diff --git a/snappy-internal.h b/snappy-internal.h
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+// Copyright 2008 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.
+//
+// Internals shared between the Snappy implementation and its unittest.
+
+#ifndef THIRD_PARTY_SNAPPY_SNAPPY_INTERNAL_H_
+#define THIRD_PARTY_SNAPPY_SNAPPY_INTERNAL_H_
+
+#include "snappy-stubs-internal.h"
+
+#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 <emmintrin.h>
+#include <tmmintrin.h>
+#endif
+
+#if SNAPPY_HAVE_NEON
+#include <arm_neon.h>
+#endif
+
+#if SNAPPY_HAVE_SSSE3 || SNAPPY_HAVE_NEON
+#define SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE 1
+#else
+#define SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE 0
+#endif
+
+namespace snappy {
+namespace internal {
+
+#if SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE
+#if SNAPPY_HAVE_SSSE3
+using V128 = __m128i;
+#elif SNAPPY_HAVE_NEON
+using V128 = uint8x16_t;
+#endif
+
+// Load 128 bits of integer data. `src` must be 16-byte aligned.
+inline V128 V128_Load(const V128* src);
+
+// Load 128 bits of integer data. `src` does not need to be aligned.
+inline V128 V128_LoadU(const V128* src);
+
+// Store 128 bits of integer data. `dst` does not need to be aligned.
+inline void V128_StoreU(V128* dst, V128 val);
+
+// Shuffle packed 8-bit integers using a shuffle mask.
+// Each packed integer in the shuffle mask must be in [0,16).
+inline V128 V128_Shuffle(V128 input, V128 shuffle_mask);
+
+// Constructs V128 with 16 chars |c|.
+inline V128 V128_DupChar(char c);
+
+#if SNAPPY_HAVE_SSSE3
+inline V128 V128_Load(const V128* src) { return _mm_load_si128(src); }
+
+inline V128 V128_LoadU(const V128* src) { return _mm_loadu_si128(src); }
+
+inline void V128_StoreU(V128* dst, V128 val) { _mm_storeu_si128(dst, val); }
+
+inline V128 V128_Shuffle(V128 input, V128 shuffle_mask) {
+  return _mm_shuffle_epi8(input, shuffle_mask);
+}
+
+inline V128 V128_DupChar(char c) { return _mm_set1_epi8(c); }
+
+#elif SNAPPY_HAVE_NEON
+inline V128 V128_Load(const V128* src) {
+  return vld1q_u8(reinterpret_cast<const uint8_t*>(src));
+}
+
+inline V128 V128_LoadU(const V128* src) {
+  return vld1q_u8(reinterpret_cast<const uint8_t*>(src));
+}
+
+inline void V128_StoreU(V128* dst, V128 val) {
+  vst1q_u8(reinterpret_cast<uint8_t*>(dst), val);
+}
+
+inline V128 V128_Shuffle(V128 input, V128 shuffle_mask) {
+  assert(vminvq_u8(shuffle_mask) >= 0 && vmaxvq_u8(shuffle_mask) <= 15);
+  return vqtbl1q_u8(input, shuffle_mask);
+}
+
+inline V128 V128_DupChar(char c) { return vdupq_n_u8(c); }
+#endif
+#endif  // SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE
+
+// Working memory performs a single allocation to hold all scratch space
+// required for compression.
+class WorkingMemory {
+ public:
+  explicit WorkingMemory(size_t input_size);
+  ~WorkingMemory();
+
+  // Allocates and clears a hash table using memory in "*this",
+  // stores the number of buckets in "*table_size" and returns a pointer to
+  // the base of the hash table.
+  uint16_t* GetHashTable(size_t fragment_size, int* table_size) const;
+  char* GetScratchInput() const { return input_; }
+  char* GetScratchOutput() const { return output_; }
+
+ private:
+  char* mem_;        // the allocated memory, never nullptr
+  size_t size_;      // the size of the allocated memory, never 0
+  uint16_t* table_;  // the pointer to the hashtable
+  char* input_;      // the pointer to the input scratch buffer
+  char* output_;     // the pointer to the output scratch buffer
+
+  // No copying
+  WorkingMemory(const WorkingMemory&);
+  void operator=(const WorkingMemory&);
+};
+
+// Flat array compression that does not emit the "uncompressed length"
+// prefix. Compresses "input" string to the "*op" buffer.
+//
+// REQUIRES: "input_length <= kBlockSize"
+// REQUIRES: "op" points to an array of memory that is at least
+// "MaxCompressedLength(input_length)" 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".
+char* CompressFragment(const char* input,
+                       size_t input_length,
+                       char* op,
+                       uint16_t* table,
+                       const int table_size);
+
+// Find the largest n such that
+//
+//   s1[0,n-1] == s2[0,n-1]
+//   and n <= (s2_limit - s2).
+//
+// Return make_pair(n, n < 8).
+// Does not read *s2_limit or beyond.
+// Does not read *(s1 + (s2_limit - s2)) or beyond.
+// Requires that s2_limit >= s2.
+//
+// In addition populate *data with the next 5 bytes from the end of the match.
+// This is only done if 8 bytes are available (s2_limit - s2 >= 8). The point is
+// that on some arch's this can be done faster in this routine than subsequent
+// loading from s2 + n.
+//
+// Separate implementation for 64-bit, little-endian cpus.
+#if !SNAPPY_IS_BIG_ENDIAN && \
+    (defined(__x86_64__) || defined(_M_X64) || defined(ARCH_PPC) || \
+     defined(ARCH_ARM))
+static inline std::pair<size_t, bool> FindMatchLength(const char* s1,
+                                                      const char* s2,
+                                                      const char* s2_limit,
+                                                      uint64_t* data) {
+  assert(s2_limit >= s2);
+  size_t matched = 0;
+
+  // This block isn't necessary for correctness; we could just start looping
+  // immediately.  As an optimization though, it is useful.  It creates some not
+  // uncommon code paths that determine, without extra effort, whether the match
+  // length is less than 8.  In short, we are hoping to avoid a conditional
+  // branch, and perhaps get better code layout from the C++ compiler.
+  if (SNAPPY_PREDICT_TRUE(s2 <= s2_limit - 16)) {
+    uint64_t a1 = UNALIGNED_LOAD64(s1);
+    uint64_t a2 = UNALIGNED_LOAD64(s2);
+    if (SNAPPY_PREDICT_TRUE(a1 != a2)) {
+      // This code is critical for performance. The reason is that it determines
+      // how much to advance `ip` (s2). This obviously depends on both the loads
+      // from the `candidate` (s1) and `ip`. Furthermore the next `candidate`
+      // depends on the advanced `ip` calculated here through a load, hash and
+      // new candidate hash lookup (a lot of cycles). This makes s1 (ie.
+      // `candidate`) the variable that limits throughput. This is the reason we
+      // go through hoops to have this function update `data` for the next iter.
+      // The straightforward code would use *data, given by
+      //
+      // *data = UNALIGNED_LOAD64(s2 + matched_bytes) (Latency of 5 cycles),
+      //
+      // as input for the hash table lookup to find next candidate. However
+      // this forces the load on the data dependency chain of s1, because
+      // matched_bytes directly depends on s1. However matched_bytes is 0..7, so
+      // we can also calculate *data by
+      //
+      // *data = AlignRight(UNALIGNED_LOAD64(s2), UNALIGNED_LOAD64(s2 + 8),
+      //                    matched_bytes);
+      //
+      // The loads do not depend on s1 anymore and are thus off the bottleneck.
+      // The straightforward implementation on x86_64 would be to use
+      //
+      // shrd rax, rdx, cl  (cl being matched_bytes * 8)
+      //
+      // unfortunately shrd with a variable shift has a 4 cycle latency. So this
+      // only wins 1 cycle. The BMI2 shrx instruction is a 1 cycle variable
+      // shift instruction but can only shift 64 bits. If we focus on just
+      // obtaining the least significant 4 bytes, we can obtain this by
+      //
+      // *data = ConditionalMove(matched_bytes < 4, UNALIGNED_LOAD64(s2),
+      //     UNALIGNED_LOAD64(s2 + 4) >> ((matched_bytes & 3) * 8);
+      //
+      // Writen like above this is not a big win, the conditional move would be
+      // a cmp followed by a cmov (2 cycles) followed by a shift (1 cycle).
+      // However matched_bytes < 4 is equal to
+      // static_cast<uint32_t>(xorval) != 0. Writen that way, the conditional
+      // move (2 cycles) can execute in parallel with FindLSBSetNonZero64
+      // (tzcnt), which takes 3 cycles.
+      uint64_t xorval = a1 ^ a2;
+      int shift = Bits::FindLSBSetNonZero64(xorval);
+      size_t matched_bytes = shift >> 3;
+#ifndef __x86_64__
+      *data = UNALIGNED_LOAD64(s2 + matched_bytes);
+#else
+      // Ideally this would just be
+      //
+      // a2 = static_cast<uint32_t>(xorval) == 0 ? a3 : a2;
+      //
+      // However clang correctly infers that the above statement participates on
+      // a critical data dependency chain and thus, unfortunately, refuses to
+      // use a conditional move (it's tuned to cut data dependencies). In this
+      // case there is a longer parallel chain anyway AND this will be fairly
+      // unpredictable.
+      uint64_t a3 = UNALIGNED_LOAD64(s2 + 4);
+      asm("testl %k2, %k2\n\t"
+          "cmovzq %1, %0\n\t"
+          : "+r"(a2)
+          : "r"(a3), "r"(xorval));
+      *data = a2 >> (shift & (3 * 8));
+#endif
+      return std::pair<size_t, bool>(matched_bytes, true);
+    } else {
+      matched = 8;
+      s2 += 8;
+    }
+  }
+
+  // Find out how long the match is. We loop over the data 64 bits at a
+  // time until we find a 64-bit block that doesn't match; then we find
+  // the first non-matching bit and use that to calculate the total
+  // length of the match.
+  while (SNAPPY_PREDICT_TRUE(s2 <= s2_limit - 16)) {
+    uint64_t a1 = UNALIGNED_LOAD64(s1 + matched);
+    uint64_t a2 = UNALIGNED_LOAD64(s2);
+    if (a1 == a2) {
+      s2 += 8;
+      matched += 8;
+    } else {
+      uint64_t xorval = a1 ^ a2;
+      int shift = Bits::FindLSBSetNonZero64(xorval);
+      size_t matched_bytes = shift >> 3;
+#ifndef __x86_64__
+      *data = UNALIGNED_LOAD64(s2 + matched_bytes);
+#else
+      uint64_t a3 = UNALIGNED_LOAD64(s2 + 4);
+      asm("testl %k2, %k2\n\t"
+          "cmovzq %1, %0\n\t"
+          : "+r"(a2)
+          : "r"(a3), "r"(xorval));
+      *data = a2 >> (shift & (3 * 8));
+#endif
+      matched += matched_bytes;
+      assert(matched >= 8);
+      return std::pair<size_t, bool>(matched, false);
+    }
+  }
+  while (SNAPPY_PREDICT_TRUE(s2 < s2_limit)) {
+    if (s1[matched] == *s2) {
+      ++s2;
+      ++matched;
+    } else {
+      if (s2 <= s2_limit - 8) {
+        *data = UNALIGNED_LOAD64(s2);
+      }
+      return std::pair<size_t, bool>(matched, matched < 8);
+    }
+  }
+  return std::pair<size_t, bool>(matched, matched < 8);
+}
+#else
+static inline std::pair<size_t, bool> FindMatchLength(const char* s1,
+                                                      const char* s2,
+                                                      const char* s2_limit,
+                                                      uint64_t* data) {
+  // Implementation based on the x86-64 version, above.
+  assert(s2_limit >= s2);
+  int matched = 0;
+
+  while (s2 <= s2_limit - 4 &&
+         UNALIGNED_LOAD32(s2) == UNALIGNED_LOAD32(s1 + matched)) {
+    s2 += 4;
+    matched += 4;
+  }
+  if (LittleEndian::IsLittleEndian() && s2 <= s2_limit - 4) {
+    uint32_t x = UNALIGNED_LOAD32(s2) ^ UNALIGNED_LOAD32(s1 + matched);
+    int matching_bits = Bits::FindLSBSetNonZero(x);
+    matched += matching_bits >> 3;
+    s2 += matching_bits >> 3;
+  } else {
+    while ((s2 < s2_limit) && (s1[matched] == *s2)) {
+      ++s2;
+      ++matched;
+    }
+  }
+  if (s2 <= s2_limit - 8) *data = LittleEndian::Load64(s2);
+  return std::pair<size_t, bool>(matched, matched < 8);
+}
+#endif
+
+// Lookup tables for decompression code.  Give --snappy_dump_decompression_table
+// to the unit test to recompute char_table.
+
+enum {
+  LITERAL = 0,
+  COPY_1_BYTE_OFFSET = 1,  // 3 bit length + 3 bits of offset in opcode
+  COPY_2_BYTE_OFFSET = 2,
+  COPY_4_BYTE_OFFSET = 3
+};
+static const int kMaximumTagLength = 5;  // COPY_4_BYTE_OFFSET plus the actual offset.
+
+// Data stored per entry in lookup table:
+//      Range   Bits-used       Description
+//      ------------------------------------
+//      1..64   0..7            Literal/copy length encoded in opcode byte
+//      0..7    8..10           Copy offset encoded in opcode byte / 256
+//      0..4    11..13          Extra bytes after opcode
+//
+// We use eight bits for the length even though 7 would have sufficed
+// because of efficiency reasons:
+//      (1) Extracting a byte is faster than a bit-field
+//      (2) It properly aligns copy offset so we do not need a <<8
+static constexpr uint16_t char_table[256] = {
+    // clang-format off
+  0x0001, 0x0804, 0x1001, 0x2001, 0x0002, 0x0805, 0x1002, 0x2002,
+  0x0003, 0x0806, 0x1003, 0x2003, 0x0004, 0x0807, 0x1004, 0x2004,
+  0x0005, 0x0808, 0x1005, 0x2005, 0x0006, 0x0809, 0x1006, 0x2006,
+  0x0007, 0x080a, 0x1007, 0x2007, 0x0008, 0x080b, 0x1008, 0x2008,
+  0x0009, 0x0904, 0x1009, 0x2009, 0x000a, 0x0905, 0x100a, 0x200a,
+  0x000b, 0x0906, 0x100b, 0x200b, 0x000c, 0x0907, 0x100c, 0x200c,
+  0x000d, 0x0908, 0x100d, 0x200d, 0x000e, 0x0909, 0x100e, 0x200e,
+  0x000f, 0x090a, 0x100f, 0x200f, 0x0010, 0x090b, 0x1010, 0x2010,
+  0x0011, 0x0a04, 0x1011, 0x2011, 0x0012, 0x0a05, 0x1012, 0x2012,
+  0x0013, 0x0a06, 0x1013, 0x2013, 0x0014, 0x0a07, 0x1014, 0x2014,
+  0x0015, 0x0a08, 0x1015, 0x2015, 0x0016, 0x0a09, 0x1016, 0x2016,
+  0x0017, 0x0a0a, 0x1017, 0x2017, 0x0018, 0x0a0b, 0x1018, 0x2018,
+  0x0019, 0x0b04, 0x1019, 0x2019, 0x001a, 0x0b05, 0x101a, 0x201a,
+  0x001b, 0x0b06, 0x101b, 0x201b, 0x001c, 0x0b07, 0x101c, 0x201c,
+  0x001d, 0x0b08, 0x101d, 0x201d, 0x001e, 0x0b09, 0x101e, 0x201e,
+  0x001f, 0x0b0a, 0x101f, 0x201f, 0x0020, 0x0b0b, 0x1020, 0x2020,
+  0x0021, 0x0c04, 0x1021, 0x2021, 0x0022, 0x0c05, 0x1022, 0x2022,
+  0x0023, 0x0c06, 0x1023, 0x2023, 0x0024, 0x0c07, 0x1024, 0x2024,
+  0x0025, 0x0c08, 0x1025, 0x2025, 0x0026, 0x0c09, 0x1026, 0x2026,
+  0x0027, 0x0c0a, 0x1027, 0x2027, 0x0028, 0x0c0b, 0x1028, 0x2028,
+  0x0029, 0x0d04, 0x1029, 0x2029, 0x002a, 0x0d05, 0x102a, 0x202a,
+  0x002b, 0x0d06, 0x102b, 0x202b, 0x002c, 0x0d07, 0x102c, 0x202c,
+  0x002d, 0x0d08, 0x102d, 0x202d, 0x002e, 0x0d09, 0x102e, 0x202e,
+  0x002f, 0x0d0a, 0x102f, 0x202f, 0x0030, 0x0d0b, 0x1030, 0x2030,
+  0x0031, 0x0e04, 0x1031, 0x2031, 0x0032, 0x0e05, 0x1032, 0x2032,
+  0x0033, 0x0e06, 0x1033, 0x2033, 0x0034, 0x0e07, 0x1034, 0x2034,
+  0x0035, 0x0e08, 0x1035, 0x2035, 0x0036, 0x0e09, 0x1036, 0x2036,
+  0x0037, 0x0e0a, 0x1037, 0x2037, 0x0038, 0x0e0b, 0x1038, 0x2038,
+  0x0039, 0x0f04, 0x1039, 0x2039, 0x003a, 0x0f05, 0x103a, 0x203a,
+  0x003b, 0x0f06, 0x103b, 0x203b, 0x003c, 0x0f07, 0x103c, 0x203c,
+  0x0801, 0x0f08, 0x103d, 0x203d, 0x1001, 0x0f09, 0x103e, 0x203e,
+  0x1801, 0x0f0a, 0x103f, 0x203f, 0x2001, 0x0f0b, 0x1040, 0x2040,
+    // clang-format on
+};
+
+}  // end namespace internal
+}  // end namespace snappy
+
+#endif  // THIRD_PARTY_SNAPPY_SNAPPY_INTERNAL_H_