media/libjpeg/jcarith.c@6474c204b198
media/libjpeg/jcarith.c
Wed, 31 Dec 2014 06:09:35 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Wed, 31 Dec 2014 06:09:35 +0100
- changeset 0
- 6474c204b198
- permissions
- -rw-r--r--
Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.
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 */
16 #define JPEG_INTERNALS
17 #include "jinclude.h"
18 #include "jpeglib.h"
21 /* Expanded entropy encoder object for arithmetic encoding. */
23 typedef struct {
24 struct jpeg_entropy_encoder pub; /* public fields */
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 */
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 */
37 unsigned int restarts_to_go; /* MCUs left in this restart interval */
38 int next_restart_num; /* next restart number to write (0-7) */
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];
44 /* Statistics bin for coding with fixed probability 0.5 */
45 unsigned char fixed_bin[4];
46 } arith_entropy_encoder;
48 typedef arith_entropy_encoder * arith_entropy_ptr;
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 */
63 #define DC_STAT_BINS 64
64 #define AC_STAT_BINS 256
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 */
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 */
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
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;
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 }
128 /*
129 * Finish up at the end of an arithmetic-compressed scan.
130 */
132 METHODDEF(void)
133 finish_pass (j_compress_ptr cinfo)
134 {
135 arith_entropy_ptr e = (arith_entropy_ptr) cinfo->entropy;
136 INT32 temp;
138 /* Section D.1.8: Termination of encoding */
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 }
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 */
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;
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 */
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 }
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 }
314 /*
315 * Emit a restart marker & resynchronize predictions.
316 */
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;
325 finish_pass(cinfo);
327 emit_byte(0xFF, cinfo);
328 emit_byte(JPEG_RST0 + restart_num, cinfo);
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 }
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 }
356 /*
357 * MCU encoding for DC initial scan (either spectral selection,
358 * or first pass of successive approximation).
359 */
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
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 }
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;
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);
393 /* Sections F.1.4.1 & F.1.4.4.1: Encoding of DC coefficients */
395 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
396 st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
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 }
443 return TRUE;
444 }
447 /*
448 * MCU encoding for AC initial scan (either spectral selection,
449 * or first pass of successive approximation).
450 */
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;
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 }
472 /* Encode the MCU data block */
473 block = MCU_data[0];
474 tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
476 /* Sections F.1.4.2 & F.1.4.4.2: Encoding of AC coefficients */
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 }
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 }
543 return TRUE;
544 }
547 /*
548 * MCU encoding for DC successive approximation refinement scan.
549 */
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;
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 }
569 st = entropy->fixed_bin; /* use fixed probability estimation */
570 Al = cinfo->Al;
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 }
578 return TRUE;
579 }
582 /*
583 * MCU encoding for AC successive approximation refinement scan.
584 */
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;
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 }
606 /* Encode the MCU data block */
607 block = MCU_data[0];
608 tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
610 /* Section G.1.3.3: Encoding of AC coefficients */
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 }
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 }
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 }
671 return TRUE;
672 }
675 /*
676 * Encode and output one MCU's worth of arithmetic-compressed coefficients.
677 */
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;
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 }
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];
706 /* Sections F.1.4.1 & F.1.4.4.1: Encoding of DC coefficients */
708 tbl = compptr->dc_tbl_no;
710 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
711 st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
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 }
757 /* Sections F.1.4.2 & F.1.4.4.2: Encoding of AC coefficients */
759 tbl = compptr->ac_tbl_no;
761 /* Establish EOB (end-of-block) index */
762 for (ke = DCTSIZE2 - 1; ke > 0; ke--)
763 if ((*block)[jpeg_natural_order[ke]]) break;
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 }
813 return TRUE;
814 }
817 /*
818 * Initialize for an arithmetic-compressed scan.
819 */
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;
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);
835 /* We assume jcmaster.c already validated the progressive scan parameters. */
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;
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 }
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 */
894 /* Initialize restart stuff */
895 entropy->restarts_to_go = cinfo->restart_interval;
896 entropy->next_restart_num = 0;
897 }
900 /*
901 * Module initialization routine for arithmetic entropy encoding.
902 */
904 GLOBAL(void)
905 jinit_arith_encoder (j_compress_ptr cinfo)
906 {
907 arith_entropy_ptr entropy;
908 int i;
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;
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 }
923 /* Initialize index for fixed probability estimation */
924 entropy->fixed_bin[0] = 113;
925 }
