diff options
Diffstat (limited to 'modules/brotli/enc/hash_longest_match_quickly_inc.h')
| -rw-r--r-- | modules/brotli/enc/hash_longest_match_quickly_inc.h | 235 |
1 files changed, 235 insertions, 0 deletions
diff --git a/modules/brotli/enc/hash_longest_match_quickly_inc.h b/modules/brotli/enc/hash_longest_match_quickly_inc.h new file mode 100644 index 000000000..a7b9639fe --- /dev/null +++ b/modules/brotli/enc/hash_longest_match_quickly_inc.h @@ -0,0 +1,235 @@ +/* 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, BUCKET_BITS, BUCKET_SWEEP, HASH_LEN, + USE_DICTIONARY + */ + +#define HashLongestMatchQuickly HASHER() + +#define BUCKET_SIZE (1 << BUCKET_BITS) + +#define HASH_MAP_SIZE (4 << BUCKET_BITS) + +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. The HashLongestMatch and HashLongestMatchQuickly + classes have separate, different implementations of hashing. */ +static uint32_t FN(HashBytes)(const uint8_t* data) { + const uint64_t h = ((BROTLI_UNALIGNED_LOAD64LE(data) << (64 - 8 * HASH_LEN)) * + kHashMul64); + /* The higher bits contain more mixture from the multiplication, + so we take our results from there. */ + return (uint32_t)(h >> (64 - BUCKET_BITS)); +} + +/* 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). Starting from the + given index, BUCKET_SWEEP buckets are used to store values of a key. */ +typedef struct HashLongestMatchQuickly { + uint32_t buckets_[BUCKET_SIZE + BUCKET_SWEEP]; +} HashLongestMatchQuickly; + +static BROTLI_INLINE HashLongestMatchQuickly* FN(Self)(HasherHandle handle) { + return (HashLongestMatchQuickly*)&(GetHasherCommon(handle)[1]); +} + +static void FN(Initialize)( + HasherHandle handle, const BrotliEncoderParams* params) { + BROTLI_UNUSED(handle); + BROTLI_UNUSED(params); +} + +static void FN(Prepare)(HasherHandle handle, BROTLI_BOOL one_shot, + size_t input_size, const uint8_t* data) { + HashLongestMatchQuickly* self = FN(Self)(handle); + /* Partial preparation is 100 times slower (per socket). */ + size_t partial_prepare_threshold = HASH_MAP_SIZE >> 7; + 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]); + memset(&self->buckets_[key], 0, BUCKET_SWEEP * sizeof(self->buckets_[0])); + } + } else { + /* It is not strictly necessary to fill this buffer here, but + not filling will make the results of the compression stochastic + (but correct). This is because random data would cause the + system to find accidentally good backward references here and there. */ + memset(&self->buckets_[0], 0, sizeof(self->buckets_)); + } +} + +static BROTLI_INLINE size_t FN(HashMemAllocInBytes)( + const BrotliEncoderParams* params, BROTLI_BOOL one_shot, + size_t input_size) { + BROTLI_UNUSED(params); + BROTLI_UNUSED(one_shot); + BROTLI_UNUSED(input_size); + return sizeof(HashLongestMatchQuickly); +} + +/* Look at 5 bytes at &data[ix & mask]. + Compute a hash from these, and store the value somewhere within + [ix .. ix+3]. */ +static BROTLI_INLINE void FN(Store)(HasherHandle handle, + const uint8_t* data, const size_t mask, const size_t ix) { + const uint32_t key = FN(HashBytes)(&data[ix & mask]); + /* Wiggle the value with the bucket sweep range. */ + const uint32_t off = (ix >> 3) % BUCKET_SWEEP; + FN(Self)(handle)->buckets_[key + off] = (uint32_t)ix; +} + +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) { + BROTLI_UNUSED(handle); + BROTLI_UNUSED(distance_cache); +} + +/* Find a longest backward match of &data[cur_ix & ring_buffer_mask] + up to the length of max_length and stores the position cur_ix in the + hash table. + + 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) { + HashLongestMatchQuickly* self = FN(Self)(handle); + const size_t best_len_in = out->len; + const size_t cur_ix_masked = cur_ix & ring_buffer_mask; + const uint32_t key = FN(HashBytes)(&data[cur_ix_masked]); + int compare_char = data[cur_ix_masked + best_len_in]; + score_t min_score = out->score; + score_t best_score = out->score; + size_t best_len = best_len_in; + size_t cached_backward = (size_t)distance_cache[0]; + size_t prev_ix = cur_ix - cached_backward; + out->len_code_delta = 0; + if (prev_ix < cur_ix) { + prev_ix &= (uint32_t)ring_buffer_mask; + if (compare_char == data[prev_ix + best_len]) { + size_t len = FindMatchLengthWithLimit(&data[prev_ix], + &data[cur_ix_masked], + max_length); + if (len >= 4) { + const score_t score = BackwardReferenceScoreUsingLastDistance(len); + if (best_score < score) { + best_score = score; + best_len = len; + out->len = len; + out->distance = cached_backward; + out->score = best_score; + compare_char = data[cur_ix_masked + best_len]; + if (BUCKET_SWEEP == 1) { + self->buckets_[key] = (uint32_t)cur_ix; + return; + } + } + } + } + } + if (BUCKET_SWEEP == 1) { + size_t backward; + size_t len; + /* Only one to look for, don't bother to prepare for a loop. */ + prev_ix = self->buckets_[key]; + self->buckets_[key] = (uint32_t)cur_ix; + backward = cur_ix - prev_ix; + prev_ix &= (uint32_t)ring_buffer_mask; + if (compare_char != data[prev_ix + best_len_in]) { + return; + } + if (BROTLI_PREDICT_FALSE(backward == 0 || backward > max_backward)) { + return; + } + len = FindMatchLengthWithLimit(&data[prev_ix], + &data[cur_ix_masked], + max_length); + if (len >= 4) { + const score_t score = BackwardReferenceScore(len, backward); + if (best_score < score) { + out->len = len; + out->distance = backward; + out->score = score; + return; + } + } + } else { + uint32_t* bucket = self->buckets_ + key; + int i; + prev_ix = *bucket++; + for (i = 0; i < BUCKET_SWEEP; ++i, prev_ix = *bucket++) { + const size_t backward = cur_ix - prev_ix; + size_t len; + prev_ix &= (uint32_t)ring_buffer_mask; + if (compare_char != data[prev_ix + best_len]) { + continue; + } + if (BROTLI_PREDICT_FALSE(backward == 0 || backward > max_backward)) { + continue; + } + len = FindMatchLengthWithLimit(&data[prev_ix], + &data[cur_ix_masked], + max_length); + if (len >= 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 = score; + compare_char = data[cur_ix_masked + best_len]; + } + } + } + } + if (USE_DICTIONARY && min_score == out->score) { + SearchInStaticDictionary(dictionary, + handle, &data[cur_ix_masked], max_length, max_backward + gap, + max_distance, out, BROTLI_TRUE); + } + self->buckets_[key + ((cur_ix >> 3) % BUCKET_SWEEP)] = (uint32_t)cur_ix; +} + +#undef HASH_MAP_SIZE +#undef BUCKET_SIZE + +#undef HashLongestMatchQuickly |