| /* NOLINT(build/header_guard) */ |
| /* Copyright 2010 Google Inc. All Rights Reserved. |
| |
| Distributed under MIT license. |
| See file LICENSE for detail or copy at https://opensource.org/licenses/MIT |
| */ |
| |
| /* template parameters: FN */ |
| |
| /* 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 (bucket_size_) to a ring buffer of |
| fixed size (block_size_). The ring buffer contains the last block_size_ |
| index positions of the given hash key in the compressed data. */ |
| |
| #define HashLongestMatch HASHER() |
| |
| static BROTLI_INLINE size_t FN(HashTypeLength)(void) { return 8; } |
| static BROTLI_INLINE size_t FN(StoreLookahead)(void) { return 8; } |
| |
| /* HashBytes is the function that chooses the bucket to place the address in. */ |
| static BROTLI_INLINE size_t FN(HashBytes)(const uint8_t* BROTLI_RESTRICT data, |
| uint64_t hash_mul) { |
| const uint64_t h = BROTLI_UNALIGNED_LOAD64LE(data) * hash_mul; |
| /* The higher bits contain more mixture from the multiplication, |
| so we take our results from there. */ |
| return (size_t)(h >> (64 - 15)); |
| } |
| |
| typedef struct HashLongestMatch { |
| /* Number of hash buckets. */ |
| size_t bucket_size_; |
| /* Only block_size_ newest backward references are kept, |
| and the older are forgotten. */ |
| size_t block_size_; |
| /* Hash multiplier tuned to match length. */ |
| uint64_t hash_mul_; |
| /* Mask for accessing entries in a block (in a ring-buffer manner). */ |
| uint32_t block_mask_; |
| |
| int block_bits_; |
| int num_last_distances_to_check_; |
| |
| /* Shortcuts. */ |
| HasherCommon* common_; |
| |
| /* --- Dynamic size members --- */ |
| |
| /* Number of entries in a particular bucket. */ |
| uint16_t* num_; /* uint16_t[bucket_size]; */ |
| |
| /* Buckets containing block_size_ of backward references. */ |
| uint32_t* buckets_; /* uint32_t[bucket_size * block_size]; */ |
| } HashLongestMatch; |
| |
| static void FN(Initialize)( |
| HasherCommon* common, HashLongestMatch* BROTLI_RESTRICT self, |
| const BrotliEncoderParams* params) { |
| self->common_ = common; |
| |
| BROTLI_UNUSED(params); |
| self->hash_mul_ = kHashMul64 << (64 - 5 * 8); |
| BROTLI_DCHECK(common->params.bucket_bits == 15); |
| self->bucket_size_ = (size_t)1 << common->params.bucket_bits; |
| self->block_bits_ = common->params.block_bits; |
| self->block_size_ = (size_t)1 << common->params.block_bits; |
| self->block_mask_ = (uint32_t)(self->block_size_ - 1); |
| self->num_last_distances_to_check_ = |
| common->params.num_last_distances_to_check; |
| self->num_ = (uint16_t*)common->extra[0]; |
| self->buckets_ = (uint32_t*)common->extra[1]; |
| } |
| |
| static void FN(Prepare)( |
| HashLongestMatch* BROTLI_RESTRICT self, BROTLI_BOOL one_shot, |
| size_t input_size, const uint8_t* BROTLI_RESTRICT data) { |
| uint16_t* BROTLI_RESTRICT num = self->num_; |
| /* Partial preparation is 100 times slower (per socket). */ |
| size_t partial_prepare_threshold = self->bucket_size_ >> 6; |
| if (one_shot && input_size <= partial_prepare_threshold) { |
| size_t i; |
| for (i = 0; i < input_size; ++i) { |
| const size_t key = FN(HashBytes)(&data[i], self->hash_mul_); |
| num[key] = 0; |
| } |
| } else { |
| memset(num, 0, self->bucket_size_ * sizeof(num[0])); |
| } |
| } |
| |
| static BROTLI_INLINE void FN(HashMemAllocInBytes)( |
| const BrotliEncoderParams* params, BROTLI_BOOL one_shot, |
| size_t input_size, size_t* alloc_size) { |
| size_t bucket_size = (size_t)1 << params->hasher.bucket_bits; |
| size_t block_size = (size_t)1 << params->hasher.block_bits; |
| BROTLI_UNUSED(one_shot); |
| BROTLI_UNUSED(input_size); |
| alloc_size[0] = sizeof(uint16_t) * bucket_size; |
| alloc_size[1] = sizeof(uint32_t) * bucket_size * block_size; |
| } |
| |
| /* Look at 4 bytes at &data[ix & mask]. |
| Compute a hash from these, and store the value of ix at that position. */ |
| static BROTLI_INLINE void FN(Store)( |
| HashLongestMatch* BROTLI_RESTRICT self, const uint8_t* BROTLI_RESTRICT data, |
| const size_t mask, const size_t ix) { |
| uint16_t* BROTLI_RESTRICT num = self->num_; |
| uint32_t* BROTLI_RESTRICT buckets = self->buckets_; |
| const size_t key = FN(HashBytes)(&data[ix & mask], self->hash_mul_); |
| const size_t minor_ix = num[key] & self->block_mask_; |
| const size_t offset = minor_ix + (key << self->block_bits_); |
| ++num[key]; |
| buckets[offset] = (uint32_t)ix; |
| } |
| |
| static BROTLI_INLINE void FN(StoreRange)(HashLongestMatch* BROTLI_RESTRICT self, |
| const uint8_t* BROTLI_RESTRICT data, const size_t mask, |
| const size_t ix_start, const size_t ix_end) { |
| size_t i; |
| for (i = ix_start; i < ix_end; ++i) { |
| FN(Store)(self, data, mask, i); |
| } |
| } |
| |
| static BROTLI_INLINE void FN(StitchToPreviousBlock)( |
| HashLongestMatch* BROTLI_RESTRICT self, |
| size_t num_bytes, size_t position, const uint8_t* ringbuffer, |
| size_t ringbuffer_mask) { |
| if (num_bytes >= FN(HashTypeLength)() - 1 && position >= 3) { |
| /* Prepare the hashes for three last bytes of the last write. |
| These could not be calculated before, since they require knowledge |
| of both the previous and the current block. */ |
| FN(Store)(self, ringbuffer, ringbuffer_mask, position - 3); |
| FN(Store)(self, ringbuffer, ringbuffer_mask, position - 2); |
| FN(Store)(self, ringbuffer, ringbuffer_mask, position - 1); |
| } |
| } |
| |
| static BROTLI_INLINE void FN(PrepareDistanceCache)( |
| HashLongestMatch* BROTLI_RESTRICT self, |
| int* BROTLI_RESTRICT distance_cache) { |
| PrepareDistanceCache(distance_cache, self->num_last_distances_to_check_); |
| } |
| |
| /* 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. |
| |
| REQUIRES: FN(PrepareDistanceCache) must be invoked for current distance cache |
| values; if this method is invoked repeatedly with the same distance |
| cache values, it is enough to invoke FN(PrepareDistanceCache) once. |
| |
| Does not look for matches longer than max_length. |
| Does not look for matches further away than max_backward. |
| Writes the best match into |out|. |
| |out|->score is updated only if a better match is found. */ |
| static BROTLI_INLINE void FN(FindLongestMatch)( |
| HashLongestMatch* BROTLI_RESTRICT self, |
| const BrotliEncoderDictionary* dictionary, |
| const uint8_t* BROTLI_RESTRICT data, const size_t ring_buffer_mask, |
| const int* BROTLI_RESTRICT distance_cache, const size_t cur_ix, |
| const size_t max_length, const size_t max_backward, |
| const size_t dictionary_distance, const size_t max_distance, |
| HasherSearchResult* BROTLI_RESTRICT out) { |
| uint16_t* BROTLI_RESTRICT num = self->num_; |
| uint32_t* BROTLI_RESTRICT buckets = self->buckets_; |
| const size_t cur_ix_masked = cur_ix & ring_buffer_mask; |
| /* Don't accept a short copy from far away. */ |
| score_t min_score = out->score; |
| score_t best_score = out->score; |
| size_t best_len = out->len; |
| size_t i; |
| BROTLI_DCHECK(cur_ix_masked + max_length <= ring_buffer_mask); |
| out->len = 0; |
| out->len_code_delta = 0; |
| /* Try last distance first. */ |
| for (i = 0; i < (size_t)self->num_last_distances_to_check_; ++i) { |
| const size_t backward = (size_t)distance_cache[i]; |
| size_t prev_ix = (size_t)(cur_ix - backward); |
| if (prev_ix >= cur_ix) { |
| continue; |
| } |
| if (BROTLI_PREDICT_FALSE(backward > max_backward)) { |
| continue; |
| } |
| prev_ix &= ring_buffer_mask; |
| |
| if (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. */ |
| score_t score = BackwardReferenceScoreUsingLastDistance(len); |
| if (best_score < score) { |
| if (i != 0) score -= BackwardReferencePenaltyUsingLastDistance(i); |
| if (best_score < score) { |
| best_score = score; |
| best_len = len; |
| out->len = best_len; |
| out->distance = backward; |
| out->score = best_score; |
| } |
| } |
| } |
| } |
| } |
| /* we require matches of len >4, so increase best_len to 3, so we can compare |
| * 4 bytes all the time. */ |
| if (best_len < 3) { |
| best_len = 3; |
| } |
| { |
| const size_t key = FN(HashBytes)(&data[cur_ix_masked], self->hash_mul_); |
| uint32_t* BROTLI_RESTRICT bucket = &buckets[key << self->block_bits_]; |
| const size_t down = |
| (num[key] > self->block_size_) ? |
| (num[key] - self->block_size_) : 0u; |
| const uint32_t first4 = BrotliUnalignedRead32(data + cur_ix_masked); |
| const size_t max_length_m4 = max_length - 4; |
| i = num[key]; |
| for (; i > down;) { |
| size_t prev_ix = bucket[--i & self->block_mask_]; |
| uint32_t current4; |
| const size_t backward = cur_ix - prev_ix; |
| if (BROTLI_PREDICT_FALSE(backward > max_backward)) { |
| break; |
| } |
| prev_ix &= ring_buffer_mask; |
| if (prev_ix + best_len > ring_buffer_mask || |
| /* compare 4 bytes ending at best_len + 1 */ |
| BrotliUnalignedRead32(&data[cur_ix_masked + best_len - 3]) != |
| BrotliUnalignedRead32(&data[prev_ix + best_len - 3])) { |
| continue; |
| } |
| current4 = BrotliUnalignedRead32(data + prev_ix); |
| if (first4 != current4) continue; |
| { |
| const size_t len = FindMatchLengthWithLimit(&data[prev_ix + 4], |
| &data[cur_ix_masked + 4], |
| max_length_m4) + 4; |
| const score_t score = BackwardReferenceScore(len, backward); |
| if (best_score < score) { |
| best_score = score; |
| best_len = len; |
| out->len = best_len; |
| out->distance = backward; |
| out->score = best_score; |
| } |
| } |
| } |
| bucket[num[key] & self->block_mask_] = (uint32_t)cur_ix; |
| ++num[key]; |
| } |
| if (min_score == out->score) { |
| SearchInStaticDictionary(dictionary, |
| self->common_, &data[cur_ix_masked], max_length, dictionary_distance, |
| max_distance, out, BROTLI_FALSE); |
| } |
| } |
| |
| #undef HashLongestMatch |