1 /* 2 * jdhuff.c 3 * 4 * Copyright (C) 1991-1997, Thomas G. Lane. 5 * Modified 2006-2012 by Guido Vollbeding. 6 * This file is part of the Independent JPEG Group's software. 7 * For conditions of distribution and use, see the accompanying README file. 8 * 9 * This file contains Huffman entropy decoding routines. 10 * Both sequential and progressive modes are supported in this single module. 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 23 24 /* Derived data constructed for each Huffman table */ 25 26 #define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */ 27 28 typedef struct { 29 /* Basic tables: (element [0] of each array is unused) */ 30 INT32 maxcode[18]; /* largest code of length k (-1 if none) */ 31 /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */ 32 INT32 valoffset[17]; /* huffval[] offset for codes of length k */ 33 /* valoffset[k] = huffval[] index of 1st symbol of code length k, less 34 * the smallest code of length k; so given a code of length k, the 35 * corresponding symbol is huffval[code + valoffset[k]] 36 */ 37 38 /* Link to public Huffman table (needed only in jpeg_huff_decode) */ 39 JHUFF_TBL *pub; 40 41 /* Lookahead tables: indexed by the next HUFF_LOOKAHEAD bits of 42 * the input data stream. If the next Huffman code is no more 43 * than HUFF_LOOKAHEAD bits long, we can obtain its length and 44 * the corresponding symbol directly from these tables. 45 */ 46 int look_nbits[1<<HUFF_LOOKAHEAD]; /* # bits, or 0 if too long */ 47 UINT8 look_sym[1<<HUFF_LOOKAHEAD]; /* symbol, or unused */ 48 } d_derived_tbl; 49 50 51 /* 52 * Fetching the next N bits from the input stream is a time-critical operation 53 * for the Huffman decoders. We implement it with a combination of inline 54 * macros and out-of-line subroutines. Note that N (the number of bits 55 * demanded at one time) never exceeds 15 for JPEG use. 56 * 57 * We read source bytes into get_buffer and dole out bits as needed. 58 * If get_buffer already contains enough bits, they are fetched in-line 59 * by the macros CHECK_BIT_BUFFER and GET_BITS. When there aren't enough 60 * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer 61 * as full as possible (not just to the number of bits needed; this 62 * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer). 63 * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension. 64 * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains 65 * at least the requested number of bits --- dummy zeroes are inserted if 66 * necessary. 67 */ 68 69 typedef INT32 bit_buf_type; /* type of bit-extraction buffer */ 70 #define BIT_BUF_SIZE 32 /* size of buffer in bits */ 71 72 /* If long is > 32 bits on your machine, and shifting/masking longs is 73 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE 74 * appropriately should be a win. Unfortunately we can't define the size 75 * with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8) 76 * because not all machines measure sizeof in 8-bit bytes. 77 */ 78 79 typedef struct { /* Bitreading state saved across MCUs */ 80 bit_buf_type get_buffer; /* current bit-extraction buffer */ 81 int bits_left; /* # of unused bits in it */ 82 } bitread_perm_state; 83 84 typedef struct { /* Bitreading working state within an MCU */ 85 /* Current data source location */ 86 /* We need a copy, rather than munging the original, in case of suspension */ 87 const JOCTET * next_input_byte; /* => next byte to read from source */ 88 size_t bytes_in_buffer; /* # of bytes remaining in source buffer */ 89 /* Bit input buffer --- note these values are kept in register variables, 90 * not in this struct, inside the inner loops. 91 */ 92 bit_buf_type get_buffer; /* current bit-extraction buffer */ 93 int bits_left; /* # of unused bits in it */ 94 /* Pointer needed by jpeg_fill_bit_buffer. */ 95 j_decompress_ptr cinfo; /* back link to decompress master record */ 96 } bitread_working_state; 97 98 /* Macros to declare and load/save bitread local variables. */ 99 #define BITREAD_STATE_VARS \ 100 register bit_buf_type get_buffer; \ 101 register int bits_left; \ 102 bitread_working_state br_state 103 104 #define BITREAD_LOAD_STATE(cinfop,permstate) \ 105 br_state.cinfo = cinfop; \ 106 br_state.next_input_byte = cinfop->src->next_input_byte; \ 107 br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \ 108 get_buffer = permstate.get_buffer; \ 109 bits_left = permstate.bits_left; 110 111 #define BITREAD_SAVE_STATE(cinfop,permstate) \ 112 cinfop->src->next_input_byte = br_state.next_input_byte; \ 113 cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \ 114 permstate.get_buffer = get_buffer; \ 115 permstate.bits_left = bits_left 116 117 /* 118 * These macros provide the in-line portion of bit fetching. 119 * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer 120 * before using GET_BITS, PEEK_BITS, or DROP_BITS. 121 * The variables get_buffer and bits_left are assumed to be locals, 122 * but the state struct might not be (jpeg_huff_decode needs this). 123 * CHECK_BIT_BUFFER(state,n,action); 124 * Ensure there are N bits in get_buffer; if suspend, take action. 125 * val = GET_BITS(n); 126 * Fetch next N bits. 127 * val = PEEK_BITS(n); 128 * Fetch next N bits without removing them from the buffer. 129 * DROP_BITS(n); 130 * Discard next N bits. 131 * The value N should be a simple variable, not an expression, because it 132 * is evaluated multiple times. 133 */ 134 135 #define CHECK_BIT_BUFFER(state,nbits,action) \ 136 { if (bits_left < (nbits)) { \ 137 if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits)) \ 138 { action; } \ 139 get_buffer = (state).get_buffer; bits_left = (state).bits_left; } } 140 141 #define GET_BITS(nbits) \ 142 (((int) (get_buffer >> (bits_left -= (nbits)))) & BIT_MASK(nbits)) 143 144 #define PEEK_BITS(nbits) \ 145 (((int) (get_buffer >> (bits_left - (nbits)))) & BIT_MASK(nbits)) 146 147 #define DROP_BITS(nbits) \ 148 (bits_left -= (nbits)) 149 150 151 /* 152 * Code for extracting next Huffman-coded symbol from input bit stream. 153 * Again, this is time-critical and we make the main paths be macros. 154 * 155 * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits 156 * without looping. Usually, more than 95% of the Huffman codes will be 8 157 * or fewer bits long. The few overlength codes are handled with a loop, 158 * which need not be inline code. 159 * 160 * Notes about the HUFF_DECODE macro: 161 * 1. Near the end of the data segment, we may fail to get enough bits 162 * for a lookahead. In that case, we do it the hard way. 163 * 2. If the lookahead table contains no entry, the next code must be 164 * more than HUFF_LOOKAHEAD bits long. 165 * 3. jpeg_huff_decode returns -1 if forced to suspend. 166 */ 167 168 #define HUFF_DECODE(result,state,htbl,failaction,slowlabel) \ 169 { register int nb, look; \ 170 if (bits_left < HUFF_LOOKAHEAD) { \ 171 if (! jpeg_fill_bit_buffer(&state,get_buffer,bits_left, 0)) {failaction;} \ 172 get_buffer = state.get_buffer; bits_left = state.bits_left; \ 173 if (bits_left < HUFF_LOOKAHEAD) { \ 174 nb = 1; goto slowlabel; \ 175 } \ 176 } \ 177 look = PEEK_BITS(HUFF_LOOKAHEAD); \ 178 if ((nb = htbl->look_nbits[look]) != 0) { \ 179 DROP_BITS(nb); \ 180 result = htbl->look_sym[look]; \ 181 } else { \ 182 nb = HUFF_LOOKAHEAD+1; \ 183 slowlabel: \ 184 if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \ 185 { failaction; } \ 186 get_buffer = state.get_buffer; bits_left = state.bits_left; \ 187 } \ 188 } 189 190 191 /* 192 * Expanded entropy decoder object for Huffman decoding. 193 * 194 * The savable_state subrecord contains fields that change within an MCU, 195 * but must not be updated permanently until we complete the MCU. 196 */ 197 198 typedef struct { 199 unsigned int EOBRUN; /* remaining EOBs in EOBRUN */ 200 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */ 201 } savable_state; 202 203 /* This macro is to work around compilers with missing or broken 204 * structure assignment. You'll need to fix this code if you have 205 * such a compiler and you change MAX_COMPS_IN_SCAN. 206 */ 207 208 #ifndef NO_STRUCT_ASSIGN 209 #define ASSIGN_STATE(dest,src) ((dest) = (src)) 210 #else 211 #if MAX_COMPS_IN_SCAN == 4 212 #define ASSIGN_STATE(dest,src) \ 213 ((dest).EOBRUN = (src).EOBRUN, \ 214 (dest).last_dc_val[0] = (src).last_dc_val[0], \ 215 (dest).last_dc_val[1] = (src).last_dc_val[1], \ 216 (dest).last_dc_val[2] = (src).last_dc_val[2], \ 217 (dest).last_dc_val[3] = (src).last_dc_val[3]) 218 #endif 219 #endif 220 221 222 typedef struct { 223 struct jpeg_entropy_decoder pub; /* public fields */ 224 225 /* These fields are loaded into local variables at start of each MCU. 226 * In case of suspension, we exit WITHOUT updating them. 227 */ 228 bitread_perm_state bitstate; /* Bit buffer at start of MCU */ 229 savable_state saved; /* Other state at start of MCU */ 230 231 /* These fields are NOT loaded into local working state. */ 232 boolean insufficient_data; /* set TRUE after emitting warning */ 233 unsigned int restarts_to_go; /* MCUs left in this restart interval */ 234 235 /* Following two fields used only in progressive mode */ 236 237 /* Pointers to derived tables (these workspaces have image lifespan) */ 238 d_derived_tbl * derived_tbls[NUM_HUFF_TBLS]; 239 240 d_derived_tbl * ac_derived_tbl; /* active table during an AC scan */ 241 242 /* Following fields used only in sequential mode */ 243 244 /* Pointers to derived tables (these workspaces have image lifespan) */ 245 d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS]; 246 d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS]; 247 248 /* Precalculated info set up by start_pass for use in decode_mcu: */ 249 250 /* Pointers to derived tables to be used for each block within an MCU */ 251 d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU]; 252 d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU]; 253 /* Whether we care about the DC and AC coefficient values for each block */ 254 int coef_limit[D_MAX_BLOCKS_IN_MCU]; 255 } huff_entropy_decoder; 256 257 typedef huff_entropy_decoder * huff_entropy_ptr; 258 259 260 static const int jpeg_zigzag_order[8][8] = { 261 { 0, 1, 5, 6, 14, 15, 27, 28 }, 262 { 2, 4, 7, 13, 16, 26, 29, 42 }, 263 { 3, 8, 12, 17, 25, 30, 41, 43 }, 264 { 9, 11, 18, 24, 31, 40, 44, 53 }, 265 { 10, 19, 23, 32, 39, 45, 52, 54 }, 266 { 20, 22, 33, 38, 46, 51, 55, 60 }, 267 { 21, 34, 37, 47, 50, 56, 59, 61 }, 268 { 35, 36, 48, 49, 57, 58, 62, 63 } 269 }; 270 271 static const int jpeg_zigzag_order7[7][7] = { 272 { 0, 1, 5, 6, 14, 15, 27 }, 273 { 2, 4, 7, 13, 16, 26, 28 }, 274 { 3, 8, 12, 17, 25, 29, 38 }, 275 { 9, 11, 18, 24, 30, 37, 39 }, 276 { 10, 19, 23, 31, 36, 40, 45 }, 277 { 20, 22, 32, 35, 41, 44, 46 }, 278 { 21, 33, 34, 42, 43, 47, 48 } 279 }; 280 281 static const int jpeg_zigzag_order6[6][6] = { 282 { 0, 1, 5, 6, 14, 15 }, 283 { 2, 4, 7, 13, 16, 25 }, 284 { 3, 8, 12, 17, 24, 26 }, 285 { 9, 11, 18, 23, 27, 32 }, 286 { 10, 19, 22, 28, 31, 33 }, 287 { 20, 21, 29, 30, 34, 35 } 288 }; 289 290 static const int jpeg_zigzag_order5[5][5] = { 291 { 0, 1, 5, 6, 14 }, 292 { 2, 4, 7, 13, 15 }, 293 { 3, 8, 12, 16, 21 }, 294 { 9, 11, 17, 20, 22 }, 295 { 10, 18, 19, 23, 24 } 296 }; 297 298 static const int jpeg_zigzag_order4[4][4] = { 299 { 0, 1, 5, 6 }, 300 { 2, 4, 7, 12 }, 301 { 3, 8, 11, 13 }, 302 { 9, 10, 14, 15 } 303 }; 304 305 static const int jpeg_zigzag_order3[3][3] = { 306 { 0, 1, 5 }, 307 { 2, 4, 6 }, 308 { 3, 7, 8 } 309 }; 310 311 static const int jpeg_zigzag_order2[2][2] = { 312 { 0, 1 }, 313 { 2, 3 } 314 }; 315 316 317 /* 318 * Compute the derived values for a Huffman table. 319 * This routine also performs some validation checks on the table. 320 */ 321 322 LOCAL(void) 323 jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno, 324 d_derived_tbl ** pdtbl) 325 { 326 JHUFF_TBL *htbl; 327 d_derived_tbl *dtbl; 328 int p, i, l, si, numsymbols; 329 int lookbits, ctr; 330 char huffsize[257]; 331 unsigned int huffcode[257]; 332 unsigned int code; 333 334 /* Note that huffsize[] and huffcode[] are filled in code-length order, 335 * paralleling the order of the symbols themselves in htbl->huffval[]. 336 */ 337 338 /* Find the input Huffman table */ 339 if (tblno < 0 || tblno >= NUM_HUFF_TBLS) 340 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno); 341 htbl = 342 isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno]; 343 if (htbl == NULL) 344 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno); 345 346 /* Allocate a workspace if we haven't already done so. */ 347 if (*pdtbl == NULL) 348 *pdtbl = (d_derived_tbl *) 349 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 350 SIZEOF(d_derived_tbl)); 351 dtbl = *pdtbl; 352 dtbl->pub = htbl; /* fill in back link */ 353 354 /* Figure C.1: make table of Huffman code length for each symbol */ 355 356 p = 0; 357 for (l = 1; l <= 16; l++) { 358 i = (int) htbl->bits[l]; 359 if (i < 0 || p + i > 256) /* protect against table overrun */ 360 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 361 while (i--) 362 huffsize[p++] = (char) l; 363 } 364 huffsize[p] = 0; 365 numsymbols = p; 366 367 /* Figure C.2: generate the codes themselves */ 368 /* We also validate that the counts represent a legal Huffman code tree. */ 369 370 code = 0; 371 si = huffsize[0]; 372 p = 0; 373 while (huffsize[p]) { 374 while (((int) huffsize[p]) == si) { 375 huffcode[p++] = code; 376 code++; 377 } 378 /* code is now 1 more than the last code used for codelength si; but 379 * it must still fit in si bits, since no code is allowed to be all ones. 380 */ 381 if (((INT32) code) >= (((INT32) 1) << si)) 382 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 383 code <<= 1; 384 si++; 385 } 386 387 /* Figure F.15: generate decoding tables for bit-sequential decoding */ 388 389 p = 0; 390 for (l = 1; l <= 16; l++) { 391 if (htbl->bits[l]) { 392 /* valoffset[l] = huffval[] index of 1st symbol of code length l, 393 * minus the minimum code of length l 394 */ 395 dtbl->valoffset[l] = (INT32) p - (INT32) huffcode[p]; 396 p += htbl->bits[l]; 397 dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */ 398 } else { 399 dtbl->maxcode[l] = -1; /* -1 if no codes of this length */ 400 } 401 } 402 dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */ 403 404 /* Compute lookahead tables to speed up decoding. 405 * First we set all the table entries to 0, indicating "too long"; 406 * then we iterate through the Huffman codes that are short enough and 407 * fill in all the entries that correspond to bit sequences starting 408 * with that code. 409 */ 410 411 MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits)); 412 413 p = 0; 414 for (l = 1; l <= HUFF_LOOKAHEAD; l++) { 415 for (i = 1; i <= (int) htbl->bits[l]; i++, p++) { 416 /* l = current code's length, p = its index in huffcode[] & huffval[]. */ 417 /* Generate left-justified code followed by all possible bit sequences */ 418 lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l); 419 for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) { 420 dtbl->look_nbits[lookbits] = l; 421 dtbl->look_sym[lookbits] = htbl->huffval[p]; 422 lookbits++; 423 } 424 } 425 } 426 427 /* Validate symbols as being reasonable. 428 * For AC tables, we make no check, but accept all byte values 0..255. 429 * For DC tables, we require the symbols to be in range 0..15. 430 * (Tighter bounds could be applied depending on the data depth and mode, 431 * but this is sufficient to ensure safe decoding.) 432 */ 433 if (isDC) { 434 for (i = 0; i < numsymbols; i++) { 435 int sym = htbl->huffval[i]; 436 if (sym < 0 || sym > 15) 437 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 438 } 439 } 440 } 441 442 443 /* 444 * Out-of-line code for bit fetching. 445 * Note: current values of get_buffer and bits_left are passed as parameters, 446 * but are returned in the corresponding fields of the state struct. 447 * 448 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width 449 * of get_buffer to be used. (On machines with wider words, an even larger 450 * buffer could be used.) However, on some machines 32-bit shifts are 451 * quite slow and take time proportional to the number of places shifted. 452 * (This is true with most PC compilers, for instance.) In this case it may 453 * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the 454 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer. 455 */ 456 457 #ifdef SLOW_SHIFT_32 458 #define MIN_GET_BITS 15 /* minimum allowable value */ 459 #else 460 #define MIN_GET_BITS (BIT_BUF_SIZE-7) 461 #endif 462 463 464 LOCAL(boolean) 465 jpeg_fill_bit_buffer (bitread_working_state * state, 466 register bit_buf_type get_buffer, register int bits_left, 467 int nbits) 468 /* Load up the bit buffer to a depth of at least nbits */ 469 { 470 /* Copy heavily used state fields into locals (hopefully registers) */ 471 register const JOCTET * next_input_byte = state->next_input_byte; 472 register size_t bytes_in_buffer = state->bytes_in_buffer; 473 j_decompress_ptr cinfo = state->cinfo; 474 475 /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */ 476 /* (It is assumed that no request will be for more than that many bits.) */ 477 /* We fail to do so only if we hit a marker or are forced to suspend. */ 478 479 if (cinfo->unread_marker == 0) { /* cannot advance past a marker */ 480 while (bits_left < MIN_GET_BITS) { 481 register int c; 482 483 /* Attempt to read a byte */ 484 if (bytes_in_buffer == 0) { 485 if (! (*cinfo->src->fill_input_buffer) (cinfo)) 486 return FALSE; 487 next_input_byte = cinfo->src->next_input_byte; 488 bytes_in_buffer = cinfo->src->bytes_in_buffer; 489 } 490 bytes_in_buffer--; 491 c = GETJOCTET(*next_input_byte++); 492 493 /* If it's 0xFF, check and discard stuffed zero byte */ 494 if (c == 0xFF) { 495 /* Loop here to discard any padding FF's on terminating marker, 496 * so that we can save a valid unread_marker value. NOTE: we will 497 * accept multiple FF's followed by a 0 as meaning a single FF data 498 * byte. This data pattern is not valid according to the standard. 499 */ 500 do { 501 if (bytes_in_buffer == 0) { 502 if (! (*cinfo->src->fill_input_buffer) (cinfo)) 503 return FALSE; 504 next_input_byte = cinfo->src->next_input_byte; 505 bytes_in_buffer = cinfo->src->bytes_in_buffer; 506 } 507 bytes_in_buffer--; 508 c = GETJOCTET(*next_input_byte++); 509 } while (c == 0xFF); 510 511 if (c == 0) { 512 /* Found FF/00, which represents an FF data byte */ 513 c = 0xFF; 514 } else { 515 /* Oops, it's actually a marker indicating end of compressed data. 516 * Save the marker code for later use. 517 * Fine point: it might appear that we should save the marker into 518 * bitread working state, not straight into permanent state. But 519 * once we have hit a marker, we cannot need to suspend within the 520 * current MCU, because we will read no more bytes from the data 521 * source. So it is OK to update permanent state right away. 522 */ 523 cinfo->unread_marker = c; 524 /* See if we need to insert some fake zero bits. */ 525 goto no_more_bytes; 526 } 527 } 528 529 /* OK, load c into get_buffer */ 530 get_buffer = (get_buffer << 8) | c; 531 bits_left += 8; 532 } /* end while */ 533 } else { 534 no_more_bytes: 535 /* We get here if we've read the marker that terminates the compressed 536 * data segment. There should be enough bits in the buffer register 537 * to satisfy the request; if so, no problem. 538 */ 539 if (nbits > bits_left) { 540 /* Uh-oh. Report corrupted data to user and stuff zeroes into 541 * the data stream, so that we can produce some kind of image. 542 * We use a nonvolatile flag to ensure that only one warning message 543 * appears per data segment. 544 */ 545 if (! ((huff_entropy_ptr) cinfo->entropy)->insufficient_data) { 546 WARNMS(cinfo, JWRN_HIT_MARKER); 547 ((huff_entropy_ptr) cinfo->entropy)->insufficient_data = TRUE; 548 } 549 /* Fill the buffer with zero bits */ 550 get_buffer <<= MIN_GET_BITS - bits_left; 551 bits_left = MIN_GET_BITS; 552 } 553 } 554 555 /* Unload the local registers */ 556 state->next_input_byte = next_input_byte; 557 state->bytes_in_buffer = bytes_in_buffer; 558 state->get_buffer = get_buffer; 559 state->bits_left = bits_left; 560 561 return TRUE; 562 } 563 564 565 /* 566 * Figure F.12: extend sign bit. 567 * On some machines, a shift and sub will be faster than a table lookup. 568 */ 569 570 #ifdef AVOID_TABLES 571 572 #define BIT_MASK(nbits) ((1<<(nbits))-1) 573 #define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) - ((1<<(s))-1) : (x)) 574 575 #else 576 577 #define BIT_MASK(nbits) bmask[nbits] 578 #define HUFF_EXTEND(x,s) ((x) <= bmask[(s) - 1] ? (x) - bmask[s] : (x)) 579 580 static const int bmask[16] = /* bmask[n] is mask for n rightmost bits */ 581 { 0, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F, 0x003F, 0x007F, 0x00FF, 582 0x01FF, 0x03FF, 0x07FF, 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF }; 583 584 #endif /* AVOID_TABLES */ 585 586 587 /* 588 * Out-of-line code for Huffman code decoding. 589 */ 590 591 LOCAL(int) 592 jpeg_huff_decode (bitread_working_state * state, 593 register bit_buf_type get_buffer, register int bits_left, 594 d_derived_tbl * htbl, int min_bits) 595 { 596 register int l = min_bits; 597 register INT32 code; 598 599 /* HUFF_DECODE has determined that the code is at least min_bits */ 600 /* bits long, so fetch that many bits in one swoop. */ 601 602 CHECK_BIT_BUFFER(*state, l, return -1); 603 code = GET_BITS(l); 604 605 /* Collect the rest of the Huffman code one bit at a time. */ 606 /* This is per Figure F.16 in the JPEG spec. */ 607 608 while (code > htbl->maxcode[l]) { 609 code <<= 1; 610 CHECK_BIT_BUFFER(*state, 1, return -1); 611 code |= GET_BITS(1); 612 l++; 613 } 614 615 /* Unload the local registers */ 616 state->get_buffer = get_buffer; 617 state->bits_left = bits_left; 618 619 /* With garbage input we may reach the sentinel value l = 17. */ 620 621 if (l > 16) { 622 WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE); 623 return 0; /* fake a zero as the safest result */ 624 } 625 626 return htbl->pub->huffval[ (int) (code + htbl->valoffset[l]) ]; 627 } 628 629 630 /* 631 * Check for a restart marker & resynchronize decoder. 632 * Returns FALSE if must suspend. 633 */ 634 635 LOCAL(boolean) 636 process_restart (j_decompress_ptr cinfo) 637 { 638 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 639 int ci; 640 641 /* Throw away any unused bits remaining in bit buffer; */ 642 /* include any full bytes in next_marker's count of discarded bytes */ 643 cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8; 644 entropy->bitstate.bits_left = 0; 645 646 /* Advance past the RSTn marker */ 647 if (! (*cinfo->marker->read_restart_marker) (cinfo)) 648 return FALSE; 649 650 /* Re-initialize DC predictions to 0 */ 651 for (ci = 0; ci < cinfo->comps_in_scan; ci++) 652 entropy->saved.last_dc_val[ci] = 0; 653 /* Re-init EOB run count, too */ 654 entropy->saved.EOBRUN = 0; 655 656 /* Reset restart counter */ 657 entropy->restarts_to_go = cinfo->restart_interval; 658 659 /* Reset out-of-data flag, unless read_restart_marker left us smack up 660 * against a marker. In that case we will end up treating the next data 661 * segment as empty, and we can avoid producing bogus output pixels by 662 * leaving the flag set. 663 */ 664 if (cinfo->unread_marker == 0) 665 entropy->insufficient_data = FALSE; 666 667 return TRUE; 668 } 669 670 671 /* 672 * Huffman MCU decoding. 673 * Each of these routines decodes and returns one MCU's worth of 674 * Huffman-compressed coefficients. 675 * The coefficients are reordered from zigzag order into natural array order, 676 * but are not dequantized. 677 * 678 * The i'th block of the MCU is stored into the block pointed to by 679 * MCU_data[i]. WE ASSUME THIS AREA IS INITIALLY ZEROED BY THE CALLER. 680 * (Wholesale zeroing is usually a little faster than retail...) 681 * 682 * We return FALSE if data source requested suspension. In that case no 683 * changes have been made to permanent state. (Exception: some output 684 * coefficients may already have been assigned. This is harmless for 685 * spectral selection, since we'll just re-assign them on the next call. 686 * Successive approximation AC refinement has to be more careful, however.) 687 */ 688 689 /* 690 * MCU decoding for DC initial scan (either spectral selection, 691 * or first pass of successive approximation). 692 */ 693 694 METHODDEF(boolean) 695 decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 696 { 697 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 698 int Al = cinfo->Al; 699 register int s, r; 700 int blkn, ci; 701 JBLOCKROW block; 702 BITREAD_STATE_VARS; 703 savable_state state; 704 d_derived_tbl * tbl; 705 jpeg_component_info * compptr; 706 707 /* Process restart marker if needed; may have to suspend */ 708 if (cinfo->restart_interval) { 709 if (entropy->restarts_to_go == 0) 710 if (! process_restart(cinfo)) 711 return FALSE; 712 } 713 714 /* If we've run out of data, just leave the MCU set to zeroes. 715 * This way, we return uniform gray for the remainder of the segment. 716 */ 717 if (! entropy->insufficient_data) { 718 719 /* Load up working state */ 720 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 721 ASSIGN_STATE(state, entropy->saved); 722 723 /* Outer loop handles each block in the MCU */ 724 725 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 726 block = MCU_data[blkn]; 727 ci = cinfo->MCU_membership[blkn]; 728 compptr = cinfo->cur_comp_info[ci]; 729 tbl = entropy->derived_tbls[compptr->dc_tbl_no]; 730 731 /* Decode a single block's worth of coefficients */ 732 733 /* Section F.2.2.1: decode the DC coefficient difference */ 734 HUFF_DECODE(s, br_state, tbl, return FALSE, label1); 735 if (s) { 736 CHECK_BIT_BUFFER(br_state, s, return FALSE); 737 r = GET_BITS(s); 738 s = HUFF_EXTEND(r, s); 739 } 740 741 /* Convert DC difference to actual value, update last_dc_val */ 742 s += state.last_dc_val[ci]; 743 state.last_dc_val[ci] = s; 744 /* Scale and output the coefficient (assumes jpeg_natural_order[0]=0) */ 745 (*block)[0] = (JCOEF) (s << Al); 746 } 747 748 /* Completed MCU, so update state */ 749 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 750 ASSIGN_STATE(entropy->saved, state); 751 } 752 753 /* Account for restart interval (no-op if not using restarts) */ 754 entropy->restarts_to_go--; 755 756 return TRUE; 757 } 758 759 760 /* 761 * MCU decoding for AC initial scan (either spectral selection, 762 * or first pass of successive approximation). 763 */ 764 765 METHODDEF(boolean) 766 decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 767 { 768 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 769 register int s, k, r; 770 unsigned int EOBRUN; 771 int Se, Al; 772 const int * natural_order; 773 JBLOCKROW block; 774 BITREAD_STATE_VARS; 775 d_derived_tbl * tbl; 776 777 /* Process restart marker if needed; may have to suspend */ 778 if (cinfo->restart_interval) { 779 if (entropy->restarts_to_go == 0) 780 if (! process_restart(cinfo)) 781 return FALSE; 782 } 783 784 /* If we've run out of data, just leave the MCU set to zeroes. 785 * This way, we return uniform gray for the remainder of the segment. 786 */ 787 if (! entropy->insufficient_data) { 788 789 Se = cinfo->Se; 790 Al = cinfo->Al; 791 natural_order = cinfo->natural_order; 792 793 /* Load up working state. 794 * We can avoid loading/saving bitread state if in an EOB run. 795 */ 796 EOBRUN = entropy->saved.EOBRUN; /* only part of saved state we need */ 797 798 /* There is always only one block per MCU */ 799 800 if (EOBRUN) /* if it's a band of zeroes... */ 801 EOBRUN--; /* ...process it now (we do nothing) */ 802 else { 803 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 804 block = MCU_data[0]; 805 tbl = entropy->ac_derived_tbl; 806 807 for (k = cinfo->Ss; k <= Se; k++) { 808 HUFF_DECODE(s, br_state, tbl, return FALSE, label2); 809 r = s >> 4; 810 s &= 15; 811 if (s) { 812 k += r; 813 CHECK_BIT_BUFFER(br_state, s, return FALSE); 814 r = GET_BITS(s); 815 s = HUFF_EXTEND(r, s); 816 /* Scale and output coefficient in natural (dezigzagged) order */ 817 (*block)[natural_order[k]] = (JCOEF) (s << Al); 818 } else { 819 if (r != 15) { /* EOBr, run length is 2^r + appended bits */ 820 if (r) { /* EOBr, r > 0 */ 821 EOBRUN = 1 << r; 822 CHECK_BIT_BUFFER(br_state, r, return FALSE); 823 r = GET_BITS(r); 824 EOBRUN += r; 825 EOBRUN--; /* this band is processed at this moment */ 826 } 827 break; /* force end-of-band */ 828 } 829 k += 15; /* ZRL: skip 15 zeroes in band */ 830 } 831 } 832 833 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 834 } 835 836 /* Completed MCU, so update state */ 837 entropy->saved.EOBRUN = EOBRUN; /* only part of saved state we need */ 838 } 839 840 /* Account for restart interval (no-op if not using restarts) */ 841 entropy->restarts_to_go--; 842 843 return TRUE; 844 } 845 846 847 /* 848 * MCU decoding for DC successive approximation refinement scan. 849 * Note: we assume such scans can be multi-component, although the spec 850 * is not very clear on the point. 851 */ 852 853 METHODDEF(boolean) 854 decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 855 { 856 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 857 int p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */ 858 int blkn; 859 JBLOCKROW block; 860 BITREAD_STATE_VARS; 861 862 /* Process restart marker if needed; may have to suspend */ 863 if (cinfo->restart_interval) { 864 if (entropy->restarts_to_go == 0) 865 if (! process_restart(cinfo)) 866 return FALSE; 867 } 868 869 /* Not worth the cycles to check insufficient_data here, 870 * since we will not change the data anyway if we read zeroes. 871 */ 872 873 /* Load up working state */ 874 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 875 876 /* Outer loop handles each block in the MCU */ 877 878 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 879 block = MCU_data[blkn]; 880 881 /* Encoded data is simply the next bit of the two's-complement DC value */ 882 CHECK_BIT_BUFFER(br_state, 1, return FALSE); 883 if (GET_BITS(1)) 884 (*block)[0] |= p1; 885 /* Note: since we use |=, repeating the assignment later is safe */ 886 } 887 888 /* Completed MCU, so update state */ 889 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 890 891 /* Account for restart interval (no-op if not using restarts) */ 892 entropy->restarts_to_go--; 893 894 return TRUE; 895 } 896 897 898 /* 899 * MCU decoding for AC successive approximation refinement scan. 900 */ 901 902 METHODDEF(boolean) 903 decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 904 { 905 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 906 register int s, k, r; 907 unsigned int EOBRUN; 908 int Se, p1, m1; 909 const int * natural_order; 910 JBLOCKROW block; 911 JCOEFPTR thiscoef; 912 BITREAD_STATE_VARS; 913 d_derived_tbl * tbl; 914 int num_newnz; 915 int newnz_pos[DCTSIZE2]; 916 917 /* Process restart marker if needed; may have to suspend */ 918 if (cinfo->restart_interval) { 919 if (entropy->restarts_to_go == 0) 920 if (! process_restart(cinfo)) 921 return FALSE; 922 } 923 924 /* If we've run out of data, don't modify the MCU. 925 */ 926 if (! entropy->insufficient_data) { 927 928 Se = cinfo->Se; 929 p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */ 930 m1 = (-1) << cinfo->Al; /* -1 in the bit position being coded */ 931 natural_order = cinfo->natural_order; 932 933 /* Load up working state */ 934 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 935 EOBRUN = entropy->saved.EOBRUN; /* only part of saved state we need */ 936 937 /* There is always only one block per MCU */ 938 block = MCU_data[0]; 939 tbl = entropy->ac_derived_tbl; 940 941 /* If we are forced to suspend, we must undo the assignments to any newly 942 * nonzero coefficients in the block, because otherwise we'd get confused 943 * next time about which coefficients were already nonzero. 944 * But we need not undo addition of bits to already-nonzero coefficients; 945 * instead, we can test the current bit to see if we already did it. 946 */ 947 num_newnz = 0; 948 949 /* initialize coefficient loop counter to start of band */ 950 k = cinfo->Ss; 951 952 if (EOBRUN == 0) { 953 do { 954 HUFF_DECODE(s, br_state, tbl, goto undoit, label3); 955 r = s >> 4; 956 s &= 15; 957 if (s) { 958 if (s != 1) /* size of new coef should always be 1 */ 959 WARNMS(cinfo, JWRN_HUFF_BAD_CODE); 960 CHECK_BIT_BUFFER(br_state, 1, goto undoit); 961 if (GET_BITS(1)) 962 s = p1; /* newly nonzero coef is positive */ 963 else 964 s = m1; /* newly nonzero coef is negative */ 965 } else { 966 if (r != 15) { 967 EOBRUN = 1 << r; /* EOBr, run length is 2^r + appended bits */ 968 if (r) { 969 CHECK_BIT_BUFFER(br_state, r, goto undoit); 970 r = GET_BITS(r); 971 EOBRUN += r; 972 } 973 break; /* rest of block is handled by EOB logic */ 974 } 975 /* note s = 0 for processing ZRL */ 976 } 977 /* Advance over already-nonzero coefs and r still-zero coefs, 978 * appending correction bits to the nonzeroes. A correction bit is 1 979 * if the absolute value of the coefficient must be increased. 980 */ 981 do { 982 thiscoef = *block + natural_order[k]; 983 if (*thiscoef) { 984 CHECK_BIT_BUFFER(br_state, 1, goto undoit); 985 if (GET_BITS(1)) { 986 if ((*thiscoef & p1) == 0) { /* do nothing if already set it */ 987 if (*thiscoef >= 0) 988 *thiscoef += p1; 989 else 990 *thiscoef += m1; 991 } 992 } 993 } else { 994 if (--r < 0) 995 break; /* reached target zero coefficient */ 996 } 997 k++; 998 } while (k <= Se); 999 if (s) { 1000 int pos = natural_order[k]; 1001 /* Output newly nonzero coefficient */ 1002 (*block)[pos] = (JCOEF) s; 1003 /* Remember its position in case we have to suspend */ 1004 newnz_pos[num_newnz++] = pos; 1005 } 1006 k++; 1007 } while (k <= Se); 1008 } 1009 1010 if (EOBRUN) { 1011 /* Scan any remaining coefficient positions after the end-of-band 1012 * (the last newly nonzero coefficient, if any). Append a correction 1013 * bit to each already-nonzero coefficient. A correction bit is 1 1014 * if the absolute value of the coefficient must be increased. 1015 */ 1016 do { 1017 thiscoef = *block + natural_order[k]; 1018 if (*thiscoef) { 1019 CHECK_BIT_BUFFER(br_state, 1, goto undoit); 1020 if (GET_BITS(1)) { 1021 if ((*thiscoef & p1) == 0) { /* do nothing if already changed it */ 1022 if (*thiscoef >= 0) 1023 *thiscoef += p1; 1024 else 1025 *thiscoef += m1; 1026 } 1027 } 1028 } 1029 k++; 1030 } while (k <= Se); 1031 /* Count one block completed in EOB run */ 1032 EOBRUN--; 1033 } 1034 1035 /* Completed MCU, so update state */ 1036 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 1037 entropy->saved.EOBRUN = EOBRUN; /* only part of saved state we need */ 1038 } 1039 1040 /* Account for restart interval (no-op if not using restarts) */ 1041 entropy->restarts_to_go--; 1042 1043 return TRUE; 1044 1045 undoit: 1046 /* Re-zero any output coefficients that we made newly nonzero */ 1047 while (num_newnz) 1048 (*block)[newnz_pos[--num_newnz]] = 0; 1049 1050 return FALSE; 1051 } 1052 1053 1054 /* 1055 * Decode one MCU's worth of Huffman-compressed coefficients, 1056 * partial blocks. 1057 */ 1058 1059 METHODDEF(boolean) 1060 decode_mcu_sub (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 1061 { 1062 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 1063 const int * natural_order; 1064 int Se, blkn; 1065 BITREAD_STATE_VARS; 1066 savable_state state; 1067 1068 /* Process restart marker if needed; may have to suspend */ 1069 if (cinfo->restart_interval) { 1070 if (entropy->restarts_to_go == 0) 1071 if (! process_restart(cinfo)) 1072 return FALSE; 1073 } 1074 1075 /* If we've run out of data, just leave the MCU set to zeroes. 1076 * This way, we return uniform gray for the remainder of the segment. 1077 */ 1078 if (! entropy->insufficient_data) { 1079 1080 natural_order = cinfo->natural_order; 1081 Se = cinfo->lim_Se; 1082 1083 /* Load up working state */ 1084 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 1085 ASSIGN_STATE(state, entropy->saved); 1086 1087 /* Outer loop handles each block in the MCU */ 1088 1089 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 1090 JBLOCKROW block = MCU_data[blkn]; 1091 d_derived_tbl * htbl; 1092 register int s, k, r; 1093 int coef_limit, ci; 1094 1095 /* Decode a single block's worth of coefficients */ 1096 1097 /* Section F.2.2.1: decode the DC coefficient difference */ 1098 htbl = entropy->dc_cur_tbls[blkn]; 1099 HUFF_DECODE(s, br_state, htbl, return FALSE, label1); 1100 1101 htbl = entropy->ac_cur_tbls[blkn]; 1102 k = 1; 1103 coef_limit = entropy->coef_limit[blkn]; 1104 if (coef_limit) { 1105 /* Convert DC difference to actual value, update last_dc_val */ 1106 if (s) { 1107 CHECK_BIT_BUFFER(br_state, s, return FALSE); 1108 r = GET_BITS(s); 1109 s = HUFF_EXTEND(r, s); 1110 } 1111 ci = cinfo->MCU_membership[blkn]; 1112 s += state.last_dc_val[ci]; 1113 state.last_dc_val[ci] = s; 1114 /* Output the DC coefficient */ 1115 (*block)[0] = (JCOEF) s; 1116 1117 /* Section F.2.2.2: decode the AC coefficients */ 1118 /* Since zeroes are skipped, output area must be cleared beforehand */ 1119 for (; k < coef_limit; k++) { 1120 HUFF_DECODE(s, br_state, htbl, return FALSE, label2); 1121 1122 r = s >> 4; 1123 s &= 15; 1124 1125 if (s) { 1126 k += r; 1127 CHECK_BIT_BUFFER(br_state, s, return FALSE); 1128 r = GET_BITS(s); 1129 s = HUFF_EXTEND(r, s); 1130 /* Output coefficient in natural (dezigzagged) order. 1131 * Note: the extra entries in natural_order[] will save us 1132 * if k > Se, which could happen if the data is corrupted. 1133 */ 1134 (*block)[natural_order[k]] = (JCOEF) s; 1135 } else { 1136 if (r != 15) 1137 goto EndOfBlock; 1138 k += 15; 1139 } 1140 } 1141 } else { 1142 if (s) { 1143 CHECK_BIT_BUFFER(br_state, s, return FALSE); 1144 DROP_BITS(s); 1145 } 1146 } 1147 1148 /* Section F.2.2.2: decode the AC coefficients */ 1149 /* In this path we just discard the values */ 1150 for (; k <= Se; k++) { 1151 HUFF_DECODE(s, br_state, htbl, return FALSE, label3); 1152 1153 r = s >> 4; 1154 s &= 15; 1155 1156 if (s) { 1157 k += r; 1158 CHECK_BIT_BUFFER(br_state, s, return FALSE); 1159 DROP_BITS(s); 1160 } else { 1161 if (r != 15) 1162 break; 1163 k += 15; 1164 } 1165 } 1166 1167 EndOfBlock: ; 1168 } 1169 1170 /* Completed MCU, so update state */ 1171 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 1172 ASSIGN_STATE(entropy->saved, state); 1173 } 1174 1175 /* Account for restart interval (no-op if not using restarts) */ 1176 entropy->restarts_to_go--; 1177 1178 return TRUE; 1179 } 1180 1181 1182 /* 1183 * Decode one MCU's worth of Huffman-compressed coefficients, 1184 * full-size blocks. 1185 */ 1186 1187 METHODDEF(boolean) 1188 decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 1189 { 1190 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 1191 int blkn; 1192 BITREAD_STATE_VARS; 1193 savable_state state; 1194 1195 /* Process restart marker if needed; may have to suspend */ 1196 if (cinfo->restart_interval) { 1197 if (entropy->restarts_to_go == 0) 1198 if (! process_restart(cinfo)) 1199 return FALSE; 1200 } 1201 1202 /* If we've run out of data, just leave the MCU set to zeroes. 1203 * This way, we return uniform gray for the remainder of the segment. 1204 */ 1205 if (! entropy->insufficient_data) { 1206 1207 /* Load up working state */ 1208 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 1209 ASSIGN_STATE(state, entropy->saved); 1210 1211 /* Outer loop handles each block in the MCU */ 1212 1213 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 1214 JBLOCKROW block = MCU_data[blkn]; 1215 d_derived_tbl * htbl; 1216 register int s, k, r; 1217 int coef_limit, ci; 1218 1219 /* Decode a single block's worth of coefficients */ 1220 1221 /* Section F.2.2.1: decode the DC coefficient difference */ 1222 htbl = entropy->dc_cur_tbls[blkn]; 1223 HUFF_DECODE(s, br_state, htbl, return FALSE, label1); 1224 1225 htbl = entropy->ac_cur_tbls[blkn]; 1226 k = 1; 1227 coef_limit = entropy->coef_limit[blkn]; 1228 if (coef_limit) { 1229 /* Convert DC difference to actual value, update last_dc_val */ 1230 if (s) { 1231 CHECK_BIT_BUFFER(br_state, s, return FALSE); 1232 r = GET_BITS(s); 1233 s = HUFF_EXTEND(r, s); 1234 } 1235 ci = cinfo->MCU_membership[blkn]; 1236 s += state.last_dc_val[ci]; 1237 state.last_dc_val[ci] = s; 1238 /* Output the DC coefficient */ 1239 (*block)[0] = (JCOEF) s; 1240 1241 /* Section F.2.2.2: decode the AC coefficients */ 1242 /* Since zeroes are skipped, output area must be cleared beforehand */ 1243 for (; k < coef_limit; k++) { 1244 HUFF_DECODE(s, br_state, htbl, return FALSE, label2); 1245 1246 r = s >> 4; 1247 s &= 15; 1248 1249 if (s) { 1250 k += r; 1251 CHECK_BIT_BUFFER(br_state, s, return FALSE); 1252 r = GET_BITS(s); 1253 s = HUFF_EXTEND(r, s); 1254 /* Output coefficient in natural (dezigzagged) order. 1255 * Note: the extra entries in jpeg_natural_order[] will save us 1256 * if k >= DCTSIZE2, which could happen if the data is corrupted. 1257 */ 1258 (*block)[jpeg_natural_order[k]] = (JCOEF) s; 1259 } else { 1260 if (r != 15) 1261 goto EndOfBlock; 1262 k += 15; 1263 } 1264 } 1265 } else { 1266 if (s) { 1267 CHECK_BIT_BUFFER(br_state, s, return FALSE); 1268 DROP_BITS(s); 1269 } 1270 } 1271 1272 /* Section F.2.2.2: decode the AC coefficients */ 1273 /* In this path we just discard the values */ 1274 for (; k < DCTSIZE2; k++) { 1275 HUFF_DECODE(s, br_state, htbl, return FALSE, label3); 1276 1277 r = s >> 4; 1278 s &= 15; 1279 1280 if (s) { 1281 k += r; 1282 CHECK_BIT_BUFFER(br_state, s, return FALSE); 1283 DROP_BITS(s); 1284 } else { 1285 if (r != 15) 1286 break; 1287 k += 15; 1288 } 1289 } 1290 1291 EndOfBlock: ; 1292 } 1293 1294 /* Completed MCU, so update state */ 1295 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 1296 ASSIGN_STATE(entropy->saved, state); 1297 } 1298 1299 /* Account for restart interval (no-op if not using restarts) */ 1300 entropy->restarts_to_go--; 1301 1302 return TRUE; 1303 } 1304 1305 1306 /* 1307 * Initialize for a Huffman-compressed scan. 1308 */ 1309 1310 METHODDEF(void) 1311 start_pass_huff_decoder (j_decompress_ptr cinfo) 1312 { 1313 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 1314 int ci, blkn, tbl, i; 1315 jpeg_component_info * compptr; 1316 1317 if (cinfo->progressive_mode) { 1318 /* Validate progressive scan parameters */ 1319 if (cinfo->Ss == 0) { 1320 if (cinfo->Se != 0) 1321 goto bad; 1322 } else { 1323 /* need not check Ss/Se < 0 since they came from unsigned bytes */ 1324 if (cinfo->Se < cinfo->Ss || cinfo->Se > cinfo->lim_Se) 1325 goto bad; 1326 /* AC scans may have only one component */ 1327 if (cinfo->comps_in_scan != 1) 1328 goto bad; 1329 } 1330 if (cinfo->Ah != 0) { 1331 /* Successive approximation refinement scan: must have Al = Ah-1. */ 1332 if (cinfo->Ah-1 != cinfo->Al) 1333 goto bad; 1334 } 1335 if (cinfo->Al > 13) { /* need not check for < 0 */ 1336 /* Arguably the maximum Al value should be less than 13 for 8-bit precision, 1337 * but the spec doesn't say so, and we try to be liberal about what we 1338 * accept. Note: large Al values could result in out-of-range DC 1339 * coefficients during early scans, leading to bizarre displays due to 1340 * overflows in the IDCT math. But we won't crash. 1341 */ 1342 bad: 1343 ERREXIT4(cinfo, JERR_BAD_PROGRESSION, 1344 cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al); 1345 } 1346 /* Update progression status, and verify that scan order is legal. 1347 * Note that inter-scan inconsistencies are treated as warnings 1348 * not fatal errors ... not clear if this is right way to behave. 1349 */ 1350 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 1351 int coefi, cindex = cinfo->cur_comp_info[ci]->component_index; 1352 int *coef_bit_ptr = & cinfo->coef_bits[cindex][0]; 1353 if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */ 1354 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0); 1355 for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) { 1356 int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi]; 1357 if (cinfo->Ah != expected) 1358 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi); 1359 coef_bit_ptr[coefi] = cinfo->Al; 1360 } 1361 } 1362 1363 /* Select MCU decoding routine */ 1364 if (cinfo->Ah == 0) { 1365 if (cinfo->Ss == 0) 1366 entropy->pub.decode_mcu = decode_mcu_DC_first; 1367 else 1368 entropy->pub.decode_mcu = decode_mcu_AC_first; 1369 } else { 1370 if (cinfo->Ss == 0) 1371 entropy->pub.decode_mcu = decode_mcu_DC_refine; 1372 else 1373 entropy->pub.decode_mcu = decode_mcu_AC_refine; 1374 } 1375 1376 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 1377 compptr = cinfo->cur_comp_info[ci]; 1378 /* Make sure requested tables are present, and compute derived tables. 1379 * We may build same derived table more than once, but it's not expensive. 1380 */ 1381 if (cinfo->Ss == 0) { 1382 if (cinfo->Ah == 0) { /* DC refinement needs no table */ 1383 tbl = compptr->dc_tbl_no; 1384 jpeg_make_d_derived_tbl(cinfo, TRUE, tbl, 1385 & entropy->derived_tbls[tbl]); 1386 } 1387 } else { 1388 tbl = compptr->ac_tbl_no; 1389 jpeg_make_d_derived_tbl(cinfo, FALSE, tbl, 1390 & entropy->derived_tbls[tbl]); 1391 /* remember the single active table */ 1392 entropy->ac_derived_tbl = entropy->derived_tbls[tbl]; 1393 } 1394 /* Initialize DC predictions to 0 */ 1395 entropy->saved.last_dc_val[ci] = 0; 1396 } 1397 1398 /* Initialize private state variables */ 1399 entropy->saved.EOBRUN = 0; 1400 } else { 1401 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG. 1402 * This ought to be an error condition, but we make it a warning because 1403 * there are some baseline files out there with all zeroes in these bytes. 1404 */ 1405 if (cinfo->Ss != 0 || cinfo->Ah != 0 || cinfo->Al != 0 || 1406 ((cinfo->is_baseline || cinfo->Se < DCTSIZE2) && 1407 cinfo->Se != cinfo->lim_Se)) 1408 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL); 1409 1410 /* Select MCU decoding routine */ 1411 /* We retain the hard-coded case for full-size blocks. 1412 * This is not necessary, but it appears that this version is slightly 1413 * more performant in the given implementation. 1414 * With an improved implementation we would prefer a single optimized 1415 * function. 1416 */ 1417 if (cinfo->lim_Se != DCTSIZE2-1) 1418 entropy->pub.decode_mcu = decode_mcu_sub; 1419 else 1420 entropy->pub.decode_mcu = decode_mcu; 1421 1422 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 1423 compptr = cinfo->cur_comp_info[ci]; 1424 /* Compute derived values for Huffman tables */ 1425 /* We may do this more than once for a table, but it's not expensive */ 1426 tbl = compptr->dc_tbl_no; 1427 jpeg_make_d_derived_tbl(cinfo, TRUE, tbl, 1428 & entropy->dc_derived_tbls[tbl]); 1429 if (cinfo->lim_Se) { /* AC needs no table when not present */ 1430 tbl = compptr->ac_tbl_no; 1431 jpeg_make_d_derived_tbl(cinfo, FALSE, tbl, 1432 & entropy->ac_derived_tbls[tbl]); 1433 } 1434 /* Initialize DC predictions to 0 */ 1435 entropy->saved.last_dc_val[ci] = 0; 1436 } 1437 1438 /* Precalculate decoding info for each block in an MCU of this scan */ 1439 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 1440 ci = cinfo->MCU_membership[blkn]; 1441 compptr = cinfo->cur_comp_info[ci]; 1442 /* Precalculate which table to use for each block */ 1443 entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no]; 1444 entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no]; 1445 /* Decide whether we really care about the coefficient values */ 1446 if (compptr->component_needed) { 1447 ci = compptr->DCT_v_scaled_size; 1448 i = compptr->DCT_h_scaled_size; 1449 switch (cinfo->lim_Se) { 1450 case (1*1-1): 1451 entropy->coef_limit[blkn] = 1; 1452 break; 1453 case (2*2-1): 1454 if (ci <= 0 || ci > 2) ci = 2; 1455 if (i <= 0 || i > 2) i = 2; 1456 entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order2[ci - 1][i - 1]; 1457 break; 1458 case (3*3-1): 1459 if (ci <= 0 || ci > 3) ci = 3; 1460 if (i <= 0 || i > 3) i = 3; 1461 entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order3[ci - 1][i - 1]; 1462 break; 1463 case (4*4-1): 1464 if (ci <= 0 || ci > 4) ci = 4; 1465 if (i <= 0 || i > 4) i = 4; 1466 entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order4[ci - 1][i - 1]; 1467 break; 1468 case (5*5-1): 1469 if (ci <= 0 || ci > 5) ci = 5; 1470 if (i <= 0 || i > 5) i = 5; 1471 entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order5[ci - 1][i - 1]; 1472 break; 1473 case (6*6-1): 1474 if (ci <= 0 || ci > 6) ci = 6; 1475 if (i <= 0 || i > 6) i = 6; 1476 entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order6[ci - 1][i - 1]; 1477 break; 1478 case (7*7-1): 1479 if (ci <= 0 || ci > 7) ci = 7; 1480 if (i <= 0 || i > 7) i = 7; 1481 entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order7[ci - 1][i - 1]; 1482 break; 1483 default: 1484 if (ci <= 0 || ci > 8) ci = 8; 1485 if (i <= 0 || i > 8) i = 8; 1486 entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order[ci - 1][i - 1]; 1487 break; 1488 } 1489 } else { 1490 entropy->coef_limit[blkn] = 0; 1491 } 1492 } 1493 } 1494 1495 /* Initialize bitread state variables */ 1496 entropy->bitstate.bits_left = 0; 1497 entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */ 1498 entropy->insufficient_data = FALSE; 1499 1500 /* Initialize restart counter */ 1501 entropy->restarts_to_go = cinfo->restart_interval; 1502 } 1503 1504 1505 /* 1506 * Module initialization routine for Huffman entropy decoding. 1507 */ 1508 1509 GLOBAL(void) 1510 jinit_huff_decoder (j_decompress_ptr cinfo) 1511 { 1512 huff_entropy_ptr entropy; 1513 int i; 1514 1515 entropy = (huff_entropy_ptr) 1516 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 1517 SIZEOF(huff_entropy_decoder)); 1518 cinfo->entropy = &entropy->pub; 1519 entropy->pub.start_pass = start_pass_huff_decoder; 1520 1521 if (cinfo->progressive_mode) { 1522 /* Create progression status table */ 1523 int *coef_bit_ptr, ci; 1524 cinfo->coef_bits = (int (*)[DCTSIZE2]) 1525 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 1526 cinfo->num_components*DCTSIZE2*SIZEOF(int)); 1527 coef_bit_ptr = & cinfo->coef_bits[0][0]; 1528 for (ci = 0; ci < cinfo->num_components; ci++) 1529 for (i = 0; i < DCTSIZE2; i++) 1530 *coef_bit_ptr++ = -1; 1531 1532 /* Mark derived tables unallocated */ 1533 for (i = 0; i < NUM_HUFF_TBLS; i++) { 1534 entropy->derived_tbls[i] = NULL; 1535 } 1536 } else { 1537 /* Mark tables unallocated */ 1538 for (i = 0; i < NUM_HUFF_TBLS; i++) { 1539 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL; 1540 } 1541 } 1542 } 1543
