Upd libc++ to 12 July 2022 81c48436bbd29736f77a111fc207e28854939907

1 files changed, 17 insertions, 0 deletions

diff --git a/contrib/libs/cxxsupp/libcxx/include/__bits b/contrib/libs/cxxsupp/libcxx/include/__bits
index f6835aa0785..c77b5c78503 100644
--- a/contrib/libs/cxxsupp/libcxx/include/__bits
+++ b/contrib/libs/cxxsupp/libcxx/include/__bits
@@ -43,6 +43,23 @@ int __libcpp_clz(unsigned long __x)      _NOEXCEPT { return __builtin_clzl(__x);
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 int __libcpp_clz(unsigned long long __x) _NOEXCEPT { return __builtin_clzll(__x); }
 
+#  ifndef _LIBCPP_HAS_NO_INT128
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+int __libcpp_clz(__uint128_t __x) _NOEXCEPT {
+  // The function is written in this form due to C++ constexpr limitations.
+  // The algorithm:
+  // - Test whether any bit in the high 64-bits is set
+  // - No bits set:
+  //   - The high 64-bits contain 64 leading zeros,
+  //   - Add the result of the low 64-bits.
+  // - Any bits set:
+  //   - The number of leading zeros of the input is the number of leading
+  //     zeros in the high 64-bits.
+  return ((__x >> 64) == 0)
+           ? (64 + __builtin_clzll(static_cast<unsigned long long>(__x)))
+           : __builtin_clzll(static_cast<unsigned long long>(__x >> 64));
+}
+#  endif
 
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 int __libcpp_popcount(unsigned __x)           _NOEXCEPT { return __builtin_popcount(__x); }