Update brotli to v1.0.0-snapshot.

third_party/brotli/enc/compress_fragment.c

+/* 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 <string.h>  /* memcmp, memcpy, memset */
+
+#include "../common/constants.h"
+#include <brotli/types.h>
+#include "./brotli_bit_stream.h"
+#include "./entropy_encode.h"
+#include "./fast_log.h"
+#include "./find_match_length.h"
+#include "./memory.h"
+#include "./port.h"
+#include "./write_bits.h"
+
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+/* Same as MaxBackwardLimit(18) */
+#define MAX_DISTANCE ((1 << 18) - BROTLI_WINDOW_GAP)
+
+/* kHashMul32 multiplier has these properties:
+   * The multiplier must be odd. Otherwise we may lose the highest bit.
+   * No long streaks of ones or zeros.
+   * 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 BROTLI_INLINE uint32_t Hash(const uint8_t* p, size_t shift) {
+  const uint64_t h = (BROTLI_UNALIGNED_LOAD64(p) << 24) * kHashMul32;
+  return (uint32_t)(h >> shift);
+}
+
+static BROTLI_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 (uint32_t)(h >> shift);
+  }
+}
+
+static BROTLI_INLINE BROTLI_BOOL IsMatch(const uint8_t* p1, const uint8_t* p2) {
+  return TO_BROTLI_BOOL(
+      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.
+   Returns estimated compression ratio millibytes/char for encoding given input
+   with generated code. */
+static size_t BuildAndStoreLiteralPrefixCode(MemoryManager* m,
+                                             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;
+  size_t i;
+  if (input_size < (1 << 15)) {
+    for (i = 0; i < input_size; ++i) {
+      ++histogram[input[i]];
+    }
+    histogram_total = input_size;
+    for (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 * BROTLI_MIN(uint32_t, histogram[i], 11u);
+      histogram[i] += adjust;
+      histogram_total += adjust;
+    }
+  } else {
+    static const size_t kSampleRate = 29;
+    for (i = 0; i < input_size; i += kSampleRate) {
+      ++histogram[input[i]];
+    }
+    histogram_total = (input_size + kSampleRate - 1) / kSampleRate;
+    for (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 * BROTLI_MIN(uint32_t, histogram[i], 11u);
+      histogram[i] += adjust;
+      histogram_total += adjust;
+    }
+  }
+  BrotliBuildAndStoreHuffmanTreeFast(m, histogram, histogram_total,
+                                     /* max_bits = */ 8,
+                                     depths, bits, storage_ix, storage);
+  if (BROTLI_IS_OOM(m)) return 0;
+  {
+    size_t literal_ratio = 0;
+    for (i = 0; i < 256; ++i) {
+      if (histogram[i]) literal_ratio += histogram[i] * depths[i];
+    }
+    /* Estimated encoding ratio, millibytes per symbol. */
+    return (literal_ratio * 125) / histogram_total;
+  }
+}
+
+/* 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. */
+  HuffmanTree tree[129];
+  uint8_t cmd_depth[BROTLI_NUM_COMMAND_SYMBOLS] = { 0 };
+  uint16_t cmd_bits[64];
+
+  BrotliCreateHuffmanTree(histogram, 64, 15, tree, depth);
+  BrotliCreateHuffmanTree(&histogram[64], 64, 14, tree, &depth[64]);
+  /* We have to jump through a few hoops 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. */
+  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);
+  BrotliConvertBitDepthsToSymbols(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);
+  BrotliConvertBitDepthsToSymbols(&depth[64], 64, &bits[64]);
+  {
+    /* Create the bit length array for the full command alphabet. */
+    size_t i;
+    memset(cmd_depth, 0, 64);  /* only 64 first values were used */
+    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 (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];
+    }
+    BrotliStoreHuffmanTree(
+        cmd_depth, BROTLI_NUM_COMMAND_SYMBOLS, tree, storage_ix, storage);
+  }
+  BrotliStoreHuffmanTree(&depth[64], 64, tree, storage_ix, storage);
+}
+
+/* REQUIRES: insertlen < 6210 */
+static BROTLI_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;
+    BrotliWriteBits(depth[code], bits[code], storage_ix, storage);
+    ++histo[code];
+  } else if (insertlen < 130) {
+    const size_t tail = insertlen - 2;
+    const uint32_t nbits = Log2FloorNonZero(tail) - 1u;
+    const size_t prefix = tail >> nbits;
+    const size_t inscode = (nbits << 1) + prefix + 42;
+    BrotliWriteBits(depth[inscode], bits[inscode], storage_ix, storage);
+    BrotliWriteBits(nbits, tail - (prefix << nbits), storage_ix, storage);
+    ++histo[inscode];
+  } else if (insertlen < 2114) {
+    const size_t tail = insertlen - 66;
+    const uint32_t nbits = Log2FloorNonZero(tail);
+    const size_t code = nbits + 50;
+    BrotliWriteBits(depth[code], bits[code], storage_ix, storage);
+    BrotliWriteBits(nbits, tail - ((size_t)1 << nbits), storage_ix, storage);
+    ++histo[code];
+  } else {
+    BrotliWriteBits(depth[61], bits[61], storage_ix, storage);
+    BrotliWriteBits(12, insertlen - 2114, storage_ix, storage);
+    ++histo[21];
+  }
+}
+
+static BROTLI_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) {
+    BrotliWriteBits(depth[62], bits[62], storage_ix, storage);
+    BrotliWriteBits(14, insertlen - 6210, storage_ix, storage);
+    ++histo[22];
+  } else {
+    BrotliWriteBits(depth[63], bits[63], storage_ix, storage);
+    BrotliWriteBits(24, insertlen - 22594, storage_ix, storage);
+    ++histo[23];
+  }
+}
+
+static BROTLI_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) {
+    BrotliWriteBits(
+        depth[copylen + 14], bits[copylen + 14], storage_ix, storage);
+    ++histo[copylen + 14];
+  } else if (copylen < 134) {
+    const size_t tail = copylen - 6;
+    const uint32_t nbits = Log2FloorNonZero(tail) - 1u;
+    const size_t prefix = tail >> nbits;
+    const size_t code = (nbits << 1) + prefix + 20;
+    BrotliWriteBits(depth[code], bits[code], storage_ix, storage);
+    BrotliWriteBits(nbits, tail - (prefix << nbits), storage_ix, storage);
+    ++histo[code];
+  } else if (copylen < 2118) {
+    const size_t tail = copylen - 70;
+    const uint32_t nbits = Log2FloorNonZero(tail);
+    const size_t code = nbits + 28;
+    BrotliWriteBits(depth[code], bits[code], storage_ix, storage);
+    BrotliWriteBits(nbits, tail - ((size_t)1 << nbits), storage_ix, storage);
+    ++histo[code];
+  } else {
+    BrotliWriteBits(depth[39], bits[39], storage_ix, storage);
+    BrotliWriteBits(24, copylen - 2118, storage_ix, storage);
+    ++histo[47];
+  }
+}
+
+static BROTLI_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) {
+    BrotliWriteBits(depth[copylen - 4], bits[copylen - 4], storage_ix, storage);
+    ++histo[copylen - 4];
+  } else if (copylen < 72) {
+    const size_t tail = copylen - 8;
+    const uint32_t nbits = Log2FloorNonZero(tail) - 1;
+    const size_t prefix = tail >> nbits;
+    const size_t code = (nbits << 1) + prefix + 4;
+    BrotliWriteBits(depth[code], bits[code], storage_ix, storage);
+    BrotliWriteBits(nbits, tail - (prefix << nbits), storage_ix, storage);
+    ++histo[code];
+  } else if (copylen < 136) {
+    const size_t tail = copylen - 8;
+    const size_t code = (tail >> 5) + 30;
+    BrotliWriteBits(depth[code], bits[code], storage_ix, storage);
+    BrotliWriteBits(5, tail & 31, storage_ix, storage);
+    BrotliWriteBits(depth[64], bits[64], storage_ix, storage);
+    ++histo[code];
+    ++histo[64];
+  } else if (copylen < 2120) {
+    const size_t tail = copylen - 72;
+    const uint32_t nbits = Log2FloorNonZero(tail);
+    const size_t code = nbits + 28;
+    BrotliWriteBits(depth[code], bits[code], storage_ix, storage);
+    BrotliWriteBits(nbits, tail - ((size_t)1 << nbits), storage_ix, storage);
+    BrotliWriteBits(depth[64], bits[64], storage_ix, storage);
+    ++histo[code];
+    ++histo[64];
+  } else {
+    BrotliWriteBits(depth[39], bits[39], storage_ix, storage);
+    BrotliWriteBits(24, copylen - 2120, storage_ix, storage);
+    BrotliWriteBits(depth[64], bits[64], storage_ix, storage);
+    ++histo[47];
+    ++histo[64];
+  }
+}
+
+static BROTLI_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) {
+  const size_t d = distance + 3;
+  const uint32_t nbits = Log2FloorNonZero(d) - 1u;
+  const size_t prefix = (d >> nbits) & 1;
+  const size_t offset = (2 + prefix) << nbits;
+  const size_t distcode = 2 * (nbits - 1) + prefix + 80;
+  BrotliWriteBits(depth[distcode], bits[distcode], storage_ix, storage);
+  BrotliWriteBits(nbits, d - offset, storage_ix, storage);
+  ++histo[distcode];
+}
+
+static BROTLI_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) {
+  size_t j;
+  for (j = 0; j < len; j++) {
+    const uint8_t lit = input[j];
+    BrotliWriteBits(depth[lit], bits[lit], storage_ix, storage);
+  }
+}
+
+/* REQUIRES: len <= 1 << 20. */
+static void BrotliStoreMetaBlockHeader(
+    size_t len, BROTLI_BOOL is_uncompressed, size_t* storage_ix,
+    uint8_t* storage) {
+  /* ISLAST */
+  BrotliWriteBits(1, 0, storage_ix, storage);
+  if (len <= (1U << 16)) {
+    /* MNIBBLES is 4 */
+    BrotliWriteBits(2, 0, storage_ix, storage);
+    BrotliWriteBits(16, len - 1, storage_ix, storage);
+  } else {
+    /* MNIBBLES is 5 */
+    BrotliWriteBits(2, 1, storage_ix, storage);
+    BrotliWriteBits(20, len - 1, storage_ix, storage);
+  }
+  /* ISUNCOMPRESSED */
+  BrotliWriteBits(1, (uint64_t)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 = BROTLI_MIN(size_t, n_bits, 8 - n_unchanged_bits);
+    size_t total_bits = n_unchanged_bits + n_changed_bits;
+    uint32_t mask =
+        (~((1u << total_bits) - 1u)) | ((1u << n_unchanged_bits) - 1u);
+    uint32_t unchanged_bits = array[byte_pos] & mask;
+    uint32_t changed_bits = bits & ((1u << n_changed_bits) - 1u);
+    array[byte_pos] =
+        (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] &= (uint8_t)mask;
+  *storage_ix = new_storage_ix;
+}
+
+static BROTLI_BOOL ShouldMergeBlock(
+    const uint8_t* data, size_t len, const uint8_t* depths) {
+  size_t histo[256] = { 0 };
+  static const size_t kSampleRate = 43;
+  size_t i;
+  for (i = 0; i < len; i += kSampleRate) {
+    ++histo[data[i]];
+  }
+  {
+    const size_t total = (len + kSampleRate - 1) / kSampleRate;
+    double r = (FastLog2(total) + 0.5) * (double)total + 200;
+    for (i = 0; i < 256; ++i) {
+      r -= (double)histo[i] * (depths[i] + FastLog2(histo[i]));
+    }
+    return TO_BROTLI_BOOL(r >= 0.0);
+  }
+}
+
+/* Acceptable loss for uncompressible speedup is 2% */
+#define MIN_RATIO 980
+
+static BROTLI_INLINE BROTLI_BOOL ShouldUseUncompressedMode(
+    const uint8_t* metablock_start, const uint8_t* next_emit,
+    const size_t insertlen, const size_t literal_ratio) {
+  const size_t compressed = (size_t)(next_emit - metablock_start);
+  if (compressed * 50 > insertlen) {
+    return BROTLI_FALSE;
+  } else {
+    return TO_BROTLI_BOOL(literal_ratio > MIN_RATIO);
+  }
+}
+
+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 = (size_t)(end - begin);
+  RewindBitPosition(storage_ix_start, storage_ix, storage);
+  BrotliStoreMetaBlockHeader(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;
+}
+
+static uint32_t kCmdHistoSeed[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,
+};
+
+static BROTLI_INLINE void BrotliCompressFragmentFastImpl(
+    MemoryManager* m, const uint8_t* input, size_t input_size,
+    BROTLI_BOOL is_last, int* table, size_t table_bits, 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) {
+  uint32_t cmd_histo[128];
+  const uint8_t* ip_end;
+
+  /* "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 size_t kInputMarginBytes = BROTLI_WINDOW_GAP;
+  const size_t kMinMatchLen = 5;
+
+  const uint8_t* metablock_start = input;
+  size_t block_size = BROTLI_MIN(size_t, 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;
+
+  uint8_t lit_depth[256];
+  uint16_t lit_bits[256];
+
+  size_t literal_ratio;
+
+  const uint8_t* ip;
+  int last_distance;
+
+  const size_t shift = 64u - table_bits;
+
+  if (input_size == 0) {
+    assert(is_last);
+    BrotliWriteBits(1, 1, storage_ix, storage);  /* islast */
+    BrotliWriteBits(1, 1, storage_ix, storage);  /* isempty */
+    *storage_ix = (*storage_ix + 7u) & ~7u;
+    return;
+  }
+
+  BrotliStoreMetaBlockHeader(block_size, 0, storage_ix, storage);
+  /* No block splits, no contexts. */
+  BrotliWriteBits(13, 0, storage_ix, storage);
+
+  literal_ratio = BuildAndStoreLiteralPrefixCode(
+      m, input, block_size, lit_depth, lit_bits, storage_ix, storage);
+  if (BROTLI_IS_OOM(m)) return;
+
+  {
+    /* Store the pre-compressed command and distance prefix codes. */
+    size_t i;
+    for (i = 0; i + 7 < *cmd_code_numbits; i += 8) {
+      BrotliWriteBits(8, cmd_code[i >> 3], storage_ix, storage);
+    }
+  }
+  BrotliWriteBits(*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. */
+  memcpy(cmd_histo, kCmdHistoSeed, sizeof(kCmdHistoSeed));
+
+  /* "ip" is the input pointer. */
+  ip = input;
+  last_distance = -1;
+  ip_end = input + block_size;
+
+  if (BROTLI_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 = BROTLI_MIN(size_t, block_size - kMinMatchLen,
+                                        input_size - kInputMarginBytes);
+    const uint8_t* ip_limit = input + len_limit;
+
+    uint32_t next_hash;
+    for (next_hash = Hash(++ip, shift); ; ) {
+      /* 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 (i.e. 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;
+      assert(next_emit < ip);
+trawl:
+      do {
+        uint32_t hash = next_hash;
+        uint32_t bytes_between_hash_lookups = skip++ >> 5;
+        assert(hash == Hash(next_ip, shift));
+        ip = next_ip;
+        next_ip = ip + bytes_between_hash_lookups;
+        if (BROTLI_PREDICT_FALSE(next_ip > ip_limit)) {
+          goto emit_remainder;
+        }
+        next_hash = Hash(next_ip, shift);
+        candidate = ip - last_distance;
+        if (IsMatch(ip, candidate)) {
+          if (BROTLI_PREDICT_TRUE(candidate < ip)) {
+            table[hash] = (int)(ip - base_ip);
+            break;
+          }
+        }
+        candidate = base_ip + table[hash];
+        assert(candidate >= base_ip);
+        assert(candidate < ip);
+
+        table[hash] = (int)(ip - base_ip);
+      } while (BROTLI_PREDICT_TRUE(!IsMatch(ip, candidate)));
+
+      /* Check copy distance. If candidate is not feasible, continue search.
+         Checking is done outside of hot loop to reduce overhead. */
+      if (ip - candidate > MAX_DISTANCE) goto trawl;
+
+      /* 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 match
+         immediately afterwards. Repeat until we find no match for the input
+         without emitting some literal 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, (size_t)(ip_end - ip) - 5);
+        int distance = (int)(base - candidate);  /* > 0 */
+        size_t insert = (size_t)(base - next_emit);
+        ip += matched;
+        assert(0 == memcmp(base, candidate, matched));
+        if (BROTLI_PREDICT_TRUE(insert < 6210)) {
+          EmitInsertLen(insert, cmd_depth, cmd_bits, cmd_histo,
+                        storage_ix, storage);
+        } else if (ShouldUseUncompressedMode(metablock_start, next_emit, insert,
+                                             literal_ratio)) {
+          EmitUncompressedMetaBlock(metablock_start, base, mlen_storage_ix - 3,
+                                    storage_ix, storage);
+          input_size -= (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) {
+          BrotliWriteBits(cmd_depth[64], cmd_bits[64], storage_ix, storage);
+          ++cmd_histo[64];
+        } else {
+          EmitDistance((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 (BROTLI_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. */
+        {
+          uint64_t input_bytes = BROTLI_UNALIGNED_LOAD64(ip - 3);
+          uint32_t prev_hash = HashBytesAtOffset(input_bytes, 0, shift);
+          uint32_t cur_hash = HashBytesAtOffset(input_bytes, 3, shift);
+          table[prev_hash] = (int)(ip - base_ip - 3);
+          prev_hash = HashBytesAtOffset(input_bytes, 1, shift);
+          table[prev_hash] = (int)(ip - base_ip - 2);
+          prev_hash = HashBytesAtOffset(input_bytes, 2, shift);
+          table[prev_hash] = (int)(ip - base_ip - 1);
+
+          candidate = base_ip + table[cur_hash];
+          table[cur_hash] = (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, (size_t)(ip_end - ip) - 5);
+        if (ip - candidate > MAX_DISTANCE) break;
+        ip += matched;
+        last_distance = (int)(base - candidate);  /* > 0 */
+        assert(0 == memcmp(base, candidate, matched));
+        EmitCopyLen(matched, cmd_depth, cmd_bits, cmd_histo,
+                    storage_ix, storage);
+        EmitDistance((size_t)last_distance, cmd_depth, cmd_bits,
+                     cmd_histo, storage_ix, storage);
+
+        next_emit = ip;
+        if (BROTLI_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. */
+        {
+          uint64_t input_bytes = BROTLI_UNALIGNED_LOAD64(ip - 3);
+          uint32_t prev_hash = HashBytesAtOffset(input_bytes, 0, shift);
+          uint32_t cur_hash = HashBytesAtOffset(input_bytes, 3, shift);
+          table[prev_hash] = (int)(ip - base_ip - 3);
+          prev_hash = HashBytesAtOffset(input_bytes, 1, shift);
+          table[prev_hash] = (int)(ip - base_ip - 2);
+          prev_hash = HashBytesAtOffset(input_bytes, 2, shift);
+          table[prev_hash] = (int)(ip - base_ip - 1);
+
+          candidate = base_ip + table[cur_hash];
+          table[cur_hash] = (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 = BROTLI_MIN(size_t, 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, (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 = (size_t)(ip_end - next_emit);
+    if (BROTLI_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,
+                                         literal_ratio)) {
+      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 = BROTLI_MIN(size_t, 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;
+    BrotliStoreMetaBlockHeader(block_size, 0, storage_ix, storage);
+    /* No block splits, no contexts. */
+    BrotliWriteBits(13, 0, storage_ix, storage);
+    literal_ratio = BuildAndStoreLiteralPrefixCode(
+        m, input, block_size, lit_depth, lit_bits, storage_ix, storage);
+    if (BROTLI_IS_OOM(m)) return;
+    BuildAndStoreCommandPrefixCode(cmd_histo, cmd_depth, cmd_bits,
+                                   storage_ix, storage);
+    goto emit_commands;
+  }
+
+  if (is_last) {
+    BrotliWriteBits(1, 1, storage_ix, storage);  /* islast */
+    BrotliWriteBits(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);
+  }
+}
+
+#define FOR_TABLE_BITS_(X) X(9) X(11) X(13) X(15)
+
+#define BAKE_METHOD_PARAM_(B) \
+static BROTLI_NOINLINE void BrotliCompressFragmentFastImpl ## B(             \
+    MemoryManager* m, const uint8_t* input, size_t input_size,               \
+    BROTLI_BOOL is_last, int* table, 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) {                                  \
+  BrotliCompressFragmentFastImpl(m, input, input_size, is_last, table, B,    \
+      cmd_depth, cmd_bits, cmd_code_numbits, cmd_code, storage_ix, storage); \
+}
+FOR_TABLE_BITS_(BAKE_METHOD_PARAM_)
+#undef BAKE_METHOD_PARAM_
+
+void BrotliCompressFragmentFast(
+    MemoryManager* m, const uint8_t* input, size_t input_size,
+    BROTLI_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) {
+  const size_t table_bits = Log2FloorNonZero(table_size);
+  switch (table_bits) {
+#define CASE_(B)                                                     \
+    case B:                                                          \
+      BrotliCompressFragmentFastImpl ## B(                           \
+          m, input, input_size, is_last, table, cmd_depth, cmd_bits, \
+          cmd_code_numbits, cmd_code, storage_ix, storage);          \
+      break;
+    FOR_TABLE_BITS_(CASE_)
+#undef CASE_
+    default: assert(0); break;
+  }
+}
+
+#undef FOR_TABLE_BITS_
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}  /* extern "C" */
+#endif