intermediate changes

ref:cde9a383711a11544ce7e107a78147fb96cc4029

1 files changed, 1688 insertions, 0 deletions

diff --git a/contrib/libs/snappy/snappy.cc b/contrib/libs/snappy/snappy.cc
new file mode 100644
index 0000000000..9351b0f21e
--- /dev/null
+++ b/contrib/libs/snappy/snappy.cc
@@ -0,0 +1,1688 @@
+// Copyright 2005 Google Inc. All Rights Reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "snappy.h"
+#include "snappy-internal.h"
+#include "snappy-sinksource.h"
+
+#if !defined(SNAPPY_HAVE_SSSE3)
+// __SSSE3__ is defined by GCC and Clang. Visual Studio doesn't target SIMD
+// support between SSE2 and AVX (so SSSE3 instructions require AVX support), and
+// defines __AVX__ when AVX support is available.
+#if defined(__SSSE3__) || defined(__AVX__)
+#define SNAPPY_HAVE_SSSE3 1
+#else
+#define SNAPPY_HAVE_SSSE3 0
+#endif
+#endif  // !defined(SNAPPY_HAVE_SSSE3)
+
+#if !defined(SNAPPY_HAVE_BMI2)
+// __BMI2__ is defined by GCC and Clang. Visual Studio doesn't target BMI2
+// specifically, but it does define __AVX2__ when AVX2 support is available.
+// Fortunately, AVX2 was introduced in Haswell, just like BMI2.
+//
+// BMI2 is not defined as a subset of AVX2 (unlike SSSE3 and AVX above). So,
+// GCC and Clang can build code with AVX2 enabled but BMI2 disabled, in which
+// case issuing BMI2 instructions results in a compiler error.
+#if defined(__BMI2__) || (defined(_MSC_VER) && defined(__AVX2__))
+#define SNAPPY_HAVE_BMI2 1
+#else
+#define SNAPPY_HAVE_BMI2 0
+#endif
+#endif  // !defined(SNAPPY_HAVE_BMI2)
+
+#if SNAPPY_HAVE_SSSE3
+// Please do not replace with <x86intrin.h>. or with headers that assume more
+// advanced SSE versions without checking with all the OWNERS.
+#include <tmmintrin.h>
+#endif
+
+#if SNAPPY_HAVE_BMI2
+// Please do not replace with <x86intrin.h>. or with headers that assume more
+// advanced SSE versions without checking with all the OWNERS.
+#include <immintrin.h>
+#endif
+
+#include <stdio.h>
+
+#include <algorithm>
+#include <string>
+#include <vector>
+#include <util/generic/string.h>
+
+namespace snappy {
+
+using internal::COPY_1_BYTE_OFFSET;
+using internal::COPY_2_BYTE_OFFSET;
+using internal::LITERAL;
+using internal::char_table;
+using internal::kMaximumTagLength;
+
+// Any hash function will produce a valid compressed bitstream, but a good
+// hash function reduces the number of collisions and thus yields better
+// compression for compressible input, and more speed for incompressible
+// input. Of course, it doesn't hurt if the hash function is reasonably fast
+// either, as it gets called a lot.
+static inline uint32 HashBytes(uint32 bytes, int shift) {
+  uint32 kMul = 0x1e35a7bd;
+  return (bytes * kMul) >> shift;
+}
+static inline uint32 Hash(const char* p, int shift) {
+  return HashBytes(UNALIGNED_LOAD32(p), shift);
+}
+
+size_t MaxCompressedLength(size_t source_len) {
+  // Compressed data can be defined as:
+  //    compressed := item* literal*
+  //    item       := literal* copy
+  //
+  // The trailing literal sequence has a space blowup of at most 62/60
+  // since a literal of length 60 needs one tag byte + one extra byte
+  // for length information.
+  //
+  // Item blowup is trickier to measure.  Suppose the "copy" op copies
+  // 4 bytes of data.  Because of a special check in the encoding code,
+  // we produce a 4-byte copy only if the offset is < 65536.  Therefore
+  // the copy op takes 3 bytes to encode, and this type of item leads
+  // to at most the 62/60 blowup for representing literals.
+  //
+  // Suppose the "copy" op copies 5 bytes of data.  If the offset is big
+  // enough, it will take 5 bytes to encode the copy op.  Therefore the
+  // worst case here is a one-byte literal followed by a five-byte copy.
+  // I.e., 6 bytes of input turn into 7 bytes of "compressed" data.
+  //
+  // This last factor dominates the blowup, so the final estimate is:
+  return 32 + source_len + source_len/6;
+}
+
+namespace {
+
+void UnalignedCopy64(const void* src, void* dst) {
+  char tmp[8];
+  memcpy(tmp, src, 8);
+  memcpy(dst, tmp, 8);
+}
+
+void UnalignedCopy128(const void* src, void* dst) {
+  // memcpy gets vectorized when the appropriate compiler options are used.
+  // For example, x86 compilers targeting SSE2+ will optimize to an SSE2 load
+  // and store.
+  char tmp[16];
+  memcpy(tmp, src, 16);
+  memcpy(dst, tmp, 16);
+}
+
+// Copy [src, src+(op_limit-op)) to [op, (op_limit-op)) a byte at a time. Used
+// for handling COPY operations where the input and output regions may overlap.
+// For example, suppose:
+//    src       == "ab"
+//    op        == src + 2
+//    op_limit  == op + 20
+// After IncrementalCopySlow(src, op, op_limit), the result will have eleven
+// copies of "ab"
+//    ababababababababababab
+// Note that this does not match the semantics of either memcpy() or memmove().
+inline char* IncrementalCopySlow(const char* src, char* op,
+                                 char* const op_limit) {
+  // TODO: Remove pragma when LLVM is aware this
+  // function is only called in cold regions and when cold regions don't get
+  // vectorized or unrolled.
+#ifdef __clang__
+#pragma clang loop unroll(disable)
+#endif
+  while (op < op_limit) {
+    *op++ = *src++;
+  }
+  return op_limit;
+}
+
+#if SNAPPY_HAVE_SSSE3
+
+// This is a table of shuffle control masks that can be used as the source
+// operand for PSHUFB to permute the contents of the destination XMM register
+// into a repeating byte pattern.
+alignas(16) const char pshufb_fill_patterns[7][16] = {
+  {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
+  {0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1},
+  {0, 1, 2, 0, 1, 2, 0, 1, 2, 0, 1, 2, 0, 1, 2, 0},
+  {0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3},
+  {0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 0, 1, 2, 3, 4, 0},
+  {0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3},
+  {0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1},
+};
+
+#endif  // SNAPPY_HAVE_SSSE3
+
+// Copy [src, src+(op_limit-op)) to [op, (op_limit-op)) but faster than
+// IncrementalCopySlow. buf_limit is the address past the end of the writable
+// region of the buffer.
+inline char* IncrementalCopy(const char* src, char* op, char* const op_limit,
+                             char* const buf_limit) {
+  // Terminology:
+  //
+  // slop = buf_limit - op
+  // pat  = op - src
+  // len  = limit - op
+  assert(src < op);
+  assert(op <= op_limit);
+  assert(op_limit <= buf_limit);
+  // NOTE: The compressor always emits 4 <= len <= 64. It is ok to assume that
+  // to optimize this function but we have to also handle other cases in case
+  // the input does not satisfy these conditions.
+
+  size_t pattern_size = op - src;
+  // The cases are split into different branches to allow the branch predictor,
+  // FDO, and static prediction hints to work better. For each input we list the
+  // ratio of invocations that match each condition.
+  //
+  // input        slop < 16   pat < 8  len > 16
+  // ------------------------------------------
+  // html|html4|cp   0%         1.01%    27.73%
+  // urls            0%         0.88%    14.79%
+  // jpg             0%        64.29%     7.14%
+  // pdf             0%         2.56%    58.06%
+  // txt[1-4]        0%         0.23%     0.97%
+  // pb              0%         0.96%    13.88%
+  // bin             0.01%     22.27%    41.17%
+  //
+  // It is very rare that we don't have enough slop for doing block copies. It
+  // is also rare that we need to expand a pattern. Small patterns are common
+  // for incompressible formats and for those we are plenty fast already.
+  // Lengths are normally not greater than 16 but they vary depending on the
+  // input. In general if we always predict len <= 16 it would be an ok
+  // prediction.
+  //
+  // In order to be fast we want a pattern >= 8 bytes and an unrolled loop
+  // copying 2x 8 bytes at a time.
+
+  // Handle the uncommon case where pattern is less than 8 bytes.
+  if (SNAPPY_PREDICT_FALSE(pattern_size < 8)) {
+#if SNAPPY_HAVE_SSSE3
+    // Load the first eight bytes into an 128-bit XMM register, then use PSHUFB
+    // to permute the register's contents in-place into a repeating sequence of
+    // the first "pattern_size" bytes.
+    // For example, suppose:
+    //    src       == "abc"
+    //    op        == op + 3
+    // After _mm_shuffle_epi8(), "pattern" will have five copies of "abc"
+    // followed by one byte of slop: abcabcabcabcabca.
+    //
+    // The non-SSE fallback implementation suffers from store-forwarding stalls
+    // because its loads and stores partly overlap. By expanding the pattern
+    // in-place, we avoid the penalty.
+    if (SNAPPY_PREDICT_TRUE(op <= buf_limit - 16)) {
+      const __m128i shuffle_mask = _mm_load_si128(
+          reinterpret_cast<const __m128i*>(pshufb_fill_patterns)
+          + pattern_size - 1);
+      const __m128i pattern = _mm_shuffle_epi8(
+          _mm_loadl_epi64(reinterpret_cast<const __m128i*>(src)), shuffle_mask);
+      // Uninitialized bytes are masked out by the shuffle mask.
+      // TODO: remove annotation and macro defs once MSan is fixed.
+      SNAPPY_ANNOTATE_MEMORY_IS_INITIALIZED(&pattern, sizeof(pattern));
+      pattern_size *= 16 / pattern_size;
+      char* op_end = std::min(op_limit, buf_limit - 15);
+      while (op < op_end) {
+        _mm_storeu_si128(reinterpret_cast<__m128i*>(op), pattern);
+        op += pattern_size;
+      }
+      if (SNAPPY_PREDICT_TRUE(op >= op_limit)) return op_limit;
+    }
+    return IncrementalCopySlow(src, op, op_limit);
+#else  // !SNAPPY_HAVE_SSSE3
+    // If plenty of buffer space remains, expand the pattern to at least 8
+    // bytes. The way the following loop is written, we need 8 bytes of buffer
+    // space if pattern_size >= 4, 11 bytes if pattern_size is 1 or 3, and 10
+    // bytes if pattern_size is 2.  Precisely encoding that is probably not
+    // worthwhile; instead, invoke the slow path if we cannot write 11 bytes
+    // (because 11 are required in the worst case).
+    if (SNAPPY_PREDICT_TRUE(op <= buf_limit - 11)) {
+      while (pattern_size < 8) {
+        UnalignedCopy64(src, op);
+        op += pattern_size;
+        pattern_size *= 2;
+      }
+      if (SNAPPY_PREDICT_TRUE(op >= op_limit)) return op_limit;
+    } else {
+      return IncrementalCopySlow(src, op, op_limit);
+    }
+#endif  // SNAPPY_HAVE_SSSE3
+  }
+  assert(pattern_size >= 8);
+
+  // Copy 2x 8 bytes at a time. Because op - src can be < 16, a single
+  // UnalignedCopy128 might overwrite data in op. UnalignedCopy64 is safe
+  // because expanding the pattern to at least 8 bytes guarantees that
+  // op - src >= 8.
+  //
+  // Typically, the op_limit is the gating factor so try to simplify the loop
+  // based on that.
+  if (SNAPPY_PREDICT_TRUE(op_limit <= buf_limit - 16)) {
+    // There is at least one, and at most four 16-byte blocks. Writing four
+    // conditionals instead of a loop allows FDO to layout the code with respect
+    // to the actual probabilities of each length.
+    // TODO: Replace with loop with trip count hint.
+    UnalignedCopy64(src, op);
+    UnalignedCopy64(src + 8, op + 8);
+
+    if (op + 16 < op_limit) {
+      UnalignedCopy64(src + 16, op + 16);
+      UnalignedCopy64(src + 24, op + 24);
+    }
+    if (op + 32 < op_limit) {
+      UnalignedCopy64(src + 32, op + 32);
+      UnalignedCopy64(src + 40, op + 40);
+    }
+    if (op + 48 < op_limit) {
+      UnalignedCopy64(src + 48, op + 48);
+      UnalignedCopy64(src + 56, op + 56);
+    }
+    return op_limit;
+  }
+
+  // Fall back to doing as much as we can with the available slop in the
+  // buffer. This code path is relatively cold however so we save code size by
+  // avoiding unrolling and vectorizing.
+  //
+  // TODO: Remove pragma when when cold regions don't get vectorized
+  // or unrolled.
+#ifdef __clang__
+#pragma clang loop unroll(disable)
+#endif
+  for (char *op_end = buf_limit - 16; op < op_end; op += 16, src += 16) {
+    UnalignedCopy64(src, op);
+    UnalignedCopy64(src + 8, op + 8);
+  }
+  if (op >= op_limit)
+    return op_limit;
+
+  // We only take this branch if we didn't have enough slop and we can do a
+  // single 8 byte copy.
+  if (SNAPPY_PREDICT_FALSE(op <= buf_limit - 8)) {
+    UnalignedCopy64(src, op);
+    src += 8;
+    op += 8;
+  }
+  return IncrementalCopySlow(src, op, op_limit);
+}
+
+}  // namespace
+
+template <bool allow_fast_path>
+static inline char* EmitLiteral(char* op,
+                                const char* literal,
+                                int len) {
+  // The vast majority of copies are below 16 bytes, for which a
+  // call to memcpy is overkill. This fast path can sometimes
+  // copy up to 15 bytes too much, but that is okay in the
+  // main loop, since we have a bit to go on for both sides:
+  //
+  //   - The input will always have kInputMarginBytes = 15 extra
+  //     available bytes, as long as we're in the main loop, and
+  //     if not, allow_fast_path = false.
+  //   - The output will always have 32 spare bytes (see
+  //     MaxCompressedLength).
+  assert(len > 0);      // Zero-length literals are disallowed
+  int n = len - 1;
+  if (allow_fast_path && len <= 16) {
+    // Fits in tag byte
+    *op++ = LITERAL | (n << 2);
+
+    UnalignedCopy128(literal, op);
+    return op + len;
+  }
+
+  if (n < 60) {
+    // Fits in tag byte
+    *op++ = LITERAL | (n << 2);
+  } else {
+    int count = (Bits::Log2Floor(n) >> 3) + 1;
+    assert(count >= 1);
+    assert(count <= 4);
+    *op++ = LITERAL | ((59 + count) << 2);
+    // Encode in upcoming bytes.
+    // Write 4 bytes, though we may care about only 1 of them. The output buffer
+    // is guaranteed to have at least 3 more spaces left as 'len >= 61' holds
+    // here and there is a memcpy of size 'len' below.
+    LittleEndian::Store32(op, n);
+    op += count;
+  }
+  memcpy(op, literal, len);
+  return op + len;
+}
+
+template <bool len_less_than_12>
+static inline char* EmitCopyAtMost64(char* op, size_t offset, size_t len) {
+  assert(len <= 64);
+  assert(len >= 4);
+  assert(offset < 65536);
+  assert(len_less_than_12 == (len < 12));
+
+  if (len_less_than_12 && SNAPPY_PREDICT_TRUE(offset < 2048)) {
+    // offset fits in 11 bits.  The 3 highest go in the top of the first byte,
+    // and the rest go in the second byte.
+    *op++ = COPY_1_BYTE_OFFSET + ((len - 4) << 2) + ((offset >> 3) & 0xe0);
+    *op++ = offset & 0xff;
+  } else {
+    // Write 4 bytes, though we only care about 3 of them.  The output buffer
+    // is required to have some slack, so the extra byte won't overrun it.
+    uint32 u = COPY_2_BYTE_OFFSET + ((len - 1) << 2) + (offset << 8);
+    LittleEndian::Store32(op, u);
+    op += 3;
+  }
+  return op;
+}
+
+template <bool len_less_than_12>
+static inline char* EmitCopy(char* op, size_t offset, size_t len) {
+  assert(len_less_than_12 == (len < 12));
+  if (len_less_than_12) {
+    return EmitCopyAtMost64</*len_less_than_12=*/true>(op, offset, len);
+  } else {
+    // A special case for len <= 64 might help, but so far measurements suggest
+    // it's in the noise.
+
+    // Emit 64 byte copies but make sure to keep at least four bytes reserved.
+    while (SNAPPY_PREDICT_FALSE(len >= 68)) {
+      op = EmitCopyAtMost64</*len_less_than_12=*/false>(op, offset, 64);
+      len -= 64;
+    }
+
+    // One or two copies will now finish the job.
+    if (len > 64) {
+      op = EmitCopyAtMost64</*len_less_than_12=*/false>(op, offset, 60);
+      len -= 60;
+    }
+
+    // Emit remainder.
+    if (len < 12) {
+      op = EmitCopyAtMost64</*len_less_than_12=*/true>(op, offset, len);
+    } else {
+      op = EmitCopyAtMost64</*len_less_than_12=*/false>(op, offset, len);
+    }
+    return op;
+  }
+}
+
+bool GetUncompressedLength(const char* start, size_t n, size_t* result) {
+  uint32 v = 0;
+  const char* limit = start + n;
+  if (Varint::Parse32WithLimit(start, limit, &v) != NULL) {
+    *result = v;
+    return true;
+  } else {
+    return false;
+  }
+}
+
+namespace {
+uint32 CalculateTableSize(uint32 input_size) {
+  static_assert(
+      kMaxHashTableSize >= kMinHashTableSize,
+      "kMaxHashTableSize should be greater or equal to kMinHashTableSize.");
+  if (input_size > kMaxHashTableSize) {
+    return kMaxHashTableSize;
+  }
+  if (input_size < kMinHashTableSize) {
+    return kMinHashTableSize;
+  }
+  // This is equivalent to Log2Ceiling(input_size), assuming input_size > 1.
+  // 2 << Log2Floor(x - 1) is equivalent to 1 << (1 + Log2Floor(x - 1)).
+  return 2u << Bits::Log2Floor(input_size - 1);
+}
+}  // namespace
+
+namespace internal {
+WorkingMemory::WorkingMemory(size_t input_size) {
+  const size_t max_fragment_size = std::min(input_size, kBlockSize);
+  const size_t table_size = CalculateTableSize(max_fragment_size);
+  size_ = table_size * sizeof(*table_) + max_fragment_size +
+          MaxCompressedLength(max_fragment_size);
+  mem_ = std::allocator<char>().allocate(size_);
+  table_ = reinterpret_cast<uint16*>(mem_);
+  input_ = mem_ + table_size * sizeof(*table_);
+  output_ = input_ + max_fragment_size;
+}
+
+WorkingMemory::~WorkingMemory() {
+  std::allocator<char>().deallocate(mem_, size_);
+}
+
+uint16* WorkingMemory::GetHashTable(size_t fragment_size,
+                                    int* table_size) const {
+  const size_t htsize = CalculateTableSize(fragment_size);
+  memset(table_, 0, htsize * sizeof(*table_));
+  *table_size = htsize;
+  return table_;
+}
+}  // end namespace internal
+
+// For 0 <= offset <= 4, GetUint32AtOffset(GetEightBytesAt(p), offset) will
+// equal UNALIGNED_LOAD32(p + offset).  Motivation: On x86-64 hardware we have
+// empirically found that overlapping loads such as
+//  UNALIGNED_LOAD32(p) ... UNALIGNED_LOAD32(p+1) ... UNALIGNED_LOAD32(p+2)
+// are slower than UNALIGNED_LOAD64(p) followed by shifts and casts to uint32.
+//
+// We have different versions for 64- and 32-bit; ideally we would avoid the
+// two functions and just inline the UNALIGNED_LOAD64 call into
+// GetUint32AtOffset, but GCC (at least not as of 4.6) is seemingly not clever
+// enough to avoid loading the value multiple times then. For 64-bit, the load
+// is done when GetEightBytesAt() is called, whereas for 32-bit, the load is
+// done at GetUint32AtOffset() time.
+
+#ifdef ARCH_K8
+
+typedef uint64 EightBytesReference;
+
+static inline EightBytesReference GetEightBytesAt(const char* ptr) {
+  return UNALIGNED_LOAD64(ptr);
+}
+
+static inline uint32 GetUint32AtOffset(uint64 v, int offset) {
+  assert(offset >= 0);
+  assert(offset <= 4);
+  return v >> (LittleEndian::IsLittleEndian() ? 8 * offset : 32 - 8 * offset);
+}
+
+#else
+
+typedef const char* EightBytesReference;
+
+static inline EightBytesReference GetEightBytesAt(const char* ptr) {
+  return ptr;
+}
+
+static inline uint32 GetUint32AtOffset(const char* v, int offset) {
+  assert(offset >= 0);
+  assert(offset <= 4);
+  return UNALIGNED_LOAD32(v + offset);
+}
+
+#endif
+
+// Flat array compression that does not emit the "uncompressed length"
+// prefix. Compresses "input" string to the "*op" buffer.
+//
+// REQUIRES: "input" is at most "kBlockSize" bytes long.
+// REQUIRES: "op" points to an array of memory that is at least
+// "MaxCompressedLength(input.size())" in size.
+// REQUIRES: All elements in "table[0..table_size-1]" are initialized to zero.
+// REQUIRES: "table_size" is a power of two
+//
+// Returns an "end" pointer into "op" buffer.
+// "end - op" is the compressed size of "input".
+namespace internal {
+char* CompressFragment(const char* input,
+                       size_t input_size,
+                       char* op,
+                       uint16* table,
+                       const int table_size) {
+  // "ip" is the input pointer, and "op" is the output pointer.
+  const char* ip = input;
+  assert(input_size <= kBlockSize);
+  assert((table_size & (table_size - 1)) == 0);  // table must be power of two
+  const int shift = 32 - Bits::Log2Floor(table_size);
+  assert(static_cast<int>(kuint32max >> shift) == table_size - 1);
+  const char* ip_end = input + input_size;
+  const char* base_ip = ip;
+  // Bytes in [next_emit, ip) will be emitted as literal bytes.  Or
+  // [next_emit, ip_end) after the main loop.
+  const char* next_emit = ip;
+
+  const size_t kInputMarginBytes = 15;
+  if (SNAPPY_PREDICT_TRUE(input_size >= kInputMarginBytes)) {
+    const char* ip_limit = input + input_size - kInputMarginBytes;
+
+    for (uint32 next_hash = Hash(++ip, shift); ; ) {
+      assert(next_emit < ip);
+      // The body of this loop calls EmitLiteral once and then EmitCopy one or
+      // more times.  (The exception is that when we're close to exhausting
+      // the input we goto emit_remainder.)
+      //
+      // In the first iteration of this loop we're just starting, so
+      // there's nothing to copy, so calling EmitLiteral once is
+      // necessary.  And we only start a new iteration when the
+      // current iteration has determined that a call to EmitLiteral will
+      // precede the next call to EmitCopy (if any).
+      //
+      // Step 1: Scan forward in the input looking for a 4-byte-long match.
+      // If we get close to exhausting the input then goto emit_remainder.
+      //
+      // Heuristic match skipping: If 32 bytes are scanned with no matches
+      // found, start looking only at every other byte. If 32 more bytes are
+      // scanned (or skipped), look at every third byte, etc.. When a match is
+      // found, immediately go back to looking at every byte. This is a small
+      // loss (~5% performance, ~0.1% density) for compressible data due to more
+      // bookkeeping, but for non-compressible data (such as JPEG) it's a huge
+      // win since the compressor quickly "realizes" the data is incompressible
+      // and doesn't bother looking for matches everywhere.
+      //
+      // The "skip" variable keeps track of how many bytes there are since the
+      // last match; dividing it by 32 (ie. right-shifting by five) gives the
+      // number of bytes to move ahead for each iteration.
+      uint32 skip = 32;
+
+      const char* next_ip = ip;
+      const char* candidate;
+      do {
+        ip = next_ip;
+        uint32 hash = next_hash;
+        assert(hash == Hash(ip, shift));
+        uint32 bytes_between_hash_lookups = skip >> 5;
+        skip += bytes_between_hash_lookups;
+        next_ip = ip + bytes_between_hash_lookups;
+        if (SNAPPY_PREDICT_FALSE(next_ip > ip_limit)) {
+          goto emit_remainder;
+        }
+        next_hash = Hash(next_ip, shift);
+        candidate = base_ip + table[hash];
+        assert(candidate >= base_ip);
+        assert(candidate < ip);
+
+        table[hash] = ip - base_ip;
+      } while (SNAPPY_PREDICT_TRUE(UNALIGNED_LOAD32(ip) !=
+                                 UNALIGNED_LOAD32(candidate)));
+
+      // Step 2: A 4-byte match has been found.  We'll later see if more
+      // than 4 bytes match.  But, prior to the match, input
+      // bytes [next_emit, ip) are unmatched.  Emit them as "literal bytes."
+      assert(next_emit + 16 <= ip_end);
+      op = EmitLiteral</*allow_fast_path=*/true>(op, next_emit, ip - next_emit);
+
+      // Step 3: Call EmitCopy, and then see if another EmitCopy could
+      // be our next move.  Repeat until we find no match for the
+      // input immediately after what was consumed by the last EmitCopy call.
+      //
+      // If we exit this loop normally then we need to call EmitLiteral next,
+      // though we don't yet know how big the literal will be.  We handle that
+      // by proceeding to the next iteration of the main loop.  We also can exit
+      // this loop via goto if we get close to exhausting the input.
+      EightBytesReference input_bytes;
+      uint32 candidate_bytes = 0;
+
+      do {
+        // We have a 4-byte match at ip, and no need to emit any
+        // "literal bytes" prior to ip.
+        const char* base = ip;
+        std::pair<size_t, bool> p =
+            FindMatchLength(candidate + 4, ip + 4, ip_end);
+        size_t matched = 4 + p.first;
+        ip += matched;
+        size_t offset = base - candidate;
+        assert(0 == memcmp(base, candidate, matched));
+        if (p.second) {
+          op = EmitCopy</*len_less_than_12=*/true>(op, offset, matched);
+        } else {
+          op = EmitCopy</*len_less_than_12=*/false>(op, offset, matched);
+        }
+        next_emit = ip;
+        if (SNAPPY_PREDICT_FALSE(ip >= ip_limit)) {
+          goto emit_remainder;
+        }
+        // We are now looking for a 4-byte match again.  We read
+        // table[Hash(ip, shift)] for that.  To improve compression,
+        // we also update table[Hash(ip - 1, shift)] and table[Hash(ip, shift)].
+        input_bytes = GetEightBytesAt(ip - 1);
+        uint32 prev_hash = HashBytes(GetUint32AtOffset(input_bytes, 0), shift);
+        table[prev_hash] = ip - base_ip - 1;
+        uint32 cur_hash = HashBytes(GetUint32AtOffset(input_bytes, 1), shift);
+        candidate = base_ip + table[cur_hash];
+        candidate_bytes = UNALIGNED_LOAD32(candidate);
+        table[cur_hash] = ip - base_ip;
+      } while (GetUint32AtOffset(input_bytes, 1) == candidate_bytes);
+
+      next_hash = HashBytes(GetUint32AtOffset(input_bytes, 2), shift);
+      ++ip;
+    }
+  }
+
+ emit_remainder:
+  // Emit the remaining bytes as a literal
+  if (next_emit < ip_end) {
+    op = EmitLiteral</*allow_fast_path=*/false>(op, next_emit,
+                                                ip_end - next_emit);
+  }
+
+  return op;
+}
+}  // end namespace internal
+
+// Called back at avery compression call to trace parameters and sizes.
+static inline void Report(const char *algorithm, size_t compressed_size,
+                          size_t uncompressed_size) {}
+
+// Signature of output types needed by decompression code.
+// The decompression code is templatized on a type that obeys this
+// signature so that we do not pay virtual function call overhead in
+// the middle of a tight decompression loop.
+//
+// class DecompressionWriter {
+//  public:
+//   // Called before decompression
+//   void SetExpectedLength(size_t length);
+//
+//   // Called after decompression
+//   bool CheckLength() const;
+//
+//   // Called repeatedly during decompression
+//   bool Append(const char* ip, size_t length);
+//   bool AppendFromSelf(uint32 offset, size_t length);
+//
+//   // The rules for how TryFastAppend differs from Append are somewhat
+//   // convoluted:
+//   //
+//   //  - TryFastAppend is allowed to decline (return false) at any
+//   //    time, for any reason -- just "return false" would be
+//   //    a perfectly legal implementation of TryFastAppend.
+//   //    The intention is for TryFastAppend to allow a fast path
+//   //    in the common case of a small append.
+//   //  - TryFastAppend is allowed to read up to <available> bytes
+//   //    from the input buffer, whereas Append is allowed to read
+//   //    <length>. However, if it returns true, it must leave
+//   //    at least five (kMaximumTagLength) bytes in the input buffer
+//   //    afterwards, so that there is always enough space to read the
+//   //    next tag without checking for a refill.
+//   //  - TryFastAppend must always return decline (return false)
+//   //    if <length> is 61 or more, as in this case the literal length is not
+//   //    decoded fully. In practice, this should not be a big problem,
+//   //    as it is unlikely that one would implement a fast path accepting
+//   //    this much data.
+//   //
+//   bool TryFastAppend(const char* ip, size_t available, size_t length);
+// };
+
+static inline uint32 ExtractLowBytes(uint32 v, int n) {
+  assert(n >= 0);
+  assert(n <= 4);
+#if SNAPPY_HAVE_BMI2
+  return _bzhi_u32(v, 8 * n);
+#else
+  // This needs to be wider than uint32 otherwise `mask << 32` will be
+  // undefined.
+  uint64 mask = 0xffffffff;
+  return v & ~(mask << (8 * n));
+#endif
+}
+
+static inline bool LeftShiftOverflows(uint8 value, uint32 shift) {
+  assert(shift < 32);
+  static const uint8 masks[] = {
+      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  //
+      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  //
+      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  //
+      0x00, 0x80, 0xc0, 0xe0, 0xf0, 0xf8, 0xfc, 0xfe};
+  return (value & masks[shift]) != 0;
+}
+
+// Helper class for decompression
+class SnappyDecompressor {
+ private:
+  Source*       reader_;         // Underlying source of bytes to decompress
+  const char*   ip_;             // Points to next buffered byte
+  const char*   ip_limit_;       // Points just past buffered bytes
+  uint32        peeked_;         // Bytes peeked from reader (need to skip)
+  bool          eof_;            // Hit end of input without an error?
+  char          scratch_[kMaximumTagLength];  // See RefillTag().
+
+  // Ensure that all of the tag metadata for the next tag is available
+  // in [ip_..ip_limit_-1].  Also ensures that [ip,ip+4] is readable even
+  // if (ip_limit_ - ip_ < 5).
+  //
+  // Returns true on success, false on error or end of input.
+  bool RefillTag();
+
+ public:
+  explicit SnappyDecompressor(Source* reader)
+      : reader_(reader),
+        ip_(NULL),
+        ip_limit_(NULL),
+        peeked_(0),
+        eof_(false) {
+  }
+
+  ~SnappyDecompressor() {
+    // Advance past any bytes we peeked at from the reader
+    reader_->Skip(peeked_);
+  }
+
+  // Returns true iff we have hit the end of the input without an error.
+  bool eof() const {
+    return eof_;
+  }
+
+  // Read the uncompressed length stored at the start of the compressed data.
+  // On success, stores the length in *result and returns true.
+  // On failure, returns false.
+  bool ReadUncompressedLength(uint32* result) {
+    assert(ip_ == NULL);       // Must not have read anything yet
+    // Length is encoded in 1..5 bytes
+    *result = 0;
+    uint32 shift = 0;
+    while (true) {
+      if (shift >= 32) return false;
+      size_t n;
+      const char* ip = reader_->Peek(&n);
+      if (n == 0) return false;
+      const unsigned char c = *(reinterpret_cast<const unsigned char*>(ip));
+      reader_->Skip(1);
+      uint32 val = c & 0x7f;
+      if (LeftShiftOverflows(static_cast<uint8>(val), shift)) return false;
+      *result |= val << shift;
+      if (c < 128) {
+        break;
+      }
+      shift += 7;
+    }
+    return true;
+  }
+
+  // Process the next item found in the input.
+  // Returns true if successful, false on error or end of input.
+  template <class Writer>
+#if defined(__GNUC__) && defined(__x86_64__)
+  __attribute__((aligned(32)))
+#endif
+  void DecompressAllTags(Writer* writer) {
+    // In x86, pad the function body to start 16 bytes later. This function has
+    // a couple of hotspots that are highly sensitive to alignment: we have
+    // observed regressions by more than 20% in some metrics just by moving the
+    // exact same code to a different position in the benchmark binary.
+    //
+    // Putting this code on a 32-byte-aligned boundary + 16 bytes makes us hit
+    // the "lucky" case consistently. Unfortunately, this is a very brittle
+    // workaround, and future differences in code generation may reintroduce
+    // this regression. If you experience a big, difficult to explain, benchmark
+    // performance regression here, first try removing this hack.
+#if defined(__GNUC__) && defined(__x86_64__)
+    // Two 8-byte "NOP DWORD ptr [EAX + EAX*1 + 00000000H]" instructions.
+    asm(".byte 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00");
+    asm(".byte 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00");
+#endif
+
+    const char* ip = ip_;
+    // We could have put this refill fragment only at the beginning of the loop.
+    // However, duplicating it at the end of each branch gives the compiler more
+    // scope to optimize the <ip_limit_ - ip> expression based on the local
+    // context, which overall increases speed.
+    #define MAYBE_REFILL() \
+        if (ip_limit_ - ip < kMaximumTagLength) { \
+          ip_ = ip; \
+          if (!RefillTag()) return; \
+          ip = ip_; \
+        }
+
+    MAYBE_REFILL();
+    for ( ;; ) {
+      const unsigned char c = *(reinterpret_cast<const unsigned char*>(ip++));
+
+      // Ratio of iterations that have LITERAL vs non-LITERAL for different
+      // inputs.
+      //
+      // input          LITERAL  NON_LITERAL
+      // -----------------------------------
+      // html|html4|cp   23%        77%
+      // urls            36%        64%
+      // jpg             47%        53%
+      // pdf             19%        81%
+      // txt[1-4]        25%        75%
+      // pb              24%        76%
+      // bin             24%        76%
+      if (SNAPPY_PREDICT_FALSE((c & 0x3) == LITERAL)) {
+        size_t literal_length = (c >> 2) + 1u;
+        if (writer->TryFastAppend(ip, ip_limit_ - ip, literal_length)) {
+          assert(literal_length < 61);
+          ip += literal_length;
+          // NOTE: There is no MAYBE_REFILL() here, as TryFastAppend()
+          // will not return true unless there's already at least five spare
+          // bytes in addition to the literal.
+          continue;
+        }
+        if (SNAPPY_PREDICT_FALSE(literal_length >= 61)) {
+          // Long literal.
+          const size_t literal_length_length = literal_length - 60;
+          literal_length =
+              ExtractLowBytes(LittleEndian::Load32(ip), literal_length_length) +
+              1;
+          ip += literal_length_length;
+        }
+
+        size_t avail = ip_limit_ - ip;
+        while (avail < literal_length) {
+          if (!writer->Append(ip, avail)) return;
+          literal_length -= avail;
+          reader_->Skip(peeked_);
+          size_t n;
+          ip = reader_->Peek(&n);
+          avail = n;
+          peeked_ = avail;
+          if (avail == 0) return;  // Premature end of input
+          ip_limit_ = ip + avail;
+        }
+        if (!writer->Append(ip, literal_length)) {
+          return;
+        }
+        ip += literal_length;
+        MAYBE_REFILL();
+      } else {
+        const size_t entry = char_table[c];
+        const size_t trailer =
+            ExtractLowBytes(LittleEndian::Load32(ip), entry >> 11);
+        const size_t length = entry & 0xff;
+        ip += entry >> 11;
+
+        // copy_offset/256 is encoded in bits 8..10.  By just fetching
+        // those bits, we get copy_offset (since the bit-field starts at
+        // bit 8).
+        const size_t copy_offset = entry & 0x700;
+        if (!writer->AppendFromSelf(copy_offset + trailer, length)) {
+          return;
+        }
+        MAYBE_REFILL();
+      }
+    }
+
+#undef MAYBE_REFILL
+  }
+};
+
+bool SnappyDecompressor::RefillTag() {
+  const char* ip = ip_;
+  if (ip == ip_limit_) {
+    // Fetch a new fragment from the reader
+    reader_->Skip(peeked_);   // All peeked bytes are used up
+    size_t n;
+    ip = reader_->Peek(&n);
+    peeked_ = n;
+    eof_ = (n == 0);
+    if (eof_) return false;
+    ip_limit_ = ip + n;
+  }
+
+  // Read the tag character
+  assert(ip < ip_limit_);
+  const unsigned char c = *(reinterpret_cast<const unsigned char*>(ip));
+  const uint32 entry = char_table[c];
+  const uint32 needed = (entry >> 11) + 1;  // +1 byte for 'c'
+  assert(needed <= sizeof(scratch_));
+
+  // Read more bytes from reader if needed
+  uint32 nbuf = ip_limit_ - ip;
+  if (nbuf < needed) {
+    // Stitch together bytes from ip and reader to form the word
+    // contents.  We store the needed bytes in "scratch_".  They
+    // will be consumed immediately by the caller since we do not
+    // read more than we need.
+    memmove(scratch_, ip, nbuf);
+    reader_->Skip(peeked_);  // All peeked bytes are used up
+    peeked_ = 0;
+    while (nbuf < needed) {
+      size_t length;
+      const char* src = reader_->Peek(&length);
+      if (length == 0) return false;
+      uint32 to_add = std::min<uint32>(needed - nbuf, length);
+      memcpy(scratch_ + nbuf, src, to_add);
+      nbuf += to_add;
+      reader_->Skip(to_add);
+    }
+    assert(nbuf == needed);
+    ip_ = scratch_;
+    ip_limit_ = scratch_ + needed;
+  } else if (nbuf < kMaximumTagLength) {
+    // Have enough bytes, but move into scratch_ so that we do not
+    // read past end of input
+    memmove(scratch_, ip, nbuf);
+    reader_->Skip(peeked_);  // All peeked bytes are used up
+    peeked_ = 0;
+    ip_ = scratch_;
+    ip_limit_ = scratch_ + nbuf;
+  } else {
+    // Pass pointer to buffer returned by reader_.
+    ip_ = ip;
+  }
+  return true;
+}
+
+template <typename Writer>
+static bool InternalUncompress(Source* r, Writer* writer) {
+  // Read the uncompressed length from the front of the compressed input
+  SnappyDecompressor decompressor(r);
+  uint32 uncompressed_len = 0;
+  if (!decompressor.ReadUncompressedLength(&uncompressed_len)) return false;
+
+  return InternalUncompressAllTags(&decompressor, writer, r->Available(),
+                                   uncompressed_len);
+}
+
+template <typename Writer>
+static bool InternalUncompressAllTags(SnappyDecompressor* decompressor,
+                                      Writer* writer,
+                                      uint32 compressed_len,
+                                      uint32 uncompressed_len) {
+  Report("snappy_uncompress", compressed_len, uncompressed_len);
+
+  writer->SetExpectedLength(uncompressed_len);
+
+  // Process the entire input
+  decompressor->DecompressAllTags(writer);
+  writer->Flush();
+  return (decompressor->eof() && writer->CheckLength());
+}
+
+bool GetUncompressedLength(Source* source, uint32* result) {
+  SnappyDecompressor decompressor(source);
+  return decompressor.ReadUncompressedLength(result);
+}
+
+size_t Compress(Source* reader, Sink* writer) {
+  size_t written = 0;
+  size_t N = reader->Available();
+  const size_t uncompressed_size = N;
+  char ulength[Varint::kMax32];
+  char* p = Varint::Encode32(ulength, N);
+  writer->Append(ulength, p-ulength);
+  written += (p - ulength);
+
+  internal::WorkingMemory wmem(N);
+
+  while (N > 0) {
+    // Get next block to compress (without copying if possible)
+    size_t fragment_size;
+    const char* fragment = reader->Peek(&fragment_size);
+    assert(fragment_size != 0);  // premature end of input
+    const size_t num_to_read = std::min(N, kBlockSize);
+    size_t bytes_read = fragment_size;
+
+    size_t pending_advance = 0;
+    if (bytes_read >= num_to_read) {
+      // Buffer returned by reader is large enough
+      pending_advance = num_to_read;
+      fragment_size = num_to_read;
+    } else {
+      char* scratch = wmem.GetScratchInput();
+      memcpy(scratch, fragment, bytes_read);
+      reader->Skip(bytes_read);
+
+      while (bytes_read < num_to_read) {
+        fragment = reader->Peek(&fragment_size);
+        size_t n = std::min<size_t>(fragment_size, num_to_read - bytes_read);
+        memcpy(scratch + bytes_read, fragment, n);
+        bytes_read += n;
+        reader->Skip(n);
+      }
+      assert(bytes_read == num_to_read);
+      fragment = scratch;
+      fragment_size = num_to_read;
+    }
+    assert(fragment_size == num_to_read);
+
+    // Get encoding table for compression
+    int table_size;
+    uint16* table = wmem.GetHashTable(num_to_read, &table_size);
+
+    // Compress input_fragment and append to dest
+    const int max_output = MaxCompressedLength(num_to_read);
+
+    // Need a scratch buffer for the output, in case the byte sink doesn't
+    // have room for us directly.
+
+    // Since we encode kBlockSize regions followed by a region
+    // which is <= kBlockSize in length, a previously allocated
+    // scratch_output[] region is big enough for this iteration.
+    char* dest = writer->GetAppendBuffer(max_output, wmem.GetScratchOutput());
+    char* end = internal::CompressFragment(fragment, fragment_size, dest, table,
+                                           table_size);
+    writer->Append(dest, end - dest);
+    written += (end - dest);
+
+    N -= num_to_read;
+    reader->Skip(pending_advance);
+  }
+
+  Report("snappy_compress", written, uncompressed_size);
+
+  return written;
+}
+
+// -----------------------------------------------------------------------
+// IOVec interfaces
+// -----------------------------------------------------------------------
+
+// A type that writes to an iovec.
+// Note that this is not a "ByteSink", but a type that matches the
+// Writer template argument to SnappyDecompressor::DecompressAllTags().
+class SnappyIOVecWriter {
+ private:
+  // output_iov_end_ is set to iov + count and used to determine when
+  // the end of the iovs is reached.
+  const struct iovec* output_iov_end_;
+
+#if !defined(NDEBUG)
+  const struct iovec* output_iov_;
+#endif  // !defined(NDEBUG)
+
+  // Current iov that is being written into.
+  const struct iovec* curr_iov_;
+
+  // Pointer to current iov's write location.
+  char* curr_iov_output_;
+
+  // Remaining bytes to write into curr_iov_output.
+  size_t curr_iov_remaining_;
+
+  // Total bytes decompressed into output_iov_ so far.
+  size_t total_written_;
+
+  // Maximum number of bytes that will be decompressed into output_iov_.
+  size_t output_limit_;
+
+  static inline char* GetIOVecPointer(const struct iovec* iov, size_t offset) {
+    return reinterpret_cast<char*>(iov->iov_base) + offset;
+  }
+
+ public:
+  // Does not take ownership of iov. iov must be valid during the
+  // entire lifetime of the SnappyIOVecWriter.
+  inline SnappyIOVecWriter(const struct iovec* iov, size_t iov_count)
+      : output_iov_end_(iov + iov_count),
+#if !defined(NDEBUG)
+        output_iov_(iov),
+#endif  // !defined(NDEBUG)
+        curr_iov_(iov),
+        curr_iov_output_(iov_count ? reinterpret_cast<char*>(iov->iov_base)
+                                   : nullptr),
+        curr_iov_remaining_(iov_count ? iov->iov_len : 0),
+        total_written_(0),
+        output_limit_(-1) {}
+
+  inline void SetExpectedLength(size_t len) {
+    output_limit_ = len;
+  }
+
+  inline bool CheckLength() const {
+    return total_written_ == output_limit_;
+  }
+
+  inline bool Append(const char* ip, size_t len) {
+    if (total_written_ + len > output_limit_) {
+      return false;
+    }
+
+    return AppendNoCheck(ip, len);
+  }
+
+  inline bool AppendNoCheck(const char* ip, size_t len) {
+    while (len > 0) {
+      if (curr_iov_remaining_ == 0) {
+        // This iovec is full. Go to the next one.
+        if (curr_iov_ + 1 >= output_iov_end_) {
+          return false;
+        }
+        ++curr_iov_;
+        curr_iov_output_ = reinterpret_cast<char*>(curr_iov_->iov_base);
+        curr_iov_remaining_ = curr_iov_->iov_len;
+      }
+
+      const size_t to_write = std::min(len, curr_iov_remaining_);
+      memcpy(curr_iov_output_, ip, to_write);
+      curr_iov_output_ += to_write;
+      curr_iov_remaining_ -= to_write;
+      total_written_ += to_write;
+      ip += to_write;
+      len -= to_write;
+    }
+
+    return true;
+  }
+
+  inline bool TryFastAppend(const char* ip, size_t available, size_t len) {
+    const size_t space_left = output_limit_ - total_written_;
+    if (len <= 16 && available >= 16 + kMaximumTagLength && space_left >= 16 &&
+        curr_iov_remaining_ >= 16) {
+      // Fast path, used for the majority (about 95%) of invocations.
+      UnalignedCopy128(ip, curr_iov_output_);
+      curr_iov_output_ += len;
+      curr_iov_remaining_ -= len;
+      total_written_ += len;
+      return true;
+    }
+
+    return false;
+  }
+
+  inline bool AppendFromSelf(size_t offset, size_t len) {
+    // See SnappyArrayWriter::AppendFromSelf for an explanation of
+    // the "offset - 1u" trick.
+    if (offset - 1u >= total_written_) {
+      return false;
+    }
+    const size_t space_left = output_limit_ - total_written_;
+    if (len > space_left) {
+      return false;
+    }
+
+    // Locate the iovec from which we need to start the copy.
+    const iovec* from_iov = curr_iov_;
+    size_t from_iov_offset = curr_iov_->iov_len - curr_iov_remaining_;
+    while (offset > 0) {
+      if (from_iov_offset >= offset) {
+        from_iov_offset -= offset;
+        break;
+      }
+
+      offset -= from_iov_offset;
+      --from_iov;
+#if !defined(NDEBUG)
+      assert(from_iov >= output_iov_);
+#endif  // !defined(NDEBUG)
+      from_iov_offset = from_iov->iov_len;
+    }
+
+    // Copy <len> bytes starting from the iovec pointed to by from_iov_index to
+    // the current iovec.
+    while (len > 0) {
+      assert(from_iov <= curr_iov_);
+      if (from_iov != curr_iov_) {
+        const size_t to_copy =
+            std::min(from_iov->iov_len - from_iov_offset, len);
+        AppendNoCheck(GetIOVecPointer(from_iov, from_iov_offset), to_copy);
+        len -= to_copy;
+        if (len > 0) {
+          ++from_iov;
+          from_iov_offset = 0;
+        }
+      } else {
+        size_t to_copy = curr_iov_remaining_;
+        if (to_copy == 0) {
+          // This iovec is full. Go to the next one.
+          if (curr_iov_ + 1 >= output_iov_end_) {
+            return false;
+          }
+          ++curr_iov_;
+          curr_iov_output_ = reinterpret_cast<char*>(curr_iov_->iov_base);
+          curr_iov_remaining_ = curr_iov_->iov_len;
+          continue;
+        }
+        if (to_copy > len) {
+          to_copy = len;
+        }
+
+        IncrementalCopy(GetIOVecPointer(from_iov, from_iov_offset),
+                        curr_iov_output_, curr_iov_output_ + to_copy,
+                        curr_iov_output_ + curr_iov_remaining_);
+        curr_iov_output_ += to_copy;
+        curr_iov_remaining_ -= to_copy;
+        from_iov_offset += to_copy;
+        total_written_ += to_copy;
+        len -= to_copy;
+      }
+    }
+
+    return true;
+  }
+
+  inline void Flush() {}
+};
+
+bool RawUncompressToIOVec(const char* compressed, size_t compressed_length,
+                          const struct iovec* iov, size_t iov_cnt) {
+  ByteArraySource reader(compressed, compressed_length);
+  return RawUncompressToIOVec(&reader, iov, iov_cnt);
+}
+
+bool RawUncompressToIOVec(Source* compressed, const struct iovec* iov,
+                          size_t iov_cnt) {
+  SnappyIOVecWriter output(iov, iov_cnt);
+  return InternalUncompress(compressed, &output);
+}
+
+// -----------------------------------------------------------------------
+// Flat array interfaces
+// -----------------------------------------------------------------------
+
+// A type that writes to a flat array.
+// Note that this is not a "ByteSink", but a type that matches the
+// Writer template argument to SnappyDecompressor::DecompressAllTags().
+class SnappyArrayWriter {
+ private:
+  char* base_;
+  char* op_;
+  char* op_limit_;
+
+ public:
+  inline explicit SnappyArrayWriter(char* dst)
+      : base_(dst),
+        op_(dst),
+        op_limit_(dst) {
+  }
+
+  inline void SetExpectedLength(size_t len) {
+    op_limit_ = op_ + len;
+  }
+
+  inline bool CheckLength() const {
+    return op_ == op_limit_;
+  }
+
+  inline bool Append(const char* ip, size_t len) {
+    char* op = op_;
+    const size_t space_left = op_limit_ - op;
+    if (space_left < len) {
+      return false;
+    }
+    memcpy(op, ip, len);
+    op_ = op + len;
+    return true;
+  }
+
+  inline bool TryFastAppend(const char* ip, size_t available, size_t len) {
+    char* op = op_;
+    const size_t space_left = op_limit_ - op;
+    if (len <= 16 && available >= 16 + kMaximumTagLength && space_left >= 16) {
+      // Fast path, used for the majority (about 95%) of invocations.
+      UnalignedCopy128(ip, op);
+      op_ = op + len;
+      return true;
+    } else {
+      return false;
+    }
+  }
+
+  inline bool AppendFromSelf(size_t offset, size_t len) {
+    char* const op_end = op_ + len;
+
+    // Check if we try to append from before the start of the buffer.
+    // Normally this would just be a check for "produced < offset",
+    // but "produced <= offset - 1u" is equivalent for every case
+    // except the one where offset==0, where the right side will wrap around
+    // to a very big number. This is convenient, as offset==0 is another
+    // invalid case that we also want to catch, so that we do not go
+    // into an infinite loop.
+    if (Produced() <= offset - 1u || op_end > op_limit_) return false;
+    op_ = IncrementalCopy(op_ - offset, op_, op_end, op_limit_);
+
+    return true;
+  }
+  inline size_t Produced() const {
+    assert(op_ >= base_);
+    return op_ - base_;
+  }
+  inline void Flush() {}
+};
+
+bool RawUncompress(const char* compressed, size_t n, char* uncompressed) {
+  ByteArraySource reader(compressed, n);
+  return RawUncompress(&reader, uncompressed);
+}
+
+bool RawUncompress(Source* compressed, char* uncompressed) {
+  SnappyArrayWriter output(uncompressed);
+  return InternalUncompress(compressed, &output);
+}
+
+bool Uncompress(const char* compressed, size_t n, std::string* uncompressed) {
+  size_t ulength;
+  if (!GetUncompressedLength(compressed, n, &ulength)) {
+    return false;
+  }
+  // On 32-bit builds: max_size() < kuint32max.  Check for that instead
+  // of crashing (e.g., consider externally specified compressed data).
+  if (ulength > uncompressed->max_size()) {
+    return false;
+  }
+  STLStringResizeUninitialized(uncompressed, ulength);
+  return RawUncompress(compressed, n, string_as_array(uncompressed));
+}
+
+bool Uncompress(const char* compressed, size_t n, TString* uncompressed) {
+  size_t ulength;
+  if (!GetUncompressedLength(compressed, n, &ulength)) {
+    return false;
+  }
+  // On 32-bit builds: max_size() < kuint32max.  Check for that instead
+  // of crashing (e.g., consider externally specified compressed data).
+  if (ulength > uncompressed->max_size()) {
+    return false;
+  }
+  uncompressed->ReserveAndResize(ulength);
+  return RawUncompress(compressed, n, uncompressed->begin());
+}
+
+// A Writer that drops everything on the floor and just does validation
+class SnappyDecompressionValidator {
+ private:
+  size_t expected_;
+  size_t produced_;
+
+ public:
+  inline SnappyDecompressionValidator() : expected_(0), produced_(0) { }
+  inline void SetExpectedLength(size_t len) {
+    expected_ = len;
+  }
+  inline bool CheckLength() const {
+    return expected_ == produced_;
+  }
+  inline bool Append(const char* ip, size_t len) {
+    produced_ += len;
+    return produced_ <= expected_;
+  }
+  inline bool TryFastAppend(const char* ip, size_t available, size_t length) {
+    return false;
+  }
+  inline bool AppendFromSelf(size_t offset, size_t len) {
+    // See SnappyArrayWriter::AppendFromSelf for an explanation of
+    // the "offset - 1u" trick.
+    if (produced_ <= offset - 1u) return false;
+    produced_ += len;
+    return produced_ <= expected_;
+  }
+  inline void Flush() {}
+};
+
+bool IsValidCompressedBuffer(const char* compressed, size_t n) {
+  ByteArraySource reader(compressed, n);
+  SnappyDecompressionValidator writer;
+  return InternalUncompress(&reader, &writer);
+}
+
+bool IsValidCompressed(Source* compressed) {
+  SnappyDecompressionValidator writer;
+  return InternalUncompress(compressed, &writer);
+}
+
+void RawCompress(const char* input,
+                 size_t input_length,
+                 char* compressed,
+                 size_t* compressed_length) {
+  ByteArraySource reader(input, input_length);
+  UncheckedByteArraySink writer(compressed);
+  Compress(&reader, &writer);
+
+  // Compute how many bytes were added
+  *compressed_length = (writer.CurrentDestination() - compressed);
+}
+
+size_t Compress(const char* input, size_t input_length,
+                std::string* compressed) {
+  // Pre-grow the buffer to the max length of the compressed output
+  STLStringResizeUninitialized(compressed, MaxCompressedLength(input_length));
+
+  size_t compressed_length;
+  RawCompress(input, input_length, string_as_array(compressed),
+              &compressed_length);
+  compressed->resize(compressed_length);
+  return compressed_length;
+}
+
+size_t Compress(const char* input, size_t input_length,
+                TString* compressed) {
+  // Pre-grow the buffer to the max length of the compressed output
+  compressed->ReserveAndResize(MaxCompressedLength(input_length));
+
+  size_t compressed_length;
+  RawCompress(input, input_length, compressed->begin(),
+              &compressed_length);
+  compressed->resize(compressed_length);
+  return compressed_length;
+}
+
+// -----------------------------------------------------------------------
+// Sink interface
+// -----------------------------------------------------------------------
+
+// A type that decompresses into a Sink. The template parameter
+// Allocator must export one method "char* Allocate(int size);", which
+// allocates a buffer of "size" and appends that to the destination.
+template <typename Allocator>
+class SnappyScatteredWriter {
+  Allocator allocator_;
+
+  // We need random access into the data generated so far.  Therefore
+  // we keep track of all of the generated data as an array of blocks.
+  // All of the blocks except the last have length kBlockSize.
+  std::vector<char*> blocks_;
+  size_t expected_;
+
+  // Total size of all fully generated blocks so far
+  size_t full_size_;
+
+  // Pointer into current output block
+  char* op_base_;       // Base of output block
+  char* op_ptr_;        // Pointer to next unfilled byte in block
+  char* op_limit_;      // Pointer just past block
+
+  inline size_t Size() const {
+    return full_size_ + (op_ptr_ - op_base_);
+  }
+
+  bool SlowAppend(const char* ip, size_t len);
+  bool SlowAppendFromSelf(size_t offset, size_t len);
+
+ public:
+  inline explicit SnappyScatteredWriter(const Allocator& allocator)
+      : allocator_(allocator),
+        full_size_(0),
+        op_base_(NULL),
+        op_ptr_(NULL),
+        op_limit_(NULL) {
+  }
+
+  inline void SetExpectedLength(size_t len) {
+    assert(blocks_.empty());
+    expected_ = len;
+  }
+
+  inline bool CheckLength() const {
+    return Size() == expected_;
+  }
+
+  // Return the number of bytes actually uncompressed so far
+  inline size_t Produced() const {
+    return Size();
+  }
+
+  inline bool Append(const char* ip, size_t len) {
+    size_t avail = op_limit_ - op_ptr_;
+    if (len <= avail) {
+      // Fast path
+      memcpy(op_ptr_, ip, len);
+      op_ptr_ += len;
+      return true;
+    } else {
+      return SlowAppend(ip, len);
+    }
+  }
+
+  inline bool TryFastAppend(const char* ip, size_t available, size_t length) {
+    char* op = op_ptr_;
+    const int space_left = op_limit_ - op;
+    if (length <= 16 && available >= 16 + kMaximumTagLength &&
+        space_left >= 16) {
+      // Fast path, used for the majority (about 95%) of invocations.
+      UnalignedCopy128(ip, op);
+      op_ptr_ = op + length;
+      return true;
+    } else {
+      return false;
+    }
+  }
+
+  inline bool AppendFromSelf(size_t offset, size_t len) {
+    char* const op_end = op_ptr_ + len;
+    // See SnappyArrayWriter::AppendFromSelf for an explanation of
+    // the "offset - 1u" trick.
+    if (SNAPPY_PREDICT_TRUE(offset - 1u < op_ptr_ - op_base_ &&
+                          op_end <= op_limit_)) {
+      // Fast path: src and dst in current block.
+      op_ptr_ = IncrementalCopy(op_ptr_ - offset, op_ptr_, op_end, op_limit_);
+      return true;
+    }
+    return SlowAppendFromSelf(offset, len);
+  }
+
+  // Called at the end of the decompress. We ask the allocator
+  // write all blocks to the sink.
+  inline void Flush() { allocator_.Flush(Produced()); }
+};
+
+template<typename Allocator>
+bool SnappyScatteredWriter<Allocator>::SlowAppend(const char* ip, size_t len) {
+  size_t avail = op_limit_ - op_ptr_;
+  while (len > avail) {
+    // Completely fill this block
+    memcpy(op_ptr_, ip, avail);
+    op_ptr_ += avail;
+    assert(op_limit_ - op_ptr_ == 0);
+    full_size_ += (op_ptr_ - op_base_);
+    len -= avail;
+    ip += avail;
+
+    // Bounds check
+    if (full_size_ + len > expected_) {
+      return false;
+    }
+
+    // Make new block
+    size_t bsize = std::min<size_t>(kBlockSize, expected_ - full_size_);
+    op_base_ = allocator_.Allocate(bsize);
+    op_ptr_ = op_base_;
+    op_limit_ = op_base_ + bsize;
+    blocks_.push_back(op_base_);
+    avail = bsize;
+  }
+
+  memcpy(op_ptr_, ip, len);
+  op_ptr_ += len;
+  return true;
+}
+
+template<typename Allocator>
+bool SnappyScatteredWriter<Allocator>::SlowAppendFromSelf(size_t offset,
+                                                         size_t len) {
+  // Overflow check
+  // See SnappyArrayWriter::AppendFromSelf for an explanation of
+  // the "offset - 1u" trick.
+  const size_t cur = Size();
+  if (offset - 1u >= cur) return false;
+  if (expected_ - cur < len) return false;
+
+  // Currently we shouldn't ever hit this path because Compress() chops the
+  // input into blocks and does not create cross-block copies. However, it is
+  // nice if we do not rely on that, since we can get better compression if we
+  // allow cross-block copies and thus might want to change the compressor in
+  // the future.
+  size_t src = cur - offset;
+  while (len-- > 0) {
+    char c = blocks_[src >> kBlockLog][src & (kBlockSize-1)];
+    Append(&c, 1);
+    src++;
+  }
+  return true;
+}
+
+class SnappySinkAllocator {
+ public:
+  explicit SnappySinkAllocator(Sink* dest): dest_(dest) {}
+  ~SnappySinkAllocator() {}
+
+  char* Allocate(int size) {
+    Datablock block(new char[size], size);
+    blocks_.push_back(block);
+    return block.data;
+  }
+
+  // We flush only at the end, because the writer wants
+  // random access to the blocks and once we hand the
+  // block over to the sink, we can't access it anymore.
+  // Also we don't write more than has been actually written
+  // to the blocks.
+  void Flush(size_t size) {
+    size_t size_written = 0;
+    size_t block_size;
+    for (int i = 0; i < blocks_.size(); ++i) {
+      block_size = std::min<size_t>(blocks_[i].size, size - size_written);
+      dest_->AppendAndTakeOwnership(blocks_[i].data, block_size,
+                                    &SnappySinkAllocator::Deleter, NULL);
+      size_written += block_size;
+    }
+    blocks_.clear();
+  }
+
+ private:
+  struct Datablock {
+    char* data;
+    size_t size;
+    Datablock(char* p, size_t s) : data(p), size(s) {}
+  };
+
+  static void Deleter(void* arg, const char* bytes, size_t size) {
+    delete[] bytes;
+  }
+
+  Sink* dest_;
+  std::vector<Datablock> blocks_;
+
+  // Note: copying this object is allowed
+};
+
+size_t UncompressAsMuchAsPossible(Source* compressed, Sink* uncompressed) {
+  SnappySinkAllocator allocator(uncompressed);
+  SnappyScatteredWriter<SnappySinkAllocator> writer(allocator);
+  InternalUncompress(compressed, &writer);
+  return writer.Produced();
+}
+
+bool Uncompress(Source* compressed, Sink* uncompressed) {
+  // Read the uncompressed length from the front of the compressed input
+  SnappyDecompressor decompressor(compressed);
+  uint32 uncompressed_len = 0;
+  if (!decompressor.ReadUncompressedLength(&uncompressed_len)) {
+    return false;
+  }
+
+  char c;
+  size_t allocated_size;
+  char* buf = uncompressed->GetAppendBufferVariable(
+      1, uncompressed_len, &c, 1, &allocated_size);
+
+  const size_t compressed_len = compressed->Available();
+  // If we can get a flat buffer, then use it, otherwise do block by block
+  // uncompression
+  if (allocated_size >= uncompressed_len) {
+    SnappyArrayWriter writer(buf);
+    bool result = InternalUncompressAllTags(&decompressor, &writer,
+                                            compressed_len, uncompressed_len);
+    uncompressed->Append(buf, writer.Produced());
+    return result;
+  } else {
+    SnappySinkAllocator allocator(uncompressed);
+    SnappyScatteredWriter<SnappySinkAllocator> writer(allocator);
+    return InternalUncompressAllTags(&decompressor, &writer, compressed_len,
+                                     uncompressed_len);
+  }
+}
+
+}  // namespace snappy