1 /* 2 * jdhuff.c 3 * 4 * This file was part of the Independent JPEG Group's software: 5 * Copyright (C) 1991-1997, Thomas G. Lane. 6 * libjpeg-turbo Modifications: 7 * Copyright (C) 2009-2011, D. R. Commander. 8 * For conditions of distribution and use, see the accompanying README file. 9 * 10 * This file contains Huffman entropy decoding routines. 11 * 12 * Much of the complexity here has to do with supporting input suspension. 13 * If the data source module demands suspension, we want to be able to back 14 * up to the start of the current MCU. To do this, we copy state variables 15 * into local working storage, and update them back to the permanent 16 * storage only upon successful completion of an MCU. 17 */ 18 19 #define JPEG_INTERNALS 20 #include "jinclude.h" 21 #include "jpeglib.h" 22 #include "jdhuff.h" /* Declarations shared with jdphuff.c */ 23 #include "jpegcomp.h" 24 25 26 /* 27 * Expanded entropy decoder object for Huffman decoding. 28 * 29 * The savable_state subrecord contains fields that change within an MCU, 30 * but must not be updated permanently until we complete the MCU. 31 */ 32 33 typedef struct { 34 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */ 35 } savable_state; 36 37 /* This macro is to work around compilers with missing or broken 38 * structure assignment. You'll need to fix this code if you have 39 * such a compiler and you change MAX_COMPS_IN_SCAN. 40 */ 41 42 #ifndef NO_STRUCT_ASSIGN 43 #define ASSIGN_STATE(dest,src) ((dest) = (src)) 44 #else 45 #if MAX_COMPS_IN_SCAN == 4 46 #define ASSIGN_STATE(dest,src) \ 47 ((dest).last_dc_val[0] = (src).last_dc_val[0], \ 48 (dest).last_dc_val[1] = (src).last_dc_val[1], \ 49 (dest).last_dc_val[2] = (src).last_dc_val[2], \ 50 (dest).last_dc_val[3] = (src).last_dc_val[3]) 51 #endif 52 #endif 53 54 55 typedef struct { 56 struct jpeg_entropy_decoder pub; /* public fields */ 57 58 /* These fields are loaded into local variables at start of each MCU. 59 * In case of suspension, we exit WITHOUT updating them. 60 */ 61 bitread_perm_state bitstate; /* Bit buffer at start of MCU */ 62 savable_state saved; /* Other state at start of MCU */ 63 64 /* These fields are NOT loaded into local working state. */ 65 unsigned int restarts_to_go; /* MCUs left in this restart interval */ 66 67 /* Pointers to derived tables (these workspaces have image lifespan) */ 68 d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS]; 69 d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS]; 70 71 /* Precalculated info set up by start_pass for use in decode_mcu: */ 72 73 /* Pointers to derived tables to be used for each block within an MCU */ 74 d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU]; 75 d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU]; 76 /* Whether we care about the DC and AC coefficient values for each block */ 77 boolean dc_needed[D_MAX_BLOCKS_IN_MCU]; 78 boolean ac_needed[D_MAX_BLOCKS_IN_MCU]; 79 } huff_entropy_decoder; 80 81 typedef huff_entropy_decoder * huff_entropy_ptr; 82 83 84 /* 85 * Initialize for a Huffman-compressed scan. 86 */ 87 88 METHODDEF(void) 89 start_pass_huff_decoder (j_decompress_ptr cinfo) 90 { 91 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 92 int ci, blkn, dctbl, actbl; 93 jpeg_component_info * compptr; 94 95 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG. 96 * This ought to be an error condition, but we make it a warning because 97 * there are some baseline files out there with all zeroes in these bytes. 98 */ 99 if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 || 100 cinfo->Ah != 0 || cinfo->Al != 0) 101 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL); 102 103 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 104 compptr = cinfo->cur_comp_info[ci]; 105 dctbl = compptr->dc_tbl_no; 106 actbl = compptr->ac_tbl_no; 107 /* Compute derived values for Huffman tables */ 108 /* We may do this more than once for a table, but it's not expensive */ 109 jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl, 110 & entropy->dc_derived_tbls[dctbl]); 111 jpeg_make_d_derived_tbl(cinfo, FALSE, actbl, 112 & entropy->ac_derived_tbls[actbl]); 113 /* Initialize DC predictions to 0 */ 114 entropy->saved.last_dc_val[ci] = 0; 115 } 116 117 /* Precalculate decoding info for each block in an MCU of this scan */ 118 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 119 ci = cinfo->MCU_membership[blkn]; 120 compptr = cinfo->cur_comp_info[ci]; 121 /* Precalculate which table to use for each block */ 122 entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no]; 123 entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no]; 124 /* Decide whether we really care about the coefficient values */ 125 if (compptr->component_needed) { 126 entropy->dc_needed[blkn] = TRUE; 127 /* we don't need the ACs if producing a 1/8th-size image */ 128 entropy->ac_needed[blkn] = (compptr->_DCT_scaled_size > 1); 129 } else { 130 entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE; 131 } 132 } 133 134 /* Initialize bitread state variables */ 135 entropy->bitstate.bits_left = 0; 136 entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */ 137 entropy->pub.insufficient_data = FALSE; 138 139 /* Initialize restart counter */ 140 entropy->restarts_to_go = cinfo->restart_interval; 141 } 142 143 144 /* 145 * Compute the derived values for a Huffman table. 146 * This routine also performs some validation checks on the table. 147 * 148 * Note this is also used by jdphuff.c. 149 */ 150 151 GLOBAL(void) 152 jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno, 153 d_derived_tbl ** pdtbl) 154 { 155 JHUFF_TBL *htbl; 156 d_derived_tbl *dtbl; 157 int p, i, l, si, numsymbols; 158 int lookbits, ctr; 159 char huffsize[257]; 160 unsigned int huffcode[257]; 161 unsigned int code; 162 163 /* Note that huffsize[] and huffcode[] are filled in code-length order, 164 * paralleling the order of the symbols themselves in htbl->huffval[]. 165 */ 166 167 /* Find the input Huffman table */ 168 if (tblno < 0 || tblno >= NUM_HUFF_TBLS) 169 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno); 170 htbl = 171 isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno]; 172 if (htbl == NULL) 173 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno); 174 175 /* Allocate a workspace if we haven't already done so. */ 176 if (*pdtbl == NULL) 177 *pdtbl = (d_derived_tbl *) 178 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 179 SIZEOF(d_derived_tbl)); 180 dtbl = *pdtbl; 181 dtbl->pub = htbl; /* fill in back link */ 182 183 /* Figure C.1: make table of Huffman code length for each symbol */ 184 185 p = 0; 186 for (l = 1; l <= 16; l++) { 187 i = (int) htbl->bits[l]; 188 if (i < 0 || p + i > 256) /* protect against table overrun */ 189 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 190 while (i--) 191 huffsize[p++] = (char) l; 192 } 193 huffsize[p] = 0; 194 numsymbols = p; 195 196 /* Figure C.2: generate the codes themselves */ 197 /* We also validate that the counts represent a legal Huffman code tree. */ 198 199 code = 0; 200 si = huffsize[0]; 201 p = 0; 202 while (huffsize[p]) { 203 while (((int) huffsize[p]) == si) { 204 huffcode[p++] = code; 205 code++; 206 } 207 /* code is now 1 more than the last code used for codelength si; but 208 * it must still fit in si bits, since no code is allowed to be all ones. 209 */ 210 if (((INT32) code) >= (((INT32) 1) << si)) 211 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 212 code <<= 1; 213 si++; 214 } 215 216 /* Figure F.15: generate decoding tables for bit-sequential decoding */ 217 218 p = 0; 219 for (l = 1; l <= 16; l++) { 220 if (htbl->bits[l]) { 221 /* valoffset[l] = huffval[] index of 1st symbol of code length l, 222 * minus the minimum code of length l 223 */ 224 dtbl->valoffset[l] = (INT32) p - (INT32) huffcode[p]; 225 p += htbl->bits[l]; 226 dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */ 227 } else { 228 dtbl->maxcode[l] = -1; /* -1 if no codes of this length */ 229 } 230 } 231 dtbl->valoffset[17] = 0; 232 dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */ 233 234 /* Compute lookahead tables to speed up decoding. 235 * First we set all the table entries to 0, indicating "too long"; 236 * then we iterate through the Huffman codes that are short enough and 237 * fill in all the entries that correspond to bit sequences starting 238 * with that code. 239 */ 240 241 for (i = 0; i < (1 << HUFF_LOOKAHEAD); i++) 242 dtbl->lookup[i] = (HUFF_LOOKAHEAD + 1) << HUFF_LOOKAHEAD; 243 244 p = 0; 245 for (l = 1; l <= HUFF_LOOKAHEAD; l++) { 246 for (i = 1; i <= (int) htbl->bits[l]; i++, p++) { 247 /* l = current code's length, p = its index in huffcode[] & huffval[]. */ 248 /* Generate left-justified code followed by all possible bit sequences */ 249 lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l); 250 for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) { 251 dtbl->lookup[lookbits] = (l << HUFF_LOOKAHEAD) | htbl->huffval[p]; 252 lookbits++; 253 } 254 } 255 } 256 257 /* Validate symbols as being reasonable. 258 * For AC tables, we make no check, but accept all byte values 0..255. 259 * For DC tables, we require the symbols to be in range 0..15. 260 * (Tighter bounds could be applied depending on the data depth and mode, 261 * but this is sufficient to ensure safe decoding.) 262 */ 263 if (isDC) { 264 for (i = 0; i < numsymbols; i++) { 265 int sym = htbl->huffval[i]; 266 if (sym < 0 || sym > 15) 267 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 268 } 269 } 270 } 271 272 273 /* 274 * Out-of-line code for bit fetching (shared with jdphuff.c). 275 * See jdhuff.h for info about usage. 276 * Note: current values of get_buffer and bits_left are passed as parameters, 277 * but are returned in the corresponding fields of the state struct. 278 * 279 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width 280 * of get_buffer to be used. (On machines with wider words, an even larger 281 * buffer could be used.) However, on some machines 32-bit shifts are 282 * quite slow and take time proportional to the number of places shifted. 283 * (This is true with most PC compilers, for instance.) In this case it may 284 * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the 285 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer. 286 */ 287 288 #ifdef SLOW_SHIFT_32 289 #define MIN_GET_BITS 15 /* minimum allowable value */ 290 #else 291 #define MIN_GET_BITS (BIT_BUF_SIZE-7) 292 #endif 293 294 295 GLOBAL(boolean) 296 jpeg_fill_bit_buffer (bitread_working_state * state, 297 register bit_buf_type get_buffer, register int bits_left, 298 int nbits) 299 /* Load up the bit buffer to a depth of at least nbits */ 300 { 301 /* Copy heavily used state fields into locals (hopefully registers) */ 302 register const JOCTET * next_input_byte = state->next_input_byte; 303 register size_t bytes_in_buffer = state->bytes_in_buffer; 304 j_decompress_ptr cinfo = state->cinfo; 305 306 /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */ 307 /* (It is assumed that no request will be for more than that many bits.) */ 308 /* We fail to do so only if we hit a marker or are forced to suspend. */ 309 310 if (cinfo->unread_marker == 0) { /* cannot advance past a marker */ 311 while (bits_left < MIN_GET_BITS) { 312 register int c; 313 314 /* Attempt to read a byte */ 315 if (bytes_in_buffer == 0) { 316 if (! (*cinfo->src->fill_input_buffer) (cinfo)) 317 return FALSE; 318 next_input_byte = cinfo->src->next_input_byte; 319 bytes_in_buffer = cinfo->src->bytes_in_buffer; 320 } 321 bytes_in_buffer--; 322 c = GETJOCTET(*next_input_byte++); 323 324 /* If it's 0xFF, check and discard stuffed zero byte */ 325 if (c == 0xFF) { 326 /* Loop here to discard any padding FF's on terminating marker, 327 * so that we can save a valid unread_marker value. NOTE: we will 328 * accept multiple FF's followed by a 0 as meaning a single FF data 329 * byte. This data pattern is not valid according to the standard. 330 */ 331 do { 332 if (bytes_in_buffer == 0) { 333 if (! (*cinfo->src->fill_input_buffer) (cinfo)) 334 return FALSE; 335 next_input_byte = cinfo->src->next_input_byte; 336 bytes_in_buffer = cinfo->src->bytes_in_buffer; 337 } 338 bytes_in_buffer--; 339 c = GETJOCTET(*next_input_byte++); 340 } while (c == 0xFF); 341 342 if (c == 0) { 343 /* Found FF/00, which represents an FF data byte */ 344 c = 0xFF; 345 } else { 346 /* Oops, it's actually a marker indicating end of compressed data. 347 * Save the marker code for later use. 348 * Fine point: it might appear that we should save the marker into 349 * bitread working state, not straight into permanent state. But 350 * once we have hit a marker, we cannot need to suspend within the 351 * current MCU, because we will read no more bytes from the data 352 * source. So it is OK to update permanent state right away. 353 */ 354 cinfo->unread_marker = c; 355 /* See if we need to insert some fake zero bits. */ 356 goto no_more_bytes; 357 } 358 } 359 360 /* OK, load c into get_buffer */ 361 get_buffer = (get_buffer << 8) | c; 362 bits_left += 8; 363 } /* end while */ 364 } else { 365 no_more_bytes: 366 /* We get here if we've read the marker that terminates the compressed 367 * data segment. There should be enough bits in the buffer register 368 * to satisfy the request; if so, no problem. 369 */ 370 if (nbits > bits_left) { 371 /* Uh-oh. Report corrupted data to user and stuff zeroes into 372 * the data stream, so that we can produce some kind of image. 373 * We use a nonvolatile flag to ensure that only one warning message 374 * appears per data segment. 375 */ 376 if (! cinfo->entropy->insufficient_data) { 377 WARNMS(cinfo, JWRN_HIT_MARKER); 378 cinfo->entropy->insufficient_data = TRUE; 379 } 380 /* Fill the buffer with zero bits */ 381 get_buffer <<= MIN_GET_BITS - bits_left; 382 bits_left = MIN_GET_BITS; 383 } 384 } 385 386 /* Unload the local registers */ 387 state->next_input_byte = next_input_byte; 388 state->bytes_in_buffer = bytes_in_buffer; 389 state->get_buffer = get_buffer; 390 state->bits_left = bits_left; 391 392 return TRUE; 393 } 394 395 396 /* Macro version of the above, which performs much better but does not 397 handle markers. We have to hand off any blocks with markers to the 398 slower routines. */ 399 400 #define GET_BYTE \ 401 { \ 402 register int c0, c1; \ 403 c0 = GETJOCTET(*buffer++); \ 404 c1 = GETJOCTET(*buffer); \ 405 /* Pre-execute most common case */ \ 406 get_buffer = (get_buffer << 8) | c0; \ 407 bits_left += 8; \ 408 if (c0 == 0xFF) { \ 409 /* Pre-execute case of FF/00, which represents an FF data byte */ \ 410 buffer++; \ 411 if (c1 != 0) { \ 412 /* Oops, it's actually a marker indicating end of compressed data. */ \ 413 cinfo->unread_marker = c1; \ 414 /* Back out pre-execution and fill the buffer with zero bits */ \ 415 buffer -= 2; \ 416 get_buffer &= ~0xFF; \ 417 } \ 418 } \ 419 } 420 421 #if __WORDSIZE == 64 || defined(_WIN64) 422 423 /* Pre-fetch 48 bytes, because the holding register is 64-bit */ 424 #define FILL_BIT_BUFFER_FAST \ 425 if (bits_left < 16) { \ 426 GET_BYTE GET_BYTE GET_BYTE GET_BYTE GET_BYTE GET_BYTE \ 427 } 428 429 #else 430 431 /* Pre-fetch 16 bytes, because the holding register is 32-bit */ 432 #define FILL_BIT_BUFFER_FAST \ 433 if (bits_left < 16) { \ 434 GET_BYTE GET_BYTE \ 435 } 436 437 #endif 438 439 440 /* 441 * Out-of-line code for Huffman code decoding. 442 * See jdhuff.h for info about usage. 443 */ 444 445 GLOBAL(int) 446 jpeg_huff_decode (bitread_working_state * state, 447 register bit_buf_type get_buffer, register int bits_left, 448 d_derived_tbl * htbl, int min_bits) 449 { 450 register int l = min_bits; 451 register INT32 code; 452 453 /* HUFF_DECODE has determined that the code is at least min_bits */ 454 /* bits long, so fetch that many bits in one swoop. */ 455 456 CHECK_BIT_BUFFER(*state, l, return -1); 457 code = GET_BITS(l); 458 459 /* Collect the rest of the Huffman code one bit at a time. */ 460 /* This is per Figure F.16 in the JPEG spec. */ 461 462 while (code > htbl->maxcode[l]) { 463 code <<= 1; 464 CHECK_BIT_BUFFER(*state, 1, return -1); 465 code |= GET_BITS(1); 466 l++; 467 } 468 469 /* Unload the local registers */ 470 state->get_buffer = get_buffer; 471 state->bits_left = bits_left; 472 473 /* With garbage input we may reach the sentinel value l = 17. */ 474 475 if (l > 16) { 476 WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE); 477 return 0; /* fake a zero as the safest result */ 478 } 479 480 return htbl->pub->huffval[ (int) (code + htbl->valoffset[l]) ]; 481 } 482 483 484 /* 485 * Figure F.12: extend sign bit. 486 * On some machines, a shift and add will be faster than a table lookup. 487 */ 488 489 #define AVOID_TABLES 490 #ifdef AVOID_TABLES 491 492 #define HUFF_EXTEND(x,s) ((x) + ((((x) - (1<<((s)-1))) >> 31) & (((-1)<<(s)) + 1))) 493 494 #else 495 496 #define HUFF_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x)) 497 498 static const int extend_test[16] = /* entry n is 2**(n-1) */ 499 { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080, 500 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 }; 501 502 static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */ 503 { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1, 504 ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1, 505 ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1, 506 ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 }; 507 508 #endif /* AVOID_TABLES */ 509 510 511 /* 512 * Check for a restart marker & resynchronize decoder. 513 * Returns FALSE if must suspend. 514 */ 515 516 LOCAL(boolean) 517 process_restart (j_decompress_ptr cinfo) 518 { 519 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 520 int ci; 521 522 /* Throw away any unused bits remaining in bit buffer; */ 523 /* include any full bytes in next_marker's count of discarded bytes */ 524 cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8; 525 entropy->bitstate.bits_left = 0; 526 527 /* Advance past the RSTn marker */ 528 if (! (*cinfo->marker->read_restart_marker) (cinfo)) 529 return FALSE; 530 531 /* Re-initialize DC predictions to 0 */ 532 for (ci = 0; ci < cinfo->comps_in_scan; ci++) 533 entropy->saved.last_dc_val[ci] = 0; 534 535 /* Reset restart counter */ 536 entropy->restarts_to_go = cinfo->restart_interval; 537 538 /* Reset out-of-data flag, unless read_restart_marker left us smack up 539 * against a marker. In that case we will end up treating the next data 540 * segment as empty, and we can avoid producing bogus output pixels by 541 * leaving the flag set. 542 */ 543 if (cinfo->unread_marker == 0) 544 entropy->pub.insufficient_data = FALSE; 545 546 return TRUE; 547 } 548 549 550 LOCAL(boolean) 551 decode_mcu_slow (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 552 { 553 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 554 BITREAD_STATE_VARS; 555 int blkn; 556 savable_state state; 557 /* Outer loop handles each block in the MCU */ 558 559 /* Load up working state */ 560 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 561 ASSIGN_STATE(state, entropy->saved); 562 563 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 564 JBLOCKROW block = MCU_data[blkn]; 565 d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn]; 566 d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn]; 567 register int s, k, r; 568 569 /* Decode a single block's worth of coefficients */ 570 571 /* Section F.2.2.1: decode the DC coefficient difference */ 572 HUFF_DECODE(s, br_state, dctbl, return FALSE, label1); 573 if (s) { 574 CHECK_BIT_BUFFER(br_state, s, return FALSE); 575 r = GET_BITS(s); 576 s = HUFF_EXTEND(r, s); 577 } 578 579 if (entropy->dc_needed[blkn]) { 580 /* Convert DC difference to actual value, update last_dc_val */ 581 int ci = cinfo->MCU_membership[blkn]; 582 s += state.last_dc_val[ci]; 583 state.last_dc_val[ci] = s; 584 /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */ 585 (*block)[0] = (JCOEF) s; 586 } 587 588 if (entropy->ac_needed[blkn]) { 589 590 /* Section F.2.2.2: decode the AC coefficients */ 591 /* Since zeroes are skipped, output area must be cleared beforehand */ 592 for (k = 1; k < DCTSIZE2; k++) { 593 HUFF_DECODE(s, br_state, actbl, return FALSE, label2); 594 595 r = s >> 4; 596 s &= 15; 597 598 if (s) { 599 k += r; 600 CHECK_BIT_BUFFER(br_state, s, return FALSE); 601 r = GET_BITS(s); 602 s = HUFF_EXTEND(r, s); 603 /* Output coefficient in natural (dezigzagged) order. 604 * Note: the extra entries in jpeg_natural_order[] will save us 605 * if k >= DCTSIZE2, which could happen if the data is corrupted. 606 */ 607 (*block)[jpeg_natural_order[k]] = (JCOEF) s; 608 } else { 609 if (r != 15) 610 break; 611 k += 15; 612 } 613 } 614 615 } else { 616 617 /* Section F.2.2.2: decode the AC coefficients */ 618 /* In this path we just discard the values */ 619 for (k = 1; k < DCTSIZE2; k++) { 620 HUFF_DECODE(s, br_state, actbl, return FALSE, label3); 621 622 r = s >> 4; 623 s &= 15; 624 625 if (s) { 626 k += r; 627 CHECK_BIT_BUFFER(br_state, s, return FALSE); 628 DROP_BITS(s); 629 } else { 630 if (r != 15) 631 break; 632 k += 15; 633 } 634 } 635 } 636 } 637 638 /* Completed MCU, so update state */ 639 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 640 ASSIGN_STATE(entropy->saved, state); 641 return TRUE; 642 } 643 644 645 LOCAL(boolean) 646 decode_mcu_fast (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 647 { 648 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 649 BITREAD_STATE_VARS; 650 JOCTET *buffer; 651 int blkn; 652 savable_state state; 653 /* Outer loop handles each block in the MCU */ 654 655 /* Load up working state */ 656 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 657 buffer = (JOCTET *) br_state.next_input_byte; 658 ASSIGN_STATE(state, entropy->saved); 659 660 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 661 JBLOCKROW block = MCU_data[blkn]; 662 d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn]; 663 d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn]; 664 register int s, k, r, l; 665 666 HUFF_DECODE_FAST(s, l, dctbl); 667 if (s) { 668 FILL_BIT_BUFFER_FAST 669 r = GET_BITS(s); 670 s = HUFF_EXTEND(r, s); 671 } 672 673 if (entropy->dc_needed[blkn]) { 674 int ci = cinfo->MCU_membership[blkn]; 675 s += state.last_dc_val[ci]; 676 state.last_dc_val[ci] = s; 677 (*block)[0] = (JCOEF) s; 678 } 679 680 if (entropy->ac_needed[blkn]) { 681 682 for (k = 1; k < DCTSIZE2; k++) { 683 HUFF_DECODE_FAST(s, l, actbl); 684 r = s >> 4; 685 s &= 15; 686 687 if (s) { 688 k += r; 689 FILL_BIT_BUFFER_FAST 690 r = GET_BITS(s); 691 s = HUFF_EXTEND(r, s); 692 (*block)[jpeg_natural_order[k]] = (JCOEF) s; 693 } else { 694 if (r != 15) break; 695 k += 15; 696 } 697 } 698 699 } else { 700 701 for (k = 1; k < DCTSIZE2; k++) { 702 HUFF_DECODE_FAST(s, l, actbl); 703 r = s >> 4; 704 s &= 15; 705 706 if (s) { 707 k += r; 708 FILL_BIT_BUFFER_FAST 709 DROP_BITS(s); 710 } else { 711 if (r != 15) break; 712 k += 15; 713 } 714 } 715 } 716 } 717 718 if (cinfo->unread_marker != 0) { 719 cinfo->unread_marker = 0; 720 return FALSE; 721 } 722 723 br_state.bytes_in_buffer -= (buffer - br_state.next_input_byte); 724 br_state.next_input_byte = buffer; 725 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 726 ASSIGN_STATE(entropy->saved, state); 727 return TRUE; 728 } 729 730 731 /* 732 * Decode and return one MCU's worth of Huffman-compressed coefficients. 733 * The coefficients are reordered from zigzag order into natural array order, 734 * but are not dequantized. 735 * 736 * The i'th block of the MCU is stored into the block pointed to by 737 * MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER. 738 * (Wholesale zeroing is usually a little faster than retail...) 739 * 740 * Returns FALSE if data source requested suspension. In that case no 741 * changes have been made to permanent state. (Exception: some output 742 * coefficients may already have been assigned. This is harmless for 743 * this module, since we'll just re-assign them on the next call.) 744 */ 745 746 #define BUFSIZE (DCTSIZE2 * 2u) 747 748 METHODDEF(boolean) 749 decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 750 { 751 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 752 int usefast = 1; 753 754 /* Process restart marker if needed; may have to suspend */ 755 if (cinfo->restart_interval) { 756 if (entropy->restarts_to_go == 0) 757 if (! process_restart(cinfo)) 758 return FALSE; 759 usefast = 0; 760 } 761 762 if (cinfo->src->bytes_in_buffer < BUFSIZE * (size_t)cinfo->blocks_in_MCU 763 || cinfo->unread_marker != 0) 764 usefast = 0; 765 766 /* If we've run out of data, just leave the MCU set to zeroes. 767 * This way, we return uniform gray for the remainder of the segment. 768 */ 769 if (! entropy->pub.insufficient_data) { 770 771 if (usefast) { 772 if (!decode_mcu_fast(cinfo, MCU_data)) goto use_slow; 773 } 774 else { 775 use_slow: 776 if (!decode_mcu_slow(cinfo, MCU_data)) return FALSE; 777 } 778 779 } 780 781 /* Account for restart interval (no-op if not using restarts) */ 782 entropy->restarts_to_go--; 783 784 return TRUE; 785 } 786 787 788 /* 789 * Module initialization routine for Huffman entropy decoding. 790 */ 791 792 GLOBAL(void) 793 jinit_huff_decoder (j_decompress_ptr cinfo) 794 { 795 huff_entropy_ptr entropy; 796 int i; 797 798 entropy = (huff_entropy_ptr) 799 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 800 SIZEOF(huff_entropy_decoder)); 801 cinfo->entropy = (struct jpeg_entropy_decoder *) entropy; 802 entropy->pub.start_pass = start_pass_huff_decoder; 803 entropy->pub.decode_mcu = decode_mcu; 804 805 /* Mark tables unallocated */ 806 for (i = 0; i < NUM_HUFF_TBLS; i++) { 807 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL; 808 } 809 } 810