Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2193 insertions, 0 deletions

diff --git a/other-licenses/snappy/src/snappy.cc b/other-licenses/snappy/src/snappy.cc
new file mode 100644
index 0000000000..57df3f11fc
--- /dev/null
+++ b/other-licenses/snappy/src/snappy.cc
@@ -0,0 +1,2193 @@
+// 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-internal.h"
+#include "snappy-sinksource.h"
+#include "snappy.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 <algorithm>
+#include <array>
+#include <cstddef>
+#include <cstdint>
+#include <cstdio>
+#include <cstring>
+#include <string>
+#include <utility>
+#include <vector>
+
+namespace snappy {
+
+namespace {
+
+// The amount of slop bytes writers are using for unconditional copies.
+constexpr int kSlopBytes = 64;
+
+using internal::char_table;
+using internal::COPY_1_BYTE_OFFSET;
+using internal::COPY_2_BYTE_OFFSET;
+using internal::COPY_4_BYTE_OFFSET;
+using internal::kMaximumTagLength;
+using internal::LITERAL;
+
+// We translate the information encoded in a tag through a lookup table to a
+// format that requires fewer instructions to decode. Effectively we store
+// the length minus the tag part of the offset. The lowest significant byte
+// thus stores the length. While total length - offset is given by
+// entry - ExtractOffset(type). The nice thing is that the subtraction
+// immediately sets the flags for the necessary check that offset >= length.
+// This folds the cmp with sub. We engineer the long literals and copy-4 to
+// always fail this check, so their presence doesn't affect the fast path.
+// To prevent literals from triggering the guard against offset < length (offset
+// does not apply to literals) the table is giving them a spurious offset of
+// 256.
+inline constexpr int16_t MakeEntry(int16_t len, int16_t offset) {
+  return len - (offset << 8);
+}
+
+inline constexpr int16_t LengthMinusOffset(int data, int type) {
+  return type == 3   ? 0xFF                    // copy-4 (or type == 3)
+         : type == 2 ? MakeEntry(data + 1, 0)  // copy-2
+         : type == 1 ? MakeEntry((data & 7) + 4, data >> 3)  // copy-1
+         : data < 60 ? MakeEntry(data + 1, 1)  // note spurious offset.
+                     : 0xFF;                   // long literal
+}
+
+inline constexpr int16_t LengthMinusOffset(uint8_t tag) {
+  return LengthMinusOffset(tag >> 2, tag & 3);
+}
+
+template <size_t... Ints>
+struct index_sequence {};
+
+template <std::size_t N, size_t... Is>
+struct make_index_sequence : make_index_sequence<N - 1, N - 1, Is...> {};
+
+template <size_t... Is>
+struct make_index_sequence<0, Is...> : index_sequence<Is...> {};
+
+template <size_t... seq>
+constexpr std::array<int16_t, 256> MakeTable(index_sequence<seq...>) {
+  return std::array<int16_t, 256>{LengthMinusOffset(seq)...};
+}
+
+// We maximally co-locate the two tables so that only one register needs to be
+// reserved for the table address.
+struct {
+  alignas(64) const std::array<int16_t, 256> length_minus_offset;
+  uint32_t extract_masks[4];  // Used for extracting offset based on tag type.
+} table = {MakeTable(make_index_sequence<256>{}), {0, 0xFF, 0xFFFF, 0}};
+
+// 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.
+inline uint32_t HashBytes(uint32_t bytes, uint32_t mask) {
+  constexpr uint32_t kMagic = 0x1e35a7bd;
+  return ((kMagic * bytes) >> (32 - kMaxHashTableBits)) & mask;
+}
+
+}  // namespace
+
+size_t MaxCompressedLength(size_t source_bytes) {
+  // 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_bytes + source_bytes / 6;
+}
+
+namespace {
+
+void UnalignedCopy64(const void* src, void* dst) {
+  char tmp[8];
+  std::memcpy(tmp, src, 8);
+  std::memcpy(dst, tmp, 8);
+}
+
+void UnalignedCopy128(const void* src, void* dst) {
+  // std::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];
+  std::memcpy(tmp, src, 16);
+  std::memcpy(dst, tmp, 16);
+}
+
+template <bool use_16bytes_chunk>
+inline void ConditionalUnalignedCopy128(const char* src, char* dst) {
+  if (use_16bytes_chunk) {
+    UnalignedCopy128(src, dst);
+  } else {
+    UnalignedCopy64(src, dst);
+    UnalignedCopy64(src + 8, dst + 8);
+  }
+}
+
+// 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 std::memcpy() or
+// std::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
+
+// Computes the bytes for shuffle control mask (please read comments on
+// 'pattern_generation_masks' as well) for the given index_offset and
+// pattern_size. For example, when the 'offset' is 6, it will generate a
+// repeating pattern of size 6. So, the first 16 byte indexes will correspond to
+// the pattern-bytes {0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3} and the
+// next 16 byte indexes will correspond to the pattern-bytes {4, 5, 0, 1, 2, 3,
+// 4, 5, 0, 1, 2, 3, 4, 5, 0, 1}. These byte index sequences are generated by
+// calling MakePatternMaskBytes(0, 6, index_sequence<16>()) and
+// MakePatternMaskBytes(16, 6, index_sequence<16>()) respectively.
+template <size_t... indexes>
+inline constexpr std::array<char, sizeof...(indexes)> MakePatternMaskBytes(
+    int index_offset, int pattern_size, index_sequence<indexes...>) {
+  return {static_cast<char>((index_offset + indexes) % pattern_size)...};
+}
+
+// Computes the shuffle control mask bytes array for given pattern-sizes and
+// returns an array.
+template <size_t... pattern_sizes_minus_one>
+inline constexpr std::array<std::array<char, sizeof(__m128i)>,
+                            sizeof...(pattern_sizes_minus_one)>
+MakePatternMaskBytesTable(int index_offset,
+                          index_sequence<pattern_sizes_minus_one...>) {
+  return {MakePatternMaskBytes(
+      index_offset, pattern_sizes_minus_one + 1,
+      make_index_sequence</*indexes=*/sizeof(__m128i)>())...};
+}
+
+// This is an array 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) constexpr std::array<std::array<char, sizeof(__m128i)>,
+                                 16> pattern_generation_masks =
+    MakePatternMaskBytesTable(
+        /*index_offset=*/0,
+        /*pattern_sizes_minus_one=*/make_index_sequence<16>());
+
+// Similar to 'pattern_generation_masks', this table is used to "rotate" the
+// pattern so that we can copy the *next 16 bytes* consistent with the pattern.
+// Basically, pattern_reshuffle_masks is a continuation of
+// pattern_generation_masks. It follows that, pattern_reshuffle_masks is same as
+// pattern_generation_masks for offsets 1, 2, 4, 8 and 16.
+alignas(16) constexpr std::array<std::array<char, sizeof(__m128i)>,
+                                 16> pattern_reshuffle_masks =
+    MakePatternMaskBytesTable(
+        /*index_offset=*/16,
+        /*pattern_sizes_minus_one=*/make_index_sequence<16>());
+
+SNAPPY_ATTRIBUTE_ALWAYS_INLINE
+static inline __m128i LoadPattern(const char* src, const size_t pattern_size) {
+  __m128i generation_mask = _mm_load_si128(reinterpret_cast<const __m128i*>(
+      pattern_generation_masks[pattern_size - 1].data()));
+  // Uninitialized bytes are masked out by the shuffle mask.
+  // TODO: remove annotation and macro defs once MSan is fixed.
+  SNAPPY_ANNOTATE_MEMORY_IS_INITIALIZED(src + pattern_size, 16 - pattern_size);
+  return _mm_shuffle_epi8(
+      _mm_loadu_si128(reinterpret_cast<const __m128i*>(src)), generation_mask);
+}
+
+SNAPPY_ATTRIBUTE_ALWAYS_INLINE
+static inline std::pair<__m128i /* pattern */, __m128i /* reshuffle_mask */>
+LoadPatternAndReshuffleMask(const char* src, const size_t pattern_size) {
+  __m128i pattern = LoadPattern(src, pattern_size);
+
+  // This mask will generate the next 16 bytes in-place. Doing so enables us to
+  // write data by at most 4 _mm_storeu_si128.
+  //
+  // For example, suppose pattern is:        abcdefabcdefabcd
+  // Shuffling with this mask will generate: efabcdefabcdefab
+  // Shuffling again will generate:          cdefabcdefabcdef
+  __m128i reshuffle_mask = _mm_load_si128(reinterpret_cast<const __m128i*>(
+      pattern_reshuffle_masks[pattern_size - 1].data()));
+  return {pattern, reshuffle_mask};
+}
+
+#endif  // SNAPPY_HAVE_SSSE3
+
+// Fallback for when we need to copy while extending the pattern, for example
+// copying 10 bytes from 3 positions back abc -> abcabcabcabca.
+//
+// REQUIRES: [dst - offset, dst + 64) is a valid address range.
+SNAPPY_ATTRIBUTE_ALWAYS_INLINE
+static inline bool Copy64BytesWithPatternExtension(char* dst, size_t offset) {
+#if SNAPPY_HAVE_SSSE3
+  if (SNAPPY_PREDICT_TRUE(offset <= 16)) {
+    switch (offset) {
+      case 0:
+        return false;
+      case 1: {
+        std::memset(dst, dst[-1], 64);
+        return true;
+      }
+      case 2:
+      case 4:
+      case 8:
+      case 16: {
+        __m128i pattern = LoadPattern(dst - offset, offset);
+        for (int i = 0; i < 4; i++) {
+          _mm_storeu_si128(reinterpret_cast<__m128i*>(dst + 16 * i), pattern);
+        }
+        return true;
+      }
+      default: {
+        auto pattern_and_reshuffle_mask =
+            LoadPatternAndReshuffleMask(dst - offset, offset);
+        __m128i pattern = pattern_and_reshuffle_mask.first;
+        __m128i reshuffle_mask = pattern_and_reshuffle_mask.second;
+        for (int i = 0; i < 4; i++) {
+          _mm_storeu_si128(reinterpret_cast<__m128i*>(dst + 16 * i), pattern);
+          pattern = _mm_shuffle_epi8(pattern, reshuffle_mask);
+        }
+        return true;
+      }
+    }
+  }
+#else
+  if (SNAPPY_PREDICT_TRUE(offset < 16)) {
+    if (SNAPPY_PREDICT_FALSE(offset == 0)) return false;
+    // Extend the pattern to the first 16 bytes.
+    for (int i = 0; i < 16; i++) dst[i] = (dst - offset)[i];
+    // Find a multiple of pattern >= 16.
+    static std::array<uint8_t, 16> pattern_sizes = []() {
+      std::array<uint8_t, 16> res;
+      for (int i = 1; i < 16; i++) res[i] = (16 / i + 1) * i;
+      return res;
+    }();
+    offset = pattern_sizes[offset];
+    for (int i = 1; i < 4; i++) {
+      std::memcpy(dst + i * 16, dst + i * 16 - offset, 16);
+    }
+    return true;
+  }
+#endif  // SNAPPY_HAVE_SSSE3
+
+  // Very rare.
+  for (int i = 0; i < 4; i++) {
+    std::memcpy(dst + i * 16, dst + i * 16 - offset, 16);
+  }
+  return true;
+}
+
+// Copy [src, src+(op_limit-op)) to [op, op_limit) 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) {
+#if SNAPPY_HAVE_SSSE3
+  constexpr int big_pattern_size_lower_bound = 16;
+#else
+  constexpr int big_pattern_size_lower_bound = 8;
+#endif
+
+  // Terminology:
+  //
+  // slop = buf_limit - op
+  // pat  = op - src
+  // len  = op_limit - op
+  assert(src < op);
+  assert(op < op_limit);
+  assert(op_limit <= buf_limit);
+  // NOTE: The copy tags use 3 or 6 bits to store the copy length, so len <= 64.
+  assert(op_limit - op <= 64);
+  // NOTE: In practice the compressor always emits len >= 4, so it is ok to
+  // assume that to optimize this function, but this is not guaranteed by the
+  // compression format, so we have to also handle len < 4 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 >= 16 bytes (or 8 bytes in non-SSE)
+  // and an unrolled loop copying 1x 16 bytes (or 2x 8 bytes in non-SSE) at a
+  // time.
+
+  // Handle the uncommon case where pattern is less than 16 (or 8 in non-SSE)
+  // bytes.
+  if (pattern_size < big_pattern_size_lower_bound) {
+#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.
+
+    // 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 - 15)) {
+      auto pattern_and_reshuffle_mask =
+          LoadPatternAndReshuffleMask(src, pattern_size);
+      __m128i pattern = pattern_and_reshuffle_mask.first;
+      __m128i reshuffle_mask = pattern_and_reshuffle_mask.second;
+
+      // 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.
+      _mm_storeu_si128(reinterpret_cast<__m128i*>(op), pattern);
+
+      if (op + 16 < op_limit) {
+        pattern = _mm_shuffle_epi8(pattern, reshuffle_mask);
+        _mm_storeu_si128(reinterpret_cast<__m128i*>(op + 16), pattern);
+      }
+      if (op + 32 < op_limit) {
+        pattern = _mm_shuffle_epi8(pattern, reshuffle_mask);
+        _mm_storeu_si128(reinterpret_cast<__m128i*>(op + 32), pattern);
+      }
+      if (op + 48 < op_limit) {
+        pattern = _mm_shuffle_epi8(pattern, reshuffle_mask);
+        _mm_storeu_si128(reinterpret_cast<__m128i*>(op + 48), pattern);
+      }
+      return op_limit;
+    }
+    char* const op_end = buf_limit - 15;
+    if (SNAPPY_PREDICT_TRUE(op < op_end)) {
+      auto pattern_and_reshuffle_mask =
+          LoadPatternAndReshuffleMask(src, pattern_size);
+      __m128i pattern = pattern_and_reshuffle_mask.first;
+      __m128i reshuffle_mask = pattern_and_reshuffle_mask.second;
+
+      // 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
+      do {
+        _mm_storeu_si128(reinterpret_cast<__m128i*>(op), pattern);
+        pattern = _mm_shuffle_epi8(pattern, reshuffle_mask);
+        op += 16;
+      } while (SNAPPY_PREDICT_TRUE(op < op_end));
+    }
+    return IncrementalCopySlow(op - pattern_size, 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 >= big_pattern_size_lower_bound);
+  constexpr bool use_16bytes_chunk = big_pattern_size_lower_bound == 16;
+
+  // Copy 1x 16 bytes (or 2x 8 bytes in non-SSE) at a time. Because op - src can
+  // be < 16 in non-SSE, 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 - 15)) {
+    // 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.
+    ConditionalUnalignedCopy128<use_16bytes_chunk>(src, op);
+    if (op + 16 < op_limit) {
+      ConditionalUnalignedCopy128<use_16bytes_chunk>(src + 16, op + 16);
+    }
+    if (op + 32 < op_limit) {
+      ConditionalUnalignedCopy128<use_16bytes_chunk>(src + 32, op + 32);
+    }
+    if (op + 48 < op_limit) {
+      ConditionalUnalignedCopy128<use_16bytes_chunk>(src + 48, op + 48);
+    }
+    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) {
+    ConditionalUnalignedCopy128<use_16bytes_chunk>(src, op);
+  }
+  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 std::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 std::memcpy() of size 'len' below.
+    LittleEndian::Store32(op, n);
+    op += count;
+  }
+  std::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) {
+    uint32_t u = (len << 2) + (offset << 8);
+    uint32_t copy1 = COPY_1_BYTE_OFFSET - (4 << 2) + ((offset >> 3) & 0xe0);
+    uint32_t copy2 = COPY_2_BYTE_OFFSET - (1 << 2);
+    // It turns out that offset < 2048 is a difficult to predict branch.
+    // `perf record` shows this is the highest percentage of branch misses in
+    // benchmarks. This code produces branch free code, the data dependency
+    // chain that bottlenecks the throughput is so long that a few extra
+    // instructions are completely free (IPC << 6 because of data deps).
+    u += offset < 2048 ? copy1 : copy2;
+    LittleEndian::Store32(op, u);
+    op += offset < 2048 ? 2 : 3;
+  } 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_t 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_t v = 0;
+  const char* limit = start + n;
+  if (Varint::Parse32WithLimit(start, limit, &v) != NULL) {
+    *result = v;
+    return true;
+  } else {
+    return false;
+  }
+}
+
+namespace {
+uint32_t CalculateTableSize(uint32_t 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_t*>(mem_);
+  input_ = mem_ + table_size * sizeof(*table_);
+  output_ = input_ + max_fragment_size;
+}
+
+WorkingMemory::~WorkingMemory() {
+  std::allocator<char>().deallocate(mem_, size_);
+}
+
+uint16_t* 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
+
+// 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_t* 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 uint32_t mask = table_size - 1;
+  const char* ip_end = input + input_size;
+  const char* base_ip = ip;
+
+  const size_t kInputMarginBytes = 15;
+  if (SNAPPY_PREDICT_TRUE(input_size >= kInputMarginBytes)) {
+    const char* ip_limit = input + input_size - kInputMarginBytes;
+
+    for (uint32_t preload = LittleEndian::Load32(ip + 1);;) {
+      // 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++;
+      uint64_t data = LittleEndian::Load64(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_t skip = 32;
+
+      const char* candidate;
+      if (ip_limit - ip >= 16) {
+        auto delta = ip - base_ip;
+        for (int j = 0; j < 4; ++j) {
+          for (int k = 0; k < 4; ++k) {
+            int i = 4 * j + k;
+            // These for-loops are meant to be unrolled. So we can freely
+            // special case the first iteration to use the value already
+            // loaded in preload.
+            uint32_t dword = i == 0 ? preload : static_cast<uint32_t>(data);
+            assert(dword == LittleEndian::Load32(ip + i));
+            uint32_t hash = HashBytes(dword, mask);
+            candidate = base_ip + table[hash];
+            assert(candidate >= base_ip);
+            assert(candidate < ip + i);
+            table[hash] = delta + i;
+            if (SNAPPY_PREDICT_FALSE(LittleEndian::Load32(candidate) == dword)) {
+              *op = LITERAL | (i << 2);
+              UnalignedCopy128(next_emit, op + 1);
+              ip += i;
+              op = op + i + 2;
+              goto emit_match;
+            }
+            data >>= 8;
+          }
+          data = LittleEndian::Load64(ip + 4 * j + 4);
+        }
+        ip += 16;
+        skip += 16;
+      }
+      while (true) {
+        assert(static_cast<uint32_t>(data) == LittleEndian::Load32(ip));
+        uint32_t hash = HashBytes(data, mask);
+        uint32_t bytes_between_hash_lookups = skip >> 5;
+        skip += bytes_between_hash_lookups;
+        const char* next_ip = ip + bytes_between_hash_lookups;
+        if (SNAPPY_PREDICT_FALSE(next_ip > ip_limit)) {
+          ip = next_emit;
+          goto emit_remainder;
+        }
+        candidate = base_ip + table[hash];
+        assert(candidate >= base_ip);
+        assert(candidate < ip);
+
+        table[hash] = ip - base_ip;
+        if (SNAPPY_PREDICT_FALSE(static_cast<uint32_t>(data) ==
+                                LittleEndian::Load32(candidate))) {
+          break;
+        }
+        data = LittleEndian::Load32(next_ip);
+        ip = next_ip;
+      }
+
+      // 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.
+    emit_match:
+      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, &data);
+        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);
+        }
+        if (SNAPPY_PREDICT_FALSE(ip >= ip_limit)) {
+          goto emit_remainder;
+        }
+        // Expect 5 bytes to match
+        assert((data & 0xFFFFFFFFFF) ==
+               (LittleEndian::Load64(ip) & 0xFFFFFFFFFF));
+        // 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, mask)] and table[Hash(ip, mask)].
+        table[HashBytes(LittleEndian::Load32(ip - 1), mask)] = ip - base_ip - 1;
+        uint32_t hash = HashBytes(data, mask);
+        candidate = base_ip + table[hash];
+        table[hash] = ip - base_ip;
+        // Measurements on the benchmarks have shown the following probabilities
+        // for the loop to exit (ie. avg. number of iterations is reciprocal).
+        // BM_Flat/6  txt1    p = 0.3-0.4
+        // BM_Flat/7  txt2    p = 0.35
+        // BM_Flat/8  txt3    p = 0.3-0.4
+        // BM_Flat/9  txt3    p = 0.34-0.4
+        // BM_Flat/10 pb      p = 0.4
+        // BM_Flat/11 gaviota p = 0.1
+        // BM_Flat/12 cp      p = 0.5
+        // BM_Flat/13 c       p = 0.3
+      } while (static_cast<uint32_t>(data) == LittleEndian::Load32(candidate));
+      // Because the least significant 5 bytes matched, we can utilize data
+      // for the next iteration.
+      preload = data >> 8;
+    }
+  }
+
+emit_remainder:
+  // Emit the remaining bytes as a literal
+  if (ip < ip_end) {
+    op = EmitLiteral</*allow_fast_path=*/false>(op, ip, ip_end - ip);
+  }
+
+  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) {
+  // TODO: Switch to [[maybe_unused]] when we can assume C++17.
+  (void)algorithm;
+  (void)compressed_size;
+  (void)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);
+//
+//   // For performance a writer may choose to donate the cursor variable to the
+//   // decompression function. The decompression will inject it in all its
+//   // function calls to the writer. Keeping the important output cursor as a
+//   // function local stack variable allows the compiler to keep it in
+//   // register, which greatly aids performance by avoiding loads and stores of
+//   // this variable in the fast path loop iterations.
+//   T GetOutputPtr() const;
+//
+//   // At end of decompression the loop donates the ownership of the cursor
+//   // variable back to the writer by calling this function.
+//   void SetOutputPtr(T op);
+//
+//   // Called after decompression
+//   bool CheckLength() const;
+//
+//   // Called repeatedly during decompression
+//   // Each function get a pointer to the op (output pointer), that the writer
+//   // can use and update. Note it's important that these functions get fully
+//   // inlined so that no actual address of the local variable needs to be
+//   // taken.
+//   bool Append(const char* ip, size_t length, T* op);
+//   bool AppendFromSelf(uint32_t offset, size_t length, T* op);
+//
+//   // 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, T* op);
+// };
+
+static inline uint32_t ExtractLowBytes(uint32_t 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_t otherwise `mask << 32` will be
+  // undefined.
+  uint64_t mask = 0xffffffff;
+  return v & ~(mask << (8 * n));
+#endif
+}
+
+static inline bool LeftShiftOverflows(uint8_t value, uint32_t shift) {
+  assert(shift < 32);
+  static const uint8_t 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;
+}
+
+inline bool Copy64BytesWithPatternExtension(ptrdiff_t dst, size_t offset) {
+  // TODO: Switch to [[maybe_unused]] when we can assume C++17.
+  (void)dst;
+  return offset != 0;
+}
+
+void MemCopy(char* dst, const uint8_t* src, size_t size) {
+  std::memcpy(dst, src, size);
+}
+
+void MemCopy(ptrdiff_t dst, const uint8_t* src, size_t size) {
+  // TODO: Switch to [[maybe_unused]] when we can assume C++17.
+  (void)dst;
+  (void)src;
+  (void)size;
+}
+
+void MemMove(char* dst, const void* src, size_t size) {
+  std::memmove(dst, src, size);
+}
+
+void MemMove(ptrdiff_t dst, const void* src, size_t size) {
+  // TODO: Switch to [[maybe_unused]] when we can assume C++17.
+  (void)dst;
+  (void)src;
+  (void)size;
+}
+
+SNAPPY_ATTRIBUTE_ALWAYS_INLINE
+size_t AdvanceToNextTag(const uint8_t** ip_p, size_t* tag) {
+  const uint8_t*& ip = *ip_p;
+  // This section is crucial for the throughput of the decompression loop.
+  // The latency of an iteration is fundamentally constrained by the
+  // following data chain on ip.
+  // ip -> c = Load(ip) -> ip1 = ip + 1 + (c & 3) -> ip = ip1 or ip2
+  //                       ip2 = ip + 2 + (c >> 2)
+  // This amounts to 8 cycles.
+  // 5 (load) + 1 (c & 3) + 1 (lea ip1, [ip + (c & 3) + 1]) + 1 (cmov)
+  size_t literal_len = *tag >> 2;
+  size_t tag_type = *tag;
+  bool is_literal;
+#if defined(__GNUC__) && defined(__x86_64__) && defined(__GCC_ASM_FLAG_OUTPUTS__)
+  // TODO clang misses the fact that the (c & 3) already correctly
+  // sets the zero flag.
+  asm("and $3, %k[tag_type]\n\t"
+      : [tag_type] "+r"(tag_type), "=@ccz"(is_literal));
+#else
+  tag_type &= 3;
+  is_literal = (tag_type == 0);
+#endif
+  // TODO
+  // This is code is subtle. Loading the values first and then cmov has less
+  // latency then cmov ip and then load. However clang would move the loads
+  // in an optimization phase, volatile prevents this transformation.
+  // Note that we have enough slop bytes (64) that the loads are always valid.
+  size_t tag_literal =
+      static_cast<const volatile uint8_t*>(ip)[1 + literal_len];
+  size_t tag_copy = static_cast<const volatile uint8_t*>(ip)[tag_type];
+  *tag = is_literal ? tag_literal : tag_copy;
+  const uint8_t* ip_copy = ip + 1 + tag_type;
+  const uint8_t* ip_literal = ip + 2 + literal_len;
+  ip = is_literal ? ip_literal : ip_copy;
+#if defined(__GNUC__) && defined(__x86_64__)
+  // TODO Clang is "optimizing" zero-extension (a totally free
+  // operation) this means that after the cmov of tag, it emits another movzb
+  // tag, byte(tag). It really matters as it's on the core chain. This dummy
+  // asm, persuades clang to do the zero-extension at the load (it's automatic)
+  // removing the expensive movzb.
+  asm("" ::"r"(tag_copy));
+#endif
+  return tag_type;
+}
+
+// Extract the offset for copy-1 and copy-2 returns 0 for literals or copy-4.
+inline uint32_t ExtractOffset(uint32_t val, size_t tag_type) {
+  return val & table.extract_masks[tag_type];
+};
+
+// Core decompression loop, when there is enough data available.
+// Decompresses the input buffer [ip, ip_limit) into the output buffer
+// [op, op_limit_min_slop). Returning when either we are too close to the end
+// of the input buffer, or we exceed op_limit_min_slop or when a exceptional
+// tag is encountered (literal of length > 60) or a copy-4.
+// Returns {ip, op} at the points it stopped decoding.
+// TODO This function probably does not need to be inlined, as it
+// should decode large chunks at a time. This allows runtime dispatch to
+// implementations based on CPU capability (BMI2 / perhaps 32 / 64 byte memcpy).
+template <typename T>
+std::pair<const uint8_t*, ptrdiff_t> DecompressBranchless(
+    const uint8_t* ip, const uint8_t* ip_limit, ptrdiff_t op, T op_base,
+    ptrdiff_t op_limit_min_slop) {
+  // We unroll the inner loop twice so we need twice the spare room.
+  op_limit_min_slop -= kSlopBytes;
+  if (2 * (kSlopBytes + 1) < ip_limit - ip && op < op_limit_min_slop) {
+    const uint8_t* const ip_limit_min_slop = ip_limit - 2 * kSlopBytes - 1;
+    ip++;
+    // ip points just past the tag and we are touching at maximum kSlopBytes
+    // in an iteration.
+    size_t tag = ip[-1];
+    do {
+      // The throughput is limited by instructions, unrolling the inner loop
+      // twice reduces the amount of instructions checking limits and also
+      // leads to reduced mov's.
+      for (int i = 0; i < 2; i++) {
+        const uint8_t* old_ip = ip;
+        assert(tag == ip[-1]);
+        // For literals tag_type = 0, hence we will always obtain 0 from
+        // ExtractLowBytes. For literals offset will thus be kLiteralOffset.
+        ptrdiff_t len_min_offset = table.length_minus_offset[tag];
+        size_t tag_type = AdvanceToNextTag(&ip, &tag);
+        uint32_t next = LittleEndian::Load32(old_ip);
+        size_t len = len_min_offset & 0xFF;
+        len_min_offset -= ExtractOffset(next, tag_type);
+        if (SNAPPY_PREDICT_FALSE(len_min_offset > 0)) {
+          if (SNAPPY_PREDICT_FALSE(len & 0x80)) {
+            // Exceptional case (long literal or copy 4).
+            // Actually doing the copy here is negatively impacting the main
+            // loop due to compiler incorrectly allocating a register for
+            // this fallback. Hence we just break.
+          break_loop:
+            ip = old_ip;
+            goto exit;
+          }
+          // Only copy-1 or copy-2 tags can get here.
+          assert(tag_type == 1 || tag_type == 2);
+          std::ptrdiff_t delta = op + len_min_offset - len;
+          // Guard against copies before the buffer start.
+          if (SNAPPY_PREDICT_FALSE(delta < 0 ||
+                                  !Copy64BytesWithPatternExtension(
+                                      op_base + op, len - len_min_offset))) {
+            goto break_loop;
+          }
+          op += len;
+          continue;
+        }
+        std::ptrdiff_t delta = op + len_min_offset - len;
+        if (SNAPPY_PREDICT_FALSE(delta < 0)) {
+#if defined(__GNUC__) && defined(__x86_64__)
+          // TODO
+          // When validating, both code path reduced to `op += len`. Ie. this
+          // becomes effectively
+          //
+          // if (delta < 0) if (tag_type != 0) goto break_loop;
+          // op += len;
+          //
+          // The compiler interchanges the predictable and almost always false
+          // first if-statement with the completely unpredictable second
+          // if-statement, putting an unpredictable branch on every iteration.
+          // This empty asm is worth almost 2x, which I think qualifies for an
+          // award for the most load-bearing empty statement.
+          asm("");
+#endif
+
+          // Due to the spurious offset in literals have this will trigger
+          // at the start of a block when op is still smaller than 256.
+          if (tag_type != 0) goto break_loop;
+          MemCopy(op_base + op, old_ip, 64);
+          op += len;
+          continue;
+        }
+
+        // For copies we need to copy from op_base + delta, for literals
+        // we need to copy from ip instead of from the stream.
+        const void* from =
+            tag_type ? reinterpret_cast<void*>(op_base + delta) : old_ip;
+        MemMove(op_base + op, from, 64);
+        op += len;
+      }
+    } while (ip < ip_limit_min_slop && op < op_limit_min_slop);
+  exit:
+    ip--;
+    assert(ip <= ip_limit);
+  }
+  return {ip, op};
+}
+
+// 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
+  // If ip < ip_limit_min_maxtaglen_ it's safe to read kMaxTagLength from
+  // buffer.
+  const char* ip_limit_min_maxtaglen_;
+  uint32_t 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();
+
+  void ResetLimit(const char* ip) {
+    ip_limit_min_maxtaglen_ =
+        ip_limit_ - std::min<ptrdiff_t>(ip_limit_ - ip, kMaximumTagLength - 1);
+  }
+
+ 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_t* result) {
+    assert(ip_ == NULL);  // Must not have read anything yet
+    // Length is encoded in 1..5 bytes
+    *result = 0;
+    uint32_t 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_t val = c & 0x7f;
+      if (LeftShiftOverflows(static_cast<uint8_t>(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) {
+    const char* ip = ip_;
+    ResetLimit(ip);
+    auto op = writer->GetOutputPtr();
+    // 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 (SNAPPY_PREDICT_FALSE(ip >= ip_limit_min_maxtaglen_)) { \
+    ip_ = ip;                                               \
+    if (SNAPPY_PREDICT_FALSE(!RefillTag())) goto exit;       \
+    ip = ip_;                                               \
+    ResetLimit(ip);                                         \
+  }                                                         \
+  preload = static_cast<uint8_t>(*ip)
+
+    // At the start of the for loop below the least significant byte of preload
+    // contains the tag.
+    uint32_t preload;
+    MAYBE_REFILL();
+    for (;;) {
+      {
+        ptrdiff_t op_limit_min_slop;
+        auto op_base = writer->GetBase(&op_limit_min_slop);
+        if (op_base) {
+          auto res =
+              DecompressBranchless(reinterpret_cast<const uint8_t*>(ip),
+                                   reinterpret_cast<const uint8_t*>(ip_limit_),
+                                   op - op_base, op_base, op_limit_min_slop);
+          ip = reinterpret_cast<const char*>(res.first);
+          op = op_base + res.second;
+          MAYBE_REFILL();
+        }
+      }
+      const uint8_t c = static_cast<uint8_t>(preload);
+      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, &op)) {
+          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.
+          preload = static_cast<uint8_t>(*ip);
+          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, &op)) goto exit;
+          literal_length -= avail;
+          reader_->Skip(peeked_);
+          size_t n;
+          ip = reader_->Peek(&n);
+          avail = n;
+          peeked_ = avail;
+          if (avail == 0) goto exit;
+          ip_limit_ = ip + avail;
+          ResetLimit(ip);
+        }
+        if (!writer->Append(ip, literal_length, &op)) goto exit;
+        ip += literal_length;
+        MAYBE_REFILL();
+      } else {
+        if (SNAPPY_PREDICT_FALSE((c & 3) == COPY_4_BYTE_OFFSET)) {
+          const size_t copy_offset = LittleEndian::Load32(ip);
+          const size_t length = (c >> 2) + 1;
+          ip += 4;
+
+          if (!writer->AppendFromSelf(copy_offset, length, &op)) goto exit;
+        } else {
+          const ptrdiff_t entry = table.length_minus_offset[c];
+          preload = LittleEndian::Load32(ip);
+          const uint32_t trailer = ExtractLowBytes(preload, c & 3);
+          const uint32_t length = entry & 0xff;
+          assert(length > 0);
+
+          // 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 uint32_t copy_offset = trailer - entry + length;
+          if (!writer->AppendFromSelf(copy_offset, length, &op)) goto exit;
+
+          ip += (c & 3);
+          // By using the result of the previous load we reduce the critical
+          // dependency chain of ip to 4 cycles.
+          preload >>= (c & 3) * 8;
+          if (ip < ip_limit_min_maxtaglen_) continue;
+        }
+        MAYBE_REFILL();
+      }
+    }
+#undef MAYBE_REFILL
+  exit:
+    writer->SetOutputPtr(op);
+  }
+};
+
+constexpr uint32_t CalculateNeeded(uint8_t tag) {
+  return ((tag & 3) == 0 && tag >= (60 * 4))
+             ? (tag >> 2) - 58
+             : (0x05030201 >> ((tag * 8) & 31)) & 0xFF;
+}
+
+#if __cplusplus >= 201402L
+constexpr bool VerifyCalculateNeeded() {
+  for (int i = 0; i < 1; i++) {
+    if (CalculateNeeded(i) != (char_table[i] >> 11) + 1) return false;
+  }
+  return true;
+}
+
+// Make sure CalculateNeeded is correct by verifying it against the established
+// table encoding the number of added bytes needed.
+static_assert(VerifyCalculateNeeded(), "");
+#endif  // c++14
+
+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));
+  // At this point make sure that the data for the next tag is consecutive.
+  // For copy 1 this means the next 2 bytes (tag and 1 byte offset)
+  // For copy 2 the next 3 bytes (tag and 2 byte offset)
+  // For copy 4 the next 5 bytes (tag and 4 byte offset)
+  // For all small literals we only need 1 byte buf for literals 60...63 the
+  // length is encoded in 1...4 extra bytes.
+  const uint32_t needed = CalculateNeeded(c);
+  assert(needed <= sizeof(scratch_));
+
+  // Read more bytes from reader if needed
+  uint32_t 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.
+    std::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_t to_add = std::min<uint32_t>(needed - nbuf, length);
+      std::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
+    std::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_t 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_t compressed_len,
+                                      uint32_t 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_t* 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();
+      std::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);
+        std::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_t* 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, char**) {
+    if (total_written_ + len > output_limit_) {
+      return false;
+    }
+
+    return AppendNoCheck(ip, len);
+  }
+
+  char* GetOutputPtr() { return nullptr; }
+  char* GetBase(ptrdiff_t*) { return nullptr; }
+  void SetOutputPtr(char* op) {
+    // TODO: Switch to [[maybe_unused]] when we can assume C++17.
+    (void)op;
+  }
+
+  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_);
+      std::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,
+                            char**) {
+    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, char**) {
+    // 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;
+        }
+        assert(to_copy > 0);
+
+        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_;
+  // If op < op_limit_min_slop_ then it's safe to unconditionally write
+  // kSlopBytes starting at op.
+  char* op_limit_min_slop_;
+
+ public:
+  inline explicit SnappyArrayWriter(char* dst)
+      : base_(dst),
+        op_(dst),
+        op_limit_(dst),
+        op_limit_min_slop_(dst) {}  // Safe default see invariant.
+
+  inline void SetExpectedLength(size_t len) {
+    op_limit_ = op_ + len;
+    // Prevent pointer from being past the buffer.
+    op_limit_min_slop_ = op_limit_ - std::min<size_t>(kSlopBytes - 1, len);
+  }
+
+  inline bool CheckLength() const { return op_ == op_limit_; }
+
+  char* GetOutputPtr() { return op_; }
+  char* GetBase(ptrdiff_t* op_limit_min_slop) {
+    *op_limit_min_slop = op_limit_min_slop_ - base_;
+    return base_;
+  }
+  void SetOutputPtr(char* op) { op_ = op; }
+
+  inline bool Append(const char* ip, size_t len, char** op_p) {
+    char* op = *op_p;
+    const size_t space_left = op_limit_ - op;
+    if (space_left < len) return false;
+    std::memcpy(op, ip, len);
+    *op_p = op + len;
+    return true;
+  }
+
+  inline bool TryFastAppend(const char* ip, size_t available, size_t len,
+                            char** op_p) {
+    char* op = *op_p;
+    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_p = op + len;
+      return true;
+    } else {
+      return false;
+    }
+  }
+
+  SNAPPY_ATTRIBUTE_ALWAYS_INLINE
+  inline bool AppendFromSelf(size_t offset, size_t len, char** op_p) {
+    assert(len > 0);
+    char* const op = *op_p;
+    assert(op >= base_);
+    char* const op_end = op + len;
+
+    // Check if we try to append from before the start of the buffer.
+    if (SNAPPY_PREDICT_FALSE(static_cast<size_t>(op - base_) < offset))
+      return false;
+
+    if (SNAPPY_PREDICT_FALSE((kSlopBytes < 64 && len > kSlopBytes) ||
+                            op >= op_limit_min_slop_ || offset < len)) {
+      if (op_end > op_limit_ || offset == 0) return false;
+      *op_p = IncrementalCopy(op - offset, op, op_end, op_limit_);
+      return true;
+    }
+    std::memmove(op, op - offset, kSlopBytes);
+    *op_p = op_end;
+    return true;
+  }
+  inline size_t Produced() const {
+    assert(op_ >= base_);
+    return op_ - base_;
+  }
+  inline void Flush() {}
+};
+
+bool RawUncompress(const char* compressed, size_t compressed_length,
+                   char* uncompressed) {
+  ByteArraySource reader(compressed, compressed_length);
+  return RawUncompress(&reader, uncompressed);
+}
+
+bool RawUncompress(Source* compressed, char* uncompressed) {
+  SnappyArrayWriter output(uncompressed);
+  return InternalUncompress(compressed, &output);
+}
+
+bool Uncompress(const char* compressed, size_t compressed_length,
+                std::string* uncompressed) {
+  size_t ulength;
+  if (!GetUncompressedLength(compressed, compressed_length, &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, compressed_length,
+                       string_as_array(uncompressed));
+}
+
+// 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; }
+  size_t GetOutputPtr() { return produced_; }
+  size_t GetBase(ptrdiff_t* op_limit_min_slop) {
+    *op_limit_min_slop = std::numeric_limits<ptrdiff_t>::max() - kSlopBytes + 1;
+    return 1;
+  }
+  void SetOutputPtr(size_t op) { produced_ = op; }
+  inline bool CheckLength() const { return expected_ == produced_; }
+  inline bool Append(const char* ip, size_t len, size_t* produced) {
+    // TODO: Switch to [[maybe_unused]] when we can assume C++17.
+    (void)ip;
+
+    *produced += len;
+    return *produced <= expected_;
+  }
+  inline bool TryFastAppend(const char* ip, size_t available, size_t length,
+                            size_t* produced) {
+    // TODO: Switch to [[maybe_unused]] when we can assume C++17.
+    (void)ip;
+    (void)available;
+    (void)length;
+    (void)produced;
+
+    return false;
+  }
+  inline bool AppendFromSelf(size_t offset, size_t len, size_t* produced) {
+    // 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 compressed_length) {
+  ByteArraySource reader(compressed, compressed_length);
+  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;
+}
+
+// -----------------------------------------------------------------------
+// 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
+  // If op < op_limit_min_slop_ then it's safe to unconditionally write
+  // kSlopBytes starting at op.
+  char* op_limit_min_slop_;
+
+  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),
+        op_limit_min_slop_(NULL) {}
+  char* GetOutputPtr() { return op_ptr_; }
+  char* GetBase(ptrdiff_t* op_limit_min_slop) {
+    *op_limit_min_slop = op_limit_min_slop_ - op_base_;
+    return op_base_;
+  }
+  void SetOutputPtr(char* op) { op_ptr_ = op; }
+
+  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, char** op_p) {
+    char* op = *op_p;
+    size_t avail = op_limit_ - op;
+    if (len <= avail) {
+      // Fast path
+      std::memcpy(op, ip, len);
+      *op_p = op + len;
+      return true;
+    } else {
+      op_ptr_ = op;
+      bool res = SlowAppend(ip, len);
+      *op_p = op_ptr_;
+      return res;
+    }
+  }
+
+  inline bool TryFastAppend(const char* ip, size_t available, size_t length,
+                            char** op_p) {
+    char* op = *op_p;
+    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_p = op + length;
+      return true;
+    } else {
+      return false;
+    }
+  }
+
+  inline bool AppendFromSelf(size_t offset, size_t len, char** op_p) {
+    char* op = *op_p;
+    assert(op >= op_base_);
+    // Check if we try to append from before the start of the buffer.
+    if (SNAPPY_PREDICT_FALSE((kSlopBytes < 64 && len > kSlopBytes) ||
+                            static_cast<size_t>(op - op_base_) < offset ||
+                            op >= op_limit_min_slop_ || offset < len)) {
+      if (offset == 0) return false;
+      if (SNAPPY_PREDICT_FALSE(static_cast<size_t>(op - op_base_) < offset ||
+                              op + len > op_limit_)) {
+        op_ptr_ = op;
+        bool res = SlowAppendFromSelf(offset, len);
+        *op_p = op_ptr_;
+        return res;
+      }
+      *op_p = IncrementalCopy(op - offset, op, op + len, op_limit_);
+      return true;
+    }
+    // Fast path
+    char* const op_end = op + len;
+    std::memmove(op, op - offset, kSlopBytes);
+    *op_p = op_end;
+    return true;
+  }
+
+  // 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
+    std::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;
+    op_limit_min_slop_ = op_limit_ - std::min<size_t>(kSlopBytes - 1, bsize);
+
+    blocks_.push_back(op_base_);
+    avail = bsize;
+  }
+
+  std::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.
+  // TODO Replace this with a properly optimized path. This is not
+  // triggered right now. But this is so super slow, that it would regress
+  // performance unacceptably if triggered.
+  size_t src = cur - offset;
+  char* op = op_ptr_;
+  while (len-- > 0) {
+    char c = blocks_[src >> kBlockLog][src & (kBlockSize - 1)];
+    if (!Append(&c, 1, &op)) {
+      op_ptr_ = op;
+      return false;
+    }
+    src++;
+  }
+  op_ptr_ = op;
+  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;
+    for (Datablock& block : blocks_) {
+      size_t block_size = std::min<size_t>(block.size, size - size_written);
+      dest_->AppendAndTakeOwnership(block.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) {
+    // TODO: Switch to [[maybe_unused]] when we can assume C++17.
+    (void)arg;
+    (void)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_t 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