/* 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_LOAD32(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]; | |
BROTLI_BOOL is_dirty_; | |
DictionarySearchStatictics dict_search_stats_; | |
size_t max_hops; | |
} HashForgetfulChain; | |
static void FN(Reset)(HashForgetfulChain* self) { | |
self->is_dirty_ = BROTLI_TRUE; | |
DictionarySearchStaticticsReset(&self->dict_search_stats_); | |
} | |
static void FN(InitEmpty)(HashForgetfulChain* self) { | |
if (self->is_dirty_) { | |
/* 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)); | |
self->is_dirty_ = BROTLI_FALSE; | |
} | |
} | |
static void FN(InitForData)(HashForgetfulChain* self, const uint8_t* data, | |
size_t num) { | |
size_t i; | |
for (i = 0; i < num; ++i) { | |
size_t bucket = FN(HashBytes)(&data[i]); | |
/* See InitEmpty comment. */ | |
self->addr[bucket] = 0xCCCCCCCC; | |
self->head[bucket] = 0xCCCC; | |
} | |
memset(self->tiny_hash, 0, sizeof(self->tiny_hash)); | |
memset(self->free_slot_idx, 0, sizeof(self->free_slot_idx)); | |
if (num != 0) { | |
self->is_dirty_ = BROTLI_FALSE; | |
} | |
} | |
static void FN(Init)( | |
MemoryManager* m, HashForgetfulChain* self, const uint8_t* data, | |
const BrotliEncoderParams* params, size_t position, size_t bytes, | |
BROTLI_BOOL is_last) { | |
/* Choose which init method is faster. | |
Init() is about 100 times faster than InitForData(). */ | |
const size_t kMaxBytesForPartialHashInit = BUCKET_SIZE >> 6; | |
BROTLI_UNUSED(m); | |
self->max_hops = (params->quality > 6 ? 7u : 8u) << (params->quality - 4); | |
if (position == 0 && is_last && bytes <= kMaxBytesForPartialHashInit) { | |
FN(InitForData)(self, data, bytes); | |
} else { | |
FN(InitEmpty)(self); | |
} | |
} | |
/* 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)(HashForgetfulChain* BROTLI_RESTRICT self, | |
const uint8_t* BROTLI_RESTRICT data, const size_t mask, const size_t ix) { | |
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)(HashForgetfulChain* self, | |
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)(self, data, mask, i); | |
} | |
} | |
static BROTLI_INLINE void FN(StitchToPreviousBlock)(HashForgetfulChain* self, | |
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)(self, ringbuffer, ring_buffer_mask, position - 3); | |
FN(Store)(self, ringbuffer, ring_buffer_mask, position - 2); | |
FN(Store)(self, ringbuffer, ring_buffer_mask, position - 1); | |
} | |
} | |
/* 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. | |
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|. | |
Returns 1 when match is found, otherwise 0. */ | |
static BROTLI_INLINE BROTLI_BOOL FN(FindLongestMatch)( | |
HashForgetfulChain* self, 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, | |
HasherSearchResult* BROTLI_RESTRICT out) { | |
const size_t cur_ix_masked = cur_ix & ring_buffer_mask; | |
BROTLI_BOOL is_match_found = BROTLI_FALSE; | |
/* Don't accept a short copy from far away. */ | |
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_x_code = 0; | |
/* Try last distance first. */ | |
for (i = 0; i < NUM_LAST_DISTANCES_TO_CHECK; ++i) { | |
const size_t idx = kDistanceCacheIndex[i]; | |
const size_t backward = | |
(size_t)(distance_cache[idx] + kDistanceCacheOffset[i]); | |
size_t prev_ix = (cur_ix - backward); | |
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, i); | |
if (best_score < score) { | |
best_score = score; | |
best_len = len; | |
out->len = best_len; | |
out->distance = backward; | |
out->score = best_score; | |
is_match_found = BROTLI_TRUE; | |
} | |
} | |
} | |
} | |
{ | |
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; | |
is_match_found = BROTLI_TRUE; | |
} | |
} | |
} | |
} | |
FN(Store)(self, data, ring_buffer_mask, cur_ix); | |
} | |
if (!is_match_found) { | |
is_match_found = SearchInStaticDictionary(&self->dict_search_stats_, | |
&data[cur_ix_masked], max_length, max_backward, out, BROTLI_FALSE); | |
} | |
return is_match_found; | |
} | |
#undef BANK_SIZE | |
#undef BUCKET_SIZE | |
#undef CAPPED_CHAINS | |
#undef HashForgetfulChain |