1 /* 2 * jcarith.c 3 * 4 * Developed 1997-2013 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.3(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->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->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 unsigned char *st; 366 int blkn, ci, tbl; 367 int v, v2, m; 368 ISHIFT_TEMPS 369 370 /* Emit restart marker if needed */ 371 if (cinfo->restart_interval) { 372 if (entropy->restarts_to_go == 0) { 373 emit_restart(cinfo, entropy->next_restart_num); 374 entropy->restarts_to_go = cinfo->restart_interval; 375 entropy->next_restart_num++; 376 entropy->next_restart_num &= 7; 377 } 378 entropy->restarts_to_go--; 379 } 380 381 /* Encode the MCU data blocks */ 382 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 383 ci = cinfo->MCU_membership[blkn]; 384 tbl = cinfo->cur_comp_info[ci]->dc_tbl_no; 385 386 /* Compute the DC value after the required point transform by Al. 387 * This is simply an arithmetic right shift. 388 */ 389 m = IRIGHT_SHIFT((int) (MCU_data[blkn][0][0]), cinfo->Al); 390 391 /* Sections F.1.4.1 & F.1.4.4.1: Encoding of DC coefficients */ 392 393 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */ 394 st = entropy->dc_stats[tbl] + entropy->dc_context[ci]; 395 396 /* Figure F.4: Encode_DC_DIFF */ 397 if ((v = m - entropy->last_dc_val[ci]) == 0) { 398 arith_encode(cinfo, st, 0); 399 entropy->dc_context[ci] = 0; /* zero diff category */ 400 } else { 401 entropy->last_dc_val[ci] = m; 402 arith_encode(cinfo, st, 1); 403 /* Figure F.6: Encoding nonzero value v */ 404 /* Figure F.7: Encoding the sign of v */ 405 if (v > 0) { 406 arith_encode(cinfo, st + 1, 0); /* Table F.4: SS = S0 + 1 */ 407 st += 2; /* Table F.4: SP = S0 + 2 */ 408 entropy->dc_context[ci] = 4; /* small positive diff category */ 409 } else { 410 v = -v; 411 arith_encode(cinfo, st + 1, 1); /* Table F.4: SS = S0 + 1 */ 412 st += 3; /* Table F.4: SN = S0 + 3 */ 413 entropy->dc_context[ci] = 8; /* small negative diff category */ 414 } 415 /* Figure F.8: Encoding the magnitude category of v */ 416 m = 0; 417 if (v -= 1) { 418 arith_encode(cinfo, st, 1); 419 m = 1; 420 v2 = v; 421 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */ 422 while (v2 >>= 1) { 423 arith_encode(cinfo, st, 1); 424 m <<= 1; 425 st += 1; 426 } 427 } 428 arith_encode(cinfo, st, 0); 429 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */ 430 if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1)) 431 entropy->dc_context[ci] = 0; /* zero diff category */ 432 else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1)) 433 entropy->dc_context[ci] += 8; /* large diff category */ 434 /* Figure F.9: Encoding the magnitude bit pattern of v */ 435 st += 14; 436 while (m >>= 1) 437 arith_encode(cinfo, st, (m & v) ? 1 : 0); 438 } 439 } 440 441 return TRUE; 442 } 443 444 445 /* 446 * MCU encoding for AC initial scan (either spectral selection, 447 * or first pass of successive approximation). 448 */ 449 450 METHODDEF(boolean) 451 encode_mcu_AC_first (j_compress_ptr cinfo, JBLOCKROW *MCU_data) 452 { 453 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 454 const int * natural_order; 455 JBLOCKROW block; 456 unsigned char *st; 457 int tbl, k, ke; 458 int v, v2, m; 459 460 /* Emit restart marker if needed */ 461 if (cinfo->restart_interval) { 462 if (entropy->restarts_to_go == 0) { 463 emit_restart(cinfo, entropy->next_restart_num); 464 entropy->restarts_to_go = cinfo->restart_interval; 465 entropy->next_restart_num++; 466 entropy->next_restart_num &= 7; 467 } 468 entropy->restarts_to_go--; 469 } 470 471 natural_order = cinfo->natural_order; 472 473 /* Encode the MCU data block */ 474 block = MCU_data[0]; 475 tbl = cinfo->cur_comp_info[0]->ac_tbl_no; 476 477 /* Sections F.1.4.2 & F.1.4.4.2: Encoding of AC coefficients */ 478 479 /* Establish EOB (end-of-block) index */ 480 ke = cinfo->Se; 481 do { 482 /* We must apply the point transform by Al. For AC coefficients this 483 * is an integer division with rounding towards 0. To do this portably 484 * in C, we shift after obtaining the absolute value. 485 */ 486 if ((v = (*block)[natural_order[ke]]) >= 0) { 487 if (v >>= cinfo->Al) break; 488 } else { 489 v = -v; 490 if (v >>= cinfo->Al) break; 491 } 492 } while (--ke); 493 494 /* Figure F.5: Encode_AC_Coefficients */ 495 for (k = cinfo->Ss - 1; k < ke;) { 496 st = entropy->ac_stats[tbl] + 3 * k; 497 arith_encode(cinfo, st, 0); /* EOB decision */ 498 for (;;) { 499 if ((v = (*block)[natural_order[++k]]) >= 0) { 500 if (v >>= cinfo->Al) { 501 arith_encode(cinfo, st + 1, 1); 502 arith_encode(cinfo, entropy->fixed_bin, 0); 503 break; 504 } 505 } else { 506 v = -v; 507 if (v >>= cinfo->Al) { 508 arith_encode(cinfo, st + 1, 1); 509 arith_encode(cinfo, entropy->fixed_bin, 1); 510 break; 511 } 512 } 513 arith_encode(cinfo, st + 1, 0); 514 st += 3; 515 } 516 st += 2; 517 /* Figure F.8: Encoding the magnitude category of v */ 518 m = 0; 519 if (v -= 1) { 520 arith_encode(cinfo, st, 1); 521 m = 1; 522 v2 = v; 523 if (v2 >>= 1) { 524 arith_encode(cinfo, st, 1); 525 m <<= 1; 526 st = entropy->ac_stats[tbl] + 527 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217); 528 while (v2 >>= 1) { 529 arith_encode(cinfo, st, 1); 530 m <<= 1; 531 st += 1; 532 } 533 } 534 } 535 arith_encode(cinfo, st, 0); 536 /* Figure F.9: Encoding the magnitude bit pattern of v */ 537 st += 14; 538 while (m >>= 1) 539 arith_encode(cinfo, st, (m & v) ? 1 : 0); 540 } 541 /* Encode EOB decision only if k < cinfo->Se */ 542 if (k < cinfo->Se) { 543 st = entropy->ac_stats[tbl] + 3 * k; 544 arith_encode(cinfo, st, 1); 545 } 546 547 return TRUE; 548 } 549 550 551 /* 552 * MCU encoding for DC successive approximation refinement scan. 553 * Note: we assume such scans can be multi-component, 554 * although the spec is not very clear on the point. 555 */ 556 557 METHODDEF(boolean) 558 encode_mcu_DC_refine (j_compress_ptr cinfo, JBLOCKROW *MCU_data) 559 { 560 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 561 unsigned char *st; 562 int Al, blkn; 563 564 /* Emit restart marker if needed */ 565 if (cinfo->restart_interval) { 566 if (entropy->restarts_to_go == 0) { 567 emit_restart(cinfo, entropy->next_restart_num); 568 entropy->restarts_to_go = cinfo->restart_interval; 569 entropy->next_restart_num++; 570 entropy->next_restart_num &= 7; 571 } 572 entropy->restarts_to_go--; 573 } 574 575 st = entropy->fixed_bin; /* use fixed probability estimation */ 576 Al = cinfo->Al; 577 578 /* Encode the MCU data blocks */ 579 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 580 /* We simply emit the Al'th bit of the DC coefficient value. */ 581 arith_encode(cinfo, st, (MCU_data[blkn][0][0] >> Al) & 1); 582 } 583 584 return TRUE; 585 } 586 587 588 /* 589 * MCU encoding for AC successive approximation refinement scan. 590 */ 591 592 METHODDEF(boolean) 593 encode_mcu_AC_refine (j_compress_ptr cinfo, JBLOCKROW *MCU_data) 594 { 595 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 596 const int * natural_order; 597 JBLOCKROW block; 598 unsigned char *st; 599 int tbl, k, ke, kex; 600 int v; 601 602 /* Emit restart marker if needed */ 603 if (cinfo->restart_interval) { 604 if (entropy->restarts_to_go == 0) { 605 emit_restart(cinfo, entropy->next_restart_num); 606 entropy->restarts_to_go = cinfo->restart_interval; 607 entropy->next_restart_num++; 608 entropy->next_restart_num &= 7; 609 } 610 entropy->restarts_to_go--; 611 } 612 613 natural_order = cinfo->natural_order; 614 615 /* Encode the MCU data block */ 616 block = MCU_data[0]; 617 tbl = cinfo->cur_comp_info[0]->ac_tbl_no; 618 619 /* Section G.1.3.3: Encoding of AC coefficients */ 620 621 /* Establish EOB (end-of-block) index */ 622 ke = cinfo->Se; 623 do { 624 /* We must apply the point transform by Al. For AC coefficients this 625 * is an integer division with rounding towards 0. To do this portably 626 * in C, we shift after obtaining the absolute value. 627 */ 628 if ((v = (*block)[natural_order[ke]]) >= 0) { 629 if (v >>= cinfo->Al) break; 630 } else { 631 v = -v; 632 if (v >>= cinfo->Al) break; 633 } 634 } while (--ke); 635 636 /* Establish EOBx (previous stage end-of-block) index */ 637 for (kex = ke; kex > 0; kex--) 638 if ((v = (*block)[natural_order[kex]]) >= 0) { 639 if (v >>= cinfo->Ah) break; 640 } else { 641 v = -v; 642 if (v >>= cinfo->Ah) break; 643 } 644 645 /* Figure G.10: Encode_AC_Coefficients_SA */ 646 for (k = cinfo->Ss - 1; k < ke;) { 647 st = entropy->ac_stats[tbl] + 3 * k; 648 if (k >= kex) 649 arith_encode(cinfo, st, 0); /* EOB decision */ 650 for (;;) { 651 if ((v = (*block)[natural_order[++k]]) >= 0) { 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, 0); 658 } 659 break; 660 } 661 } else { 662 v = -v; 663 if (v >>= cinfo->Al) { 664 if (v >> 1) /* previously nonzero coef */ 665 arith_encode(cinfo, st + 2, (v & 1)); 666 else { /* newly nonzero coef */ 667 arith_encode(cinfo, st + 1, 1); 668 arith_encode(cinfo, entropy->fixed_bin, 1); 669 } 670 break; 671 } 672 } 673 arith_encode(cinfo, st + 1, 0); 674 st += 3; 675 } 676 } 677 /* Encode EOB decision only if k < cinfo->Se */ 678 if (k < cinfo->Se) { 679 st = entropy->ac_stats[tbl] + 3 * k; 680 arith_encode(cinfo, st, 1); 681 } 682 683 return TRUE; 684 } 685 686 687 /* 688 * Encode and output one MCU's worth of arithmetic-compressed coefficients. 689 */ 690 691 METHODDEF(boolean) 692 encode_mcu (j_compress_ptr cinfo, JBLOCKROW *MCU_data) 693 { 694 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 695 const int * natural_order; 696 JBLOCKROW block; 697 unsigned char *st; 698 int tbl, k, ke; 699 int v, v2, m; 700 int blkn, ci; 701 jpeg_component_info * compptr; 702 703 /* Emit restart marker if needed */ 704 if (cinfo->restart_interval) { 705 if (entropy->restarts_to_go == 0) { 706 emit_restart(cinfo, entropy->next_restart_num); 707 entropy->restarts_to_go = cinfo->restart_interval; 708 entropy->next_restart_num++; 709 entropy->next_restart_num &= 7; 710 } 711 entropy->restarts_to_go--; 712 } 713 714 natural_order = cinfo->natural_order; 715 716 /* Encode the MCU data blocks */ 717 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 718 block = MCU_data[blkn]; 719 ci = cinfo->MCU_membership[blkn]; 720 compptr = cinfo->cur_comp_info[ci]; 721 722 /* Sections F.1.4.1 & F.1.4.4.1: Encoding of DC coefficients */ 723 724 tbl = compptr->dc_tbl_no; 725 726 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */ 727 st = entropy->dc_stats[tbl] + entropy->dc_context[ci]; 728 729 /* Figure F.4: Encode_DC_DIFF */ 730 if ((v = (*block)[0] - entropy->last_dc_val[ci]) == 0) { 731 arith_encode(cinfo, st, 0); 732 entropy->dc_context[ci] = 0; /* zero diff category */ 733 } else { 734 entropy->last_dc_val[ci] = (*block)[0]; 735 arith_encode(cinfo, st, 1); 736 /* Figure F.6: Encoding nonzero value v */ 737 /* Figure F.7: Encoding the sign of v */ 738 if (v > 0) { 739 arith_encode(cinfo, st + 1, 0); /* Table F.4: SS = S0 + 1 */ 740 st += 2; /* Table F.4: SP = S0 + 2 */ 741 entropy->dc_context[ci] = 4; /* small positive diff category */ 742 } else { 743 v = -v; 744 arith_encode(cinfo, st + 1, 1); /* Table F.4: SS = S0 + 1 */ 745 st += 3; /* Table F.4: SN = S0 + 3 */ 746 entropy->dc_context[ci] = 8; /* small negative diff category */ 747 } 748 /* Figure F.8: Encoding the magnitude category of v */ 749 m = 0; 750 if (v -= 1) { 751 arith_encode(cinfo, st, 1); 752 m = 1; 753 v2 = v; 754 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */ 755 while (v2 >>= 1) { 756 arith_encode(cinfo, st, 1); 757 m <<= 1; 758 st += 1; 759 } 760 } 761 arith_encode(cinfo, st, 0); 762 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */ 763 if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1)) 764 entropy->dc_context[ci] = 0; /* zero diff category */ 765 else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1)) 766 entropy->dc_context[ci] += 8; /* large diff category */ 767 /* Figure F.9: Encoding the magnitude bit pattern of v */ 768 st += 14; 769 while (m >>= 1) 770 arith_encode(cinfo, st, (m & v) ? 1 : 0); 771 } 772 773 /* Sections F.1.4.2 & F.1.4.4.2: Encoding of AC coefficients */ 774 775 if ((ke = cinfo->lim_Se) == 0) continue; 776 tbl = compptr->ac_tbl_no; 777 778 /* Establish EOB (end-of-block) index */ 779 do { 780 if ((*block)[natural_order[ke]]) break; 781 } while (--ke); 782 783 /* Figure F.5: Encode_AC_Coefficients */ 784 for (k = 0; k < ke;) { 785 st = entropy->ac_stats[tbl] + 3 * k; 786 arith_encode(cinfo, st, 0); /* EOB decision */ 787 while ((v = (*block)[natural_order[++k]]) == 0) { 788 arith_encode(cinfo, st + 1, 0); 789 st += 3; 790 } 791 arith_encode(cinfo, st + 1, 1); 792 /* Figure F.6: Encoding nonzero value v */ 793 /* Figure F.7: Encoding the sign of v */ 794 if (v > 0) { 795 arith_encode(cinfo, entropy->fixed_bin, 0); 796 } else { 797 v = -v; 798 arith_encode(cinfo, entropy->fixed_bin, 1); 799 } 800 st += 2; 801 /* Figure F.8: Encoding the magnitude category of v */ 802 m = 0; 803 if (v -= 1) { 804 arith_encode(cinfo, st, 1); 805 m = 1; 806 v2 = v; 807 if (v2 >>= 1) { 808 arith_encode(cinfo, st, 1); 809 m <<= 1; 810 st = entropy->ac_stats[tbl] + 811 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217); 812 while (v2 >>= 1) { 813 arith_encode(cinfo, st, 1); 814 m <<= 1; 815 st += 1; 816 } 817 } 818 } 819 arith_encode(cinfo, st, 0); 820 /* Figure F.9: Encoding the magnitude bit pattern of v */ 821 st += 14; 822 while (m >>= 1) 823 arith_encode(cinfo, st, (m & v) ? 1 : 0); 824 } 825 /* Encode EOB decision only if k < cinfo->lim_Se */ 826 if (k < cinfo->lim_Se) { 827 st = entropy->ac_stats[tbl] + 3 * k; 828 arith_encode(cinfo, st, 1); 829 } 830 } 831 832 return TRUE; 833 } 834 835 836 /* 837 * Initialize for an arithmetic-compressed scan. 838 */ 839 840 METHODDEF(void) 841 start_pass (j_compress_ptr cinfo, boolean gather_statistics) 842 { 843 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 844 int ci, tbl; 845 jpeg_component_info * compptr; 846 847 if (gather_statistics) 848 /* Make sure to avoid that in the master control logic! 849 * We are fully adaptive here and need no extra 850 * statistics gathering pass! 851 */ 852 ERREXIT(cinfo, JERR_NOT_COMPILED); 853 854 /* We assume jcmaster.c already validated the progressive scan parameters. */ 855 856 /* Select execution routines */ 857 if (cinfo->progressive_mode) { 858 if (cinfo->Ah == 0) { 859 if (cinfo->Ss == 0) 860 entropy->pub.encode_mcu = encode_mcu_DC_first; 861 else 862 entropy->pub.encode_mcu = encode_mcu_AC_first; 863 } else { 864 if (cinfo->Ss == 0) 865 entropy->pub.encode_mcu = encode_mcu_DC_refine; 866 else 867 entropy->pub.encode_mcu = encode_mcu_AC_refine; 868 } 869 } else 870 entropy->pub.encode_mcu = encode_mcu; 871 872 /* Allocate & initialize requested statistics areas */ 873 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 874 compptr = cinfo->cur_comp_info[ci]; 875 /* DC needs no table for refinement scan */ 876 if (cinfo->Ss == 0 && cinfo->Ah == 0) { 877 tbl = compptr->dc_tbl_no; 878 if (tbl < 0 || tbl >= NUM_ARITH_TBLS) 879 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl); 880 if (entropy->dc_stats[tbl] == NULL) 881 entropy->dc_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small) 882 ((j_common_ptr) cinfo, JPOOL_IMAGE, DC_STAT_BINS); 883 MEMZERO(entropy->dc_stats[tbl], DC_STAT_BINS); 884 /* Initialize DC predictions to 0 */ 885 entropy->last_dc_val[ci] = 0; 886 entropy->dc_context[ci] = 0; 887 } 888 /* AC needs no table when not present */ 889 if (cinfo->Se) { 890 tbl = compptr->ac_tbl_no; 891 if (tbl < 0 || tbl >= NUM_ARITH_TBLS) 892 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl); 893 if (entropy->ac_stats[tbl] == NULL) 894 entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small) 895 ((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS); 896 MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS); 897 #ifdef CALCULATE_SPECTRAL_CONDITIONING 898 if (cinfo->progressive_mode) 899 /* Section G.1.3.2: Set appropriate arithmetic conditioning value Kx */ 900 cinfo->arith_ac_K[tbl] = cinfo->Ss + ((8 + cinfo->Se - cinfo->Ss) >> 4); 901 #endif 902 } 903 } 904 905 /* Initialize arithmetic encoding variables */ 906 entropy->c = 0; 907 entropy->a = 0x10000L; 908 entropy->sc = 0; 909 entropy->zc = 0; 910 entropy->ct = 11; 911 entropy->buffer = -1; /* empty */ 912 913 /* Initialize restart stuff */ 914 entropy->restarts_to_go = cinfo->restart_interval; 915 entropy->next_restart_num = 0; 916 } 917 918 919 /* 920 * Module initialization routine for arithmetic entropy encoding. 921 */ 922 923 GLOBAL(void) 924 jinit_arith_encoder (j_compress_ptr cinfo) 925 { 926 arith_entropy_ptr entropy; 927 int i; 928 929 entropy = (arith_entropy_ptr) 930 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 931 SIZEOF(arith_entropy_encoder)); 932 cinfo->entropy = &entropy->pub; 933 entropy->pub.start_pass = start_pass; 934 entropy->pub.finish_pass = finish_pass; 935 936 /* Mark tables unallocated */ 937 for (i = 0; i < NUM_ARITH_TBLS; i++) { 938 entropy->dc_stats[i] = NULL; 939 entropy->ac_stats[i] = NULL; 940 } 941 942 /* Initialize index for fixed probability estimation */ 943 entropy->fixed_bin[0] = 113; 944 } 945