diff options
Diffstat (limited to 'modules/brotli/enc/hash_forgetful_chain_inc.h')
| -rw-r--r-- | modules/brotli/enc/hash_forgetful_chain_inc.h | 254 |
1 files changed, 254 insertions, 0 deletions
diff --git a/modules/brotli/enc/hash_forgetful_chain_inc.h b/modules/brotli/enc/hash_forgetful_chain_inc.h new file mode 100644 index 000000000..41cb3ff03 --- /dev/null +++ b/modules/brotli/enc/hash_forgetful_chain_inc.h @@ -0,0 +1,254 @@ +/* NOLINT(build/header_guard) */ +/* Copyright 2016 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, NUM_BANKS, BANK_BITS, + NUM_LAST_DISTANCES_TO_CHECK */ + +/* A (forgetful) hash table to the data seen by the compressor, to + help create backward references to previous data. + + Hashes are stored in chains which are bucketed to groups. Group of chains + share a storage "bank". When more than "bank size" chain nodes are added, + oldest nodes are replaced; this way several chains may share a tail. */ + +#define HashForgetfulChain HASHER() + +#define BANK_SIZE (1 << BANK_BITS) + +/* Number of hash buckets. */ +#define BUCKET_SIZE (1 << BUCKET_BITS) + +#define CAPPED_CHAINS 0 + +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 BROTLI_INLINE size_t FN(HashBytes)(const uint8_t* data) { + const 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 h >> (32 - BUCKET_BITS); +} + +typedef struct FN(Slot) { + uint16_t delta; + uint16_t next; +} FN(Slot); + +typedef struct FN(Bank) { + FN(Slot) slots[BANK_SIZE]; +} FN(Bank); + +typedef struct HashForgetfulChain { + uint32_t addr[BUCKET_SIZE]; + uint16_t head[BUCKET_SIZE]; + /* Truncated hash used for quick rejection of "distance cache" candidates. */ + uint8_t tiny_hash[65536]; + FN(Bank) banks[NUM_BANKS]; + uint16_t free_slot_idx[NUM_BANKS]; + size_t max_hops; +} HashForgetfulChain; + +static BROTLI_INLINE HashForgetfulChain* FN(Self)(HasherHandle handle) { + return (HashForgetfulChain*)&(GetHasherCommon(handle)[1]); +} + +static void FN(Initialize)( + HasherHandle handle, const BrotliEncoderParams* params) { + FN(Self)(handle)->max_hops = + (params->quality > 6 ? 7u : 8u) << (params->quality - 4); +} + +static void FN(Prepare)(HasherHandle handle, BROTLI_BOOL one_shot, + size_t input_size, const uint8_t* data) { + HashForgetfulChain* self = FN(Self)(handle); + /* Partial preparation is 100 times slower (per socket). */ + size_t partial_prepare_threshold = BUCKET_SIZE >> 6; + if (one_shot && input_size <= partial_prepare_threshold) { + size_t i; + for (i = 0; i < input_size; ++i) { + size_t bucket = FN(HashBytes)(&data[i]); + /* See InitEmpty comment. */ + self->addr[bucket] = 0xCCCCCCCC; + self->head[bucket] = 0xCCCC; + } + } else { + /* Fill |addr| array with 0xCCCCCCCC value. Because of wrapping, position + processed by hasher never reaches 3GB + 64M; this makes all new chains + to be terminated after the first node. */ + memset(self->addr, 0xCC, sizeof(self->addr)); + memset(self->head, 0, sizeof(self->head)); + } + memset(self->tiny_hash, 0, sizeof(self->tiny_hash)); + memset(self->free_slot_idx, 0, sizeof(self->free_slot_idx)); +} + +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(HashForgetfulChain); +} + +/* Look at 4 bytes at &data[ix & mask]. Compute a hash from these, and prepend + node to corresponding chain; also update tiny_hash for current position. */ +static BROTLI_INLINE void FN(Store)(HasherHandle BROTLI_RESTRICT handle, + const uint8_t* BROTLI_RESTRICT data, const size_t mask, const size_t ix) { + HashForgetfulChain* self = FN(Self)(handle); + const size_t key = FN(HashBytes)(&data[ix & mask]); + const size_t bank = key & (NUM_BANKS - 1); + const size_t idx = self->free_slot_idx[bank]++ & (BANK_SIZE - 1); + size_t delta = ix - self->addr[key]; + self->tiny_hash[(uint16_t)ix] = (uint8_t)key; + if (delta > 0xFFFF) delta = CAPPED_CHAINS ? 0 : 0xFFFF; + self->banks[bank].slots[idx].delta = (uint16_t)delta; + self->banks[bank].slots[idx].next = self->head[key]; + self->addr[key] = (uint32_t)ix; + self->head[key] = (uint16_t)idx; +} + +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 ring_buffer_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, ring_buffer_mask, position - 3); + FN(Store)(handle, ringbuffer, ring_buffer_mask, position - 2); + FN(Store)(handle, ringbuffer, ring_buffer_mask, position - 1); + } +} + +static BROTLI_INLINE void FN(PrepareDistanceCache)( + HasherHandle handle, int* BROTLI_RESTRICT distance_cache) { + BROTLI_UNUSED(handle); + PrepareDistanceCache(distance_cache, 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) { + HashForgetfulChain* self = FN(Self)(handle); + 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; + const size_t key = FN(HashBytes)(&data[cur_ix_masked]); + const uint8_t tiny_hash = (uint8_t)(key); + out->len = 0; + out->len_code_delta = 0; + /* Try last distance first. */ + for (i = 0; i < NUM_LAST_DISTANCES_TO_CHECK; ++i) { + const size_t backward = (size_t)distance_cache[i]; + size_t prev_ix = (cur_ix - backward); + /* For distance code 0 we want to consider 2-byte matches. */ + if (i > 0 && self->tiny_hash[(uint16_t)prev_ix] != tiny_hash) continue; + if (prev_ix >= cur_ix || backward > max_backward) { + continue; + } + prev_ix &= ring_buffer_mask; + { + const size_t len = FindMatchLengthWithLimit(&data[prev_ix], + &data[cur_ix_masked], + max_length); + if (len >= 2) { + 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 size_t bank = key & (NUM_BANKS - 1); + size_t backward = 0; + size_t hops = self->max_hops; + size_t delta = cur_ix - self->addr[key]; + size_t slot = self->head[key]; + while (hops--) { + size_t prev_ix; + size_t last = slot; + backward += delta; + if (backward > max_backward || (CAPPED_CHAINS && !delta)) break; + prev_ix = (cur_ix - backward) & ring_buffer_mask; + slot = self->banks[bank].slots[last].next; + delta = self->banks[bank].slots[last].delta; + 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; + } + } + } + } + FN(Store)(handle, data, ring_buffer_mask, cur_ix); + } + if (out->score == min_score) { + SearchInStaticDictionary(dictionary, + handle, &data[cur_ix_masked], max_length, max_backward + gap, + max_distance, out, BROTLI_FALSE); + } +} + +#undef BANK_SIZE +#undef BUCKET_SIZE +#undef CAPPED_CHAINS + +#undef HashForgetfulChain |