254 lines
9.4 KiB
C
254 lines
9.4 KiB
C
/* NOLINT(build/header_guard) */
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/* Copyright 2016 Google Inc. All Rights Reserved.
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Distributed under MIT license.
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See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
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*/
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/* template parameters: FN, BUCKET_BITS, NUM_BANKS, BANK_BITS,
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NUM_LAST_DISTANCES_TO_CHECK */
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/* A (forgetful) hash table to the data seen by the compressor, to
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help create backward references to previous data.
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Hashes are stored in chains which are bucketed to groups. Group of chains
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share a storage "bank". When more than "bank size" chain nodes are added,
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oldest nodes are replaced; this way several chains may share a tail. */
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#define HashForgetfulChain HASHER()
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#define BANK_SIZE (1 << BANK_BITS)
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/* Number of hash buckets. */
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#define BUCKET_SIZE (1 << BUCKET_BITS)
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#define CAPPED_CHAINS 0
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static BROTLI_INLINE size_t FN(HashTypeLength)(void) { return 4; }
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static BROTLI_INLINE size_t FN(StoreLookahead)(void) { return 4; }
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/* HashBytes is the function that chooses the bucket to place the address in.*/
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static BROTLI_INLINE size_t FN(HashBytes)(const uint8_t *data) {
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const uint32_t h = BROTLI_UNALIGNED_LOAD32(data) * kHashMul32;
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/* The higher bits contain more mixture from the multiplication,
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so we take our results from there. */
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return h >> (32 - BUCKET_BITS);
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}
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typedef struct FN(Slot) {
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uint16_t delta;
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uint16_t next;
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} FN(Slot);
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typedef struct FN(Bank) {
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FN(Slot) slots[BANK_SIZE];
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} FN(Bank);
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typedef struct HashForgetfulChain {
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uint32_t addr[BUCKET_SIZE];
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uint16_t head[BUCKET_SIZE];
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/* Truncated hash used for quick rejection of "distance cache" candidates. */
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uint8_t tiny_hash[65536];
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FN(Bank) banks[NUM_BANKS];
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uint16_t free_slot_idx[NUM_BANKS];
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size_t max_hops;
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} HashForgetfulChain;
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static BROTLI_INLINE HashForgetfulChain* FN(Self)(HasherHandle handle) {
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return (HashForgetfulChain*)&(GetHasherCommon(handle)[1]);
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}
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static void FN(Initialize)(
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HasherHandle handle, const BrotliEncoderParams* params) {
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FN(Self)(handle)->max_hops =
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(params->quality > 6 ? 7u : 8u) << (params->quality - 4);
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}
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static void FN(Prepare)(HasherHandle handle, BROTLI_BOOL one_shot,
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size_t input_size, const uint8_t* data) {
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HashForgetfulChain* self = FN(Self)(handle);
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/* Partial preparation is 100 times slower (per socket). */
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size_t partial_prepare_threshold = BUCKET_SIZE >> 6;
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if (one_shot && input_size <= partial_prepare_threshold) {
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size_t i;
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for (i = 0; i < input_size; ++i) {
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size_t bucket = FN(HashBytes)(&data[i]);
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/* See InitEmpty comment. */
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self->addr[bucket] = 0xCCCCCCCC;
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self->head[bucket] = 0xCCCC;
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}
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} else {
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/* Fill |addr| array with 0xCCCCCCCC value. Because of wrapping, position
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processed by hasher never reaches 3GB + 64M; this makes all new chains
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to be terminated after the first node. */
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memset(self->addr, 0xCC, sizeof(self->addr));
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memset(self->head, 0, sizeof(self->head));
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}
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memset(self->tiny_hash, 0, sizeof(self->tiny_hash));
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memset(self->free_slot_idx, 0, sizeof(self->free_slot_idx));
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}
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static BROTLI_INLINE size_t FN(HashMemAllocInBytes)(
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const BrotliEncoderParams* params, BROTLI_BOOL one_shot,
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size_t input_size) {
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BROTLI_UNUSED(params);
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BROTLI_UNUSED(one_shot);
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BROTLI_UNUSED(input_size);
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return sizeof(HashForgetfulChain);
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}
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/* Look at 4 bytes at &data[ix & mask]. Compute a hash from these, and prepend
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node to corresponding chain; also update tiny_hash for current position. */
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static BROTLI_INLINE void FN(Store)(HasherHandle BROTLI_RESTRICT handle,
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const uint8_t* BROTLI_RESTRICT data, const size_t mask, const size_t ix) {
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HashForgetfulChain* self = FN(Self)(handle);
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const size_t key = FN(HashBytes)(&data[ix & mask]);
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const size_t bank = key & (NUM_BANKS - 1);
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const size_t idx = self->free_slot_idx[bank]++ & (BANK_SIZE - 1);
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size_t delta = ix - self->addr[key];
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self->tiny_hash[(uint16_t)ix] = (uint8_t)key;
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if (delta > 0xFFFF) delta = CAPPED_CHAINS ? 0 : 0xFFFF;
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self->banks[bank].slots[idx].delta = (uint16_t)delta;
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self->banks[bank].slots[idx].next = self->head[key];
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self->addr[key] = (uint32_t)ix;
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self->head[key] = (uint16_t)idx;
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}
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static BROTLI_INLINE void FN(StoreRange)(HasherHandle handle,
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const uint8_t *data, const size_t mask, const size_t ix_start,
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const size_t ix_end) {
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size_t i;
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for (i = ix_start; i < ix_end; ++i) {
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FN(Store)(handle, data, mask, i);
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}
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}
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static BROTLI_INLINE void FN(StitchToPreviousBlock)(HasherHandle handle,
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size_t num_bytes, size_t position, const uint8_t* ringbuffer,
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size_t ring_buffer_mask) {
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if (num_bytes >= FN(HashTypeLength)() - 1 && position >= 3) {
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/* Prepare the hashes for three last bytes of the last write.
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These could not be calculated before, since they require knowledge
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of both the previous and the current block. */
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FN(Store)(handle, ringbuffer, ring_buffer_mask, position - 3);
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FN(Store)(handle, ringbuffer, ring_buffer_mask, position - 2);
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FN(Store)(handle, ringbuffer, ring_buffer_mask, position - 1);
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}
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}
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static BROTLI_INLINE void FN(PrepareDistanceCache)(
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HasherHandle handle, int* BROTLI_RESTRICT distance_cache) {
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BROTLI_UNUSED(handle);
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PrepareDistanceCache(distance_cache, NUM_LAST_DISTANCES_TO_CHECK);
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}
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/* Find a longest backward match of &data[cur_ix] up to the length of
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max_length and stores the position cur_ix in the hash table.
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REQUIRES: FN(PrepareDistanceCache) must be invoked for current distance cache
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values; if this method is invoked repeatedly with the same distance
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cache values, it is enough to invoke FN(PrepareDistanceCache) once.
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Does not look for matches longer than max_length.
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Does not look for matches further away than max_backward.
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Writes the best match into |out|.
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|out|->score is updated only if a better match is found. */
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static BROTLI_INLINE void FN(FindLongestMatch)(HasherHandle handle,
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const BrotliDictionary* dictionary, const uint16_t* dictionary_hash,
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const uint8_t* BROTLI_RESTRICT data, const size_t ring_buffer_mask,
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const int* BROTLI_RESTRICT distance_cache,
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const size_t cur_ix, const size_t max_length, const size_t max_backward,
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HasherSearchResult* BROTLI_RESTRICT out) {
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HashForgetfulChain* self = FN(Self)(handle);
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const size_t cur_ix_masked = cur_ix & ring_buffer_mask;
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/* Don't accept a short copy from far away. */
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score_t min_score = out->score;
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score_t best_score = out->score;
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size_t best_len = out->len;
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size_t i;
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const size_t key = FN(HashBytes)(&data[cur_ix_masked]);
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const uint8_t tiny_hash = (uint8_t)(key);
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out->len = 0;
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out->len_code_delta = 0;
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/* Try last distance first. */
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for (i = 0; i < NUM_LAST_DISTANCES_TO_CHECK; ++i) {
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const size_t backward = (size_t)distance_cache[i];
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size_t prev_ix = (cur_ix - backward);
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/* For distance code 0 we want to consider 2-byte matches. */
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if (i > 0 && self->tiny_hash[(uint16_t)prev_ix] != tiny_hash) continue;
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if (prev_ix >= cur_ix || backward > max_backward) {
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continue;
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}
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prev_ix &= ring_buffer_mask;
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{
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const size_t len = FindMatchLengthWithLimit(&data[prev_ix],
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&data[cur_ix_masked],
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max_length);
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if (len >= 2) {
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score_t score = BackwardReferenceScoreUsingLastDistance(len);
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if (best_score < score) {
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if (i != 0) score -= BackwardReferencePenaltyUsingLastDistance(i);
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if (best_score < score) {
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best_score = score;
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best_len = len;
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out->len = best_len;
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out->distance = backward;
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out->score = best_score;
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}
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}
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}
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}
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}
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{
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const size_t bank = key & (NUM_BANKS - 1);
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size_t backward = 0;
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size_t hops = self->max_hops;
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size_t delta = cur_ix - self->addr[key];
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size_t slot = self->head[key];
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while (hops--) {
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size_t prev_ix;
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size_t last = slot;
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backward += delta;
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if (backward > max_backward || (CAPPED_CHAINS && !delta)) break;
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prev_ix = (cur_ix - backward) & ring_buffer_mask;
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slot = self->banks[bank].slots[last].next;
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delta = self->banks[bank].slots[last].delta;
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if (cur_ix_masked + best_len > ring_buffer_mask ||
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prev_ix + best_len > ring_buffer_mask ||
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data[cur_ix_masked + best_len] != data[prev_ix + best_len]) {
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continue;
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}
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{
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const size_t len = FindMatchLengthWithLimit(&data[prev_ix],
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&data[cur_ix_masked],
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max_length);
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if (len >= 4) {
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/* Comparing for >= 3 does not change the semantics, but just saves
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for a few unnecessary binary logarithms in backward reference
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score, since we are not interested in such short matches. */
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score_t score = BackwardReferenceScore(len, backward);
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if (best_score < score) {
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best_score = score;
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best_len = len;
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out->len = best_len;
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out->distance = backward;
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out->score = best_score;
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}
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}
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}
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}
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FN(Store)(handle, data, ring_buffer_mask, cur_ix);
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}
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if (out->score == min_score) {
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SearchInStaticDictionary(dictionary, dictionary_hash,
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handle, &data[cur_ix_masked], max_length, max_backward, out,
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BROTLI_FALSE);
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}
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}
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#undef BANK_SIZE
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#undef BUCKET_SIZE
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#undef CAPPED_CHAINS
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#undef HashForgetfulChain
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