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Unified Diff: third_party/brotli/enc/hash_longest_match_inc.h

Issue 2537133002: Update brotli to v1.0.0-snapshot. (Closed)
Patch Set: Fixed typo Created 4 years ago
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Index: third_party/brotli/enc/hash_longest_match_inc.h
diff --git a/third_party/brotli/enc/hash_longest_match_inc.h b/third_party/brotli/enc/hash_longest_match_inc.h
new file mode 100644
index 0000000000000000000000000000000000000000..5e934bac01921b3e643a01d0cb7849147b9db909
--- /dev/null
+++ b/third_party/brotli/enc/hash_longest_match_inc.h
@@ -0,0 +1,241 @@
+/* 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 ring-buffer 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 initialization 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 (BROTLI_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 (BROTLI_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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