1 /* 2 * jdhuff.c 3 * 4 * Copyright (C) 1991-1997, 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 LOCAL(boolean) process_restart (j_decompress_ptr cinfo); 23 24 25 /* 26 * Expanded entropy decoder object for Huffman decoding. 27 * 28 * The savable_state subrecord contains fields that change within an MCU, 29 * but must not be updated permanently until we complete the MCU. 30 */ 31 32 typedef struct { 33 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */ 34 } savable_state; 35 36 /* This macro is to work around compilers with missing or broken 37 * structure assignment. You'll need to fix this code if you have 38 * such a compiler and you change MAX_COMPS_IN_SCAN. 39 */ 40 41 #ifndef NO_STRUCT_ASSIGN 42 #define ASSIGN_STATE(dest,src) ((dest) = (src)) 43 #else 44 #if MAX_COMPS_IN_SCAN == 4 45 #define ASSIGN_STATE(dest,src) \ 46 ((dest).last_dc_val[0] = (src).last_dc_val[0], \ 47 (dest).last_dc_val[1] = (src).last_dc_val[1], \ 48 (dest).last_dc_val[2] = (src).last_dc_val[2], \ 49 (dest).last_dc_val[3] = (src).last_dc_val[3]) 50 #endif 51 #endif 52 53 54 typedef struct { 55 struct jpeg_entropy_decoder pub; /* public fields */ 56 57 /* These fields are loaded into local variables at start of each MCU. 58 * In case of suspension, we exit WITHOUT updating them. 59 */ 60 bitread_perm_state bitstate; /* Bit buffer at start of MCU */ 61 savable_state saved; /* Other state at start of MCU */ 62 63 /* These fields are NOT loaded into local working state. */ 64 unsigned int restarts_to_go; /* MCUs left in this restart interval */ 65 66 /* Pointers to derived tables (these workspaces have image lifespan) */ 67 d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS]; 68 d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS]; 69 70 /* Precalculated info set up by start_pass for use in decode_mcu: */ 71 72 /* Pointers to derived tables to be used for each block within an MCU */ 73 d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU]; 74 d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU]; 75 /* Whether we care about the DC and AC coefficient values for each block */ 76 boolean dc_needed[D_MAX_BLOCKS_IN_MCU]; 77 boolean ac_needed[D_MAX_BLOCKS_IN_MCU]; 78 } huff_entropy_decoder; 79 80 typedef huff_entropy_decoder * huff_entropy_ptr; 81 82 /* 83 * Initialize for a Huffman-compressed scan. 84 */ 85 86 METHODDEF(void) 87 start_pass_huff_decoder (j_decompress_ptr cinfo) 88 { 89 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 90 int ci, blkn, dctbl, actbl; 91 jpeg_component_info * compptr; 92 93 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG. 94 * This ought to be an error condition, but we make it a warning because 95 * there are some baseline files out there with all zeroes in these bytes. 96 */ 97 if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 || 98 cinfo->Ah != 0 || cinfo->Al != 0) 99 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL); 100 101 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 102 compptr = cinfo->cur_comp_info[ci]; 103 dctbl = compptr->dc_tbl_no; 104 actbl = compptr->ac_tbl_no; 105 /* Compute derived values for Huffman tables */ 106 /* We may do this more than once for a table, but it's not expensive */ 107 jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl, 108 & entropy->dc_derived_tbls[dctbl]); 109 jpeg_make_d_derived_tbl(cinfo, FALSE, actbl, 110 & entropy->ac_derived_tbls[actbl]); 111 /* Initialize DC predictions to 0 */ 112 entropy->saved.last_dc_val[ci] = 0; 113 } 114 115 /* Precalculate decoding info for each block in an MCU of this scan */ 116 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 117 ci = cinfo->MCU_membership[blkn]; 118 compptr = cinfo->cur_comp_info[ci]; 119 /* Precalculate which table to use for each block */ 120 entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no]; 121 entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no]; 122 /* Decide whether we really care about the coefficient values */ 123 if (compptr->component_needed) { 124 entropy->dc_needed[blkn] = TRUE; 125 /* we don't need the ACs if producing a 1/8th-size image */ 126 entropy->ac_needed[blkn] = (compptr->DCT_scaled_size > 1); 127 } else { 128 entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE; 129 } 130 } 131 132 /* Initialize bitread state variables */ 133 entropy->bitstate.bits_left = 0; 134 entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */ 135 entropy->pub.insufficient_data = FALSE; 136 137 /* Initialize restart counter */ 138 entropy->restarts_to_go = cinfo->restart_interval; 139 } 140 141 142 /* 143 * Compute the derived values for a Huffman table. 144 * This routine also performs some validation checks on the table. 145 * 146 * Note this is also used by jdphuff.c. 147 */ 148 149 GLOBAL(void) 150 jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno, 151 d_derived_tbl ** pdtbl) 152 { 153 JHUFF_TBL *htbl; 154 d_derived_tbl *dtbl; 155 int p, i, l, si, numsymbols; 156 int lookbits, ctr; 157 char huffsize[257]; 158 unsigned int huffcode[257]; 159 unsigned int code; 160 161 /* Note that huffsize[] and huffcode[] are filled in code-length order, 162 * paralleling the order of the symbols themselves in htbl->huffval[]. 163 */ 164 165 /* Find the input Huffman table */ 166 if (tblno < 0 || tblno >= NUM_HUFF_TBLS) 167 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno); 168 htbl = 169 isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno]; 170 if (htbl == NULL) 171 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno); 172 173 /* Allocate a workspace if we haven't already done so. */ 174 if (*pdtbl == NULL) 175 *pdtbl = (d_derived_tbl *) 176 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 177 SIZEOF(d_derived_tbl)); 178 dtbl = *pdtbl; 179 dtbl->pub = htbl; /* fill in back link */ 180 181 /* Figure C.1: make table of Huffman code length for each symbol */ 182 183 p = 0; 184 for (l = 1; l <= 16; l++) { 185 i = (int) htbl->bits[l]; 186 if (i < 0 || p + i > 256) /* protect against table overrun */ 187 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 188 while (i--) 189 huffsize[p++] = (char) l; 190 } 191 huffsize[p] = 0; 192 numsymbols = p; 193 194 /* Figure C.2: generate the codes themselves */ 195 /* We also validate that the counts represent a legal Huffman code tree. */ 196 197 code = 0; 198 si = huffsize[0]; 199 p = 0; 200 while (huffsize[p]) { 201 while (((int) huffsize[p]) == si) { 202 huffcode[p++] = code; 203 code++; 204 } 205 /* code is now 1 more than the last code used for codelength si; but 206 * it must still fit in si bits, since no code is allowed to be all ones. 207 */ 208 if (((INT32) code) >= (((INT32) 1) << si)) 209 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 210 code <<= 1; 211 si++; 212 } 213 214 /* Figure F.15: generate decoding tables for bit-sequential decoding */ 215 216 p = 0; 217 for (l = 1; l <= 16; l++) { 218 if (htbl->bits[l]) { 219 /* valoffset[l] = huffval[] index of 1st symbol of code length l, 220 * minus the minimum code of length l 221 */ 222 dtbl->valoffset[l] = (INT32) p - (INT32) huffcode[p]; 223 p += htbl->bits[l]; 224 dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */ 225 } else { 226 dtbl->maxcode[l] = -1; /* -1 if no codes of this length */ 227 } 228 } 229 dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */ 230 231 /* Compute lookahead tables to speed up decoding. 232 * First we set all the table entries to 0, indicating "too long"; 233 * then we iterate through the Huffman codes that are short enough and 234 * fill in all the entries that correspond to bit sequences starting 235 * with that code. 236 */ 237 238 MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits)); 239 240 p = 0; 241 for (l = 1; l <= HUFF_LOOKAHEAD; l++) { 242 for (i = 1; i <= (int) htbl->bits[l]; i++, p++) { 243 /* l = current code's length, p = its index in huffcode[] & huffval[]. */ 244 /* Generate left-justified code followed by all possible bit sequences */ 245 lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l); 246 for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) { 247 dtbl->look_nbits[lookbits] = l; 248 dtbl->look_sym[lookbits] = htbl->huffval[p]; 249 lookbits++; 250 } 251 } 252 } 253 254 /* Validate symbols as being reasonable. 255 * For AC tables, we make no check, but accept all byte values 0..255. 256 * For DC tables, we require the symbols to be in range 0..15. 257 * (Tighter bounds could be applied depending on the data depth and mode, 258 * but this is sufficient to ensure safe decoding.) 259 */ 260 if (isDC) { 261 for (i = 0; i < numsymbols; i++) { 262 int sym = htbl->huffval[i]; 263 if (sym < 0 || sym > 15) 264 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 265 } 266 } 267 } 268 269 270 /* 271 * Out-of-line code for bit fetching (shared with jdphuff.c). 272 * See jdhuff.h for info about usage. 273 * Note: current values of get_buffer and bits_left are passed as parameters, 274 * but are returned in the corresponding fields of the state struct. 275 * 276 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width 277 * of get_buffer to be used. (On machines with wider words, an even larger 278 * buffer could be used.) However, on some machines 32-bit shifts are 279 * quite slow and take time proportional to the number of places shifted. 280 * (This is true with most PC compilers, for instance.) In this case it may 281 * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the 282 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer. 283 */ 284 285 #ifdef SLOW_SHIFT_32 286 #define MIN_GET_BITS 15 /* minimum allowable value */ 287 #else 288 #define MIN_GET_BITS (BIT_BUF_SIZE-7) 289 #endif 290 291 292 GLOBAL(boolean) 293 jpeg_fill_bit_buffer (bitread_working_state * state, 294 register bit_buf_type get_buffer, register int bits_left, 295 int nbits) 296 /* Load up the bit buffer to a depth of at least nbits */ 297 { 298 /* Copy heavily used state fields into locals (hopefully registers) */ 299 register const JOCTET * next_input_byte = state->next_input_byte; 300 register size_t bytes_in_buffer = state->bytes_in_buffer; 301 j_decompress_ptr cinfo = state->cinfo; 302 303 /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */ 304 /* (It is assumed that no request will be for more than that many bits.) */ 305 /* We fail to do so only if we hit a marker or are forced to suspend. */ 306 307 if (cinfo->unread_marker == 0) { /* cannot advance past a marker */ 308 while (bits_left < MIN_GET_BITS) { 309 register int c; 310 311 /* Attempt to read a byte */ 312 if (bytes_in_buffer == 0) { 313 if (! (*cinfo->src->fill_input_buffer) (cinfo)) 314 return FALSE; 315 next_input_byte = cinfo->src->next_input_byte; 316 bytes_in_buffer = cinfo->src->bytes_in_buffer; 317 } 318 bytes_in_buffer--; 319 c = GETJOCTET(*next_input_byte++); 320 321 /* If it's 0xFF, check and discard stuffed zero byte */ 322 if (c == 0xFF) { 323 /* Loop here to discard any padding FF's on terminating marker, 324 * so that we can save a valid unread_marker value. NOTE: we will 325 * accept multiple FF's followed by a 0 as meaning a single FF data 326 * byte. This data pattern is not valid according to the standard. 327 */ 328 do { 329 if (bytes_in_buffer == 0) { 330 if (! (*cinfo->src->fill_input_buffer) (cinfo)) 331 return FALSE; 332 next_input_byte = cinfo->src->next_input_byte; 333 bytes_in_buffer = cinfo->src->bytes_in_buffer; 334 } 335 bytes_in_buffer--; 336 c = GETJOCTET(*next_input_byte++); 337 } while (c == 0xFF); 338 339 if (c == 0) { 340 /* Found FF/00, which represents an FF data byte */ 341 c = 0xFF; 342 } else { 343 /* Oops, it's actually a marker indicating end of compressed data. 344 * Save the marker code for later use. 345 * Fine point: it might appear that we should save the marker into 346 * bitread working state, not straight into permanent state. But 347 * once we have hit a marker, we cannot need to suspend within the 348 * current MCU, because we will read no more bytes from the data 349 * source. So it is OK to update permanent state right away. 350 */ 351 cinfo->unread_marker = c; 352 /* See if we need to insert some fake zero bits. */ 353 goto no_more_bytes; 354 } 355 } 356 357 /* OK, load c into get_buffer */ 358 get_buffer = (get_buffer << 8) | c; 359 bits_left += 8; 360 } /* end while */ 361 } else { 362 no_more_bytes: 363 /* We get here if we've read the marker that terminates the compressed 364 * data segment. There should be enough bits in the buffer register 365 * to satisfy the request; if so, no problem. 366 */ 367 if (nbits > bits_left) { 368 /* Uh-oh. Report corrupted data to user and stuff zeroes into 369 * the data stream, so that we can produce some kind of image. 370 * We use a nonvolatile flag to ensure that only one warning message 371 * appears per data segment. 372 */ 373 if (! cinfo->entropy->insufficient_data) { 374 WARNMS(cinfo, JWRN_HIT_MARKER); 375 cinfo->entropy->insufficient_data = TRUE; 376 } 377 /* Fill the buffer with zero bits */ 378 get_buffer <<= MIN_GET_BITS - bits_left; 379 bits_left = MIN_GET_BITS; 380 } 381 } 382 383 /* Unload the local registers */ 384 state->next_input_byte = next_input_byte; 385 state->bytes_in_buffer = bytes_in_buffer; 386 state->get_buffer = get_buffer; 387 state->bits_left = bits_left; 388 389 return TRUE; 390 } 391 392 393 /* 394 * Out-of-line code for Huffman code decoding. 395 * See jdhuff.h for info about usage. 396 */ 397 398 GLOBAL(int) 399 jpeg_huff_decode (bitread_working_state * state, 400 register bit_buf_type get_buffer, register int bits_left, 401 d_derived_tbl * htbl, int min_bits) 402 { 403 register int l = min_bits; 404 register INT32 code; 405 406 /* HUFF_DECODE has determined that the code is at least min_bits */ 407 /* bits long, so fetch that many bits in one swoop. */ 408 409 CHECK_BIT_BUFFER(*state, l, return -1); 410 code = GET_BITS(l); 411 412 /* Collect the rest of the Huffman code one bit at a time. */ 413 /* This is per Figure F.16 in the JPEG spec. */ 414 415 while (code > htbl->maxcode[l]) { 416 code <<= 1; 417 CHECK_BIT_BUFFER(*state, 1, return -1); 418 code |= GET_BITS(1); 419 l++; 420 } 421 422 /* Unload the local registers */ 423 state->get_buffer = get_buffer; 424 state->bits_left = bits_left; 425 426 /* With garbage input we may reach the sentinel value l = 17. */ 427 428 if (l > 16) { 429 WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE); 430 return 0; /* fake a zero as the safest result */ 431 } 432 433 return htbl->pub->huffval[ (int) (code + htbl->valoffset[l]) ]; 434 } 435 436 437 /* 438 * Figure F.12: extend sign bit. 439 * On some machines, a shift and add will be faster than a table lookup. 440 */ 441 442 #ifdef AVOID_TABLES 443 444 #define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x)) 445 446 #else 447 448 #define HUFF_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x)) 449 450 static const int extend_test[16] = /* entry n is 2**(n-1) */ 451 { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080, 452 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 }; 453 454 static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */ 455 { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1, 456 ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1, 457 ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1, 458 ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 }; 459 460 #endif /* AVOID_TABLES */ 461 462 463 /* 464 * Check for a restart marker & resynchronize decoder. 465 * Returns FALSE if must suspend. 466 */ 467 468 LOCAL(boolean) 469 process_restart (j_decompress_ptr cinfo) 470 { 471 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 472 int ci; 473 474 /* Throw away any unused bits remaining in bit buffer; */ 475 /* include any full bytes in next_marker's count of discarded bytes */ 476 cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8; 477 entropy->bitstate.bits_left = 0; 478 479 /* Advance past the RSTn marker */ 480 if (! (*cinfo->marker->read_restart_marker) (cinfo)) 481 return FALSE; 482 483 /* Re-initialize DC predictions to 0 */ 484 for (ci = 0; ci < cinfo->comps_in_scan; ci++) 485 entropy->saved.last_dc_val[ci] = 0; 486 487 /* Reset restart counter */ 488 entropy->restarts_to_go = cinfo->restart_interval; 489 490 /* Reset out-of-data flag, unless read_restart_marker left us smack up 491 * against a marker. In that case we will end up treating the next data 492 * segment as empty, and we can avoid producing bogus output pixels by 493 * leaving the flag set. 494 */ 495 if (cinfo->unread_marker == 0) 496 entropy->pub.insufficient_data = FALSE; 497 498 return TRUE; 499 } 500 501 /* 502 * Save the current Huffman deocde position and the DC coefficients 503 * for each component into bitstream_offset and dc_info[], respectively. 504 */ 505 METHODDEF(void) 506 get_huffman_decoder_configuration(j_decompress_ptr cinfo, 507 huffman_offset_data *offset) 508 { 509 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 510 short int *dc_info = offset->prev_dc; 511 int i; 512 jpeg_get_huffman_decoder_configuration(cinfo, offset); 513 for (i = 0; i < cinfo->comps_in_scan; i++) { 514 dc_info[i] = entropy->saved.last_dc_val[i]; 515 } 516 } 517 518 /* 519 * Save the current Huffman decoder position and the bit buffer 520 * into bitstream_offset and get_buffer, respectively. 521 */ 522 GLOBAL(void) 523 jpeg_get_huffman_decoder_configuration(j_decompress_ptr cinfo, 524 huffman_offset_data *offset) 525 { 526 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 527 528 if (cinfo->restart_interval) { 529 // We are at the end of a data segment 530 if (entropy->restarts_to_go == 0) 531 if (! process_restart(cinfo)) 532 return; 533 } 534 535 // Save restarts_to_go and next_restart_num 536 offset->restarts_to_go = (unsigned short) entropy->restarts_to_go; 537 offset->next_restart_num = cinfo->marker->next_restart_num; 538 539 offset->bitstream_offset = 540 (jget_input_stream_position(cinfo) << LOG_TWO_BIT_BUF_SIZE) 541 + entropy->bitstate.bits_left; 542 543 offset->get_buffer = entropy->bitstate.get_buffer; 544 } 545 546 /* 547 * Configure the Huffman decoder to decode the image 548 * starting from the bitstream position recorded in offset. 549 */ 550 METHODDEF(void) 551 configure_huffman_decoder(j_decompress_ptr cinfo, huffman_offset_data offset) 552 { 553 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 554 short int *dc_info = offset.prev_dc; 555 int i; 556 jpeg_configure_huffman_decoder(cinfo, offset); 557 for (i = 0; i < cinfo->comps_in_scan; i++) { 558 entropy->saved.last_dc_val[i] = dc_info[i]; 559 } 560 } 561 562 /* 563 * Configure the Huffman decoder reader position and bit buffer. 564 */ 565 GLOBAL(void) 566 jpeg_configure_huffman_decoder(j_decompress_ptr cinfo, 567 huffman_offset_data offset) 568 { 569 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 570 571 // Restore restarts_to_go and next_restart_num 572 cinfo->unread_marker = 0; 573 entropy->restarts_to_go = offset.restarts_to_go; 574 cinfo->marker->next_restart_num = offset.next_restart_num; 575 576 unsigned int bitstream_offset = offset.bitstream_offset; 577 int blkn, i; 578 579 unsigned int byte_offset = bitstream_offset >> LOG_TWO_BIT_BUF_SIZE; 580 unsigned int bit_in_bit_buffer = 581 bitstream_offset & ((1 << LOG_TWO_BIT_BUF_SIZE) - 1); 582 583 jset_input_stream_position_bit(cinfo, byte_offset, 584 bit_in_bit_buffer, offset.get_buffer); 585 } 586 587 /* 588 * Decode and return one MCU's worth of Huffman-compressed coefficients. 589 * The coefficients are reordered from zigzag order into natural array order, 590 * but are not dequantized. 591 * 592 * The i'th block of the MCU is stored into the block pointed to by 593 * MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER. 594 * (Wholesale zeroing is usually a little faster than retail...) 595 * 596 * Returns FALSE if data source requested suspension. In that case no 597 * changes have been made to permanent state. (Exception: some output 598 * coefficients may already have been assigned. This is harmless for 599 * this module, since we'll just re-assign them on the next call.) 600 */ 601 602 METHODDEF(boolean) 603 decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 604 { 605 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 606 int blkn; 607 BITREAD_STATE_VARS; 608 savable_state state; 609 610 /* Process restart marker if needed; may have to suspend */ 611 if (cinfo->restart_interval) { 612 if (entropy->restarts_to_go == 0) 613 if (! process_restart(cinfo)) 614 return FALSE; 615 } 616 617 /* If we've run out of data, just leave the MCU set to zeroes. 618 * This way, we return uniform gray for the remainder of the segment. 619 */ 620 if (! entropy->pub.insufficient_data) { 621 /* Load up working state */ 622 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 623 ASSIGN_STATE(state, entropy->saved); 624 625 /* Outer loop handles each block in the MCU */ 626 627 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 628 JBLOCKROW block = MCU_data[blkn]; 629 d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn]; 630 d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn]; 631 register int s, k, r; 632 633 /* Decode a single block's worth of coefficients */ 634 635 /* Section F.2.2.1: decode the DC coefficient difference */ 636 HUFF_DECODE(s, br_state, dctbl, return FALSE, label1); 637 if (s) { 638 CHECK_BIT_BUFFER(br_state, s, return FALSE); 639 r = GET_BITS(s); 640 s = HUFF_EXTEND(r, s); 641 } 642 643 if (entropy->dc_needed[blkn]) { 644 /* Convert DC difference to actual value, update last_dc_val */ 645 int ci = cinfo->MCU_membership[blkn]; 646 s += state.last_dc_val[ci]; 647 state.last_dc_val[ci] = s; 648 /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */ 649 (*block)[0] = (JCOEF) s; 650 } 651 652 if (entropy->ac_needed[blkn]) { 653 654 /* Section F.2.2.2: decode the AC coefficients */ 655 /* Since zeroes are skipped, output area must be cleared beforehand */ 656 for (k = 1; k < DCTSIZE2; k++) { 657 HUFF_DECODE(s, br_state, actbl, return FALSE, label2); 658 659 r = s >> 4; 660 s &= 15; 661 662 if (s) { 663 k += r; 664 CHECK_BIT_BUFFER(br_state, s, return FALSE); 665 r = GET_BITS(s); 666 s = HUFF_EXTEND(r, s); 667 /* Output coefficient in natural (dezigzagged) order. 668 * Note: the extra entries in jpeg_natural_order[] will save us 669 * if k >= DCTSIZE2, which could happen if the data is corrupted. 670 */ 671 (*block)[jpeg_natural_order[k]] = (JCOEF) s; 672 } else { 673 if (r != 15) 674 break; 675 k += 15; 676 } 677 } 678 679 } else { 680 681 /* Section F.2.2.2: decode the AC coefficients */ 682 /* In this path we just discard the values */ 683 for (k = 1; k < DCTSIZE2; k++) { 684 HUFF_DECODE(s, br_state, actbl, return FALSE, label3); 685 686 r = s >> 4; 687 s &= 15; 688 689 if (s) { 690 k += r; 691 CHECK_BIT_BUFFER(br_state, s, return FALSE); 692 DROP_BITS(s); 693 } else { 694 if (r != 15) 695 break; 696 k += 15; 697 } 698 } 699 700 } 701 } 702 703 /* Completed MCU, so update state */ 704 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 705 ASSIGN_STATE(entropy->saved, state); 706 } 707 708 /* Account for restart interval (no-op if not using restarts) */ 709 entropy->restarts_to_go--; 710 711 return TRUE; 712 } 713 714 /* 715 * Decode one MCU's worth of Huffman-compressed coefficients. 716 * The propose of this method is to calculate the 717 * data length of one MCU in Huffman-coded format. 718 * Therefore, all coefficients are discarded. 719 */ 720 721 METHODDEF(boolean) 722 decode_mcu_discard_coef (j_decompress_ptr cinfo) 723 { 724 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 725 int blkn; 726 BITREAD_STATE_VARS; 727 savable_state state; 728 729 /* Process restart marker if needed; may have to suspend */ 730 if (cinfo->restart_interval) { 731 if (entropy->restarts_to_go == 0) 732 if (! process_restart(cinfo)) 733 return FALSE; 734 } 735 736 if (! entropy->pub.insufficient_data) { 737 738 /* Load up working state */ 739 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 740 ASSIGN_STATE(state, entropy->saved); 741 742 /* Outer loop handles each block in the MCU */ 743 744 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 745 d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn]; 746 d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn]; 747 register int s, k, r; 748 749 /* Decode a single block's worth of coefficients */ 750 751 /* Section F.2.2.1: decode the DC coefficient difference */ 752 HUFF_DECODE(s, br_state, dctbl, return FALSE, label1); 753 if (s) { 754 CHECK_BIT_BUFFER(br_state, s, return FALSE); 755 r = GET_BITS(s); 756 s = HUFF_EXTEND(r, s); 757 } 758 759 /* discard all coefficients */ 760 if (entropy->dc_needed[blkn]) { 761 /* Convert DC difference to actual value, update last_dc_val */ 762 int ci = cinfo->MCU_membership[blkn]; 763 s += state.last_dc_val[ci]; 764 state.last_dc_val[ci] = s; 765 } 766 for (k = 1; k < DCTSIZE2; k++) { 767 HUFF_DECODE(s, br_state, actbl, return FALSE, label3); 768 769 r = s >> 4; 770 s &= 15; 771 772 if (s) { 773 k += r; 774 CHECK_BIT_BUFFER(br_state, s, return FALSE); 775 DROP_BITS(s); 776 } else { 777 if (r != 15) 778 break; 779 k += 15; 780 } 781 } 782 } 783 784 /* Completed MCU, so update state */ 785 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 786 ASSIGN_STATE(entropy->saved, state); 787 } 788 789 /* Account for restart interval (no-op if not using restarts) */ 790 entropy->restarts_to_go--; 791 792 return TRUE; 793 } 794 795 796 /* 797 * Module initialization routine for Huffman entropy decoding. 798 */ 799 800 GLOBAL(void) 801 jinit_huff_decoder (j_decompress_ptr cinfo) 802 { 803 huff_entropy_ptr entropy; 804 int i; 805 806 entropy = (huff_entropy_ptr) 807 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 808 SIZEOF(huff_entropy_decoder)); 809 cinfo->entropy = (struct jpeg_entropy_decoder *) entropy; 810 entropy->pub.start_pass = start_pass_huff_decoder; 811 entropy->pub.decode_mcu = decode_mcu; 812 entropy->pub.decode_mcu_discard_coef = decode_mcu_discard_coef; 813 entropy->pub.configure_huffman_decoder = configure_huffman_decoder; 814 entropy->pub.get_huffman_decoder_configuration = 815 get_huffman_decoder_configuration; 816 entropy->pub.index = NULL; 817 818 /* Mark tables unallocated */ 819 for (i = 0; i < NUM_HUFF_TBLS; i++) { 820 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL; 821 } 822 } 823 824 /* 825 * Call after jpeg_read_header 826 */ 827 GLOBAL(void) 828 jpeg_create_huffman_index(j_decompress_ptr cinfo, huffman_index *index) 829 { 830 int i, s; 831 index->scan_count = 1; 832 index->total_iMCU_rows = cinfo->total_iMCU_rows; 833 index->scan = (huffman_scan_header*)malloc(index->scan_count 834 * sizeof(huffman_scan_header)); 835 index->scan[0].offset = (huffman_offset_data**)malloc(cinfo->total_iMCU_rows 836 * sizeof(huffman_offset_data*)); 837 index->scan[0].prev_MCU_offset.bitstream_offset = 0; 838 index->MCU_sample_size = DEFAULT_MCU_SAMPLE_SIZE; 839 840 index->mem_used = sizeof(huffman_scan_header) 841 + cinfo->total_iMCU_rows * sizeof(huffman_offset_data*); 842 } 843 844 GLOBAL(void) 845 jpeg_destroy_huffman_index(huffman_index *index) 846 { 847 int i, j; 848 for (i = 0; i < index->scan_count; i++) { 849 for(j = 0; j < index->total_iMCU_rows; j++) { 850 free(index->scan[i].offset[j]); 851 } 852 free(index->scan[i].offset); 853 } 854 free(index->scan); 855 } 856 857 /* 858 * Set the reader byte position to offset 859 */ 860 GLOBAL(void) 861 jset_input_stream_position(j_decompress_ptr cinfo, int offset) 862 { 863 if (cinfo->src->seek_input_data) { 864 cinfo->src->seek_input_data(cinfo, offset); 865 } else { 866 cinfo->src->bytes_in_buffer = cinfo->src->current_offset - offset; 867 cinfo->src->next_input_byte = cinfo->src->start_input_byte + offset; 868 } 869 } 870 871 /* 872 * Set the reader byte position to offset and bit position to bit_left 873 * with bit buffer set to buf. 874 */ 875 GLOBAL(void) 876 jset_input_stream_position_bit(j_decompress_ptr cinfo, 877 int byte_offset, int bit_left, INT32 buf) 878 { 879 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 880 881 entropy->bitstate.bits_left = bit_left; 882 entropy->bitstate.get_buffer = buf; 883 884 jset_input_stream_position(cinfo, byte_offset); 885 } 886 887 /* 888 * Get the current reader byte position. 889 */ 890 GLOBAL(int) 891 jget_input_stream_position(j_decompress_ptr cinfo) 892 { 893 return cinfo->src->current_offset - cinfo->src->bytes_in_buffer; 894 } 895
