Thomas G. Lane | 2cbeb8a | 1991-10-07 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * jchuff.c |
| 3 | * |
| 4 | * Copyright (C) 1991, Thomas G. Lane. |
| 5 | * This file is part of the Independent JPEG Group's software. |
| 6 | * For conditions of distribution and use, see the accompanying README file. |
| 7 | * |
| 8 | * This file contains Huffman entropy encoding routines. |
| 9 | * These routines are invoked via the methods entropy_encode, |
| 10 | * entropy_encoder_init/term, and entropy_optimize. |
| 11 | */ |
| 12 | |
| 13 | #include "jinclude.h" |
| 14 | |
| 15 | |
| 16 | /* Static variables to avoid passing 'round extra parameters */ |
| 17 | |
| 18 | static compress_info_ptr cinfo; |
| 19 | |
| 20 | static INT32 huff_put_buffer; /* current bit-accumulation buffer */ |
| 21 | static int huff_put_bits; /* # of bits now in it */ |
| 22 | |
| 23 | static char * output_buffer; /* output buffer */ |
| 24 | static int bytes_in_buffer; |
| 25 | |
| 26 | |
| 27 | |
| 28 | LOCAL void |
| 29 | fix_huff_tbl (HUFF_TBL * htbl) |
| 30 | /* Compute derived values for a Huffman table */ |
| 31 | { |
| 32 | int p, i, l, lastp, si; |
| 33 | char huffsize[257]; |
| 34 | UINT16 huffcode[257]; |
| 35 | UINT16 code; |
| 36 | |
| 37 | /* Figure 7.3.5.4.2.1: make table of Huffman code length for each symbol */ |
| 38 | /* Note that this is in code-length order. */ |
| 39 | |
| 40 | p = 0; |
| 41 | for (l = 1; l <= 16; l++) { |
| 42 | for (i = 1; i <= htbl->bits[l]; i++) |
| 43 | huffsize[p++] = l; |
| 44 | } |
| 45 | huffsize[p] = 0; |
| 46 | lastp = p; |
| 47 | |
| 48 | /* Figure 7.3.5.4.2.2: generate the codes themselves */ |
| 49 | /* Note that this is in code-length order. */ |
| 50 | |
| 51 | code = 0; |
| 52 | si = huffsize[0]; |
| 53 | p = 0; |
| 54 | while (huffsize[p]) { |
| 55 | while (huffsize[p] == si) { |
| 56 | huffcode[p++] = code; |
| 57 | code++; |
| 58 | } |
| 59 | code <<= 1; |
| 60 | si++; |
| 61 | } |
| 62 | |
| 63 | /* Figure 7.3.5.4.2.3: generate encoding tables */ |
| 64 | /* These are code and size indexed by symbol value */ |
| 65 | |
| 66 | for (p = 0; p < lastp; p++) { |
| 67 | htbl->ehufco[htbl->huffval[p]] = huffcode[p]; |
| 68 | htbl->ehufsi[htbl->huffval[p]] = huffsize[p]; |
| 69 | } |
| 70 | |
| 71 | /* Figure 13.4.2.3.1: generate decoding tables */ |
| 72 | |
| 73 | p = 0; |
| 74 | for (l = 1; l <= 16; l++) { |
| 75 | if (htbl->bits[l]) { |
| 76 | htbl->valptr[l] = p; /* huffval[] index of 1st sym of code len l */ |
| 77 | htbl->mincode[l] = huffcode[p]; /* minimum code of length l */ |
| 78 | p += htbl->bits[l]; |
| 79 | htbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */ |
| 80 | } else { |
| 81 | htbl->maxcode[l] = -1; |
| 82 | } |
| 83 | } |
| 84 | } |
| 85 | |
| 86 | |
| 87 | /* Outputting bytes to the file */ |
| 88 | |
| 89 | LOCAL void |
| 90 | flush_bytes (void) |
| 91 | { |
| 92 | if (bytes_in_buffer) |
| 93 | (*cinfo->methods->entropy_output) (cinfo, output_buffer, bytes_in_buffer); |
| 94 | bytes_in_buffer = 0; |
| 95 | } |
| 96 | |
| 97 | |
| 98 | #define emit_byte(val) ((bytes_in_buffer >= JPEG_BUF_SIZE ? \ |
| 99 | (flush_bytes(), 0) : 0), \ |
| 100 | output_buffer[bytes_in_buffer] = (val), \ |
| 101 | bytes_in_buffer++) |
| 102 | |
| 103 | |
| 104 | |
| 105 | /* Outputting bits to the file */ |
| 106 | |
| 107 | /* Only the right 24 bits of huff_put_buffer are used; the valid bits are |
| 108 | * left-justified in this part. At most 16 bits can be passed to emit_bits |
| 109 | * in one call, and we never retain more than 7 bits in huff_put_buffer |
| 110 | * between calls, so 24 bits are sufficient. |
| 111 | */ |
| 112 | |
| 113 | LOCAL void |
| 114 | emit_bits (UINT16 code, int size) |
| 115 | { |
| 116 | /* This routine is heavily used, so it's worth coding tightly. */ |
| 117 | register INT32 put_buffer = code; |
| 118 | register int put_bits = huff_put_bits; |
| 119 | |
| 120 | put_buffer &= (((INT32) 1) << size) - 1; /* Mask off any excess bits in code */ |
| 121 | |
| 122 | put_bits += size; /* new number of bits in buffer */ |
| 123 | |
| 124 | put_buffer <<= 24 - put_bits; /* align incoming bits */ |
| 125 | |
| 126 | put_buffer |= huff_put_buffer; /* and merge with old buffer contents */ |
| 127 | |
| 128 | while (put_bits >= 8) { |
| 129 | int c = (int) ((put_buffer >> 16) & 0xFF); |
| 130 | |
| 131 | emit_byte(c); |
| 132 | if (c == 0xFF) { /* need to stuff a zero byte? */ |
| 133 | emit_byte(0); |
| 134 | } |
| 135 | put_buffer <<= 8; |
| 136 | put_bits -= 8; |
| 137 | } |
| 138 | |
| 139 | huff_put_buffer = put_buffer; /* Update global variables */ |
| 140 | huff_put_bits = put_bits; |
| 141 | } |
| 142 | |
| 143 | |
| 144 | LOCAL void |
| 145 | flush_bits (void) |
| 146 | { |
| 147 | emit_bits((UINT16) 0x7F, 7); /* fill any partial byte with ones */ |
| 148 | huff_put_buffer = 0; /* and reset bit-buffer to empty */ |
| 149 | huff_put_bits = 0; |
| 150 | } |
| 151 | |
| 152 | |
| 153 | |
| 154 | /* Encode a single block's worth of coefficients */ |
| 155 | /* Note that the DC coefficient has already been converted to a difference */ |
| 156 | |
| 157 | LOCAL void |
| 158 | encode_one_block (JBLOCK block, HUFF_TBL *dctbl, HUFF_TBL *actbl) |
| 159 | { |
| 160 | register INT32 temp; |
| 161 | register int nbits; |
| 162 | register int k, r, i; |
| 163 | |
| 164 | /* Encode the DC coefficient difference per section 7.3.5.1 */ |
| 165 | |
| 166 | /* Find the number of bits needed for the magnitude of the coefficient */ |
| 167 | temp = block[0]; |
| 168 | if (temp < 0) temp = -temp; |
| 169 | |
| 170 | nbits = 0; |
| 171 | while (temp) { |
| 172 | nbits++; |
| 173 | temp >>= 1; |
| 174 | } |
| 175 | |
| 176 | /* Emit the Huffman-coded symbol for the number of bits */ |
| 177 | emit_bits(dctbl->ehufco[nbits], dctbl->ehufsi[nbits]); |
| 178 | |
| 179 | /* If positive, emit nbits low order bits; */ |
| 180 | /* if negative, emit nbits low order bits of value-1 */ |
| 181 | if ((temp = block[0]) < 0) |
| 182 | temp--; |
| 183 | |
| 184 | emit_bits((UINT16) temp, nbits); |
| 185 | |
| 186 | /* Encode the AC coefficients per section 7.3.5.2 */ |
| 187 | |
| 188 | r = 0; /* r = run length of zeros */ |
| 189 | |
| 190 | for (k = 1; k < DCTSIZE2; k++) { |
| 191 | if ((temp = block[k]) == 0) { |
| 192 | r++; |
| 193 | } else { |
| 194 | /* if run length > 15, must emit special run-length-16 codes (0xF0) */ |
| 195 | while (r > 15) { |
| 196 | emit_bits(actbl->ehufco[0xF0], actbl->ehufsi[0xF0]); |
| 197 | r -= 16; |
| 198 | } |
| 199 | |
| 200 | /* Find the number of bits needed for the magnitude of the coefficient */ |
| 201 | if (temp < 0) temp = -temp; |
| 202 | |
| 203 | nbits = 1; /* there must be at least one 1 bit */ |
| 204 | while (temp >>= 1) |
| 205 | nbits++; |
| 206 | |
| 207 | /* Emit Huffman symbol for run length / number of bits */ |
| 208 | i = (r << 4) + nbits; |
| 209 | emit_bits(actbl->ehufco[i], actbl->ehufsi[i]); |
| 210 | |
| 211 | /* If positive, emit nbits low order bits; */ |
| 212 | /* if negative, emit nbits low order bits of value-1 */ |
| 213 | if ((temp = block[k]) < 0) |
| 214 | temp--; |
| 215 | |
| 216 | emit_bits((UINT16) temp, nbits); |
| 217 | |
| 218 | r = 0; |
| 219 | } |
| 220 | } |
| 221 | |
| 222 | /* If the last coef(s) were zero, emit an end-of-block code */ |
| 223 | if (r > 0) |
| 224 | emit_bits(actbl->ehufco[0], actbl->ehufsi[0]); |
| 225 | } |
| 226 | |
| 227 | |
| 228 | |
| 229 | /* |
| 230 | * Initialize for a Huffman-compressed scan. |
| 231 | * This is invoked after writing the SOS marker. |
| 232 | * The pipeline controller must establish the entropy_output method pointer |
| 233 | * before calling this routine. |
| 234 | */ |
| 235 | |
| 236 | METHODDEF void |
| 237 | huff_init (compress_info_ptr xinfo) |
| 238 | { |
| 239 | short ci; |
| 240 | jpeg_component_info * compptr; |
| 241 | |
| 242 | /* Initialize static variables */ |
| 243 | cinfo = xinfo; |
| 244 | huff_put_buffer = 0; |
| 245 | huff_put_bits = 0; |
| 246 | |
| 247 | /* Initialize the output buffer */ |
| 248 | output_buffer = (char *) (*cinfo->emethods->alloc_small) |
| 249 | ((size_t) JPEG_BUF_SIZE); |
| 250 | bytes_in_buffer = 0; |
| 251 | |
| 252 | for (ci = 0; ci < cinfo->comps_in_scan; ci++) { |
| 253 | compptr = cinfo->cur_comp_info[ci]; |
| 254 | /* Make sure requested tables are present */ |
| 255 | if (cinfo->dc_huff_tbl_ptrs[compptr->dc_tbl_no] == NULL || |
| 256 | cinfo->ac_huff_tbl_ptrs[compptr->ac_tbl_no] == NULL) |
| 257 | ERREXIT(cinfo->emethods, "Use of undefined Huffman table"); |
| 258 | /* Compute derived values for Huffman tables */ |
| 259 | /* We may do this more than once for same table, but it's not a big deal */ |
| 260 | fix_huff_tbl(cinfo->dc_huff_tbl_ptrs[compptr->dc_tbl_no]); |
| 261 | fix_huff_tbl(cinfo->ac_huff_tbl_ptrs[compptr->ac_tbl_no]); |
| 262 | /* Initialize DC predictions to 0 */ |
| 263 | cinfo->last_dc_val[ci] = 0; |
| 264 | } |
| 265 | |
| 266 | /* Initialize restart stuff */ |
| 267 | cinfo->restarts_to_go = cinfo->restart_interval; |
| 268 | cinfo->next_restart_num = 0; |
| 269 | } |
| 270 | |
| 271 | |
| 272 | /* |
| 273 | * Emit a restart marker & resynchronize predictions. |
| 274 | */ |
| 275 | |
| 276 | LOCAL void |
| 277 | emit_restart (compress_info_ptr cinfo) |
| 278 | { |
| 279 | short ci; |
| 280 | |
| 281 | flush_bits(); |
| 282 | |
| 283 | emit_byte(0xFF); |
| 284 | emit_byte(RST0 + cinfo->next_restart_num); |
| 285 | |
| 286 | /* Re-initialize DC predictions to 0 */ |
| 287 | for (ci = 0; ci < cinfo->comps_in_scan; ci++) |
| 288 | cinfo->last_dc_val[ci] = 0; |
| 289 | |
| 290 | /* Update restart state */ |
| 291 | cinfo->restarts_to_go = cinfo->restart_interval; |
| 292 | cinfo->next_restart_num++; |
| 293 | cinfo->next_restart_num &= 7; |
| 294 | } |
| 295 | |
| 296 | |
| 297 | /* |
| 298 | * Encode and output one MCU's worth of Huffman-compressed coefficients. |
| 299 | */ |
| 300 | |
| 301 | METHODDEF void |
| 302 | huff_encode (compress_info_ptr cinfo, JBLOCK *MCU_data) |
| 303 | { |
| 304 | short blkn, ci; |
| 305 | jpeg_component_info * compptr; |
| 306 | JCOEF temp; |
| 307 | |
| 308 | /* Account for restart interval, emit restart marker if needed */ |
| 309 | if (cinfo->restart_interval) { |
| 310 | if (cinfo->restarts_to_go == 0) |
| 311 | emit_restart(cinfo); |
| 312 | cinfo->restarts_to_go--; |
| 313 | } |
| 314 | |
| 315 | for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { |
| 316 | ci = cinfo->MCU_membership[blkn]; |
| 317 | compptr = cinfo->cur_comp_info[ci]; |
| 318 | /* Convert DC value to difference, update last_dc_val */ |
| 319 | temp = MCU_data[blkn][0]; |
| 320 | MCU_data[blkn][0] -= cinfo->last_dc_val[ci]; |
| 321 | cinfo->last_dc_val[ci] = temp; |
| 322 | encode_one_block(MCU_data[blkn], |
| 323 | cinfo->dc_huff_tbl_ptrs[compptr->dc_tbl_no], |
| 324 | cinfo->ac_huff_tbl_ptrs[compptr->ac_tbl_no]); |
| 325 | } |
| 326 | } |
| 327 | |
| 328 | |
| 329 | /* |
| 330 | * Finish up at the end of a Huffman-compressed scan. |
| 331 | */ |
| 332 | |
| 333 | METHODDEF void |
| 334 | huff_term (compress_info_ptr cinfo) |
| 335 | { |
| 336 | /* Flush out the last data */ |
| 337 | flush_bits(); |
| 338 | flush_bytes(); |
| 339 | /* Release the I/O buffer */ |
| 340 | (*cinfo->emethods->free_small) ((void *) output_buffer); |
| 341 | } |
| 342 | |
| 343 | |
| 344 | |
| 345 | |
| 346 | /* |
| 347 | * Huffman coding optimization. |
| 348 | * |
| 349 | * This actually is optimization, in the sense that we find the best possible |
| 350 | * Huffman table(s) for the given data. We first scan the supplied data and |
| 351 | * count the number of uses of each symbol that is to be Huffman-coded. |
| 352 | * (This process must agree with the code above.) Then we build an |
| 353 | * optimal Huffman coding tree for the observed counts. |
| 354 | */ |
| 355 | |
| 356 | #ifdef ENTROPY_OPT_SUPPORTED |
| 357 | |
| 358 | |
| 359 | /* These are static so htest_one_block can find 'em */ |
| 360 | static long * dc_count_ptrs[NUM_HUFF_TBLS]; |
| 361 | static long * ac_count_ptrs[NUM_HUFF_TBLS]; |
| 362 | |
| 363 | |
| 364 | LOCAL void |
| 365 | gen_huff_coding (compress_info_ptr cinfo, HUFF_TBL *htbl, long freq[]) |
| 366 | /* Generate the optimal coding for the given counts */ |
| 367 | { |
| 368 | #define MAX_CLEN 32 /* assumed maximum initial code length */ |
| 369 | UINT8 bits[MAX_CLEN+1]; /* bits[k] = # of symbols with code length k */ |
| 370 | short codesize[257]; /* codesize[k] = code length of symbol k */ |
| 371 | short others[257]; /* next symbol in current branch of tree */ |
| 372 | int c1, c2; |
| 373 | int p, i, j; |
| 374 | long v; |
| 375 | |
| 376 | /* This algorithm is explained in section 13.2 of JPEG-8-R8 */ |
| 377 | |
| 378 | MEMZERO((void *) bits, SIZEOF(bits)); |
| 379 | MEMZERO((void *) codesize, SIZEOF(codesize)); |
| 380 | for (i = 0; i < 257; i++) |
| 381 | others[i] = -1; /* init links to empty */ |
| 382 | |
| 383 | freq[256] = 1; /* make sure there is a nonzero count */ |
| 384 | /* including the pseudo-symbol 256 in the Huffman procedure guarantees |
| 385 | * that no real symbol is given code-value of all ones, because 256 |
| 386 | * will be placed in the largest codeword category. |
| 387 | */ |
| 388 | |
| 389 | /* Huffman's basic algorithm to assign optimal code lengths to symbols */ |
| 390 | |
| 391 | for (;;) { |
| 392 | /* Find the smallest nonzero frequency, set c1 = its symbol */ |
| 393 | /* In case of ties, take the larger symbol number */ |
| 394 | c1 = -1; |
| 395 | v = 1000000000L; |
| 396 | for (i = 0; i <= 256; i++) { |
| 397 | if (freq[i] && freq[i] <= v) { |
| 398 | v = freq[i]; |
| 399 | c1 = i; |
| 400 | } |
| 401 | } |
| 402 | |
| 403 | /* Find the next smallest nonzero frequency, set c2 = its symbol */ |
| 404 | /* In case of ties, take the larger symbol number */ |
| 405 | c2 = -1; |
| 406 | v = 1000000000L; |
| 407 | for (i = 0; i <= 256; i++) { |
| 408 | if (freq[i] && freq[i] <= v && i != c1) { |
| 409 | v = freq[i]; |
| 410 | c2 = i; |
| 411 | } |
| 412 | } |
| 413 | |
| 414 | /* Done if we've merged everything into one frequency */ |
| 415 | if (c2 < 0) |
| 416 | break; |
| 417 | |
| 418 | /* Else merge the two counts/trees */ |
| 419 | freq[c1] += freq[c2]; |
| 420 | freq[c2] = 0; |
| 421 | |
| 422 | /* Increment the codesize of everything in c1's tree branch */ |
| 423 | codesize[c1]++; |
| 424 | while (others[c1] >= 0) { |
| 425 | c1 = others[c1]; |
| 426 | codesize[c1]++; |
| 427 | } |
| 428 | |
| 429 | others[c1] = c2; /* chain c2 onto c1's tree branch */ |
| 430 | |
| 431 | /* Increment the codesize of everything in c2's tree branch */ |
| 432 | codesize[c2]++; |
| 433 | while (others[c2] >= 0) { |
| 434 | c2 = others[c2]; |
| 435 | codesize[c2]++; |
| 436 | } |
| 437 | } |
| 438 | |
| 439 | /* Now count the number of symbols of each code length */ |
| 440 | for (i = 0; i <= 256; i++) { |
| 441 | if (codesize[i]) { |
| 442 | /* The JPEG standard seems to think that this can't happen, */ |
| 443 | /* but I'm paranoid... */ |
| 444 | if (codesize[i] > MAX_CLEN) |
| 445 | ERREXIT(cinfo->emethods, "Huffman code size table overflow"); |
| 446 | |
| 447 | bits[codesize[i]]++; |
| 448 | } |
| 449 | } |
| 450 | |
| 451 | /* JPEG doesn't allow symbols with code lengths over 16 bits, so if the pure |
| 452 | * Huffman procedure assigned any such lengths, we must adjust the coding. |
| 453 | * Here is what the JPEG spec says about how this next bit works: |
| 454 | * Since symbols are paired for the longest Huffman code, the symbols are |
| 455 | * removed from this length category two at a time. The prefix for the pair |
| 456 | * (which is one bit shorter) is allocated to one of the pair; then, |
| 457 | * skipping the BITS entry for that prefix length, a code word from the next |
| 458 | * shortest nonzero BITS entry is converted into a prefix for two code words |
| 459 | * one bit longer. |
| 460 | */ |
| 461 | |
| 462 | for (i = MAX_CLEN; i > 16; i--) { |
| 463 | while (bits[i] > 0) { |
| 464 | j = i - 2; /* find length of new prefix to be used */ |
| 465 | while (bits[j] == 0) |
| 466 | j--; |
| 467 | |
| 468 | bits[i] -= 2; /* remove two symbols */ |
| 469 | bits[i-1]++; /* one goes in this length */ |
| 470 | bits[j+1] += 2; /* two new symbols in this length */ |
| 471 | bits[j]--; /* symbol of this length is now a prefix */ |
| 472 | } |
| 473 | } |
| 474 | |
| 475 | /* Remove the count for the pseudo-symbol 256 from the largest codelength */ |
| 476 | while (bits[i] == 0) /* find largest codelength still in use */ |
| 477 | i--; |
| 478 | bits[i]--; |
| 479 | |
| 480 | /* Return final symbol counts (only for lengths 0..16) */ |
| 481 | memcpy((void *) htbl->bits, (void *) bits, SIZEOF(htbl->bits)); |
| 482 | |
| 483 | /* Return a list of the symbols sorted by code length */ |
| 484 | /* It's not real clear to me why we don't need to consider the codelength |
| 485 | * changes made above, but the JPEG spec seems to think this works. |
| 486 | */ |
| 487 | p = 0; |
| 488 | for (i = 1; i <= MAX_CLEN; i++) { |
| 489 | for (j = 0; j <= 255; j++) { |
| 490 | if (codesize[j] == i) { |
| 491 | htbl->huffval[p] = j; |
| 492 | p++; |
| 493 | } |
| 494 | } |
| 495 | } |
| 496 | } |
| 497 | |
| 498 | |
| 499 | /* Process a single block's worth of coefficients */ |
| 500 | /* Note that the DC coefficient has already been converted to a difference */ |
| 501 | |
| 502 | LOCAL void |
| 503 | htest_one_block (JBLOCK block, JCOEF block0, |
| 504 | long dc_counts[], long ac_counts[]) |
| 505 | { |
| 506 | register INT32 temp; |
| 507 | register int nbits; |
| 508 | register int k, r; |
| 509 | |
| 510 | /* Encode the DC coefficient difference per section 7.3.5.1 */ |
| 511 | |
| 512 | /* Find the number of bits needed for the magnitude of the coefficient */ |
| 513 | temp = block0; |
| 514 | if (temp < 0) temp = -temp; |
| 515 | |
| 516 | for (nbits = 0; temp; nbits++) |
| 517 | temp >>= 1; |
| 518 | |
| 519 | /* Count the Huffman symbol for the number of bits */ |
| 520 | dc_counts[nbits]++; |
| 521 | |
| 522 | /* Encode the AC coefficients per section 7.3.5.2 */ |
| 523 | |
| 524 | r = 0; /* r = run length of zeros */ |
| 525 | |
| 526 | for (k = 1; k < DCTSIZE2; k++) { |
| 527 | if ((temp = block[k]) == 0) { |
| 528 | r++; |
| 529 | } else { |
| 530 | /* if run length > 15, must emit special run-length-16 codes (0xF0) */ |
| 531 | while (r > 15) { |
| 532 | ac_counts[0xF0]++; |
| 533 | r -= 16; |
| 534 | } |
| 535 | |
| 536 | /* Find the number of bits needed for the magnitude of the coefficient */ |
| 537 | if (temp < 0) temp = -temp; |
| 538 | |
| 539 | for (nbits = 0; temp; nbits++) |
| 540 | temp >>= 1; |
| 541 | |
| 542 | /* Count Huffman symbol for run length / number of bits */ |
| 543 | ac_counts[(r << 4) + nbits]++; |
| 544 | |
| 545 | r = 0; |
| 546 | } |
| 547 | } |
| 548 | |
| 549 | /* If the last coef(s) were zero, emit an end-of-block code */ |
| 550 | if (r > 0) |
| 551 | ac_counts[0]++; |
| 552 | } |
| 553 | |
| 554 | |
| 555 | |
| 556 | /* |
| 557 | * Trial-encode one MCU's worth of Huffman-compressed coefficients. |
| 558 | */ |
| 559 | |
| 560 | LOCAL void |
| 561 | htest_encode (compress_info_ptr cinfo, JBLOCK *MCU_data) |
| 562 | { |
| 563 | short blkn, ci; |
| 564 | jpeg_component_info * compptr; |
| 565 | |
| 566 | /* Take care of restart intervals if needed */ |
| 567 | if (cinfo->restart_interval) { |
| 568 | if (cinfo->restarts_to_go == 0) { |
| 569 | /* Re-initialize DC predictions to 0 */ |
| 570 | for (ci = 0; ci < cinfo->comps_in_scan; ci++) |
| 571 | cinfo->last_dc_val[ci] = 0; |
| 572 | /* Update restart state */ |
| 573 | cinfo->restarts_to_go = cinfo->restart_interval; |
| 574 | } |
| 575 | cinfo->restarts_to_go--; |
| 576 | } |
| 577 | |
| 578 | for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { |
| 579 | ci = cinfo->MCU_membership[blkn]; |
| 580 | compptr = cinfo->cur_comp_info[ci]; |
| 581 | /* NB: unlike the real entropy encoder, we may not change the input data */ |
| 582 | htest_one_block(MCU_data[blkn], |
| 583 | (JCOEF) (MCU_data[blkn][0] - cinfo->last_dc_val[ci]), |
| 584 | dc_count_ptrs[compptr->dc_tbl_no], |
| 585 | ac_count_ptrs[compptr->ac_tbl_no]); |
| 586 | cinfo->last_dc_val[ci] = MCU_data[blkn][0]; |
| 587 | } |
| 588 | } |
| 589 | |
| 590 | |
| 591 | |
| 592 | /* |
| 593 | * Find the best coding parameters for a Huffman-coded scan. |
| 594 | * When called, the scan data has already been converted to a sequence of |
| 595 | * MCU groups of quantized coefficients, which are stored in a "big" array. |
| 596 | * The source_method knows how to iterate through that array. |
| 597 | * On return, the MCU data is unmodified, but the Huffman tables referenced |
| 598 | * by the scan components may have been altered. |
| 599 | */ |
| 600 | |
| 601 | METHODDEF void |
| 602 | huff_optimize (compress_info_ptr cinfo, MCU_output_caller_ptr source_method) |
| 603 | /* Optimize Huffman-coding parameters (Huffman symbol table) */ |
| 604 | { |
| 605 | int i, tbl; |
| 606 | HUFF_TBL **htblptr; |
| 607 | |
| 608 | /* Allocate and zero the count tables */ |
| 609 | /* Note that gen_huff_coding expects 257 entries in each table! */ |
| 610 | |
| 611 | for (i = 0; i < NUM_HUFF_TBLS; i++) { |
| 612 | dc_count_ptrs[i] = NULL; |
| 613 | ac_count_ptrs[i] = NULL; |
| 614 | } |
| 615 | |
| 616 | for (i = 0; i < cinfo->comps_in_scan; i++) { |
| 617 | /* Create DC table */ |
| 618 | tbl = cinfo->cur_comp_info[i]->dc_tbl_no; |
| 619 | if (dc_count_ptrs[tbl] == NULL) { |
| 620 | dc_count_ptrs[tbl] = (long *) (*cinfo->emethods->alloc_small) |
| 621 | (257 * SIZEOF(long)); |
| 622 | MEMZERO((void *) dc_count_ptrs[tbl], 257 * SIZEOF(long)); |
| 623 | } |
| 624 | /* Create AC table */ |
| 625 | tbl = cinfo->cur_comp_info[i]->ac_tbl_no; |
| 626 | if (ac_count_ptrs[tbl] == NULL) { |
| 627 | ac_count_ptrs[tbl] = (long *) (*cinfo->emethods->alloc_small) |
| 628 | (257 * SIZEOF(long)); |
| 629 | MEMZERO((void *) ac_count_ptrs[tbl], 257 * SIZEOF(long)); |
| 630 | } |
| 631 | } |
| 632 | |
| 633 | /* Initialize DC predictions to 0 */ |
| 634 | for (i = 0; i < cinfo->comps_in_scan; i++) { |
| 635 | cinfo->last_dc_val[i] = 0; |
| 636 | } |
| 637 | /* Initialize restart stuff */ |
| 638 | cinfo->restarts_to_go = cinfo->restart_interval; |
| 639 | |
| 640 | /* Scan the MCU data, count symbol uses */ |
| 641 | (*source_method) (cinfo, htest_encode); |
| 642 | |
| 643 | /* Now generate optimal Huffman tables */ |
| 644 | for (tbl = 0; tbl < NUM_HUFF_TBLS; tbl++) { |
| 645 | if (dc_count_ptrs[tbl] != NULL) { |
| 646 | htblptr = & cinfo->dc_huff_tbl_ptrs[tbl]; |
| 647 | if (*htblptr == NULL) |
| 648 | *htblptr = (*cinfo->emethods->alloc_small) (SIZEOF(HUFF_TBL)); |
| 649 | /* Set sent_table FALSE so updated table will be written to JPEG file. */ |
| 650 | (*htblptr)->sent_table = FALSE; |
| 651 | /* Compute the optimal Huffman encoding */ |
| 652 | gen_huff_coding(cinfo, *htblptr, dc_count_ptrs[tbl]); |
| 653 | /* Release the count table */ |
| 654 | (*cinfo->emethods->free_small) ((void *) dc_count_ptrs[tbl]); |
| 655 | } |
| 656 | if (ac_count_ptrs[tbl] != NULL) { |
| 657 | htblptr = & cinfo->ac_huff_tbl_ptrs[tbl]; |
| 658 | if (*htblptr == NULL) |
| 659 | *htblptr = (*cinfo->emethods->alloc_small) (SIZEOF(HUFF_TBL)); |
| 660 | /* Set sent_table FALSE so updated table will be written to JPEG file. */ |
| 661 | (*htblptr)->sent_table = FALSE; |
| 662 | /* Compute the optimal Huffman encoding */ |
| 663 | gen_huff_coding(cinfo, *htblptr, ac_count_ptrs[tbl]); |
| 664 | /* Release the count table */ |
| 665 | (*cinfo->emethods->free_small) ((void *) ac_count_ptrs[tbl]); |
| 666 | } |
| 667 | } |
| 668 | } |
| 669 | |
| 670 | |
| 671 | #endif /* ENTROPY_OPT_SUPPORTED */ |
| 672 | |
| 673 | |
| 674 | /* |
| 675 | * The method selection routine for Huffman entropy encoding. |
| 676 | */ |
| 677 | |
| 678 | GLOBAL void |
| 679 | jselchuffman (compress_info_ptr cinfo) |
| 680 | { |
| 681 | if (! cinfo->arith_code) { |
| 682 | cinfo->methods->entropy_encoder_init = huff_init; |
| 683 | cinfo->methods->entropy_encode = huff_encode; |
| 684 | cinfo->methods->entropy_encoder_term = huff_term; |
| 685 | #ifdef ENTROPY_OPT_SUPPORTED |
| 686 | cinfo->methods->entropy_optimize = huff_optimize; |
| 687 | #endif |
| 688 | } |
| 689 | } |