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280 lines
10 KiB
C
280 lines
10 KiB
C
/* NOLINT(build/header_guard) */
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/* Copyright 2010 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 */
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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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This is a hash map of fixed size (bucket_size_) to a ring buffer of
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fixed size (block_size_). The ring buffer contains the last block_size_
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index positions of the given hash key in the compressed data. */
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#define HashLongestMatch HASHER()
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static BROTLI_INLINE size_t FN(HashTypeLength)(void) { return 8; }
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static BROTLI_INLINE size_t FN(StoreLookahead)(void) { return 8; }
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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* BROTLI_RESTRICT data,
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uint64_t hash_mul) {
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const uint64_t h = BROTLI_UNALIGNED_LOAD64LE(data) * hash_mul;
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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 (size_t)(h >> (64 - 15));
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}
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typedef struct HashLongestMatch {
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/* Number of hash buckets. */
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size_t bucket_size_;
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/* Only block_size_ newest backward references are kept,
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and the older are forgotten. */
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size_t block_size_;
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/* Hash multiplier tuned to match length. */
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uint64_t hash_mul_;
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/* Mask for accessing entries in a block (in a ring-buffer manner). */
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uint32_t block_mask_;
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int block_bits_;
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int num_last_distances_to_check_;
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/* Shortcuts. */
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HasherCommon* common_;
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/* --- Dynamic size members --- */
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/* Number of entries in a particular bucket. */
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uint16_t* num_; /* uint16_t[bucket_size]; */
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/* Buckets containing block_size_ of backward references. */
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uint32_t* buckets_; /* uint32_t[bucket_size * block_size]; */
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} HashLongestMatch;
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static void FN(Initialize)(
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HasherCommon* common, HashLongestMatch* BROTLI_RESTRICT self,
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const BrotliEncoderParams* params) {
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self->common_ = common;
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BROTLI_UNUSED(params);
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self->hash_mul_ = kHashMul64 << (64 - 5 * 8);
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BROTLI_DCHECK(common->params.bucket_bits == 15);
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self->bucket_size_ = (size_t)1 << common->params.bucket_bits;
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self->block_bits_ = common->params.block_bits;
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self->block_size_ = (size_t)1 << common->params.block_bits;
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self->block_mask_ = (uint32_t)(self->block_size_ - 1);
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self->num_last_distances_to_check_ =
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common->params.num_last_distances_to_check;
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self->num_ = (uint16_t*)common->extra[0];
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self->buckets_ = (uint32_t*)common->extra[1];
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}
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static void FN(Prepare)(
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HashLongestMatch* BROTLI_RESTRICT self, BROTLI_BOOL one_shot,
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size_t input_size, const uint8_t* BROTLI_RESTRICT data) {
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uint16_t* BROTLI_RESTRICT num = self->num_;
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/* Partial preparation is 100 times slower (per socket). */
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size_t partial_prepare_threshold = self->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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const size_t key = FN(HashBytes)(&data[i], self->hash_mul_);
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num[key] = 0;
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}
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} else {
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memset(num, 0, self->bucket_size_ * sizeof(num[0]));
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}
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}
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static BROTLI_INLINE void FN(HashMemAllocInBytes)(
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const BrotliEncoderParams* params, BROTLI_BOOL one_shot,
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size_t input_size, size_t* alloc_size) {
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size_t bucket_size = (size_t)1 << params->hasher.bucket_bits;
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size_t block_size = (size_t)1 << params->hasher.block_bits;
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BROTLI_UNUSED(one_shot);
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BROTLI_UNUSED(input_size);
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alloc_size[0] = sizeof(uint16_t) * bucket_size;
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alloc_size[1] = sizeof(uint32_t) * bucket_size * block_size;
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}
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/* Look at 4 bytes at &data[ix & mask].
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Compute a hash from these, and store the value of ix at that position. */
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static BROTLI_INLINE void FN(Store)(
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HashLongestMatch* BROTLI_RESTRICT self, const uint8_t* BROTLI_RESTRICT data,
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const size_t mask, const size_t ix) {
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uint16_t* BROTLI_RESTRICT num = self->num_;
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uint32_t* BROTLI_RESTRICT buckets = self->buckets_;
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const size_t key = FN(HashBytes)(&data[ix & mask], self->hash_mul_);
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const size_t minor_ix = num[key] & self->block_mask_;
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const size_t offset = minor_ix + (key << self->block_bits_);
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++num[key];
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buckets[offset] = (uint32_t)ix;
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}
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static BROTLI_INLINE void FN(StoreRange)(HashLongestMatch* BROTLI_RESTRICT self,
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const uint8_t* BROTLI_RESTRICT data, const size_t mask,
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const size_t ix_start, 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)(self, data, mask, i);
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}
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}
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static BROTLI_INLINE void FN(StitchToPreviousBlock)(
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HashLongestMatch* BROTLI_RESTRICT self,
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size_t num_bytes, size_t position, const uint8_t* ringbuffer,
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size_t ringbuffer_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)(self, ringbuffer, ringbuffer_mask, position - 3);
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FN(Store)(self, ringbuffer, ringbuffer_mask, position - 2);
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FN(Store)(self, ringbuffer, ringbuffer_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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HashLongestMatch* BROTLI_RESTRICT self,
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int* BROTLI_RESTRICT distance_cache) {
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PrepareDistanceCache(distance_cache, self->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)(
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HashLongestMatch* BROTLI_RESTRICT self,
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const BrotliEncoderDictionary* dictionary,
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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, const size_t cur_ix,
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const size_t max_length, const size_t max_backward,
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const size_t dictionary_distance, const size_t max_distance,
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HasherSearchResult* BROTLI_RESTRICT out) {
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uint16_t* BROTLI_RESTRICT num = self->num_;
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uint32_t* BROTLI_RESTRICT buckets = self->buckets_;
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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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/* Precalculate the hash key and prefetch the bucket. */
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const size_t key = FN(HashBytes)(&data[cur_ix_masked], self->hash_mul_);
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uint32_t* BROTLI_RESTRICT bucket = &buckets[key << self->block_bits_];
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PREFETCH_L1(bucket);
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if (self->block_bits_ > 4) PREFETCH_L1(bucket + 16);
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out->len = 0;
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out->len_code_delta = 0;
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BROTLI_DCHECK(cur_ix_masked + max_length <= ring_buffer_mask);
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/* Try last distance first. */
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for (i = 0; i < (size_t)self->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 = (size_t)(cur_ix - backward);
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if (prev_ix >= cur_ix) {
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continue;
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}
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if (BROTLI_PREDICT_FALSE(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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if (cur_ix_masked + best_len > ring_buffer_mask) {
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break;
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}
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if (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 >= 3 || (len == 2 && i < 2)) {
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/* Comparing for >= 2 does not change the semantics, but just saves for
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a few unnecessary binary logarithms in backward reference score,
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since we are not interested in such short matches. */
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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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/* we require matches of len >4, so increase best_len to 3, so we can compare
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* 4 bytes all the time. */
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if (best_len < 3) {
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best_len = 3;
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}
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{
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const size_t down =
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(num[key] > self->block_size_) ?
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(num[key] - self->block_size_) : 0u;
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const uint32_t first4 = BrotliUnalignedRead32(data + cur_ix_masked);
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const size_t max_length_m4 = max_length - 4;
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i = num[key];
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for (; i > down;) {
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size_t prev_ix = bucket[--i & self->block_mask_];
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uint32_t current4;
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const size_t backward = cur_ix - prev_ix;
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if (BROTLI_PREDICT_FALSE(backward > max_backward)) {
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break;
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}
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prev_ix &= ring_buffer_mask;
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if (cur_ix_masked + best_len > ring_buffer_mask) {
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break;
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}
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if (prev_ix + best_len > ring_buffer_mask ||
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/* compare 4 bytes ending at best_len + 1 */
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BrotliUnalignedRead32(&data[cur_ix_masked + best_len - 3]) !=
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BrotliUnalignedRead32(&data[prev_ix + best_len - 3])) {
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continue;
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}
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current4 = BrotliUnalignedRead32(data + prev_ix);
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if (first4 != current4) continue;
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{
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const size_t len = FindMatchLengthWithLimit(&data[prev_ix + 4],
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&data[cur_ix_masked + 4],
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max_length_m4) + 4;
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const 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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bucket[num[key] & self->block_mask_] = (uint32_t)cur_ix;
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++num[key];
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}
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if (min_score == out->score) {
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SearchInStaticDictionary(dictionary,
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self->common_, &data[cur_ix_masked], max_length, dictionary_distance,
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max_distance, out, BROTLI_FALSE);
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}
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}
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#undef HashLongestMatch
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