| 1 | // license:BSD-3-Clause\r |
| 2 | // copyright-holders:Aaron Giles\r |
| 3 | /***************************************************************************\r |
| 4 | \r |
| 5 | huffman.c\r |
| 6 | \r |
| 7 | Static Huffman compression and decompression helpers.\r |
| 8 | \r |
| 9 | ****************************************************************************\r |
| 10 | \r |
| 11 | Maximum codelength is officially (alphabetsize - 1). This would be 255 bits\r |
| 12 | (since we use 1 byte values). However, it is also dependent upon the number\r |
| 13 | of samples used, as follows:\r |
| 14 | \r |
| 15 | 2 bits -> 3..4 samples\r |
| 16 | 3 bits -> 5..7 samples\r |
| 17 | 4 bits -> 8..12 samples\r |
| 18 | 5 bits -> 13..20 samples\r |
| 19 | 6 bits -> 21..33 samples\r |
| 20 | 7 bits -> 34..54 samples\r |
| 21 | 8 bits -> 55..88 samples\r |
| 22 | 9 bits -> 89..143 samples\r |
| 23 | 10 bits -> 144..232 samples\r |
| 24 | 11 bits -> 233..376 samples\r |
| 25 | 12 bits -> 377..609 samples\r |
| 26 | 13 bits -> 610..986 samples\r |
| 27 | 14 bits -> 987..1596 samples\r |
| 28 | 15 bits -> 1597..2583 samples\r |
| 29 | 16 bits -> 2584..4180 samples -> note that a 4k data size guarantees codelength <= 16 bits\r |
| 30 | 17 bits -> 4181..6764 samples\r |
| 31 | 18 bits -> 6765..10945 samples\r |
| 32 | 19 bits -> 10946..17710 samples\r |
| 33 | 20 bits -> 17711..28656 samples\r |
| 34 | 21 bits -> 28657..46367 samples\r |
| 35 | 22 bits -> 46368..75024 samples\r |
| 36 | 23 bits -> 75025..121392 samples\r |
| 37 | 24 bits -> 121393..196417 samples\r |
| 38 | 25 bits -> 196418..317810 samples\r |
| 39 | 26 bits -> 317811..514228 samples\r |
| 40 | 27 bits -> 514229..832039 samples\r |
| 41 | 28 bits -> 832040..1346268 samples\r |
| 42 | 29 bits -> 1346269..2178308 samples\r |
| 43 | 30 bits -> 2178309..3524577 samples\r |
| 44 | 31 bits -> 3524578..5702886 samples\r |
| 45 | 32 bits -> 5702887..9227464 samples\r |
| 46 | \r |
| 47 | Looking at it differently, here is where powers of 2 fall into these buckets:\r |
| 48 | \r |
| 49 | 256 samples -> 11 bits max\r |
| 50 | 512 samples -> 12 bits max\r |
| 51 | 1k samples -> 14 bits max\r |
| 52 | 2k samples -> 15 bits max\r |
| 53 | 4k samples -> 16 bits max\r |
| 54 | 8k samples -> 18 bits max\r |
| 55 | 16k samples -> 19 bits max\r |
| 56 | 32k samples -> 21 bits max\r |
| 57 | 64k samples -> 22 bits max\r |
| 58 | 128k samples -> 24 bits max\r |
| 59 | 256k samples -> 25 bits max\r |
| 60 | 512k samples -> 27 bits max\r |
| 61 | 1M samples -> 28 bits max\r |
| 62 | 2M samples -> 29 bits max\r |
| 63 | 4M samples -> 31 bits max\r |
| 64 | 8M samples -> 32 bits max\r |
| 65 | \r |
| 66 | ****************************************************************************\r |
| 67 | \r |
| 68 | Delta-RLE encoding works as follows:\r |
| 69 | \r |
| 70 | Starting value is assumed to be 0. All data is encoded as a delta\r |
| 71 | from the previous value, such that final[i] = final[i - 1] + delta.\r |
| 72 | Long runs of 0s are RLE-encoded as follows:\r |
| 73 | \r |
| 74 | 0x100 = repeat count of 8\r |
| 75 | 0x101 = repeat count of 9\r |
| 76 | 0x102 = repeat count of 10\r |
| 77 | 0x103 = repeat count of 11\r |
| 78 | 0x104 = repeat count of 12\r |
| 79 | 0x105 = repeat count of 13\r |
| 80 | 0x106 = repeat count of 14\r |
| 81 | 0x107 = repeat count of 15\r |
| 82 | 0x108 = repeat count of 16\r |
| 83 | 0x109 = repeat count of 32\r |
| 84 | 0x10a = repeat count of 64\r |
| 85 | 0x10b = repeat count of 128\r |
| 86 | 0x10c = repeat count of 256\r |
| 87 | 0x10d = repeat count of 512\r |
| 88 | 0x10e = repeat count of 1024\r |
| 89 | 0x10f = repeat count of 2048\r |
| 90 | \r |
| 91 | Note that repeat counts are reset at the end of a row, so if a 0 run\r |
| 92 | extends to the end of a row, a large repeat count may be used.\r |
| 93 | \r |
| 94 | The reason for starting the run counts at 8 is that 0 is expected to\r |
| 95 | be the most common symbol, and is typically encoded in 1 or 2 bits.\r |
| 96 | \r |
| 97 | ***************************************************************************/\r |
| 98 | \r |
| 99 | #include <stdlib.h>\r |
| 100 | #include <assert.h>\r |
| 101 | #include <stdio.h>\r |
| 102 | #include <string.h>\r |
| 103 | \r |
| 104 | #include "huffman.h"\r |
| 105 | \r |
| 106 | #define MAX(x,y) ((x) > (y) ? (x) : (y))\r |
| 107 | \r |
| 108 | //**************************************************************************\r |
| 109 | // MACROS\r |
| 110 | //**************************************************************************\r |
| 111 | \r |
| 112 | #define MAKE_LOOKUP(code,bits) (((code) << 5) | ((bits) & 0x1f))\r |
| 113 | \r |
| 114 | \r |
| 115 | //**************************************************************************\r |
| 116 | // IMPLEMENTATION\r |
| 117 | //**************************************************************************\r |
| 118 | \r |
| 119 | //-------------------------------------------------\r |
| 120 | // huffman_context_base - create an encoding/\r |
| 121 | // decoding context\r |
| 122 | //-------------------------------------------------\r |
| 123 | \r |
| 124 | struct huffman_decoder* create_huffman_decoder(int numcodes, int maxbits)\r |
| 125 | {\r |
| 126 | struct huffman_decoder* decoder;\r |
| 127 | \r |
| 128 | /* limit to 24 bits */\r |
| 129 | if (maxbits > 24)\r |
| 130 | return NULL;\r |
| 131 | \r |
| 132 | decoder = (struct huffman_decoder*)malloc(sizeof(struct huffman_decoder));\r |
| 133 | decoder->numcodes = numcodes;\r |
| 134 | decoder->maxbits = maxbits;\r |
| 135 | decoder->lookup = (lookup_value*)malloc(sizeof(lookup_value) * (1 << maxbits));\r |
| 136 | decoder->huffnode = (struct node_t*)malloc(sizeof(struct node_t) * numcodes);\r |
| 137 | decoder->datahisto = NULL;\r |
| 138 | decoder->prevdata = 0;\r |
| 139 | decoder->rleremaining = 0;\r |
| 140 | return decoder;\r |
| 141 | }\r |
| 142 | \r |
| 143 | //-------------------------------------------------\r |
| 144 | // decode_one - decode a single code from the\r |
| 145 | // huffman stream\r |
| 146 | //-------------------------------------------------\r |
| 147 | \r |
| 148 | uint32_t huffman_decode_one(struct huffman_decoder* decoder, struct bitstream* bitbuf)\r |
| 149 | {\r |
| 150 | /* peek ahead to get maxbits worth of data */\r |
| 151 | uint32_t bits = bitstream_peek(bitbuf, decoder->maxbits);\r |
| 152 | \r |
| 153 | /* look it up, then remove the actual number of bits for this code */\r |
| 154 | lookup_value lookup = decoder->lookup[bits];\r |
| 155 | bitstream_remove(bitbuf, lookup & 0x1f);\r |
| 156 | \r |
| 157 | /* return the value */\r |
| 158 | return lookup >> 5;\r |
| 159 | }\r |
| 160 | \r |
| 161 | //-------------------------------------------------\r |
| 162 | // import_tree_rle - import an RLE-encoded\r |
| 163 | // huffman tree from a source data stream\r |
| 164 | //-------------------------------------------------\r |
| 165 | \r |
| 166 | enum huffman_error huffman_import_tree_rle(struct huffman_decoder* decoder, struct bitstream* bitbuf)\r |
| 167 | {\r |
| 168 | enum huffman_error error;\r |
| 169 | int curnode;\r |
| 170 | // bits per entry depends on the maxbits\r |
| 171 | int numbits;\r |
| 172 | if (decoder->maxbits >= 16)\r |
| 173 | numbits = 5;\r |
| 174 | else if (decoder->maxbits >= 8)\r |
| 175 | numbits = 4;\r |
| 176 | else\r |
| 177 | numbits = 3;\r |
| 178 | \r |
| 179 | // loop until we read all the nodes\r |
| 180 | for (curnode = 0; curnode < decoder->numcodes; )\r |
| 181 | {\r |
| 182 | // a non-one value is just raw\r |
| 183 | int nodebits = bitstream_read(bitbuf, numbits);\r |
| 184 | if (nodebits != 1)\r |
| 185 | decoder->huffnode[curnode++].numbits = nodebits;\r |
| 186 | \r |
| 187 | // a one value is an escape code\r |
| 188 | else\r |
| 189 | {\r |
| 190 | // a double 1 is just a single 1\r |
| 191 | nodebits = bitstream_read(bitbuf, numbits);\r |
| 192 | if (nodebits == 1)\r |
| 193 | decoder->huffnode[curnode++].numbits = nodebits;\r |
| 194 | \r |
| 195 | // otherwise, we need one for value for the repeat count\r |
| 196 | else\r |
| 197 | {\r |
| 198 | int repcount = bitstream_read(bitbuf, numbits) + 3;\r |
| 199 | while (repcount--)\r |
| 200 | decoder->huffnode[curnode++].numbits = nodebits;\r |
| 201 | }\r |
| 202 | }\r |
| 203 | }\r |
| 204 | \r |
| 205 | // make sure we ended up with the right number\r |
| 206 | if (curnode != decoder->numcodes)\r |
| 207 | return HUFFERR_INVALID_DATA;\r |
| 208 | \r |
| 209 | // assign canonical codes for all nodes based on their code lengths\r |
| 210 | error = huffman_assign_canonical_codes(decoder);\r |
| 211 | if (error != HUFFERR_NONE)\r |
| 212 | return error;\r |
| 213 | \r |
| 214 | // build the lookup table\r |
| 215 | huffman_build_lookup_table(decoder);\r |
| 216 | \r |
| 217 | // determine final input length and report errors\r |
| 218 | return bitstream_overflow(bitbuf) ? HUFFERR_INPUT_BUFFER_TOO_SMALL : HUFFERR_NONE;\r |
| 219 | }\r |
| 220 | \r |
| 221 | \r |
| 222 | //-------------------------------------------------\r |
| 223 | // import_tree_huffman - import a huffman-encoded\r |
| 224 | // huffman tree from a source data stream\r |
| 225 | //-------------------------------------------------\r |
| 226 | \r |
| 227 | enum huffman_error huffman_import_tree_huffman(struct huffman_decoder* decoder, struct bitstream* bitbuf)\r |
| 228 | {\r |
| 229 | int index;\r |
| 230 | int start;\r |
| 231 | int count = 0;\r |
| 232 | uint8_t rlefullbits = 0;\r |
| 233 | int last = 0;\r |
| 234 | int curcode;\r |
| 235 | enum huffman_error error;\r |
| 236 | uint32_t temp;\r |
| 237 | // start by parsing the lengths for the small tree\r |
| 238 | struct huffman_decoder* smallhuff = create_huffman_decoder(24, 6);\r |
| 239 | \r |
| 240 | smallhuff->huffnode[0].numbits = bitstream_read(bitbuf, 3);\r |
| 241 | start = bitstream_read(bitbuf, 3) + 1;\r |
| 242 | \r |
| 243 | for (index = 1; index < 24; index++)\r |
| 244 | {\r |
| 245 | if (index < start || count == 7)\r |
| 246 | smallhuff->huffnode[index].numbits = 0;\r |
| 247 | else\r |
| 248 | {\r |
| 249 | count = bitstream_read(bitbuf, 3);\r |
| 250 | smallhuff->huffnode[index].numbits = (count == 7) ? 0 : count;\r |
| 251 | }\r |
| 252 | }\r |
| 253 | \r |
| 254 | // then regenerate the tree\r |
| 255 | error = huffman_assign_canonical_codes(smallhuff);\r |
| 256 | if (error != HUFFERR_NONE)\r |
| 257 | return error;\r |
| 258 | huffman_build_lookup_table(smallhuff);\r |
| 259 | \r |
| 260 | // determine the maximum length of an RLE count\r |
| 261 | temp = decoder->numcodes - 9;\r |
| 262 | while (temp != 0)\r |
| 263 | temp >>= 1, rlefullbits++;\r |
| 264 | \r |
| 265 | // now process the rest of the data\r |
| 266 | for (curcode = 0; curcode < decoder->numcodes; )\r |
| 267 | {\r |
| 268 | int value = huffman_decode_one(smallhuff, bitbuf);\r |
| 269 | if (value != 0)\r |
| 270 | decoder->huffnode[curcode++].numbits = last = value - 1;\r |
| 271 | else\r |
| 272 | {\r |
| 273 | int count = bitstream_read(bitbuf, 3) + 2;\r |
| 274 | if (count == 7+2)\r |
| 275 | count += bitstream_read(bitbuf, rlefullbits);\r |
| 276 | for ( ; count != 0 && curcode < decoder->numcodes; count--)\r |
| 277 | decoder->huffnode[curcode++].numbits = last;\r |
| 278 | }\r |
| 279 | }\r |
| 280 | \r |
| 281 | // make sure we ended up with the right number\r |
| 282 | if (curcode != decoder->numcodes)\r |
| 283 | return HUFFERR_INVALID_DATA;\r |
| 284 | \r |
| 285 | // assign canonical codes for all nodes based on their code lengths\r |
| 286 | error = huffman_assign_canonical_codes(decoder);\r |
| 287 | if (error != HUFFERR_NONE)\r |
| 288 | return error;\r |
| 289 | \r |
| 290 | // build the lookup table\r |
| 291 | huffman_build_lookup_table(decoder);\r |
| 292 | \r |
| 293 | // determine final input length and report errors\r |
| 294 | return bitstream_overflow(bitbuf) ? HUFFERR_INPUT_BUFFER_TOO_SMALL : HUFFERR_NONE;\r |
| 295 | }\r |
| 296 | \r |
| 297 | \r |
| 298 | //-------------------------------------------------\r |
| 299 | // compute_tree_from_histo - common backend for\r |
| 300 | // computing a tree based on the data histogram\r |
| 301 | //-------------------------------------------------\r |
| 302 | \r |
| 303 | enum huffman_error huffman_compute_tree_from_histo(struct huffman_decoder* decoder)\r |
| 304 | {\r |
| 305 | int i;\r |
| 306 | uint32_t upperweight;\r |
| 307 | uint32_t lowerweight = 0;\r |
| 308 | // compute the number of data items in the histogram\r |
| 309 | uint32_t sdatacount = 0;\r |
| 310 | for (i = 0; i < decoder->numcodes; i++)\r |
| 311 | sdatacount += decoder->datahisto[i];\r |
| 312 | \r |
| 313 | // binary search to achieve the optimum encoding\r |
| 314 | upperweight = sdatacount * 2;\r |
| 315 | while (1)\r |
| 316 | {\r |
| 317 | // build a tree using the current weight\r |
| 318 | uint32_t curweight = (upperweight + lowerweight) / 2;\r |
| 319 | int curmaxbits = huffman_build_tree(decoder, sdatacount, curweight);\r |
| 320 | \r |
| 321 | // apply binary search here\r |
| 322 | if (curmaxbits <= decoder->maxbits)\r |
| 323 | {\r |
| 324 | lowerweight = curweight;\r |
| 325 | \r |
| 326 | // early out if it worked with the raw weights, or if we're done searching\r |
| 327 | if (curweight == sdatacount || (upperweight - lowerweight) <= 1)\r |
| 328 | break;\r |
| 329 | }\r |
| 330 | else\r |
| 331 | upperweight = curweight;\r |
| 332 | }\r |
| 333 | \r |
| 334 | // assign canonical codes for all nodes based on their code lengths\r |
| 335 | return huffman_assign_canonical_codes(decoder);\r |
| 336 | }\r |
| 337 | \r |
| 338 | \r |
| 339 | \r |
| 340 | //**************************************************************************\r |
| 341 | // INTERNAL FUNCTIONS\r |
| 342 | //**************************************************************************\r |
| 343 | \r |
| 344 | //-------------------------------------------------\r |
| 345 | // tree_node_compare - compare two tree nodes\r |
| 346 | // by weight\r |
| 347 | //-------------------------------------------------\r |
| 348 | \r |
| 349 | static int huffman_tree_node_compare(const void *item1, const void *item2)\r |
| 350 | {\r |
| 351 | const struct node_t *node1 = *(const struct node_t **)item1;\r |
| 352 | const struct node_t *node2 = *(const struct node_t **)item2;\r |
| 353 | if (node2->weight != node1->weight)\r |
| 354 | return node2->weight - node1->weight;\r |
| 355 | if (node2->bits - node1->bits == 0)\r |
| 356 | fprintf(stderr, "identical node sort keys, should not happen!\n");\r |
| 357 | return (int)node1->bits - (int)node2->bits;\r |
| 358 | }\r |
| 359 | \r |
| 360 | \r |
| 361 | //-------------------------------------------------\r |
| 362 | // build_tree - build a huffman tree based on the\r |
| 363 | // data distribution\r |
| 364 | //-------------------------------------------------\r |
| 365 | \r |
| 366 | int huffman_build_tree(struct huffman_decoder* decoder, uint32_t totaldata, uint32_t totalweight)\r |
| 367 | {\r |
| 368 | int curcode;\r |
| 369 | int nextalloc;\r |
| 370 | int maxbits = 0;\r |
| 371 | // make a list of all non-zero nodes\r |
| 372 | struct node_t** list = (struct node_t**)malloc(sizeof(struct node_t*) * decoder->numcodes * 2);\r |
| 373 | int listitems = 0;\r |
| 374 | memset(decoder->huffnode, 0, decoder->numcodes * sizeof(decoder->huffnode[0]));\r |
| 375 | for (curcode = 0; curcode < decoder->numcodes; curcode++)\r |
| 376 | if (decoder->datahisto[curcode] != 0)\r |
| 377 | {\r |
| 378 | list[listitems++] = &decoder->huffnode[curcode];\r |
| 379 | decoder->huffnode[curcode].count = decoder->datahisto[curcode];\r |
| 380 | decoder->huffnode[curcode].bits = curcode;\r |
| 381 | \r |
| 382 | // scale the weight by the current effective length, ensuring we don't go to 0\r |
| 383 | decoder->huffnode[curcode].weight = ((uint64_t)decoder->datahisto[curcode]) * ((uint64_t)totalweight) / ((uint64_t)totaldata);\r |
| 384 | if (decoder->huffnode[curcode].weight == 0)\r |
| 385 | decoder->huffnode[curcode].weight = 1;\r |
| 386 | }\r |
| 387 | /*\r |
| 388 | fprintf(stderr, "Pre-sort:\n");\r |
| 389 | for (int i = 0; i < listitems; i++) {\r |
| 390 | fprintf(stderr, "weight: %d code: %d\n", list[i]->m_weight, list[i]->m_bits);\r |
| 391 | }\r |
| 392 | */\r |
| 393 | // sort the list by weight, largest weight first\r |
| 394 | qsort(&list[0], listitems, sizeof(list[0]), huffman_tree_node_compare);\r |
| 395 | /*\r |
| 396 | fprintf(stderr, "Post-sort:\n");\r |
| 397 | for (int i = 0; i < listitems; i++) {\r |
| 398 | fprintf(stderr, "weight: %d code: %d\n", list[i]->m_weight, list[i]->m_bits);\r |
| 399 | }\r |
| 400 | fprintf(stderr, "===================\n");\r |
| 401 | */\r |
| 402 | // now build the tree\r |
| 403 | nextalloc = decoder->numcodes;\r |
| 404 | \r |
| 405 | while (listitems > 1)\r |
| 406 | {\r |
| 407 | int curitem;\r |
| 408 | // remove lowest two items\r |
| 409 | struct node_t* node1 = &(*list[--listitems]);\r |
| 410 | struct node_t* node0 = &(*list[--listitems]);\r |
| 411 | \r |
| 412 | // create new node\r |
| 413 | struct node_t* newnode = &decoder->huffnode[nextalloc++];\r |
| 414 | newnode->parent = NULL;\r |
| 415 | node0->parent = node1->parent = newnode;\r |
| 416 | newnode->weight = node0->weight + node1->weight;\r |
| 417 | \r |
| 418 | // insert into list at appropriate location\r |
| 419 | for (curitem = 0; curitem < listitems; curitem++)\r |
| 420 | if (newnode->weight > list[curitem]->weight)\r |
| 421 | {\r |
| 422 | memmove(&list[curitem+1], &list[curitem], (listitems - curitem) * sizeof(list[0]));\r |
| 423 | break;\r |
| 424 | }\r |
| 425 | list[curitem] = newnode;\r |
| 426 | listitems++;\r |
| 427 | }\r |
| 428 | \r |
| 429 | // compute the number of bits in each code, and fill in another histogram\r |
| 430 | for (curcode = 0; curcode < decoder->numcodes; curcode++)\r |
| 431 | {\r |
| 432 | struct node_t* node = &decoder->huffnode[curcode];\r |
| 433 | node->numbits = 0;\r |
| 434 | node->bits = 0;\r |
| 435 | \r |
| 436 | // if we have a non-zero weight, compute the number of bits\r |
| 437 | if (node->weight > 0)\r |
| 438 | {\r |
| 439 | struct node_t *curnode;\r |
| 440 | // determine the number of bits for this node\r |
| 441 | for (curnode = node; curnode->parent != NULL; curnode = curnode->parent)\r |
| 442 | node->numbits++;\r |
| 443 | if (node->numbits == 0)\r |
| 444 | node->numbits = 1;\r |
| 445 | \r |
| 446 | // keep track of the max\r |
| 447 | maxbits = MAX(maxbits, ((int)node->numbits));\r |
| 448 | }\r |
| 449 | }\r |
| 450 | return maxbits;\r |
| 451 | }\r |
| 452 | \r |
| 453 | \r |
| 454 | //-------------------------------------------------\r |
| 455 | // assign_canonical_codes - assign canonical codes\r |
| 456 | // to all the nodes based on the number of bits\r |
| 457 | // in each\r |
| 458 | //-------------------------------------------------\r |
| 459 | \r |
| 460 | enum huffman_error huffman_assign_canonical_codes(struct huffman_decoder* decoder)\r |
| 461 | {\r |
| 462 | int curcode, codelen;\r |
| 463 | uint32_t curstart = 0;\r |
| 464 | \r |
| 465 | // build up a histogram of bit lengths\r |
| 466 | uint32_t bithisto[33] = { 0 };\r |
| 467 | for (curcode = 0; curcode < decoder->numcodes; curcode++)\r |
| 468 | {\r |
| 469 | struct node_t* node = &decoder->huffnode[curcode];\r |
| 470 | if (node->numbits > decoder->maxbits)\r |
| 471 | return HUFFERR_INTERNAL_INCONSISTENCY;\r |
| 472 | if (node->numbits <= 32)\r |
| 473 | bithisto[node->numbits]++;\r |
| 474 | }\r |
| 475 | \r |
| 476 | // for each code length, determine the starting code number\r |
| 477 | for (codelen = 32; codelen > 0; codelen--)\r |
| 478 | {\r |
| 479 | uint32_t nextstart = (curstart + bithisto[codelen]) >> 1;\r |
| 480 | if (codelen != 1 && nextstart * 2 != (curstart + bithisto[codelen]))\r |
| 481 | return HUFFERR_INTERNAL_INCONSISTENCY;\r |
| 482 | bithisto[codelen] = curstart;\r |
| 483 | curstart = nextstart;\r |
| 484 | }\r |
| 485 | \r |
| 486 | // now assign canonical codes\r |
| 487 | for (curcode = 0; curcode < decoder->numcodes; curcode++)\r |
| 488 | {\r |
| 489 | struct node_t* node = &decoder->huffnode[curcode];\r |
| 490 | if (node->numbits > 0)\r |
| 491 | node->bits = bithisto[node->numbits]++;\r |
| 492 | }\r |
| 493 | return HUFFERR_NONE;\r |
| 494 | }\r |
| 495 | \r |
| 496 | \r |
| 497 | //-------------------------------------------------\r |
| 498 | // build_lookup_table - build a lookup table for\r |
| 499 | // fast decoding\r |
| 500 | //-------------------------------------------------\r |
| 501 | \r |
| 502 | void huffman_build_lookup_table(struct huffman_decoder* decoder)\r |
| 503 | {\r |
| 504 | int curcode;\r |
| 505 | // iterate over all codes\r |
| 506 | for (curcode = 0; curcode < decoder->numcodes; curcode++)\r |
| 507 | {\r |
| 508 | // process all nodes which have non-zero bits\r |
| 509 | struct node_t* node = &decoder->huffnode[curcode];\r |
| 510 | if (node->numbits > 0)\r |
| 511 | {\r |
| 512 | int shift;\r |
| 513 | lookup_value *dest;\r |
| 514 | lookup_value *destend;\r |
| 515 | \r |
| 516 | // set up the entry\r |
| 517 | lookup_value value = MAKE_LOOKUP(curcode, node->numbits);\r |
| 518 | \r |
| 519 | // fill all matching entries\r |
| 520 | shift = decoder->maxbits - node->numbits;\r |
| 521 | dest = &decoder->lookup[node->bits << shift];\r |
| 522 | destend = &decoder->lookup[((node->bits + 1) << shift) - 1];\r |
| 523 | \r |
| 524 | while (dest <= destend)\r |
| 525 | *dest++ = value;\r |
| 526 | }\r |
| 527 | }\r |
| 528 | }\r |