hash_longest_match64_inc.h (10655B)
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 19 static BROTLI_INLINE size_t FN(HashTypeLength)(void) { return 8; } 20 static BROTLI_INLINE size_t FN(StoreLookahead)(void) { return 8; } 21 22 /* HashBytes is the function that chooses the bucket to place the address in. */ 23 static BROTLI_INLINE size_t FN(HashBytes)(const uint8_t* BROTLI_RESTRICT data, 24 uint64_t hash_mul) { 25 const uint64_t h = BROTLI_UNALIGNED_LOAD64LE(data) * hash_mul; 26 /* The higher bits contain more mixture from the multiplication, 27 so we take our results from there. */ 28 return (size_t)(h >> (64 - 15)); 29 } 30 31 typedef struct HashLongestMatch { 32 /* Number of hash buckets. */ 33 size_t bucket_size_; 34 /* Only block_size_ newest backward references are kept, 35 and the older are forgotten. */ 36 size_t block_size_; 37 /* Hash multiplier tuned to match length. */ 38 uint64_t hash_mul_; 39 /* Mask for accessing entries in a block (in a ring-buffer manner). */ 40 uint32_t block_mask_; 41 42 int block_bits_; 43 int num_last_distances_to_check_; 44 45 /* Shortcuts. */ 46 HasherCommon* common_; 47 48 /* --- Dynamic size members --- */ 49 50 /* Number of entries in a particular bucket. */ 51 uint16_t* num_; /* uint16_t[bucket_size]; */ 52 53 /* Buckets containing block_size_ of backward references. */ 54 uint32_t* buckets_; /* uint32_t[bucket_size * block_size]; */ 55 } HashLongestMatch; 56 57 static void FN(Initialize)( 58 HasherCommon* common, HashLongestMatch* BROTLI_RESTRICT self, 59 const BrotliEncoderParams* params) { 60 self->common_ = common; 61 62 BROTLI_UNUSED(params); 63 self->hash_mul_ = kHashMul64 << (64 - 5 * 8); 64 BROTLI_DCHECK(common->params.bucket_bits == 15); 65 self->bucket_size_ = (size_t)1 << common->params.bucket_bits; 66 self->block_bits_ = common->params.block_bits; 67 self->block_size_ = (size_t)1 << common->params.block_bits; 68 self->block_mask_ = (uint32_t)(self->block_size_ - 1); 69 self->num_last_distances_to_check_ = 70 common->params.num_last_distances_to_check; 71 self->num_ = (uint16_t*)common->extra[0]; 72 self->buckets_ = (uint32_t*)common->extra[1]; 73 } 74 75 static void FN(Prepare)( 76 HashLongestMatch* BROTLI_RESTRICT self, BROTLI_BOOL one_shot, 77 size_t input_size, const uint8_t* BROTLI_RESTRICT data) { 78 uint16_t* BROTLI_RESTRICT num = self->num_; 79 /* Partial preparation is 100 times slower (per socket). */ 80 size_t partial_prepare_threshold = self->bucket_size_ >> 6; 81 if (one_shot && input_size <= partial_prepare_threshold) { 82 size_t i; 83 for (i = 0; i < input_size; ++i) { 84 const size_t key = FN(HashBytes)(&data[i], self->hash_mul_); 85 num[key] = 0; 86 } 87 } else { 88 memset(num, 0, self->bucket_size_ * sizeof(num[0])); 89 } 90 } 91 92 static BROTLI_INLINE void FN(HashMemAllocInBytes)( 93 const BrotliEncoderParams* params, BROTLI_BOOL one_shot, 94 size_t input_size, size_t* alloc_size) { 95 size_t bucket_size = (size_t)1 << params->hasher.bucket_bits; 96 size_t block_size = (size_t)1 << params->hasher.block_bits; 97 BROTLI_UNUSED(one_shot); 98 BROTLI_UNUSED(input_size); 99 alloc_size[0] = sizeof(uint16_t) * bucket_size; 100 alloc_size[1] = sizeof(uint32_t) * bucket_size * block_size; 101 } 102 103 /* Look at 4 bytes at &data[ix & mask]. 104 Compute a hash from these, and store the value of ix at that position. */ 105 static BROTLI_INLINE void FN(Store)( 106 HashLongestMatch* BROTLI_RESTRICT self, const uint8_t* BROTLI_RESTRICT data, 107 const size_t mask, const size_t ix) { 108 uint16_t* BROTLI_RESTRICT num = self->num_; 109 uint32_t* BROTLI_RESTRICT buckets = self->buckets_; 110 const size_t key = FN(HashBytes)(&data[ix & mask], self->hash_mul_); 111 const size_t minor_ix = num[key] & self->block_mask_; 112 const size_t offset = minor_ix + (key << self->block_bits_); 113 ++num[key]; 114 buckets[offset] = (uint32_t)ix; 115 } 116 117 static BROTLI_INLINE void FN(StoreRange)(HashLongestMatch* BROTLI_RESTRICT self, 118 const uint8_t* BROTLI_RESTRICT data, const size_t mask, 119 const size_t ix_start, const size_t ix_end) { 120 size_t i; 121 for (i = ix_start; i < ix_end; ++i) { 122 FN(Store)(self, data, mask, i); 123 } 124 } 125 126 static BROTLI_INLINE void FN(StitchToPreviousBlock)( 127 HashLongestMatch* BROTLI_RESTRICT self, 128 size_t num_bytes, size_t position, const uint8_t* ringbuffer, 129 size_t ringbuffer_mask) { 130 if (num_bytes >= FN(HashTypeLength)() - 1 && position >= 3) { 131 /* Prepare the hashes for three last bytes of the last write. 132 These could not be calculated before, since they require knowledge 133 of both the previous and the current block. */ 134 FN(Store)(self, ringbuffer, ringbuffer_mask, position - 3); 135 FN(Store)(self, ringbuffer, ringbuffer_mask, position - 2); 136 FN(Store)(self, ringbuffer, ringbuffer_mask, position - 1); 137 } 138 } 139 140 static BROTLI_INLINE void FN(PrepareDistanceCache)( 141 HashLongestMatch* BROTLI_RESTRICT self, 142 int* BROTLI_RESTRICT distance_cache) { 143 PrepareDistanceCache(distance_cache, self->num_last_distances_to_check_); 144 } 145 146 /* Find a longest backward match of &data[cur_ix] up to the length of 147 max_length and stores the position cur_ix in the hash table. 148 149 REQUIRES: FN(PrepareDistanceCache) must be invoked for current distance cache 150 values; if this method is invoked repeatedly with the same distance 151 cache values, it is enough to invoke FN(PrepareDistanceCache) once. 152 153 Does not look for matches longer than max_length. 154 Does not look for matches further away than max_backward. 155 Writes the best match into |out|. 156 |out|->score is updated only if a better match is found. */ 157 static BROTLI_INLINE void FN(FindLongestMatch)( 158 HashLongestMatch* BROTLI_RESTRICT self, 159 const BrotliEncoderDictionary* dictionary, 160 const uint8_t* BROTLI_RESTRICT data, const size_t ring_buffer_mask, 161 const int* BROTLI_RESTRICT distance_cache, const size_t cur_ix, 162 const size_t max_length, const size_t max_backward, 163 const size_t dictionary_distance, const size_t max_distance, 164 HasherSearchResult* BROTLI_RESTRICT out) { 165 uint16_t* BROTLI_RESTRICT num = self->num_; 166 uint32_t* BROTLI_RESTRICT buckets = self->buckets_; 167 const size_t cur_ix_masked = cur_ix & ring_buffer_mask; 168 /* Don't accept a short copy from far away. */ 169 score_t min_score = out->score; 170 score_t best_score = out->score; 171 size_t best_len = out->len; 172 size_t i; 173 /* Precalculate the hash key and prefetch the bucket. */ 174 const size_t key = FN(HashBytes)(&data[cur_ix_masked], self->hash_mul_); 175 uint32_t* BROTLI_RESTRICT bucket = &buckets[key << self->block_bits_]; 176 PREFETCH_L1(bucket); 177 if (self->block_bits_ > 4) PREFETCH_L1(bucket + 16); 178 out->len = 0; 179 out->len_code_delta = 0; 180 181 BROTLI_DCHECK(cur_ix_masked + max_length <= ring_buffer_mask); 182 183 /* Try last distance first. */ 184 for (i = 0; i < (size_t)self->num_last_distances_to_check_; ++i) { 185 const size_t backward = (size_t)distance_cache[i]; 186 size_t prev_ix = (size_t)(cur_ix - backward); 187 if (prev_ix >= cur_ix) { 188 continue; 189 } 190 if (BROTLI_PREDICT_FALSE(backward > max_backward)) { 191 continue; 192 } 193 prev_ix &= ring_buffer_mask; 194 195 if (cur_ix_masked + best_len > ring_buffer_mask) { 196 break; 197 } 198 if (prev_ix + best_len > ring_buffer_mask || 199 data[cur_ix_masked + best_len] != data[prev_ix + best_len]) { 200 continue; 201 } 202 { 203 const size_t len = FindMatchLengthWithLimit(&data[prev_ix], 204 &data[cur_ix_masked], 205 max_length); 206 if (len >= 3 || (len == 2 && i < 2)) { 207 /* Comparing for >= 2 does not change the semantics, but just saves for 208 a few unnecessary binary logarithms in backward reference score, 209 since we are not interested in such short matches. */ 210 score_t score = BackwardReferenceScoreUsingLastDistance(len); 211 if (best_score < score) { 212 if (i != 0) score -= BackwardReferencePenaltyUsingLastDistance(i); 213 if (best_score < score) { 214 best_score = score; 215 best_len = len; 216 out->len = best_len; 217 out->distance = backward; 218 out->score = best_score; 219 } 220 } 221 } 222 } 223 } 224 /* we require matches of len >4, so increase best_len to 3, so we can compare 225 * 4 bytes all the time. */ 226 if (best_len < 3) { 227 best_len = 3; 228 } 229 { 230 const size_t down = 231 (num[key] > self->block_size_) ? 232 (num[key] - self->block_size_) : 0u; 233 const uint32_t first4 = BrotliUnalignedRead32(data + cur_ix_masked); 234 const size_t max_length_m4 = max_length - 4; 235 i = num[key]; 236 for (; i > down;) { 237 size_t prev_ix = bucket[--i & self->block_mask_]; 238 uint32_t current4; 239 const size_t backward = cur_ix - prev_ix; 240 if (BROTLI_PREDICT_FALSE(backward > max_backward)) { 241 break; 242 } 243 prev_ix &= ring_buffer_mask; 244 if (cur_ix_masked + best_len > ring_buffer_mask) { 245 break; 246 } 247 if (prev_ix + best_len > ring_buffer_mask || 248 /* compare 4 bytes ending at best_len + 1 */ 249 BrotliUnalignedRead32(&data[cur_ix_masked + best_len - 3]) != 250 BrotliUnalignedRead32(&data[prev_ix + best_len - 3])) { 251 continue; 252 } 253 current4 = BrotliUnalignedRead32(data + prev_ix); 254 if (first4 != current4) continue; 255 { 256 const size_t len = FindMatchLengthWithLimit(&data[prev_ix + 4], 257 &data[cur_ix_masked + 4], 258 max_length_m4) + 4; 259 const score_t score = BackwardReferenceScore(len, backward); 260 if (best_score < score) { 261 best_score = score; 262 best_len = len; 263 out->len = best_len; 264 out->distance = backward; 265 out->score = best_score; 266 } 267 } 268 } 269 bucket[num[key] & self->block_mask_] = (uint32_t)cur_ix; 270 ++num[key]; 271 } 272 if (min_score == out->score) { 273 SearchInStaticDictionary(dictionary, 274 self->common_, &data[cur_ix_masked], max_length, dictionary_distance, 275 max_distance, out, BROTLI_FALSE); 276 } 277 } 278 279 #undef HashLongestMatch