1/* NOLINT(build/header_guard) */
2/* Copyright 2010 Google Inc. All Rights Reserved.
3
4   Distributed under MIT license.
5   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
6*/
7
8/* template parameters: FN */
9
10/* A (forgetful) hash table to the data seen by the compressor, to
11   help create backward references to previous data.
12
13   This is a hash map of fixed size (bucket_size_) to a ring buffer of
14   fixed size (block_size_). The ring buffer contains the last block_size_
15   index positions of the given hash key in the compressed data. */
16
17#define HashLongestMatch HASHER()
18
19static BROTLI_INLINE size_t FN(HashTypeLength)(void) { return 8; }
20static BROTLI_INLINE size_t FN(StoreLookahead)(void) { return 8; }
21
22/* HashBytes is the function that chooses the bucket to place the address in. */
23static BROTLI_INLINE uint32_t FN(HashBytes)(const uint8_t *data,
24                                            const uint64_t mask,
25                                            const int shift) {
26  const uint64_t h = (BROTLI_UNALIGNED_LOAD64(data) & mask) * kHashMul64Long;
27  /* The higher bits contain more mixture from the multiplication,
28     so we take our results from there. */
29  return (uint32_t)(h >> shift);
30}
31
32typedef struct HashLongestMatch {
33  /* Number of hash buckets. */
34  size_t bucket_size_;
35  /* Only block_size_ newest backward references are kept,
36     and the older are forgotten. */
37  size_t block_size_;
38  /* Left-shift for computing hash bucket index from hash value. */
39  int hash_shift_;
40  /* Mask for selecting the next 4-8 bytes of input */
41  uint64_t hash_mask_;
42  /* Mask for accessing entries in a block (in a ring-buffer manner). */
43  uint32_t block_mask_;
44
45  /* --- Dynamic size members --- */
46
47  /* Number of entries in a particular bucket. */
48  /* uint16_t num[bucket_size]; */
49
50  /* Buckets containing block_size_ of backward references. */
51  /* uint32_t* buckets[bucket_size * block_size]; */
52} HashLongestMatch;
53
54static BROTLI_INLINE HashLongestMatch* FN(Self)(HasherHandle handle) {
55  return (HashLongestMatch*)&(GetHasherCommon(handle)[1]);
56}
57
58static BROTLI_INLINE uint16_t* FN(Num)(HashLongestMatch* self) {
59  return (uint16_t*)(&self[1]);
60}
61
62static BROTLI_INLINE uint32_t* FN(Buckets)(HashLongestMatch* self) {
63  return (uint32_t*)(&FN(Num)(self)[self->bucket_size_]);
64}
65
66static void FN(Initialize)(
67    HasherHandle handle, const BrotliEncoderParams* params) {
68  HasherCommon* common = GetHasherCommon(handle);
69  HashLongestMatch* self = FN(Self)(handle);
70  BROTLI_UNUSED(params);
71  self->hash_shift_ = 64 - common->params.bucket_bits;
72  self->hash_mask_ = (~((uint64_t)0U)) >> (64 - 8 * common->params.hash_len);
73  self->bucket_size_ = (size_t)1 << common->params.bucket_bits;
74  self->block_size_ = (size_t)1 << common->params.block_bits;
75  self->block_mask_ = (uint32_t)(self->block_size_ - 1);
76}
77
78static void FN(Prepare)(HasherHandle handle, BROTLI_BOOL one_shot,
79    size_t input_size, const uint8_t* data) {
80  HashLongestMatch* self = FN(Self)(handle);
81  uint16_t* num = FN(Num)(self);
82  /* Partial preparation is 100 times slower (per socket). */
83  size_t partial_prepare_threshold = self->bucket_size_ >> 6;
84  if (one_shot && input_size <= partial_prepare_threshold) {
85    size_t i;
86    for (i = 0; i < input_size; ++i) {
87      const uint32_t key = FN(HashBytes)(&data[i], self->hash_mask_,
88                                         self->hash_shift_);
89      num[key] = 0;
90    }
91  } else {
92    memset(num, 0, self->bucket_size_ * sizeof(num[0]));
93  }
94}
95
96static BROTLI_INLINE size_t FN(HashMemAllocInBytes)(
97    const BrotliEncoderParams* params, BROTLI_BOOL one_shot,
98    size_t input_size) {
99  size_t bucket_size = (size_t)1 << params->hasher.bucket_bits;
100  size_t block_size = (size_t)1 << params->hasher.block_bits;
101  BROTLI_UNUSED(one_shot);
102  BROTLI_UNUSED(input_size);
103  return sizeof(HashLongestMatch) + bucket_size * (2 + 4 * block_size);
104}
105
106/* Look at 4 bytes at &data[ix & mask].
107   Compute a hash from these, and store the value of ix at that position. */
108static BROTLI_INLINE void FN(Store)(HasherHandle handle, const uint8_t *data,
109    const size_t mask, const size_t ix) {
110  HashLongestMatch* self = FN(Self)(handle);
111  uint16_t* num = FN(Num)(self);
112  const uint32_t key = FN(HashBytes)(&data[ix & mask], self->hash_mask_,
113                                     self->hash_shift_);
114  const size_t minor_ix = num[key] & self->block_mask_;
115  const size_t offset =
116      minor_ix + (key << GetHasherCommon(handle)->params.block_bits);
117  FN(Buckets)(self)[offset] = (uint32_t)ix;
118  ++num[key];
119}
120
121static BROTLI_INLINE void FN(StoreRange)(HasherHandle handle,
122    const uint8_t *data, const size_t mask, const size_t ix_start,
123    const size_t ix_end) {
124  size_t i;
125  for (i = ix_start; i < ix_end; ++i) {
126    FN(Store)(handle, data, mask, i);
127  }
128}
129
130static BROTLI_INLINE void FN(StitchToPreviousBlock)(HasherHandle handle,
131    size_t num_bytes, size_t position, const uint8_t* ringbuffer,
132    size_t ringbuffer_mask) {
133  if (num_bytes >= FN(HashTypeLength)() - 1 && position >= 3) {
134    /* Prepare the hashes for three last bytes of the last write.
135       These could not be calculated before, since they require knowledge
136       of both the previous and the current block. */
137    FN(Store)(handle, ringbuffer, ringbuffer_mask, position - 3);
138    FN(Store)(handle, ringbuffer, ringbuffer_mask, position - 2);
139    FN(Store)(handle, ringbuffer, ringbuffer_mask, position - 1);
140  }
141}
142
143static BROTLI_INLINE void FN(PrepareDistanceCache)(
144    HasherHandle handle, int* BROTLI_RESTRICT distance_cache) {
145  PrepareDistanceCache(distance_cache,
146      GetHasherCommon(handle)->params.num_last_distances_to_check);
147}
148
149/* Find a longest backward match of &data[cur_ix] up to the length of
150   max_length and stores the position cur_ix in the hash table.
151
152   REQUIRES: FN(PrepareDistanceCache) must be invoked for current distance cache
153             values; if this method is invoked repeatedly with the same distance
154             cache values, it is enough to invoke FN(PrepareDistanceCache) once.
155
156   Does not look for matches longer than max_length.
157   Does not look for matches further away than max_backward.
158   Writes the best match into |out|.
159   Returns true when match is found, otherwise false. */
160static BROTLI_INLINE BROTLI_BOOL FN(FindLongestMatch)(HasherHandle handle,
161    const BrotliDictionary* dictionary, const uint16_t* dictionary_hash,
162    const uint8_t* BROTLI_RESTRICT data, const size_t ring_buffer_mask,
163    const int* BROTLI_RESTRICT distance_cache, const size_t cur_ix,
164    const size_t max_length, const size_t max_backward,
165    HasherSearchResult* BROTLI_RESTRICT out) {
166  HasherCommon* common = GetHasherCommon(handle);
167  HashLongestMatch* self = FN(Self)(handle);
168  uint16_t* num = FN(Num)(self);
169  uint32_t* buckets = FN(Buckets)(self);
170  const size_t cur_ix_masked = cur_ix & ring_buffer_mask;
171  BROTLI_BOOL is_match_found = BROTLI_FALSE;
172  /* Don't accept a short copy from far away. */
173  score_t best_score = out->score;
174  size_t best_len = out->len;
175  size_t i;
176  out->len = 0;
177  out->len_x_code = 0;
178  /* Try last distance first. */
179  for (i = 0; i < (size_t)common->params.num_last_distances_to_check; ++i) {
180    const size_t backward = (size_t)distance_cache[i];
181    size_t prev_ix = (size_t)(cur_ix - backward);
182    if (prev_ix >= cur_ix) {
183      continue;
184    }
185    if (BROTLI_PREDICT_FALSE(backward > max_backward)) {
186      continue;
187    }
188    prev_ix &= ring_buffer_mask;
189
190    if (cur_ix_masked + best_len > ring_buffer_mask ||
191        prev_ix + best_len > ring_buffer_mask ||
192        data[cur_ix_masked + best_len] != data[prev_ix + best_len]) {
193      continue;
194    }
195    {
196      const size_t len = FindMatchLengthWithLimit(&data[prev_ix],
197                                                  &data[cur_ix_masked],
198                                                  max_length);
199      if (len >= 3 || (len == 2 && i < 2)) {
200        /* Comparing for >= 2 does not change the semantics, but just saves for
201           a few unnecessary binary logarithms in backward reference score,
202           since we are not interested in such short matches. */
203        score_t score = BackwardReferenceScoreUsingLastDistance(len);
204        if (best_score < score) {
205          if (i != 0) score -= BackwardReferencePenaltyUsingLastDistance(i);
206          if (best_score < score) {
207            best_score = score;
208            best_len = len;
209            out->len = best_len;
210            out->distance = backward;
211            out->score = best_score;
212            is_match_found = BROTLI_TRUE;
213          }
214        }
215      }
216    }
217  }
218  {
219    const uint32_t key = FN(HashBytes)(
220        &data[cur_ix_masked], self->hash_mask_, self->hash_shift_);
221    uint32_t* BROTLI_RESTRICT bucket =
222        &buckets[key << common->params.block_bits];
223    const size_t down =
224        (num[key] > self->block_size_) ?
225        (num[key] - self->block_size_) : 0u;
226    for (i = num[key]; i > down;) {
227      size_t prev_ix = bucket[--i & self->block_mask_];
228      const size_t backward = cur_ix - prev_ix;
229      if (BROTLI_PREDICT_FALSE(backward > max_backward)) {
230        break;
231      }
232      prev_ix &= ring_buffer_mask;
233      if (cur_ix_masked + best_len > ring_buffer_mask ||
234          prev_ix + best_len > ring_buffer_mask ||
235          data[cur_ix_masked + best_len] != data[prev_ix + best_len]) {
236        continue;
237      }
238      {
239        const size_t len = FindMatchLengthWithLimit(&data[prev_ix],
240                                                    &data[cur_ix_masked],
241                                                    max_length);
242        if (len >= 4) {
243          /* Comparing for >= 3 does not change the semantics, but just saves
244             for a few unnecessary binary logarithms in backward reference
245             score, since we are not interested in such short matches. */
246          score_t score = BackwardReferenceScore(len, backward);
247          if (best_score < score) {
248            best_score = score;
249            best_len = len;
250            out->len = best_len;
251            out->distance = backward;
252            out->score = best_score;
253            is_match_found = BROTLI_TRUE;
254          }
255        }
256      }
257    }
258    bucket[num[key] & self->block_mask_] = (uint32_t)cur_ix;
259    ++num[key];
260  }
261  if (!is_match_found) {
262    is_match_found = SearchInStaticDictionary(dictionary, dictionary_hash,
263        handle, &data[cur_ix_masked], max_length, max_backward, out,
264        BROTLI_FALSE);
265  }
266  return is_match_found;
267}
268
269#undef HashLongestMatch
270