diff options
Diffstat (limited to 'modules/brotli/enc/hash_longest_match64_inc.h')
| -rw-r--r-- | modules/brotli/enc/hash_longest_match64_inc.h | 267 |
1 files changed, 267 insertions, 0 deletions
diff --git a/modules/brotli/enc/hash_longest_match64_inc.h b/modules/brotli/enc/hash_longest_match64_inc.h new file mode 100644 index 000000000..cb953a644 --- /dev/null +++ b/modules/brotli/enc/hash_longest_match64_inc.h @@ -0,0 +1,267 @@ +/* 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 uint32_t FN(HashBytes)(const uint8_t* data, + const uint64_t mask, + const int shift) { + const uint64_t h = (BROTLI_UNALIGNED_LOAD64LE(data) & mask) * kHashMul64Long; + /* 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 selecting the next 4-8 bytes of input */ + uint64_t hash_mask_; + /* 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_ = 64 - common->params.bucket_bits; + self->hash_mask_ = (~((uint64_t)0U)) >> (64 - 8 * common->params.hash_len); + 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_mask_, + 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_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 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 gap, const size_t max_distance, + 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_mask_, 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, + handle, &data[cur_ix_masked], max_length, max_backward + gap, + max_distance, out, BROTLI_FALSE); + } +} + +#undef HashLongestMatch |