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/* 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, BLOCK_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.
This is a hash map of fixed size (BUCKET_SIZE) to a ring buffer of
fixed size (BLOCK_SIZE). The ring buffer contains the last BLOCK_SIZE
index positions of the given hash key in the compressed data. */
#define HashLongestMatch HASHER()
/* Number of hash buckets. */
#define BUCKET_SIZE (1 << BUCKET_BITS)
/* Only BLOCK_SIZE newest backward references are kept,
and the older are forgotten. */
#define BLOCK_SIZE (1u << BLOCK_BITS)
/* Mask for accessing entries in a block (in a ringbuffer manner). */
#define BLOCK_MASK ((1 << BLOCK_BITS) - 1)
#define HASH_MAP_SIZE (2 << BUCKET_BITS)
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. The HashLongestMatch and HashLongestMatchQuickly
classes have separate, different implementations of hashing. */
static uint32_t FN(HashBytes)(const uint8_t *data) {
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 HashLongestMatch {
/* Number of entries in a particular bucket. */
uint16_t num_[BUCKET_SIZE];
/* Buckets containing BLOCK_SIZE of backward references. */
uint32_t buckets_[BLOCK_SIZE << BUCKET_BITS];
/* True if num_ array needs to be initialized. */
BROTLI_BOOL is_dirty_;
DictionarySearchStatictics dict_search_stats_;
} HashLongestMatch;
static void FN(Reset)(HashLongestMatch* self) {
self->is_dirty_ = BROTLI_TRUE;
DictionarySearchStaticticsReset(&self->dict_search_stats_);
}
static void FN(InitEmpty)(HashLongestMatch* self) {
if (self->is_dirty_) {
memset(self->num_, 0, sizeof(self->num_));
self->is_dirty_ = BROTLI_FALSE;
}
}
static void FN(InitForData)(HashLongestMatch* self, const uint8_t* data,
size_t num) {
size_t i;
for (i = 0; i < num; ++i) {
const uint32_t key = FN(HashBytes)(&data[i]);
self->num_[key] = 0;
}
if (num != 0) {
self->is_dirty_ = BROTLI_FALSE;
}
}
static void FN(Init)(
MemoryManager* m, HashLongestMatch* 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 = HASH_MAP_SIZE >> 7;
BROTLI_UNUSED(m);
BROTLI_UNUSED(params);
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 store the value of ix at that position. */
static BROTLI_INLINE void FN(Store)(HashLongestMatch* self, const uint8_t *data,
const size_t mask, const size_t ix) {
const uint32_t key = FN(HashBytes)(&data[ix & mask]);
const size_t minor_ix = self->num_[key] & BLOCK_MASK;
self->buckets_[minor_ix + (key << BLOCK_BITS)] = (uint32_t)ix;
++self->num_[key];
}
static BROTLI_INLINE void FN(StoreRange)(HashLongestMatch* 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)(HashLongestMatch* self,
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)(self, ringbuffer, ringbuffer_mask, position - 3);
FN(Store)(self, ringbuffer, ringbuffer_mask, position - 2);
FN(Store)(self, ringbuffer, ringbuffer_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 true when match is found, otherwise false. */
static BROTLI_INLINE BROTLI_BOOL FN(FindLongestMatch)(HashLongestMatch* 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;
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 = (size_t)(cur_ix - backward);
if (prev_ix >= cur_ix) {
continue;
}
if (PREDICT_FALSE(backward > max_backward)) {
continue;
}
prev_ix &= ring_buffer_mask;
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 >= 3 || (len == 2 && i < 2)) {
/* Comparing for >= 2 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 = 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 uint32_t key = FN(HashBytes)(&data[cur_ix_masked]);
uint32_t* BROTLI_RESTRICT bucket = &self->buckets_[key << BLOCK_BITS];
const size_t down =
(self->num_[key] > BLOCK_SIZE) ? (self->num_[key] - BLOCK_SIZE) : 0u;
for (i = self->num_[key]; i > down;) {
size_t prev_ix = bucket[--i & BLOCK_MASK];
const size_t backward = cur_ix - prev_ix;
if (PREDICT_FALSE(backward > max_backward)) {
break;
}
prev_ix &= ring_buffer_mask;
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;
}
}
}
}
bucket[self->num_[key] & BLOCK_MASK] = (uint32_t)cur_ix;
++self->num_[key];
}
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 HASH_MAP_SIZE
#undef BLOCK_MASK
#undef BLOCK_SIZE
#undef BUCKET_SIZE
#undef HashLongestMatch
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