Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 1 | // Copyright 2010 Google Inc. All Rights Reserved. |
| 2 | // |
| 3 | // Licensed under the Apache License, Version 2.0 (the "License"); |
| 4 | // you may not use this file except in compliance with the License. |
| 5 | // You may obtain a copy of the License at |
| 6 | // |
| 7 | // http://www.apache.org/licenses/LICENSE-2.0 |
| 8 | // |
| 9 | // Unless required by applicable law or agreed to in writing, software |
| 10 | // distributed under the License is distributed on an "AS IS" BASIS, |
| 11 | // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 12 | // See the License for the specific language governing permissions and |
| 13 | // limitations under the License. |
| 14 | // |
| 15 | // A (forgetful) hash table to the data seen by the compressor, to |
| 16 | // help create backward references to previous data. |
| 17 | |
| 18 | #ifndef BROTLI_ENC_HASH_H_ |
| 19 | #define BROTLI_ENC_HASH_H_ |
| 20 | |
| 21 | #include <stddef.h> |
| 22 | #include <stdint.h> |
| 23 | #include <string.h> |
| 24 | #include <sys/types.h> |
| 25 | #include <algorithm> |
Roderick Sheeter | 2e5995b | 2013-12-12 10:43:05 -0800 | [diff] [blame] | 26 | #include <cstdlib> |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 27 | #include <memory> |
Zoltan Szabadka | 2733d6c | 2014-02-17 14:25:36 +0100 | [diff] [blame] | 28 | #include <string> |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 29 | |
Zoltan Szabadka | 2733d6c | 2014-02-17 14:25:36 +0100 | [diff] [blame] | 30 | #include "./transform.h" |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 31 | #include "./fast_log.h" |
| 32 | #include "./find_match_length.h" |
| 33 | #include "./port.h" |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 34 | #include "./static_dict.h" |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 35 | |
| 36 | namespace brotli { |
| 37 | |
| 38 | // kHashMul32 multiplier has these properties: |
| 39 | // * The multiplier must be odd. Otherwise we may lose the highest bit. |
| 40 | // * No long streaks of 1s or 0s. |
| 41 | // * There is no effort to ensure that it is a prime, the oddity is enough |
| 42 | // for this use. |
| 43 | // * The number has been tuned heuristically against compression benchmarks. |
| 44 | static const uint32_t kHashMul32 = 0x1e35a7bd; |
| 45 | |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 46 | template<int kShiftBits, int kMinLength> |
| 47 | inline uint32_t Hash(const uint8_t *data) { |
| 48 | if (kMinLength <= 3) { |
| 49 | // If kMinLength is 2 or 3, we hash the first 3 bytes of data. |
| 50 | uint32_t h = (BROTLI_UNALIGNED_LOAD32(data) & 0xffffff) * kHashMul32; |
| 51 | // The higher bits contain more mixture from the multiplication, |
| 52 | // so we take our results from there. |
| 53 | return h >> (32 - kShiftBits); |
| 54 | } else { |
| 55 | // If kMinLength is at least 4, we hash the first 4 bytes of data. |
| 56 | uint32_t h = BROTLI_UNALIGNED_LOAD32(data) * kHashMul32; |
| 57 | // The higher bits contain more mixture from the multiplication, |
| 58 | // so we take our results from there. |
| 59 | return h >> (32 - kShiftBits); |
| 60 | } |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 61 | } |
| 62 | |
| 63 | // Usually, we always choose the longest backward reference. This function |
| 64 | // allows for the exception of that rule. |
| 65 | // |
| 66 | // If we choose a backward reference that is further away, it will |
| 67 | // usually be coded with more bits. We approximate this by assuming |
| 68 | // log2(distance). If the distance can be expressed in terms of the |
| 69 | // last four distances, we use some heuristic constants to estimate |
| 70 | // the bits cost. For the first up to four literals we use the bit |
| 71 | // cost of the literals from the literal cost model, after that we |
| 72 | // use the average bit cost of the cost model. |
| 73 | // |
| 74 | // This function is used to sometimes discard a longer backward reference |
| 75 | // when it is not much longer and the bit cost for encoding it is more |
| 76 | // than the saved literals. |
| 77 | inline double BackwardReferenceScore(double average_cost, |
| 78 | double start_cost4, |
| 79 | double start_cost3, |
| 80 | double start_cost2, |
| 81 | int copy_length, |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 82 | int backward_reference_offset) { |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 83 | double retval = 0; |
| 84 | switch (copy_length) { |
| 85 | case 2: retval = start_cost2; break; |
| 86 | case 3: retval = start_cost3; break; |
| 87 | default: retval = start_cost4 + (copy_length - 4) * average_cost; break; |
| 88 | } |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 89 | retval -= 1.20 * Log2Floor(backward_reference_offset); |
| 90 | return retval; |
| 91 | } |
| 92 | |
| 93 | inline double BackwardReferenceScoreUsingLastDistance(double average_cost, |
| 94 | double start_cost4, |
| 95 | double start_cost3, |
| 96 | double start_cost2, |
| 97 | int copy_length, |
| 98 | int distance_short_code) { |
| 99 | double retval = 0; |
| 100 | switch (copy_length) { |
| 101 | case 2: retval = start_cost2; break; |
| 102 | case 3: retval = start_cost3; break; |
| 103 | default: retval = start_cost4 + (copy_length - 4) * average_cost; break; |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 104 | } |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 105 | static const double kDistanceShortCodeBitCost[16] = { |
| 106 | -0.6, 0.95, 1.17, 1.27, |
| 107 | 0.93, 0.93, 0.96, 0.96, 0.99, 0.99, |
| 108 | 1.05, 1.05, 1.15, 1.15, 1.25, 1.25 |
| 109 | }; |
| 110 | retval -= kDistanceShortCodeBitCost[distance_short_code]; |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 111 | return retval; |
| 112 | } |
| 113 | |
| 114 | // A (forgetful) hash table to the data seen by the compressor, to |
| 115 | // help create backward references to previous data. |
| 116 | // |
| 117 | // This is a hash map of fixed size (kBucketSize) to a ring buffer of |
| 118 | // fixed size (kBlockSize). The ring buffer contains the last kBlockSize |
| 119 | // index positions of the given hash key in the compressed data. |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 120 | template <int kBucketBits, int kBlockBits, int kMinLength> |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 121 | class HashLongestMatch { |
| 122 | public: |
| 123 | HashLongestMatch() |
Zoltan Szabadka | 1571db3 | 2013-11-15 19:02:17 +0100 | [diff] [blame] | 124 | : last_distance1_(4), |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 125 | last_distance2_(11), |
| 126 | last_distance3_(15), |
| 127 | last_distance4_(16), |
| 128 | insert_length_(0), |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 129 | average_cost_(5.4), |
| 130 | static_dict_(NULL) { |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 131 | Reset(); |
| 132 | } |
| 133 | void Reset() { |
| 134 | std::fill(&num_[0], &num_[sizeof(num_) / sizeof(num_[0])], 0); |
| 135 | } |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 136 | void SetStaticDictionary(const StaticDictionary *dict) { |
| 137 | static_dict_ = dict; |
| 138 | } |
| 139 | bool HasStaticDictionary() const { |
| 140 | return static_dict_ != NULL; |
| 141 | } |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 142 | |
| 143 | // Look at 3 bytes at data. |
| 144 | // Compute a hash from these, and store the value of ix at that position. |
| 145 | inline void Store(const uint8_t *data, const int ix) { |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 146 | const uint32_t key = Hash<kBucketBits, kMinLength>(data); |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 147 | const int minor_ix = num_[key] & kBlockMask; |
| 148 | buckets_[key][minor_ix] = ix; |
| 149 | ++num_[key]; |
| 150 | } |
| 151 | |
| 152 | // Store hashes for a range of data. |
| 153 | void StoreHashes(const uint8_t *data, size_t len, int startix, int mask) { |
| 154 | for (int p = 0; p < len; ++p) { |
| 155 | Store(&data[p & mask], startix + p); |
| 156 | } |
| 157 | } |
| 158 | |
| 159 | // Find a longest backward match of &data[cur_ix] up to the length of |
| 160 | // max_length. |
| 161 | // |
| 162 | // Does not look for matches longer than max_length. |
| 163 | // Does not look for matches further away than max_backward. |
| 164 | // Writes the best found match length into best_len_out. |
| 165 | // Writes the index (&data[index]) offset from the start of the best match |
| 166 | // into best_distance_out. |
| 167 | // Write the score of the best match into best_score_out. |
| 168 | bool FindLongestMatch(const uint8_t * __restrict data, |
Zoltan Szabadka | 1571db3 | 2013-11-15 19:02:17 +0100 | [diff] [blame] | 169 | const float * __restrict literal_cost, |
| 170 | const size_t ring_buffer_mask, |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 171 | const uint32_t cur_ix, |
| 172 | uint32_t max_length, |
| 173 | const uint32_t max_backward, |
| 174 | size_t * __restrict best_len_out, |
Roderick Sheeter | 437bbad | 2013-11-19 14:32:56 -0800 | [diff] [blame] | 175 | size_t * __restrict best_len_code_out, |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 176 | size_t * __restrict best_distance_out, |
Zoltan Szabadka | cbd5cb5 | 2014-02-14 15:04:23 +0100 | [diff] [blame] | 177 | double * __restrict best_score_out, |
| 178 | bool * __restrict in_dictionary) { |
| 179 | *in_dictionary = true; |
| 180 | *best_len_code_out = 0; |
Zoltan Szabadka | 1571db3 | 2013-11-15 19:02:17 +0100 | [diff] [blame] | 181 | const size_t cur_ix_masked = cur_ix & ring_buffer_mask; |
| 182 | const double start_cost4 = literal_cost == NULL ? 20 : |
| 183 | literal_cost[cur_ix_masked] + |
| 184 | literal_cost[(cur_ix + 1) & ring_buffer_mask] + |
| 185 | literal_cost[(cur_ix + 2) & ring_buffer_mask] + |
| 186 | literal_cost[(cur_ix + 3) & ring_buffer_mask]; |
| 187 | const double start_cost3 = literal_cost == NULL ? 15 : |
| 188 | literal_cost[cur_ix_masked] + |
| 189 | literal_cost[(cur_ix + 1) & ring_buffer_mask] + |
| 190 | literal_cost[(cur_ix + 2) & ring_buffer_mask] + 0.3; |
| 191 | double start_cost2 = literal_cost == NULL ? 10 : |
| 192 | literal_cost[cur_ix_masked] + |
| 193 | literal_cost[(cur_ix + 1) & ring_buffer_mask] + 1.2; |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 194 | bool match_found = false; |
| 195 | // Don't accept a short copy from far away. |
Zoltan Szabadka | 0829e37 | 2014-03-25 16:48:25 +0100 | [diff] [blame] | 196 | double best_score = 8.115; |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 197 | if (insert_length_ < 4) { |
Zoltan Szabadka | cbd5cb5 | 2014-02-14 15:04:23 +0100 | [diff] [blame] | 198 | double cost_diff[4] = { 0.10, 0.04, 0.02, 0.01 }; |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 199 | best_score += cost_diff[insert_length_]; |
| 200 | } |
| 201 | size_t best_len = *best_len_out; |
| 202 | *best_len_out = 0; |
| 203 | size_t best_ix = 1; |
| 204 | // Try last distance first. |
| 205 | for (int i = 0; i < 16; ++i) { |
Zoltan Szabadka | 1571db3 | 2013-11-15 19:02:17 +0100 | [diff] [blame] | 206 | size_t prev_ix = cur_ix; |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 207 | switch(i) { |
| 208 | case 0: prev_ix -= last_distance1_; break; |
| 209 | case 1: prev_ix -= last_distance2_; break; |
| 210 | case 2: prev_ix -= last_distance3_; break; |
| 211 | case 3: prev_ix -= last_distance4_; break; |
| 212 | |
| 213 | case 4: prev_ix -= last_distance1_ - 1; break; |
| 214 | case 5: prev_ix -= last_distance1_ + 1; break; |
| 215 | case 6: prev_ix -= last_distance1_ - 2; break; |
| 216 | case 7: prev_ix -= last_distance1_ + 2; break; |
| 217 | case 8: prev_ix -= last_distance1_ - 3; break; |
| 218 | case 9: prev_ix -= last_distance1_ + 3; break; |
| 219 | |
| 220 | case 10: prev_ix -= last_distance2_ - 1; break; |
| 221 | case 11: prev_ix -= last_distance2_ + 1; break; |
| 222 | case 12: prev_ix -= last_distance2_ - 2; break; |
| 223 | case 13: prev_ix -= last_distance2_ + 2; break; |
| 224 | case 14: prev_ix -= last_distance2_ - 3; break; |
| 225 | case 15: prev_ix -= last_distance2_ + 3; break; |
| 226 | } |
| 227 | if (prev_ix >= cur_ix) { |
| 228 | continue; |
| 229 | } |
| 230 | const size_t backward = cur_ix - prev_ix; |
| 231 | if (PREDICT_FALSE(backward > max_backward)) { |
| 232 | continue; |
| 233 | } |
Zoltan Szabadka | 1571db3 | 2013-11-15 19:02:17 +0100 | [diff] [blame] | 234 | prev_ix &= ring_buffer_mask; |
Zoltan Szabadka | 40955ce | 2014-01-06 16:01:57 +0100 | [diff] [blame] | 235 | if (cur_ix_masked + best_len > ring_buffer_mask || |
| 236 | prev_ix + best_len > ring_buffer_mask || |
| 237 | data[cur_ix_masked + best_len] != data[prev_ix + best_len]) { |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 238 | continue; |
| 239 | } |
| 240 | const size_t len = |
Zoltan Szabadka | 1571db3 | 2013-11-15 19:02:17 +0100 | [diff] [blame] | 241 | FindMatchLengthWithLimit(&data[prev_ix], &data[cur_ix_masked], |
| 242 | max_length); |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 243 | if (len >= std::max(kMinLength, 3) || |
| 244 | (kMinLength == 2 && len == 2 && i < 2)) { |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 245 | // Comparing for >= 2 does not change the semantics, but just saves for |
| 246 | // a few unnecessary binary logarithms in backward reference score, |
| 247 | // since we are not interested in such short matches. |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 248 | const double score = BackwardReferenceScoreUsingLastDistance( |
| 249 | average_cost_, |
| 250 | start_cost4, |
| 251 | start_cost3, |
| 252 | start_cost2, |
| 253 | len, i); |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 254 | if (best_score < score) { |
| 255 | best_score = score; |
| 256 | best_len = len; |
| 257 | best_ix = backward; |
| 258 | *best_len_out = best_len; |
Roderick Sheeter | 437bbad | 2013-11-19 14:32:56 -0800 | [diff] [blame] | 259 | *best_len_code_out = best_len; |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 260 | *best_distance_out = best_ix; |
| 261 | *best_score_out = best_score; |
| 262 | match_found = true; |
Zoltan Szabadka | cbd5cb5 | 2014-02-14 15:04:23 +0100 | [diff] [blame] | 263 | *in_dictionary = backward > max_backward; |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 264 | } |
| 265 | } |
| 266 | } |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 267 | if (kMinLength == 2) { |
| 268 | int stop = int(cur_ix) - 64; |
| 269 | if (stop < 0) { stop = 0; } |
| 270 | start_cost2 -= 1.0; |
| 271 | for (int i = cur_ix - 1; i > stop; --i) { |
| 272 | size_t prev_ix = i; |
| 273 | const size_t backward = cur_ix - prev_ix; |
| 274 | if (PREDICT_FALSE(backward > max_backward)) { |
| 275 | break; |
| 276 | } |
| 277 | prev_ix &= ring_buffer_mask; |
| 278 | if (data[cur_ix_masked] != data[prev_ix] || |
| 279 | data[cur_ix_masked + 1] != data[prev_ix + 1]) { |
| 280 | continue; |
| 281 | } |
| 282 | int len = 2; |
| 283 | const double score = start_cost2 - 2.3 * Log2Floor(backward); |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 284 | |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 285 | if (best_score < score) { |
| 286 | best_score = score; |
| 287 | best_len = len; |
| 288 | best_ix = backward; |
| 289 | *best_len_out = best_len; |
| 290 | *best_len_code_out = best_len; |
| 291 | *best_distance_out = best_ix; |
| 292 | match_found = true; |
| 293 | } |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 294 | } |
| 295 | } |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 296 | const uint32_t key = Hash<kBucketBits, kMinLength>(&data[cur_ix_masked]); |
| 297 | const int * __restrict const bucket = &buckets_[key][0]; |
| 298 | const int down = (num_[key] > kBlockSize) ? (num_[key] - kBlockSize) : 0; |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 299 | for (int i = num_[key] - 1; i >= down; --i) { |
Roderick Sheeter | 437bbad | 2013-11-19 14:32:56 -0800 | [diff] [blame] | 300 | int prev_ix = bucket[i & kBlockMask]; |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 301 | if (prev_ix >= 0) { |
Roderick Sheeter | 437bbad | 2013-11-19 14:32:56 -0800 | [diff] [blame] | 302 | const size_t backward = cur_ix - prev_ix; |
| 303 | if (PREDICT_FALSE(backward > max_backward)) { |
| 304 | break; |
| 305 | } |
| 306 | prev_ix &= ring_buffer_mask; |
Zoltan Szabadka | 40955ce | 2014-01-06 16:01:57 +0100 | [diff] [blame] | 307 | if (cur_ix_masked + best_len > ring_buffer_mask || |
| 308 | prev_ix + best_len > ring_buffer_mask || |
| 309 | data[cur_ix_masked + best_len] != data[prev_ix + best_len]) { |
Roderick Sheeter | 437bbad | 2013-11-19 14:32:56 -0800 | [diff] [blame] | 310 | continue; |
| 311 | } |
| 312 | const size_t len = |
| 313 | FindMatchLengthWithLimit(&data[prev_ix], &data[cur_ix_masked], |
| 314 | max_length); |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 315 | if (len >= std::max(kMinLength, 3)) { |
Roderick Sheeter | 437bbad | 2013-11-19 14:32:56 -0800 | [diff] [blame] | 316 | // Comparing for >= 3 does not change the semantics, but just saves |
| 317 | // for a few unnecessary binary logarithms in backward reference |
| 318 | // score, since we are not interested in such short matches. |
| 319 | const double score = BackwardReferenceScore(average_cost_, |
| 320 | start_cost4, |
| 321 | start_cost3, |
| 322 | start_cost2, |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 323 | len, backward); |
Roderick Sheeter | 437bbad | 2013-11-19 14:32:56 -0800 | [diff] [blame] | 324 | if (best_score < score) { |
| 325 | best_score = score; |
| 326 | best_len = len; |
| 327 | best_ix = backward; |
| 328 | *best_len_out = best_len; |
| 329 | *best_len_code_out = best_len; |
| 330 | *best_distance_out = best_ix; |
| 331 | *best_score_out = best_score; |
| 332 | match_found = true; |
Zoltan Szabadka | cbd5cb5 | 2014-02-14 15:04:23 +0100 | [diff] [blame] | 333 | *in_dictionary = false; |
Roderick Sheeter | 437bbad | 2013-11-19 14:32:56 -0800 | [diff] [blame] | 334 | } |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 335 | } |
| 336 | } |
| 337 | } |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 338 | if (static_dict_ != NULL) { |
| 339 | // We decide based on first 4 bytes how many bytes to test for. |
| 340 | int prefix = BROTLI_UNALIGNED_LOAD32(&data[cur_ix_masked]); |
| 341 | int maxlen = static_dict_->GetLength(prefix); |
| 342 | for (int len = std::min<size_t>(maxlen, max_length); |
| 343 | len > best_len && len >= 4; --len) { |
| 344 | std::string snippet((const char *)&data[cur_ix_masked], len); |
| 345 | int copy_len_code; |
| 346 | int word_id; |
| 347 | if (static_dict_->Get(snippet, ©_len_code, &word_id)) { |
| 348 | const size_t backward = max_backward + word_id + 1; |
| 349 | const double score = BackwardReferenceScore(average_cost_, |
| 350 | start_cost4, |
| 351 | start_cost3, |
| 352 | start_cost2, |
| 353 | len, backward); |
| 354 | if (best_score < score) { |
| 355 | best_score = score; |
| 356 | best_len = len; |
| 357 | best_ix = backward; |
| 358 | *best_len_out = best_len; |
| 359 | *best_len_code_out = copy_len_code; |
| 360 | *best_distance_out = best_ix; |
| 361 | *best_score_out = best_score; |
| 362 | match_found = true; |
| 363 | *in_dictionary = true; |
| 364 | } |
| 365 | } |
| 366 | } |
| 367 | } |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 368 | return match_found; |
| 369 | } |
| 370 | |
| 371 | void set_last_distance(int v) { |
| 372 | if (last_distance1_ != v) { |
| 373 | last_distance4_ = last_distance3_; |
| 374 | last_distance3_ = last_distance2_; |
| 375 | last_distance2_ = last_distance1_; |
| 376 | last_distance1_ = v; |
| 377 | } |
| 378 | } |
| 379 | |
| 380 | int last_distance() const { return last_distance1_; } |
| 381 | |
| 382 | void set_insert_length(int v) { insert_length_ = v; } |
| 383 | |
| 384 | void set_average_cost(double v) { average_cost_ = v; } |
| 385 | |
| 386 | private: |
| 387 | // Number of hash buckets. |
| 388 | static const uint32_t kBucketSize = 1 << kBucketBits; |
| 389 | |
| 390 | // Only kBlockSize newest backward references are kept, |
| 391 | // and the older are forgotten. |
| 392 | static const uint32_t kBlockSize = 1 << kBlockBits; |
| 393 | |
| 394 | // Mask for accessing entries in a block (in a ringbuffer manner). |
| 395 | static const uint32_t kBlockMask = (1 << kBlockBits) - 1; |
| 396 | |
| 397 | // Number of entries in a particular bucket. |
| 398 | uint16_t num_[kBucketSize]; |
| 399 | |
| 400 | // Buckets containing kBlockSize of backward references. |
Roderick Sheeter | 437bbad | 2013-11-19 14:32:56 -0800 | [diff] [blame] | 401 | int buckets_[kBucketSize][kBlockSize]; |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 402 | |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 403 | int last_distance1_; |
| 404 | int last_distance2_; |
| 405 | int last_distance3_; |
| 406 | int last_distance4_; |
| 407 | |
| 408 | // Cost adjustment for how many literals we are planning to insert |
| 409 | // anyway. |
| 410 | int insert_length_; |
| 411 | |
| 412 | double average_cost_; |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 413 | |
| 414 | const StaticDictionary *static_dict_; |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 415 | }; |
| 416 | |
Zoltan Szabadka | 278b894 | 2014-03-20 14:32:35 +0100 | [diff] [blame] | 417 | struct Hashers { |
| 418 | enum Type { |
| 419 | HASH_15_8_4 = 0, |
| 420 | HASH_15_8_2 = 1, |
| 421 | }; |
| 422 | |
| 423 | void Init(Type type) { |
| 424 | switch (type) { |
| 425 | case HASH_15_8_4: |
| 426 | hash_15_8_4.reset(new HashLongestMatch<15, 8, 4>()); |
| 427 | break; |
| 428 | case HASH_15_8_2: |
| 429 | hash_15_8_2.reset(new HashLongestMatch<15, 8, 2>()); |
| 430 | break; |
| 431 | default: |
| 432 | break; |
| 433 | } |
| 434 | } |
| 435 | |
| 436 | void SetStaticDictionary(const StaticDictionary *dict) { |
| 437 | if (hash_15_8_4.get() != NULL) hash_15_8_4->SetStaticDictionary(dict); |
| 438 | if (hash_15_8_2.get() != NULL) hash_15_8_2->SetStaticDictionary(dict); |
| 439 | } |
| 440 | |
| 441 | std::unique_ptr<HashLongestMatch<15, 8, 4> > hash_15_8_4; |
| 442 | std::unique_ptr<HashLongestMatch<15, 8, 2> > hash_15_8_2; |
| 443 | }; |
Zoltan Szabadka | 1571db3 | 2013-11-15 19:02:17 +0100 | [diff] [blame] | 444 | |
Zoltan Szabadka | 79e99af | 2013-10-23 13:06:13 +0200 | [diff] [blame] | 445 | } // namespace brotli |
| 446 | |
| 447 | #endif // BROTLI_ENC_HASH_H_ |