;
+    stack[depth++] = tree;
+    tree = tree->Edge(kBack)->btree();
+  }
+  if (!tree->refcount.IsOne()) return result;
+
+  // Validate we ended on a non shared flat.
+  CordRep* rep = tree->Edge(kBack);
+  if (!(rep->IsFlat() && rep->refcount.IsOne())) return result;
+
+  // Verify it has at least the requested extra capacity.
+  CordRepFlat* flat = rep->flat();
+  const size_t length = flat->length;
+  const size_t avail = flat->Capacity() - flat->length;
+  if (extra_capacity > avail) return result;
+
+  // Set the extracted flat in the result.
+  result.extracted = flat;
+
+  // Cascading delete all nodes that become empty.
+  while (tree->size() == 1) {
+    CordRepBtree::Delete(tree);
+    if (--depth < 0) {
+      // We consumed the entire tree: return nullptr for new tree.
+      result.tree = nullptr;
+      return result;
+    }
+    rep = tree;
+    tree = stack[depth];
+  }
+
+  // Remove the edge or cascaded up parent node.
+  tree->set_end(tree->end() - 1);
+  tree->length -= length;
+
+  // Adjust lengths up the tree.
+  while (depth > 0) {
+    tree = stack[--depth];
+    tree->length -= length;
+  }
+
+  // Remove unnecessary top nodes with size = 1. This may iterate all the way
+  // down to the leaf node in which case we simply return the remaining last
+  // edge in that node and the extracted flat.
+  while (tree->size() == 1) {
+    int height = tree->height();
+    rep = tree->Edge(kBack);
+    Delete(tree);
+    if (height == 0) {
+      // We consumed the leaf: return the sole data edge as the new tree.
+      result.tree = rep;
+      return result;
+    }
+    tree = rep->btree();
+  }
+
+  // Done: return the (new) top level node and extracted flat.
+  result.tree = tree;
+  return result;
+}
+
 }  // namespace cord_internal
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree.h
index 8c78892520..c6d01fdda3 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree.h
@@ -22,6 +22,7 @@
 #include "y_absl/base/config.h"
 #include "y_absl/base/internal/raw_logging.h"
 #include "y_absl/base/optimization.h"
+#include "y_absl/strings/internal/cord_data_edge.h"
 #include "y_absl/strings/internal/cord_internal.h"
 #include "y_absl/strings/internal/cord_rep_flat.h"
 #include "y_absl/strings/string_view.h"
@@ -163,6 +164,9 @@ class CordRepBtree : public CordRep {
   // typically after a ref_count.Decrement() on the last reference count.
   static void Destroy(CordRepBtree* tree);
 
+  // Destruction
+  static void Delete(CordRepBtree* tree) { delete tree; }
+
   // Use CordRep::Unref() as we overload for y_absl::Span<CordRep* const>.
   using CordRep::Unref;
 
@@ -240,11 +244,41 @@ class CordRepBtree : public CordRep {
   // length of the flat node and involved tree nodes have been increased by
   // `span.length()`. The caller is responsible for immediately assigning values
   // to all uninitialized data reference by the returned span.
-  // Requires `this->refcount.IsMutable()`: this function forces the
-  // caller to do this fast path check on the top level node, as this is the
-  // most commonly shared node of a cord tree.
+  // Requires `this->refcount.IsOne()`: this function forces the caller to do
+  // this fast path check on the top level node, as this is the most commonly
+  // shared node of a cord tree.
   Span<char> GetAppendBuffer(size_t size);
 
+  // Extracts the right-most data edge from this tree iff:
+  // - the tree and all internal edges to the right-most node are not shared.
+  // - the right-most node is a FLAT node and not shared.
+  // - the right-most node has at least the desired extra capacity.
+  //
+  // Returns {tree, nullptr} if any of the above conditions are not met.
+  // This method effectively removes data from the tree. The intent of this
+  // method is to allow applications appending small string data to use
+  // pre-existing capacity, and add the modified rep back to the tree.
+  //
+  // Simplified such code would look similar to this:
+  //   void MyTreeBuilder::Append(string_view data) {
+  //     ExtractResult result = CordRepBtree::ExtractAppendBuffer(tree_, 1);
+  //     if (CordRep* rep = result.extracted) {
+  //       size_t available = rep->Capacity() - rep->length;
+  //       size_t n = std::min(data.size(), n);
+  //       memcpy(rep->Data(), data.data(), n);
+  //       rep->length += n;
+  //       data.remove_prefix(n);
+  //       if (!result.tree->IsBtree()) {
+  //         tree_ = CordRepBtree::Create(result.tree);
+  //       }
+  //       tree_ = CordRepBtree::Append(tree_, rep);
+  //     }
+  //     ...
+  //     // Remaining edge in `result.tree`.
+  //   }
+  static ExtractResult ExtractAppendBuffer(CordRepBtree* tree,
+                                           size_t extra_capacity = 1);
+
   // Returns the `height` of the tree. The height of a tree is limited to
   // kMaxHeight. `height` is implemented as an `int` as in some places we
   // use negative (-1) values for 'data edges'.
@@ -277,13 +311,6 @@ class CordRepBtree : public CordRep {
   // Requires this instance to be a leaf node, and `index` to be valid index.
   inline y_absl::string_view Data(size_t index) const;
 
-  static const char* EdgeDataPtr(const CordRep* r);
-  static y_absl::string_view EdgeData(const CordRep* r);
-
-  // Returns true if the provided rep is a FLAT, EXTERNAL or a SUBSTRING node
-  // holding a FLAT or EXTERNAL child rep.
-  static bool IsDataEdge(const CordRep* rep);
-
   // Diagnostics: returns true if `tree` is valid and internally consistent.
   // If `shallow` is false, then the provided top level node and all child nodes
   // below it are recursively checked. If `shallow` is true, only the provided
@@ -410,12 +437,6 @@ class CordRepBtree : public CordRep {
   // Requires `offset` < length.
   Position IndexBeyond(size_t offset) const;
 
-  // Destruction
-  static void DestroyLeaf(CordRepBtree* tree, size_t begin, size_t end);
-  static void DestroyNonLeaf(CordRepBtree* tree, size_t begin, size_t end);
-  static void DestroyTree(CordRepBtree* tree, size_t begin, size_t end);
-  static void Delete(CordRepBtree* tree) { delete tree; }
-
   // Creates a new leaf node containing as much data as possible from `data`.
   // The data is added either forwards or reversed depending on `edge_type`.
   // Callers must check the length of the returned node to determine if all data
@@ -604,34 +625,11 @@ inline y_absl::Span<CordRep* const> CordRepBtree::Edges(size_t begin,
   return {edges_ + begin, static_cast<size_t>(end - begin)};
 }
 
-inline const char* CordRepBtree::EdgeDataPtr(const CordRep* r) {
-  assert(IsDataEdge(r));
-  size_t offset = 0;
-  if (r->tag == SUBSTRING) {
-    offset = r->substring()->start;
-    r = r->substring()->child;
-  }
-  return (r->tag >= FLAT ? r->flat()->Data() : r->external()->base) + offset;
-}
-
-inline y_absl::string_view CordRepBtree::EdgeData(const CordRep* r) {
-  return y_absl::string_view(EdgeDataPtr(r), r->length);
-}
-
 inline y_absl::string_view CordRepBtree::Data(size_t index) const {
   assert(height() == 0);
   return EdgeData(Edge(index));
 }
 
-inline bool CordRepBtree::IsDataEdge(const CordRep* rep) {
-  // The fast path is that `rep` is an EXTERNAL or FLAT node, making the below
-  // if a single, well predicted branch. We then repeat the FLAT or EXTERNAL
-  // check in the slow path the SUBSTRING check to optimize for the hot path.
-  if (rep->tag == EXTERNAL || rep->tag >= FLAT) return true;
-  if (rep->tag == SUBSTRING) rep = rep->substring()->child;
-  return rep->tag == EXTERNAL || rep->tag >= FLAT;
-}
-
 inline CordRepBtree* CordRepBtree::New(int height) {
   CordRepBtree* tree = new CordRepBtree;
   tree->length = 0;
@@ -659,19 +657,6 @@ inline CordRepBtree* CordRepBtree::New(CordRepBtree* front,
   return tree;
 }
 
-inline void CordRepBtree::DestroyTree(CordRepBtree* tree, size_t begin,
-                                      size_t end) {
-  if (tree->height() == 0) {
-    DestroyLeaf(tree, begin, end);
-  } else {
-    DestroyNonLeaf(tree, begin, end);
-  }
-}
-
-inline void CordRepBtree::Destroy(CordRepBtree* tree) {
-  DestroyTree(tree, tree->begin(), tree->end());
-}
-
 inline void CordRepBtree::Unref(y_absl::Span<CordRep* const> edges) {
   for (CordRep* edge : edges) {
     if (Y_ABSL_PREDICT_FALSE(!edge->refcount.Decrement())) {
@@ -731,7 +716,7 @@ inline void CordRepBtree::AlignBegin() {
     // size, and then do overlapping load/store of up to 4 pointers (inlined as
     // XMM, YMM or ZMM load/store) and up to 2 pointers (XMM / YMM), which is a)
     // compact and b) not clobbering any registers.
-    Y_ABSL_INTERNAL_ASSUME(new_end <= kMaxCapacity);
+    Y_ABSL_ASSUME(new_end <= kMaxCapacity);
 #ifdef __clang__
 #pragma unroll 1
 #endif
@@ -749,7 +734,7 @@ inline void CordRepBtree::AlignEnd() {
     const size_t new_end = end() + delta;
     set_begin(new_begin);
     set_end(new_end);
-    Y_ABSL_INTERNAL_ASSUME(new_end <= kMaxCapacity);
+    Y_ABSL_ASSUME(new_end <= kMaxCapacity);
 #ifdef __clang__
 #pragma unroll 1
 #endif
@@ -849,7 +834,7 @@ inline CordRepBtree* CordRepBtree::Create(CordRep* rep) {
 }
 
 inline Span<char> CordRepBtree::GetAppendBuffer(size_t size) {
-  assert(refcount.IsMutable());
+  assert(refcount.IsOne());
   CordRepBtree* tree = this;
   const int height = this->height();
   CordRepBtree* n1 = tree;
@@ -858,21 +843,21 @@ inline Span<char> CordRepBtree::GetAppendBuffer(size_t size) {
   switch (height) {
     case 3:
       tree = tree->Edge(kBack)->btree();
-      if (!tree->refcount.IsMutable()) return {};
+      if (!tree->refcount.IsOne()) return {};
       n2 = tree;
       Y_ABSL_FALLTHROUGH_INTENDED;
     case 2:
       tree = tree->Edge(kBack)->btree();
-      if (!tree->refcount.IsMutable()) return {};
+      if (!tree->refcount.IsOne()) return {};
       n1 = tree;
       Y_ABSL_FALLTHROUGH_INTENDED;
     case 1:
       tree = tree->Edge(kBack)->btree();
-      if (!tree->refcount.IsMutable()) return {};
+      if (!tree->refcount.IsOne()) return {};
       Y_ABSL_FALLTHROUGH_INTENDED;
     case 0:
       CordRep* edge = tree->Edge(kBack);
-      if (!edge->refcount.IsMutable()) return {};
+      if (!edge->refcount.IsOne()) return {};
       if (edge->tag < FLAT) return {};
       size_t avail = edge->flat()->Capacity() - edge->length;
       if (avail == 0) return {};
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_navigator.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_navigator.cc
index a94d4e0ae6..861a3c034b 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_navigator.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_navigator.cc
@@ -16,6 +16,7 @@
 
 #include <cassert>
 
+#include "y_absl/strings/internal/cord_data_edge.h"
 #include "y_absl/strings/internal/cord_internal.h"
 #include "y_absl/strings/internal/cord_rep_btree.h"
 
@@ -39,7 +40,7 @@ inline CordRep* Substring(CordRep* rep, size_t offset, size_t n) {
   assert(n <= rep->length);
   assert(offset < rep->length);
   assert(offset <= rep->length - n);
-  assert(CordRepBtree::IsDataEdge(rep));
+  assert(IsDataEdge(rep));
 
   if (n == 0) return nullptr;
   if (n == rep->length) return CordRep::Ref(rep);
@@ -49,6 +50,7 @@ inline CordRep* Substring(CordRep* rep, size_t offset, size_t n) {
     rep = rep->substring()->child;
   }
 
+  assert(rep->IsExternal() || rep->IsFlat());
   CordRepSubstring* substring = new CordRepSubstring();
   substring->length = n;
   substring->tag = SUBSTRING;
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_navigator.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_navigator.h
index f4c09864e0..1508126e97 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_navigator.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_navigator.h
@@ -143,8 +143,8 @@ class CordRepBtreeNavigator {
   // `index_` and `node_` contain the navigation state as the 'path' to the
   // current data edge which is at `node_[0]->Edge(index_[0])`. The contents
   // of these are undefined until the instance is initialized (`height_ >= 0`).
-  uint8_t index_[CordRepBtree::kMaxHeight];
-  CordRepBtree* node_[CordRepBtree::kMaxHeight];
+  uint8_t index_[CordRepBtree::kMaxDepth];
+  CordRepBtree* node_[CordRepBtree::kMaxDepth];
 };
 
 // Returns true if this instance is not empty.
@@ -173,6 +173,7 @@ template <CordRepBtree::EdgeType edge_type>
 inline CordRep* CordRepBtreeNavigator::Init(CordRepBtree* tree) {
   assert(tree != nullptr);
   assert(tree->size() > 0);
+  assert(tree->height() <= CordRepBtree::kMaxHeight);
   int height = height_ = tree->height();
   size_t index = tree->index(edge_type);
   node_[height] = tree;
@@ -206,6 +207,7 @@ inline CordRepBtreeNavigator::Position CordRepBtreeNavigator::Seek(
 inline CordRepBtreeNavigator::Position CordRepBtreeNavigator::InitOffset(
     CordRepBtree* tree, size_t offset) {
   assert(tree != nullptr);
+  assert(tree->height() <= CordRepBtree::kMaxHeight);
   if (Y_ABSL_PREDICT_FALSE(offset >= tree->length)) return {nullptr, 0};
   height_ = tree->height();
   node_[height_] = tree;
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_reader.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_reader.cc
index 53010139e2..ee2ef490ea 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_reader.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_reader.cc
@@ -17,6 +17,7 @@
 #include <cassert>
 
 #include "y_absl/base/config.h"
+#include "y_absl/strings/internal/cord_data_edge.h"
 #include "y_absl/strings/internal/cord_internal.h"
 #include "y_absl/strings/internal/cord_rep_btree.h"
 #include "y_absl/strings/internal/cord_rep_btree_navigator.h"
@@ -44,7 +45,7 @@ y_absl::string_view CordRepBtreeReader::Read(size_t n, size_t chunk_size,
   // can directly return the substring into the current data edge as the next
   // chunk. We can easily establish from the above code that `navigator_.Next()`
   // has not been called as that requires `chunk_size` to be zero.
-  if (n < chunk_size) return CordRepBtree::EdgeData(edge).substr(result.n);
+  if (n < chunk_size) return EdgeData(edge).substr(result.n);
 
   // The amount of data taken from the last edge is `chunk_size` and `result.n`
   // contains the offset into the current edge trailing the read data (which can
@@ -60,7 +61,7 @@ y_absl::string_view CordRepBtreeReader::Read(size_t n, size_t chunk_size,
   // We did not read all data, return remaining data from current edge.
   edge = navigator_.Current();
   remaining_ -= consumed_by_read + edge->length;
-  return CordRepBtree::EdgeData(edge).substr(result.n);
+  return EdgeData(edge).substr(result.n);
 }
 
 }  // namespace cord_internal
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_reader.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_reader.h
index d5473df29d..78d18ee7eb 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_reader.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_btree_reader.h
@@ -18,6 +18,7 @@
 #include <cassert>
 
 #include "y_absl/base/config.h"
+#include "y_absl/strings/internal/cord_data_edge.h"
 #include "y_absl/strings/internal/cord_internal.h"
 #include "y_absl/strings/internal/cord_rep_btree.h"
 #include "y_absl/strings/internal/cord_rep_btree_navigator.h"
@@ -167,7 +168,7 @@ inline y_absl::string_view CordRepBtreeReader::Init(CordRepBtree* tree) {
   assert(tree != nullptr);
   const CordRep* edge = navigator_.InitFirst(tree);
   remaining_ = tree->length - edge->length;
-  return CordRepBtree::EdgeData(edge);
+  return EdgeData(edge);
 }
 
 inline y_absl::string_view CordRepBtreeReader::Next() {
@@ -175,7 +176,7 @@ inline y_absl::string_view CordRepBtreeReader::Next() {
   const CordRep* edge = navigator_.Next();
   assert(edge != nullptr);
   remaining_ -= edge->length;
-  return CordRepBtree::EdgeData(edge);
+  return EdgeData(edge);
 }
 
 inline y_absl::string_view CordRepBtreeReader::Skip(size_t skip) {
@@ -190,7 +191,7 @@ inline y_absl::string_view CordRepBtreeReader::Skip(size_t skip) {
   // The combined length of all edges skipped before `pos.edge` is `skip -
   // pos.offset`, all of which are 'consumed', as well as the current edge.
   remaining_ -= skip - pos.offset + pos.edge->length;
-  return CordRepBtree::EdgeData(pos.edge).substr(pos.offset);
+  return EdgeData(pos.edge).substr(pos.offset);
 }
 
 inline y_absl::string_view CordRepBtreeReader::Seek(size_t offset) {
@@ -199,7 +200,7 @@ inline y_absl::string_view CordRepBtreeReader::Seek(size_t offset) {
     remaining_ = 0;
     return {};
   }
-  y_absl::string_view chunk = CordRepBtree::EdgeData(pos.edge).substr(pos.offset);
+  y_absl::string_view chunk = EdgeData(pos.edge).substr(pos.offset);
   remaining_ = length() - offset - chunk.length();
   return chunk;
 }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_consume.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_consume.cc
index 02a142d70a..a72823ece5 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_consume.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_consume.cc
@@ -40,88 +40,21 @@ CordRep* ClipSubstring(CordRepSubstring* substring) {
   return child;
 }
 
-// Unrefs the provided `concat`, and returns `{concat->left, concat->right}`
-// Adds or assumes a reference on `concat->left` and `concat->right`.
-// Returns an array of 2 elements containing the left and right nodes.
-std::array<CordRep*, 2> ClipConcat(CordRepConcat* concat) {
-  std::array<CordRep*, 2> result{concat->left, concat->right};
-  if (concat->refcount.IsOne()) {
-    delete concat;
-  } else {
-    CordRep::Ref(result[0]);
-    CordRep::Ref(result[1]);
-    CordRep::Unref(concat);
-  }
-  return result;
-}
+}  // namespace
 
-void Consume(bool forward, CordRep* rep, ConsumeFn consume_fn) {
+void Consume(CordRep* rep, ConsumeFn consume_fn) {
   size_t offset = 0;
   size_t length = rep->length;
-  struct Entry {
-    CordRep* rep;
-    size_t offset;
-    size_t length;
-  };
-  y_absl::InlinedVector<Entry, 40> stack;
-
-  for (;;) {
-    if (rep->tag == CONCAT) {
-      std::array<CordRep*, 2> res = ClipConcat(rep->concat());
-      CordRep* left = res[0];
-      CordRep* right = res[1];
-
-      if (left->length <= offset) {
-        // Don't need left node
-        offset -= left->length;
-        CordRep::Unref(left);
-        rep = right;
-        continue;
-      }
 
-      size_t length_left = left->length - offset;
-      if (length_left >= length) {
-        // Don't need right node
-        CordRep::Unref(right);
-        rep = left;
-        continue;
-      }
-
-      // Need both nodes
-      size_t length_right = length - length_left;
-      if (forward) {
-        stack.push_back({right, 0, length_right});
-        rep = left;
-        length = length_left;
-      } else {
-        stack.push_back({left, offset, length_left});
-        rep = right;
-        offset = 0;
-        length = length_right;
-      }
-    } else if (rep->tag == SUBSTRING) {
-      offset += rep->substring()->start;
-      rep = ClipSubstring(rep->substring());
-    } else {
-      consume_fn(rep, offset, length);
-      if (stack.empty()) return;
-
-      rep = stack.back().rep;
-      offset = stack.back().offset;
-      length = stack.back().length;
-      stack.pop_back();
-    }
+  if (rep->tag == SUBSTRING) {
+    offset += rep->substring()->start;
+    rep = ClipSubstring(rep->substring());
   }
-}
-
-}  // namespace
-
-void Consume(CordRep* rep, ConsumeFn consume_fn) {
-  return Consume(true, rep, std::move(consume_fn));
+  consume_fn(rep, offset, length);
 }
 
 void ReverseConsume(CordRep* rep, ConsumeFn consume_fn) {
-  return Consume(false, rep, std::move(consume_fn));
+  return Consume(rep, std::move(consume_fn));
 }
 
 }  // namespace cord_internal
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_crc.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_crc.cc
new file mode 100644
index 0000000000..a2f6382f72
--- /dev/null
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_crc.cc
@@ -0,0 +1,54 @@
+// Copyright 2021 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "y_absl/strings/internal/cord_rep_crc.h"
+
+#include <cassert>
+#include <cstdint>
+
+#include "y_absl/base/config.h"
+#include "y_absl/strings/internal/cord_internal.h"
+
+namespace y_absl {
+Y_ABSL_NAMESPACE_BEGIN
+namespace cord_internal {
+
+CordRepCrc* CordRepCrc::New(CordRep* child, uint32_t crc) {
+  assert(child != nullptr);
+  if (child->IsCrc()) {
+    if (child->refcount.IsOne()) {
+      child->crc()->crc = crc;
+      return child->crc();
+    }
+    CordRep* old = child;
+    child = old->crc()->child;
+    CordRep::Ref(child);
+    CordRep::Unref(old);
+  }
+  auto* new_cordrep = new CordRepCrc;
+  new_cordrep->length = child->length;
+  new_cordrep->tag = cord_internal::CRC;
+  new_cordrep->child = child;
+  new_cordrep->crc = crc;
+  return new_cordrep;
+}
+
+void CordRepCrc::Destroy(CordRepCrc* node) {
+  CordRep::Unref(node->child);
+  delete node;
+}
+
+}  // namespace cord_internal
+Y_ABSL_NAMESPACE_END
+}  // namespace y_absl
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_crc.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_crc.h
new file mode 100644
index 0000000000..15d22fa248
--- /dev/null
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_crc.h
@@ -0,0 +1,102 @@
+// Copyright 2021 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef Y_ABSL_STRINGS_INTERNAL_CORD_REP_CRC_H_
+#define Y_ABSL_STRINGS_INTERNAL_CORD_REP_CRC_H_
+
+#include <cassert>
+#include <cstdint>
+
+#include "y_absl/base/config.h"
+#include "y_absl/base/optimization.h"
+#include "y_absl/strings/internal/cord_internal.h"
+
+namespace y_absl {
+Y_ABSL_NAMESPACE_BEGIN
+namespace cord_internal {
+
+// CordRepCrc is a CordRep node intended only to appear at the top level of a
+// cord tree.  It associates an "expected CRC" with the contained data, to allow
+// for easy passage of checksum data in Cord data flows.
+//
+// From Cord's perspective, the crc value has no semantics; any validation of
+// the contained checksum is the user's responsibility.
+struct CordRepCrc : public CordRep {
+  CordRep* child;
+  uint32_t crc;
+
+  // Consumes `child` and returns a CordRepCrc prefixed tree containing `child`.
+  // If the specified `child` is itself a CordRepCrc node, then this method
+  // either replaces the existing node, or directly updates the crc value in it
+  // depending on the node being shared or not, i.e.: refcount.IsOne().
+  // `child` must not be null. Never returns null.
+  static CordRepCrc* New(CordRep* child, uint32_t crc);
+
+  // Destroys (deletes) the provided node. `node` must not be null.
+  static void Destroy(CordRepCrc* node);
+};
+
+// Consumes `rep` and returns a CordRep* with any outer CordRepCrc wrapper
+// removed.  This is usually a no-op (returning `rep`), but this will remove and
+// unref an outer CordRepCrc node.
+inline CordRep* RemoveCrcNode(CordRep* rep) {
+  assert(rep != nullptr);
+  if (Y_ABSL_PREDICT_FALSE(rep->IsCrc())) {
+    CordRep* child = rep->crc()->child;
+    if (rep->refcount.IsOne()) {
+      delete rep->crc();
+    } else {
+      CordRep::Ref(child);
+      CordRep::Unref(rep);
+    }
+    return child;
+  }
+  return rep;
+}
+
+// Returns `rep` if it is not a CordRepCrc node, or its child if it is.
+// Does not consume or create a reference on `rep` or the returned value.
+inline CordRep* SkipCrcNode(CordRep* rep) {
+  assert(rep != nullptr);
+  if (Y_ABSL_PREDICT_FALSE(rep->IsCrc())) {
+    return rep->crc()->child;
+  } else {
+    return rep;
+  }
+}
+
+inline const CordRep* SkipCrcNode(const CordRep* rep) {
+  assert(rep != nullptr);
+  if (Y_ABSL_PREDICT_FALSE(rep->IsCrc())) {
+    return rep->crc()->child;
+  } else {
+    return rep;
+  }
+}
+
+inline CordRepCrc* CordRep::crc() {
+  assert(IsCrc());
+  return static_cast<CordRepCrc*>(this);
+}
+
+inline const CordRepCrc* CordRep::crc() const {
+  assert(IsCrc());
+  return static_cast<const CordRepCrc*>(this);
+}
+
+}  // namespace cord_internal
+Y_ABSL_NAMESPACE_END
+}  // namespace y_absl
+
+#endif  // Y_ABSL_STRINGS_INTERNAL_CORD_REP_CRC_H_
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_flat.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_flat.h
index bcd5bf428e..b5ac831903 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_flat.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_flat.h
@@ -20,6 +20,8 @@
 #include <cstdint>
 #include <memory>
 
+#include "y_absl/base/config.h"
+#include "y_absl/base/macros.h"
 #include "y_absl/strings/internal/cord_internal.h"
 
 namespace y_absl {
@@ -42,23 +44,45 @@ static constexpr size_t kMinFlatSize = 32;
 static constexpr size_t kMaxFlatSize = 4096;
 static constexpr size_t kMaxFlatLength = kMaxFlatSize - kFlatOverhead;
 static constexpr size_t kMinFlatLength = kMinFlatSize - kFlatOverhead;
+static constexpr size_t kMaxLargeFlatSize = 256 * 1024;
+static constexpr size_t kMaxLargeFlatLength = kMaxLargeFlatSize - kFlatOverhead;
 
+// kTagBase should make the Size <--> Tag computation resilient
+// against changes to the value of FLAT when we add a new tag..
+static constexpr uint8_t kTagBase = FLAT - 4;
+
+// Converts the provided rounded size to the corresponding tag
 constexpr uint8_t AllocatedSizeToTagUnchecked(size_t size) {
-  return static_cast<uint8_t>((size <= 1024) ? size / 8 + 1
-                                             : 129 + size / 32 - 1024 / 32);
+  return static_cast<uint8_t>(size <= 512 ? kTagBase + size / 8
+                              : size <= 8192
+                                  ? kTagBase + 512 / 8 + size / 64 - 512 / 64
+                                  : kTagBase + 512 / 8 + ((8192 - 512) / 64) +
+                                        size / 4096 - 8192 / 4096);
+}
+
+// Converts the provided tag to the corresponding allocated size
+constexpr size_t TagToAllocatedSize(uint8_t tag) {
+  return (tag <= kTagBase + 512 / 8) ? tag * 8 - kTagBase * 8
+         : (tag <= kTagBase + (512 / 8) + ((8192 - 512) / 64))
+             ? 512 + tag * 64 - kTagBase * 64 - 512 / 8 * 64
+             : 8192 + tag * 4096 - kTagBase * 4096 -
+                   ((512 / 8) + ((8192 - 512) / 64)) * 4096;
 }
 
-static_assert(kMinFlatSize / 8 + 1 >= FLAT, "");
-static_assert(AllocatedSizeToTagUnchecked(kMaxFlatSize) <= MAX_FLAT_TAG, "");
+static_assert(AllocatedSizeToTagUnchecked(kMinFlatSize) == FLAT, "");
+static_assert(AllocatedSizeToTagUnchecked(kMaxLargeFlatSize) == MAX_FLAT_TAG,
+              "");
 
-// Helper functions for rounded div, and rounding to exact sizes.
-constexpr size_t DivUp(size_t n, size_t m) { return (n + m - 1) / m; }
-constexpr size_t RoundUp(size_t n, size_t m) { return DivUp(n, m) * m; }
+// RoundUp logically performs `((n + m - 1) / m) * m` to round up to the nearest
+// multiple of `m`, optimized for the invariant that `m` is a power of 2.
+constexpr size_t RoundUp(size_t n, size_t m) {
+  return (n + m - 1) & (0 - m);
+}
 
 // Returns the size to the nearest equal or larger value that can be
 // expressed exactly as a tag value.
 inline size_t RoundUpForTag(size_t size) {
-  return RoundUp(size, (size <= 1024) ? 8 : 32);
+  return RoundUp(size, (size <= 512) ? 8 : (size <= 8192 ? 64 : 4096));
 }
 
 // Converts the allocated size to a tag, rounding down if the size
@@ -71,26 +95,26 @@ inline uint8_t AllocatedSizeToTag(size_t size) {
   return tag;
 }
 
-// Converts the provided tag to the corresponding allocated size
-constexpr size_t TagToAllocatedSize(uint8_t tag) {
-  return (tag <= 129) ? ((tag - 1) * 8) : (1024 + (tag - 129) * 32);
-}
-
 // Converts the provided tag to the corresponding available data length
 constexpr size_t TagToLength(uint8_t tag) {
   return TagToAllocatedSize(tag) - kFlatOverhead;
 }
 
 // Enforce that kMaxFlatSize maps to a well-known exact tag value.
-static_assert(TagToAllocatedSize(225) == kMaxFlatSize, "Bad tag logic");
+static_assert(TagToAllocatedSize(MAX_FLAT_TAG) == kMaxLargeFlatSize,
+              "Bad tag logic");
 
 struct CordRepFlat : public CordRep {
+  // Tag for explicit 'large flat' allocation
+  struct Large {};
+
   // Creates a new flat node.
-  static CordRepFlat* New(size_t len) {
+  template <size_t max_flat_size, typename... Args>
+  static CordRepFlat* NewImpl(size_t len, Args... args Y_ABSL_ATTRIBUTE_UNUSED) {
     if (len <= kMinFlatLength) {
       len = kMinFlatLength;
-    } else if (len > kMaxFlatLength) {
-      len = kMaxFlatLength;
+    } else if (len > max_flat_size - kFlatOverhead) {
+      len = max_flat_size - kFlatOverhead;
     }
 
     // Round size up so it matches a size we can exactly express in a tag.
@@ -101,6 +125,12 @@ struct CordRepFlat : public CordRep {
     return rep;
   }
 
+  static CordRepFlat* New(size_t len) { return NewImpl<kMaxFlatSize>(len); }
+
+  static CordRepFlat* New(Large, size_t len) {
+    return NewImpl<kMaxLargeFlatSize>(len);
+  }
+
   // Deletes a CordRepFlat instance created previously through a call to New().
   // Flat CordReps are allocated and constructed with raw ::operator new and
   // placement new, and must be destructed and deallocated accordingly.
@@ -117,6 +147,17 @@ struct CordRepFlat : public CordRep {
 #endif
   }
 
+  // Create a CordRepFlat containing `data`, with an optional additional
+  // extra capacity of up to `extra` bytes. Requires that `data.size()`
+  // is less than kMaxFlatLength.
+  static CordRepFlat* Create(y_absl::string_view data, size_t extra = 0) {
+    assert(data.size() <= kMaxFlatLength);
+    CordRepFlat* flat = New(data.size() + (std::min)(extra, kMaxFlatLength));
+    memcpy(flat->Data(), data.data(), data.size());
+    flat->length = data.size();
+    return flat;
+  }
+
   // Returns a pointer to the data inside this flat rep.
   char* Data() { return reinterpret_cast<char*>(storage); }
   const char* Data() const { return reinterpret_cast<const char*>(storage); }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_ring.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_ring.cc
index d961db7192..f05aa5ffa7 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_ring.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cord_rep_ring.cc
@@ -129,7 +129,9 @@ class CordRepRing::Filler {
   index_type pos_;
 };
 
-constexpr size_t CordRepRing::kMaxCapacity; // NOLINT: needed for c++11
+#ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+constexpr size_t CordRepRing::kMaxCapacity;
+#endif
 
 bool CordRepRing::IsValid(std::ostream& output) const {
   if (capacity_ == 0) {
@@ -277,7 +279,7 @@ CordRepRing* CordRepRing::Mutable(CordRepRing* rep, size_t extra) {
   // Get current number of entries, and check for max capacity.
   size_t entries = rep->entries();
 
-  if (!rep->refcount.IsMutable()) {
+  if (!rep->refcount.IsOne()) {
     return Copy(rep, rep->head(), rep->tail(), extra);
   } else if (entries + extra > rep->capacity()) {
     const size_t min_grow = rep->capacity() + rep->capacity() / 2;
@@ -292,10 +294,10 @@ CordRepRing* CordRepRing::Mutable(CordRepRing* rep, size_t extra) {
 }
 
 Span<char> CordRepRing::GetAppendBuffer(size_t size) {
-  assert(refcount.IsMutable());
+  assert(refcount.IsOne());
   index_type back = retreat(tail_);
   CordRep* child = entry_child(back);
-  if (child->tag >= FLAT && child->refcount.IsMutable()) {
+  if (child->tag >= FLAT && child->refcount.IsOne()) {
     size_t capacity = child->flat()->Capacity();
     pos_type end_pos = entry_end_pos(back);
     size_t data_offset = entry_data_offset(back);
@@ -312,10 +314,10 @@ Span<char> CordRepRing::GetAppendBuffer(size_t size) {
 }
 
 Span<char> CordRepRing::GetPrependBuffer(size_t size) {
-  assert(refcount.IsMutable());
+  assert(refcount.IsOne());
   CordRep* child = entry_child(head_);
   size_t data_offset = entry_data_offset(head_);
-  if (data_offset && child->refcount.IsMutable() && child->tag >= FLAT) {
+  if (data_offset && child->refcount.IsOne() && child->tag >= FLAT) {
     size_t n = (std::min)(data_offset, size);
     this->length += n;
     begin_pos_ -= n;
@@ -504,7 +506,7 @@ CordRepRing* CordRepRing::Prepend(CordRepRing* rep, CordRep* child) {
 
 CordRepRing* CordRepRing::Append(CordRepRing* rep, y_absl::string_view data,
                                  size_t extra) {
-  if (rep->refcount.IsMutable()) {
+  if (rep->refcount.IsOne()) {
     Span<char> avail = rep->GetAppendBuffer(data.length());
     if (!avail.empty()) {
       memcpy(avail.data(), data.data(), avail.length());
@@ -538,7 +540,7 @@ CordRepRing* CordRepRing::Append(CordRepRing* rep, y_absl::string_view data,
 
 CordRepRing* CordRepRing::Prepend(CordRepRing* rep, y_absl::string_view data,
                                   size_t extra) {
-  if (rep->refcount.IsMutable()) {
+  if (rep->refcount.IsOne()) {
     Span<char> avail = rep->GetPrependBuffer(data.length());
     if (!avail.empty()) {
       const char* tail = data.data() + data.length() - avail.length();
@@ -678,7 +680,7 @@ CordRepRing* CordRepRing::SubRing(CordRepRing* rep, size_t offset,
   Position tail = rep->FindTail(head.index, offset + len);
   const size_t new_entries = rep->entries(head.index, tail.index);
 
-  if (rep->refcount.IsMutable() && extra <= (rep->capacity() - new_entries)) {
+  if (rep->refcount.IsOne() && extra <= (rep->capacity() - new_entries)) {
     // We adopt a privately owned rep and no extra entries needed.
     if (head.index != rep->head_) UnrefEntries(rep, rep->head_, head.index);
     if (tail.index != rep->tail_) UnrefEntries(rep, tail.index, rep->tail_);
@@ -715,7 +717,7 @@ CordRepRing* CordRepRing::RemovePrefix(CordRepRing* rep, size_t len,
   }
 
   Position head = rep->Find(len);
-  if (rep->refcount.IsMutable()) {
+  if (rep->refcount.IsOne()) {
     if (head.index != rep->head_) UnrefEntries(rep, rep->head_, head.index);
     rep->head_ = head.index;
   } else {
@@ -745,7 +747,7 @@ CordRepRing* CordRepRing::RemoveSuffix(CordRepRing* rep, size_t len,
   }
 
   Position tail = rep->FindTail(rep->length - len);
-  if (rep->refcount.IsMutable()) {
+  if (rep->refcount.IsOne()) {
     // We adopt a privately owned rep, scrub.
     if (tail.index != rep->tail_) UnrefEntries(rep, tail.index, rep->tail_);
     rep->tail_ = tail.index;
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cordz_info.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cordz_info.cc
index ae35341f2a..bc257c9be2 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cordz_info.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cordz_info.cc
@@ -20,6 +20,7 @@
 #include "y_absl/debugging/stacktrace.h"
 #include "y_absl/strings/internal/cord_internal.h"
 #include "y_absl/strings/internal/cord_rep_btree.h"
+#include "y_absl/strings/internal/cord_rep_crc.h"
 #include "y_absl/strings/internal/cord_rep_ring.h"
 #include "y_absl/strings/internal/cordz_handle.h"
 #include "y_absl/strings/internal/cordz_statistics.h"
@@ -33,7 +34,9 @@ namespace cord_internal {
 
 using ::y_absl::base_internal::SpinLockHolder;
 
+#ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 constexpr int CordzInfo::kMaxStackDepth;
+#endif
 
 Y_ABSL_CONST_INIT CordzInfo::List CordzInfo::global_list_{y_absl::kConstInit};
 
@@ -81,6 +84,14 @@ class CordRepAnalyzer {
     size_t refcount = rep->refcount.Get();
     RepRef repref{rep, (refcount > 1) ? refcount - 1 : 1};
 
+    // Process the top level CRC node, if present.
+    if (repref.rep->tag == CRC) {
+      statistics_.node_count++;
+      statistics_.node_counts.crc++;
+      memory_usage_.Add(sizeof(CordRepCrc), repref.refcount);
+      repref = repref.Child(repref.rep->crc()->child);
+    }
+
     // Process all top level linear nodes (substrings and flats).
     repref = CountLinearReps(repref, memory_usage_);
 
@@ -89,8 +100,6 @@ class CordRepAnalyzer {
         AnalyzeRing(repref);
       } else if (repref.rep->tag == BTREE) {
         AnalyzeBtree(repref);
-      } else if (repref.rep->tag == CONCAT) {
-        AnalyzeConcat(repref);
       } else {
         // We should have either a concat, btree, or ring node if not null.
         assert(false);
@@ -132,14 +141,6 @@ class CordRepAnalyzer {
     }
   };
 
-  // Returns `rr` if `rr.rep` is not null and a CONCAT type.
-  // Asserts that `rr.rep` is a concat node or null.
-  static RepRef AssertConcat(RepRef repref) {
-    const CordRep* rep = repref.rep;
-    assert(rep == nullptr || rep->tag == CONCAT);
-    return (rep != nullptr && rep->tag == CONCAT) ? repref : RepRef{nullptr, 0};
-  }
-
   // Counts a flat of the provide allocated size
   void CountFlat(size_t size) {
     statistics_.node_count++;
@@ -192,34 +193,6 @@ class CordRepAnalyzer {
     return rep;
   }
 
-  // Analyzes the provided concat node in a flattened recursive way.
-  void AnalyzeConcat(RepRef rep) {
-    y_absl::InlinedVector<RepRef, 47> pending;
-
-    while (rep.rep != nullptr) {
-      const CordRepConcat* concat = rep.rep->concat();
-      RepRef left = rep.Child(concat->left);
-      RepRef right = rep.Child(concat->right);
-
-      statistics_.node_count++;
-      statistics_.node_counts.concat++;
-      memory_usage_.Add(sizeof(CordRepConcat), rep.refcount);
-
-      right = AssertConcat(CountLinearReps(right, memory_usage_));
-      rep = AssertConcat(CountLinearReps(left, memory_usage_));
-      if (rep.rep != nullptr) {
-        if (right.rep != nullptr) {
-          pending.push_back(right);
-        }
-      } else if (right.rep != nullptr) {
-        rep = right;
-      } else if (!pending.empty()) {
-        rep = pending.back();
-        pending.pop_back();
-      }
-    }
-  }
-
   // Analyzes the provided ring.
   void AnalyzeRing(RepRef rep) {
     statistics_.node_count++;
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cordz_statistics.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cordz_statistics.h
index 29ca3d1fcc..01194adeed 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cordz_statistics.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cordz_statistics.h
@@ -41,6 +41,7 @@ struct CordzStatistics {
     size_t concat = 0;     // #concat reps
     size_t ring = 0;       // #ring buffer reps
     size_t btree = 0;      // #btree reps
+    size_t crc = 0;        // #crc reps
   };
 
   // The size of the cord in bytes. This matches the result of Cord::size().
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cordz_update_tracker.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cordz_update_tracker.h
index bb9fae0e6f..0ff3eae6e8 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cordz_update_tracker.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/cordz_update_tracker.h
@@ -39,8 +39,8 @@ class CordzUpdateTracker {
   // Tracked update methods.
   enum MethodIdentifier {
     kUnknown,
-    kAppendBuffer,
     kAppendCord,
+    kAppendCordBuffer,
     kAppendExternalMemory,
     kAppendString,
     kAssignCord,
@@ -50,16 +50,18 @@ class CordzUpdateTracker {
     kConstructorString,
     kCordReader,
     kFlatten,
+    kGetAppendBuffer,
     kGetAppendRegion,
     kMakeCordFromExternal,
     kMoveAppendCord,
     kMoveAssignCord,
     kMovePrependCord,
-    kPrependBuffer,
     kPrependCord,
+    kPrependCordBuffer,
     kPrependString,
     kRemovePrefix,
     kRemoveSuffix,
+    kSetExpectedChecksum,
     kSubCord,
 
     // kNumMethods defines the number of entries: must be the last entry.
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/escaping.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/escaping.cc
index 1105bbe1f9..9e7c766565 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/escaping.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/escaping.cc
@@ -21,7 +21,7 @@ namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
 namespace strings_internal {
 
-const char kBase64Chars[] =
+Y_ABSL_CONST_INIT const char kBase64Chars[] =
     "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
 size_t CalculateBase64EscapedLenInternal(size_t input_len, bool do_padding) {
@@ -102,8 +102,8 @@ size_t Base64EscapeInternal(const unsigned char* src, size_t szsrc, char* dest,
     }
   }
   // To save time, we didn't update szdest or szsrc in the loop.  So do it now.
-  szdest = limit_dest - cur_dest;
-  szsrc = limit_src - cur_src;
+  szdest = static_cast<size_t>(limit_dest - cur_dest);
+  szsrc = static_cast<size_t>(limit_src - cur_src);
 
   /* now deal with the tail (<=3 bytes) */
   switch (szsrc) {
@@ -154,7 +154,8 @@ size_t Base64EscapeInternal(const unsigned char* src, size_t szsrc, char* dest,
       // the loop because the loop above always reads 4 bytes, and the fourth
       // byte is past the end of the input.
       if (szdest < 4) return 0;
-      uint32_t in = (cur_src[0] << 16) + y_absl::big_endian::Load16(cur_src + 1);
+      uint32_t in =
+          (uint32_t{cur_src[0]} << 16) + y_absl::big_endian::Load16(cur_src + 1);
       cur_dest[0] = base64[in >> 18];
       in &= 0x3FFFF;
       cur_dest[1] = base64[in >> 12];
@@ -172,7 +173,7 @@ size_t Base64EscapeInternal(const unsigned char* src, size_t szsrc, char* dest,
       Y_ABSL_RAW_LOG(FATAL, "Logic problem? szsrc = %zu", szsrc);
       break;
   }
-  return (cur_dest - dest);
+  return static_cast<size_t>(cur_dest - dest);
 }
 
 }  // namespace strings_internal
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/ostringstream.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/ostringstream.cc
index c850f8abb1..2c23a18e12 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/ostringstream.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/ostringstream.cc
@@ -27,7 +27,7 @@ OStringStream::Buf::int_type OStringStream::overflow(int c) {
 
 std::streamsize OStringStream::xsputn(const char* s, std::streamsize n) {
   assert(s_);
-  s_->append(s, n);
+  s_->append(s, static_cast<size_t>(n));
   return n;
 }
 
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/arg.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/arg.cc
index 5f4399c9da..0d503208f0 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/arg.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/arg.cc
@@ -320,7 +320,7 @@ bool ConvertIntArg(T v, const FormatConversionSpecImpl conv,
       return ConvertFloatImpl(static_cast<double>(v), conv, sink);
 
     default:
-       Y_ABSL_INTERNAL_ASSUME(false);
+       Y_ABSL_ASSUME(false);
   }
 
   if (conv.is_basic()) {
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/arg.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/arg.h
index 67ac59122b..f6621166e5 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/arg.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/arg.h
@@ -145,7 +145,7 @@ StringConvertResult FormatConvertImpl(const AbslCord& value,
   size_t space_remaining = 0;
 
   int width = conv.width();
-  if (width >= 0) space_remaining = width;
+  if (width >= 0) space_remaining = static_cast<size_t>(width);
 
   size_t to_write = value.size();
 
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/bind.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/bind.h
index 4f254951fd..3688b503af 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/bind.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/bind.h
@@ -25,6 +25,7 @@
 #include "y_absl/strings/internal/str_format/checker.h"
 #include "y_absl/strings/internal/str_format/parser.h"
 #include "y_absl/types/span.h"
+#include "y_absl/utility/utility.h"
 
 namespace y_absl {
 Y_ABSL_NAMESPACE_BEGIN
@@ -87,6 +88,36 @@ class FormatSpecTemplate
     : public MakeDependent<UntypedFormatSpec, Args...>::type {
   using Base = typename MakeDependent<UntypedFormatSpec, Args...>::type;
 
+  template <bool res>
+  struct ErrorMaker {
+    constexpr bool operator()(int) const { return res; }
+  };
+
+  template <int i, int j>
+  static constexpr bool CheckArity(ErrorMaker<true> SpecifierCount = {},
+                                   ErrorMaker<i == j> ParametersPassed = {}) {
+    static_assert(SpecifierCount(i) == ParametersPassed(j),
+                  "Number of arguments passed must match the number of "
+                  "conversion specifiers.");
+    return true;
+  }
+
+  template <FormatConversionCharSet specified, FormatConversionCharSet passed,
+            int arg>
+  static constexpr bool CheckMatch(
+      ErrorMaker<Contains(specified, passed)> MismatchedArgumentNumber = {}) {
+    static_assert(MismatchedArgumentNumber(arg),
+                  "Passed argument must match specified format.");
+    return true;
+  }
+
+  template <FormatConversionCharSet... C, size_t... I>
+  static bool CheckMatches(y_absl::index_sequence<I...>) {
+    bool res[] = {true, CheckMatch<Args, C, I + 1>()...};
+    (void)res;
+    return true;
+  }
+
  public:
 #ifdef Y_ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
 
@@ -112,7 +143,8 @@ class FormatSpecTemplate
   template <typename T = void>
   FormatSpecTemplate(string_view s)  // NOLINT
       __attribute__((enable_if(str_format_internal::EnsureConstexpr(s),
-                               "constexpr trap"))) {
+                               "constexpr trap")))
+      : Base("to avoid noise in the compiler error") {
     static_assert(sizeof(T*) == 0,
                   "Format specified does not match the arguments passed.");
   }
@@ -133,13 +165,12 @@ class FormatSpecTemplate
 
 #endif  // Y_ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
 
-  template <
-      FormatConversionCharSet... C,
-      typename = typename std::enable_if<sizeof...(C) == sizeof...(Args)>::type,
-      typename = typename std::enable_if<AllOf(Contains(Args,
-                                                        C)...)>::type>
+  template <FormatConversionCharSet... C>
   FormatSpecTemplate(const ExtendedParsedFormat<C...>& pc)  // NOLINT
-      : Base(&pc) {}
+      : Base(&pc) {
+    CheckArity<sizeof...(C), sizeof...(Args)>();
+    CheckMatches<C...>(y_absl::make_index_sequence<sizeof...(C)>{});
+  }
 };
 
 class Streamable {
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/checker.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/checker.h
index a10724d870..e262c6ba87 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/checker.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/checker.h
@@ -22,9 +22,14 @@
 // Compile time check support for entry points.
 
 #ifndef Y_ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
-#if Y_ABSL_HAVE_ATTRIBUTE(enable_if) && !defined(__native_client__)
+// We disable format checker under vscode intellisense compilation.
+// See https://github.com/microsoft/vscode-cpptools/issues/3683 for
+// more details.
+#if Y_ABSL_HAVE_ATTRIBUTE(enable_if) && !defined(__native_client__) && \
+    !defined(__INTELLISENSE__)
 #define Y_ABSL_INTERNAL_ENABLE_FORMAT_CHECKER 1
-#endif  // Y_ABSL_HAVE_ATTRIBUTE(enable_if) && !defined(__native_client__)
+#endif  // Y_ABSL_HAVE_ATTRIBUTE(enable_if) && !defined(__native_client__) &&
+        // !defined(__INTELLISENSE__)
 #endif  // Y_ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
 
 namespace y_absl {
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/extension.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/extension.cc
index 24e0ec7a13..db6182f35d 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/extension.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/extension.cc
@@ -33,6 +33,8 @@ TString FlagsToString(Flags v) {
   return s;
 }
 
+#ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+
 #define Y_ABSL_INTERNAL_X_VAL(id) \
   constexpr y_absl::FormatConversionChar FormatConversionCharInternal::id;
 Y_ABSL_INTERNAL_CONVERSION_CHARS_EXPAND_(Y_ABSL_INTERNAL_X_VAL, )
@@ -45,17 +47,14 @@ constexpr y_absl::FormatConversionChar FormatConversionCharInternal::kNone;
 Y_ABSL_INTERNAL_CONVERSION_CHARS_EXPAND_(Y_ABSL_INTERNAL_CHAR_SET_CASE, )
 #undef Y_ABSL_INTERNAL_CHAR_SET_CASE
 
-// NOLINTNEXTLINE(readability-redundant-declaration)
 constexpr FormatConversionCharSet FormatConversionCharSetInternal::kStar;
-// NOLINTNEXTLINE(readability-redundant-declaration)
 constexpr FormatConversionCharSet FormatConversionCharSetInternal::kIntegral;
-// NOLINTNEXTLINE(readability-redundant-declaration)
 constexpr FormatConversionCharSet FormatConversionCharSetInternal::kFloating;
-// NOLINTNEXTLINE(readability-redundant-declaration)
 constexpr FormatConversionCharSet FormatConversionCharSetInternal::kNumeric;
-// NOLINTNEXTLINE(readability-redundant-declaration)
 constexpr FormatConversionCharSet FormatConversionCharSetInternal::kPointer;
 
+#endif  // Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+
 bool FormatSinkImpl::PutPaddedString(string_view value, int width,
                                      int precision, bool left) {
   size_t space_remaining = 0;
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/extension.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/extension.h
index 836bd1a10c..cc1a5d6bad 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/extension.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/extension.h
@@ -19,6 +19,7 @@
 #include <limits.h>
 
 #include <cstddef>
+#include <cstdint>
 #include <cstring>
 #include <ostream>
 
@@ -70,7 +71,7 @@ class FormatSinkImpl {
   ~FormatSinkImpl() { Flush(); }
 
   void Flush() {
-    raw_.Write(string_view(buf_, pos_ - buf_));
+    raw_.Write(string_view(buf_, static_cast<size_t>(pos_ - buf_)));
     pos_ = buf_;
   }
 
@@ -120,7 +121,9 @@ class FormatSinkImpl {
   }
 
  private:
-  size_t Avail() const { return buf_ + sizeof(buf_) - pos_; }
+  size_t Avail() const {
+    return static_cast<size_t>(buf_ + sizeof(buf_) - pos_);
+  }
 
   FormatRawSinkImpl raw_;
   size_t size_ = 0;
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/output.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/output.h
index 7732b5e5e1..e6bebabf9c 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/output.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/output.h
@@ -22,6 +22,7 @@
 #define Y_ABSL_STRINGS_INTERNAL_STR_FORMAT_OUTPUT_H_
 
 #include <cstdio>
+#include <ios>
 #include <ostream>
 #include <util/generic/string.h>
 
@@ -71,7 +72,7 @@ inline void AbslFormatFlush(TString* out, string_view s) {
   out->append(s.data(), s.size());
 }
 inline void AbslFormatFlush(std::ostream* out, string_view s) {
-  out->write(s.data(), s.size());
+  out->write(s.data(), static_cast<std::streamsize>(s.size()));
 }
 
 inline void AbslFormatFlush(FILERawSink* sink, string_view v) {
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/parser.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/parser.h
index 68b6654be9..16bc0b12be 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/parser.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_format/parser.h
@@ -151,7 +151,8 @@ bool ParseFormatString(string_view src, Consumer consumer) {
   const char* p = src.data();
   const char* const end = p + src.size();
   while (p != end) {
-    const char* percent = static_cast<const char*>(memchr(p, '%', end - p));
+    const char* percent =
+        static_cast<const char*>(memchr(p, '%', static_cast<size_t>(end - p)));
     if (!percent) {
       // We found the last substring.
       return consumer.Append(string_view(p, end - p));
@@ -242,7 +243,8 @@ class ParsedFormatBase {
     string_view text(base, 0);
     for (const auto& item : items_) {
       const char* const end = text.data() + text.size();
-      text = string_view(end, (base + item.text_end) - end);
+      text =
+          string_view(end, static_cast<size_t>((base + item.text_end) - end));
       if (item.is_conversion) {
         if (!consumer.ConvertOne(item.conv, text)) return false;
       } else {
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_join_internal.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_join_internal.h
index 7313192abf..d4ef8a2c86 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_join_internal.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/str_join_internal.h
@@ -229,10 +229,11 @@ TString JoinAlgorithm(Iterator start, Iterator end, y_absl::string_view s,
   TString result;
   if (start != end) {
     // Sums size
-    size_t result_size = start->size();
+    auto&& start_value = *start;
+    size_t result_size = start_value.size();
     for (Iterator it = start; ++it != end;) {
       result_size += s.size();
-      result_size += it->size();
+      result_size += (*it).size();
     }
 
     if (result_size > 0) {
@@ -240,13 +241,15 @@ TString JoinAlgorithm(Iterator start, Iterator end, y_absl::string_view s,
 
       // Joins strings
       char* result_buf = &*result.begin();
-      memcpy(result_buf, start->data(), start->size());
-      result_buf += start->size();
+
+      memcpy(result_buf, start_value.data(), start_value.size());
+      result_buf += start_value.size();
       for (Iterator it = start; ++it != end;) {
         memcpy(result_buf, s.data(), s.size());
         result_buf += s.size();
-        memcpy(result_buf, it->data(), it->size());
-        result_buf += it->size();
+        auto&& value = *it;
+        memcpy(result_buf, value.data(), value.size());
+        result_buf += value.size();
       }
     }
   }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/string_constant.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/string_constant.h
index f46e814eff..d325f5e2a9 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/string_constant.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/string_constant.h
@@ -35,17 +35,25 @@ namespace strings_internal {
 // below.
 template <typename T>
 struct StringConstant {
+ private:
+  static constexpr bool TryConstexprEval(y_absl::string_view view) {
+    return view.empty() || 2 * view[0] != 1;
+  }
+
+ public:
   static constexpr y_absl::string_view value = T{}();
   constexpr y_absl::string_view operator()() const { return value; }
 
   // Check to be sure `view` points to constant data.
   // Otherwise, it can't be constant evaluated.
-  static_assert(value.empty() || 2 * value[0] != 1,
+  static_assert(TryConstexprEval(value),
                 "The input string_view must point to constant data.");
 };
 
+#ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 template <typename T>
-constexpr y_absl::string_view StringConstant<T>::value;  // NOLINT
+constexpr y_absl::string_view StringConstant<T>::value;
+#endif
 
 // Factory function for `StringConstant` instances.
 // It supports callables that have a constexpr default constructor and a
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/utf8.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/utf8.cc
index bccb5bf81e..c49e650158 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/utf8.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/internal/utf8.cc
@@ -25,25 +25,25 @@ size_t EncodeUTF8Char(char *buffer, char32_t utf8_char) {
     *buffer = static_cast<char>(utf8_char);
     return 1;
   } else if (utf8_char <= 0x7FF) {
-    buffer[1] = 0x80 | (utf8_char & 0x3F);
+    buffer[1] = static_cast<char>(0x80 | (utf8_char & 0x3F));
     utf8_char >>= 6;
-    buffer[0] = 0xC0 | utf8_char;
+    buffer[0] = static_cast<char>(0xC0 | utf8_char);
     return 2;
   } else if (utf8_char <= 0xFFFF) {
-    buffer[2] = 0x80 | (utf8_char & 0x3F);
+    buffer[2] = static_cast<char>(0x80 | (utf8_char & 0x3F));
     utf8_char >>= 6;
-    buffer[1] = 0x80 | (utf8_char & 0x3F);
+    buffer[1] = static_cast<char>(0x80 | (utf8_char & 0x3F));
     utf8_char >>= 6;
-    buffer[0] = 0xE0 | utf8_char;
+    buffer[0] = static_cast<char>(0xE0 | utf8_char);
     return 3;
   } else {
-    buffer[3] = 0x80 | (utf8_char & 0x3F);
+    buffer[3] = static_cast<char>(0x80 | (utf8_char & 0x3F));
     utf8_char >>= 6;
-    buffer[2] = 0x80 | (utf8_char & 0x3F);
+    buffer[2] = static_cast<char>(0x80 | (utf8_char & 0x3F));
     utf8_char >>= 6;
-    buffer[1] = 0x80 | (utf8_char & 0x3F);
+    buffer[1] = static_cast<char>(0x80 | (utf8_char & 0x3F));
     utf8_char >>= 6;
-    buffer[0] = 0xF0 | utf8_char;
+    buffer[0] = static_cast<char>(0xF0 | utf8_char);
     return 4;
   }
 }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/numbers.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/numbers.cc
index fec739ec89..e2c8ddf329 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/numbers.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/numbers.cc
@@ -757,8 +757,8 @@ struct LookupTables {
 //
 // uint128& operator/=(uint128) is not constexpr, so hardcode the resulting
 // array to avoid a static initializer.
-template<>
-const uint128 LookupTables<uint128>::kVmaxOverBase[] = {
+template <>
+Y_ABSL_CONST_INIT const uint128 LookupTables<uint128>::kVmaxOverBase[] = {
     0,
     0,
     MakeUint128(9223372036854775807u, 18446744073709551615u),
@@ -809,8 +809,8 @@ const uint128 LookupTables<uint128>::kVmaxOverBase[] = {
 //
 // int128& operator/=(int128) is not constexpr, so hardcode the resulting array
 // to avoid a static initializer.
-template<>
-const int128 LookupTables<int128>::kVmaxOverBase[] = {
+template <>
+Y_ABSL_CONST_INIT const int128 LookupTables<int128>::kVmaxOverBase[] = {
     0,
     0,
     MakeInt128(4611686018427387903, 18446744073709551615u),
@@ -862,8 +862,8 @@ const int128 LookupTables<int128>::kVmaxOverBase[] = {
 //
 // int128& operator/=(int128) is not constexpr, so hardcode the resulting array
 // to avoid a static initializer.
-template<>
-const int128 LookupTables<int128>::kVminOverBase[] = {
+template <>
+Y_ABSL_CONST_INIT const int128 LookupTables<int128>::kVminOverBase[] = {
     0,
     0,
     MakeInt128(-4611686018427387904, 0u),
@@ -904,11 +904,11 @@ const int128 LookupTables<int128>::kVminOverBase[] = {
 };
 
 template <typename IntType>
-const IntType LookupTables<IntType>::kVmaxOverBase[] =
+Y_ABSL_CONST_INIT const IntType LookupTables<IntType>::kVmaxOverBase[] =
     X_OVER_BASE_INITIALIZER(std::numeric_limits<IntType>::max());
 
 template <typename IntType>
-const IntType LookupTables<IntType>::kVminOverBase[] =
+Y_ABSL_CONST_INIT const IntType LookupTables<IntType>::kVminOverBase[] =
     X_OVER_BASE_INITIALIZER(std::numeric_limits<IntType>::min());
 
 #undef X_OVER_BASE_INITIALIZER
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/numbers.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/numbers.h
index 3f19d1dacd..b16ac44d0c 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/numbers.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/numbers.h
@@ -23,12 +23,12 @@
 #ifndef Y_ABSL_STRINGS_NUMBERS_H_
 #define Y_ABSL_STRINGS_NUMBERS_H_
 
-#ifdef __SSE4_2__
+#ifdef __SSSE3__
+#include <tmmintrin.h>
+#endif
+
 #ifdef _MSC_VER
 #include <intrin.h>
-#else
-#include <x86intrin.h>
-#endif
 #endif
 
 #include <cstddef>
@@ -40,14 +40,7 @@
 #include <type_traits>
 
 #include "y_absl/base/config.h"
-#ifdef __SSE4_2__
-// TODO(jorg): Remove this when we figure out the right way
-// to swap bytes on SSE 4.2 that works with the compilers
-// we claim to support.  Also, add tests for the compiler
-// that doesn't support the Intel _bswap64 intrinsic but
-// does support all the SSE 4.2 intrinsics
 #include "y_absl/base/internal/endian.h"
-#endif
 #include "y_absl/base/macros.h"
 #include "y_absl/base/port.h"
 #include "y_absl/numeric/bits.h"
@@ -185,16 +178,19 @@ char* FastIntToBuffer(int_type i, char* buffer) {
   // TODO(jorg): This signed-ness check is used because it works correctly
   // with enums, and it also serves to check that int_type is not a pointer.
   // If one day something like std::is_signed<enum E> works, switch to it.
-  if (static_cast<int_type>(1) - 2 < 0) {  // Signed
-    if (sizeof(i) > 32 / 8) {           // 33-bit to 64-bit
+  // These conditions are constexpr bools to suppress MSVC warning C4127.
+  constexpr bool kIsSigned = static_cast<int_type>(1) - 2 < 0;
+  constexpr bool kUse64Bit = sizeof(i) > 32 / 8;
+  if (kIsSigned) {
+    if (kUse64Bit) {
       return FastIntToBuffer(static_cast<int64_t>(i), buffer);
-    } else {  // 32-bit or less
+    } else {
       return FastIntToBuffer(static_cast<int32_t>(i), buffer);
     }
-  } else {                     // Unsigned
-    if (sizeof(i) > 32 / 8) {  // 33-bit to 64-bit
+  } else {
+    if (kUse64Bit) {
       return FastIntToBuffer(static_cast<uint64_t>(i), buffer);
-    } else {  // 32-bit or less
+    } else {
       return FastIntToBuffer(static_cast<uint32_t>(i), buffer);
     }
   }
@@ -213,22 +209,25 @@ Y_ABSL_MUST_USE_RESULT bool safe_strtoi_base(y_absl::string_view s, int_type* ou
   // TODO(jorg): This signed-ness check is used because it works correctly
   // with enums, and it also serves to check that int_type is not a pointer.
   // If one day something like std::is_signed<enum E> works, switch to it.
-  if (static_cast<int_type>(1) - 2 < 0) {  // Signed
-    if (sizeof(*out) == 64 / 8) {       // 64-bit
+  // These conditions are constexpr bools to suppress MSVC warning C4127.
+  constexpr bool kIsSigned = static_cast<int_type>(1) - 2 < 0;
+  constexpr bool kUse64Bit = sizeof(*out) == 64 / 8;
+  if (kIsSigned) {
+    if (kUse64Bit) {
       int64_t val;
       parsed = numbers_internal::safe_strto64_base(s, &val, base);
       *out = static_cast<int_type>(val);
-    } else {  // 32-bit
+    } else {
       int32_t val;
       parsed = numbers_internal::safe_strto32_base(s, &val, base);
       *out = static_cast<int_type>(val);
     }
-  } else {                         // Unsigned
-    if (sizeof(*out) == 64 / 8) {  // 64-bit
+  } else {
+    if (kUse64Bit) {
       uint64_t val;
       parsed = numbers_internal::safe_strtou64_base(s, &val, base);
       *out = static_cast<int_type>(val);
-    } else {  // 32-bit
+    } else {
       uint32_t val;
       parsed = numbers_internal::safe_strtou32_base(s, &val, base);
       *out = static_cast<int_type>(val);
@@ -244,7 +243,7 @@ Y_ABSL_MUST_USE_RESULT bool safe_strtoi_base(y_absl::string_view s, int_type* ou
 // Returns the number of non-pad digits of the output (it can never be zero
 // since 0 has one digit).
 inline size_t FastHexToBufferZeroPad16(uint64_t val, char* out) {
-#ifdef __SSE4_2__
+#ifdef Y_ABSL_INTERNAL_HAVE_SSSE3
   uint64_t be = y_absl::big_endian::FromHost64(val);
   const auto kNibbleMask = _mm_set1_epi8(0xf);
   const auto kHexDigits = _mm_setr_epi8('0', '1', '2', '3', '4', '5', '6', '7',
@@ -263,7 +262,7 @@ inline size_t FastHexToBufferZeroPad16(uint64_t val, char* out) {
   }
 #endif
   // | 0x1 so that even 0 has 1 digit.
-  return 16 - countl_zero(val | 0x1) / 4;
+  return 16 - static_cast<size_t>(countl_zero(val | 0x1) / 4);
 }
 
 }  // namespace numbers_internal
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/str_cat.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/str_cat.h
index 4f5e6e4df6..59ef206816 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/str_cat.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/str_cat.h
@@ -214,23 +214,29 @@ class AlphaNum {
   // A bool ctor would also convert incoming pointers (bletch).
 
   AlphaNum(int x)  // NOLINT(runtime/explicit)
-      : piece_(digits_,
-               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+      : piece_(digits_, static_cast<size_t>(
+                            numbers_internal::FastIntToBuffer(x, digits_) -
+                            &digits_[0])) {}
   AlphaNum(unsigned int x)  // NOLINT(runtime/explicit)
-      : piece_(digits_,
-               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+      : piece_(digits_, static_cast<size_t>(
+                            numbers_internal::FastIntToBuffer(x, digits_) -
+                            &digits_[0])) {}
   AlphaNum(long x)  // NOLINT(*)
-      : piece_(digits_,
-               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+      : piece_(digits_, static_cast<size_t>(
+                            numbers_internal::FastIntToBuffer(x, digits_) -
+                            &digits_[0])) {}
   AlphaNum(unsigned long x)  // NOLINT(*)
-      : piece_(digits_,
-               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+      : piece_(digits_, static_cast<size_t>(
+                            numbers_internal::FastIntToBuffer(x, digits_) -
+                            &digits_[0])) {}
   AlphaNum(long long x)  // NOLINT(*)
-      : piece_(digits_,
-               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+      : piece_(digits_, static_cast<size_t>(
+                            numbers_internal::FastIntToBuffer(x, digits_) -
+                            &digits_[0])) {}
   AlphaNum(unsigned long long x)  // NOLINT(*)
-      : piece_(digits_,
-               numbers_internal::FastIntToBuffer(x, digits_) - &digits_[0]) {}
+      : piece_(digits_, static_cast<size_t>(
+                            numbers_internal::FastIntToBuffer(x, digits_) -
+                            &digits_[0])) {}
 
   AlphaNum(float f)  // NOLINT(runtime/explicit)
       : piece_(digits_, numbers_internal::SixDigitsToBuffer(f, digits_)) {}
@@ -245,7 +251,8 @@ class AlphaNum {
       const strings_internal::AlphaNumBuffer<size>& buf)
       : piece_(&buf.data[0], buf.size) {}
 
-  AlphaNum(const char* c_str) : piece_(c_str) {}  // NOLINT(runtime/explicit)
+  AlphaNum(const char* c_str)                     // NOLINT(runtime/explicit)
+      : piece_(NullSafeStringView(c_str)) {}      // NOLINT(runtime/explicit)
   AlphaNum(y_absl::string_view pc) : piece_(pc) {}  // NOLINT(runtime/explicit)
 
   template <typename Allocator>
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/str_join.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/str_join.h
index 613934b466..f23fe9d102 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/str_join.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/str_join.h
@@ -72,21 +72,15 @@ Y_ABSL_NAMESPACE_BEGIN
 // functions. You may provide your own Formatter to enable `y_absl::StrJoin()` to
 // work with arbitrary types.
 //
-// The following is an example of a custom Formatter that simply uses
-// `std::to_string()` to format an integer as a TString.
-//
-//   struct MyFormatter {
-//     void operator()(TString* out, int i) const {
-//       out->append(std::to_string(i));
-//     }
-//   };
-//
-// You would use the above formatter by passing an instance of it as the final
-// argument to `y_absl::StrJoin()`:
-//
-//   std::vector<int> v = {1, 2, 3, 4};
-//   TString s = y_absl::StrJoin(v, "-", MyFormatter());
-//   EXPECT_EQ("1-2-3-4", s);
+// The following is an example of a custom Formatter that uses
+// `y_absl::FormatDuration` to join a list of `y_absl::Duration`s.
+//
+//   std::vector<y_absl::Duration> v = {y_absl::Seconds(1), y_absl::Milliseconds(10)};
+//   TString s =
+//       y_absl::StrJoin(v, ", ", [](TString* out, y_absl::Duration dur) {
+//         y_absl::StrAppend(out, y_absl::FormatDuration(dur));
+//       });
+//   EXPECT_EQ("1s, 10ms", s);
 //
 // The following standard formatters are provided within this file:
 //
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/str_split.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/str_split.h
index 6b3faa11ea..8cc36e1c6b 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/str_split.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/str_split.h
@@ -461,8 +461,7 @@ using EnableSplitIfString =
 // first two split strings become the `std::pair` `.first` and `.second`
 // members, respectively. The remaining split substrings are discarded. If there
 // are less than two split substrings, the empty string is used for the
-// corresponding
-// `std::pair` member.
+// corresponding `std::pair` member.
 //
 // Example:
 //
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/string_view.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/string_view.cc
index f58c65269b..cfc9f7cdb2 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/string_view.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/string_view.cc
@@ -207,22 +207,11 @@ string_view::size_type string_view::find_last_not_of(
   return npos;
 }
 
-// MSVC has non-standard behavior that implicitly creates definitions for static
-// const members. These implicit definitions conflict with explicit out-of-class
-// member definitions that are required by the C++ standard, resulting in
-// LNK1169 "multiply defined" errors at link time. __declspec(selectany) asks
-// MSVC to choose only one definition for the symbol it decorates. See details
-// at https://msdn.microsoft.com/en-us/library/34h23df8(v=vs.100).aspx
-#ifdef _MSC_VER
-#define Y_ABSL_STRING_VIEW_SELECTANY __declspec(selectany)
-#else
-#define Y_ABSL_STRING_VIEW_SELECTANY
-#endif
 
-Y_ABSL_STRING_VIEW_SELECTANY
+#ifdef Y_ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
 constexpr string_view::size_type string_view::npos;
-Y_ABSL_STRING_VIEW_SELECTANY
 constexpr string_view::size_type string_view::kMaxSize;
+#endif
 
 Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/string_view.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/string_view.h
index 443759051e..3c725fbf5d 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/string_view.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/string_view.h
@@ -57,8 +57,9 @@ Y_ABSL_NAMESPACE_END
 
 #error "std::string_view should be used in all configurations"
 
-#if Y_ABSL_HAVE_BUILTIN(__builtin_memcmp) || \
-    (defined(__GNUC__) && !defined(__clang__))
+#if Y_ABSL_HAVE_BUILTIN(__builtin_memcmp) ||        \
+    (defined(__GNUC__) && !defined(__clang__)) || \
+    (defined(_MSC_VER) && _MSC_VER >= 1928)
 #define Y_ABSL_INTERNAL_STRING_VIEW_MEMCMP __builtin_memcmp
 #else  // Y_ABSL_HAVE_BUILTIN(__builtin_memcmp)
 #define Y_ABSL_INTERNAL_STRING_VIEW_MEMCMP memcmp
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/strip.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/strip.h
index c202cc68ba..1d1d16e698 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/strip.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/strip.h
@@ -34,8 +34,9 @@ Y_ABSL_NAMESPACE_BEGIN
 
 // ConsumePrefix()
 //
-// Strips the `expected` prefix from the start of the given string, returning
-// `true` if the strip operation succeeded or false otherwise.
+// Strips the `expected` prefix, if found, from the start of `str`.
+// If the operation succeeded, `true` is returned.  If not, `false`
+// is returned and `str` is not modified.
 //
 // Example:
 //
@@ -49,8 +50,9 @@ inline bool ConsumePrefix(y_absl::string_view* str, y_absl::string_view expected
 }
 // ConsumeSuffix()
 //
-// Strips the `expected` suffix from the end of the given string, returning
-// `true` if the strip operation succeeded or false otherwise.
+// Strips the `expected` suffix, if found, from the end of `str`.
+// If the operation succeeded, `true` is returned.  If not, `false`
+// is returned and `str` is not modified.
 //
 // Example:
 //
@@ -65,7 +67,7 @@ inline bool ConsumeSuffix(y_absl::string_view* str, y_absl::string_view expected
 
 // StripPrefix()
 //
-// Returns a view into the input string 'str' with the given 'prefix' removed,
+// Returns a view into the input string `str` with the given `prefix` removed,
 // but leaving the original string intact. If the prefix does not match at the
 // start of the string, returns the original string instead.
 Y_ABSL_MUST_USE_RESULT inline y_absl::string_view StripPrefix(
@@ -76,7 +78,7 @@ Y_ABSL_MUST_USE_RESULT inline y_absl::string_view StripPrefix(
 
 // StripSuffix()
 //
-// Returns a view into the input string 'str' with the given 'suffix' removed,
+// Returns a view into the input string `str` with the given `suffix` removed,
 // but leaving the original string intact. If the suffix does not match at the
 // end of the string, returns the original string instead.
 Y_ABSL_MUST_USE_RESULT inline y_absl::string_view StripSuffix(
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/substitute.h b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/substitute.h
index f956619957..cb49392ddb 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/strings/substitute.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/strings/substitute.h
@@ -161,8 +161,8 @@ class Arg {
   Arg(Hex hex);  // NOLINT(runtime/explicit)
   Arg(Dec dec);  // NOLINT(runtime/explicit)
 
-  // vector<bool>::reference and const_reference require special help to
-  // convert to `AlphaNum` because it requires two user defined conversions.
+  // vector<bool>::reference and const_reference require special help to convert
+  // to `Arg` because it requires two user defined conversions.
   template <typename T,
             y_absl::enable_if_t<
                 std::is_class<T>::value &&
@@ -176,6 +176,14 @@ class Arg {
   // "0x<hex value>". However, in the case of `nullptr`, "NULL" is printed.
   Arg(const void* value);  // NOLINT(runtime/explicit)
 
+  // Normal enums are already handled by the integer formatters.
+  // This overload matches only scoped enums.
+  template <typename T,
+            typename = typename std::enable_if<
+                std::is_enum<T>{} && !std::is_convertible<T, int>{}>::type>
+  Arg(T value)  // NOLINT(google-explicit-constructor)
+      : Arg(static_cast<typename std::underlying_type<T>::type>(value)) {}
+
   Arg(const Arg&) = delete;
   Arg& operator=(const Arg&) = delete;
 
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/create_thread_identity.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/create_thread_identity.cc
index 446b3b2c6b..95787d5605 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/create_thread_identity.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/create_thread_identity.cc
@@ -38,7 +38,7 @@ Y_ABSL_CONST_INIT static base_internal::ThreadIdentity* thread_identity_freelist
 
 // A per-thread destructor for reclaiming associated ThreadIdentity objects.
 // Since we must preserve their storage we cache them for re-use.
-void ReclaimThreadIdentity(void* v) {
+static void ReclaimThreadIdentity(void* v) {
   base_internal::ThreadIdentity* identity =
       static_cast<base_internal::ThreadIdentity*>(v);
 
@@ -48,8 +48,6 @@ void ReclaimThreadIdentity(void* v) {
     base_internal::LowLevelAlloc::Free(identity->per_thread_synch.all_locks);
   }
 
-  PerThreadSem::Destroy(identity);
-
   // We must explicitly clear the current thread's identity:
   // (a) Subsequent (unrelated) per-thread destructors may require an identity.
   //     We must guarantee a new identity is used in this case (this instructor
@@ -71,7 +69,12 @@ static intptr_t RoundUp(intptr_t addr, intptr_t align) {
   return (addr + align - 1) & ~(align - 1);
 }
 
-static void ResetThreadIdentity(base_internal::ThreadIdentity* identity) {
+void OneTimeInitThreadIdentity(base_internal::ThreadIdentity* identity) {
+  PerThreadSem::Init(identity);
+}
+
+static void ResetThreadIdentityBetweenReuse(
+    base_internal::ThreadIdentity* identity) {
   base_internal::PerThreadSynch* pts = &identity->per_thread_synch;
   pts->next = nullptr;
   pts->skip = nullptr;
@@ -116,8 +119,9 @@ static base_internal::ThreadIdentity* NewThreadIdentity() {
     identity = reinterpret_cast<base_internal::ThreadIdentity*>(
         RoundUp(reinterpret_cast<intptr_t>(allocation),
                 base_internal::PerThreadSynch::kAlignment));
+    OneTimeInitThreadIdentity(identity);
   }
-  ResetThreadIdentity(identity);
+  ResetThreadIdentityBetweenReuse(identity);
 
   return identity;
 }
@@ -127,7 +131,6 @@ static base_internal::ThreadIdentity* NewThreadIdentity() {
 // REQUIRES: CurrentThreadIdentity(false) == nullptr
 base_internal::ThreadIdentity* CreateThreadIdentity() {
   base_internal::ThreadIdentity* identity = NewThreadIdentity();
-  PerThreadSem::Init(identity);
   // Associate the value with the current thread, and attach our destructor.
   base_internal::SetCurrentThreadIdentity(identity, ReclaimThreadIdentity);
   return identity;
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/create_thread_identity.h b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/create_thread_identity.h
index a7e22c04ac..79064340e5 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/create_thread_identity.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/create_thread_identity.h
@@ -36,10 +36,6 @@ namespace synchronization_internal {
 // For private use only.
 base_internal::ThreadIdentity* CreateThreadIdentity();
 
-// A per-thread destructor for reclaiming associated ThreadIdentity objects.
-// For private use only.
-void ReclaimThreadIdentity(void* v);
-
 // Returns the ThreadIdentity object representing the calling thread; guaranteed
 // to be unique for its lifetime.  The returned object will remain valid for the
 // program's lifetime; although it may be re-assigned to a subsequent thread.
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/per_thread_sem.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/per_thread_sem.cc
index 85299308ad..d581d826af 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/per_thread_sem.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/per_thread_sem.cc
@@ -47,10 +47,6 @@ void PerThreadSem::Init(base_internal::ThreadIdentity *identity) {
   identity->is_idle.store(false, std::memory_order_relaxed);
 }
 
-void PerThreadSem::Destroy(base_internal::ThreadIdentity *identity) {
-  Waiter::GetWaiter(identity)->~Waiter();
-}
-
 void PerThreadSem::Tick(base_internal::ThreadIdentity *identity) {
   const int ticker =
       identity->ticker.fetch_add(1, std::memory_order_relaxed) + 1;
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/per_thread_sem.h b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/per_thread_sem.h
index 5e5c875486..6c7ae2f8c7 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/per_thread_sem.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/per_thread_sem.h
@@ -66,10 +66,6 @@ class PerThreadSem {
   // REQUIRES: May only be called by ThreadIdentity.
   static void Init(base_internal::ThreadIdentity* identity);
 
-  // Destroy the PerThreadSem associated with "identity".
-  // REQUIRES: May only be called by ThreadIdentity.
-  static void Destroy(base_internal::ThreadIdentity* identity);
-
   // Increments "identity"'s count.
   static inline void Post(base_internal::ThreadIdentity* identity);
 
@@ -81,8 +77,7 @@ class PerThreadSem {
   // Permitted callers.
   friend class PerThreadSemTest;
   friend class y_absl::Mutex;
-  friend y_absl::base_internal::ThreadIdentity* CreateThreadIdentity();
-  friend void ReclaimThreadIdentity(void* v);
+  friend void OneTimeInitThreadIdentity(y_absl::base_internal::ThreadIdentity*);
 };
 
 }  // namespace synchronization_internal
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/waiter.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/waiter.cc
index b69a0513f6..7c8c7988ae 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/waiter.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/waiter.cc
@@ -71,8 +71,6 @@ Waiter::Waiter() {
   futex_.store(0, std::memory_order_relaxed);
 }
 
-Waiter::~Waiter() = default;
-
 bool Waiter::Wait(KernelTimeout t) {
   // Loop until we can atomically decrement futex from a positive
   // value, waiting on a futex while we believe it is zero.
@@ -161,18 +159,6 @@ Waiter::Waiter() {
   wakeup_count_ = 0;
 }
 
-Waiter::~Waiter() {
-  const int err = pthread_mutex_destroy(&mu_);
-  if (err != 0) {
-    Y_ABSL_RAW_LOG(FATAL, "pthread_mutex_destroy failed: %d", err);
-  }
-
-  const int err2 = pthread_cond_destroy(&cv_);
-  if (err2 != 0) {
-    Y_ABSL_RAW_LOG(FATAL, "pthread_cond_destroy failed: %d", err2);
-  }
-}
-
 bool Waiter::Wait(KernelTimeout t) {
   struct timespec abs_timeout;
   if (t.has_timeout()) {
@@ -240,12 +226,6 @@ Waiter::Waiter() {
   wakeups_.store(0, std::memory_order_relaxed);
 }
 
-Waiter::~Waiter() {
-  if (sem_destroy(&sem_) != 0) {
-    Y_ABSL_RAW_LOG(FATAL, "sem_destroy failed with errno %d\n", errno);
-  }
-}
-
 bool Waiter::Wait(KernelTimeout t) {
   struct timespec abs_timeout;
   if (t.has_timeout()) {
@@ -363,11 +343,6 @@ Waiter::Waiter() {
   wakeup_count_ = 0;
 }
 
-// SRW locks and condition variables do not need to be explicitly destroyed.
-// https://docs.microsoft.com/en-us/windows/win32/api/synchapi/nf-synchapi-initializesrwlock
-// https://stackoverflow.com/questions/28975958/why-does-windows-have-no-deleteconditionvariable-function-to-go-together-with
-Waiter::~Waiter() = default;
-
 bool Waiter::Wait(KernelTimeout t) {
   SRWLOCK *mu = WinHelper::GetLock(this);
   CONDITION_VARIABLE *cv = WinHelper::GetCond(this);
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/waiter.h b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/waiter.h
index 4eb96ee824..17e81655fc 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/waiter.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/internal/waiter.h
@@ -71,9 +71,6 @@ class Waiter {
   Waiter(const Waiter&) = delete;
   Waiter& operator=(const Waiter&) = delete;
 
-  // Destroy any data to track waits.
-  ~Waiter();
-
   // Blocks the calling thread until a matching call to `Post()` or
   // `t` has passed. Returns `true` if woken (`Post()` called),
   // `false` on timeout.
@@ -106,6 +103,12 @@ class Waiter {
 #endif
 
  private:
+  // The destructor must not be called since Mutex/CondVar
+  // can use PerThreadSem/Waiter after the thread exits.
+  // Waiter objects are embedded in ThreadIdentity objects,
+  // which are reused via a freelist and are never destroyed.
+  ~Waiter() = delete;
+
 #if Y_ABSL_WAITER_MODE == Y_ABSL_WAITER_MODE_FUTEX
   // Futexes are defined by specification to be 32-bits.
   // Thus std::atomic<int32_t> must be just an int32_t with lockfree methods.
@@ -136,8 +139,11 @@ class Waiter {
   // REQUIRES: WinHelper::GetLock(this) must be held.
   void InternalCondVarPoke();
 
-  // We can't include Windows.h in our headers, so we use aligned charachter
+  // We can't include Windows.h in our headers, so we use aligned character
   // buffers to define the storage of SRWLOCK and CONDITION_VARIABLE.
+  // SRW locks and condition variables do not need to be explicitly destroyed.
+  // https://docs.microsoft.com/en-us/windows/win32/api/synchapi/nf-synchapi-initializesrwlock
+  // https://stackoverflow.com/questions/28975958/why-does-windows-have-no-deleteconditionvariable-function-to-go-together-with
   alignas(void*) unsigned char mu_storage_[sizeof(void*)];
   alignas(void*) unsigned char cv_storage_[sizeof(void*)];
   int waiter_count_;
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/mutex.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/mutex.cc
index 09b7acbccd..27e6a84f7a 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/mutex.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/mutex.cc
@@ -109,7 +109,7 @@ static inline bool EvalConditionAnnotated(const Condition *cond, Mutex *mu,
                                           bool locking, bool trylock,
                                           bool read_lock);
 
-void RegisterMutexProfiler(void (*fn)(int64_t wait_timestamp)) {
+void RegisterMutexProfiler(void (*fn)(int64_t wait_cycles)) {
   submit_profile_data.Store(fn);
 }
 
@@ -1744,23 +1744,33 @@ Y_ABSL_XRAY_LOG_ARGS(1) void Mutex::ReaderUnlock() {
   Y_ABSL_TSAN_MUTEX_POST_UNLOCK(this, __tsan_mutex_read_lock);
 }
 
-// The zap_desig_waker bitmask is used to clear the designated waker flag in
-// the mutex if this thread has blocked, and therefore may be the designated
-// waker.
-static const intptr_t zap_desig_waker[] = {
-    ~static_cast<intptr_t>(0),  // not blocked
-    ~static_cast<intptr_t>(
-        kMuDesig)  // blocked; turn off the designated waker bit
-};
+// Clears the designated waker flag in the mutex if this thread has blocked, and
+// therefore may be the designated waker.
+static intptr_t ClearDesignatedWakerMask(int flag) {
+  assert(flag >= 0);
+  assert(flag <= 1);
+  switch (flag) {
+    case 0:  // not blocked
+      return ~static_cast<intptr_t>(0);
+    case 1:  // blocked; turn off the designated waker bit
+      return ~static_cast<intptr_t>(kMuDesig);
+  }
+  Y_ABSL_INTERNAL_UNREACHABLE;
+}
 
-// The ignore_waiting_writers bitmask is used to ignore the existence
-// of waiting writers if a reader that has already blocked once
-// wakes up.
-static const intptr_t ignore_waiting_writers[] = {
-    ~static_cast<intptr_t>(0),  // not blocked
-    ~static_cast<intptr_t>(
-        kMuWrWait)  // blocked; pretend there are no waiting writers
-};
+// Conditionally ignores the existence of waiting writers if a reader that has
+// already blocked once wakes up.
+static intptr_t IgnoreWaitingWritersMask(int flag) {
+  assert(flag >= 0);
+  assert(flag <= 1);
+  switch (flag) {
+    case 0:  // not blocked
+      return ~static_cast<intptr_t>(0);
+    case 1:  // blocked; pretend there are no waiting writers
+      return ~static_cast<intptr_t>(kMuWrWait);
+  }
+  Y_ABSL_INTERNAL_UNREACHABLE;
+}
 
 // Internal version of LockWhen().  See LockSlowWithDeadline()
 Y_ABSL_ATTRIBUTE_NOINLINE void Mutex::LockSlow(MuHow how, const Condition *cond,
@@ -1852,8 +1862,10 @@ bool Mutex::LockSlowWithDeadline(MuHow how, const Condition *cond,
   bool unlock = false;
   if ((v & how->fast_need_zero) == 0 &&  // try fast acquire
       mu_.compare_exchange_strong(
-          v, (how->fast_or | (v & zap_desig_waker[flags & kMuHasBlocked])) +
-                 how->fast_add,
+          v,
+          (how->fast_or |
+           (v & ClearDesignatedWakerMask(flags & kMuHasBlocked))) +
+              how->fast_add,
           std::memory_order_acquire, std::memory_order_relaxed)) {
     if (cond == nullptr ||
         EvalConditionAnnotated(cond, this, true, false, how == kShared)) {
@@ -1927,9 +1939,10 @@ void Mutex::LockSlowLoop(SynchWaitParams *waitp, int flags) {
     CheckForMutexCorruption(v, "Lock");
     if ((v & waitp->how->slow_need_zero) == 0) {
       if (mu_.compare_exchange_strong(
-              v, (waitp->how->fast_or |
-                  (v & zap_desig_waker[flags & kMuHasBlocked])) +
-                     waitp->how->fast_add,
+              v,
+              (waitp->how->fast_or |
+               (v & ClearDesignatedWakerMask(flags & kMuHasBlocked))) +
+                  waitp->how->fast_add,
               std::memory_order_acquire, std::memory_order_relaxed)) {
         if (waitp->cond == nullptr ||
             EvalConditionAnnotated(waitp->cond, this, true, false,
@@ -1946,8 +1959,9 @@ void Mutex::LockSlowLoop(SynchWaitParams *waitp, int flags) {
       if ((v & (kMuSpin|kMuWait)) == 0) {   // no waiters
         // This thread tries to become the one and only waiter.
         PerThreadSynch *new_h = Enqueue(nullptr, waitp, v, flags);
-        intptr_t nv = (v & zap_desig_waker[flags & kMuHasBlocked] & kMuLow) |
-                      kMuWait;
+        intptr_t nv =
+            (v & ClearDesignatedWakerMask(flags & kMuHasBlocked) & kMuLow) |
+            kMuWait;
         Y_ABSL_RAW_CHECK(new_h != nullptr, "Enqueue to empty list failed");
         if (waitp->how == kExclusive && (v & kMuReader) != 0) {
           nv |= kMuWrWait;
@@ -1961,12 +1975,13 @@ void Mutex::LockSlowLoop(SynchWaitParams *waitp, int flags) {
           waitp->thread->waitp = nullptr;
         }
       } else if ((v & waitp->how->slow_inc_need_zero &
-                  ignore_waiting_writers[flags & kMuHasBlocked]) == 0) {
+                  IgnoreWaitingWritersMask(flags & kMuHasBlocked)) == 0) {
         // This is a reader that needs to increment the reader count,
         // but the count is currently held in the last waiter.
         if (mu_.compare_exchange_strong(
-                v, (v & zap_desig_waker[flags & kMuHasBlocked]) | kMuSpin |
-                       kMuReader,
+                v,
+                (v & ClearDesignatedWakerMask(flags & kMuHasBlocked)) |
+                    kMuSpin | kMuReader,
                 std::memory_order_acquire, std::memory_order_relaxed)) {
           PerThreadSynch *h = GetPerThreadSynch(v);
           h->readers += kMuOne;       // inc reader count in waiter
@@ -1987,8 +2002,9 @@ void Mutex::LockSlowLoop(SynchWaitParams *waitp, int flags) {
         }
       } else if ((v & kMuSpin) == 0 &&  // attempt to queue ourselves
                  mu_.compare_exchange_strong(
-                     v, (v & zap_desig_waker[flags & kMuHasBlocked]) | kMuSpin |
-                            kMuWait,
+                     v,
+                     (v & ClearDesignatedWakerMask(flags & kMuHasBlocked)) |
+                         kMuSpin | kMuWait,
                      std::memory_order_acquire, std::memory_order_relaxed)) {
         PerThreadSynch *h = GetPerThreadSynch(v);
         PerThreadSynch *new_h = Enqueue(h, waitp, v, flags);
@@ -2315,19 +2331,21 @@ Y_ABSL_ATTRIBUTE_NOINLINE void Mutex::UnlockSlow(SynchWaitParams *waitp) {
   }                            // end of for(;;)-loop
 
   if (wake_list != kPerThreadSynchNull) {
-    int64_t enqueue_timestamp = wake_list->waitp->contention_start_cycles;
-    bool cond_waiter = wake_list->cond_waiter;
+    int64_t wait_cycles = 0;
+    int64_t now = base_internal::CycleClock::Now();
     do {
+      // Sample lock contention events only if the waiter was trying to acquire
+      // the lock, not waiting on a condition variable or Condition.
+      if (!wake_list->cond_waiter) {
+        wait_cycles += (now - wake_list->waitp->contention_start_cycles);
+        wake_list->waitp->contention_start_cycles = now;
+      }
       wake_list = Wakeup(wake_list);              // wake waiters
     } while (wake_list != kPerThreadSynchNull);
-    if (!cond_waiter) {
-      // Sample lock contention events only if the (first) waiter was trying to
-      // acquire the lock, not waiting on a condition variable or Condition.
-      int64_t wait_cycles =
-          base_internal::CycleClock::Now() - enqueue_timestamp;
+    if (wait_cycles > 0) {
       mutex_tracer("slow release", this, wait_cycles);
       Y_ABSL_TSAN_MUTEX_PRE_DIVERT(this, 0);
-      submit_profile_data(enqueue_timestamp);
+      submit_profile_data(wait_cycles);
       Y_ABSL_TSAN_MUTEX_POST_DIVERT(this, 0);
     }
   }
@@ -2492,9 +2510,9 @@ void CondVar::Remove(PerThreadSynch *s) {
 // before calling Mutex::UnlockSlow(), the Mutex code might be re-entered (via
 // the logging code, or via a Condition function) and might potentially attempt
 // to block this thread.  That would be a problem if the thread were already on
-// a the condition variable waiter queue.  Thus, we use the waitp->cv_word
-// to tell the unlock code to call CondVarEnqueue() to queue the thread on the
-// condition variable queue just before the mutex is to be unlocked, and (most
+// a condition variable waiter queue.  Thus, we use the waitp->cv_word to tell
+// the unlock code to call CondVarEnqueue() to queue the thread on the condition
+// variable queue just before the mutex is to be unlocked, and (most
 // importantly) after any call to an external routine that might re-enter the
 // mutex code.
 static void CondVarEnqueue(SynchWaitParams *waitp) {
@@ -2557,6 +2575,23 @@ bool CondVar::WaitCommon(Mutex *mutex, KernelTimeout t) {
   while (waitp.thread->state.load(std::memory_order_acquire) ==
          PerThreadSynch::kQueued) {
     if (!Mutex::DecrementSynchSem(mutex, waitp.thread, t)) {
+      // DecrementSynchSem returned due to timeout.
+      // Now we will either (1) remove ourselves from the wait list in Remove
+      // below, in which case Remove will set thread.state = kAvailable and
+      // we will not call DecrementSynchSem again; or (2) Signal/SignalAll
+      // has removed us concurrently and is calling Wakeup, which will set
+      // thread.state = kAvailable and post to the semaphore.
+      // It's important to reset the timeout for the case (2) because otherwise
+      // we can live-lock in this loop since DecrementSynchSem will always
+      // return immediately due to timeout, but Signal/SignalAll is not
+      // necessary set thread.state = kAvailable yet (and is not scheduled
+      // due to thread priorities or other scheduler artifacts).
+      // Note this could also be resolved if Signal/SignalAll would set
+      // thread.state = kAvailable while holding the wait list spin lock.
+      // But this can't be easily done for SignalAll since it grabs the whole
+      // wait list with a single compare-exchange and does not really grab
+      // the spin lock.
+      t = KernelTimeout::Never();
       this->Remove(waitp.thread);
       rc = true;
     }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/mutex.h b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/mutex.h
index fab53e867b..1cadd01bd8 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/mutex.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/mutex.h
@@ -174,9 +174,12 @@ class Y_ABSL_LOCKABLE Mutex {
 
   // Mutex::AssertHeld()
   //
-  // Return immediately if this thread holds the `Mutex` exclusively (in write
-  // mode). Otherwise, may report an error (typically by crashing with a
-  // diagnostic), or may return immediately.
+  // Require that the mutex be held exclusively (write mode) by this thread.
+  //
+  // If the mutex is not currently held by this thread, this function may report
+  // an error (typically by crashing with a diagnostic) or it may do nothing.
+  // This function is intended only as a tool to assist debugging; it doesn't
+  // guarantee correctness.
   void AssertHeld() const Y_ABSL_ASSERT_EXCLUSIVE_LOCK();
 
   // ---------------------------------------------------------------------------
@@ -236,9 +239,13 @@ class Y_ABSL_LOCKABLE Mutex {
 
   // Mutex::AssertReaderHeld()
   //
-  // Returns immediately if this thread holds the `Mutex` in at least shared
-  // mode (read mode). Otherwise, may report an error (typically by
-  // crashing with a diagnostic), or may return immediately.
+  // Require that the mutex be held at least in shared mode (read mode) by this
+  // thread.
+  //
+  // If the mutex is not currently held by this thread, this function may report
+  // an error (typically by crashing with a diagnostic) or it may do nothing.
+  // This function is intended only as a tool to assist debugging; it doesn't
+  // guarantee correctness.
   void AssertReaderHeld() const Y_ABSL_ASSERT_SHARED_LOCK();
 
   // Mutex::WriterLock()
@@ -984,14 +991,15 @@ inline Condition::Condition(const T *object,
 // Register a hook for profiling support.
 //
 // The function pointer registered here will be called whenever a mutex is
-// contended.  The callback is given the y_absl/base/cycleclock.h timestamp when
-// waiting began.
+// contended.  The callback is given the cycles for which waiting happened (as
+// measured by //y_absl/base/internal/cycleclock.h, and which may not
+// be real "cycle" counts.)
 //
 // Calls to this function do not race or block, but there is no ordering
 // guaranteed between calls to this function and call to the provided hook.
 // In particular, the previously registered hook may still be called for some
 // time after this function returns.
-void RegisterMutexProfiler(void (*fn)(int64_t wait_timestamp));
+void RegisterMutexProfiler(void (*fn)(int64_t wait_cycles));
 
 // Register a hook for Mutex tracing.
 //
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/notification.h b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/notification.h
index 0794cc35e9..e4a77271e9 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/notification.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/synchronization/notification.h
@@ -22,7 +22,7 @@
 // The `Notification` object maintains a private boolean "notified" state that
 // transitions to `true` at most once. The `Notification` class provides the
 // following primary member functions:
-//   * `HasBeenNotified() `to query its state
+//   * `HasBeenNotified()` to query its state
 //   * `WaitForNotification*()` to have threads wait until the "notified" state
 //      is `true`.
 //   * `Notify()` to set the notification's "notified" state to `true` and
@@ -52,6 +52,7 @@
 
 #include <atomic>
 
+#include "y_absl/base/attributes.h"
 #include "y_absl/base/macros.h"
 #include "y_absl/synchronization/mutex.h"
 #include "y_absl/time/time.h"
@@ -74,7 +75,7 @@ class Notification {
   // Notification::HasBeenNotified()
   //
   // Returns the value of the notification's internal "notified" state.
-  bool HasBeenNotified() const {
+  Y_ABSL_MUST_USE_RESULT bool HasBeenNotified() const {
     return HasBeenNotifiedInternal(&this->notified_yet_);
   }
 
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/time/duration.cc b/contrib/restricted/abseil-cpp-tstring/y_absl/time/duration.cc
index cc646c8870..c9a3b73b73 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/time/duration.cc
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/time/duration.cc
@@ -766,13 +766,14 @@ void AppendNumberUnit(TString* out, double n, DisplayUnit unit) {
 //   is non-zero.
 // Unlike Go, we format the zero duration as 0, with no unit.
 TString FormatDuration(Duration d) {
-  const Duration min_duration = Seconds(kint64min);
-  if (d == min_duration) {
+  constexpr Duration kMinDuration = Seconds(kint64min);
+  TString s;
+  if (d == kMinDuration) {
     // Avoid needing to negate kint64min by directly returning what the
     // following code should produce in that case.
-    return "-2562047788015215h30m8s";
+    s = "-2562047788015215h30m8s";
+    return s;
   }
-  TString s;
   if (d < ZeroDuration()) {
     s.append("-");
     d = -d;
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/time/internal/cctz/include/cctz/civil_time_detail.h b/contrib/restricted/abseil-cpp-tstring/y_absl/time/internal/cctz/include/cctz/civil_time_detail.h
index f2385d6754..b5cd52c7cf 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/time/internal/cctz/include/cctz/civil_time_detail.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/time/internal/cctz/include/cctz/civil_time_detail.h
@@ -84,14 +84,13 @@ CONSTEXPR_F bool is_leap_year(year_t y) noexcept {
   return y % 4 == 0 && (y % 100 != 0 || y % 400 == 0);
 }
 CONSTEXPR_F int year_index(year_t y, month_t m) noexcept {
-  return (static_cast<int>((y + (m > 2)) % 400) + 400) % 400;
+  const int yi = static_cast<int>((y + (m > 2)) % 400);
+  return yi < 0 ? yi + 400 : yi;
 }
-CONSTEXPR_F int days_per_century(year_t y, month_t m) noexcept {
-  const int yi = year_index(y, m);
+CONSTEXPR_F int days_per_century(int yi) noexcept {
   return 36524 + (yi == 0 || yi > 300);
 }
-CONSTEXPR_F int days_per_4years(year_t y, month_t m) noexcept {
-  const int yi = year_index(y, m);
+CONSTEXPR_F int days_per_4years(int yi) noexcept {
   return 1460 + (yi == 0 || yi > 300 || (yi - 1) % 100 < 96);
 }
 CONSTEXPR_F int days_per_year(year_t y, month_t m) noexcept {
@@ -133,17 +132,22 @@ CONSTEXPR_F fields n_day(year_t y, month_t m, diff_t d, diff_t cd, hour_t hh,
     }
   }
   if (d > 365) {
+    int yi = year_index(ey, m);  // Index into Gregorian 400 year cycle.
     for (;;) {
-      int n = days_per_century(ey, m);
+      int n = days_per_century(yi);
       if (d <= n) break;
       d -= n;
       ey += 100;
+      yi += 100;
+      if (yi >= 400) yi -= 400;
     }
     for (;;) {
-      int n = days_per_4years(ey, m);
+      int n = days_per_4years(yi);
       if (d <= n) break;
       d -= n;
       ey += 4;
+      yi += 4;
+      if (yi >= 400) yi -= 400;
     }
     for (;;) {
       int n = days_per_year(ey, m);
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/time/time.h b/contrib/restricted/abseil-cpp-tstring/y_absl/time/time.h
index e3df4abd21..99009dfc30 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/time/time.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/time/time.h
@@ -120,7 +120,7 @@ using EnableIfFloat =
 
 // Duration
 //
-// The `y_absl::Duration` class represents a signed, fixed-length span of time.
+// The `y_absl::Duration` class represents a signed, fixed-length amount of time.
 // A `Duration` is generated using a unit-specific factory function, or is
 // the result of subtracting one `y_absl::Time` from another. Durations behave
 // like unit-safe integers and they support all the natural integer-like
@@ -162,7 +162,7 @@ class Duration {
   constexpr Duration() : rep_hi_(0), rep_lo_(0) {}  // zero-length duration
 
   // Copyable.
-#if !defined(__clang__) && defined(_MSC_VER) && _MSC_VER < 1910
+#if !defined(__clang__) && defined(_MSC_VER) && _MSC_VER < 1930
   // Explicitly defining the constexpr copy constructor avoids an MSVC bug.
   constexpr Duration(const Duration& d)
       : rep_hi_(d.rep_hi_), rep_lo_(d.rep_lo_) {}
@@ -579,7 +579,7 @@ bool ParseDuration(y_absl::string_view dur_string, Duration* d);
 
 // AbslParseFlag()
 //
-// Parses a command-line flag string representation `text` into a a Duration
+// Parses a command-line flag string representation `text` into a Duration
 // value. Duration flags must be specified in a format that is valid input for
 // `y_absl::ParseDuration()`.
 bool AbslParseFlag(y_absl::string_view text, Duration* dst, TString* error);
@@ -750,23 +750,24 @@ constexpr Time UnixEpoch() { return Time(); }
 constexpr Time UniversalEpoch() {
   // 719162 is the number of days from 0001-01-01 to 1970-01-01,
   // assuming the Gregorian calendar.
-  return Time(time_internal::MakeDuration(-24 * 719162 * int64_t{3600}, 0U));
+  return Time(
+      time_internal::MakeDuration(-24 * 719162 * int64_t{3600}, uint32_t{0}));
 }
 
 // InfiniteFuture()
 //
 // Returns an `y_absl::Time` that is infinitely far in the future.
 constexpr Time InfiniteFuture() {
-  return Time(
-      time_internal::MakeDuration((std::numeric_limits<int64_t>::max)(), ~0U));
+  return Time(time_internal::MakeDuration((std::numeric_limits<int64_t>::max)(),
+                                          ~uint32_t{0}));
 }
 
 // InfinitePast()
 //
 // Returns an `y_absl::Time` that is infinitely far in the past.
 constexpr Time InfinitePast() {
-  return Time(
-      time_internal::MakeDuration((std::numeric_limits<int64_t>::min)(), ~0U));
+  return Time(time_internal::MakeDuration((std::numeric_limits<int64_t>::min)(),
+                                          ~uint32_t{0}));
 }
 
 // FromUnixNanos()
@@ -1422,14 +1423,17 @@ constexpr int64_t GetRepHi(Duration d) { return d.rep_hi_; }
 constexpr uint32_t GetRepLo(Duration d) { return d.rep_lo_; }
 
 // Returns true iff d is positive or negative infinity.
-constexpr bool IsInfiniteDuration(Duration d) { return GetRepLo(d) == ~0U; }
+constexpr bool IsInfiniteDuration(Duration d) {
+  return GetRepLo(d) == ~uint32_t{0};
+}
 
 // Returns an infinite Duration with the opposite sign.
 // REQUIRES: IsInfiniteDuration(d)
 constexpr Duration OppositeInfinity(Duration d) {
   return GetRepHi(d) < 0
-             ? MakeDuration((std::numeric_limits<int64_t>::max)(), ~0U)
-             : MakeDuration((std::numeric_limits<int64_t>::min)(), ~0U);
+             ? MakeDuration((std::numeric_limits<int64_t>::max)(), ~uint32_t{0})
+             : MakeDuration((std::numeric_limits<int64_t>::min)(),
+                            ~uint32_t{0});
 }
 
 // Returns (-n)-1 (equivalently -(n+1)) without avoidable overflow.
@@ -1568,7 +1572,7 @@ constexpr Duration operator-(Duration d) {
 
 constexpr Duration InfiniteDuration() {
   return time_internal::MakeDuration((std::numeric_limits<int64_t>::max)(),
-                                     ~0U);
+                                     ~uint32_t{0});
 }
 
 constexpr Duration FromChrono(const std::chrono::nanoseconds& d) {
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/types/internal/optional.h b/contrib/restricted/abseil-cpp-tstring/y_absl/types/internal/optional.h
index 9b20551d2e..34ae94b275 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/types/internal/optional.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/types/internal/optional.h
@@ -91,7 +91,15 @@ class optional_data_dtor_base {
 
   void destruct() noexcept {
     if (engaged_) {
+      // `data_` must be initialized if `engaged_` is true.
+#if Y_ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(12, 0)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
       data_.~T();
+#if Y_ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(12, 0)
+#pragma GCC diagnostic pop
+#endif
       engaged_ = false;
     }
   }
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/types/internal/variant.h b/contrib/restricted/abseil-cpp-tstring/y_absl/types/internal/variant.h
index 606d985526..03fb92016a 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/types/internal/variant.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/types/internal/variant.h
@@ -16,8 +16,8 @@
 // separate file to avoid cluttering the top of the API header with
 // implementation details.
 
-#ifndef Y_ABSL_TYPES_variant_internal_H_
-#define Y_ABSL_TYPES_variant_internal_H_
+#ifndef Y_ABSL_TYPES_VARIANT_INTERNAL_H_
+#define Y_ABSL_TYPES_VARIANT_INTERNAL_H_
 
 #include <cassert>
 #include <cstddef>
@@ -1643,4 +1643,4 @@ Y_ABSL_NAMESPACE_END
 }  // namespace y_absl
 
 #endif  // !defined(Y_ABSL_USES_STD_VARIANT)
-#endif  // Y_ABSL_TYPES_variant_internal_H_
+#endif  // Y_ABSL_TYPES_VARIANT_INTERNAL_H_
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/types/optional.h b/contrib/restricted/abseil-cpp-tstring/y_absl/types/optional.h
index 6c988a64ce..2a71ecb6c4 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/types/optional.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/types/optional.h
@@ -282,15 +282,16 @@ class optional : private optional_internal::optional_data<T>,
   optional& operator=(optional&& src) = default;
 
   // Value assignment operators
-  template <
-      typename U = T,
-      typename = typename std::enable_if<y_absl::conjunction<
-          y_absl::negation<
-              std::is_same<optional<T>, typename std::decay<U>::type>>,
-          y_absl::negation<
-              y_absl::conjunction<std::is_scalar<T>,
-                                std::is_same<T, typename std::decay<U>::type>>>,
-          std::is_constructible<T, U>, std::is_assignable<T&, U>>::value>::type>
+  template <typename U = T,
+            int&...,  // Workaround an internal compiler error in GCC 5 to 10.
+            typename = typename std::enable_if<y_absl::conjunction<
+                y_absl::negation<
+                    std::is_same<optional<T>, typename std::decay<U>::type> >,
+                y_absl::negation<y_absl::conjunction<
+                    std::is_scalar<T>,
+                    std::is_same<T, typename std::decay<U>::type> > >,
+                std::is_constructible<T, U>,
+                std::is_assignable<T&, U> >::value>::type>
   optional& operator=(U&& v) {
     this->assign(std::forward<U>(v));
     return *this;
@@ -298,13 +299,14 @@ class optional : private optional_internal::optional_data<T>,
 
   template <
       typename U,
+      int&...,  // Workaround an internal compiler error in GCC 5 to 10.
       typename = typename std::enable_if<y_absl::conjunction<
-          y_absl::negation<std::is_same<T, U>>,
+          y_absl::negation<std::is_same<T, U> >,
           std::is_constructible<T, const U&>, std::is_assignable<T&, const U&>,
           y_absl::negation<
               optional_internal::
                   is_constructible_convertible_assignable_from_optional<
-                      T, U>>>::value>::type>
+                      T, U> > >::value>::type>
   optional& operator=(const optional<U>& rhs) {
     if (rhs) {
       this->assign(*rhs);
@@ -315,13 +317,14 @@ class optional : private optional_internal::optional_data<T>,
   }
 
   template <typename U,
+            int&...,  // Workaround an internal compiler error in GCC 5 to 10.
             typename = typename std::enable_if<y_absl::conjunction<
-                y_absl::negation<std::is_same<T, U>>, std::is_constructible<T, U>,
-                std::is_assignable<T&, U>,
+                y_absl::negation<std::is_same<T, U> >,
+                std::is_constructible<T, U>, std::is_assignable<T&, U>,
                 y_absl::negation<
                     optional_internal::
                         is_constructible_convertible_assignable_from_optional<
-                            T, U>>>::value>::type>
+                            T, U> > >::value>::type>
   optional& operator=(optional<U>&& rhs) {
     if (rhs) {
       this->assign(std::move(*rhs));
diff --git a/contrib/restricted/abseil-cpp-tstring/y_absl/types/span.h b/contrib/restricted/abseil-cpp-tstring/y_absl/types/span.h
index 5961eb9927..ec5338601d 100644
--- a/contrib/restricted/abseil-cpp-tstring/y_absl/types/span.h
+++ b/contrib/restricted/abseil-cpp-tstring/y_absl/types/span.h
@@ -664,7 +664,8 @@ constexpr Span<T> MakeSpan(T* ptr, size_t size) noexcept {
 
 template <int&... ExplicitArgumentBarrier, typename T>
 Span<T> MakeSpan(T* begin, T* end) noexcept {
-  return Y_ABSL_HARDENING_ASSERT(begin <= end), Span<T>(begin, end - begin);
+  return Y_ABSL_HARDENING_ASSERT(begin <= end),
+         Span<T>(begin, static_cast<size_t>(end - begin));
 }
 
 template <int&... ExplicitArgumentBarrier, typename C>