jdhuff.cpp (17556B)
1 /* 2 * jdhuff.c 3 * 4 * Copyright (C) 1991-1995, 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 decoding routines. 9 * 10 * Much of the complexity here has to do with supporting input suspension. 11 * If the data source module demands suspension, we want to be able to back 12 * up to the start of the current MCU. To do this, we copy state variables 13 * into local working storage, and update them back to the permanent 14 * storage only upon successful completion of an MCU. 15 */ 16 17 #define JPEG_INTERNALS 18 #include "jinclude.h" 19 #include "jpeglib.h" 20 #include "jdhuff.h" /* Declarations shared with jdphuff.c */ 21 22 23 /* 24 * Expanded entropy decoder object for Huffman decoding. 25 * 26 * The savable_state subrecord contains fields that change within an MCU, 27 * but must not be updated permanently until we complete the MCU. 28 */ 29 30 typedef struct { 31 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */ 32 } savable_state; 33 34 /* This macro is to work around compilers with missing or broken 35 * structure assignment. You'll need to fix this code if you have 36 * such a compiler and you change MAX_COMPS_IN_SCAN. 37 */ 38 39 #ifndef NO_STRUCT_ASSIGN 40 #define ASSIGN_STATE(dest,src) ((dest) = (src)) 41 #else 42 #if MAX_COMPS_IN_SCAN == 4 43 #define ASSIGN_STATE(dest,src) \ 44 ((dest).last_dc_val[0] = (src).last_dc_val[0], \ 45 (dest).last_dc_val[1] = (src).last_dc_val[1], \ 46 (dest).last_dc_val[2] = (src).last_dc_val[2], \ 47 (dest).last_dc_val[3] = (src).last_dc_val[3]) 48 #endif 49 #endif 50 51 52 typedef struct { 53 struct jpeg_entropy_decoder pub; /* public fields */ 54 55 /* These fields are loaded into local variables at start of each MCU. 56 * In case of suspension, we exit WITHOUT updating them. 57 */ 58 bitread_perm_state bitstate; /* Bit buffer at start of MCU */ 59 savable_state saved; /* Other state at start of MCU */ 60 61 /* These fields are NOT loaded into local working state. */ 62 unsigned int restarts_to_go; /* MCUs left in this restart interval */ 63 64 /* Pointers to derived tables (these workspaces have image lifespan) */ 65 d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS]; 66 d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS]; 67 } huff_entropy_decoder; 68 69 typedef huff_entropy_decoder * huff_entropy_ptr; 70 71 72 /* 73 * Initialize for a Huffman-compressed scan. 74 */ 75 76 METHODDEF void 77 start_pass_huff_decoder (j_decompress_ptr cinfo) 78 { 79 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 80 int ci, dctbl, actbl; 81 jpeg_component_info * compptr; 82 83 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG. 84 * This ought to be an error condition, but we make it a warning because 85 * there are some baseline files out there with all zeroes in these bytes. 86 */ 87 if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 || 88 cinfo->Ah != 0 || cinfo->Al != 0) 89 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL); 90 91 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 92 compptr = cinfo->cur_comp_info[ci]; 93 dctbl = compptr->dc_tbl_no; 94 actbl = compptr->ac_tbl_no; 95 /* Make sure requested tables are present */ 96 if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS || 97 cinfo->dc_huff_tbl_ptrs[dctbl] == NULL) 98 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl); 99 if (actbl < 0 || actbl >= NUM_HUFF_TBLS || 100 cinfo->ac_huff_tbl_ptrs[actbl] == NULL) 101 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl); 102 /* Compute derived values for Huffman tables */ 103 /* We may do this more than once for a table, but it's not expensive */ 104 jpeg_make_d_derived_tbl(cinfo, cinfo->dc_huff_tbl_ptrs[dctbl], 105 & entropy->dc_derived_tbls[dctbl]); 106 jpeg_make_d_derived_tbl(cinfo, cinfo->ac_huff_tbl_ptrs[actbl], 107 & entropy->ac_derived_tbls[actbl]); 108 /* Initialize DC predictions to 0 */ 109 entropy->saved.last_dc_val[ci] = 0; 110 } 111 112 /* Initialize bitread state variables */ 113 entropy->bitstate.bits_left = 0; 114 entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */ 115 entropy->bitstate.printed_eod = FALSE; 116 117 /* Initialize restart counter */ 118 entropy->restarts_to_go = cinfo->restart_interval; 119 } 120 121 122 /* 123 * Compute the derived values for a Huffman table. 124 * Note this is also used by jdphuff.c. 125 */ 126 127 GLOBAL void 128 jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, JHUFF_TBL * htbl, 129 d_derived_tbl ** pdtbl) 130 { 131 d_derived_tbl *dtbl; 132 int p, i, l, si; 133 int lookbits, ctr; 134 char huffsize[257]; 135 unsigned int huffcode[257]; 136 unsigned int code; 137 138 /* Allocate a workspace if we haven't already done so. */ 139 if (*pdtbl == NULL) 140 *pdtbl = (d_derived_tbl *) 141 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 142 SIZEOF(d_derived_tbl)); 143 dtbl = *pdtbl; 144 dtbl->pub = htbl; /* fill in back link */ 145 146 /* Figure C.1: make table of Huffman code length for each symbol */ 147 /* Note that this is in code-length order. */ 148 149 p = 0; 150 for (l = 1; l <= 16; l++) { 151 for (i = 1; i <= (int) htbl->bits[l]; i++) 152 huffsize[p++] = (char) l; 153 } 154 huffsize[p] = 0; 155 156 /* Figure C.2: generate the codes themselves */ 157 /* Note that this is in code-length order. */ 158 159 code = 0; 160 si = huffsize[0]; 161 p = 0; 162 while (huffsize[p]) { 163 while (((int) huffsize[p]) == si) { 164 huffcode[p++] = code; 165 code++; 166 } 167 code <<= 1; 168 si++; 169 } 170 171 /* Figure F.15: generate decoding tables for bit-sequential decoding */ 172 173 p = 0; 174 for (l = 1; l <= 16; l++) { 175 if (htbl->bits[l]) { 176 dtbl->valptr[l] = p; /* huffval[] index of 1st symbol of code length l */ 177 dtbl->mincode[l] = huffcode[p]; /* minimum code of length l */ 178 p += htbl->bits[l]; 179 dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */ 180 } else { 181 dtbl->maxcode[l] = -1; /* -1 if no codes of this length */ 182 } 183 } 184 dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */ 185 186 /* Compute lookahead tables to speed up decoding. 187 * First we set all the table entries to 0, indicating "too long"; 188 * then we iterate through the Huffman codes that are short enough and 189 * fill in all the entries that correspond to bit sequences starting 190 * with that code. 191 */ 192 193 MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits)); 194 195 p = 0; 196 for (l = 1; l <= HUFF_LOOKAHEAD; l++) { 197 for (i = 1; i <= (int) htbl->bits[l]; i++, p++) { 198 /* l = current code's length, p = its index in huffcode[] & huffval[]. */ 199 /* Generate left-justified code followed by all possible bit sequences */ 200 lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l); 201 for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) { 202 dtbl->look_nbits[lookbits] = l; 203 dtbl->look_sym[lookbits] = htbl->huffval[p]; 204 lookbits++; 205 } 206 } 207 } 208 } 209 210 211 /* 212 * Out-of-line code for bit fetching (shared with jdphuff.c). 213 * See jdhuff.h for info about usage. 214 * Note: current values of get_buffer and bits_left are passed as parameters, 215 * but are returned in the corresponding fields of the state struct. 216 * 217 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width 218 * of get_buffer to be used. (On machines with wider words, an even larger 219 * buffer could be used.) However, on some machines 32-bit shifts are 220 * quite slow and take time proportional to the number of places shifted. 221 * (This is true with most PC compilers, for instance.) In this case it may 222 * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the 223 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer. 224 */ 225 226 #ifdef SLOW_SHIFT_32 227 #define MIN_GET_BITS 15 /* minimum allowable value */ 228 #else 229 #define MIN_GET_BITS (BIT_BUF_SIZE-7) 230 #endif 231 232 233 GLOBAL boolean 234 jpeg_fill_bit_buffer (bitread_working_state * state, 235 register bit_buf_type get_buffer, register int bits_left, 236 int nbits) 237 /* Load up the bit buffer to a depth of at least nbits */ 238 { 239 /* Copy heavily used state fields into locals (hopefully registers) */ 240 register const JOCTET * next_input_byte = state->next_input_byte; 241 register size_t bytes_in_buffer = state->bytes_in_buffer; 242 register int c; 243 244 /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */ 245 /* (It is assumed that no request will be for more than that many bits.) */ 246 247 while (bits_left < MIN_GET_BITS) { 248 /* Attempt to read a byte */ 249 if (state->unread_marker != 0) 250 goto no_more_data; /* can't advance past a marker */ 251 252 if (bytes_in_buffer == 0) { 253 if (! (*state->cinfo->src->fill_input_buffer) (state->cinfo)) 254 return FALSE; 255 next_input_byte = state->cinfo->src->next_input_byte; 256 bytes_in_buffer = state->cinfo->src->bytes_in_buffer; 257 } 258 bytes_in_buffer--; 259 c = GETJOCTET(*next_input_byte++); 260 261 /* If it's 0xFF, check and discard stuffed zero byte */ 262 if (c == 0xFF) { 263 do { 264 if (bytes_in_buffer == 0) { 265 if (! (*state->cinfo->src->fill_input_buffer) (state->cinfo)) 266 return FALSE; 267 next_input_byte = state->cinfo->src->next_input_byte; 268 bytes_in_buffer = state->cinfo->src->bytes_in_buffer; 269 } 270 bytes_in_buffer--; 271 c = GETJOCTET(*next_input_byte++); 272 } while (c == 0xFF); 273 274 if (c == 0) { 275 /* Found FF/00, which represents an FF data byte */ 276 c = 0xFF; 277 } else { 278 /* Oops, it's actually a marker indicating end of compressed data. */ 279 /* Better put it back for use later */ 280 state->unread_marker = c; 281 282 no_more_data: 283 /* There should be enough bits still left in the data segment; */ 284 /* if so, just break out of the outer while loop. */ 285 if (bits_left >= nbits) 286 break; 287 /* Uh-oh. Report corrupted data to user and stuff zeroes into 288 * the data stream, so that we can produce some kind of image. 289 * Note that this code will be repeated for each byte demanded 290 * for the rest of the segment. We use a nonvolatile flag to ensure 291 * that only one warning message appears. 292 */ 293 if (! *(state->printed_eod_ptr)) { 294 WARNMS(state->cinfo, JWRN_HIT_MARKER); 295 *(state->printed_eod_ptr) = TRUE; 296 } 297 c = 0; /* insert a zero byte into bit buffer */ 298 } 299 } 300 301 /* OK, load c into get_buffer */ 302 get_buffer = (get_buffer << 8) | c; 303 bits_left += 8; 304 } 305 306 /* Unload the local registers */ 307 state->next_input_byte = next_input_byte; 308 state->bytes_in_buffer = bytes_in_buffer; 309 state->get_buffer = get_buffer; 310 state->bits_left = bits_left; 311 312 return TRUE; 313 } 314 315 316 /* 317 * Out-of-line code for Huffman code decoding. 318 * See jdhuff.h for info about usage. 319 */ 320 321 GLOBAL int 322 jpeg_huff_decode (bitread_working_state * state, 323 register bit_buf_type get_buffer, register int bits_left, 324 d_derived_tbl * htbl, int min_bits) 325 { 326 register int l = min_bits; 327 register INT32 code; 328 329 /* HUFF_DECODE has determined that the code is at least min_bits */ 330 /* bits long, so fetch that many bits in one swoop. */ 331 332 CHECK_BIT_BUFFER(*state, l, return -1); 333 code = GET_BITS(l); 334 335 /* Collect the rest of the Huffman code one bit at a time. */ 336 /* This is per Figure F.16 in the JPEG spec. */ 337 338 while (code > htbl->maxcode[l]) { 339 code <<= 1; 340 CHECK_BIT_BUFFER(*state, 1, return -1); 341 code |= GET_BITS(1); 342 l++; 343 } 344 345 /* Unload the local registers */ 346 state->get_buffer = get_buffer; 347 state->bits_left = bits_left; 348 349 /* With garbage input we may reach the sentinel value l = 17. */ 350 351 if (l > 16) { 352 WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE); 353 return 0; /* fake a zero as the safest result */ 354 } 355 356 return htbl->pub->huffval[ htbl->valptr[l] + 357 ((int) (code - htbl->mincode[l])) ]; 358 } 359 360 361 /* 362 * Figure F.12: extend sign bit. 363 * On some machines, a shift and add will be faster than a table lookup. 364 */ 365 366 #ifdef AVOID_TABLES 367 368 #define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x)) 369 370 #else 371 372 #define HUFF_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x)) 373 374 static const int extend_test[16] = /* entry n is 2**(n-1) */ 375 { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080, 376 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 }; 377 378 static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */ 379 { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1, 380 ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1, 381 ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1, 382 ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 }; 383 384 #endif /* AVOID_TABLES */ 385 386 387 /* 388 * Check for a restart marker & resynchronize decoder. 389 * Returns FALSE if must suspend. 390 */ 391 392 LOCAL boolean 393 process_restart (j_decompress_ptr cinfo) 394 { 395 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 396 int ci; 397 398 /* Throw away any unused bits remaining in bit buffer; */ 399 /* include any full bytes in next_marker's count of discarded bytes */ 400 cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8; 401 entropy->bitstate.bits_left = 0; 402 403 /* Advance past the RSTn marker */ 404 if (! (*cinfo->marker->read_restart_marker) (cinfo)) 405 return FALSE; 406 407 /* Re-initialize DC predictions to 0 */ 408 for (ci = 0; ci < cinfo->comps_in_scan; ci++) 409 entropy->saved.last_dc_val[ci] = 0; 410 411 /* Reset restart counter */ 412 entropy->restarts_to_go = cinfo->restart_interval; 413 414 /* Next segment can get another out-of-data warning */ 415 entropy->bitstate.printed_eod = FALSE; 416 417 return TRUE; 418 } 419 420 421 /* 422 * Decode and return one MCU's worth of Huffman-compressed coefficients. 423 * The coefficients are reordered from zigzag order into natural array order, 424 * but are not dequantized. 425 * 426 * The i'th block of the MCU is stored into the block pointed to by 427 * MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER. 428 * (Wholesale zeroing is usually a little faster than retail...) 429 * 430 * Returns FALSE if data source requested suspension. In that case no 431 * changes have been made to permanent state. (Exception: some output 432 * coefficients may already have been assigned. This is harmless for 433 * this module, since we'll just re-assign them on the next call.) 434 */ 435 436 METHODDEF boolean 437 decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 438 { 439 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 440 register int s, k, r; 441 int blkn, ci; 442 JBLOCKROW block; 443 BITREAD_STATE_VARS; 444 savable_state state; 445 d_derived_tbl * dctbl; 446 d_derived_tbl * actbl; 447 jpeg_component_info * compptr; 448 449 /* Process restart marker if needed; may have to suspend */ 450 if (cinfo->restart_interval) { 451 if (entropy->restarts_to_go == 0) 452 if (! process_restart(cinfo)) 453 return FALSE; 454 } 455 456 /* Load up working state */ 457 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 458 ASSIGN_STATE(state, entropy->saved); 459 460 /* Outer loop handles each block in the MCU */ 461 462 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 463 block = MCU_data[blkn]; 464 ci = cinfo->MCU_membership[blkn]; 465 compptr = cinfo->cur_comp_info[ci]; 466 dctbl = entropy->dc_derived_tbls[compptr->dc_tbl_no]; 467 actbl = entropy->ac_derived_tbls[compptr->ac_tbl_no]; 468 469 /* Decode a single block's worth of coefficients */ 470 471 /* Section F.2.2.1: decode the DC coefficient difference */ 472 HUFF_DECODE(s, br_state, dctbl, return FALSE, label1); 473 if (s) { 474 CHECK_BIT_BUFFER(br_state, s, return FALSE); 475 r = GET_BITS(s); 476 s = HUFF_EXTEND(r, s); 477 } 478 479 /* Shortcut if component's values are not interesting */ 480 if (! compptr->component_needed) 481 goto skip_ACs; 482 483 /* Convert DC difference to actual value, update last_dc_val */ 484 s += state.last_dc_val[ci]; 485 state.last_dc_val[ci] = s; 486 /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */ 487 (*block)[0] = (JCOEF) s; 488 489 /* Do we need to decode the AC coefficients for this component? */ 490 if (compptr->DCT_scaled_size > 1) { 491 492 /* Section F.2.2.2: decode the AC coefficients */ 493 /* Since zeroes are skipped, output area must be cleared beforehand */ 494 for (k = 1; k < DCTSIZE2; k++) { 495 HUFF_DECODE(s, br_state, actbl, return FALSE, label2); 496 497 r = s >> 4; 498 s &= 15; 499 500 if (s) { 501 k += r; 502 CHECK_BIT_BUFFER(br_state, s, return FALSE); 503 r = GET_BITS(s); 504 s = HUFF_EXTEND(r, s); 505 /* Output coefficient in natural (dezigzagged) order. 506 * Note: the extra entries in jpeg_natural_order[] will save us 507 * if k >= DCTSIZE2, which could happen if the data is corrupted. 508 */ 509 (*block)[jpeg_natural_order[k]] = (JCOEF) s; 510 } else { 511 if (r != 15) 512 break; 513 k += 15; 514 } 515 } 516 517 } else { 518 skip_ACs: 519 520 /* Section F.2.2.2: decode the AC coefficients */ 521 /* In this path we just discard the values */ 522 for (k = 1; k < DCTSIZE2; k++) { 523 HUFF_DECODE(s, br_state, actbl, return FALSE, label3); 524 525 r = s >> 4; 526 s &= 15; 527 528 if (s) { 529 k += r; 530 CHECK_BIT_BUFFER(br_state, s, return FALSE); 531 DROP_BITS(s); 532 } else { 533 if (r != 15) 534 break; 535 k += 15; 536 } 537 } 538 539 } 540 } 541 542 /* Completed MCU, so update state */ 543 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 544 ASSIGN_STATE(entropy->saved, state); 545 546 /* Account for restart interval (no-op if not using restarts) */ 547 entropy->restarts_to_go--; 548 549 return TRUE; 550 } 551 552 553 /* 554 * Module initialization routine for Huffman entropy decoding. 555 */ 556 557 GLOBAL void 558 jinit_huff_decoder (j_decompress_ptr cinfo) 559 { 560 huff_entropy_ptr entropy; 561 int i; 562 563 entropy = (huff_entropy_ptr) 564 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 565 SIZEOF(huff_entropy_decoder)); 566 cinfo->entropy = (struct jpeg_entropy_decoder *) entropy; 567 entropy->pub.start_pass = start_pass_huff_decoder; 568 entropy->pub.decode_mcu = decode_mcu; 569 570 /* Mark tables unallocated */ 571 for (i = 0; i < NUM_HUFF_TBLS; i++) { 572 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL; 573 } 574 }