1/*
2 * jchuff.c
3 *
4 * This file was part of the Independent JPEG Group's software:
5 * Copyright (C) 1991-1997, Thomas G. Lane.
6 * libjpeg-turbo Modifications:
7 * Copyright (C) 2009-2011, 2014-2016, 2018-2021, D. R. Commander.
8 * Copyright (C) 2015, Matthieu Darbois.
9 * Copyright (C) 2018, Matthias Räncker.
10 * Copyright (C) 2020, Arm Limited.
11 * For conditions of distribution and use, see the accompanying README.ijg
12 * file.
13 *
14 * This file contains Huffman entropy encoding routines.
15 *
16 * Much of the complexity here has to do with supporting output suspension.
17 * If the data destination module demands suspension, we want to be able to
18 * back up to the start of the current MCU. To do this, we copy state
19 * variables into local working storage, and update them back to the
20 * permanent JPEG objects only upon successful completion of an MCU.
21 *
22 * NOTE: All referenced figures are from
23 * Recommendation ITU-T T.81 (1992) | ISO/IEC 10918-1:1994.
24 */
25
26#define JPEG_INTERNALS
27#include "jinclude.h"
28#include "jpeglib.h"
29#include "jsimd.h"
30#include "jconfigint.h"
31#include <limits.h>
32
33/*
34 * NOTE: If USE_CLZ_INTRINSIC is defined, then clz/bsr instructions will be
35 * used for bit counting rather than the lookup table. This will reduce the
36 * memory footprint by 64k, which is important for some mobile applications
37 * that create many isolated instances of libjpeg-turbo (web browsers, for
38 * instance.) This may improve performance on some mobile platforms as well.
39 * This feature is enabled by default only on Arm processors, because some x86
40 * chips have a slow implementation of bsr, and the use of clz/bsr cannot be
41 * shown to have a significant performance impact even on the x86 chips that
42 * have a fast implementation of it. When building for Armv6, you can
43 * explicitly disable the use of clz/bsr by adding -mthumb to the compiler
44 * flags (this defines __thumb__).
45 */
46
47#if defined(__arm__) || defined(__aarch64__) || defined(_M_ARM) || \
48 defined(_M_ARM64)
49#if !defined(__thumb__) || defined(__thumb2__)
50#define USE_CLZ_INTRINSIC
51#endif
52#endif
53
54#ifdef USE_CLZ_INTRINSIC
55#if defined(_MSC_VER) && !defined(__clang__)
56#define JPEG_NBITS_NONZERO(x) (32 - _CountLeadingZeros(x))
57#else
58#define JPEG_NBITS_NONZERO(x) (32 - __builtin_clz(x))
59#endif
60#define JPEG_NBITS(x) (x ? JPEG_NBITS_NONZERO(x) : 0)
61#else
62#include "jpeg_nbits_table.h"
63#define JPEG_NBITS(x) (jpeg_nbits_table[x])
64#define JPEG_NBITS_NONZERO(x) JPEG_NBITS(x)
65#endif
66
67
68/* Expanded entropy encoder object for Huffman encoding.
69 *
70 * The savable_state subrecord contains fields that change within an MCU,
71 * but must not be updated permanently until we complete the MCU.
72 */
73
74#if defined(__x86_64__) && defined(__ILP32__)
75typedef unsigned long long bit_buf_type;
76#else
77typedef size_t bit_buf_type;
78#endif
79
80/* NOTE: The more optimal Huffman encoding algorithm is only used by the
81 * intrinsics implementation of the Arm Neon SIMD extensions, which is why we
82 * retain the old Huffman encoder behavior when using the GAS implementation.
83 */
84#if defined(WITH_SIMD) && !(defined(__arm__) || defined(__aarch64__) || \
85 defined(_M_ARM) || defined(_M_ARM64))
86typedef unsigned long long simd_bit_buf_type;
87#else
88typedef bit_buf_type simd_bit_buf_type;
89#endif
90
91#if (defined(SIZEOF_SIZE_T) && SIZEOF_SIZE_T == 8) || defined(_WIN64) || \
92 (defined(__x86_64__) && defined(__ILP32__))
93#define BIT_BUF_SIZE 64
94#elif (defined(SIZEOF_SIZE_T) && SIZEOF_SIZE_T == 4) || defined(_WIN32)
95#define BIT_BUF_SIZE 32
96#else
97#error Cannot determine word size
98#endif
99#define SIMD_BIT_BUF_SIZE (sizeof(simd_bit_buf_type) * 8)
100
101typedef struct {
102 union {
103 bit_buf_type c;
104 simd_bit_buf_type simd;
105 } put_buffer; /* current bit accumulation buffer */
106 int free_bits; /* # of bits available in it */
107 /* (Neon GAS: # of bits now in it) */
108 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
109} savable_state;
110
111typedef struct {
112 struct jpeg_entropy_encoder pub; /* public fields */
113
114 savable_state saved; /* Bit buffer & DC state at start of MCU */
115
116 /* These fields are NOT loaded into local working state. */
117 unsigned int restarts_to_go; /* MCUs left in this restart interval */
118 int next_restart_num; /* next restart number to write (0-7) */
119
120 /* Pointers to derived tables (these workspaces have image lifespan) */
121 c_derived_tbl *dc_derived_tbls[NUM_HUFF_TBLS];
122 c_derived_tbl *ac_derived_tbls[NUM_HUFF_TBLS];
123
124#ifdef ENTROPY_OPT_SUPPORTED /* Statistics tables for optimization */
125 long *dc_count_ptrs[NUM_HUFF_TBLS];
126 long *ac_count_ptrs[NUM_HUFF_TBLS];
127#endif
128
129 int simd;
130} huff_entropy_encoder;
131
132typedef huff_entropy_encoder *huff_entropy_ptr;
133
134/* Working state while writing an MCU.
135 * This struct contains all the fields that are needed by subroutines.
136 */
137
138typedef struct {
139 JOCTET *next_output_byte; /* => next byte to write in buffer */
140 size_t free_in_buffer; /* # of byte spaces remaining in buffer */
141 savable_state cur; /* Current bit buffer & DC state */
142 j_compress_ptr cinfo; /* dump_buffer needs access to this */
143 int simd;
144} working_state;
145
146
147/* Forward declarations */
148METHODDEF(boolean) encode_mcu_huff(j_compress_ptr cinfo, JBLOCKROW *MCU_data);
149METHODDEF(void) finish_pass_huff(j_compress_ptr cinfo);
150#ifdef ENTROPY_OPT_SUPPORTED
151METHODDEF(boolean) encode_mcu_gather(j_compress_ptr cinfo,
152 JBLOCKROW *MCU_data);
153METHODDEF(void) finish_pass_gather(j_compress_ptr cinfo);
154#endif
155
156
157/*
158 * Initialize for a Huffman-compressed scan.
159 * If gather_statistics is TRUE, we do not output anything during the scan,
160 * just count the Huffman symbols used and generate Huffman code tables.
161 */
162
163METHODDEF(void)
164start_pass_huff(j_compress_ptr cinfo, boolean gather_statistics)
165{
166 huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;
167 int ci, dctbl, actbl;
168 jpeg_component_info *compptr;
169
170 if (gather_statistics) {
171#ifdef ENTROPY_OPT_SUPPORTED
172 entropy->pub.encode_mcu = encode_mcu_gather;
173 entropy->pub.finish_pass = finish_pass_gather;
174#else
175 ERREXIT(cinfo, JERR_NOT_COMPILED);
176#endif
177 } else {
178 entropy->pub.encode_mcu = encode_mcu_huff;
179 entropy->pub.finish_pass = finish_pass_huff;
180 }
181
182 entropy->simd = jsimd_can_huff_encode_one_block();
183
184 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
185 compptr = cinfo->cur_comp_info[ci];
186 dctbl = compptr->dc_tbl_no;
187 actbl = compptr->ac_tbl_no;
188 if (gather_statistics) {
189#ifdef ENTROPY_OPT_SUPPORTED
190 /* Check for invalid table indexes */
191 /* (make_c_derived_tbl does this in the other path) */
192 if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS)
193 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);
194 if (actbl < 0 || actbl >= NUM_HUFF_TBLS)
195 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);
196 /* Allocate and zero the statistics tables */
197 /* Note that jpeg_gen_optimal_table expects 257 entries in each table! */
198 if (entropy->dc_count_ptrs[dctbl] == NULL)
199 entropy->dc_count_ptrs[dctbl] = (long *)
200 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
201 257 * sizeof(long));
202 MEMZERO(entropy->dc_count_ptrs[dctbl], 257 * sizeof(long));
203 if (entropy->ac_count_ptrs[actbl] == NULL)
204 entropy->ac_count_ptrs[actbl] = (long *)
205 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
206 257 * sizeof(long));
207 MEMZERO(entropy->ac_count_ptrs[actbl], 257 * sizeof(long));
208#endif
209 } else {
210 /* Compute derived values for Huffman tables */
211 /* We may do this more than once for a table, but it's not expensive */
212 jpeg_make_c_derived_tbl(cinfo, TRUE, dctbl,
213 &entropy->dc_derived_tbls[dctbl]);
214 jpeg_make_c_derived_tbl(cinfo, FALSE, actbl,
215 &entropy->ac_derived_tbls[actbl]);
216 }
217 /* Initialize DC predictions to 0 */
218 entropy->saved.last_dc_val[ci] = 0;
219 }
220
221 /* Initialize bit buffer to empty */
222 if (entropy->simd) {
223 entropy->saved.put_buffer.simd = 0;
224#if defined(__aarch64__) && !defined(NEON_INTRINSICS)
225 entropy->saved.free_bits = 0;
226#else
227 entropy->saved.free_bits = SIMD_BIT_BUF_SIZE;
228#endif
229 } else {
230 entropy->saved.put_buffer.c = 0;
231 entropy->saved.free_bits = BIT_BUF_SIZE;
232 }
233
234 /* Initialize restart stuff */
235 entropy->restarts_to_go = cinfo->restart_interval;
236 entropy->next_restart_num = 0;
237}
238
239
240/*
241 * Compute the derived values for a Huffman table.
242 * This routine also performs some validation checks on the table.
243 *
244 * Note this is also used by jcphuff.c.
245 */
246
247GLOBAL(void)
248jpeg_make_c_derived_tbl(j_compress_ptr cinfo, boolean isDC, int tblno,
249 c_derived_tbl **pdtbl)
250{
251 JHUFF_TBL *htbl;
252 c_derived_tbl *dtbl;
253 int p, i, l, lastp, si, maxsymbol;
254 char huffsize[257];
255 unsigned int huffcode[257];
256 unsigned int code;
257
258 /* Note that huffsize[] and huffcode[] are filled in code-length order,
259 * paralleling the order of the symbols themselves in htbl->huffval[].
260 */
261
262 /* Find the input Huffman table */
263 if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
264 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
265 htbl =
266 isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
267 if (htbl == NULL)
268 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
269
270 /* Allocate a workspace if we haven't already done so. */
271 if (*pdtbl == NULL)
272 *pdtbl = (c_derived_tbl *)
273 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
274 sizeof(c_derived_tbl));
275 dtbl = *pdtbl;
276
277 /* Figure C.1: make table of Huffman code length for each symbol */
278
279 p = 0;
280 for (l = 1; l <= 16; l++) {
281 i = (int)htbl->bits[l];
282 if (i < 0 || p + i > 256) /* protect against table overrun */
283 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
284 while (i--)
285 huffsize[p++] = (char)l;
286 }
287 huffsize[p] = 0;
288 lastp = p;
289
290 /* Figure C.2: generate the codes themselves */
291 /* We also validate that the counts represent a legal Huffman code tree. */
292
293 code = 0;
294 si = huffsize[0];
295 p = 0;
296 while (huffsize[p]) {
297 while (((int)huffsize[p]) == si) {
298 huffcode[p++] = code;
299 code++;
300 }
301 /* code is now 1 more than the last code used for codelength si; but
302 * it must still fit in si bits, since no code is allowed to be all ones.
303 */
304 if (((JLONG)code) >= (((JLONG)1) << si))
305 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
306 code <<= 1;
307 si++;
308 }
309
310 /* Figure C.3: generate encoding tables */
311 /* These are code and size indexed by symbol value */
312
313 /* Set all codeless symbols to have code length 0;
314 * this lets us detect duplicate VAL entries here, and later
315 * allows emit_bits to detect any attempt to emit such symbols.
316 */
317 MEMZERO(dtbl->ehufco, sizeof(dtbl->ehufco));
318 MEMZERO(dtbl->ehufsi, sizeof(dtbl->ehufsi));
319
320 /* This is also a convenient place to check for out-of-range
321 * and duplicated VAL entries. We allow 0..255 for AC symbols
322 * but only 0..15 for DC. (We could constrain them further
323 * based on data depth and mode, but this seems enough.)
324 */
325 maxsymbol = isDC ? 15 : 255;
326
327 for (p = 0; p < lastp; p++) {
328 i = htbl->huffval[p];
329 if (i < 0 || i > maxsymbol || dtbl->ehufsi[i])
330 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
331 dtbl->ehufco[i] = huffcode[p];
332 dtbl->ehufsi[i] = huffsize[p];
333 }
334}
335
336
337/* Outputting bytes to the file */
338
339/* Emit a byte, taking 'action' if must suspend. */
340#define emit_byte(state, val, action) { \
341 *(state)->next_output_byte++ = (JOCTET)(val); \
342 if (--(state)->free_in_buffer == 0) \
343 if (!dump_buffer(state)) \
344 { action; } \
345}
346
347
348LOCAL(boolean)
349dump_buffer(working_state *state)
350/* Empty the output buffer; return TRUE if successful, FALSE if must suspend */
351{
352 struct jpeg_destination_mgr *dest = state->cinfo->dest;
353
354 if (!(*dest->empty_output_buffer) (state->cinfo))
355 return FALSE;
356 /* After a successful buffer dump, must reset buffer pointers */
357 state->next_output_byte = dest->next_output_byte;
358 state->free_in_buffer = dest->free_in_buffer;
359 return TRUE;
360}
361
362
363/* Outputting bits to the file */
364
365/* Output byte b and, speculatively, an additional 0 byte. 0xFF must be
366 * encoded as 0xFF 0x00, so the output buffer pointer is advanced by 2 if the
367 * byte is 0xFF. Otherwise, the output buffer pointer is advanced by 1, and
368 * the speculative 0 byte will be overwritten by the next byte.
369 */
370#define EMIT_BYTE(b) { \
371 buffer[0] = (JOCTET)(b); \
372 buffer[1] = 0; \
373 buffer -= -2 + ((JOCTET)(b) < 0xFF); \
374}
375
376/* Output the entire bit buffer. If there are no 0xFF bytes in it, then write
377 * directly to the output buffer. Otherwise, use the EMIT_BYTE() macro to
378 * encode 0xFF as 0xFF 0x00.
379 */
380#if BIT_BUF_SIZE == 64
381
382#define FLUSH() { \
383 if (put_buffer & 0x8080808080808080 & ~(put_buffer + 0x0101010101010101)) { \
384 EMIT_BYTE(put_buffer >> 56) \
385 EMIT_BYTE(put_buffer >> 48) \
386 EMIT_BYTE(put_buffer >> 40) \
387 EMIT_BYTE(put_buffer >> 32) \
388 EMIT_BYTE(put_buffer >> 24) \
389 EMIT_BYTE(put_buffer >> 16) \
390 EMIT_BYTE(put_buffer >> 8) \
391 EMIT_BYTE(put_buffer ) \
392 } else { \
393 buffer[0] = (JOCTET)(put_buffer >> 56); \
394 buffer[1] = (JOCTET)(put_buffer >> 48); \
395 buffer[2] = (JOCTET)(put_buffer >> 40); \
396 buffer[3] = (JOCTET)(put_buffer >> 32); \
397 buffer[4] = (JOCTET)(put_buffer >> 24); \
398 buffer[5] = (JOCTET)(put_buffer >> 16); \
399 buffer[6] = (JOCTET)(put_buffer >> 8); \
400 buffer[7] = (JOCTET)(put_buffer); \
401 buffer += 8; \
402 } \
403}
404
405#else
406
407#define FLUSH() { \
408 if (put_buffer & 0x80808080 & ~(put_buffer + 0x01010101)) { \
409 EMIT_BYTE(put_buffer >> 24) \
410 EMIT_BYTE(put_buffer >> 16) \
411 EMIT_BYTE(put_buffer >> 8) \
412 EMIT_BYTE(put_buffer ) \
413 } else { \
414 buffer[0] = (JOCTET)(put_buffer >> 24); \
415 buffer[1] = (JOCTET)(put_buffer >> 16); \
416 buffer[2] = (JOCTET)(put_buffer >> 8); \
417 buffer[3] = (JOCTET)(put_buffer); \
418 buffer += 4; \
419 } \
420}
421
422#endif
423
424/* Fill the bit buffer to capacity with the leading bits from code, then output
425 * the bit buffer and put the remaining bits from code into the bit buffer.
426 */
427#define PUT_AND_FLUSH(code, size) { \
428 put_buffer = (put_buffer << (size + free_bits)) | (code >> -free_bits); \
429 FLUSH() \
430 free_bits += BIT_BUF_SIZE; \
431 put_buffer = code; \
432}
433
434/* Insert code into the bit buffer and output the bit buffer if needed.
435 * NOTE: We can't flush with free_bits == 0, since the left shift in
436 * PUT_AND_FLUSH() would have undefined behavior.
437 */
438#define PUT_BITS(code, size) { \
439 free_bits -= size; \
440 if (free_bits < 0) \
441 PUT_AND_FLUSH(code, size) \
442 else \
443 put_buffer = (put_buffer << size) | code; \
444}
445
446#define PUT_CODE(code, size) { \
447 temp &= (((JLONG)1) << nbits) - 1; \
448 temp |= code << nbits; \
449 nbits += size; \
450 PUT_BITS(temp, nbits) \
451}
452
453
454/* Although it is exceedingly rare, it is possible for a Huffman-encoded
455 * coefficient block to be larger than the 128-byte unencoded block. For each
456 * of the 64 coefficients, PUT_BITS is invoked twice, and each invocation can
457 * theoretically store 16 bits (for a maximum of 2048 bits or 256 bytes per
458 * encoded block.) If, for instance, one artificially sets the AC
459 * coefficients to alternating values of 32767 and -32768 (using the JPEG
460 * scanning order-- 1, 8, 16, etc.), then this will produce an encoded block
461 * larger than 200 bytes.
462 */
463#define BUFSIZE (DCTSIZE2 * 8)
464
465#define LOAD_BUFFER() { \
466 if (state->free_in_buffer < BUFSIZE) { \
467 localbuf = 1; \
468 buffer = _buffer; \
469 } else \
470 buffer = state->next_output_byte; \
471}
472
473#define STORE_BUFFER() { \
474 if (localbuf) { \
475 size_t bytes, bytestocopy; \
476 bytes = buffer - _buffer; \
477 buffer = _buffer; \
478 while (bytes > 0) { \
479 bytestocopy = MIN(bytes, state->free_in_buffer); \
480 MEMCOPY(state->next_output_byte, buffer, bytestocopy); \
481 state->next_output_byte += bytestocopy; \
482 buffer += bytestocopy; \
483 state->free_in_buffer -= bytestocopy; \
484 if (state->free_in_buffer == 0) \
485 if (!dump_buffer(state)) return FALSE; \
486 bytes -= bytestocopy; \
487 } \
488 } else { \
489 state->free_in_buffer -= (buffer - state->next_output_byte); \
490 state->next_output_byte = buffer; \
491 } \
492}
493
494
495LOCAL(boolean)
496flush_bits(working_state *state)
497{
498 JOCTET _buffer[BUFSIZE], *buffer, temp;
499 simd_bit_buf_type put_buffer; int put_bits;
500 int localbuf = 0;
501
502 if (state->simd) {
503#if defined(__aarch64__) && !defined(NEON_INTRINSICS)
504 put_bits = state->cur.free_bits;
505#else
506 put_bits = SIMD_BIT_BUF_SIZE - state->cur.free_bits;
507#endif
508 put_buffer = state->cur.put_buffer.simd;
509 } else {
510 put_bits = BIT_BUF_SIZE - state->cur.free_bits;
511 put_buffer = state->cur.put_buffer.c;
512 }
513
514 LOAD_BUFFER()
515
516 while (put_bits >= 8) {
517 put_bits -= 8;
518 temp = (JOCTET)(put_buffer >> put_bits);
519 EMIT_BYTE(temp)
520 }
521 if (put_bits) {
522 /* fill partial byte with ones */
523 temp = (JOCTET)((put_buffer << (8 - put_bits)) | (0xFF >> put_bits));
524 EMIT_BYTE(temp)
525 }
526
527 if (state->simd) { /* and reset bit buffer to empty */
528 state->cur.put_buffer.simd = 0;
529#if defined(__aarch64__) && !defined(NEON_INTRINSICS)
530 state->cur.free_bits = 0;
531#else
532 state->cur.free_bits = SIMD_BIT_BUF_SIZE;
533#endif
534 } else {
535 state->cur.put_buffer.c = 0;
536 state->cur.free_bits = BIT_BUF_SIZE;
537 }
538 STORE_BUFFER()
539
540 return TRUE;
541}
542
543
544/* Encode a single block's worth of coefficients */
545
546LOCAL(boolean)
547encode_one_block_simd(working_state *state, JCOEFPTR block, int last_dc_val,
548 c_derived_tbl *dctbl, c_derived_tbl *actbl)
549{
550 JOCTET _buffer[BUFSIZE], *buffer;
551 int localbuf = 0;
552
553 LOAD_BUFFER()
554
555 buffer = jsimd_huff_encode_one_block(state, buffer, block, last_dc_val,
556 dctbl, actbl);
557
558 STORE_BUFFER()
559
560 return TRUE;
561}
562
563LOCAL(boolean)
564encode_one_block(working_state *state, JCOEFPTR block, int last_dc_val,
565 c_derived_tbl *dctbl, c_derived_tbl *actbl)
566{
567 int temp, nbits, free_bits;
568 bit_buf_type put_buffer;
569 JOCTET _buffer[BUFSIZE], *buffer;
570 int localbuf = 0;
571
572 free_bits = state->cur.free_bits;
573 put_buffer = state->cur.put_buffer.c;
574 LOAD_BUFFER()
575
576 /* Encode the DC coefficient difference per section F.1.2.1 */
577
578 temp = block[0] - last_dc_val;
579
580 /* This is a well-known technique for obtaining the absolute value without a
581 * branch. It is derived from an assembly language technique presented in
582 * "How to Optimize for the Pentium Processors", Copyright (c) 1996, 1997 by
583 * Agner Fog. This code assumes we are on a two's complement machine.
584 */
585 nbits = temp >> (CHAR_BIT * sizeof(int) - 1);
586 temp += nbits;
587 nbits ^= temp;
588
589 /* Find the number of bits needed for the magnitude of the coefficient */
590 nbits = JPEG_NBITS(nbits);
591
592 /* Emit the Huffman-coded symbol for the number of bits.
593 * Emit that number of bits of the value, if positive,
594 * or the complement of its magnitude, if negative.
595 */
596 PUT_CODE(dctbl->ehufco[nbits], dctbl->ehufsi[nbits])
597
598 /* Encode the AC coefficients per section F.1.2.2 */
599
600 {
601 int r = 0; /* r = run length of zeros */
602
603/* Manually unroll the k loop to eliminate the counter variable. This
604 * improves performance greatly on systems with a limited number of
605 * registers (such as x86.)
606 */
607#define kloop(jpeg_natural_order_of_k) { \
608 if ((temp = block[jpeg_natural_order_of_k]) == 0) { \
609 r += 16; \
610 } else { \
611 /* Branch-less absolute value, bitwise complement, etc., same as above */ \
612 nbits = temp >> (CHAR_BIT * sizeof(int) - 1); \
613 temp += nbits; \
614 nbits ^= temp; \
615 nbits = JPEG_NBITS_NONZERO(nbits); \
616 /* if run length > 15, must emit special run-length-16 codes (0xF0) */ \
617 while (r >= 16 * 16) { \
618 r -= 16 * 16; \
619 PUT_BITS(actbl->ehufco[0xf0], actbl->ehufsi[0xf0]) \
620 } \
621 /* Emit Huffman symbol for run length / number of bits */ \
622 r += nbits; \
623 PUT_CODE(actbl->ehufco[r], actbl->ehufsi[r]) \
624 r = 0; \
625 } \
626}
627
628 /* One iteration for each value in jpeg_natural_order[] */
629 kloop(1); kloop(8); kloop(16); kloop(9); kloop(2); kloop(3);
630 kloop(10); kloop(17); kloop(24); kloop(32); kloop(25); kloop(18);
631 kloop(11); kloop(4); kloop(5); kloop(12); kloop(19); kloop(26);
632 kloop(33); kloop(40); kloop(48); kloop(41); kloop(34); kloop(27);
633 kloop(20); kloop(13); kloop(6); kloop(7); kloop(14); kloop(21);
634 kloop(28); kloop(35); kloop(42); kloop(49); kloop(56); kloop(57);
635 kloop(50); kloop(43); kloop(36); kloop(29); kloop(22); kloop(15);
636 kloop(23); kloop(30); kloop(37); kloop(44); kloop(51); kloop(58);
637 kloop(59); kloop(52); kloop(45); kloop(38); kloop(31); kloop(39);
638 kloop(46); kloop(53); kloop(60); kloop(61); kloop(54); kloop(47);
639 kloop(55); kloop(62); kloop(63);
640
641 /* If the last coef(s) were zero, emit an end-of-block code */
642 if (r > 0) {
643 PUT_BITS(actbl->ehufco[0], actbl->ehufsi[0])
644 }
645 }
646
647 state->cur.put_buffer.c = put_buffer;
648 state->cur.free_bits = free_bits;
649 STORE_BUFFER()
650
651 return TRUE;
652}
653
654
655/*
656 * Emit a restart marker & resynchronize predictions.
657 */
658
659LOCAL(boolean)
660emit_restart(working_state *state, int restart_num)
661{
662 int ci;
663
664 if (!flush_bits(state))
665 return FALSE;
666
667 emit_byte(state, 0xFF, return FALSE);
668 emit_byte(state, JPEG_RST0 + restart_num, return FALSE);
669
670 /* Re-initialize DC predictions to 0 */
671 for (ci = 0; ci < state->cinfo->comps_in_scan; ci++)
672 state->cur.last_dc_val[ci] = 0;
673
674 /* The restart counter is not updated until we successfully write the MCU. */
675
676 return TRUE;
677}
678
679
680/*
681 * Encode and output one MCU's worth of Huffman-compressed coefficients.
682 */
683
684METHODDEF(boolean)
685encode_mcu_huff(j_compress_ptr cinfo, JBLOCKROW *MCU_data)
686{
687 huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;
688 working_state state;
689 int blkn, ci;
690 jpeg_component_info *compptr;
691
692 /* Load up working state */
693 state.next_output_byte = cinfo->dest->next_output_byte;
694 state.free_in_buffer = cinfo->dest->free_in_buffer;
695 state.cur = entropy->saved;
696 state.cinfo = cinfo;
697 state.simd = entropy->simd;
698
699 /* Emit restart marker if needed */
700 if (cinfo->restart_interval) {
701 if (entropy->restarts_to_go == 0)
702 if (!emit_restart(&state, entropy->next_restart_num))
703 return FALSE;
704 }
705
706 /* Encode the MCU data blocks */
707 if (entropy->simd) {
708 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
709 ci = cinfo->MCU_membership[blkn];
710 compptr = cinfo->cur_comp_info[ci];
711 if (!encode_one_block_simd(&state,
712 MCU_data[blkn][0], state.cur.last_dc_val[ci],
713 entropy->dc_derived_tbls[compptr->dc_tbl_no],
714 entropy->ac_derived_tbls[compptr->ac_tbl_no]))
715 return FALSE;
716 /* Update last_dc_val */
717 state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];
718 }
719 } else {
720 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
721 ci = cinfo->MCU_membership[blkn];
722 compptr = cinfo->cur_comp_info[ci];
723 if (!encode_one_block(&state,
724 MCU_data[blkn][0], state.cur.last_dc_val[ci],
725 entropy->dc_derived_tbls[compptr->dc_tbl_no],
726 entropy->ac_derived_tbls[compptr->ac_tbl_no]))
727 return FALSE;
728 /* Update last_dc_val */
729 state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];
730 }
731 }
732
733 /* Completed MCU, so update state */
734 cinfo->dest->next_output_byte = state.next_output_byte;
735 cinfo->dest->free_in_buffer = state.free_in_buffer;
736 entropy->saved = state.cur;
737
738 /* Update restart-interval state too */
739 if (cinfo->restart_interval) {
740 if (entropy->restarts_to_go == 0) {
741 entropy->restarts_to_go = cinfo->restart_interval;
742 entropy->next_restart_num++;
743 entropy->next_restart_num &= 7;
744 }
745 entropy->restarts_to_go--;
746 }
747
748 return TRUE;
749}
750
751
752/*
753 * Finish up at the end of a Huffman-compressed scan.
754 */
755
756METHODDEF(void)
757finish_pass_huff(j_compress_ptr cinfo)
758{
759 huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;
760 working_state state;
761
762 /* Load up working state ... flush_bits needs it */
763 state.next_output_byte = cinfo->dest->next_output_byte;
764 state.free_in_buffer = cinfo->dest->free_in_buffer;
765 state.cur = entropy->saved;
766 state.cinfo = cinfo;
767 state.simd = entropy->simd;
768
769 /* Flush out the last data */
770 if (!flush_bits(&state))
771 ERREXIT(cinfo, JERR_CANT_SUSPEND);
772
773 /* Update state */
774 cinfo->dest->next_output_byte = state.next_output_byte;
775 cinfo->dest->free_in_buffer = state.free_in_buffer;
776 entropy->saved = state.cur;
777}
778
779
780/*
781 * Huffman coding optimization.
782 *
783 * We first scan the supplied data and count the number of uses of each symbol
784 * that is to be Huffman-coded. (This process MUST agree with the code above.)
785 * Then we build a Huffman coding tree for the observed counts.
786 * Symbols which are not needed at all for the particular image are not
787 * assigned any code, which saves space in the DHT marker as well as in
788 * the compressed data.
789 */
790
791#ifdef ENTROPY_OPT_SUPPORTED
792
793
794/* Process a single block's worth of coefficients */
795
796LOCAL(void)
797htest_one_block(j_compress_ptr cinfo, JCOEFPTR block, int last_dc_val,
798 long dc_counts[], long ac_counts[])
799{
800 register int temp;
801 register int nbits;
802 register int k, r;
803
804 /* Encode the DC coefficient difference per section F.1.2.1 */
805
806 temp = block[0] - last_dc_val;
807 if (temp < 0)
808 temp = -temp;
809
810 /* Find the number of bits needed for the magnitude of the coefficient */
811 nbits = 0;
812 while (temp) {
813 nbits++;
814 temp >>= 1;
815 }
816 /* Check for out-of-range coefficient values.
817 * Since we're encoding a difference, the range limit is twice as much.
818 */
819 if (nbits > MAX_COEF_BITS + 1)
820 ERREXIT(cinfo, JERR_BAD_DCT_COEF);
821
822 /* Count the Huffman symbol for the number of bits */
823 dc_counts[nbits]++;
824
825 /* Encode the AC coefficients per section F.1.2.2 */
826
827 r = 0; /* r = run length of zeros */
828
829 for (k = 1; k < DCTSIZE2; k++) {
830 if ((temp = block[jpeg_natural_order[k]]) == 0) {
831 r++;
832 } else {
833 /* if run length > 15, must emit special run-length-16 codes (0xF0) */
834 while (r > 15) {
835 ac_counts[0xF0]++;
836 r -= 16;
837 }
838
839 /* Find the number of bits needed for the magnitude of the coefficient */
840 if (temp < 0)
841 temp = -temp;
842
843 /* Find the number of bits needed for the magnitude of the coefficient */
844 nbits = 1; /* there must be at least one 1 bit */
845 while ((temp >>= 1))
846 nbits++;
847 /* Check for out-of-range coefficient values */
848 if (nbits > MAX_COEF_BITS)
849 ERREXIT(cinfo, JERR_BAD_DCT_COEF);
850
851 /* Count Huffman symbol for run length / number of bits */
852 ac_counts[(r << 4) + nbits]++;
853
854 r = 0;
855 }
856 }
857
858 /* If the last coef(s) were zero, emit an end-of-block code */
859 if (r > 0)
860 ac_counts[0]++;
861}
862
863
864/*
865 * Trial-encode one MCU's worth of Huffman-compressed coefficients.
866 * No data is actually output, so no suspension return is possible.
867 */
868
869METHODDEF(boolean)
870encode_mcu_gather(j_compress_ptr cinfo, JBLOCKROW *MCU_data)
871{
872 huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;
873 int blkn, ci;
874 jpeg_component_info *compptr;
875
876 /* Take care of restart intervals if needed */
877 if (cinfo->restart_interval) {
878 if (entropy->restarts_to_go == 0) {
879 /* Re-initialize DC predictions to 0 */
880 for (ci = 0; ci < cinfo->comps_in_scan; ci++)
881 entropy->saved.last_dc_val[ci] = 0;
882 /* Update restart state */
883 entropy->restarts_to_go = cinfo->restart_interval;
884 }
885 entropy->restarts_to_go--;
886 }
887
888 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
889 ci = cinfo->MCU_membership[blkn];
890 compptr = cinfo->cur_comp_info[ci];
891 htest_one_block(cinfo, MCU_data[blkn][0], entropy->saved.last_dc_val[ci],
892 entropy->dc_count_ptrs[compptr->dc_tbl_no],
893 entropy->ac_count_ptrs[compptr->ac_tbl_no]);
894 entropy->saved.last_dc_val[ci] = MCU_data[blkn][0][0];
895 }
896
897 return TRUE;
898}
899
900
901/*
902 * Generate the best Huffman code table for the given counts, fill htbl.
903 * Note this is also used by jcphuff.c.
904 *
905 * The JPEG standard requires that no symbol be assigned a codeword of all
906 * one bits (so that padding bits added at the end of a compressed segment
907 * can't look like a valid code). Because of the canonical ordering of
908 * codewords, this just means that there must be an unused slot in the
909 * longest codeword length category. Annex K (Clause K.2) of
910 * Rec. ITU-T T.81 (1992) | ISO/IEC 10918-1:1994 suggests reserving such a slot
911 * by pretending that symbol 256 is a valid symbol with count 1. In theory
912 * that's not optimal; giving it count zero but including it in the symbol set
913 * anyway should give a better Huffman code. But the theoretically better code
914 * actually seems to come out worse in practice, because it produces more
915 * all-ones bytes (which incur stuffed zero bytes in the final file). In any
916 * case the difference is tiny.
917 *
918 * The JPEG standard requires Huffman codes to be no more than 16 bits long.
919 * If some symbols have a very small but nonzero probability, the Huffman tree
920 * must be adjusted to meet the code length restriction. We currently use
921 * the adjustment method suggested in JPEG section K.2. This method is *not*
922 * optimal; it may not choose the best possible limited-length code. But
923 * typically only very-low-frequency symbols will be given less-than-optimal
924 * lengths, so the code is almost optimal. Experimental comparisons against
925 * an optimal limited-length-code algorithm indicate that the difference is
926 * microscopic --- usually less than a hundredth of a percent of total size.
927 * So the extra complexity of an optimal algorithm doesn't seem worthwhile.
928 */
929
930GLOBAL(void)
931jpeg_gen_optimal_table(j_compress_ptr cinfo, JHUFF_TBL *htbl, long freq[])
932{
933#define MAX_CLEN 32 /* assumed maximum initial code length */
934 UINT8 bits[MAX_CLEN + 1]; /* bits[k] = # of symbols with code length k */
935 int codesize[257]; /* codesize[k] = code length of symbol k */
936 int others[257]; /* next symbol in current branch of tree */
937 int c1, c2;
938 int p, i, j;
939 long v;
940
941 /* This algorithm is explained in section K.2 of the JPEG standard */
942
943 MEMZERO(bits, sizeof(bits));
944 MEMZERO(codesize, sizeof(codesize));
945 for (i = 0; i < 257; i++)
946 others[i] = -1; /* init links to empty */
947
948 freq[256] = 1; /* make sure 256 has a nonzero count */
949 /* Including the pseudo-symbol 256 in the Huffman procedure guarantees
950 * that no real symbol is given code-value of all ones, because 256
951 * will be placed last in the largest codeword category.
952 */
953
954 /* Huffman's basic algorithm to assign optimal code lengths to symbols */
955
956 for (;;) {
957 /* Find the smallest nonzero frequency, set c1 = its symbol */
958 /* In case of ties, take the larger symbol number */
959 c1 = -1;
960 v = 1000000000L;
961 for (i = 0; i <= 256; i++) {
962 if (freq[i] && freq[i] <= v) {
963 v = freq[i];
964 c1 = i;
965 }
966 }
967
968 /* Find the next smallest nonzero frequency, set c2 = its symbol */
969 /* In case of ties, take the larger symbol number */
970 c2 = -1;
971 v = 1000000000L;
972 for (i = 0; i <= 256; i++) {
973 if (freq[i] && freq[i] <= v && i != c1) {
974 v = freq[i];
975 c2 = i;
976 }
977 }
978
979 /* Done if we've merged everything into one frequency */
980 if (c2 < 0)
981 break;
982
983 /* Else merge the two counts/trees */
984 freq[c1] += freq[c2];
985 freq[c2] = 0;
986
987 /* Increment the codesize of everything in c1's tree branch */
988 codesize[c1]++;
989 while (others[c1] >= 0) {
990 c1 = others[c1];
991 codesize[c1]++;
992 }
993
994 others[c1] = c2; /* chain c2 onto c1's tree branch */
995
996 /* Increment the codesize of everything in c2's tree branch */
997 codesize[c2]++;
998 while (others[c2] >= 0) {
999 c2 = others[c2];
1000 codesize[c2]++;
1001 }
1002 }
1003
1004 /* Now count the number of symbols of each code length */
1005 for (i = 0; i <= 256; i++) {
1006 if (codesize[i]) {
1007 /* The JPEG standard seems to think that this can't happen, */
1008 /* but I'm paranoid... */
1009 if (codesize[i] > MAX_CLEN)
1010 ERREXIT(cinfo, JERR_HUFF_CLEN_OVERFLOW);
1011
1012 bits[codesize[i]]++;
1013 }
1014 }
1015
1016 /* JPEG doesn't allow symbols with code lengths over 16 bits, so if the pure
1017 * Huffman procedure assigned any such lengths, we must adjust the coding.
1018 * Here is what Rec. ITU-T T.81 | ISO/IEC 10918-1 says about how this next
1019 * bit works: Since symbols are paired for the longest Huffman code, the
1020 * symbols are removed from this length category two at a time. The prefix
1021 * for the pair (which is one bit shorter) is allocated to one of the pair;
1022 * then, skipping the BITS entry for that prefix length, a code word from the
1023 * next shortest nonzero BITS entry is converted into a prefix for two code
1024 * words one bit longer.
1025 */
1026
1027 for (i = MAX_CLEN; i > 16; i--) {
1028 while (bits[i] > 0) {
1029 j = i - 2; /* find length of new prefix to be used */
1030 while (bits[j] == 0)
1031 j--;
1032
1033 bits[i] -= 2; /* remove two symbols */
1034 bits[i - 1]++; /* one goes in this length */
1035 bits[j + 1] += 2; /* two new symbols in this length */
1036 bits[j]--; /* symbol of this length is now a prefix */
1037 }
1038 }
1039
1040 /* Remove the count for the pseudo-symbol 256 from the largest codelength */
1041 while (bits[i] == 0) /* find largest codelength still in use */
1042 i--;
1043 bits[i]--;
1044
1045 /* Return final symbol counts (only for lengths 0..16) */
1046 MEMCOPY(htbl->bits, bits, sizeof(htbl->bits));
1047
1048 /* Return a list of the symbols sorted by code length */
1049 /* It's not real clear to me why we don't need to consider the codelength
1050 * changes made above, but Rec. ITU-T T.81 | ISO/IEC 10918-1 seems to think
1051 * this works.
1052 */
1053 p = 0;
1054 for (i = 1; i <= MAX_CLEN; i++) {
1055 for (j = 0; j <= 255; j++) {
1056 if (codesize[j] == i) {
1057 htbl->huffval[p] = (UINT8)j;
1058 p++;
1059 }
1060 }
1061 }
1062
1063 /* Set sent_table FALSE so updated table will be written to JPEG file. */
1064 htbl->sent_table = FALSE;
1065}
1066
1067
1068/*
1069 * Finish up a statistics-gathering pass and create the new Huffman tables.
1070 */
1071
1072METHODDEF(void)
1073finish_pass_gather(j_compress_ptr cinfo)
1074{
1075 huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;
1076 int ci, dctbl, actbl;
1077 jpeg_component_info *compptr;
1078 JHUFF_TBL **htblptr;
1079 boolean did_dc[NUM_HUFF_TBLS];
1080 boolean did_ac[NUM_HUFF_TBLS];
1081
1082 /* It's important not to apply jpeg_gen_optimal_table more than once
1083 * per table, because it clobbers the input frequency counts!
1084 */
1085 MEMZERO(did_dc, sizeof(did_dc));
1086 MEMZERO(did_ac, sizeof(did_ac));
1087
1088 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
1089 compptr = cinfo->cur_comp_info[ci];
1090 dctbl = compptr->dc_tbl_no;
1091 actbl = compptr->ac_tbl_no;
1092 if (!did_dc[dctbl]) {
1093 htblptr = &cinfo->dc_huff_tbl_ptrs[dctbl];
1094 if (*htblptr == NULL)
1095 *htblptr = jpeg_alloc_huff_table((j_common_ptr)cinfo);
1096 jpeg_gen_optimal_table(cinfo, *htblptr, entropy->dc_count_ptrs[dctbl]);
1097 did_dc[dctbl] = TRUE;
1098 }
1099 if (!did_ac[actbl]) {
1100 htblptr = &cinfo->ac_huff_tbl_ptrs[actbl];
1101 if (*htblptr == NULL)
1102 *htblptr = jpeg_alloc_huff_table((j_common_ptr)cinfo);
1103 jpeg_gen_optimal_table(cinfo, *htblptr, entropy->ac_count_ptrs[actbl]);
1104 did_ac[actbl] = TRUE;
1105 }
1106 }
1107}
1108
1109
1110#endif /* ENTROPY_OPT_SUPPORTED */
1111
1112
1113/*
1114 * Module initialization routine for Huffman entropy encoding.
1115 */
1116
1117GLOBAL(void)
1118jinit_huff_encoder(j_compress_ptr cinfo)
1119{
1120 huff_entropy_ptr entropy;
1121 int i;
1122
1123 entropy = (huff_entropy_ptr)
1124 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
1125 sizeof(huff_entropy_encoder));
1126 cinfo->entropy = (struct jpeg_entropy_encoder *)entropy;
1127 entropy->pub.start_pass = start_pass_huff;
1128
1129 /* Mark tables unallocated */
1130 for (i = 0; i < NUM_HUFF_TBLS; i++) {
1131 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
1132#ifdef ENTROPY_OPT_SUPPORTED
1133 entropy->dc_count_ptrs[i] = entropy->ac_count_ptrs[i] = NULL;
1134#endif
1135 }
1136}
1137