| /* 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 4; } |
| static BROTLI_INLINE size_t FN(StoreLookahead)(void) { return 4; } |
| |
| /* HashBytes is the function that chooses the bucket to place the address in. */ |
| static uint32_t FN(HashBytes)(const uint8_t *data, const int shift) { |
| uint32_t h = BROTLI_UNALIGNED_LOAD32LE(data) * kHashMul32; |
| /* The higher bits contain more mixture from the multiplication, |
| so we take our results from there. */ |
| return (uint32_t)(h >> shift); |
| } |
| |
| 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_; |
| /* Left-shift for computing hash bucket index from hash value. */ |
| int hash_shift_; |
| /* Mask for accessing entries in a block (in a ring-buffer manner). */ |
| uint32_t block_mask_; |
| |
| /* --- Dynamic size members --- */ |
| |
| /* Number of entries in a particular bucket. */ |
| /* uint16_t num[bucket_size]; */ |
| |
| /* Buckets containing block_size_ of backward references. */ |
| /* uint32_t* buckets[bucket_size * block_size]; */ |
| } HashLongestMatch; |
| |
| static BROTLI_INLINE HashLongestMatch* FN(Self)(HasherHandle handle) { |
| return (HashLongestMatch*)&(GetHasherCommon(handle)[1]); |
| } |
| |
| static BROTLI_INLINE uint16_t* FN(Num)(HashLongestMatch* self) { |
| return (uint16_t*)(&self[1]); |
| } |
| |
| static BROTLI_INLINE uint32_t* FN(Buckets)(HashLongestMatch* self) { |
| return (uint32_t*)(&FN(Num)(self)[self->bucket_size_]); |
| } |
| |
| static void FN(Initialize)( |
| HasherHandle handle, const BrotliEncoderParams* params) { |
| HasherCommon* common = GetHasherCommon(handle); |
| HashLongestMatch* self = FN(Self)(handle); |
| BROTLI_UNUSED(params); |
| self->hash_shift_ = 32 - common->params.bucket_bits; |
| self->bucket_size_ = (size_t)1 << common->params.bucket_bits; |
| self->block_size_ = (size_t)1 << common->params.block_bits; |
| self->block_mask_ = (uint32_t)(self->block_size_ - 1); |
| } |
| |
| static void FN(Prepare)(HasherHandle handle, BROTLI_BOOL one_shot, |
| size_t input_size, const uint8_t* data) { |
| HashLongestMatch* self = FN(Self)(handle); |
| uint16_t* num = FN(Num)(self); |
| /* 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 uint32_t key = FN(HashBytes)(&data[i], self->hash_shift_); |
| num[key] = 0; |
| } |
| } else { |
| memset(num, 0, self->bucket_size_ * sizeof(num[0])); |
| } |
| } |
| |
| static BROTLI_INLINE size_t FN(HashMemAllocInBytes)( |
| const BrotliEncoderParams* params, BROTLI_BOOL one_shot, |
| size_t input_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); |
| return sizeof(HashLongestMatch) + bucket_size * (2 + 4 * 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)(HasherHandle handle, const uint8_t* data, |
| const size_t mask, const size_t ix) { |
| HashLongestMatch* self = FN(Self)(handle); |
| uint16_t* num = FN(Num)(self); |
| const uint32_t key = FN(HashBytes)(&data[ix & mask], self->hash_shift_); |
| const size_t minor_ix = num[key] & self->block_mask_; |
| const size_t offset = |
| minor_ix + (key << GetHasherCommon(handle)->params.block_bits); |
| FN(Buckets)(self)[offset] = (uint32_t)ix; |
| ++num[key]; |
| } |
| |
| static BROTLI_INLINE void FN(StoreRange)(HasherHandle handle, |
| const uint8_t *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)(handle, data, mask, i); |
| } |
| } |
| |
| static BROTLI_INLINE void FN(StitchToPreviousBlock)(HasherHandle handle, |
| 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)(handle, ringbuffer, ringbuffer_mask, position - 3); |
| FN(Store)(handle, ringbuffer, ringbuffer_mask, position - 2); |
| FN(Store)(handle, ringbuffer, ringbuffer_mask, position - 1); |
| } |
| } |
| |
| static BROTLI_INLINE void FN(PrepareDistanceCache)( |
| HasherHandle handle, int* BROTLI_RESTRICT distance_cache) { |
| PrepareDistanceCache(distance_cache, |
| GetHasherCommon(handle)->params.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)(HasherHandle handle, |
| const BrotliDictionary* dictionary, const uint16_t* dictionary_hash, |
| 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 gap, |
| HasherSearchResult* BROTLI_RESTRICT out) { |
| HasherCommon* common = GetHasherCommon(handle); |
| HashLongestMatch* self = FN(Self)(handle); |
| uint16_t* num = FN(Num)(self); |
| uint32_t* buckets = FN(Buckets)(self); |
| 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; |
| out->len = 0; |
| out->len_code_delta = 0; |
| /* Try last distance first. */ |
| for (i = 0; i < (size_t)common->params.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 (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. */ |
| 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; |
| } |
| } |
| } |
| } |
| } |
| { |
| const uint32_t key = |
| FN(HashBytes)(&data[cur_ix_masked], self->hash_shift_); |
| uint32_t* BROTLI_RESTRICT bucket = |
| &buckets[key << common->params.block_bits]; |
| const size_t down = |
| (num[key] > self->block_size_) ? (num[key] - self->block_size_) : 0u; |
| for (i = num[key]; i > down;) { |
| size_t prev_ix = bucket[--i & self->block_mask_]; |
| const size_t backward = cur_ix - prev_ix; |
| if (BROTLI_PREDICT_FALSE(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. */ |
| 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, dictionary_hash, |
| handle, &data[cur_ix_masked], max_length, max_backward + gap, out, |
| BROTLI_FALSE); |
| } |
| } |
| |
| #undef HashLongestMatch |