Added brotli enc/ and tools/ directories.

third_party/brotli/enc/hash.h

+/* Copyright 2010 Google Inc. All Rights Reserved.
+
+   Distributed under MIT license.
+   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
+*/
+
+// A (forgetful) hash table to the data seen by the compressor, to
+// help create backward references to previous data.
+
+#ifndef BROTLI_ENC_HASH_H_
+#define BROTLI_ENC_HASH_H_
+
+#include <sys/types.h>
+#include <algorithm>
+#include <cstring>
+#include <limits>
+
+#include "./dictionary_hash.h"
+#include "./fast_log.h"
+#include "./find_match_length.h"
+#include "./port.h"
+#include "./prefix.h"
+#include "./static_dict.h"
+#include "./transform.h"
+#include "./types.h"
+
+namespace brotli {
+
+static const size_t kMaxTreeSearchDepth = 64;
+static const size_t kMaxTreeCompLength = 128;
+
+static const uint32_t kDistanceCacheIndex[] = {
+  0, 1, 2, 3, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1,
+};
+static const int kDistanceCacheOffset[] = {
+  0, 0, 0, 0, -1, 1, -2, 2, -3, 3, -1, 1, -2, 2, -3, 3
+};
+
+static const uint32_t kCutoffTransformsCount = 10;
+static const uint8_t kCutoffTransforms[] = {
+  0, 12, 27, 23, 42, 63, 56, 48, 59, 64
+};
+
+// 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;
+
+template<int kShiftBits>
+inline uint32_t Hash(const uint8_t *data) {
+  uint32_t h = BROTLI_UNALIGNED_LOAD32(data) * kHashMul32;
+  // The higher bits contain more mixture from the multiplication,
+  // so we take our results from there.
+  return h >> (32 - kShiftBits);
+}
+
+// Usually, we always choose the longest backward reference. This function
+// allows for the exception of that rule.
+//
+// If we choose a backward reference that is further away, it will
+// usually be coded with more bits. We approximate this by assuming
+// log2(distance). If the distance can be expressed in terms of the
+// last four distances, we use some heuristic constants to estimate
+// the bits cost. For the first up to four literals we use the bit
+// cost of the literals from the literal cost model, after that we
+// use the average bit cost of the cost model.
+//
+// This function is used to sometimes discard a longer backward reference
+// when it is not much longer and the bit cost for encoding it is more
+// than the saved literals.
+//
+// backward_reference_offset MUST be positive.
+inline double BackwardReferenceScore(size_t copy_length,
+                                     size_t backward_reference_offset) {
+  return 5.4 * static_cast<double>(copy_length) -
+      1.20 * Log2FloorNonZero(backward_reference_offset);
+}
+
+inline double BackwardReferenceScoreUsingLastDistance(size_t copy_length,
+    size_t distance_short_code) {
+  static const double kDistanceShortCodeBitCost[16] = {
+    -0.6, 0.95, 1.17, 1.27,
+    0.93, 0.93, 0.96, 0.96, 0.99, 0.99,
+    1.05, 1.05, 1.15, 1.15, 1.25, 1.25
+  };
+  return 5.4 * static_cast<double>(copy_length) -
+      kDistanceShortCodeBitCost[distance_short_code];
+}
+
+struct BackwardMatch {
+  BackwardMatch(void) : distance(0), length_and_code(0) {}
+
+  BackwardMatch(size_t dist, size_t len)
+      : distance(static_cast<uint32_t>(dist))
+      , length_and_code(static_cast<uint32_t>(len << 5)) {}
+
+  BackwardMatch(size_t dist, size_t len, size_t len_code)
+      : distance(static_cast<uint32_t>(dist))
+      , length_and_code(static_cast<uint32_t>(
+            (len << 5) | (len == len_code ? 0 : len_code))) {}
+
+  size_t length(void) const {
+    return length_and_code >> 5;
+  }
+  size_t length_code(void) const {
+    size_t code = length_and_code & 31;
+    return code ? code : length();
+  }
+
+  uint32_t distance;
+  uint32_t length_and_code;
+};
+
+// A (forgetful) hash table to the data seen by the compressor, to
+// help create backward references to previous data.
+//
+// This is a hash map of fixed size (kBucketSize). Starting from the
+// given index, kBucketSweep buckets are used to store values of a key.
+template <int kBucketBits, int kBucketSweep, bool kUseDictionary>
+class HashLongestMatchQuickly {
+ public:
+  HashLongestMatchQuickly(void) {
+    Reset();
+  }
+  void Reset(void) {
+    need_init_ = true;
+    num_dict_lookups_ = 0;
+    num_dict_matches_ = 0;
+  }
+  void Init(void) {
+    if (need_init_) {
+      // It is not strictly necessary to fill this buffer here, but
+      // not filling will make the results of the compression stochastic
+      // (but correct). This is because random data would cause the
+      // system to find accidentally good backward references here and there.
+      memset(&buckets_[0], 0, sizeof(buckets_));
+      need_init_ = false;
+    }
+  }
+  void InitForData(const uint8_t* data, size_t num) {
+    for (size_t i = 0; i < num; ++i) {
+      const uint32_t key = HashBytes(&data[i]);
+      memset(&buckets_[key], 0, kBucketSweep * sizeof(buckets_[0]));
+      need_init_ = false;
+    }
+  }
+  // Look at 4 bytes at data.
+  // Compute a hash from these, and store the value somewhere within
+  // [ix .. ix+3].
+  inline void Store(const uint8_t *data, const uint32_t ix) {
+    const uint32_t key = HashBytes(data);
+    // Wiggle the value with the bucket sweep range.
+    const uint32_t off = (ix >> 3) % kBucketSweep;
+    buckets_[key + off] = ix;
+  }
+
+  // Find a longest backward match of &ring_buffer[cur_ix & ring_buffer_mask]
+  // up to the length of max_length and stores the position cur_ix in the
+  // hash table.
+  //
+  // Does not look for matches longer than max_length.
+  // Does not look for matches further away than max_backward.
+  // Writes the best found match length into best_len_out.
+  // Writes the index (&data[index]) of the start of the best match into
+  // best_distance_out.
+  inline bool FindLongestMatch(const uint8_t * __restrict ring_buffer,
+                               const size_t ring_buffer_mask,
+                               const int* __restrict distance_cache,
+                               const size_t cur_ix,
+                               const size_t max_length,
+                               const size_t max_backward,
+                               size_t * __restrict best_len_out,
+                               size_t * __restrict best_len_code_out,
+                               size_t * __restrict best_distance_out,
+                               double* __restrict best_score_out) {
+    const size_t best_len_in = *best_len_out;
+    const size_t cur_ix_masked = cur_ix & ring_buffer_mask;
+    const uint32_t key = HashBytes(&ring_buffer[cur_ix_masked]);
+    int compare_char = ring_buffer[cur_ix_masked + best_len_in];
+    double best_score = *best_score_out;
+    size_t best_len = best_len_in;
+    size_t cached_backward = static_cast<size_t>(distance_cache[0]);
+    size_t prev_ix = cur_ix - cached_backward;
+    bool match_found = false;
+    if (prev_ix < cur_ix) {
+      prev_ix &= static_cast<uint32_t>(ring_buffer_mask);
+      if (compare_char == ring_buffer[prev_ix + best_len]) {
+        size_t len = FindMatchLengthWithLimit(&ring_buffer[prev_ix],
+                                              &ring_buffer[cur_ix_masked],
+                                              max_length);
+        if (len >= 4) {
+          best_score = BackwardReferenceScoreUsingLastDistance(len, 0);
+          best_len = len;
+          *best_len_out = len;
+          *best_len_code_out = len;
+          *best_distance_out = cached_backward;
+          *best_score_out = best_score;
+          compare_char = ring_buffer[cur_ix_masked + best_len];
+          if (kBucketSweep == 1) {
+            buckets_[key] = static_cast<uint32_t>(cur_ix);
+            return true;
+          } else {
+            match_found = true;
+          }
+        }
+      }
+    }
+    if (kBucketSweep == 1) {
+      // Only one to look for, don't bother to prepare for a loop.
+      prev_ix = buckets_[key];
+      buckets_[key] = static_cast<uint32_t>(cur_ix);
+      size_t backward = cur_ix - prev_ix;
+      prev_ix &= static_cast<uint32_t>(ring_buffer_mask);
+      if (compare_char != ring_buffer[prev_ix + best_len_in]) {
+        return false;
+      }
+      if (PREDICT_FALSE(backward == 0 || backward > max_backward)) {
+        return false;
+      }
+      const size_t len = FindMatchLengthWithLimit(&ring_buffer[prev_ix],
+                                                  &ring_buffer[cur_ix_masked],
+                                                  max_length);
+      if (len >= 4) {
+        *best_len_out = len;
+        *best_len_code_out = len;
+        *best_distance_out = backward;
+        *best_score_out = BackwardReferenceScore(len, backward);
+        return true;
+      }
+    } else {
+      uint32_t *bucket = buckets_ + key;
+      prev_ix = *bucket++;
+      for (int i = 0; i < kBucketSweep; ++i, prev_ix = *bucket++) {
+        const size_t backward = cur_ix - prev_ix;
+        prev_ix &= static_cast<uint32_t>(ring_buffer_mask);
+        if (compare_char != ring_buffer[prev_ix + best_len]) {
+          continue;
+        }
+        if (PREDICT_FALSE(backward == 0 || backward > max_backward)) {
+          continue;
+        }
+        const size_t len = FindMatchLengthWithLimit(&ring_buffer[prev_ix],
+                                                    &ring_buffer[cur_ix_masked],
+                                                    max_length);
+        if (len >= 4) {
+          const double score = BackwardReferenceScore(len, backward);
+          if (best_score < score) {
+            best_score = score;
+            best_len = len;
+            *best_len_out = best_len;
+            *best_len_code_out = best_len;
+            *best_distance_out = backward;
+            *best_score_out = score;
+            compare_char = ring_buffer[cur_ix_masked + best_len];
+            match_found = true;
+          }
+        }
+      }
+    }
+    if (kUseDictionary && !match_found &&
+        num_dict_matches_ >= (num_dict_lookups_ >> 7)) {
+      ++num_dict_lookups_;
+      const uint32_t dict_key = Hash<14>(&ring_buffer[cur_ix_masked]) << 1;
+      const uint16_t v = kStaticDictionaryHash[dict_key];
+      if (v > 0) {
+        const uint32_t len = v & 31;
+        const uint32_t dist = v >> 5;
+        const size_t offset =
+            kBrotliDictionaryOffsetsByLength[len] + len * dist;
+        if (len <= max_length) {
+          const size_t matchlen =
+              FindMatchLengthWithLimit(&ring_buffer[cur_ix_masked],
+                                       &kBrotliDictionary[offset], len);
+          if (matchlen + kCutoffTransformsCount > len && matchlen > 0) {
+            const size_t transform_id = kCutoffTransforms[len - matchlen];
+            const size_t word_id =
+                transform_id * (1u << kBrotliDictionarySizeBitsByLength[len]) +
+                dist;
+            const size_t backward = max_backward + word_id + 1;
+            const double score = BackwardReferenceScore(matchlen, backward);
+            if (best_score < score) {
+              ++num_dict_matches_;
+              best_score = score;
+              best_len = matchlen;
+              *best_len_out = best_len;
+              *best_len_code_out = len;
+              *best_distance_out = backward;
+              *best_score_out = best_score;
+              match_found = true;
+            }
+          }
+        }
+      }
+    }
+    const uint32_t off = (cur_ix >> 3) % kBucketSweep;
+    buckets_[key + off] = static_cast<uint32_t>(cur_ix);
+    return match_found;
+  }
+
+  enum { kHashLength = 5 };
+  enum { kHashTypeLength = 8 };
+  // HashBytes is the function that chooses the bucket to place
+  // the address in. The HashLongestMatch and HashLongestMatchQuickly
+  // classes have separate, different implementations of hashing.
+  static uint32_t HashBytes(const uint8_t *data) {
+    // Computing a hash based on 5 bytes works much better for
+    // qualities 1 and 3, where the next hash value is likely to replace
+    uint64_t h = (BROTLI_UNALIGNED_LOAD64(data) << 24) * kHashMul32;
+    // The higher bits contain more mixture from the multiplication,
+    // so we take our results from there.
+    return static_cast<uint32_t>(h >> (64 - kBucketBits));
+  }
+
+  enum { kHashMapSize = 4 << kBucketBits };
+
+ private:
+  static const uint32_t kBucketSize = 1 << kBucketBits;
+  uint32_t buckets_[kBucketSize + kBucketSweep];
+  // True if buckets_ array needs to be initialized.
+  bool need_init_;
+  size_t num_dict_lookups_;
+  size_t num_dict_matches_;
+};
+
+// A (forgetful) hash table to the data seen by the compressor, to
+// help create backward references to previous data.
+//
+// This is a hash map of fixed size (kBucketSize) to a ring buffer of
+// fixed size (kBlockSize). The ring buffer contains the last kBlockSize
+// index positions of the given hash key in the compressed data.
+template <int kBucketBits,
+          int kBlockBits,
+          int kNumLastDistancesToCheck>
+class HashLongestMatch {
+ public:
+  HashLongestMatch(void) {
+    Reset();
+  }
+
+  void Reset(void) {
+    need_init_ = true;
+    num_dict_lookups_ = 0;
+    num_dict_matches_ = 0;
+  }
+
+  void Init(void) {
+    if (need_init_) {
+      memset(&num_[0], 0, sizeof(num_));
+      need_init_ = false;
+    }
+  }
+
+  void InitForData(const uint8_t* data, size_t num) {
+    for (size_t i = 0; i < num; ++i) {
+      const uint32_t key = HashBytes(&data[i]);
+      num_[key] = 0;
+      need_init_ = false;
+    }
+  }
+
+  // Look at 3 bytes at data.
+  // Compute a hash from these, and store the value of ix at that position.
+  inline void Store(const uint8_t *data, const uint32_t ix) {
+    const uint32_t key = HashBytes(data);
+    const int minor_ix = num_[key] & kBlockMask;
+    buckets_[key][minor_ix] = ix;
+    ++num_[key];
+  }
+
+  // Find a longest backward match of &data[cur_ix] up to the length of
+  // max_length and stores the position cur_ix in the hash table.
+  //
+  // Does not look for matches longer than max_length.
+  // Does not look for matches further away than max_backward.
+  // Writes the best found match length into best_len_out.
+  // Writes the index (&data[index]) offset from the start of the best match
+  // into best_distance_out.
+  // Write the score of the best match into best_score_out.
+  bool FindLongestMatch(const uint8_t * __restrict data,
+                        const size_t ring_buffer_mask,
+                        const int* __restrict distance_cache,
+                        const size_t cur_ix,
+                        const size_t max_length,
+                        const size_t max_backward,
+                        size_t * __restrict best_len_out,
+                        size_t * __restrict best_len_code_out,
+                        size_t * __restrict best_distance_out,
+                        double * __restrict best_score_out) {
+    *best_len_code_out = 0;
+    const size_t cur_ix_masked = cur_ix & ring_buffer_mask;
+    bool match_found = false;
+    // Don't accept a short copy from far away.
+    double best_score = *best_score_out;
+    size_t best_len = *best_len_out;
+    *best_len_out = 0;
+    // Try last distance first.
+    for (size_t i = 0; i < kNumLastDistancesToCheck; ++i) {
+      const size_t idx = kDistanceCacheIndex[i];
+      const size_t backward =
+          static_cast<size_t>(distance_cache[idx] + kDistanceCacheOffset[i]);
+      size_t prev_ix = static_cast<size_t>(cur_ix - backward);
+      if (prev_ix >= cur_ix) {
+        continue;
+      }
+      if (PREDICT_FALSE(backward > max_backward)) {
+        continue;
+      }
+      prev_ix &= ring_buffer_mask;
+
+      if (cur_ix_masked + best_len > ring_buffer_mask ||
+          prev_ix + best_len > ring_buffer_mask ||
+          data[cur_ix_masked + best_len] != data[prev_ix + best_len]) {
+        continue;
+      }
+      const size_t len = FindMatchLengthWithLimit(&data[prev_ix],
+                                                  &data[cur_ix_masked],
+                                                  max_length);
+      if (len >= 3 || (len == 2 && i < 2)) {
+        // Comparing for >= 2 does not change the semantics, but just saves for
+        // a few unnecessary binary logarithms in backward reference score,
+        // since we are not interested in such short matches.
+        double score = BackwardReferenceScoreUsingLastDistance(len, i);
+        if (best_score < score) {
+          best_score = score;
+          best_len = len;
+          *best_len_out = best_len;
+          *best_len_code_out = best_len;
+          *best_distance_out = backward;
+          *best_score_out = best_score;
+          match_found = true;
+        }
+      }
+    }
+    const uint32_t key = HashBytes(&data[cur_ix_masked]);
+    const uint32_t * __restrict const bucket = &buckets_[key][0];
+    const size_t down = (num_[key] > kBlockSize) ? (num_[key] - kBlockSize) : 0;
+    for (size_t i = num_[key]; i > down;) {
+      --i;
+      size_t prev_ix = bucket[i & kBlockMask];
+      const size_t backward = cur_ix - prev_ix;
+      if (PREDICT_FALSE(backward == 0 || backward > max_backward)) {
+        break;
+      }
+      prev_ix &= ring_buffer_mask;
+      if (cur_ix_masked + best_len > ring_buffer_mask ||
+          prev_ix + best_len > ring_buffer_mask ||
+          data[cur_ix_masked + best_len] != data[prev_ix + best_len]) {
+        continue;
+      }
+      const size_t len = FindMatchLengthWithLimit(&data[prev_ix],
+                                                  &data[cur_ix_masked],
+                                                  max_length);
+      if (len >= 4) {
+        // Comparing for >= 3 does not change the semantics, but just saves
+        // for a few unnecessary binary logarithms in backward reference
+        // score, since we are not interested in such short matches.
+        double score = BackwardReferenceScore(len, backward);
+        if (best_score < score) {
+          best_score = score;
+          best_len = len;
+          *best_len_out = best_len;
+          *best_len_code_out = best_len;
+          *best_distance_out = backward;
+          *best_score_out = best_score;
+          match_found = true;
+        }
+      }
+    }
+    buckets_[key][num_[key] & kBlockMask] = static_cast<uint32_t>(cur_ix);
+    ++num_[key];
+    if (!match_found && num_dict_matches_ >= (num_dict_lookups_ >> 7)) {
+      size_t dict_key = Hash<14>(&data[cur_ix_masked]) << 1;
+      for (int k = 0; k < 2; ++k, ++dict_key) {
+        ++num_dict_lookups_;
+        const uint16_t v = kStaticDictionaryHash[dict_key];
+        if (v > 0) {
+          const size_t len = v & 31;
+          const size_t dist = v >> 5;
+          const size_t offset =
+              kBrotliDictionaryOffsetsByLength[len] + len * dist;
+          if (len <= max_length) {
+            const size_t matchlen =
+                FindMatchLengthWithLimit(&data[cur_ix_masked],
+                                         &kBrotliDictionary[offset], len);
+            if (matchlen + kCutoffTransformsCount > len && matchlen > 0) {
+              const size_t transform_id = kCutoffTransforms[len - matchlen];
+              const size_t word_id =
+                  transform_id * (1 << kBrotliDictionarySizeBitsByLength[len]) +
+                  dist;
+              const size_t backward = max_backward + word_id + 1;
+              double score = BackwardReferenceScore(matchlen, backward);
+              if (best_score < score) {
+                ++num_dict_matches_;
+                best_score = score;
+                best_len = matchlen;
+                *best_len_out = best_len;
+                *best_len_code_out = len;
+                *best_distance_out = backward;
+                *best_score_out = best_score;
+                match_found = true;
+              }
+            }
+          }
+        }
+      }
+    }
+    return match_found;
+  }
+
+  // Finds all backward matches of &data[cur_ix & ring_buffer_mask] up to the
+  // length of max_length and stores the position cur_ix in the hash table.
+  //
+  // Sets *num_matches to the number of matches found, and stores the found
+  // matches in matches[0] to matches[*num_matches - 1]. The matches will be
+  // sorted by strictly increasing length and (non-strictly) increasing
+  // distance.
+  size_t FindAllMatches(const uint8_t* data,
+                        const size_t ring_buffer_mask,
+                        const size_t cur_ix,
+                        const size_t max_length,
+                        const size_t max_backward,
+                        BackwardMatch* matches) {
+    BackwardMatch* const orig_matches = matches;
+    const size_t cur_ix_masked = cur_ix & ring_buffer_mask;
+    size_t best_len = 1;
+    size_t stop = cur_ix - 64;
+    if (cur_ix < 64) { stop = 0; }
+    for (size_t i = cur_ix - 1; i > stop && best_len <= 2; --i) {
+      size_t prev_ix = i;
+      const size_t backward = cur_ix - prev_ix;
+      if (PREDICT_FALSE(backward > max_backward)) {
+        break;
+      }
+      prev_ix &= ring_buffer_mask;
+      if (data[cur_ix_masked] != data[prev_ix] ||
+          data[cur_ix_masked + 1] != data[prev_ix + 1]) {
+        continue;
+      }
+      const size_t len =
+          FindMatchLengthWithLimit(&data[prev_ix], &data[cur_ix_masked],
+                                   max_length);
+      if (len > best_len) {
+        best_len = len;
+        *matches++ = BackwardMatch(backward, len);
+      }
+    }
+    const uint32_t key = HashBytes(&data[cur_ix_masked]);
+    const uint32_t * __restrict const bucket = &buckets_[key][0];
+    const size_t down = (num_[key] > kBlockSize) ? (num_[key] - kBlockSize) : 0;
+    for (size_t i = num_[key]; i > down;) {
+      --i;
+      size_t prev_ix = bucket[i & kBlockMask];
+      const size_t backward = cur_ix - prev_ix;
+      if (PREDICT_FALSE(backward == 0 || backward > max_backward)) {
+        break;
+      }
+      prev_ix &= ring_buffer_mask;
+      if (cur_ix_masked + best_len > ring_buffer_mask ||
+          prev_ix + best_len > ring_buffer_mask ||
+          data[cur_ix_masked + best_len] != data[prev_ix + best_len]) {
+        continue;
+      }
+      const size_t len =
+          FindMatchLengthWithLimit(&data[prev_ix], &data[cur_ix_masked],
+                                   max_length);
+      if (len > best_len) {
+        best_len = len;
+        *matches++ = BackwardMatch(backward, len);
+      }
+    }
+    buckets_[key][num_[key] & kBlockMask] = static_cast<uint32_t>(cur_ix);
+    ++num_[key];
+    uint32_t dict_matches[kMaxDictionaryMatchLen + 1];
+    for (size_t i = 0; i <= kMaxDictionaryMatchLen; ++i) {
+      dict_matches[i] = kInvalidMatch;
+    }
+    size_t minlen = std::max<size_t>(4, best_len + 1);
+    if (FindAllStaticDictionaryMatches(&data[cur_ix_masked], minlen, max_length,
+                                       &dict_matches[0])) {
+      size_t maxlen = std::min<size_t>(kMaxDictionaryMatchLen, max_length);
+      for (size_t l = minlen; l <= maxlen; ++l) {
+        uint32_t dict_id = dict_matches[l];
+        if (dict_id < kInvalidMatch) {
+          *matches++ = BackwardMatch(max_backward + (dict_id >> 5) + 1, l,
+                                     dict_id & 31);
+        }
+      }
+    }
+    return static_cast<size_t>(matches - orig_matches);
+  }
+
+  enum { kHashLength = 4 };
+  enum { kHashTypeLength = 4 };
+
+  // HashBytes is the function that chooses the bucket to place
+  // the address in. The HashLongestMatch and HashLongestMatchQuickly
+  // classes have separate, different implementations of hashing.
+  static uint32_t HashBytes(const uint8_t *data) {
+    uint32_t h = BROTLI_UNALIGNED_LOAD32(data) * kHashMul32;
+    // The higher bits contain more mixture from the multiplication,
+    // so we take our results from there.
+    return h >> (32 - kBucketBits);
+  }
+
+  enum { kHashMapSize = 2 << kBucketBits };
+
+  static const size_t kMaxNumMatches = 64 + (1 << kBlockBits);
+
+ private:
+  // Number of hash buckets.
+  static const uint32_t kBucketSize = 1 << kBucketBits;
+
+  // Only kBlockSize newest backward references are kept,
+  // and the older are forgotten.
+  static const uint32_t kBlockSize = 1 << kBlockBits;
+
+  // Mask for accessing entries in a block (in a ringbuffer manner).
+  static const uint32_t kBlockMask = (1 << kBlockBits) - 1;
+
+  // Number of entries in a particular bucket.
+  uint16_t num_[kBucketSize];
+
+  // Buckets containing kBlockSize of backward references.
+  uint32_t buckets_[kBucketSize][kBlockSize];
+
+  // True if num_ array needs to be initialized.
+  bool need_init_;
+
+  size_t num_dict_lookups_;
+  size_t num_dict_matches_;
+};
+
+// A (forgetful) hash table where each hash bucket contains a binary tree of
+// sequences whose first 4 bytes share the same hash code.
+// Each sequence is kMaxTreeCompLength long and is identified by its starting
+// position in the input data. The binary tree is sorted by the lexicographic
+// order of the sequences, and it is also a max-heap with respect to the
+// starting positions.
+class HashToBinaryTree {
+ public:
+  HashToBinaryTree() : forest_(NULL) {
+    Reset();
+  }
+
+  ~HashToBinaryTree() {
+    delete[] forest_;
+  }
+
+  void Reset() {
+    need_init_ = true;
+  }
+
+  void Init(int lgwin, size_t position, size_t bytes, bool is_last) {
+    if (need_init_) {
+      window_mask_ = (1u << lgwin) - 1u;
+      invalid_pos_ = static_cast<uint32_t>(-window_mask_);
+      for (uint32_t i = 0; i < kBucketSize; i++) {
+        buckets_[i] = invalid_pos_;
+      }
+      size_t num_nodes = (position == 0 && is_last) ? bytes : window_mask_ + 1;
+      forest_ = new uint32_t[2 * num_nodes];
+      need_init_ = false;
+    }
+  }
+
+  // Finds all backward matches of &data[cur_ix & ring_buffer_mask] up to the
+  // length of max_length and stores the position cur_ix in the hash table.
+  //
+  // Sets *num_matches to the number of matches found, and stores the found
+  // matches in matches[0] to matches[*num_matches - 1]. The matches will be
+  // sorted by strictly increasing length and (non-strictly) increasing
+  // distance.
+  size_t FindAllMatches(const uint8_t* data,
+                        const size_t ring_buffer_mask,
+                        const size_t cur_ix,
+                        const size_t max_length,
+                        const size_t max_backward,
+                        BackwardMatch* matches) {
+    BackwardMatch* const orig_matches = matches;
+    const size_t cur_ix_masked = cur_ix & ring_buffer_mask;
+    size_t best_len = 1;
+    size_t stop = cur_ix - 64;
+    if (cur_ix < 64) { stop = 0; }
+    for (size_t i = cur_ix - 1; i > stop && best_len <= 2; --i) {
+      size_t prev_ix = i;
+      const size_t backward = cur_ix - prev_ix;
+      if (PREDICT_FALSE(backward > max_backward)) {
+        break;
+      }
+      prev_ix &= ring_buffer_mask;
+      if (data[cur_ix_masked] != data[prev_ix] ||
+          data[cur_ix_masked + 1] != data[prev_ix + 1]) {
+        continue;
+      }
+      const size_t len =
+          FindMatchLengthWithLimit(&data[prev_ix], &data[cur_ix_masked],
+                                   max_length);
+      if (len > best_len) {
+        best_len = len;
+        *matches++ = BackwardMatch(backward, len);
+      }
+    }
+    if (best_len < max_length) {
+      matches = StoreAndFindMatches(data, cur_ix, ring_buffer_mask,
+                                    max_length, &best_len, matches);
+    }
+    uint32_t dict_matches[kMaxDictionaryMatchLen + 1];
+    for (size_t i = 0; i <= kMaxDictionaryMatchLen; ++i) {
+      dict_matches[i] = kInvalidMatch;
+    }
+    size_t minlen = std::max<size_t>(4, best_len + 1);
+    if (FindAllStaticDictionaryMatches(&data[cur_ix_masked], minlen, max_length,
+                                       &dict_matches[0])) {
+      size_t maxlen = std::min<size_t>(kMaxDictionaryMatchLen, max_length);
+      for (size_t l = minlen; l <= maxlen; ++l) {
+        uint32_t dict_id = dict_matches[l];
+        if (dict_id < kInvalidMatch) {
+          *matches++ = BackwardMatch(max_backward + (dict_id >> 5) + 1, l,
+                                     dict_id & 31);
+        }
+      }
+    }
+    return static_cast<size_t>(matches - orig_matches);
+  }
+
+  // Stores the hash of the next 4 bytes and re-roots the binary tree at the
+  // current sequence, without returning any matches.
+  // REQUIRES: cur_ix + kMaxTreeCompLength <= end-of-current-block
+  void Store(const uint8_t* data,
+             const size_t ring_buffer_mask,
+             const size_t cur_ix) {
+    size_t best_len = 0;
+    StoreAndFindMatches(data, cur_ix, ring_buffer_mask, kMaxTreeCompLength,
+                        &best_len, NULL);
+  }
+
+  void StitchToPreviousBlock(size_t num_bytes,
+                             size_t position,
+                             const uint8_t* ringbuffer,
+                             size_t ringbuffer_mask) {
+    if (num_bytes >= 3 && position >= kMaxTreeCompLength) {
+      // Store the last `kMaxTreeCompLength - 1` positions in the hasher.
+      // These could not be calculated before, since they require knowledge
+      // of both the previous and the current block.
+      const size_t i_start = position - kMaxTreeCompLength + 1;
+      const size_t i_end = std::min(position, i_start + num_bytes);
+      for (size_t i = i_start; i < i_end; ++i) {
+        // We know that i + kMaxTreeCompLength <= position + num_bytes, i.e. the
+        // end of the current block and that we have at least
+        // kMaxTreeCompLength tail in the ringbuffer.
+        Store(ringbuffer, ringbuffer_mask, i);
+      }
+    }
+  }
+
+  static const size_t kMaxNumMatches = 64 + kMaxTreeSearchDepth;
+
+ private:
+  // Stores the hash of the next 4 bytes and in a single tree-traversal, the
+  // hash bucket's binary tree is searched for matches and is re-rooted at the
+  // current position.
+  //
+  // If less than kMaxTreeCompLength data is available, the hash bucket of the
+  // current position is searched for matches, but the state of the hash table
+  // is not changed, since we can not know the final sorting order of the
+  // current (incomplete) sequence.
+  //
+  // This function must be called with increasing cur_ix positions.
+  BackwardMatch* StoreAndFindMatches(const uint8_t* const __restrict data,
+                                     const size_t cur_ix,
+                                     const size_t ring_buffer_mask,
+                                     const size_t max_length,
+                                     size_t* const __restrict best_len,
+                                     BackwardMatch* __restrict matches) {
+    const size_t cur_ix_masked = cur_ix & ring_buffer_mask;
+    const size_t max_backward = window_mask_ - 15;
+    const size_t max_comp_len = std::min(max_length, kMaxTreeCompLength);
+    const bool reroot_tree = max_length >= kMaxTreeCompLength;
+    const uint32_t key = HashBytes(&data[cur_ix_masked]);
+    size_t prev_ix = buckets_[key];
+    // The forest index of the rightmost node of the left subtree of the new
+    // root, updated as we traverse and reroot the tree of the hash bucket.
+    size_t node_left = LeftChildIndex(cur_ix);
+    // The forest index of the leftmost node of the right subtree of the new
+    // root, updated as we traverse and reroot the tree of the hash bucket.
+    size_t node_right = RightChildIndex(cur_ix);
+    // The match length of the rightmost node of the left subtree of the new
+    // root, updated as we traverse and reroot the tree of the hash bucket.
+    size_t best_len_left = 0;
+    // The match length of the leftmost node of the right subtree of the new
+    // root, updated as we traverse and reroot the tree of the hash bucket.
+    size_t best_len_right = 0;
+    if (reroot_tree) {
+      buckets_[key] = static_cast<uint32_t>(cur_ix);
+    }
+    for (size_t depth_remaining = kMaxTreeSearchDepth; ; --depth_remaining) {
+      const size_t backward = cur_ix - prev_ix;
+      const size_t prev_ix_masked = prev_ix & ring_buffer_mask;
+      if (backward == 0 || backward > max_backward || depth_remaining == 0) {
+        if (reroot_tree) {
+          forest_[node_left] = invalid_pos_;
+          forest_[node_right] = invalid_pos_;
+        }
+        break;
+      }
+      const size_t cur_len = std::min(best_len_left, best_len_right);
+      const size_t len = cur_len +
+          FindMatchLengthWithLimit(&data[cur_ix_masked + cur_len],
+                                   &data[prev_ix_masked + cur_len],
+                                   max_length - cur_len);
+      if (len > *best_len) {
+        *best_len = len;
+        if (matches) {
+          *matches++ = BackwardMatch(backward, len);
+        }
+        if (len >= max_comp_len) {
+          if (reroot_tree) {
+            forest_[node_left] = forest_[LeftChildIndex(prev_ix)];
+            forest_[node_right] = forest_[RightChildIndex(prev_ix)];
+          }
+          break;
+        }
+      }
+      if (data[cur_ix_masked + len] > data[prev_ix_masked + len]) {
+        best_len_left = len;
+        if (reroot_tree) {
+          forest_[node_left] = static_cast<uint32_t>(prev_ix);
+        }
+        node_left = RightChildIndex(prev_ix);
+        prev_ix = forest_[node_left];
+      } else {
+        best_len_right = len;
+        if (reroot_tree) {
+          forest_[node_right] = static_cast<uint32_t>(prev_ix);
+        }
+        node_right = LeftChildIndex(prev_ix);
+        prev_ix = forest_[node_right];
+      }
+    }
+    return matches;
+  }
+
+  inline size_t LeftChildIndex(const size_t pos) {
+    return 2 * (pos & window_mask_);
+  }
+
+  inline size_t RightChildIndex(const size_t pos) {
+    return 2 * (pos & window_mask_) + 1;
+  }
+
+  static uint32_t HashBytes(const uint8_t *data) {
+    uint32_t h = BROTLI_UNALIGNED_LOAD32(data) * kHashMul32;
+    // The higher bits contain more mixture from the multiplication,
+    // so we take our results from there.
+    return h >> (32 - kBucketBits);
+  }
+
+  static const int kBucketBits = 17;
+  static const size_t kBucketSize = 1 << kBucketBits;
+
+  // The window size minus 1
+  size_t window_mask_;
+
+  // Hash table that maps the 4-byte hashes of the sequence to the last
+  // position where this hash was found, which is the root of the binary
+  // tree of sequences that share this hash bucket.
+  uint32_t buckets_[kBucketSize];
+
+  // The union of the binary trees of each hash bucket. The root of the tree
+  // corresponding to a hash is a sequence starting at buckets_[hash] and
+  // the left and right children of a sequence starting at pos are
+  // forest_[2 * pos] and forest_[2 * pos + 1].
+  uint32_t* forest_;
+
+  // A position used to mark a non-existent sequence, i.e. a tree is empty if
+  // its root is at invalid_pos_ and a node is a leaf if both its children
+  // are at invalid_pos_.
+  uint32_t invalid_pos_;
+
+  bool need_init_;
+};
+
+struct Hashers {
+  // For kBucketSweep == 1, enabling the dictionary lookup makes compression
+  // a little faster (0.5% - 1%) and it compresses 0.15% better on small text
+  // and html inputs.
+  typedef HashLongestMatchQuickly<16, 1, true> H2;
+  typedef HashLongestMatchQuickly<16, 2, false> H3;
+  typedef HashLongestMatchQuickly<17, 4, true> H4;
+  typedef HashLongestMatch<14, 4, 4> H5;
+  typedef HashLongestMatch<14, 5, 4> H6;
+  typedef HashLongestMatch<15, 6, 10> H7;
+  typedef HashLongestMatch<15, 7, 10> H8;
+  typedef HashLongestMatch<15, 8, 16> H9;
+  typedef HashToBinaryTree H10;
+
+  Hashers(void) : hash_h2(0), hash_h3(0), hash_h4(0), hash_h5(0),
+                  hash_h6(0), hash_h7(0), hash_h8(0), hash_h9(0), hash_h10(0) {}
+
+  ~Hashers(void) {
+    delete hash_h2;
+    delete hash_h3;
+    delete hash_h4;
+    delete hash_h5;
+    delete hash_h6;
+    delete hash_h7;
+    delete hash_h8;
+    delete hash_h9;
+    delete hash_h10;
+  }
+
+  void Init(int type) {
+    switch (type) {
+      case 2: hash_h2 = new H2; break;
+      case 3: hash_h3 = new H3; break;
+      case 4: hash_h4 = new H4; break;
+      case 5: hash_h5 = new H5; break;
+      case 6: hash_h6 = new H6; break;
+      case 7: hash_h7 = new H7; break;
+      case 8: hash_h8 = new H8; break;
+      case 9: hash_h9 = new H9; break;
+      case 10: hash_h10 = new H10; break;
+      default: break;
+    }
+  }
+
+  template<typename Hasher>
+  void WarmupHash(const size_t size, const uint8_t* dict, Hasher* hasher) {
+    hasher->Init();
+    for (size_t i = 0; i + Hasher::kHashTypeLength - 1 < size; i++) {
+      hasher->Store(&dict[i], static_cast<uint32_t>(i));
+    }
+  }
+
+  // Custom LZ77 window.
+  void PrependCustomDictionary(
+      int type, int lgwin, const size_t size, const uint8_t* dict) {
+    switch (type) {
+      case 2: WarmupHash(size, dict, hash_h2); break;
+      case 3: WarmupHash(size, dict, hash_h3); break;
+      case 4: WarmupHash(size, dict, hash_h4); break;
+      case 5: WarmupHash(size, dict, hash_h5); break;
+      case 6: WarmupHash(size, dict, hash_h6); break;
+      case 7: WarmupHash(size, dict, hash_h7); break;
+      case 8: WarmupHash(size, dict, hash_h8); break;
+      case 9: WarmupHash(size, dict, hash_h9); break;
+      case 10:
+        hash_h10->Init(lgwin, 0, size, false);
+        for (size_t i = 0; i + kMaxTreeCompLength - 1 < size; ++i) {
+          hash_h10->Store(dict, std::numeric_limits<size_t>::max(), i);
+        }
+        break;
+      default: break;
+    }
+  }
+
+
+  H2* hash_h2;
+  H3* hash_h3;
+  H4* hash_h4;
+  H5* hash_h5;
+  H6* hash_h6;
+  H7* hash_h7;
+  H8* hash_h8;
+  H9* hash_h9;
+  H10* hash_h10;
+};
+
+}  // namespace brotli
+
+#endif  // BROTLI_ENC_HASH_H_