Zoltan Szabadka | c66e4e3 | 2013-10-23 13:06:13 +0200 | [diff] [blame^] | 1 | // Copyright 2013 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 | // Implementation of Brotli compressor. |
| 16 | |
| 17 | #include "./encode.h" |
| 18 | |
| 19 | #include <algorithm> |
| 20 | #include <limits> |
| 21 | |
| 22 | #include "./backward_references.h" |
| 23 | #include "./bit_cost.h" |
| 24 | #include "./block_splitter.h" |
| 25 | #include "./cluster.h" |
| 26 | #include "./context.h" |
| 27 | #include "./entropy_encode.h" |
| 28 | #include "./fast_log.h" |
| 29 | #include "./histogram.h" |
| 30 | #include "./prefix.h" |
| 31 | #include "./write_bits.h" |
| 32 | |
| 33 | namespace brotli { |
| 34 | |
| 35 | template<int kSize> |
| 36 | double Entropy(const std::vector<Histogram<kSize> >& histograms) { |
| 37 | double retval = 0; |
| 38 | for (int i = 0; i < histograms.size(); ++i) { |
| 39 | retval += histograms[i].EntropyBitCost(); |
| 40 | } |
| 41 | return retval; |
| 42 | } |
| 43 | |
| 44 | void EncodeSize(size_t len, int* storage_ix, uint8_t* storage) { |
| 45 | std::vector<uint8_t> len_bytes; |
| 46 | while (len > 0) { |
| 47 | len_bytes.push_back(len & 0xff); |
| 48 | len >>= 8; |
| 49 | }; |
| 50 | WriteBits(3, len_bytes.size(), storage_ix, storage); |
| 51 | for (int i = 0; i < len_bytes.size(); ++i) { |
| 52 | WriteBits(8, len_bytes[i], storage_ix, storage); |
| 53 | } |
| 54 | } |
| 55 | |
| 56 | void EncodeMetaBlockLength(int input_size_bits, |
| 57 | size_t meta_block_size, |
| 58 | bool is_last_meta_block, |
| 59 | int* storage_ix, uint8_t* storage) { |
| 60 | WriteBits(1, is_last_meta_block, storage_ix, storage); |
| 61 | if (is_last_meta_block) return; |
| 62 | while (input_size_bits > 0) { |
| 63 | WriteBits(8, meta_block_size & 0xff, storage_ix, storage); |
| 64 | meta_block_size >>= 8; |
| 65 | input_size_bits -= 8; |
| 66 | } |
| 67 | if (input_size_bits > 0) { |
| 68 | WriteBits(input_size_bits, meta_block_size, storage_ix, storage); |
| 69 | } |
| 70 | } |
| 71 | |
| 72 | template<int kSize> |
| 73 | void EntropyEncode(int val, const EntropyCode<kSize>& code, |
| 74 | int* storage_ix, uint8_t* storage) { |
| 75 | if (code.count_ <= 1) { |
| 76 | return; |
| 77 | }; |
| 78 | WriteBits(code.depth_[val], code.bits_[val], storage_ix, storage); |
| 79 | } |
| 80 | |
| 81 | void StoreHuffmanTreeOfHuffmanTreeToBitMask( |
| 82 | const uint8_t* code_length_bitdepth, |
| 83 | int* storage_ix, uint8_t* storage) { |
| 84 | static const uint8_t kStorageOrder[kCodeLengthCodes] = { |
| 85 | 17, 18, 0, 1, 2, 3, 4, 5, 16, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 |
| 86 | }; |
| 87 | // Throw away trailing zeros: |
| 88 | int codes_to_store = kCodeLengthCodes; |
| 89 | for (; codes_to_store > 4; --codes_to_store) { |
| 90 | if (code_length_bitdepth[kStorageOrder[codes_to_store - 1]] != 0) { |
| 91 | break; |
| 92 | } |
| 93 | } |
| 94 | WriteBits(4, codes_to_store - 4, storage_ix, storage); |
| 95 | for (int i = 0; i < codes_to_store; ++i) { |
| 96 | WriteBits(3, code_length_bitdepth[kStorageOrder[i]], storage_ix, storage); |
| 97 | } |
| 98 | } |
| 99 | |
| 100 | void StoreHuffmanTreeToBitMask( |
| 101 | const uint8_t* huffman_tree, |
| 102 | const uint8_t* huffman_tree_extra_bits, |
| 103 | const int huffman_tree_size, |
| 104 | const EntropyCode<kCodeLengthCodes>& entropy, |
| 105 | int* storage_ix, uint8_t* storage) { |
| 106 | for (int i = 0; i < huffman_tree_size; ++i) { |
| 107 | const int ix = huffman_tree[i]; |
| 108 | const int extra_bits = huffman_tree_extra_bits[i]; |
| 109 | EntropyEncode(ix, entropy, storage_ix, storage); |
| 110 | switch (ix) { |
| 111 | case 16: |
| 112 | WriteBits(2, extra_bits, storage_ix, storage); |
| 113 | break; |
| 114 | case 17: |
| 115 | WriteBits(3, extra_bits, storage_ix, storage); |
| 116 | break; |
| 117 | case 18: |
| 118 | WriteBits(7, extra_bits, storage_ix, storage); |
| 119 | break; |
| 120 | } |
| 121 | } |
| 122 | } |
| 123 | |
| 124 | template<int kSize> |
| 125 | void StoreHuffmanCode(const EntropyCode<kSize>& code, int alphabet_size, |
| 126 | int* storage_ix, uint8_t* storage) { |
| 127 | const int kMaxBits = 8; |
| 128 | const int kMaxSymbol = 1 << kMaxBits; |
| 129 | |
| 130 | if (code.count_ == 0) { // emit minimal tree for empty cases |
| 131 | // bits: small tree marker: 1, count-1: 0, large 8-bit code: 0, code: 0 |
| 132 | WriteBits(4, 0x01, storage_ix, storage); |
| 133 | return; |
| 134 | } |
| 135 | if (code.count_ <= 2 && |
| 136 | code.symbols_[0] < kMaxSymbol && |
| 137 | code.symbols_[1] < kMaxSymbol) { |
| 138 | // Small tree marker to encode 1 or 2 symbols. |
| 139 | WriteBits(1, 1, storage_ix, storage); |
| 140 | WriteBits(1, code.count_ - 1, storage_ix, storage); |
| 141 | if (code.symbols_[0] <= 1) { |
| 142 | // Code bit for small (1 bit) symbol value. |
| 143 | WriteBits(1, 0, storage_ix, storage); |
| 144 | WriteBits(1, code.symbols_[0], storage_ix, storage); |
| 145 | } else { |
| 146 | WriteBits(1, 1, storage_ix, storage); |
| 147 | WriteBits(8, code.symbols_[0], storage_ix, storage); |
| 148 | } |
| 149 | if (code.count_ == 2) { |
| 150 | WriteBits(8, code.symbols_[1], storage_ix, storage); |
| 151 | } |
| 152 | return; |
| 153 | } |
| 154 | WriteBits(1, 0, storage_ix, storage); |
| 155 | |
| 156 | uint8_t huffman_tree[kSize]; |
| 157 | uint8_t huffman_tree_extra_bits[kSize]; |
| 158 | int huffman_tree_size = 0; |
| 159 | WriteHuffmanTree(&code.depth_[0], |
| 160 | alphabet_size, |
| 161 | &huffman_tree[0], |
| 162 | &huffman_tree_extra_bits[0], |
| 163 | &huffman_tree_size); |
| 164 | Histogram<kCodeLengthCodes> huffman_tree_histogram; |
| 165 | memset(huffman_tree_histogram.data_, 0, sizeof(huffman_tree_histogram.data_)); |
| 166 | for (int i = 0; i < huffman_tree_size; ++i) { |
| 167 | huffman_tree_histogram.Add(huffman_tree[i]); |
| 168 | } |
| 169 | EntropyCode<kCodeLengthCodes> huffman_tree_entropy; |
| 170 | BuildEntropyCode(huffman_tree_histogram, 7, kCodeLengthCodes, |
| 171 | &huffman_tree_entropy); |
| 172 | Histogram<kCodeLengthCodes> trimmed_histogram = huffman_tree_histogram; |
| 173 | uint8_t* last_code = &huffman_tree[huffman_tree_size - 1]; |
| 174 | while (*last_code == 0 || *last_code >= 17) { |
| 175 | trimmed_histogram.Remove(*last_code--); |
| 176 | } |
| 177 | int trimmed_size = trimmed_histogram.total_count_; |
| 178 | bool write_length = false; |
| 179 | if (trimmed_size > 1 && trimmed_size < huffman_tree_size) { |
| 180 | EntropyCode<kCodeLengthCodes> trimmed_entropy; |
| 181 | BuildEntropyCode(trimmed_histogram, 7, kCodeLengthCodes, &trimmed_entropy); |
| 182 | int huffman_bit_cost = HuffmanTreeBitCost(huffman_tree_histogram, |
| 183 | huffman_tree_entropy); |
| 184 | int trimmed_bit_cost = HuffmanTreeBitCost(trimmed_histogram, |
| 185 | trimmed_entropy);; |
| 186 | const int nbits = Log2Ceiling(trimmed_size - 1); |
| 187 | const int nbitpairs = (nbits == 0) ? 1 : (nbits + 1) / 2; |
| 188 | if (trimmed_bit_cost + 3 + 2 * nbitpairs < huffman_bit_cost) { |
| 189 | write_length = true; |
| 190 | huffman_tree_size = trimmed_size; |
| 191 | huffman_tree_entropy = trimmed_entropy; |
| 192 | } |
| 193 | } |
| 194 | |
| 195 | StoreHuffmanTreeOfHuffmanTreeToBitMask( |
| 196 | &huffman_tree_entropy.depth_[0], storage_ix, storage); |
| 197 | WriteBits(1, write_length, storage_ix, storage); |
| 198 | if (write_length) { |
| 199 | const int nbits = Log2Ceiling(huffman_tree_size - 1); |
| 200 | const int nbitpairs = (nbits == 0) ? 1 : (nbits + 1) / 2; |
| 201 | WriteBits(3, nbitpairs - 1, storage_ix, storage); |
| 202 | WriteBits(nbitpairs * 2, huffman_tree_size - 2, storage_ix, storage); |
| 203 | } |
| 204 | StoreHuffmanTreeToBitMask(&huffman_tree[0], &huffman_tree_extra_bits[0], |
| 205 | huffman_tree_size, huffman_tree_entropy, |
| 206 | storage_ix, storage); |
| 207 | } |
| 208 | |
| 209 | template<int kSize> |
| 210 | void StoreHuffmanCodes(const std::vector<EntropyCode<kSize> >& codes, |
| 211 | int alphabet_size, |
| 212 | int* storage_ix, uint8_t* storage) { |
| 213 | for (int i = 0; i < codes.size(); ++i) { |
| 214 | StoreHuffmanCode(codes[i], alphabet_size, storage_ix, storage); |
| 215 | } |
| 216 | } |
| 217 | |
| 218 | void EncodeCommand(const Command& cmd, |
| 219 | const EntropyCodeCommand& entropy, |
| 220 | int* storage_ix, uint8_t* storage) { |
| 221 | int code = cmd.command_prefix_; |
| 222 | EntropyEncode(code, entropy, storage_ix, storage); |
| 223 | if (code >= 128) { |
| 224 | code -= 128; |
| 225 | } |
| 226 | int insert_extra_bits = InsertLengthExtraBits(code); |
| 227 | uint64_t insert_extra_bits_val = |
| 228 | cmd.insert_length_ - InsertLengthOffset(code); |
| 229 | int copy_extra_bits = CopyLengthExtraBits(code); |
| 230 | uint64_t copy_extra_bits_val = cmd.copy_length_ - CopyLengthOffset(code); |
| 231 | if (insert_extra_bits > 0) { |
| 232 | WriteBits(insert_extra_bits, insert_extra_bits_val, storage_ix, storage); |
| 233 | } |
| 234 | if (copy_extra_bits > 0) { |
| 235 | WriteBits(copy_extra_bits, copy_extra_bits_val, storage_ix, storage); |
| 236 | } |
| 237 | } |
| 238 | |
| 239 | void EncodeCopyDistance(const Command& cmd, const EntropyCodeDistance& entropy, |
| 240 | int* storage_ix, uint8_t* storage) { |
| 241 | int code = cmd.distance_prefix_; |
| 242 | int extra_bits = cmd.distance_extra_bits_; |
| 243 | uint64_t extra_bits_val = cmd.distance_extra_bits_value_; |
| 244 | EntropyEncode(code, entropy, storage_ix, storage); |
| 245 | if (extra_bits > 0) { |
| 246 | WriteBits(extra_bits, extra_bits_val, storage_ix, storage); |
| 247 | } |
| 248 | } |
| 249 | |
| 250 | |
| 251 | void ComputeDistanceShortCodes(std::vector<Command>* cmds) { |
| 252 | static const int kIndexOffset[16] = { |
| 253 | 3, 2, 1, 0, 3, 3, 3, 3, 3, 3, 2, 2, 2, 2, 2, 2 |
| 254 | }; |
| 255 | static const int kValueOffset[16] = { |
| 256 | 0, 0, 0, 0, -1, 1, -2, 2, -3, 3, -1, 1, -2, 2, -3, 3 |
| 257 | }; |
| 258 | int dist_ringbuffer[4] = { 4, 11, 15, 16 }; |
| 259 | int ringbuffer_idx = 0; |
| 260 | for (int i = 0; i < cmds->size(); ++i) { |
| 261 | int cur_dist = (*cmds)[i].copy_distance_; |
| 262 | if (cur_dist == 0) break; |
| 263 | int dist_code = cur_dist + 16; |
| 264 | for (int k = 0; k < 16; ++k) { |
| 265 | // Only accept more popular choices. |
| 266 | if (cur_dist < 11 && ((k >= 2 && k < 4) || k >= 6)) { |
| 267 | // Typically unpopular ranges, don't replace a short distance |
| 268 | // with them. |
| 269 | continue; |
| 270 | } |
| 271 | int comp = (dist_ringbuffer[(ringbuffer_idx + kIndexOffset[k]) & 3] + |
| 272 | kValueOffset[k]); |
| 273 | if (cur_dist == comp) { |
| 274 | dist_code = k + 1; |
| 275 | break; |
| 276 | } |
| 277 | } |
| 278 | if (dist_code > 1) { |
| 279 | dist_ringbuffer[ringbuffer_idx & 3] = cur_dist; |
| 280 | ++ringbuffer_idx; |
| 281 | } |
| 282 | (*cmds)[i].distance_code_ = dist_code; |
| 283 | } |
| 284 | } |
| 285 | |
| 286 | void ComputeCommandPrefixes(std::vector<Command>* cmds, |
| 287 | int num_direct_distance_codes, |
| 288 | int distance_postfix_bits) { |
| 289 | for (int i = 0; i < cmds->size(); ++i) { |
| 290 | Command* cmd = &(*cmds)[i]; |
| 291 | cmd->command_prefix_ = CommandPrefix(cmd->insert_length_, |
| 292 | cmd->copy_length_); |
| 293 | if (cmd->copy_length_ > 0) { |
| 294 | PrefixEncodeCopyDistance(cmd->distance_code_, |
| 295 | num_direct_distance_codes, |
| 296 | distance_postfix_bits, |
| 297 | &cmd->distance_prefix_, |
| 298 | &cmd->distance_extra_bits_, |
| 299 | &cmd->distance_extra_bits_value_); |
| 300 | } |
| 301 | if (cmd->command_prefix_ < 128 && cmd->distance_prefix_ == 0) { |
| 302 | cmd->distance_prefix_ = 0xffff; |
| 303 | } else { |
| 304 | cmd->command_prefix_ += 128; |
| 305 | } |
| 306 | } |
| 307 | } |
| 308 | |
| 309 | int IndexOf(const std::vector<int>& v, int value) { |
| 310 | for (int i = 0; i < v.size(); ++i) { |
| 311 | if (v[i] == value) return i; |
| 312 | } |
| 313 | return -1; |
| 314 | } |
| 315 | |
| 316 | void MoveToFront(std::vector<int>* v, int index) { |
| 317 | int value = (*v)[index]; |
| 318 | for (int i = index; i > 0; --i) { |
| 319 | (*v)[i] = (*v)[i - 1]; |
| 320 | } |
| 321 | (*v)[0] = value; |
| 322 | } |
| 323 | |
| 324 | std::vector<int> MoveToFrontTransform(const std::vector<int>& v) { |
| 325 | if (v.empty()) return v; |
| 326 | std::vector<int> mtf(*max_element(v.begin(), v.end()) + 1); |
| 327 | for (int i = 0; i < mtf.size(); ++i) mtf[i] = i; |
| 328 | std::vector<int> result(v.size()); |
| 329 | for (int i = 0; i < v.size(); ++i) { |
| 330 | int index = IndexOf(mtf, v[i]); |
| 331 | result[i] = index; |
| 332 | MoveToFront(&mtf, index); |
| 333 | } |
| 334 | return result; |
| 335 | } |
| 336 | |
| 337 | // Finds runs of zeros in v_in and replaces them with a prefix code of the run |
| 338 | // length plus extra bits in *v_out and *extra_bits. Non-zero values in v_in are |
| 339 | // shifted by *max_length_prefix. Will not create prefix codes bigger than the |
| 340 | // initial value of *max_run_length_prefix. The prefix code of run length L is |
| 341 | // simply Log2Floor(L) and the number of extra bits is the same as the prefix |
| 342 | // code. |
| 343 | void RunLengthCodeZeros(const std::vector<int>& v_in, |
| 344 | int* max_run_length_prefix, |
| 345 | std::vector<int>* v_out, |
| 346 | std::vector<int>* extra_bits) { |
| 347 | int max_reps = 0; |
| 348 | for (int i = 0; i < v_in.size();) { |
| 349 | for (; i < v_in.size() && v_in[i] != 0; ++i) ; |
| 350 | int reps = 0; |
| 351 | for (; i < v_in.size() && v_in[i] == 0; ++i) { |
| 352 | ++reps; |
| 353 | } |
| 354 | max_reps = std::max(reps, max_reps); |
| 355 | } |
| 356 | int max_prefix = max_reps > 0 ? Log2Floor(max_reps) : 0; |
| 357 | *max_run_length_prefix = std::min(max_prefix, *max_run_length_prefix); |
| 358 | for (int i = 0; i < v_in.size();) { |
| 359 | if (v_in[i] != 0) { |
| 360 | v_out->push_back(v_in[i] + *max_run_length_prefix); |
| 361 | extra_bits->push_back(0); |
| 362 | ++i; |
| 363 | } else { |
| 364 | int reps = 1; |
| 365 | for (uint32_t k = i + 1; k < v_in.size() && v_in[k] == 0; ++k) { |
| 366 | ++reps; |
| 367 | } |
| 368 | i += reps; |
| 369 | while (reps) { |
| 370 | if (reps < (2 << *max_run_length_prefix)) { |
| 371 | int run_length_prefix = Log2Floor(reps); |
| 372 | v_out->push_back(run_length_prefix); |
| 373 | extra_bits->push_back(reps - (1 << run_length_prefix)); |
| 374 | break; |
| 375 | } else { |
| 376 | v_out->push_back(*max_run_length_prefix); |
| 377 | extra_bits->push_back((1 << *max_run_length_prefix) - 1); |
| 378 | reps -= (2 << *max_run_length_prefix) - 1; |
| 379 | } |
| 380 | } |
| 381 | } |
| 382 | } |
| 383 | } |
| 384 | |
| 385 | // Returns a maximum zero-run-length-prefix value such that run-length coding |
| 386 | // zeros in v with this maximum prefix value and then encoding the resulting |
| 387 | // histogram and entropy-coding v produces the least amount of bits. |
| 388 | int BestMaxZeroRunLengthPrefix(const std::vector<int>& v) { |
| 389 | int min_cost = std::numeric_limits<int>::max(); |
| 390 | int best_max_prefix = 0; |
| 391 | for (int max_prefix = 0; max_prefix <= 16; ++max_prefix) { |
| 392 | std::vector<int> rle_symbols; |
| 393 | std::vector<int> extra_bits; |
| 394 | int max_run_length_prefix = max_prefix; |
| 395 | RunLengthCodeZeros(v, &max_run_length_prefix, &rle_symbols, &extra_bits); |
| 396 | if (max_run_length_prefix < max_prefix) break; |
| 397 | HistogramLiteral histogram; |
| 398 | for (int i = 0; i < rle_symbols.size(); ++i) { |
| 399 | histogram.Add(rle_symbols[i]); |
| 400 | } |
| 401 | int bit_cost = PopulationCost(histogram); |
| 402 | if (max_prefix > 0) { |
| 403 | bit_cost += 4; |
| 404 | } |
| 405 | for (int i = 1; i <= max_prefix; ++i) { |
| 406 | bit_cost += histogram.data_[i] * i; // extra bits |
| 407 | } |
| 408 | if (bit_cost < min_cost) { |
| 409 | min_cost = bit_cost; |
| 410 | best_max_prefix = max_prefix; |
| 411 | } |
| 412 | } |
| 413 | return best_max_prefix; |
| 414 | } |
| 415 | |
| 416 | void EncodeContextMap(const std::vector<int>& context_map, |
| 417 | int context_mode, |
| 418 | int context_mode_bits, |
| 419 | int num_clusters, |
| 420 | int* storage_ix, uint8_t* storage) { |
| 421 | if (context_mode == 0) { |
| 422 | WriteBits(1, 0, storage_ix, storage); // no context |
| 423 | return; |
| 424 | } |
| 425 | |
| 426 | WriteBits(1, 1, storage_ix, storage); // have context |
| 427 | if (context_mode_bits > 0) { |
| 428 | WriteBits(context_mode_bits, context_mode - 1, storage_ix, storage); |
| 429 | } |
| 430 | WriteBits(8, num_clusters - 1, storage_ix, storage); |
| 431 | |
| 432 | if (num_clusters == 1 || num_clusters == context_map.size()) { |
| 433 | return; |
| 434 | } |
| 435 | |
| 436 | std::vector<int> transformed_symbols = MoveToFrontTransform(context_map); |
| 437 | std::vector<int> rle_symbols; |
| 438 | std::vector<int> extra_bits; |
| 439 | int max_run_length_prefix = BestMaxZeroRunLengthPrefix(transformed_symbols); |
| 440 | RunLengthCodeZeros(transformed_symbols, &max_run_length_prefix, |
| 441 | &rle_symbols, &extra_bits); |
| 442 | HistogramLiteral symbol_histogram; |
| 443 | for (int i = 0; i < rle_symbols.size(); ++i) { |
| 444 | symbol_histogram.Add(rle_symbols[i]); |
| 445 | } |
| 446 | EntropyCodeLiteral symbol_code; |
| 447 | BuildEntropyCode(symbol_histogram, 15, num_clusters + max_run_length_prefix, |
| 448 | &symbol_code); |
| 449 | bool use_rle = max_run_length_prefix > 0; |
| 450 | WriteBits(1, use_rle, storage_ix, storage); |
| 451 | if (use_rle) { |
| 452 | WriteBits(4, max_run_length_prefix - 1, storage_ix, storage); |
| 453 | } |
| 454 | StoreHuffmanCode(symbol_code, num_clusters + max_run_length_prefix, |
| 455 | storage_ix, storage); |
| 456 | for (int i = 0; i < rle_symbols.size(); ++i) { |
| 457 | EntropyEncode(rle_symbols[i], symbol_code, storage_ix, storage); |
| 458 | if (rle_symbols[i] > 0 && rle_symbols[i] <= max_run_length_prefix) { |
| 459 | WriteBits(rle_symbols[i], extra_bits[i], storage_ix, storage); |
| 460 | } |
| 461 | } |
| 462 | WriteBits(1, 1, storage_ix, storage); // use move-to-front |
| 463 | } |
| 464 | |
| 465 | template<int kSize> |
| 466 | void BuildEntropyCodes(const std::vector<Histogram<kSize> >& histograms, |
| 467 | int alphabet_size, |
| 468 | std::vector<EntropyCode<kSize> >* entropy_codes) { |
| 469 | entropy_codes->resize(histograms.size()); |
| 470 | for (int i = 0; i < histograms.size(); ++i) { |
| 471 | BuildEntropyCode(histograms[i], 15, alphabet_size, &(*entropy_codes)[i]); |
| 472 | } |
| 473 | } |
| 474 | |
| 475 | struct BlockSplitCode { |
| 476 | EntropyCodeLiteral block_type_code; |
| 477 | EntropyCodeBlockLength block_len_code; |
| 478 | }; |
| 479 | |
| 480 | void EncodeBlockLength(const EntropyCodeBlockLength& entropy, |
| 481 | int length, |
| 482 | int* storage_ix, uint8_t* storage) { |
| 483 | int len_code = BlockLengthPrefix(length); |
| 484 | int extra_bits = BlockLengthExtraBits(len_code); |
| 485 | int extra_bits_value = length - BlockLengthOffset(len_code); |
| 486 | EntropyEncode(len_code, entropy, storage_ix, storage); |
| 487 | |
| 488 | if (extra_bits > 0) { |
| 489 | WriteBits(extra_bits, extra_bits_value, storage_ix, storage); |
| 490 | } |
| 491 | } |
| 492 | |
| 493 | void ComputeBlockTypeShortCodes(BlockSplit* split) { |
| 494 | if (split->num_types_ <= 1) { |
| 495 | split->num_types_ = 1; |
| 496 | return; |
| 497 | } |
| 498 | int ringbuffer[2] = { 0, 1 }; |
| 499 | size_t index = 0; |
| 500 | for (int i = 0; i < split->types_.size(); ++i) { |
| 501 | int type = split->types_[i]; |
| 502 | int type_code; |
| 503 | if (type == ringbuffer[index & 1]) { |
| 504 | type_code = 0; |
| 505 | } else if (type == ringbuffer[(index - 1) & 1] + 1) { |
| 506 | type_code = 1; |
| 507 | } else { |
| 508 | type_code = type + 2; |
| 509 | } |
| 510 | ringbuffer[index & 1] = type; |
| 511 | ++index; |
| 512 | split->type_codes_.push_back(type_code); |
| 513 | } |
| 514 | } |
| 515 | |
| 516 | void BuildAndEncodeBlockSplitCode(const BlockSplit& split, |
| 517 | BlockSplitCode* code, |
| 518 | int* storage_ix, uint8_t* storage) { |
| 519 | if (split.num_types_ <= 1) { |
| 520 | WriteBits(1, 0, storage_ix, storage); |
| 521 | return; |
| 522 | } |
| 523 | WriteBits(1, 1, storage_ix, storage); |
| 524 | HistogramLiteral type_histo; |
| 525 | for (int i = 0; i < split.type_codes_.size(); ++i) { |
| 526 | type_histo.Add(split.type_codes_[i]); |
| 527 | } |
| 528 | BuildEntropyCode(type_histo, 15, split.num_types_ + 2, |
| 529 | &code->block_type_code); |
| 530 | HistogramBlockLength length_histo; |
| 531 | for (int i = 0; i < split.lengths_.size(); ++i) { |
| 532 | length_histo.Add(BlockLengthPrefix(split.lengths_[i])); |
| 533 | } |
| 534 | BuildEntropyCode(length_histo, 15, kNumBlockLenPrefixes, |
| 535 | &code->block_len_code); |
| 536 | WriteBits(8, split.num_types_ - 1, storage_ix, storage); |
| 537 | StoreHuffmanCode(code->block_type_code, split.num_types_ + 2, |
| 538 | storage_ix, storage); |
| 539 | StoreHuffmanCode(code->block_len_code, kNumBlockLenPrefixes, |
| 540 | storage_ix, storage); |
| 541 | EncodeBlockLength(code->block_len_code, split.lengths_[0], |
| 542 | storage_ix, storage); |
| 543 | } |
| 544 | |
| 545 | void MoveAndEncode(const BlockSplitCode& code, |
| 546 | BlockSplitIterator* it, |
| 547 | int* storage_ix, uint8_t* storage) { |
| 548 | if (it->length_ == 0) { |
| 549 | ++it->idx_; |
| 550 | it->type_ = it->split_.types_[it->idx_]; |
| 551 | it->length_ = it->split_.lengths_[it->idx_]; |
| 552 | uint8_t type_code = it->split_.type_codes_[it->idx_]; |
| 553 | EntropyEncode(type_code, code.block_type_code, storage_ix, storage); |
| 554 | EncodeBlockLength(code.block_len_code, it->length_, storage_ix, storage); |
| 555 | } |
| 556 | --it->length_; |
| 557 | } |
| 558 | |
| 559 | struct EncodingParams { |
| 560 | int num_direct_distance_codes; |
| 561 | int distance_postfix_bits; |
| 562 | int literal_context_mode; |
| 563 | int distance_context_mode; |
| 564 | }; |
| 565 | |
| 566 | struct MetaBlock { |
| 567 | std::vector<Command> cmds; |
| 568 | EncodingParams params; |
| 569 | BlockSplit literal_split; |
| 570 | BlockSplit command_split; |
| 571 | BlockSplit distance_split; |
| 572 | std::vector<int> literal_context_map; |
| 573 | std::vector<int> distance_context_map; |
| 574 | std::vector<HistogramLiteral> literal_histograms; |
| 575 | std::vector<HistogramCommand> command_histograms; |
| 576 | std::vector<HistogramDistance> distance_histograms; |
| 577 | }; |
| 578 | |
| 579 | void BuildMetaBlock(const EncodingParams& params, |
| 580 | const std::vector<Command>& cmds, |
| 581 | const uint8_t* input_buffer, |
| 582 | size_t pos, |
| 583 | MetaBlock* mb) { |
| 584 | mb->cmds = cmds; |
| 585 | mb->params = params; |
| 586 | ComputeCommandPrefixes(&mb->cmds, |
| 587 | mb->params.num_direct_distance_codes, |
| 588 | mb->params.distance_postfix_bits); |
| 589 | SplitBlock(mb->cmds, |
| 590 | input_buffer + pos, |
| 591 | &mb->literal_split, |
| 592 | &mb->command_split, |
| 593 | &mb->distance_split); |
| 594 | ComputeBlockTypeShortCodes(&mb->literal_split); |
| 595 | ComputeBlockTypeShortCodes(&mb->command_split); |
| 596 | ComputeBlockTypeShortCodes(&mb->distance_split); |
| 597 | |
| 598 | int num_literal_contexts_per_block_type = |
| 599 | NumContexts(mb->params.literal_context_mode); |
| 600 | int num_literal_contexts = |
| 601 | mb->literal_split.num_types_ * |
| 602 | num_literal_contexts_per_block_type; |
| 603 | int num_distance_contexts_per_block_type = |
| 604 | (mb->params.distance_context_mode > 0 ? 4 : 1); |
| 605 | int num_distance_contexts = |
| 606 | mb->distance_split.num_types_ * |
| 607 | num_distance_contexts_per_block_type; |
| 608 | std::vector<HistogramLiteral> literal_histograms(num_literal_contexts); |
| 609 | mb->command_histograms.resize(mb->command_split.num_types_); |
| 610 | std::vector<HistogramDistance> distance_histograms(num_distance_contexts); |
| 611 | BuildHistograms(mb->cmds, |
| 612 | mb->literal_split, |
| 613 | mb->command_split, |
| 614 | mb->distance_split, |
| 615 | input_buffer, |
| 616 | pos, |
| 617 | mb->params.literal_context_mode, |
| 618 | mb->params.distance_context_mode, |
| 619 | &literal_histograms, |
| 620 | &mb->command_histograms, |
| 621 | &distance_histograms); |
| 622 | |
| 623 | // Histogram ids need to fit in one byte and there are 16 ids reserved for |
| 624 | // run length codes, which leaves a maximum number of 240 histograms. |
| 625 | static const int kMaxNumberOfHistograms = 240; |
| 626 | |
| 627 | mb->literal_histograms = literal_histograms; |
| 628 | if (mb->params.literal_context_mode > 0) { |
| 629 | ClusterHistograms(literal_histograms, |
| 630 | num_literal_contexts_per_block_type, |
| 631 | mb->literal_split.num_types_, |
| 632 | kMaxNumberOfHistograms, |
| 633 | &mb->literal_histograms, |
| 634 | &mb->literal_context_map); |
| 635 | } |
| 636 | |
| 637 | mb->distance_histograms = distance_histograms; |
| 638 | if (mb->params.distance_context_mode > 0) { |
| 639 | ClusterHistograms(distance_histograms, |
| 640 | num_distance_contexts_per_block_type, |
| 641 | mb->distance_split.num_types_, |
| 642 | kMaxNumberOfHistograms, |
| 643 | &mb->distance_histograms, |
| 644 | &mb->distance_context_map); |
| 645 | } |
| 646 | } |
| 647 | |
| 648 | size_t MetaBlockLength(const std::vector<Command>& cmds) { |
| 649 | size_t length = 0; |
| 650 | for (int i = 0; i < cmds.size(); ++i) { |
| 651 | const Command& cmd = cmds[i]; |
| 652 | length += cmd.insert_length_ + cmd.copy_length_; |
| 653 | } |
| 654 | return length; |
| 655 | } |
| 656 | |
| 657 | void StoreMetaBlock(const MetaBlock& mb, |
| 658 | const uint8_t* input_buffer, |
| 659 | int input_size_bits, |
| 660 | bool is_last, |
| 661 | size_t* pos, |
| 662 | int* storage_ix, uint8_t* storage) { |
| 663 | size_t length = MetaBlockLength(mb.cmds); |
| 664 | const size_t end_pos = *pos + length; |
| 665 | EncodeMetaBlockLength(input_size_bits, length - 1, is_last, |
| 666 | storage_ix, storage); |
| 667 | BlockSplitCode literal_split_code; |
| 668 | BlockSplitCode command_split_code; |
| 669 | BlockSplitCode distance_split_code; |
| 670 | BuildAndEncodeBlockSplitCode(mb.literal_split, &literal_split_code, |
| 671 | storage_ix, storage); |
| 672 | BuildAndEncodeBlockSplitCode(mb.command_split, &command_split_code, |
| 673 | storage_ix, storage); |
| 674 | BuildAndEncodeBlockSplitCode(mb.distance_split, &distance_split_code, |
| 675 | storage_ix, storage); |
| 676 | WriteBits(2, mb.params.distance_postfix_bits, storage_ix, storage); |
| 677 | WriteBits(4, |
| 678 | mb.params.num_direct_distance_codes >> |
| 679 | mb.params.distance_postfix_bits, storage_ix, storage); |
| 680 | int num_distance_codes = |
| 681 | kNumDistanceShortCodes + mb.params.num_direct_distance_codes + |
| 682 | (48 << mb.params.distance_postfix_bits); |
| 683 | EncodeContextMap(mb.literal_context_map, mb.params.literal_context_mode, 4, |
| 684 | mb.literal_histograms.size(), storage_ix, storage); |
| 685 | EncodeContextMap(mb.distance_context_map, mb.params.distance_context_mode, 0, |
| 686 | mb.distance_histograms.size(), storage_ix, storage); |
| 687 | std::vector<EntropyCodeLiteral> literal_codes; |
| 688 | std::vector<EntropyCodeCommand> command_codes; |
| 689 | std::vector<EntropyCodeDistance> distance_codes; |
| 690 | BuildEntropyCodes(mb.literal_histograms, 256, &literal_codes); |
| 691 | BuildEntropyCodes(mb.command_histograms, kNumCommandPrefixes, |
| 692 | &command_codes); |
| 693 | BuildEntropyCodes(mb.distance_histograms, num_distance_codes, |
| 694 | &distance_codes); |
| 695 | StoreHuffmanCodes(literal_codes, 256, storage_ix, storage); |
| 696 | StoreHuffmanCodes(command_codes, kNumCommandPrefixes, storage_ix, storage); |
| 697 | StoreHuffmanCodes(distance_codes, num_distance_codes, storage_ix, storage); |
| 698 | BlockSplitIterator literal_it(mb.literal_split); |
| 699 | BlockSplitIterator command_it(mb.command_split); |
| 700 | BlockSplitIterator distance_it(mb.distance_split); |
| 701 | for (int i = 0; i < mb.cmds.size(); ++i) { |
| 702 | const Command& cmd = mb.cmds[i]; |
| 703 | MoveAndEncode(command_split_code, &command_it, storage_ix, storage); |
| 704 | EncodeCommand(cmd, command_codes[command_it.type_], storage_ix, storage); |
| 705 | for (int j = 0; j < cmd.insert_length_; ++j) { |
| 706 | MoveAndEncode(literal_split_code, &literal_it, storage_ix, storage); |
| 707 | int histogram_idx = literal_it.type_; |
| 708 | if (mb.params.literal_context_mode > 0) { |
| 709 | uint8_t prev_byte = *pos > 0 ? input_buffer[*pos - 1] : 0; |
| 710 | uint8_t prev_byte2 = *pos > 1 ? input_buffer[*pos - 2] : 0; |
| 711 | uint8_t prev_byte3 = *pos > 2 ? input_buffer[*pos - 3] : 0; |
| 712 | int context = (literal_it.type_ * |
| 713 | NumContexts(mb.params.literal_context_mode) + |
| 714 | Context(prev_byte, prev_byte2, prev_byte3, |
| 715 | mb.params.literal_context_mode)); |
| 716 | histogram_idx = mb.literal_context_map[context]; |
| 717 | } |
| 718 | EntropyEncode(input_buffer[(*pos)++], |
| 719 | literal_codes[histogram_idx], storage_ix, storage); |
| 720 | } |
| 721 | if (*pos < end_pos && cmd.distance_prefix_ != 0xffff) { |
| 722 | MoveAndEncode(distance_split_code, &distance_it, storage_ix, storage); |
| 723 | int histogram_index = distance_it.type_; |
| 724 | if (mb.params.distance_context_mode > 0) { |
| 725 | int context = distance_it.type_ << 2; |
| 726 | context += (cmd.copy_length_ > 4) ? 3 : cmd.copy_length_ - 2; |
| 727 | histogram_index = mb.distance_context_map[context]; |
| 728 | } |
| 729 | EncodeCopyDistance(cmd, distance_codes[histogram_index], |
| 730 | storage_ix, storage); |
| 731 | } |
| 732 | *pos += cmd.copy_length_; |
| 733 | } |
| 734 | } |
| 735 | |
| 736 | int BrotliCompressBuffer(size_t input_size, |
| 737 | const uint8_t* input_buffer, |
| 738 | size_t* encoded_size, |
| 739 | uint8_t* encoded_buffer) { |
| 740 | int storage_ix = 0; |
| 741 | uint8_t* storage = encoded_buffer; |
| 742 | WriteBitsPrepareStorage(storage_ix, storage); |
| 743 | EncodeSize(input_size, &storage_ix, storage); |
| 744 | |
| 745 | if (input_size == 0) { |
| 746 | *encoded_size = (storage_ix + 7) >> 3; |
| 747 | return 1; |
| 748 | } |
| 749 | int input_size_bits = Log2Ceiling(input_size); |
| 750 | |
| 751 | std::vector<Command> all_commands; |
| 752 | CreateBackwardReferences(input_buffer, input_size, &all_commands); |
| 753 | ComputeDistanceShortCodes(&all_commands); |
| 754 | |
| 755 | std::vector<std::vector<Command> > meta_block_commands; |
| 756 | SplitBlockByTotalLength(all_commands, input_size, 2 << 20, |
| 757 | &meta_block_commands); |
| 758 | |
| 759 | size_t pos = 0; |
| 760 | for (int block_idx = 0; block_idx < meta_block_commands.size(); ++block_idx) { |
| 761 | const std::vector<Command>& commands = meta_block_commands[block_idx]; |
| 762 | bool is_last_meta_block = (block_idx + 1 == meta_block_commands.size()); |
| 763 | EncodingParams params; |
| 764 | params.num_direct_distance_codes = 12; |
| 765 | params.distance_postfix_bits = 1; |
| 766 | params.literal_context_mode = CONTEXT_SIGNED_MIXED_3BYTE; |
| 767 | params.distance_context_mode = 1; |
| 768 | MetaBlock mb; |
| 769 | BuildMetaBlock(params, commands, input_buffer, pos, &mb); |
| 770 | StoreMetaBlock(mb, input_buffer, input_size_bits, is_last_meta_block, |
| 771 | &pos, &storage_ix, storage); |
| 772 | } |
| 773 | |
| 774 | *encoded_size = (storage_ix + 7) >> 3; |
| 775 | return 1; |
| 776 | } |
| 777 | |
| 778 | } // namespace brotli |