Added brotli enc/ and tools/ directories.

third_party/brotli/enc/compress_fragment.cc

+/* Copyright 2015 Google Inc. All Rights Reserved.
+
+   Distributed under MIT license.
+   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
+*/
+
+// Function for fast encoding of an input fragment, independently from the input
+// history. This function uses one-pass processing: when we find a backward
+// match, we immediately emit the corresponding command and literal codes to
+// the bit stream.
+//
+// Adapted from the CompressFragment() function in
+// https://github.com/google/snappy/blob/master/snappy.cc
+
+#include "./compress_fragment.h"
+
+#include <algorithm>
+#include <cstring>
+
+#include "./brotli_bit_stream.h"
+#include "./entropy_encode.h"
+#include "./fast_log.h"
+#include "./find_match_length.h"
+#include "./port.h"
+#include "./types.h"
+#include "./write_bits.h"
+
+namespace brotli {
+
+// kHashMul32 multiplier has these properties:
+// * The multiplier must be odd. Otherwise we may lose the highest bit.
+// * No long streaks of 1s or 0s.
+// * There is no effort to ensure that it is a prime, the oddity is enough
+//   for this use.
+// * The number has been tuned heuristically against compression benchmarks.
+static const uint32_t kHashMul32 = 0x1e35a7bd;
+
+static inline uint32_t Hash(const uint8_t* p, size_t shift) {
+  const uint64_t h = (BROTLI_UNALIGNED_LOAD64(p) << 24) * kHashMul32;
+  return static_cast<uint32_t>(h >> shift);
+}
+
+static inline uint32_t HashBytesAtOffset(uint64_t v, int offset, size_t shift) {
+  assert(offset >= 0);
+  assert(offset <= 3);
+  const uint64_t h = ((v >> (8 * offset)) << 24) * kHashMul32;
+  return static_cast<uint32_t>(h >> shift);
+}
+
+static inline int IsMatch(const uint8_t* p1, const uint8_t* p2) {
+  return (BROTLI_UNALIGNED_LOAD32(p1) == BROTLI_UNALIGNED_LOAD32(p2) &&
+          p1[4] == p2[4]);
+}
+
+// Builds a literal prefix code into "depths" and "bits" based on the statistics
+// of the "input" string and stores it into the bit stream.
+// Note that the prefix code here is built from the pre-LZ77 input, therefore
+// we can only approximate the statistics of the actual literal stream.
+// Moreover, for long inputs we build a histogram from a sample of the input
+// and thus have to assign a non-zero depth for each literal.
+static void BuildAndStoreLiteralPrefixCode(const uint8_t* input,
+                                           const size_t input_size,
+                                           uint8_t depths[256],
+                                           uint16_t bits[256],
+                                           size_t* storage_ix,
+                                           uint8_t* storage) {
+  uint32_t histogram[256] = { 0 };
+  size_t histogram_total;
+  if (input_size < (1 << 15)) {
+    for (size_t i = 0; i < input_size; ++i)  {
+      ++histogram[input[i]];
+    }
+    histogram_total = input_size;
+    for (size_t i = 0; i < 256; ++i) {
+      // We weigh the first 11 samples with weight 3 to account for the
+      // balancing effect of the LZ77 phase on the histogram.
+      const uint32_t adjust = 2 * std::min(histogram[i], 11u);
+      histogram[i] += adjust;
+      histogram_total += adjust;
+    }
+  } else {
+    static const size_t kSampleRate = 29;
+    for (size_t i = 0; i < input_size; i += kSampleRate) {
+      ++histogram[input[i]];
+    }
+    histogram_total = (input_size + kSampleRate - 1) / kSampleRate;
+    for (size_t i = 0; i < 256; ++i) {
+      // We add 1 to each population count to avoid 0 bit depths (since this is
+      // only a sample and we don't know if the symbol appears or not), and we
+      // weigh the first 11 samples with weight 3 to account for the balancing
+      // effect of the LZ77 phase on the histogram (more frequent symbols are
+      // more likely to be in backward references instead as literals).
+      const uint32_t adjust = 1 + 2 * std::min(histogram[i], 11u);
+      histogram[i] += adjust;
+      histogram_total += adjust;
+    }
+  }
+  BuildAndStoreHuffmanTreeFast(histogram, histogram_total,
+                               /* max_bits = */ 8,
+                               depths, bits, storage_ix, storage);
+}
+
+// Builds a command and distance prefix code (each 64 symbols) into "depth" and
+// "bits" based on "histogram" and stores it into the bit stream.
+static void BuildAndStoreCommandPrefixCode(const uint32_t histogram[128],
+                                           uint8_t depth[128],
+                                           uint16_t bits[128],
+                                           size_t* storage_ix,
+                                           uint8_t* storage) {
+  // Tree size for building a tree over 64 symbols is 2 * 64 + 1.
+  static const size_t kTreeSize = 129;
+  HuffmanTree tree[kTreeSize];
+  CreateHuffmanTree(histogram, 64, 15, tree, depth);
+  CreateHuffmanTree(&histogram[64], 64, 14, tree, &depth[64]);
+  // We have to jump through a few hoopes here in order to compute
+  // the command bits because the symbols are in a different order than in
+  // the full alphabet. This looks complicated, but having the symbols
+  // in this order in the command bits saves a few branches in the Emit*
+  // functions.
+  uint8_t cmd_depth[64];
+  uint16_t cmd_bits[64];
+  memcpy(cmd_depth, depth, 24);
+  memcpy(cmd_depth + 24, depth + 40, 8);
+  memcpy(cmd_depth + 32, depth + 24, 8);
+  memcpy(cmd_depth + 40, depth + 48, 8);
+  memcpy(cmd_depth + 48, depth + 32, 8);
+  memcpy(cmd_depth + 56, depth + 56, 8);
+  ConvertBitDepthsToSymbols(cmd_depth, 64, cmd_bits);
+  memcpy(bits, cmd_bits, 48);
+  memcpy(bits + 24, cmd_bits + 32, 16);
+  memcpy(bits + 32, cmd_bits + 48, 16);
+  memcpy(bits + 40, cmd_bits + 24, 16);
+  memcpy(bits + 48, cmd_bits + 40, 16);
+  memcpy(bits + 56, cmd_bits + 56, 16);
+  ConvertBitDepthsToSymbols(&depth[64], 64, &bits[64]);
+  {
+    // Create the bit length array for the full command alphabet.
+    uint8_t cmd_depth[704] = { 0 };
+    memcpy(cmd_depth, depth, 8);
+    memcpy(cmd_depth + 64, depth + 8, 8);
+    memcpy(cmd_depth + 128, depth + 16, 8);
+    memcpy(cmd_depth + 192, depth + 24, 8);
+    memcpy(cmd_depth + 384, depth + 32, 8);
+    for (size_t i = 0; i < 8; ++i) {
+      cmd_depth[128 + 8 * i] = depth[40 + i];
+      cmd_depth[256 + 8 * i] = depth[48 + i];
+      cmd_depth[448 + 8 * i] = depth[56 + i];
+    }
+    StoreHuffmanTree(cmd_depth, 704, tree, storage_ix, storage);
+  }
+  StoreHuffmanTree(&depth[64], 64, tree, storage_ix, storage);
+}
+
+// REQUIRES: insertlen < 6210
+inline void EmitInsertLen(size_t insertlen,
+                          const uint8_t depth[128],
+                          const uint16_t bits[128],
+                          uint32_t histo[128],
+                          size_t* storage_ix,
+                          uint8_t* storage) {
+  if (insertlen < 6) {
+    const size_t code = insertlen + 40;
+    WriteBits(depth[code], bits[code], storage_ix, storage);
+    ++histo[code];
+  } else if (insertlen < 130) {
+    insertlen -= 2;
+    const uint32_t nbits = Log2FloorNonZero(insertlen) - 1u;
+    const size_t prefix = insertlen >> nbits;
+    const size_t inscode = (nbits << 1) + prefix + 42;
+    WriteBits(depth[inscode], bits[inscode], storage_ix, storage);
+    WriteBits(nbits, insertlen - (prefix << nbits), storage_ix, storage);
+    ++histo[inscode];
+  } else if (insertlen < 2114) {
+    insertlen -= 66;
+    const uint32_t nbits = Log2FloorNonZero(insertlen);
+    const size_t code = nbits + 50;
+    WriteBits(depth[code], bits[code], storage_ix, storage);
+    WriteBits(nbits, insertlen - (1 << nbits), storage_ix, storage);
+    ++histo[code];
+  } else {
+    WriteBits(depth[61], bits[61], storage_ix, storage);
+    WriteBits(12, insertlen - 2114, storage_ix, storage);
+    ++histo[21];
+  }
+}
+
+inline void EmitLongInsertLen(size_t insertlen,
+                              const uint8_t depth[128],
+                              const uint16_t bits[128],
+                              uint32_t histo[128],
+                              size_t* storage_ix,
+                              uint8_t* storage) {
+  if (insertlen < 22594) {
+    WriteBits(depth[62], bits[62], storage_ix, storage);
+    WriteBits(14, insertlen - 6210, storage_ix, storage);
+    ++histo[22];
+  } else {
+    WriteBits(depth[63], bits[63], storage_ix, storage);
+    WriteBits(24, insertlen - 22594, storage_ix, storage);
+    ++histo[23];
+  }
+}
+
+inline void EmitCopyLen(size_t copylen,
+                        const uint8_t depth[128],
+                        const uint16_t bits[128],
+                        uint32_t histo[128],
+                        size_t* storage_ix,
+                        uint8_t* storage) {
+  if (copylen < 10) {
+    WriteBits(depth[copylen + 14], bits[copylen + 14], storage_ix, storage);
+    ++histo[copylen + 14];
+  } else if (copylen < 134) {
+    copylen -= 6;
+    const uint32_t nbits = Log2FloorNonZero(copylen) - 1u;
+    const size_t prefix = copylen >> nbits;
+    const size_t code = (nbits << 1) + prefix + 20;
+    WriteBits(depth[code], bits[code], storage_ix, storage);
+    WriteBits(nbits, copylen - (prefix << nbits), storage_ix, storage);
+    ++histo[code];
+  } else if (copylen < 2118) {
+    copylen -= 70;
+    const uint32_t nbits = Log2FloorNonZero(copylen);
+    const size_t code = nbits + 28;
+    WriteBits(depth[code], bits[code], storage_ix, storage);
+    WriteBits(nbits, copylen - (1 << nbits), storage_ix, storage);
+    ++histo[code];
+  } else {
+    WriteBits(depth[39], bits[39], storage_ix, storage);
+    WriteBits(24, copylen - 2118, storage_ix, storage);
+    ++histo[47];
+  }
+}
+
+inline void EmitCopyLenLastDistance(size_t copylen,
+                                    const uint8_t depth[128],
+                                    const uint16_t bits[128],
+                                    uint32_t histo[128],
+                                    size_t* storage_ix,
+                                    uint8_t* storage) {
+  if (copylen < 12) {
+    WriteBits(depth[copylen - 4], bits[copylen - 4], storage_ix, storage);
+    ++histo[copylen - 4];
+  } else if (copylen < 72) {
+    copylen -= 8;
+    const uint32_t nbits = Log2FloorNonZero(copylen) - 1;
+    const size_t prefix = copylen >> nbits;
+    const size_t code = (nbits << 1) + prefix + 4;
+    WriteBits(depth[code], bits[code], storage_ix, storage);
+    WriteBits(nbits, copylen - (prefix << nbits), storage_ix, storage);
+    ++histo[code];
+  } else if (copylen < 136) {
+    copylen -= 8;
+    const size_t code = (copylen >> 5) + 30;
+    WriteBits(depth[code], bits[code], storage_ix, storage);
+    WriteBits(5, copylen & 31, storage_ix, storage);
+    WriteBits(depth[64], bits[64], storage_ix, storage);
+    ++histo[code];
+    ++histo[64];
+  } else if (copylen < 2120) {
+    copylen -= 72;
+    const uint32_t nbits = Log2FloorNonZero(copylen);
+    const size_t code = nbits + 28;
+    WriteBits(depth[code], bits[code], storage_ix, storage);
+    WriteBits(nbits, copylen - (1 << nbits), storage_ix, storage);
+    WriteBits(depth[64], bits[64], storage_ix, storage);
+    ++histo[code];
+    ++histo[64];
+  } else {
+    WriteBits(depth[39], bits[39], storage_ix, storage);
+    WriteBits(24, copylen - 2120, storage_ix, storage);
+    WriteBits(depth[64], bits[64], storage_ix, storage);
+    ++histo[47];
+    ++histo[64];
+  }
+}
+
+inline void EmitDistance(size_t distance,
+                         const uint8_t depth[128],
+                         const uint16_t bits[128],
+                         uint32_t histo[128],
+                         size_t* storage_ix, uint8_t* storage) {
+  distance += 3;
+  const uint32_t nbits = Log2FloorNonZero(distance) - 1u;
+  const size_t prefix = (distance >> nbits) & 1;
+  const size_t offset = (2 + prefix) << nbits;
+  const size_t distcode = 2 * (nbits - 1) + prefix + 80;
+  WriteBits(depth[distcode], bits[distcode], storage_ix, storage);
+  WriteBits(nbits, distance - offset, storage_ix, storage);
+  ++histo[distcode];
+}
+
+inline void EmitLiterals(const uint8_t* input, const size_t len,
+                         const uint8_t depth[256], const uint16_t bits[256],
+                         size_t* storage_ix, uint8_t* storage) {
+  for (size_t j = 0; j < len; j++) {
+    const uint8_t lit = input[j];
+    WriteBits(depth[lit], bits[lit], storage_ix, storage);
+  }
+}
+
+// REQUIRES: len <= 1 << 20.
+static void StoreMetaBlockHeader(
+    size_t len, bool is_uncompressed, size_t* storage_ix, uint8_t* storage) {
+  // ISLAST
+  WriteBits(1, 0, storage_ix, storage);
+  if (len <= (1U << 16)) {
+    // MNIBBLES is 4
+    WriteBits(2, 0, storage_ix, storage);
+    WriteBits(16, len - 1, storage_ix, storage);
+  } else {
+    // MNIBBLES is 5
+    WriteBits(2, 1, storage_ix, storage);
+    WriteBits(20, len - 1, storage_ix, storage);
+  }
+  // ISUNCOMPRESSED
+  WriteBits(1, is_uncompressed, storage_ix, storage);
+}
+
+static void UpdateBits(size_t n_bits,
+                       uint32_t bits,
+                       size_t pos,
+                       uint8_t *array) {
+  while (n_bits > 0) {
+    size_t byte_pos = pos >> 3;
+    size_t n_unchanged_bits = pos & 7;
+    size_t n_changed_bits = std::min(n_bits, 8 - n_unchanged_bits);
+    size_t total_bits = n_unchanged_bits + n_changed_bits;
+    uint32_t mask = (~((1 << total_bits) - 1)) | ((1 << n_unchanged_bits) - 1);
+    uint32_t unchanged_bits = array[byte_pos] & mask;
+    uint32_t changed_bits = bits & ((1 << n_changed_bits) - 1);
+    array[byte_pos] =
+        static_cast<uint8_t>((changed_bits << n_unchanged_bits) |
+                             unchanged_bits);
+    n_bits -= n_changed_bits;
+    bits >>= n_changed_bits;
+    pos += n_changed_bits;
+  }
+}
+
+static void RewindBitPosition(const size_t new_storage_ix,
+                              size_t* storage_ix, uint8_t* storage) {
+  const size_t bitpos = new_storage_ix & 7;
+  const size_t mask = (1u << bitpos) - 1;
+  storage[new_storage_ix >> 3] &= static_cast<uint8_t>(mask);
+  *storage_ix = new_storage_ix;
+}
+
+static bool ShouldMergeBlock(const uint8_t* data, size_t len,
+                             const uint8_t* depths) {
+  size_t histo[256] = { 0 };
+  static const size_t kSampleRate = 43;
+  for (size_t i = 0; i < len; i += kSampleRate) {
+    ++histo[data[i]];
+  }
+  const size_t total = (len + kSampleRate - 1) / kSampleRate;
+  double r = (FastLog2(total) + 0.5) * static_cast<double>(total) + 200;
+  for (size_t i = 0; i < 256; ++i) {
+    r -= static_cast<double>(histo[i]) * (depths[i] + FastLog2(histo[i]));
+  }
+  return r >= 0.0;
+}
+
+inline bool ShouldUseUncompressedMode(const uint8_t* metablock_start,
+                                      const uint8_t* next_emit,
+                                      const size_t insertlen,
+                                      const uint8_t literal_depths[256]) {
+  const size_t compressed = static_cast<size_t>(next_emit - metablock_start);
+  if (compressed * 50 > insertlen) {
+    return false;
+  }
+  static const double kAcceptableLossForUncompressibleSpeedup = 0.02;
+  static const double kMinEntropy =
+      8 * (1.0 - kAcceptableLossForUncompressibleSpeedup);
+  uint32_t sum = 0;
+  for (int i = 0; i < 256; ++i) {
+    const uint32_t n = literal_depths[i];
+    sum += n << (15 - n);
+  }
+  return sum > static_cast<uint32_t>((1 << 15) * kMinEntropy);
+}
+
+static void EmitUncompressedMetaBlock(const uint8_t* begin, const uint8_t* end,
+                                      const size_t storage_ix_start,
+                                      size_t* storage_ix, uint8_t* storage) {
+  const size_t len = static_cast<size_t>(end - begin);
+  RewindBitPosition(storage_ix_start, storage_ix, storage);
+  StoreMetaBlockHeader(len, 1, storage_ix, storage);
+  *storage_ix = (*storage_ix + 7u) & ~7u;
+  memcpy(&storage[*storage_ix >> 3], begin, len);
+  *storage_ix += len << 3;
+  storage[*storage_ix >> 3] = 0;
+}
+
+void BrotliCompressFragmentFast(const uint8_t* input, size_t input_size,
+                                bool is_last,
+                                int* table, size_t table_size,
+                                uint8_t cmd_depth[128], uint16_t cmd_bits[128],
+                                size_t* cmd_code_numbits, uint8_t* cmd_code,
+                                size_t* storage_ix, uint8_t* storage) {
+  if (input_size == 0) {
+    assert(is_last);
+    WriteBits(1, 1, storage_ix, storage);  // islast
+    WriteBits(1, 1, storage_ix, storage);  // isempty
+    *storage_ix = (*storage_ix + 7u) & ~7u;
+    return;
+  }
+
+  // "next_emit" is a pointer to the first byte that is not covered by a
+  // previous copy. Bytes between "next_emit" and the start of the next copy or
+  // the end of the input will be emitted as literal bytes.
+  const uint8_t* next_emit = input;
+  // Save the start of the first block for position and distance computations.
+  const uint8_t* base_ip = input;
+
+  static const size_t kFirstBlockSize = 3 << 15;
+  static const size_t kMergeBlockSize = 1 << 16;
+
+  const uint8_t* metablock_start = input;
+  size_t block_size = std::min(input_size, kFirstBlockSize);
+  size_t total_block_size = block_size;
+  // Save the bit position of the MLEN field of the meta-block header, so that
+  // we can update it later if we decide to extend this meta-block.
+  size_t mlen_storage_ix = *storage_ix + 3;
+  StoreMetaBlockHeader(block_size, 0, storage_ix, storage);
+  // No block splits, no contexts.
+  WriteBits(13, 0, storage_ix, storage);
+
+  uint8_t lit_depth[256] = { 0 };
+  uint16_t lit_bits[256] = { 0 };
+  BuildAndStoreLiteralPrefixCode(input, block_size, lit_depth, lit_bits,
+                                 storage_ix, storage);
+
+  // Store the pre-compressed command and distance prefix codes.
+  for (size_t i = 0; i + 7 < *cmd_code_numbits; i += 8) {
+    WriteBits(8, cmd_code[i >> 3], storage_ix, storage);
+  }
+  WriteBits(*cmd_code_numbits & 7, cmd_code[*cmd_code_numbits >> 3],
+            storage_ix, storage);
+
+ emit_commands:
+  // Initialize the command and distance histograms. We will gather
+  // statistics of command and distance codes during the processing
+  // of this block and use it to update the command and distance
+  // prefix codes for the next block.
+  uint32_t cmd_histo[128] = {
+    0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0,
+    0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 0, 0, 0, 0,
+  };
+
+  // "ip" is the input pointer.
+  const uint8_t* ip = input;
+  assert(table_size);
+  assert(table_size <= (1u << 31));
+  assert((table_size & (table_size - 1)) == 0);  // table must be power of two
+  const size_t shift = 64u - Log2FloorNonZero(table_size);
+  assert(table_size - 1 == static_cast<size_t>(
+      MAKE_UINT64_T(0xFFFFFFFF, 0xFFFFFF) >> shift));
+  const uint8_t* ip_end = input + block_size;
+
+  int last_distance = -1;
+  const size_t kInputMarginBytes = 16;
+  const size_t kMinMatchLen = 5;
+  if (PREDICT_TRUE(block_size >= kInputMarginBytes)) {
+    // For the last block, we need to keep a 16 bytes margin so that we can be
+    // sure that all distances are at most window size - 16.
+    // For all other blocks, we only need to keep a margin of 5 bytes so that
+    // we don't go over the block size with a copy.
+    const size_t len_limit = std::min(block_size - kMinMatchLen,
+                                      input_size - kInputMarginBytes);
+    const uint8_t* ip_limit = input + len_limit;
+
+    for (uint32_t next_hash = Hash(++ip, shift); ; ) {
+      assert(next_emit < ip);
+      // Step 1: Scan forward in the input looking for a 5-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, 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 uint8_t* next_ip = ip;
+      const uint8_t* candidate;
+      do {
+        ip = next_ip;
+        uint32_t hash = next_hash;
+        assert(hash == Hash(ip, shift));
+        uint32_t bytes_between_hash_lookups = skip++ >> 5;
+        next_ip = ip + bytes_between_hash_lookups;
+        if (PREDICT_FALSE(next_ip > ip_limit)) {
+          goto emit_remainder;
+        }
+        next_hash = Hash(next_ip, shift);
+        candidate = ip - last_distance;
+        if (IsMatch(ip, candidate)) {
+          if (PREDICT_TRUE(candidate < ip)) {
+            table[hash] = static_cast<int>(ip - base_ip);
+            break;
+          }
+        }
+        candidate = base_ip + table[hash];
+        assert(candidate >= base_ip);
+        assert(candidate < ip);
+
+        table[hash] = static_cast<int>(ip - base_ip);
+      } while (PREDICT_TRUE(!IsMatch(ip, candidate)));
+
+      // Step 2: Emit the found match together with the literal bytes from
+      // "next_emit" to the bit stream, and then see if we can find a next macth
+      // immediately afterwards. Repeat until we find no match for the input
+      // without emitting some literal bytes.
+      uint64_t input_bytes;
+
+      {
+        // We have a 5-byte match at ip, and we need to emit bytes in
+        // [next_emit, ip).
+        const uint8_t* base = ip;
+        size_t matched = 5 + FindMatchLengthWithLimit(
+            candidate + 5, ip + 5, static_cast<size_t>(ip_end - ip) - 5);
+        ip += matched;
+        int distance = static_cast<int>(base - candidate);  /* > 0 */
+        size_t insert = static_cast<size_t>(base - next_emit);
+        assert(0 == memcmp(base, candidate, matched));
+        if (PREDICT_TRUE(insert < 6210)) {
+          EmitInsertLen(insert, cmd_depth, cmd_bits, cmd_histo,
+                        storage_ix, storage);
+        } else if (ShouldUseUncompressedMode(metablock_start, next_emit, insert,
+                                             lit_depth)) {
+          EmitUncompressedMetaBlock(metablock_start, base, mlen_storage_ix - 3,
+                                    storage_ix, storage);
+          input_size -= static_cast<size_t>(base - input);
+          input = base;
+          next_emit = input;
+          goto next_block;
+        } else {
+          EmitLongInsertLen(insert, cmd_depth, cmd_bits, cmd_histo,
+                            storage_ix, storage);
+        }
+        EmitLiterals(next_emit, insert, lit_depth, lit_bits,
+                     storage_ix, storage);
+        if (distance == last_distance) {
+          WriteBits(cmd_depth[64], cmd_bits[64], storage_ix, storage);
+          ++cmd_histo[64];
+        } else {
+          EmitDistance(static_cast<size_t>(distance), cmd_depth, cmd_bits,
+                       cmd_histo, storage_ix, storage);
+          last_distance = distance;
+        }
+        EmitCopyLenLastDistance(matched, cmd_depth, cmd_bits, cmd_histo,
+                                storage_ix, storage);
+
+        next_emit = ip;
+        if (PREDICT_FALSE(ip >= ip_limit)) {
+          goto emit_remainder;
+        }
+        // We could immediately start working at ip now, but to improve
+        // compression we first update "table" with the hashes of some positions
+        // within the last copy.
+        input_bytes = BROTLI_UNALIGNED_LOAD64(ip - 3);
+        uint32_t prev_hash = HashBytesAtOffset(input_bytes, 0, shift);
+        table[prev_hash] = static_cast<int>(ip - base_ip - 3);
+        prev_hash = HashBytesAtOffset(input_bytes, 1, shift);
+        table[prev_hash] = static_cast<int>(ip - base_ip - 2);
+        prev_hash = HashBytesAtOffset(input_bytes, 2, shift);
+        table[prev_hash] = static_cast<int>(ip - base_ip - 1);
+
+        uint32_t cur_hash = HashBytesAtOffset(input_bytes, 3, shift);
+        candidate = base_ip + table[cur_hash];
+        table[cur_hash] = static_cast<int>(ip - base_ip);
+      }
+
+      while (IsMatch(ip, candidate)) {
+        // We have a 5-byte match at ip, and no need to emit any literal bytes
+        // prior to ip.
+        const uint8_t* base = ip;
+        size_t matched = 5 + FindMatchLengthWithLimit(
+            candidate + 5, ip + 5, static_cast<size_t>(ip_end - ip) - 5);
+        ip += matched;
+        last_distance = static_cast<int>(base - candidate);  /* > 0 */
+        assert(0 == memcmp(base, candidate, matched));
+        EmitCopyLen(matched, cmd_depth, cmd_bits, cmd_histo,
+                    storage_ix, storage);
+        EmitDistance(static_cast<size_t>(last_distance), cmd_depth, cmd_bits,
+                     cmd_histo, storage_ix, storage);
+
+        next_emit = ip;
+        if (PREDICT_FALSE(ip >= ip_limit)) {
+          goto emit_remainder;
+        }
+        // We could immediately start working at ip now, but to improve
+        // compression we first update "table" with the hashes of some positions
+        // within the last copy.
+        input_bytes = BROTLI_UNALIGNED_LOAD64(ip - 3);
+        uint32_t prev_hash = HashBytesAtOffset(input_bytes, 0, shift);
+        table[prev_hash] = static_cast<int>(ip - base_ip - 3);
+        prev_hash = HashBytesAtOffset(input_bytes, 1, shift);
+        table[prev_hash] = static_cast<int>(ip - base_ip - 2);
+        prev_hash = HashBytesAtOffset(input_bytes, 2, shift);
+        table[prev_hash] = static_cast<int>(ip - base_ip - 1);
+
+        uint32_t cur_hash = HashBytesAtOffset(input_bytes, 3, shift);
+        candidate = base_ip + table[cur_hash];
+        table[cur_hash] = static_cast<int>(ip - base_ip);
+      }
+
+      next_hash = Hash(++ip, shift);
+    }
+  }
+
+ emit_remainder:
+  assert(next_emit <= ip_end);
+  input += block_size;
+  input_size -= block_size;
+  block_size = std::min(input_size, kMergeBlockSize);
+
+  // Decide if we want to continue this meta-block instead of emitting the
+  // last insert-only command.
+  if (input_size > 0 &&
+      total_block_size + block_size <= (1 << 20) &&
+      ShouldMergeBlock(input, block_size, lit_depth)) {
+    assert(total_block_size > (1 << 16));
+    // Update the size of the current meta-block and continue emitting commands.
+    // We can do this because the current size and the new size both have 5
+    // nibbles.
+    total_block_size += block_size;
+    UpdateBits(20, static_cast<uint32_t>(total_block_size - 1),
+               mlen_storage_ix, storage);
+    goto emit_commands;
+  }
+
+  // Emit the remaining bytes as literals.
+  if (next_emit < ip_end) {
+    const size_t insert = static_cast<size_t>(ip_end - next_emit);
+    if (PREDICT_TRUE(insert < 6210)) {
+      EmitInsertLen(insert, cmd_depth, cmd_bits, cmd_histo,
+                    storage_ix, storage);
+      EmitLiterals(next_emit, insert, lit_depth, lit_bits, storage_ix, storage);
+    } else if (ShouldUseUncompressedMode(metablock_start, next_emit, insert,
+                                         lit_depth)) {
+      EmitUncompressedMetaBlock(metablock_start, ip_end, mlen_storage_ix - 3,
+                                storage_ix, storage);
+    } else {
+      EmitLongInsertLen(insert, cmd_depth, cmd_bits, cmd_histo,
+                        storage_ix, storage);
+      EmitLiterals(next_emit, insert, lit_depth, lit_bits,
+                   storage_ix, storage);
+    }
+  }
+  next_emit = ip_end;
+
+next_block:
+  // If we have more data, write a new meta-block header and prefix codes and
+  // then continue emitting commands.
+  if (input_size > 0) {
+    metablock_start = input;
+    block_size = std::min(input_size, kFirstBlockSize);
+    total_block_size = block_size;
+    // Save the bit position of the MLEN field of the meta-block header, so that
+    // we can update it later if we decide to extend this meta-block.
+    mlen_storage_ix = *storage_ix + 3;
+    StoreMetaBlockHeader(block_size, 0, storage_ix, storage);
+    // No block splits, no contexts.
+    WriteBits(13, 0, storage_ix, storage);
+    memset(lit_depth, 0, sizeof(lit_depth));
+    memset(lit_bits, 0, sizeof(lit_bits));
+    BuildAndStoreLiteralPrefixCode(input, block_size, lit_depth, lit_bits,
+                                   storage_ix, storage);
+    BuildAndStoreCommandPrefixCode(cmd_histo, cmd_depth, cmd_bits,
+                                   storage_ix, storage);
+    goto emit_commands;
+  }
+
+  if (is_last) {
+    WriteBits(1, 1, storage_ix, storage);  // islast
+    WriteBits(1, 1, storage_ix, storage);  // isempty
+    *storage_ix = (*storage_ix + 7u) & ~7u;
+  } else {
+    // If this is not the last block, update the command and distance prefix
+    // codes for the next block and store the compressed forms.
+    cmd_code[0] = 0;
+    *cmd_code_numbits = 0;
+    BuildAndStoreCommandPrefixCode(cmd_histo, cmd_depth, cmd_bits,
+                                   cmd_code_numbits, cmd_code);
+  }
+}
+
+}  // namespace brotli