1 /* 2 * jcarith.c 3 * 4 * Developed 1997-2009 by Guido Vollbeding. 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 portable arithmetic entropy encoding routines for JPEG 9 * (implementing the ISO/IEC IS 10918-1 and CCITT Recommendation ITU-T T.81). 10 * 11 * Both sequential and progressive modes are supported in this single module. 12 * 13 * Suspension is not currently supported in this module. 14 */ 15 16 #define JPEG_INTERNALS 17 #include "jinclude.h" 18 #include "jpeglib.h" 19 20 21 /* Expanded entropy encoder object for arithmetic encoding. */ 22 23 typedef struct { 24 struct jpeg_entropy_encoder pub; /* public fields */ 25 26 INT32 c; /* C register, base of coding interval, layout as in sec. D.1.3 */ 27 INT32 a; /* A register, normalized size of coding interval */ 28 INT32 sc; /* counter for stacked 0xFF values which might overflow */ 29 INT32 zc; /* counter for pending 0x00 output values which might * 30 * be discarded at the end ("Pacman" termination) */ 31 int ct; /* bit shift counter, determines when next byte will be written */ 32 int buffer; /* buffer for most recent output byte != 0xFF */ 33 34 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */ 35 int dc_context[MAX_COMPS_IN_SCAN]; /* context index for DC conditioning */ 36 37 unsigned int restarts_to_go; /* MCUs left in this restart interval */ 38 int next_restart_num; /* next restart number to write (0-7) */ 39 40 /* Pointers to statistics areas (these workspaces have image lifespan) */ 41 unsigned char * dc_stats[NUM_ARITH_TBLS]; 42 unsigned char * ac_stats[NUM_ARITH_TBLS]; 43 44 /* Statistics bin for coding with fixed probability 0.5 */ 45 unsigned char fixed_bin[4]; 46 } arith_entropy_encoder; 47 48 typedef arith_entropy_encoder * arith_entropy_ptr; 49 50 /* The following two definitions specify the allocation chunk size 51 * for the statistics area. 52 * According to sections F.1.4.4.1.3 and F.1.4.4.2, we need at least 53 * 49 statistics bins for DC, and 245 statistics bins for AC coding. 54 * 55 * We use a compact representation with 1 byte per statistics bin, 56 * thus the numbers directly represent byte sizes. 57 * This 1 byte per statistics bin contains the meaning of the MPS 58 * (more probable symbol) in the highest bit (mask 0x80), and the 59 * index into the probability estimation state machine table 60 * in the lower bits (mask 0x7F). 61 */ 62 63 #define DC_STAT_BINS 64 64 #define AC_STAT_BINS 256 65 66 /* NOTE: Uncomment the following #define if you want to use the 67 * given formula for calculating the AC conditioning parameter Kx 68 * for spectral selection progressive coding in section G.1.3.2 69 * of the spec (Kx = Kmin + SRL (8 + Se - Kmin) 4). 70 * Although the spec and P&M authors claim that this "has proven 71 * to give good results for 8 bit precision samples", I'm not 72 * convinced yet that this is really beneficial. 73 * Early tests gave only very marginal compression enhancements 74 * (a few - around 5 or so - bytes even for very large files), 75 * which would turn out rather negative if we'd suppress the 76 * DAC (Define Arithmetic Conditioning) marker segments for 77 * the default parameters in the future. 78 * Note that currently the marker writing module emits 12-byte 79 * DAC segments for a full-component scan in a color image. 80 * This is not worth worrying about IMHO. However, since the 81 * spec defines the default values to be used if the tables 82 * are omitted (unlike Huffman tables, which are required 83 * anyway), one might optimize this behaviour in the future, 84 * and then it would be disadvantageous to use custom tables if 85 * they don't provide sufficient gain to exceed the DAC size. 86 * 87 * On the other hand, I'd consider it as a reasonable result 88 * that the conditioning has no significant influence on the 89 * compression performance. This means that the basic 90 * statistical model is already rather stable. 91 * 92 * Thus, at the moment, we use the default conditioning values 93 * anyway, and do not use the custom formula. 94 * 95 #define CALCULATE_SPECTRAL_CONDITIONING 96 */ 97 98 /* IRIGHT_SHIFT is like RIGHT_SHIFT, but works on int rather than INT32. 99 * We assume that int right shift is unsigned if INT32 right shift is, 100 * which should be safe. 101 */ 102 103 #ifdef RIGHT_SHIFT_IS_UNSIGNED 104 #define ISHIFT_TEMPS int ishift_temp; 105 #define IRIGHT_SHIFT(x,shft) \ 106 ((ishift_temp = (x)) < 0 ? \ 107 (ishift_temp >> (shft)) | ((~0) << (16-(shft))) : \ 108 (ishift_temp >> (shft))) 109 #else 110 #define ISHIFT_TEMPS 111 #define IRIGHT_SHIFT(x,shft) ((x) >> (shft)) 112 #endif 113 114 115 LOCAL(void) 116 emit_byte (int val, j_compress_ptr cinfo) 117 /* Write next output byte; we do not support suspension in this module. */ 118 { 119 struct jpeg_destination_mgr * dest = cinfo->dest; 120 121 *dest->next_output_byte++ = (JOCTET) val; 122 if (--dest->free_in_buffer == 0) 123 if (! (*dest->empty_output_buffer) (cinfo)) 124 ERREXIT(cinfo, JERR_CANT_SUSPEND); 125 } 126 127 128 /* 129 * Finish up at the end of an arithmetic-compressed scan. 130 */ 131 132 METHODDEF(void) 133 finish_pass (j_compress_ptr cinfo) 134 { 135 arith_entropy_ptr e = (arith_entropy_ptr) cinfo->entropy; 136 INT32 temp; 137 138 /* Section D.1.8: Termination of encoding */ 139 140 /* Find the e->c in the coding interval with the largest 141 * number of trailing zero bits */ 142 if ((temp = (e->a - 1 + e->c) & 0xFFFF0000L) < e->c) 143 e->c = temp + 0x8000L; 144 else 145 e->c = temp; 146 /* Send remaining bytes to output */ 147 e->c <<= e->ct; 148 if (e->c & 0xF8000000L) { 149 /* One final overflow has to be handled */ 150 if (e->buffer >= 0) { 151 if (e->zc) 152 do emit_byte(0x00, cinfo); 153 while (--e->zc); 154 emit_byte(e->buffer + 1, cinfo); 155 if (e->buffer + 1 == 0xFF) 156 emit_byte(0x00, cinfo); 157 } 158 e->zc += e->sc; /* carry-over converts stacked 0xFF bytes to 0x00 */ 159 e->sc = 0; 160 } else { 161 if (e->buffer == 0) 162 ++e->zc; 163 else if (e->buffer >= 0) { 164 if (e->zc) 165 do emit_byte(0x00, cinfo); 166 while (--e->zc); 167 emit_byte(e->buffer, cinfo); 168 } 169 if (e->sc) { 170 if (e->zc) 171 do emit_byte(0x00, cinfo); 172 while (--e->zc); 173 do { 174 emit_byte(0xFF, cinfo); 175 emit_byte(0x00, cinfo); 176 } while (--e->sc); 177 } 178 } 179 /* Output final bytes only if they are not 0x00 */ 180 if (e->c & 0x7FFF800L) { 181 if (e->zc) /* output final pending zero bytes */ 182 do emit_byte(0x00, cinfo); 183 while (--e->zc); 184 emit_byte((e->c >> 19) & 0xFF, cinfo); 185 if (((e->c >> 19) & 0xFF) == 0xFF) 186 emit_byte(0x00, cinfo); 187 if (e->c & 0x7F800L) { 188 emit_byte((e->c >> 11) & 0xFF, cinfo); 189 if (((e->c >> 11) & 0xFF) == 0xFF) 190 emit_byte(0x00, cinfo); 191 } 192 } 193 } 194 195 196 /* 197 * The core arithmetic encoding routine (common in JPEG and JBIG). 198 * This needs to go as fast as possible. 199 * Machine-dependent optimization facilities 200 * are not utilized in this portable implementation. 201 * However, this code should be fairly efficient and 202 * may be a good base for further optimizations anyway. 203 * 204 * Parameter 'val' to be encoded may be 0 or 1 (binary decision). 205 * 206 * Note: I've added full "Pacman" termination support to the 207 * byte output routines, which is equivalent to the optional 208 * Discard_final_zeros procedure (Figure D.15) in the spec. 209 * Thus, we always produce the shortest possible output 210 * stream compliant to the spec (no trailing zero bytes, 211 * except for FF stuffing). 212 * 213 * I've also introduced a new scheme for accessing 214 * the probability estimation state machine table, 215 * derived from Markus Kuhn's JBIG implementation. 216 */ 217 218 LOCAL(void) 219 arith_encode (j_compress_ptr cinfo, unsigned char *st, int val) 220 { 221 register arith_entropy_ptr e = (arith_entropy_ptr) cinfo->entropy; 222 register unsigned char nl, nm; 223 register INT32 qe, temp; 224 register int sv; 225 226 /* Fetch values from our compact representation of Table D.2: 227 * Qe values and probability estimation state machine 228 */ 229 sv = *st; 230 qe = jpeg_aritab[sv & 0x7F]; /* => Qe_Value */ 231 nl = qe & 0xFF; qe >>= 8; /* Next_Index_LPS + Switch_MPS */ 232 nm = qe & 0xFF; qe >>= 8; /* Next_Index_MPS */ 233 234 /* Encode & estimation procedures per sections D.1.4 & D.1.5 */ 235 e->a -= qe; 236 if (val != (sv >> 7)) { 237 /* Encode the less probable symbol */ 238 if (e->a >= qe) { 239 /* If the interval size (qe) for the less probable symbol (LPS) 240 * is larger than the interval size for the MPS, then exchange 241 * the two symbols for coding efficiency, otherwise code the LPS 242 * as usual: */ 243 e->c += e->a; 244 e->a = qe; 245 } 246 *st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */ 247 } else { 248 /* Encode the more probable symbol */ 249 if (e->a >= 0x8000L) 250 return; /* A >= 0x8000 -> ready, no renormalization required */ 251 if (e->a < qe) { 252 /* If the interval size (qe) for the less probable symbol (LPS) 253 * is larger than the interval size for the MPS, then exchange 254 * the two symbols for coding efficiency: */ 255 e->c += e->a; 256 e->a = qe; 257 } 258 *st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */ 259 } 260 261 /* Renormalization & data output per section D.1.6 */ 262 do { 263 e->a <<= 1; 264 e->c <<= 1; 265 if (--e->ct == 0) { 266 /* Another byte is ready for output */ 267 temp = e->c >> 19; 268 if (temp > 0xFF) { 269 /* Handle overflow over all stacked 0xFF bytes */ 270 if (e->buffer >= 0) { 271 if (e->zc) 272 do emit_byte(0x00, cinfo); 273 while (--e->zc); 274 emit_byte(e->buffer + 1, cinfo); 275 if (e->buffer + 1 == 0xFF) 276 emit_byte(0x00, cinfo); 277 } 278 e->zc += e->sc; /* carry-over converts stacked 0xFF bytes to 0x00 */ 279 e->sc = 0; 280 /* Note: The 3 spacer bits in the C register guarantee 281 * that the new buffer byte can't be 0xFF here 282 * (see page 160 in the P&M JPEG book). */ 283 e->buffer = temp & 0xFF; /* new output byte, might overflow later */ 284 } else if (temp == 0xFF) { 285 ++e->sc; /* stack 0xFF byte (which might overflow later) */ 286 } else { 287 /* Output all stacked 0xFF bytes, they will not overflow any more */ 288 if (e->buffer == 0) 289 ++e->zc; 290 else if (e->buffer >= 0) { 291 if (e->zc) 292 do emit_byte(0x00, cinfo); 293 while (--e->zc); 294 emit_byte(e->buffer, cinfo); 295 } 296 if (e->sc) { 297 if (e->zc) 298 do emit_byte(0x00, cinfo); 299 while (--e->zc); 300 do { 301 emit_byte(0xFF, cinfo); 302 emit_byte(0x00, cinfo); 303 } while (--e->sc); 304 } 305 e->buffer = temp & 0xFF; /* new output byte (can still overflow) */ 306 } 307 e->c &= 0x7FFFFL; 308 e->ct += 8; 309 } 310 } while (e->a < 0x8000L); 311 } 312 313 314 /* 315 * Emit a restart marker & resynchronize predictions. 316 */ 317 318 LOCAL(void) 319 emit_restart (j_compress_ptr cinfo, int restart_num) 320 { 321 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 322 int ci; 323 jpeg_component_info * compptr; 324 325 finish_pass(cinfo); 326 327 emit_byte(0xFF, cinfo); 328 emit_byte(JPEG_RST0 + restart_num, cinfo); 329 330 /* Re-initialize statistics areas */ 331 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 332 compptr = cinfo->cur_comp_info[ci]; 333 /* DC needs no table for refinement scan */ 334 if (cinfo->progressive_mode == 0 || (cinfo->Ss == 0 && cinfo->Ah == 0)) { 335 MEMZERO(entropy->dc_stats[compptr->dc_tbl_no], DC_STAT_BINS); 336 /* Reset DC predictions to 0 */ 337 entropy->last_dc_val[ci] = 0; 338 entropy->dc_context[ci] = 0; 339 } 340 /* AC needs no table when not present */ 341 if (cinfo->progressive_mode == 0 || cinfo->Se) { 342 MEMZERO(entropy->ac_stats[compptr->ac_tbl_no], AC_STAT_BINS); 343 } 344 } 345 346 /* Reset arithmetic encoding variables */ 347 entropy->c = 0; 348 entropy->a = 0x10000L; 349 entropy->sc = 0; 350 entropy->zc = 0; 351 entropy->ct = 11; 352 entropy->buffer = -1; /* empty */ 353 } 354 355 356 /* 357 * MCU encoding for DC initial scan (either spectral selection, 358 * or first pass of successive approximation). 359 */ 360 361 METHODDEF(boolean) 362 encode_mcu_DC_first (j_compress_ptr cinfo, JBLOCKROW *MCU_data) 363 { 364 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 365 JBLOCKROW block; 366 unsigned char *st; 367 int blkn, ci, tbl; 368 int v, v2, m; 369 ISHIFT_TEMPS 370 371 /* Emit restart marker if needed */ 372 if (cinfo->restart_interval) { 373 if (entropy->restarts_to_go == 0) { 374 emit_restart(cinfo, entropy->next_restart_num); 375 entropy->restarts_to_go = cinfo->restart_interval; 376 entropy->next_restart_num++; 377 entropy->next_restart_num &= 7; 378 } 379 entropy->restarts_to_go--; 380 } 381 382 /* Encode the MCU data blocks */ 383 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 384 block = MCU_data[blkn]; 385 ci = cinfo->MCU_membership[blkn]; 386 tbl = cinfo->cur_comp_info[ci]->dc_tbl_no; 387 388 /* Compute the DC value after the required point transform by Al. 389 * This is simply an arithmetic right shift. 390 */ 391 m = IRIGHT_SHIFT((int) ((*block)[0]), cinfo->Al); 392 393 /* Sections F.1.4.1 & F.1.4.4.1: Encoding of DC coefficients */ 394 395 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */ 396 st = entropy->dc_stats[tbl] + entropy->dc_context[ci]; 397 398 /* Figure F.4: Encode_DC_DIFF */ 399 if ((v = m - entropy->last_dc_val[ci]) == 0) { 400 arith_encode(cinfo, st, 0); 401 entropy->dc_context[ci] = 0; /* zero diff category */ 402 } else { 403 entropy->last_dc_val[ci] = m; 404 arith_encode(cinfo, st, 1); 405 /* Figure F.6: Encoding nonzero value v */ 406 /* Figure F.7: Encoding the sign of v */ 407 if (v > 0) { 408 arith_encode(cinfo, st + 1, 0); /* Table F.4: SS = S0 + 1 */ 409 st += 2; /* Table F.4: SP = S0 + 2 */ 410 entropy->dc_context[ci] = 4; /* small positive diff category */ 411 } else { 412 v = -v; 413 arith_encode(cinfo, st + 1, 1); /* Table F.4: SS = S0 + 1 */ 414 st += 3; /* Table F.4: SN = S0 + 3 */ 415 entropy->dc_context[ci] = 8; /* small negative diff category */ 416 } 417 /* Figure F.8: Encoding the magnitude category of v */ 418 m = 0; 419 if (v -= 1) { 420 arith_encode(cinfo, st, 1); 421 m = 1; 422 v2 = v; 423 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */ 424 while (v2 >>= 1) { 425 arith_encode(cinfo, st, 1); 426 m <<= 1; 427 st += 1; 428 } 429 } 430 arith_encode(cinfo, st, 0); 431 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */ 432 if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1)) 433 entropy->dc_context[ci] = 0; /* zero diff category */ 434 else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1)) 435 entropy->dc_context[ci] += 8; /* large diff category */ 436 /* Figure F.9: Encoding the magnitude bit pattern of v */ 437 st += 14; 438 while (m >>= 1) 439 arith_encode(cinfo, st, (m & v) ? 1 : 0); 440 } 441 } 442 443 return TRUE; 444 } 445 446 447 /* 448 * MCU encoding for AC initial scan (either spectral selection, 449 * or first pass of successive approximation). 450 */ 451 452 METHODDEF(boolean) 453 encode_mcu_AC_first (j_compress_ptr cinfo, JBLOCKROW *MCU_data) 454 { 455 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 456 JBLOCKROW block; 457 unsigned char *st; 458 int tbl, k, ke; 459 int v, v2, m; 460 461 /* Emit restart marker if needed */ 462 if (cinfo->restart_interval) { 463 if (entropy->restarts_to_go == 0) { 464 emit_restart(cinfo, entropy->next_restart_num); 465 entropy->restarts_to_go = cinfo->restart_interval; 466 entropy->next_restart_num++; 467 entropy->next_restart_num &= 7; 468 } 469 entropy->restarts_to_go--; 470 } 471 472 /* Encode the MCU data block */ 473 block = MCU_data[0]; 474 tbl = cinfo->cur_comp_info[0]->ac_tbl_no; 475 476 /* Sections F.1.4.2 & F.1.4.4.2: Encoding of AC coefficients */ 477 478 /* Establish EOB (end-of-block) index */ 479 for (ke = cinfo->Se; ke > 0; ke--) 480 /* We must apply the point transform by Al. For AC coefficients this 481 * is an integer division with rounding towards 0. To do this portably 482 * in C, we shift after obtaining the absolute value. 483 */ 484 if ((v = (*block)[jpeg_natural_order[ke]]) >= 0) { 485 if (v >>= cinfo->Al) break; 486 } else { 487 v = -v; 488 if (v >>= cinfo->Al) break; 489 } 490 491 /* Figure F.5: Encode_AC_Coefficients */ 492 for (k = cinfo->Ss; k <= ke; k++) { 493 st = entropy->ac_stats[tbl] + 3 * (k - 1); 494 arith_encode(cinfo, st, 0); /* EOB decision */ 495 for (;;) { 496 if ((v = (*block)[jpeg_natural_order[k]]) >= 0) { 497 if (v >>= cinfo->Al) { 498 arith_encode(cinfo, st + 1, 1); 499 arith_encode(cinfo, entropy->fixed_bin, 0); 500 break; 501 } 502 } else { 503 v = -v; 504 if (v >>= cinfo->Al) { 505 arith_encode(cinfo, st + 1, 1); 506 arith_encode(cinfo, entropy->fixed_bin, 1); 507 break; 508 } 509 } 510 arith_encode(cinfo, st + 1, 0); st += 3; k++; 511 } 512 st += 2; 513 /* Figure F.8: Encoding the magnitude category of v */ 514 m = 0; 515 if (v -= 1) { 516 arith_encode(cinfo, st, 1); 517 m = 1; 518 v2 = v; 519 if (v2 >>= 1) { 520 arith_encode(cinfo, st, 1); 521 m <<= 1; 522 st = entropy->ac_stats[tbl] + 523 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217); 524 while (v2 >>= 1) { 525 arith_encode(cinfo, st, 1); 526 m <<= 1; 527 st += 1; 528 } 529 } 530 } 531 arith_encode(cinfo, st, 0); 532 /* Figure F.9: Encoding the magnitude bit pattern of v */ 533 st += 14; 534 while (m >>= 1) 535 arith_encode(cinfo, st, (m & v) ? 1 : 0); 536 } 537 /* Encode EOB decision only if k <= cinfo->Se */ 538 if (k <= cinfo->Se) { 539 st = entropy->ac_stats[tbl] + 3 * (k - 1); 540 arith_encode(cinfo, st, 1); 541 } 542 543 return TRUE; 544 } 545 546 547 /* 548 * MCU encoding for DC successive approximation refinement scan. 549 */ 550 551 METHODDEF(boolean) 552 encode_mcu_DC_refine (j_compress_ptr cinfo, JBLOCKROW *MCU_data) 553 { 554 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 555 unsigned char *st; 556 int Al, blkn; 557 558 /* Emit restart marker if needed */ 559 if (cinfo->restart_interval) { 560 if (entropy->restarts_to_go == 0) { 561 emit_restart(cinfo, entropy->next_restart_num); 562 entropy->restarts_to_go = cinfo->restart_interval; 563 entropy->next_restart_num++; 564 entropy->next_restart_num &= 7; 565 } 566 entropy->restarts_to_go--; 567 } 568 569 st = entropy->fixed_bin; /* use fixed probability estimation */ 570 Al = cinfo->Al; 571 572 /* Encode the MCU data blocks */ 573 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 574 /* We simply emit the Al'th bit of the DC coefficient value. */ 575 arith_encode(cinfo, st, (MCU_data[blkn][0][0] >> Al) & 1); 576 } 577 578 return TRUE; 579 } 580 581 582 /* 583 * MCU encoding for AC successive approximation refinement scan. 584 */ 585 586 METHODDEF(boolean) 587 encode_mcu_AC_refine (j_compress_ptr cinfo, JBLOCKROW *MCU_data) 588 { 589 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 590 JBLOCKROW block; 591 unsigned char *st; 592 int tbl, k, ke, kex; 593 int v; 594 595 /* Emit restart marker if needed */ 596 if (cinfo->restart_interval) { 597 if (entropy->restarts_to_go == 0) { 598 emit_restart(cinfo, entropy->next_restart_num); 599 entropy->restarts_to_go = cinfo->restart_interval; 600 entropy->next_restart_num++; 601 entropy->next_restart_num &= 7; 602 } 603 entropy->restarts_to_go--; 604 } 605 606 /* Encode the MCU data block */ 607 block = MCU_data[0]; 608 tbl = cinfo->cur_comp_info[0]->ac_tbl_no; 609 610 /* Section G.1.3.3: Encoding of AC coefficients */ 611 612 /* Establish EOB (end-of-block) index */ 613 for (ke = cinfo->Se; ke > 0; ke--) 614 /* We must apply the point transform by Al. For AC coefficients this 615 * is an integer division with rounding towards 0. To do this portably 616 * in C, we shift after obtaining the absolute value. 617 */ 618 if ((v = (*block)[jpeg_natural_order[ke]]) >= 0) { 619 if (v >>= cinfo->Al) break; 620 } else { 621 v = -v; 622 if (v >>= cinfo->Al) break; 623 } 624 625 /* Establish EOBx (previous stage end-of-block) index */ 626 for (kex = ke; kex > 0; kex--) 627 if ((v = (*block)[jpeg_natural_order[kex]]) >= 0) { 628 if (v >>= cinfo->Ah) break; 629 } else { 630 v = -v; 631 if (v >>= cinfo->Ah) break; 632 } 633 634 /* Figure G.10: Encode_AC_Coefficients_SA */ 635 for (k = cinfo->Ss; k <= ke; k++) { 636 st = entropy->ac_stats[tbl] + 3 * (k - 1); 637 if (k > kex) 638 arith_encode(cinfo, st, 0); /* EOB decision */ 639 for (;;) { 640 if ((v = (*block)[jpeg_natural_order[k]]) >= 0) { 641 if (v >>= cinfo->Al) { 642 if (v >> 1) /* previously nonzero coef */ 643 arith_encode(cinfo, st + 2, (v & 1)); 644 else { /* newly nonzero coef */ 645 arith_encode(cinfo, st + 1, 1); 646 arith_encode(cinfo, entropy->fixed_bin, 0); 647 } 648 break; 649 } 650 } else { 651 v = -v; 652 if (v >>= cinfo->Al) { 653 if (v >> 1) /* previously nonzero coef */ 654 arith_encode(cinfo, st + 2, (v & 1)); 655 else { /* newly nonzero coef */ 656 arith_encode(cinfo, st + 1, 1); 657 arith_encode(cinfo, entropy->fixed_bin, 1); 658 } 659 break; 660 } 661 } 662 arith_encode(cinfo, st + 1, 0); st += 3; k++; 663 } 664 } 665 /* Encode EOB decision only if k <= cinfo->Se */ 666 if (k <= cinfo->Se) { 667 st = entropy->ac_stats[tbl] + 3 * (k - 1); 668 arith_encode(cinfo, st, 1); 669 } 670 671 return TRUE; 672 } 673 674 675 /* 676 * Encode and output one MCU's worth of arithmetic-compressed coefficients. 677 */ 678 679 METHODDEF(boolean) 680 encode_mcu (j_compress_ptr cinfo, JBLOCKROW *MCU_data) 681 { 682 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 683 jpeg_component_info * compptr; 684 JBLOCKROW block; 685 unsigned char *st; 686 int blkn, ci, tbl, k, ke; 687 int v, v2, m; 688 689 /* Emit restart marker if needed */ 690 if (cinfo->restart_interval) { 691 if (entropy->restarts_to_go == 0) { 692 emit_restart(cinfo, entropy->next_restart_num); 693 entropy->restarts_to_go = cinfo->restart_interval; 694 entropy->next_restart_num++; 695 entropy->next_restart_num &= 7; 696 } 697 entropy->restarts_to_go--; 698 } 699 700 /* Encode the MCU data blocks */ 701 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 702 block = MCU_data[blkn]; 703 ci = cinfo->MCU_membership[blkn]; 704 compptr = cinfo->cur_comp_info[ci]; 705 706 /* Sections F.1.4.1 & F.1.4.4.1: Encoding of DC coefficients */ 707 708 tbl = compptr->dc_tbl_no; 709 710 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */ 711 st = entropy->dc_stats[tbl] + entropy->dc_context[ci]; 712 713 /* Figure F.4: Encode_DC_DIFF */ 714 if ((v = (*block)[0] - entropy->last_dc_val[ci]) == 0) { 715 arith_encode(cinfo, st, 0); 716 entropy->dc_context[ci] = 0; /* zero diff category */ 717 } else { 718 entropy->last_dc_val[ci] = (*block)[0]; 719 arith_encode(cinfo, st, 1); 720 /* Figure F.6: Encoding nonzero value v */ 721 /* Figure F.7: Encoding the sign of v */ 722 if (v > 0) { 723 arith_encode(cinfo, st + 1, 0); /* Table F.4: SS = S0 + 1 */ 724 st += 2; /* Table F.4: SP = S0 + 2 */ 725 entropy->dc_context[ci] = 4; /* small positive diff category */ 726 } else { 727 v = -v; 728 arith_encode(cinfo, st + 1, 1); /* Table F.4: SS = S0 + 1 */ 729 st += 3; /* Table F.4: SN = S0 + 3 */ 730 entropy->dc_context[ci] = 8; /* small negative diff category */ 731 } 732 /* Figure F.8: Encoding the magnitude category of v */ 733 m = 0; 734 if (v -= 1) { 735 arith_encode(cinfo, st, 1); 736 m = 1; 737 v2 = v; 738 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */ 739 while (v2 >>= 1) { 740 arith_encode(cinfo, st, 1); 741 m <<= 1; 742 st += 1; 743 } 744 } 745 arith_encode(cinfo, st, 0); 746 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */ 747 if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1)) 748 entropy->dc_context[ci] = 0; /* zero diff category */ 749 else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1)) 750 entropy->dc_context[ci] += 8; /* large diff category */ 751 /* Figure F.9: Encoding the magnitude bit pattern of v */ 752 st += 14; 753 while (m >>= 1) 754 arith_encode(cinfo, st, (m & v) ? 1 : 0); 755 } 756 757 /* Sections F.1.4.2 & F.1.4.4.2: Encoding of AC coefficients */ 758 759 tbl = compptr->ac_tbl_no; 760 761 /* Establish EOB (end-of-block) index */ 762 for (ke = DCTSIZE2 - 1; ke > 0; ke--) 763 if ((*block)[jpeg_natural_order[ke]]) break; 764 765 /* Figure F.5: Encode_AC_Coefficients */ 766 for (k = 1; k <= ke; k++) { 767 st = entropy->ac_stats[tbl] + 3 * (k - 1); 768 arith_encode(cinfo, st, 0); /* EOB decision */ 769 while ((v = (*block)[jpeg_natural_order[k]]) == 0) { 770 arith_encode(cinfo, st + 1, 0); st += 3; k++; 771 } 772 arith_encode(cinfo, st + 1, 1); 773 /* Figure F.6: Encoding nonzero value v */ 774 /* Figure F.7: Encoding the sign of v */ 775 if (v > 0) { 776 arith_encode(cinfo, entropy->fixed_bin, 0); 777 } else { 778 v = -v; 779 arith_encode(cinfo, entropy->fixed_bin, 1); 780 } 781 st += 2; 782 /* Figure F.8: Encoding the magnitude category of v */ 783 m = 0; 784 if (v -= 1) { 785 arith_encode(cinfo, st, 1); 786 m = 1; 787 v2 = v; 788 if (v2 >>= 1) { 789 arith_encode(cinfo, st, 1); 790 m <<= 1; 791 st = entropy->ac_stats[tbl] + 792 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217); 793 while (v2 >>= 1) { 794 arith_encode(cinfo, st, 1); 795 m <<= 1; 796 st += 1; 797 } 798 } 799 } 800 arith_encode(cinfo, st, 0); 801 /* Figure F.9: Encoding the magnitude bit pattern of v */ 802 st += 14; 803 while (m >>= 1) 804 arith_encode(cinfo, st, (m & v) ? 1 : 0); 805 } 806 /* Encode EOB decision only if k <= DCTSIZE2 - 1 */ 807 if (k <= DCTSIZE2 - 1) { 808 st = entropy->ac_stats[tbl] + 3 * (k - 1); 809 arith_encode(cinfo, st, 1); 810 } 811 } 812 813 return TRUE; 814 } 815 816 817 /* 818 * Initialize for an arithmetic-compressed scan. 819 */ 820 821 METHODDEF(void) 822 start_pass (j_compress_ptr cinfo, boolean gather_statistics) 823 { 824 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 825 int ci, tbl; 826 jpeg_component_info * compptr; 827 828 if (gather_statistics) 829 /* Make sure to avoid that in the master control logic! 830 * We are fully adaptive here and need no extra 831 * statistics gathering pass! 832 */ 833 ERREXIT(cinfo, JERR_NOT_COMPILED); 834 835 /* We assume jcmaster.c already validated the progressive scan parameters. */ 836 837 /* Select execution routines */ 838 if (cinfo->progressive_mode) { 839 if (cinfo->Ah == 0) { 840 if (cinfo->Ss == 0) 841 entropy->pub.encode_mcu = encode_mcu_DC_first; 842 else 843 entropy->pub.encode_mcu = encode_mcu_AC_first; 844 } else { 845 if (cinfo->Ss == 0) 846 entropy->pub.encode_mcu = encode_mcu_DC_refine; 847 else 848 entropy->pub.encode_mcu = encode_mcu_AC_refine; 849 } 850 } else 851 entropy->pub.encode_mcu = encode_mcu; 852 853 /* Allocate & initialize requested statistics areas */ 854 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 855 compptr = cinfo->cur_comp_info[ci]; 856 /* DC needs no table for refinement scan */ 857 if (cinfo->progressive_mode == 0 || (cinfo->Ss == 0 && cinfo->Ah == 0)) { 858 tbl = compptr->dc_tbl_no; 859 if (tbl < 0 || tbl >= NUM_ARITH_TBLS) 860 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl); 861 if (entropy->dc_stats[tbl] == NULL) 862 entropy->dc_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small) 863 ((j_common_ptr) cinfo, JPOOL_IMAGE, DC_STAT_BINS); 864 MEMZERO(entropy->dc_stats[tbl], DC_STAT_BINS); 865 /* Initialize DC predictions to 0 */ 866 entropy->last_dc_val[ci] = 0; 867 entropy->dc_context[ci] = 0; 868 } 869 /* AC needs no table when not present */ 870 if (cinfo->progressive_mode == 0 || cinfo->Se) { 871 tbl = compptr->ac_tbl_no; 872 if (tbl < 0 || tbl >= NUM_ARITH_TBLS) 873 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl); 874 if (entropy->ac_stats[tbl] == NULL) 875 entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small) 876 ((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS); 877 MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS); 878 #ifdef CALCULATE_SPECTRAL_CONDITIONING 879 if (cinfo->progressive_mode) 880 /* Section G.1.3.2: Set appropriate arithmetic conditioning value Kx */ 881 cinfo->arith_ac_K[tbl] = cinfo->Ss + ((8 + cinfo->Se - cinfo->Ss) >> 4); 882 #endif 883 } 884 } 885 886 /* Initialize arithmetic encoding variables */ 887 entropy->c = 0; 888 entropy->a = 0x10000L; 889 entropy->sc = 0; 890 entropy->zc = 0; 891 entropy->ct = 11; 892 entropy->buffer = -1; /* empty */ 893 894 /* Initialize restart stuff */ 895 entropy->restarts_to_go = cinfo->restart_interval; 896 entropy->next_restart_num = 0; 897 } 898 899 900 /* 901 * Module initialization routine for arithmetic entropy encoding. 902 */ 903 904 GLOBAL(void) 905 jinit_arith_encoder (j_compress_ptr cinfo) 906 { 907 arith_entropy_ptr entropy; 908 int i; 909 910 entropy = (arith_entropy_ptr) 911 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 912 SIZEOF(arith_entropy_encoder)); 913 cinfo->entropy = (struct jpeg_entropy_encoder *) entropy; 914 entropy->pub.start_pass = start_pass; 915 entropy->pub.finish_pass = finish_pass; 916 917 /* Mark tables unallocated */ 918 for (i = 0; i < NUM_ARITH_TBLS; i++) { 919 entropy->dc_stats[i] = NULL; 920 entropy->ac_stats[i] = NULL; 921 } 922 923 /* Initialize index for fixed probability estimation */ 924 entropy->fixed_bin[0] = 113; 925 } 926
