1 #if !defined(_FX_JPEG_TURBO_)
2 /*
3 * jchuff.c
4 *
5 * Copyright (C) 1991-1997, Thomas G. Lane.
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 encoding routines.
10 *
11 * Much of the complexity here has to do with supporting output suspension.
12 * If the data destination module demands suspension, we want to be able to
13 * back up to the start of the current MCU. To do this, we copy state
14 * variables into local working storage, and update them back to the
15 * permanent JPEG objects only upon successful completion of an MCU.
16 */
17
18 #define JPEG_INTERNALS
19 #include "jinclude.h"
20 #include "jpeglib.h"
21 #include "jchuff.h" /* Declarations shared with jcphuff.c */
22
23 #ifdef _FX_MANAGED_CODE_
24 #define savable_state savable_state_c
25 #endif
26
27 /* Expanded entropy encoder object for Huffman encoding.
28 *
29 * The savable_state subrecord contains fields that change within an MCU,
30 * but must not be updated permanently until we complete the MCU.
31 */
32
33 typedef struct {
34 INT32 put_buffer; /* current bit-accumulation buffer */
35 int put_bits; /* # of bits now in it */
36 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
37 } savable_state;
38
39 /* This macro is to work around compilers with missing or broken
40 * structure assignment. You'll need to fix this code if you have
41 * such a compiler and you change MAX_COMPS_IN_SCAN.
42 */
43
44 #ifndef NO_STRUCT_ASSIGN
45 #define ASSIGN_STATE(dest,src) ((dest) = (src))
46 #else
47 #if MAX_COMPS_IN_SCAN == 4
48 #define ASSIGN_STATE(dest,src) \
49 ((dest).put_buffer = (src).put_buffer, \
50 (dest).put_bits = (src).put_bits, \
51 (dest).last_dc_val[0] = (src).last_dc_val[0], \
52 (dest).last_dc_val[1] = (src).last_dc_val[1], \
53 (dest).last_dc_val[2] = (src).last_dc_val[2], \
54 (dest).last_dc_val[3] = (src).last_dc_val[3])
55 #endif
56 #endif
57
58
59 typedef struct {
60 struct jpeg_entropy_encoder pub; /* public fields */
61
62 savable_state saved; /* Bit buffer & DC state at start of MCU */
63
64 /* These fields are NOT loaded into local working state. */
65 unsigned int restarts_to_go; /* MCUs left in this restart interval */
66 int next_restart_num; /* next restart number to write (0-7) */
67
68 /* Pointers to derived tables (these workspaces have image lifespan) */
69 c_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
70 c_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
71
72 #ifdef ENTROPY_OPT_SUPPORTED /* Statistics tables for optimization */
73 long * dc_count_ptrs[NUM_HUFF_TBLS];
74 long * ac_count_ptrs[NUM_HUFF_TBLS];
75 #endif
76 } huff_entropy_encoder;
77
78 typedef huff_entropy_encoder * huff_entropy_ptr;
79
80 /* Working state while writing an MCU.
81 * This struct contains all the fields that are needed by subroutines.
82 */
83
84 typedef struct {
85 JOCTET * next_output_byte; /* => next byte to write in buffer */
86 size_t free_in_buffer; /* # of byte spaces remaining in buffer */
87 savable_state cur; /* Current bit buffer & DC state */
88 j_compress_ptr cinfo; /* dump_buffer needs access to this */
89 } working_state;
90
91
92 /* Forward declarations */
93 METHODDEF(boolean) encode_mcu_huff JPP((j_compress_ptr cinfo,
94 JBLOCKROW *MCU_data));
95 METHODDEF(void) finish_pass_huff JPP((j_compress_ptr cinfo));
96 #ifdef ENTROPY_OPT_SUPPORTED
97 METHODDEF(boolean) encode_mcu_gather JPP((j_compress_ptr cinfo,
98 JBLOCKROW *MCU_data));
99 METHODDEF(void) finish_pass_gather JPP((j_compress_ptr cinfo));
100 #endif
101
102
103 /*
104 * Initialize for a Huffman-compressed scan.
105 * If gather_statistics is TRUE, we do not output anything during the scan,
106 * just count the Huffman symbols used and generate Huffman code tables.
107 */
108
109 METHODDEF(void)
start_pass_huff(j_compress_ptr cinfo,boolean gather_statistics)110 start_pass_huff (j_compress_ptr cinfo, boolean gather_statistics)
111 {
112 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
113 int ci, dctbl, actbl;
114 jpeg_component_info * compptr;
115
116 if (gather_statistics) {
117 #ifdef ENTROPY_OPT_SUPPORTED
118 entropy->pub.encode_mcu = encode_mcu_gather;
119 entropy->pub.finish_pass = finish_pass_gather;
120 #else
121 ERREXIT(cinfo, JERR_NOT_COMPILED);
122 #endif
123 } else {
124 entropy->pub.encode_mcu = encode_mcu_huff;
125 entropy->pub.finish_pass = finish_pass_huff;
126 }
127
128 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
129 compptr = cinfo->cur_comp_info[ci];
130 dctbl = compptr->dc_tbl_no;
131 actbl = compptr->ac_tbl_no;
132 if (gather_statistics) {
133 #ifdef ENTROPY_OPT_SUPPORTED
134 /* Check for invalid table indexes */
135 /* (make_c_derived_tbl does this in the other path) */
136 if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS)
137 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);
138 if (actbl < 0 || actbl >= NUM_HUFF_TBLS)
139 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);
140 /* Allocate and zero the statistics tables */
141 /* Note that jpeg_gen_optimal_table expects 257 entries in each table! */
142 if (entropy->dc_count_ptrs[dctbl] == NULL)
143 entropy->dc_count_ptrs[dctbl] = (long *)
144 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
145 257 * SIZEOF(long));
146 MEMZERO(entropy->dc_count_ptrs[dctbl], 257 * SIZEOF(long));
147 if (entropy->ac_count_ptrs[actbl] == NULL)
148 entropy->ac_count_ptrs[actbl] = (long *)
149 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
150 257 * SIZEOF(long));
151 MEMZERO(entropy->ac_count_ptrs[actbl], 257 * SIZEOF(long));
152 #endif
153 } else {
154 /* Compute derived values for Huffman tables */
155 /* We may do this more than once for a table, but it's not expensive */
156 jpeg_make_c_derived_tbl(cinfo, TRUE, dctbl,
157 & entropy->dc_derived_tbls[dctbl]);
158 jpeg_make_c_derived_tbl(cinfo, FALSE, actbl,
159 & entropy->ac_derived_tbls[actbl]);
160 }
161 /* Initialize DC predictions to 0 */
162 entropy->saved.last_dc_val[ci] = 0;
163 }
164
165 /* Initialize bit buffer to empty */
166 entropy->saved.put_buffer = 0;
167 entropy->saved.put_bits = 0;
168
169 /* Initialize restart stuff */
170 entropy->restarts_to_go = cinfo->restart_interval;
171 entropy->next_restart_num = 0;
172 }
173
174
175 /*
176 * Compute the derived values for a Huffman table.
177 * This routine also performs some validation checks on the table.
178 *
179 * Note this is also used by jcphuff.c.
180 */
181
182 GLOBAL(void)
jpeg_make_c_derived_tbl(j_compress_ptr cinfo,boolean isDC,int tblno,c_derived_tbl ** pdtbl)183 jpeg_make_c_derived_tbl (j_compress_ptr cinfo, boolean isDC, int tblno,
184 c_derived_tbl ** pdtbl)
185 {
186 JHUFF_TBL *htbl;
187 c_derived_tbl *dtbl;
188 int p, i, l, lastp, _si, maxsymbol;
189 char huffsize[257];
190 unsigned int huffcode[257];
191 unsigned int code;
192
193 /* Note that huffsize[] and huffcode[] are filled in code-length order,
194 * paralleling the order of the symbols themselves in htbl->huffval[].
195 */
196
197 /* Find the input Huffman table */
198 if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
199 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
200 htbl =
201 isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
202 if (htbl == NULL)
203 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
204
205 /* Allocate a workspace if we haven't already done so. */
206 if (*pdtbl == NULL)
207 *pdtbl = (c_derived_tbl *)
208 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
209 SIZEOF(c_derived_tbl));
210 dtbl = *pdtbl;
211
212 /* Figure C.1: make table of Huffman code length for each symbol */
213
214 p = 0;
215 for (l = 1; l <= 16; l++) {
216 i = (int) htbl->bits[l];
217 if (i < 0 || p + i > 256) /* protect against table overrun */
218 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
219 while (i--)
220 huffsize[p++] = (char) l;
221 }
222 huffsize[p] = 0;
223 lastp = p;
224
225 /* Figure C.2: generate the codes themselves */
226 /* We also validate that the counts represent a legal Huffman code tree. */
227
228 code = 0;
229 _si = huffsize[0];
230 p = 0;
231 while (huffsize[p]) {
232 while (((int) huffsize[p]) == _si) {
233 huffcode[p++] = code;
234 code++;
235 }
236 /* code is now 1 more than the last code used for codelength si; but
237 * it must still fit in si bits, since no code is allowed to be all ones.
238 */
239 if (((INT32) code) >= (((INT32) 1) << _si))
240 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
241 code <<= 1;
242 _si++;
243 }
244
245 /* Figure C.3: generate encoding tables */
246 /* These are code and size indexed by symbol value */
247
248 /* Set all codeless symbols to have code length 0;
249 * this lets us detect duplicate VAL entries here, and later
250 * allows emit_bits to detect any attempt to emit such symbols.
251 */
252 MEMZERO(dtbl->ehufsi, SIZEOF(dtbl->ehufsi));
253
254 /* This is also a convenient place to check for out-of-range
255 * and duplicated VAL entries. We allow 0..255 for AC symbols
256 * but only 0..15 for DC. (We could constrain them further
257 * based on data depth and mode, but this seems enough.)
258 */
259 maxsymbol = isDC ? 15 : 255;
260
261 for (p = 0; p < lastp; p++) {
262 i = htbl->huffval[p];
263 if (i < 0 || i > maxsymbol || dtbl->ehufsi[i])
264 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
265 dtbl->ehufco[i] = huffcode[p];
266 dtbl->ehufsi[i] = huffsize[p];
267 }
268 }
269
270
271 /* Outputting bytes to the file */
272
273 /* Emit a byte, taking 'action' if must suspend. */
274 #define emit_byte(state,val,action) \
275 { *(state)->next_output_byte++ = (JOCTET) (val); \
276 if (--(state)->free_in_buffer == 0) \
277 if (! dump_buffer(state)) \
278 { action; } }
279
280
281 LOCAL(boolean)
dump_buffer(working_state * state)282 dump_buffer (working_state * state)
283 /* Empty the output buffer; return TRUE if successful, FALSE if must suspend */
284 {
285 struct jpeg_destination_mgr * dest = state->cinfo->dest;
286
287 if (! (*dest->empty_output_buffer) (state->cinfo))
288 return FALSE;
289 /* After a successful buffer dump, must reset buffer pointers */
290 state->next_output_byte = dest->next_output_byte;
291 state->free_in_buffer = dest->free_in_buffer;
292 return TRUE;
293 }
294
295
296 /* Outputting bits to the file */
297
298 /* Only the right 24 bits of put_buffer are used; the valid bits are
299 * left-justified in this part. At most 16 bits can be passed to emit_bits
300 * in one call, and we never retain more than 7 bits in put_buffer
301 * between calls, so 24 bits are sufficient.
302 */
303
304 INLINE
LOCAL(boolean)305 LOCAL(boolean)
306 emit_bits (working_state * state, unsigned int code, int size)
307 /* Emit some bits; return TRUE if successful, FALSE if must suspend */
308 {
309 /* This routine is heavily used, so it's worth coding tightly. */
310 register INT32 put_buffer = (INT32) code;
311 register int put_bits = state->cur.put_bits;
312
313 /* if size is 0, caller used an invalid Huffman table entry */
314 if (size == 0)
315 ERREXIT(state->cinfo, JERR_HUFF_MISSING_CODE);
316
317 put_buffer &= (((INT32) 1)<<size) - 1; /* mask off any extra bits in code */
318
319 put_bits += size; /* new number of bits in buffer */
320
321 put_buffer <<= 24 - put_bits; /* align incoming bits */
322
323 put_buffer |= state->cur.put_buffer; /* and merge with old buffer contents */
324
325 while (put_bits >= 8) {
326 int c = (int) ((put_buffer >> 16) & 0xFF);
327
328 emit_byte(state, c, return FALSE);
329 if (c == 0xFF) { /* need to stuff a zero byte? */
330 emit_byte(state, 0, return FALSE);
331 }
332 put_buffer <<= 8;
333 put_bits -= 8;
334 }
335
336 state->cur.put_buffer = put_buffer; /* update state variables */
337 state->cur.put_bits = put_bits;
338
339 return TRUE;
340 }
341
342
343 LOCAL(boolean)
flush_bits(working_state * state)344 flush_bits (working_state * state)
345 {
346 if (! emit_bits(state, 0x7F, 7)) /* fill any partial byte with ones */
347 return FALSE;
348 state->cur.put_buffer = 0; /* and reset bit-buffer to empty */
349 state->cur.put_bits = 0;
350 return TRUE;
351 }
352
353
354 /* Encode a single block's worth of coefficients */
355
356 LOCAL(boolean)
encode_one_block(working_state * state,JCOEFPTR block,int last_dc_val,c_derived_tbl * dctbl,c_derived_tbl * actbl)357 encode_one_block (working_state * state, JCOEFPTR block, int last_dc_val,
358 c_derived_tbl *dctbl, c_derived_tbl *actbl)
359 {
360 register int temp, temp2;
361 register int nbits;
362 register int k, r, i;
363
364 /* Encode the DC coefficient difference per section F.1.2.1 */
365
366 temp = temp2 = block[0] - last_dc_val;
367
368 if (temp < 0) {
369 temp = -temp; /* temp is abs value of input */
370 /* For a negative input, want temp2 = bitwise complement of abs(input) */
371 /* This code assumes we are on a two's complement machine */
372 temp2--;
373 }
374
375 /* Find the number of bits needed for the magnitude of the coefficient */
376 nbits = 0;
377 while (temp) {
378 nbits++;
379 temp >>= 1;
380 }
381 /* Check for out-of-range coefficient values.
382 * Since we're encoding a difference, the range limit is twice as much.
383 */
384 if (nbits > MAX_COEF_BITS+1)
385 ERREXIT(state->cinfo, JERR_BAD_DCT_COEF);
386
387 /* Emit the Huffman-coded symbol for the number of bits */
388 if (! emit_bits(state, dctbl->ehufco[nbits], dctbl->ehufsi[nbits]))
389 return FALSE;
390
391 /* Emit that number of bits of the value, if positive, */
392 /* or the complement of its magnitude, if negative. */
393 if (nbits) /* emit_bits rejects calls with size 0 */
394 if (! emit_bits(state, (unsigned int) temp2, nbits))
395 return FALSE;
396
397 /* Encode the AC coefficients per section F.1.2.2 */
398
399 r = 0; /* r = run length of zeros */
400
401 for (k = 1; k < DCTSIZE2; k++) {
402 if ((temp = block[jpeg_natural_order[k]]) == 0) {
403 r++;
404 } else {
405 /* if run length > 15, must emit special run-length-16 codes (0xF0) */
406 while (r > 15) {
407 if (! emit_bits(state, actbl->ehufco[0xF0], actbl->ehufsi[0xF0]))
408 return FALSE;
409 r -= 16;
410 }
411
412 temp2 = temp;
413 if (temp < 0) {
414 temp = -temp; /* temp is abs value of input */
415 /* This code assumes we are on a two's complement machine */
416 temp2--;
417 }
418
419 /* Find the number of bits needed for the magnitude of the coefficient */
420 nbits = 1; /* there must be at least one 1 bit */
421 while ((temp >>= 1))
422 nbits++;
423 /* Check for out-of-range coefficient values */
424 if (nbits > MAX_COEF_BITS)
425 ERREXIT(state->cinfo, JERR_BAD_DCT_COEF);
426
427 /* Emit Huffman symbol for run length / number of bits */
428 i = (r << 4) + nbits;
429 if (! emit_bits(state, actbl->ehufco[i], actbl->ehufsi[i]))
430 return FALSE;
431
432 /* Emit that number of bits of the value, if positive, */
433 /* or the complement of its magnitude, if negative. */
434 if (! emit_bits(state, (unsigned int) temp2, nbits))
435 return FALSE;
436
437 r = 0;
438 }
439 }
440
441 /* If the last coef(s) were zero, emit an end-of-block code */
442 if (r > 0)
443 if (! emit_bits(state, actbl->ehufco[0], actbl->ehufsi[0]))
444 return FALSE;
445
446 return TRUE;
447 }
448
449
450 /*
451 * Emit a restart marker & resynchronize predictions.
452 */
453
454 LOCAL(boolean)
emit_restart(working_state * state,int restart_num)455 emit_restart (working_state * state, int restart_num)
456 {
457 int ci;
458
459 if (! flush_bits(state))
460 return FALSE;
461
462 emit_byte(state, 0xFF, return FALSE);
463 emit_byte(state, JPEG_RST0 + restart_num, return FALSE);
464
465 /* Re-initialize DC predictions to 0 */
466 for (ci = 0; ci < state->cinfo->comps_in_scan; ci++)
467 state->cur.last_dc_val[ci] = 0;
468
469 /* The restart counter is not updated until we successfully write the MCU. */
470
471 return TRUE;
472 }
473
474
475 /*
476 * Encode and output one MCU's worth of Huffman-compressed coefficients.
477 */
478
479 METHODDEF(boolean)
encode_mcu_huff(j_compress_ptr cinfo,JBLOCKROW * MCU_data)480 encode_mcu_huff (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
481 {
482 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
483 working_state state;
484 int blkn, ci;
485 jpeg_component_info * compptr;
486
487 /* Load up working state */
488 state.next_output_byte = cinfo->dest->next_output_byte;
489 state.free_in_buffer = cinfo->dest->free_in_buffer;
490 ASSIGN_STATE(state.cur, entropy->saved);
491 state.cinfo = cinfo;
492
493 /* Emit restart marker if needed */
494 if (cinfo->restart_interval) {
495 if (entropy->restarts_to_go == 0)
496 if (! emit_restart(&state, entropy->next_restart_num))
497 return FALSE;
498 }
499
500 /* Encode the MCU data blocks */
501 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
502 ci = cinfo->MCU_membership[blkn];
503 compptr = cinfo->cur_comp_info[ci];
504 if (! encode_one_block(&state,
505 MCU_data[blkn][0], state.cur.last_dc_val[ci],
506 entropy->dc_derived_tbls[compptr->dc_tbl_no],
507 entropy->ac_derived_tbls[compptr->ac_tbl_no]))
508 return FALSE;
509 /* Update last_dc_val */
510 state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];
511 }
512
513 /* Completed MCU, so update state */
514 cinfo->dest->next_output_byte = state.next_output_byte;
515 cinfo->dest->free_in_buffer = state.free_in_buffer;
516 ASSIGN_STATE(entropy->saved, state.cur);
517
518 /* Update restart-interval state too */
519 if (cinfo->restart_interval) {
520 if (entropy->restarts_to_go == 0) {
521 entropy->restarts_to_go = cinfo->restart_interval;
522 entropy->next_restart_num++;
523 entropy->next_restart_num &= 7;
524 }
525 entropy->restarts_to_go--;
526 }
527
528 return TRUE;
529 }
530
531
532 /*
533 * Finish up at the end of a Huffman-compressed scan.
534 */
535
536 METHODDEF(void)
finish_pass_huff(j_compress_ptr cinfo)537 finish_pass_huff (j_compress_ptr cinfo)
538 {
539 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
540 working_state state;
541
542 /* Load up working state ... flush_bits needs it */
543 state.next_output_byte = cinfo->dest->next_output_byte;
544 state.free_in_buffer = cinfo->dest->free_in_buffer;
545 ASSIGN_STATE(state.cur, entropy->saved);
546 state.cinfo = cinfo;
547
548 /* Flush out the last data */
549 if (! flush_bits(&state))
550 ERREXIT(cinfo, JERR_CANT_SUSPEND);
551
552 /* Update state */
553 cinfo->dest->next_output_byte = state.next_output_byte;
554 cinfo->dest->free_in_buffer = state.free_in_buffer;
555 ASSIGN_STATE(entropy->saved, state.cur);
556 }
557
558
559 /*
560 * Huffman coding optimization.
561 *
562 * We first scan the supplied data and count the number of uses of each symbol
563 * that is to be Huffman-coded. (This process MUST agree with the code above.)
564 * Then we build a Huffman coding tree for the observed counts.
565 * Symbols which are not needed at all for the particular image are not
566 * assigned any code, which saves space in the DHT marker as well as in
567 * the compressed data.
568 */
569
570 #ifdef ENTROPY_OPT_SUPPORTED
571
572
573 /* Process a single block's worth of coefficients */
574
575 LOCAL(void)
htest_one_block(j_compress_ptr cinfo,JCOEFPTR block,int last_dc_val,long dc_counts[],long ac_counts[])576 htest_one_block (j_compress_ptr cinfo, JCOEFPTR block, int last_dc_val,
577 long dc_counts[], long ac_counts[])
578 {
579 register int temp;
580 register int nbits;
581 register int k, r;
582
583 /* Encode the DC coefficient difference per section F.1.2.1 */
584
585 temp = block[0] - last_dc_val;
586 if (temp < 0)
587 temp = -temp;
588
589 /* Find the number of bits needed for the magnitude of the coefficient */
590 nbits = 0;
591 while (temp) {
592 nbits++;
593 temp >>= 1;
594 }
595 /* Check for out-of-range coefficient values.
596 * Since we're encoding a difference, the range limit is twice as much.
597 */
598 if (nbits > MAX_COEF_BITS+1)
599 ERREXIT(cinfo, JERR_BAD_DCT_COEF);
600
601 /* Count the Huffman symbol for the number of bits */
602 dc_counts[nbits]++;
603
604 /* Encode the AC coefficients per section F.1.2.2 */
605
606 r = 0; /* r = run length of zeros */
607
608 for (k = 1; k < DCTSIZE2; k++) {
609 if ((temp = block[jpeg_natural_order[k]]) == 0) {
610 r++;
611 } else {
612 /* if run length > 15, must emit special run-length-16 codes (0xF0) */
613 while (r > 15) {
614 ac_counts[0xF0]++;
615 r -= 16;
616 }
617
618 /* Find the number of bits needed for the magnitude of the coefficient */
619 if (temp < 0)
620 temp = -temp;
621
622 /* Find the number of bits needed for the magnitude of the coefficient */
623 nbits = 1; /* there must be at least one 1 bit */
624 while ((temp >>= 1))
625 nbits++;
626 /* Check for out-of-range coefficient values */
627 if (nbits > MAX_COEF_BITS)
628 ERREXIT(cinfo, JERR_BAD_DCT_COEF);
629
630 /* Count Huffman symbol for run length / number of bits */
631 ac_counts[(r << 4) + nbits]++;
632
633 r = 0;
634 }
635 }
636
637 /* If the last coef(s) were zero, emit an end-of-block code */
638 if (r > 0)
639 ac_counts[0]++;
640 }
641
642
643 /*
644 * Trial-encode one MCU's worth of Huffman-compressed coefficients.
645 * No data is actually output, so no suspension return is possible.
646 */
647
648 METHODDEF(boolean)
encode_mcu_gather(j_compress_ptr cinfo,JBLOCKROW * MCU_data)649 encode_mcu_gather (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
650 {
651 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
652 int blkn, ci;
653 jpeg_component_info * compptr;
654
655 /* Take care of restart intervals if needed */
656 if (cinfo->restart_interval) {
657 if (entropy->restarts_to_go == 0) {
658 /* Re-initialize DC predictions to 0 */
659 for (ci = 0; ci < cinfo->comps_in_scan; ci++)
660 entropy->saved.last_dc_val[ci] = 0;
661 /* Update restart state */
662 entropy->restarts_to_go = cinfo->restart_interval;
663 }
664 entropy->restarts_to_go--;
665 }
666
667 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
668 ci = cinfo->MCU_membership[blkn];
669 compptr = cinfo->cur_comp_info[ci];
670 htest_one_block(cinfo, MCU_data[blkn][0], entropy->saved.last_dc_val[ci],
671 entropy->dc_count_ptrs[compptr->dc_tbl_no],
672 entropy->ac_count_ptrs[compptr->ac_tbl_no]);
673 entropy->saved.last_dc_val[ci] = MCU_data[blkn][0][0];
674 }
675
676 return TRUE;
677 }
678
679
680 /*
681 * Generate the best Huffman code table for the given counts, fill htbl.
682 * Note this is also used by jcphuff.c.
683 *
684 * The JPEG standard requires that no symbol be assigned a codeword of all
685 * one bits (so that padding bits added at the end of a compressed segment
686 * can't look like a valid code). Because of the canonical ordering of
687 * codewords, this just means that there must be an unused slot in the
688 * longest codeword length category. Section K.2 of the JPEG spec suggests
689 * reserving such a slot by pretending that symbol 256 is a valid symbol
690 * with count 1. In theory that's not optimal; giving it count zero but
691 * including it in the symbol set anyway should give a better Huffman code.
692 * But the theoretically better code actually seems to come out worse in
693 * practice, because it produces more all-ones bytes (which incur stuffed
694 * zero bytes in the final file). In any case the difference is tiny.
695 *
696 * The JPEG standard requires Huffman codes to be no more than 16 bits long.
697 * If some symbols have a very small but nonzero probability, the Huffman tree
698 * must be adjusted to meet the code length restriction. We currently use
699 * the adjustment method suggested in JPEG section K.2. This method is *not*
700 * optimal; it may not choose the best possible limited-length code. But
701 * typically only very-low-frequency symbols will be given less-than-optimal
702 * lengths, so the code is almost optimal. Experimental comparisons against
703 * an optimal limited-length-code algorithm indicate that the difference is
704 * microscopic --- usually less than a hundredth of a percent of total size.
705 * So the extra complexity of an optimal algorithm doesn't seem worthwhile.
706 */
707
708 GLOBAL(void)
jpeg_gen_optimal_table(j_compress_ptr cinfo,JHUFF_TBL * htbl,long freq[])709 jpeg_gen_optimal_table (j_compress_ptr cinfo, JHUFF_TBL * htbl, long freq[])
710 {
711 #define MAX_CLEN 32 /* assumed maximum initial code length */
712 UINT8 bits[MAX_CLEN+1]; /* bits[k] = # of symbols with code length k */
713 int codesize[257]; /* codesize[k] = code length of symbol k */
714 int others[257]; /* next symbol in current branch of tree */
715 int c1, c2;
716 int p, i, j;
717 long v;
718
719 /* This algorithm is explained in section K.2 of the JPEG standard */
720
721 MEMZERO(bits, SIZEOF(bits));
722 MEMZERO(codesize, SIZEOF(codesize));
723 for (i = 0; i < 257; i++)
724 others[i] = -1; /* init links to empty */
725
726 freq[256] = 1; /* make sure 256 has a nonzero count */
727 /* Including the pseudo-symbol 256 in the Huffman procedure guarantees
728 * that no real symbol is given code-value of all ones, because 256
729 * will be placed last in the largest codeword category.
730 */
731
732 /* Huffman's basic algorithm to assign optimal code lengths to symbols */
733
734 for (;;) {
735 /* Find the smallest nonzero frequency, set c1 = its symbol */
736 /* In case of ties, take the larger symbol number */
737 c1 = -1;
738 v = 1000000000L;
739 for (i = 0; i <= 256; i++) {
740 if (freq[i] && freq[i] <= v) {
741 v = freq[i];
742 c1 = i;
743 }
744 }
745
746 /* Find the next smallest nonzero frequency, set c2 = its symbol */
747 /* In case of ties, take the larger symbol number */
748 c2 = -1;
749 v = 1000000000L;
750 for (i = 0; i <= 256; i++) {
751 if (freq[i] && freq[i] <= v && i != c1) {
752 v = freq[i];
753 c2 = i;
754 }
755 }
756
757 /* Done if we've merged everything into one frequency */
758 if (c2 < 0)
759 break;
760
761 /* Else merge the two counts/trees */
762 freq[c1] += freq[c2];
763 freq[c2] = 0;
764
765 /* Increment the codesize of everything in c1's tree branch */
766 codesize[c1]++;
767 while (others[c1] >= 0) {
768 c1 = others[c1];
769 codesize[c1]++;
770 }
771
772 others[c1] = c2; /* chain c2 onto c1's tree branch */
773
774 /* Increment the codesize of everything in c2's tree branch */
775 codesize[c2]++;
776 while (others[c2] >= 0) {
777 c2 = others[c2];
778 codesize[c2]++;
779 }
780 }
781
782 /* Now count the number of symbols of each code length */
783 for (i = 0; i <= 256; i++) {
784 if (codesize[i]) {
785 /* The JPEG standard seems to think that this can't happen, */
786 /* but I'm paranoid... */
787 if (codesize[i] > MAX_CLEN)
788 ERREXIT(cinfo, JERR_HUFF_CLEN_OVERFLOW);
789
790 bits[codesize[i]]++;
791 }
792 }
793
794 /* JPEG doesn't allow symbols with code lengths over 16 bits, so if the pure
795 * Huffman procedure assigned any such lengths, we must adjust the coding.
796 * Here is what the JPEG spec says about how this next bit works:
797 * Since symbols are paired for the longest Huffman code, the symbols are
798 * removed from this length category two at a time. The prefix for the pair
799 * (which is one bit shorter) is allocated to one of the pair; then,
800 * skipping the BITS entry for that prefix length, a code word from the next
801 * shortest nonzero BITS entry is converted into a prefix for two code words
802 * one bit longer.
803 */
804
805 for (i = MAX_CLEN; i > 16; i--) {
806 while (bits[i] > 0) {
807 j = i - 2; /* find length of new prefix to be used */
808 while (bits[j] == 0)
809 j--;
810
811 bits[i] -= 2; /* remove two symbols */
812 bits[i-1]++; /* one goes in this length */
813 bits[j+1] += 2; /* two new symbols in this length */
814 bits[j]--; /* symbol of this length is now a prefix */
815 }
816 }
817
818 /* Remove the count for the pseudo-symbol 256 from the largest codelength */
819 while (bits[i] == 0) /* find largest codelength still in use */
820 i--;
821 bits[i]--;
822
823 /* Return final symbol counts (only for lengths 0..16) */
824 MEMCOPY(htbl->bits, bits, SIZEOF(htbl->bits));
825
826 /* Return a list of the symbols sorted by code length */
827 /* It's not real clear to me why we don't need to consider the codelength
828 * changes made above, but the JPEG spec seems to think this works.
829 */
830 p = 0;
831 for (i = 1; i <= MAX_CLEN; i++) {
832 for (j = 0; j <= 255; j++) {
833 if (codesize[j] == i) {
834 htbl->huffval[p] = (UINT8) j;
835 p++;
836 }
837 }
838 }
839
840 /* Set sent_table FALSE so updated table will be written to JPEG file. */
841 htbl->sent_table = FALSE;
842 }
843
844
845 /*
846 * Finish up a statistics-gathering pass and create the new Huffman tables.
847 */
848
849 METHODDEF(void)
finish_pass_gather(j_compress_ptr cinfo)850 finish_pass_gather (j_compress_ptr cinfo)
851 {
852 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
853 int ci, dctbl, actbl;
854 jpeg_component_info * compptr;
855 JHUFF_TBL **htblptr;
856 boolean did_dc[NUM_HUFF_TBLS];
857 boolean did_ac[NUM_HUFF_TBLS];
858
859 /* It's important not to apply jpeg_gen_optimal_table more than once
860 * per table, because it clobbers the input frequency counts!
861 */
862 MEMZERO(did_dc, SIZEOF(did_dc));
863 MEMZERO(did_ac, SIZEOF(did_ac));
864
865 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
866 compptr = cinfo->cur_comp_info[ci];
867 dctbl = compptr->dc_tbl_no;
868 actbl = compptr->ac_tbl_no;
869 if (! did_dc[dctbl]) {
870 htblptr = & cinfo->dc_huff_tbl_ptrs[dctbl];
871 if (*htblptr == NULL)
872 *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
873 jpeg_gen_optimal_table(cinfo, *htblptr, entropy->dc_count_ptrs[dctbl]);
874 did_dc[dctbl] = TRUE;
875 }
876 if (! did_ac[actbl]) {
877 htblptr = & cinfo->ac_huff_tbl_ptrs[actbl];
878 if (*htblptr == NULL)
879 *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
880 jpeg_gen_optimal_table(cinfo, *htblptr, entropy->ac_count_ptrs[actbl]);
881 did_ac[actbl] = TRUE;
882 }
883 }
884 }
885
886
887 #endif /* ENTROPY_OPT_SUPPORTED */
888
889
890 /*
891 * Module initialization routine for Huffman entropy encoding.
892 */
893
894 GLOBAL(void)
jinit_huff_encoder(j_compress_ptr cinfo)895 jinit_huff_encoder (j_compress_ptr cinfo)
896 {
897 huff_entropy_ptr entropy;
898 int i;
899
900 entropy = (huff_entropy_ptr)
901 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
902 SIZEOF(huff_entropy_encoder));
903 cinfo->entropy = (struct jpeg_entropy_encoder *) entropy;
904 entropy->pub.start_pass = start_pass_huff;
905
906 /* Mark tables unallocated */
907 for (i = 0; i < NUM_HUFF_TBLS; i++) {
908 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
909 #ifdef ENTROPY_OPT_SUPPORTED
910 entropy->dc_count_ptrs[i] = entropy->ac_count_ptrs[i] = NULL;
911 #endif
912 }
913 }
914
915 #endif //_FX_JPEG_TURBO_
916