1 | /* NOLINT(build/header_guard) */ |
2 | /* Copyright 2010 Google Inc. All Rights Reserved. |
3 | |
4 | Distributed under MIT license. |
5 | See file LICENSE for detail or copy at https://opensource.org/licenses/MIT |
6 | */ |
7 | |
8 | /* template parameters: FN */ |
9 | |
10 | /* A (forgetful) hash table to the data seen by the compressor, to |
11 | help create backward references to previous data. |
12 | |
13 | This is a hash map of fixed size (bucket_size_) to a ring buffer of |
14 | fixed size (block_size_). The ring buffer contains the last block_size_ |
15 | index positions of the given hash key in the compressed data. */ |
16 | |
17 | #define HashLongestMatch HASHER() |
18 | |
19 | static BROTLI_INLINE size_t FN(HashTypeLength)(void) { return 8; } |
20 | static BROTLI_INLINE size_t FN(StoreLookahead)(void) { return 8; } |
21 | |
22 | /* HashBytes is the function that chooses the bucket to place the address in. */ |
23 | static BROTLI_INLINE uint32_t FN(HashBytes)(const uint8_t* data, |
24 | const uint64_t mask, |
25 | const int shift) { |
26 | const uint64_t h = (BROTLI_UNALIGNED_LOAD64LE(data) & mask) * kHashMul64Long; |
27 | /* The higher bits contain more mixture from the multiplication, |
28 | so we take our results from there. */ |
29 | return (uint32_t)(h >> shift); |
30 | } |
31 | |
32 | typedef struct HashLongestMatch { |
33 | /* Number of hash buckets. */ |
34 | size_t bucket_size_; |
35 | /* Only block_size_ newest backward references are kept, |
36 | and the older are forgotten. */ |
37 | size_t block_size_; |
38 | /* Left-shift for computing hash bucket index from hash value. */ |
39 | int hash_shift_; |
40 | /* Mask for selecting the next 4-8 bytes of input */ |
41 | uint64_t hash_mask_; |
42 | /* Mask for accessing entries in a block (in a ring-buffer manner). */ |
43 | uint32_t block_mask_; |
44 | |
45 | /* --- Dynamic size members --- */ |
46 | |
47 | /* Number of entries in a particular bucket. */ |
48 | /* uint16_t num[bucket_size]; */ |
49 | |
50 | /* Buckets containing block_size_ of backward references. */ |
51 | /* uint32_t* buckets[bucket_size * block_size]; */ |
52 | } HashLongestMatch; |
53 | |
54 | static BROTLI_INLINE HashLongestMatch* FN(Self)(HasherHandle handle) { |
55 | return (HashLongestMatch*)&(GetHasherCommon(handle)[1]); |
56 | } |
57 | |
58 | static BROTLI_INLINE uint16_t* FN(Num)(HashLongestMatch* self) { |
59 | return (uint16_t*)(&self[1]); |
60 | } |
61 | |
62 | static BROTLI_INLINE uint32_t* FN(Buckets)(HashLongestMatch* self) { |
63 | return (uint32_t*)(&FN(Num)(self)[self->bucket_size_]); |
64 | } |
65 | |
66 | static void FN(Initialize)( |
67 | HasherHandle handle, const BrotliEncoderParams* params) { |
68 | HasherCommon* common = GetHasherCommon(handle); |
69 | HashLongestMatch* self = FN(Self)(handle); |
70 | BROTLI_UNUSED(params); |
71 | self->hash_shift_ = 64 - common->params.bucket_bits; |
72 | self->hash_mask_ = (~((uint64_t)0U)) >> (64 - 8 * common->params.hash_len); |
73 | self->bucket_size_ = (size_t)1 << common->params.bucket_bits; |
74 | self->block_size_ = (size_t)1 << common->params.block_bits; |
75 | self->block_mask_ = (uint32_t)(self->block_size_ - 1); |
76 | } |
77 | |
78 | static void FN(Prepare)(HasherHandle handle, BROTLI_BOOL one_shot, |
79 | size_t input_size, const uint8_t* data) { |
80 | HashLongestMatch* self = FN(Self)(handle); |
81 | uint16_t* num = FN(Num)(self); |
82 | /* Partial preparation is 100 times slower (per socket). */ |
83 | size_t partial_prepare_threshold = self->bucket_size_ >> 6; |
84 | if (one_shot && input_size <= partial_prepare_threshold) { |
85 | size_t i; |
86 | for (i = 0; i < input_size; ++i) { |
87 | const uint32_t key = FN(HashBytes)(&data[i], self->hash_mask_, |
88 | self->hash_shift_); |
89 | num[key] = 0; |
90 | } |
91 | } else { |
92 | memset(num, 0, self->bucket_size_ * sizeof(num[0])); |
93 | } |
94 | } |
95 | |
96 | static BROTLI_INLINE size_t FN(HashMemAllocInBytes)( |
97 | const BrotliEncoderParams* params, BROTLI_BOOL one_shot, |
98 | size_t input_size) { |
99 | size_t bucket_size = (size_t)1 << params->hasher.bucket_bits; |
100 | size_t block_size = (size_t)1 << params->hasher.block_bits; |
101 | BROTLI_UNUSED(one_shot); |
102 | BROTLI_UNUSED(input_size); |
103 | return sizeof(HashLongestMatch) + bucket_size * (2 + 4 * block_size); |
104 | } |
105 | |
106 | /* Look at 4 bytes at &data[ix & mask]. |
107 | Compute a hash from these, and store the value of ix at that position. */ |
108 | static BROTLI_INLINE void FN(Store)(HasherHandle handle, const uint8_t* data, |
109 | const size_t mask, const size_t ix) { |
110 | HashLongestMatch* self = FN(Self)(handle); |
111 | uint16_t* num = FN(Num)(self); |
112 | const uint32_t key = FN(HashBytes)(&data[ix & mask], self->hash_mask_, |
113 | self->hash_shift_); |
114 | const size_t minor_ix = num[key] & self->block_mask_; |
115 | const size_t offset = |
116 | minor_ix + (key << GetHasherCommon(handle)->params.block_bits); |
117 | FN(Buckets)(self)[offset] = (uint32_t)ix; |
118 | ++num[key]; |
119 | } |
120 | |
121 | static BROTLI_INLINE void FN(StoreRange)(HasherHandle handle, |
122 | const uint8_t* data, const size_t mask, const size_t ix_start, |
123 | const size_t ix_end) { |
124 | size_t i; |
125 | for (i = ix_start; i < ix_end; ++i) { |
126 | FN(Store)(handle, data, mask, i); |
127 | } |
128 | } |
129 | |
130 | static BROTLI_INLINE void FN(StitchToPreviousBlock)(HasherHandle handle, |
131 | size_t num_bytes, size_t position, const uint8_t* ringbuffer, |
132 | size_t ringbuffer_mask) { |
133 | if (num_bytes >= FN(HashTypeLength)() - 1 && position >= 3) { |
134 | /* Prepare the hashes for three last bytes of the last write. |
135 | These could not be calculated before, since they require knowledge |
136 | of both the previous and the current block. */ |
137 | FN(Store)(handle, ringbuffer, ringbuffer_mask, position - 3); |
138 | FN(Store)(handle, ringbuffer, ringbuffer_mask, position - 2); |
139 | FN(Store)(handle, ringbuffer, ringbuffer_mask, position - 1); |
140 | } |
141 | } |
142 | |
143 | static BROTLI_INLINE void FN(PrepareDistanceCache)( |
144 | HasherHandle handle, int* BROTLI_RESTRICT distance_cache) { |
145 | PrepareDistanceCache(distance_cache, |
146 | GetHasherCommon(handle)->params.num_last_distances_to_check); |
147 | } |
148 | |
149 | /* Find a longest backward match of &data[cur_ix] up to the length of |
150 | max_length and stores the position cur_ix in the hash table. |
151 | |
152 | REQUIRES: FN(PrepareDistanceCache) must be invoked for current distance cache |
153 | values; if this method is invoked repeatedly with the same distance |
154 | cache values, it is enough to invoke FN(PrepareDistanceCache) once. |
155 | |
156 | Does not look for matches longer than max_length. |
157 | Does not look for matches further away than max_backward. |
158 | Writes the best match into |out|. |
159 | |out|->score is updated only if a better match is found. */ |
160 | static BROTLI_INLINE void FN(FindLongestMatch)(HasherHandle handle, |
161 | const BrotliEncoderDictionary* dictionary, |
162 | const uint8_t* BROTLI_RESTRICT data, const size_t ring_buffer_mask, |
163 | const int* BROTLI_RESTRICT distance_cache, const size_t cur_ix, |
164 | const size_t max_length, const size_t max_backward, |
165 | const size_t gap, const size_t max_distance, |
166 | HasherSearchResult* BROTLI_RESTRICT out) { |
167 | HasherCommon* common = GetHasherCommon(handle); |
168 | HashLongestMatch* self = FN(Self)(handle); |
169 | uint16_t* num = FN(Num)(self); |
170 | uint32_t* buckets = FN(Buckets)(self); |
171 | const size_t cur_ix_masked = cur_ix & ring_buffer_mask; |
172 | /* Don't accept a short copy from far away. */ |
173 | score_t min_score = out->score; |
174 | score_t best_score = out->score; |
175 | size_t best_len = out->len; |
176 | size_t i; |
177 | out->len = 0; |
178 | out->len_code_delta = 0; |
179 | /* Try last distance first. */ |
180 | for (i = 0; i < (size_t)common->params.num_last_distances_to_check; ++i) { |
181 | const size_t backward = (size_t)distance_cache[i]; |
182 | size_t prev_ix = (size_t)(cur_ix - backward); |
183 | if (prev_ix >= cur_ix) { |
184 | continue; |
185 | } |
186 | if (BROTLI_PREDICT_FALSE(backward > max_backward)) { |
187 | continue; |
188 | } |
189 | prev_ix &= ring_buffer_mask; |
190 | |
191 | if (cur_ix_masked + best_len > ring_buffer_mask || |
192 | prev_ix + best_len > ring_buffer_mask || |
193 | data[cur_ix_masked + best_len] != data[prev_ix + best_len]) { |
194 | continue; |
195 | } |
196 | { |
197 | const size_t len = FindMatchLengthWithLimit(&data[prev_ix], |
198 | &data[cur_ix_masked], |
199 | max_length); |
200 | if (len >= 3 || (len == 2 && i < 2)) { |
201 | /* Comparing for >= 2 does not change the semantics, but just saves for |
202 | a few unnecessary binary logarithms in backward reference score, |
203 | since we are not interested in such short matches. */ |
204 | score_t score = BackwardReferenceScoreUsingLastDistance(len); |
205 | if (best_score < score) { |
206 | if (i != 0) score -= BackwardReferencePenaltyUsingLastDistance(i); |
207 | if (best_score < score) { |
208 | best_score = score; |
209 | best_len = len; |
210 | out->len = best_len; |
211 | out->distance = backward; |
212 | out->score = best_score; |
213 | } |
214 | } |
215 | } |
216 | } |
217 | } |
218 | { |
219 | const uint32_t key = FN(HashBytes)( |
220 | &data[cur_ix_masked], self->hash_mask_, self->hash_shift_); |
221 | uint32_t* BROTLI_RESTRICT bucket = |
222 | &buckets[key << common->params.block_bits]; |
223 | const size_t down = |
224 | (num[key] > self->block_size_) ? |
225 | (num[key] - self->block_size_) : 0u; |
226 | for (i = num[key]; i > down;) { |
227 | size_t prev_ix = bucket[--i & self->block_mask_]; |
228 | const size_t backward = cur_ix - prev_ix; |
229 | if (BROTLI_PREDICT_FALSE(backward > max_backward)) { |
230 | break; |
231 | } |
232 | prev_ix &= ring_buffer_mask; |
233 | if (cur_ix_masked + best_len > ring_buffer_mask || |
234 | prev_ix + best_len > ring_buffer_mask || |
235 | data[cur_ix_masked + best_len] != data[prev_ix + best_len]) { |
236 | continue; |
237 | } |
238 | { |
239 | const size_t len = FindMatchLengthWithLimit(&data[prev_ix], |
240 | &data[cur_ix_masked], |
241 | max_length); |
242 | if (len >= 4) { |
243 | /* Comparing for >= 3 does not change the semantics, but just saves |
244 | for a few unnecessary binary logarithms in backward reference |
245 | score, since we are not interested in such short matches. */ |
246 | score_t score = BackwardReferenceScore(len, backward); |
247 | if (best_score < score) { |
248 | best_score = score; |
249 | best_len = len; |
250 | out->len = best_len; |
251 | out->distance = backward; |
252 | out->score = best_score; |
253 | } |
254 | } |
255 | } |
256 | } |
257 | bucket[num[key] & self->block_mask_] = (uint32_t)cur_ix; |
258 | ++num[key]; |
259 | } |
260 | if (min_score == out->score) { |
261 | SearchInStaticDictionary(dictionary, |
262 | handle, &data[cur_ix_masked], max_length, max_backward + gap, |
263 | max_distance, out, BROTLI_FALSE); |
264 | } |
265 | } |
266 | |
267 | #undef HashLongestMatch |
268 | |