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get_bits.h
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1 /*
2  * copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
3  *
4  * This file is part of FFmpeg.
5  *
6  * FFmpeg is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU Lesser General Public
8  * License as published by the Free Software Foundation; either
9  * version 2.1 of the License, or (at your option) any later version.
10  *
11  * FFmpeg is distributed in the hope that it will be useful,
12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14  * Lesser General Public License for more details.
15  *
16  * You should have received a copy of the GNU Lesser General Public
17  * License along with FFmpeg; if not, write to the Free Software
18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19  */
20 
21 /**
22  * @file
23  * bitstream reader API header.
24  */
25 
26 #ifndef AVCODEC_GET_BITS_H
27 #define AVCODEC_GET_BITS_H
28 
29 #include <stdint.h>
30 
31 #include "libavutil/common.h"
32 #include "libavutil/intreadwrite.h"
33 #include "libavutil/log.h"
34 #include "libavutil/avassert.h"
35 #include "mathops.h"
36 
37 /*
38  * Safe bitstream reading:
39  * optionally, the get_bits API can check to ensure that we
40  * don't read past input buffer boundaries. This is protected
41  * with CONFIG_SAFE_BITSTREAM_READER at the global level, and
42  * then below that with UNCHECKED_BITSTREAM_READER at the per-
43  * decoder level. This means that decoders that check internally
44  * can "#define UNCHECKED_BITSTREAM_READER 1" to disable
45  * overread checks.
46  * Boundary checking causes a minor performance penalty so for
47  * applications that won't want/need this, it can be disabled
48  * globally using "#define CONFIG_SAFE_BITSTREAM_READER 0".
49  */
50 #ifndef UNCHECKED_BITSTREAM_READER
51 #define UNCHECKED_BITSTREAM_READER !CONFIG_SAFE_BITSTREAM_READER
52 #endif
53 
54 typedef struct GetBitContext {
56  int index;
60 
61 #define VLC_TYPE int16_t
62 
63 typedef struct VLC {
64  int bits;
65  VLC_TYPE (*table)[2]; ///< code, bits
67 } VLC;
68 
69 typedef struct RL_VLC_ELEM {
70  int16_t level;
71  int8_t len;
73 } RL_VLC_ELEM;
74 
75 /* Bitstream reader API docs:
76  * name
77  * arbitrary name which is used as prefix for the internal variables
78  *
79  * gb
80  * getbitcontext
81  *
82  * OPEN_READER(name, gb)
83  * load gb into local variables
84  *
85  * CLOSE_READER(name, gb)
86  * store local vars in gb
87  *
88  * UPDATE_CACHE(name, gb)
89  * Refill the internal cache from the bitstream.
90  * After this call at least MIN_CACHE_BITS will be available.
91  *
92  * GET_CACHE(name, gb)
93  * Will output the contents of the internal cache,
94  * next bit is MSB of 32 or 64 bit (FIXME 64bit).
95  *
96  * SHOW_UBITS(name, gb, num)
97  * Will return the next num bits.
98  *
99  * SHOW_SBITS(name, gb, num)
100  * Will return the next num bits and do sign extension.
101  *
102  * SKIP_BITS(name, gb, num)
103  * Will skip over the next num bits.
104  * Note, this is equivalent to SKIP_CACHE; SKIP_COUNTER.
105  *
106  * SKIP_CACHE(name, gb, num)
107  * Will remove the next num bits from the cache (note SKIP_COUNTER
108  * MUST be called before UPDATE_CACHE / CLOSE_READER).
109  *
110  * SKIP_COUNTER(name, gb, num)
111  * Will increment the internal bit counter (see SKIP_CACHE & SKIP_BITS).
112  *
113  * LAST_SKIP_BITS(name, gb, num)
114  * Like SKIP_BITS, to be used if next call is UPDATE_CACHE or CLOSE_READER.
115  *
116  * For examples see get_bits, show_bits, skip_bits, get_vlc.
117  */
118 
119 #ifdef LONG_BITSTREAM_READER
120 # define MIN_CACHE_BITS 32
121 #else
122 # define MIN_CACHE_BITS 25
123 #endif
124 
125 #if UNCHECKED_BITSTREAM_READER
126 #define OPEN_READER(name, gb) \
127  unsigned int name ## _index = (gb)->index; \
128  unsigned int av_unused name ## _cache
129 
130 #define HAVE_BITS_REMAINING(name, gb) 1
131 #else
132 #define OPEN_READER(name, gb) \
133  unsigned int name ## _index = (gb)->index; \
134  unsigned int av_unused name ## _cache = 0; \
135  unsigned int av_unused name ## _size_plus8 = (gb)->size_in_bits_plus8
136 
137 #define HAVE_BITS_REMAINING(name, gb) name ## _index < name ## _size_plus8
138 #endif
139 
140 #define CLOSE_READER(name, gb) (gb)->index = name ## _index
141 
142 # ifdef LONG_BITSTREAM_READER
143 
144 # define UPDATE_CACHE_LE(name, gb) name ## _cache = \
145  AV_RL64((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)
146 
147 # define UPDATE_CACHE_BE(name, gb) name ## _cache = \
148  AV_RB64((gb)->buffer + (name ## _index >> 3)) >> (32 - (name ## _index & 7))
149 
150 #else
151 
152 # define UPDATE_CACHE_LE(name, gb) name ## _cache = \
153  AV_RL32((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)
154 
155 # define UPDATE_CACHE_BE(name, gb) name ## _cache = \
156  AV_RB32((gb)->buffer + (name ## _index >> 3)) << (name ## _index & 7)
157 
158 #endif
159 
160 
161 #ifdef BITSTREAM_READER_LE
162 
163 # define UPDATE_CACHE(name, gb) UPDATE_CACHE_LE(name, gb)
164 
165 # define SKIP_CACHE(name, gb, num) name ## _cache >>= (num)
166 
167 #else
168 
169 # define UPDATE_CACHE(name, gb) UPDATE_CACHE_BE(name, gb)
170 
171 # define SKIP_CACHE(name, gb, num) name ## _cache <<= (num)
172 
173 #endif
174 
175 #if UNCHECKED_BITSTREAM_READER
176 # define SKIP_COUNTER(name, gb, num) name ## _index += (num)
177 #else
178 # define SKIP_COUNTER(name, gb, num) \
179  name ## _index = FFMIN(name ## _size_plus8, name ## _index + (num))
180 #endif
181 
182 #define SKIP_BITS(name, gb, num) \
183  do { \
184  SKIP_CACHE(name, gb, num); \
185  SKIP_COUNTER(name, gb, num); \
186  } while (0)
187 
188 #define LAST_SKIP_BITS(name, gb, num) SKIP_COUNTER(name, gb, num)
189 
190 #define SHOW_UBITS_LE(name, gb, num) zero_extend(name ## _cache, num)
191 #define SHOW_SBITS_LE(name, gb, num) sign_extend(name ## _cache, num)
192 
193 #define SHOW_UBITS_BE(name, gb, num) NEG_USR32(name ## _cache, num)
194 #define SHOW_SBITS_BE(name, gb, num) NEG_SSR32(name ## _cache, num)
195 
196 #ifdef BITSTREAM_READER_LE
197 # define SHOW_UBITS(name, gb, num) SHOW_UBITS_LE(name, gb, num)
198 # define SHOW_SBITS(name, gb, num) SHOW_SBITS_LE(name, gb, num)
199 #else
200 # define SHOW_UBITS(name, gb, num) SHOW_UBITS_BE(name, gb, num)
201 # define SHOW_SBITS(name, gb, num) SHOW_SBITS_BE(name, gb, num)
202 #endif
203 
204 #define GET_CACHE(name, gb) ((uint32_t) name ## _cache)
205 
206 static inline int get_bits_count(const GetBitContext *s)
207 {
208  return s->index;
209 }
210 
211 static inline void skip_bits_long(GetBitContext *s, int n)
212 {
213 #if UNCHECKED_BITSTREAM_READER
214  s->index += n;
215 #else
216  s->index += av_clip(n, -s->index, s->size_in_bits_plus8 - s->index);
217 #endif
218 }
219 
220 /**
221  * read mpeg1 dc style vlc (sign bit + mantissa with no MSB).
222  * if MSB not set it is negative
223  * @param n length in bits
224  */
225 static inline int get_xbits(GetBitContext *s, int n)
226 {
227  register int sign;
228  register int32_t cache;
229  OPEN_READER(re, s);
230  av_assert2(n>0 && n<=25);
231  UPDATE_CACHE(re, s);
232  cache = GET_CACHE(re, s);
233  sign = ~cache >> 31;
234  LAST_SKIP_BITS(re, s, n);
235  CLOSE_READER(re, s);
236  return (NEG_USR32(sign ^ cache, n) ^ sign) - sign;
237 }
238 
239 static inline int get_sbits(GetBitContext *s, int n)
240 {
241  register int tmp;
242  OPEN_READER(re, s);
243  av_assert2(n>0 && n<=25);
244  UPDATE_CACHE(re, s);
245  tmp = SHOW_SBITS(re, s, n);
246  LAST_SKIP_BITS(re, s, n);
247  CLOSE_READER(re, s);
248  return tmp;
249 }
250 
251 /**
252  * Read 1-25 bits.
253  */
254 static inline unsigned int get_bits(GetBitContext *s, int n)
255 {
256  register int tmp;
257  OPEN_READER(re, s);
258  av_assert2(n>0 && n<=25);
259  UPDATE_CACHE(re, s);
260  tmp = SHOW_UBITS(re, s, n);
261  LAST_SKIP_BITS(re, s, n);
262  CLOSE_READER(re, s);
263  return tmp;
264 }
265 
266 static inline unsigned int get_bits_le(GetBitContext *s, int n)
267 {
268  register int tmp;
269  OPEN_READER(re, s);
270  av_assert2(n>0 && n<=25);
271  UPDATE_CACHE_LE(re, s);
272  tmp = SHOW_UBITS_LE(re, s, n);
273  LAST_SKIP_BITS(re, s, n);
274  CLOSE_READER(re, s);
275  return tmp;
276 }
277 
278 /**
279  * Show 1-25 bits.
280  */
281 static inline unsigned int show_bits(GetBitContext *s, int n)
282 {
283  register int tmp;
284  OPEN_READER(re, s);
285  av_assert2(n>0 && n<=25);
286  UPDATE_CACHE(re, s);
287  tmp = SHOW_UBITS(re, s, n);
288  return tmp;
289 }
290 
291 static inline void skip_bits(GetBitContext *s, int n)
292 {
293  OPEN_READER(re, s);
294  LAST_SKIP_BITS(re, s, n);
295  CLOSE_READER(re, s);
296 }
297 
298 static inline unsigned int get_bits1(GetBitContext *s)
299 {
300  unsigned int index = s->index;
301  uint8_t result = s->buffer[index >> 3];
302 #ifdef BITSTREAM_READER_LE
303  result >>= index & 7;
304  result &= 1;
305 #else
306  result <<= index & 7;
307  result >>= 8 - 1;
308 #endif
309 #if !UNCHECKED_BITSTREAM_READER
310  if (s->index < s->size_in_bits_plus8)
311 #endif
312  index++;
313  s->index = index;
314 
315  return result;
316 }
317 
318 static inline unsigned int show_bits1(GetBitContext *s)
319 {
320  return show_bits(s, 1);
321 }
322 
323 static inline void skip_bits1(GetBitContext *s)
324 {
325  skip_bits(s, 1);
326 }
327 
328 /**
329  * Read 0-32 bits.
330  */
331 static inline unsigned int get_bits_long(GetBitContext *s, int n)
332 {
333  if (!n) {
334  return 0;
335  } else if (n <= MIN_CACHE_BITS) {
336  return get_bits(s, n);
337  } else {
338 #ifdef BITSTREAM_READER_LE
339  unsigned ret = get_bits(s, 16);
340  return ret | (get_bits(s, n - 16) << 16);
341 #else
342  unsigned ret = get_bits(s, 16) << (n - 16);
343  return ret | get_bits(s, n - 16);
344 #endif
345  }
346 }
347 
348 /**
349  * Read 0-64 bits.
350  */
351 static inline uint64_t get_bits64(GetBitContext *s, int n)
352 {
353  if (n <= 32) {
354  return get_bits_long(s, n);
355  } else {
356 #ifdef BITSTREAM_READER_LE
357  uint64_t ret = get_bits_long(s, 32);
358  return ret | (uint64_t) get_bits_long(s, n - 32) << 32;
359 #else
360  uint64_t ret = (uint64_t) get_bits_long(s, n - 32) << 32;
361  return ret | get_bits_long(s, 32);
362 #endif
363  }
364 }
365 
366 /**
367  * Read 0-32 bits as a signed integer.
368  */
369 static inline int get_sbits_long(GetBitContext *s, int n)
370 {
371  return sign_extend(get_bits_long(s, n), n);
372 }
373 
374 /**
375  * Show 0-32 bits.
376  */
377 static inline unsigned int show_bits_long(GetBitContext *s, int n)
378 {
379  if (n <= MIN_CACHE_BITS) {
380  return show_bits(s, n);
381  } else {
382  GetBitContext gb = *s;
383  return get_bits_long(&gb, n);
384  }
385 }
386 
387 static inline int check_marker(GetBitContext *s, const char *msg)
388 {
389  int bit = get_bits1(s);
390  if (!bit)
391  av_log(NULL, AV_LOG_INFO, "Marker bit missing %s\n", msg);
392 
393  return bit;
394 }
395 
396 /**
397  * Initialize GetBitContext.
398  * @param buffer bitstream buffer, must be FF_INPUT_BUFFER_PADDING_SIZE bytes
399  * larger than the actual read bits because some optimized bitstream
400  * readers read 32 or 64 bit at once and could read over the end
401  * @param bit_size the size of the buffer in bits
402  * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
403  */
404 static inline int init_get_bits(GetBitContext *s, const uint8_t *buffer,
405  int bit_size)
406 {
407  int buffer_size;
408  int ret = 0;
409 
410  if (bit_size >= INT_MAX - 7 || bit_size < 0 || !buffer) {
411  bit_size = 0;
412  buffer = NULL;
413  ret = AVERROR_INVALIDDATA;
414  }
415 
416  buffer_size = (bit_size + 7) >> 3;
417 
418  s->buffer = buffer;
419  s->size_in_bits = bit_size;
420  s->size_in_bits_plus8 = bit_size + 8;
421  s->buffer_end = buffer + buffer_size;
422  s->index = 0;
423 
424  return ret;
425 }
426 
427 /**
428  * Initialize GetBitContext.
429  * @param buffer bitstream buffer, must be FF_INPUT_BUFFER_PADDING_SIZE bytes
430  * larger than the actual read bits because some optimized bitstream
431  * readers read 32 or 64 bit at once and could read over the end
432  * @param byte_size the size of the buffer in bytes
433  * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
434  */
435 static inline int init_get_bits8(GetBitContext *s, const uint8_t *buffer,
436  int byte_size)
437 {
438  if (byte_size > INT_MAX / 8 || byte_size < 0)
439  byte_size = -1;
440  return init_get_bits(s, buffer, byte_size * 8);
441 }
442 
443 static inline const uint8_t *align_get_bits(GetBitContext *s)
444 {
445  int n = -get_bits_count(s) & 7;
446  if (n)
447  skip_bits(s, n);
448  return s->buffer + (s->index >> 3);
449 }
450 
451 #define init_vlc(vlc, nb_bits, nb_codes, \
452  bits, bits_wrap, bits_size, \
453  codes, codes_wrap, codes_size, \
454  flags) \
455  ff_init_vlc_sparse(vlc, nb_bits, nb_codes, \
456  bits, bits_wrap, bits_size, \
457  codes, codes_wrap, codes_size, \
458  NULL, 0, 0, flags)
459 
460 int ff_init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,
461  const void *bits, int bits_wrap, int bits_size,
462  const void *codes, int codes_wrap, int codes_size,
463  const void *symbols, int symbols_wrap, int symbols_size,
464  int flags);
465 void ff_free_vlc(VLC *vlc);
466 
467 #define INIT_VLC_LE 2
468 #define INIT_VLC_USE_NEW_STATIC 4
469 
470 #define INIT_VLC_STATIC(vlc, bits, a, b, c, d, e, f, g, static_size) \
471  do { \
472  static VLC_TYPE table[static_size][2]; \
473  (vlc)->table = table; \
474  (vlc)->table_allocated = static_size; \
475  init_vlc(vlc, bits, a, b, c, d, e, f, g, INIT_VLC_USE_NEW_STATIC); \
476  } while (0)
477 
478 /**
479  * If the vlc code is invalid and max_depth=1, then no bits will be removed.
480  * If the vlc code is invalid and max_depth>1, then the number of bits removed
481  * is undefined.
482  */
483 #define GET_VLC(code, name, gb, table, bits, max_depth) \
484  do { \
485  int n, nb_bits; \
486  unsigned int index; \
487  \
488  index = SHOW_UBITS(name, gb, bits); \
489  code = table[index][0]; \
490  n = table[index][1]; \
491  \
492  if (max_depth > 1 && n < 0) { \
493  LAST_SKIP_BITS(name, gb, bits); \
494  UPDATE_CACHE(name, gb); \
495  \
496  nb_bits = -n; \
497  \
498  index = SHOW_UBITS(name, gb, nb_bits) + code; \
499  code = table[index][0]; \
500  n = table[index][1]; \
501  if (max_depth > 2 && n < 0) { \
502  LAST_SKIP_BITS(name, gb, nb_bits); \
503  UPDATE_CACHE(name, gb); \
504  \
505  nb_bits = -n; \
506  \
507  index = SHOW_UBITS(name, gb, nb_bits) + code; \
508  code = table[index][0]; \
509  n = table[index][1]; \
510  } \
511  } \
512  SKIP_BITS(name, gb, n); \
513  } while (0)
514 
515 #define GET_RL_VLC_INTERNAL(level, run, name, gb, table, bits, \
516  max_depth, need_update) \
517  do { \
518  int n, nb_bits; \
519  unsigned int index; \
520  \
521  index = SHOW_UBITS(name, gb, bits); \
522  level = table[index].level; \
523  n = table[index].len; \
524  \
525  if (max_depth > 1 && n < 0) { \
526  SKIP_BITS(name, gb, bits); \
527  if (need_update) { \
528  UPDATE_CACHE(name, gb); \
529  } \
530  \
531  nb_bits = -n; \
532  \
533  index = SHOW_UBITS(name, gb, nb_bits) + level; \
534  level = table[index].level; \
535  n = table[index].len; \
536  } \
537  run = table[index].run; \
538  SKIP_BITS(name, gb, n); \
539  } while (0)
540 
541 /**
542  * Parse a vlc code.
543  * @param bits is the number of bits which will be read at once, must be
544  * identical to nb_bits in init_vlc()
545  * @param max_depth is the number of times bits bits must be read to completely
546  * read the longest vlc code
547  * = (max_vlc_length + bits - 1) / bits
548  */
550  int bits, int max_depth)
551 {
552  int code;
553 
554  OPEN_READER(re, s);
555  UPDATE_CACHE(re, s);
556 
557  GET_VLC(code, re, s, table, bits, max_depth);
558 
559  CLOSE_READER(re, s);
560 
561  return code;
562 }
563 
564 static inline int decode012(GetBitContext *gb)
565 {
566  int n;
567  n = get_bits1(gb);
568  if (n == 0)
569  return 0;
570  else
571  return get_bits1(gb) + 1;
572 }
573 
574 static inline int decode210(GetBitContext *gb)
575 {
576  if (get_bits1(gb))
577  return 0;
578  else
579  return 2 - get_bits1(gb);
580 }
581 
582 static inline int get_bits_left(GetBitContext *gb)
583 {
584  return gb->size_in_bits - get_bits_count(gb);
585 }
586 
587 static inline int skip_1stop_8data_bits(GetBitContext *gb)
588 {
589  if (get_bits_left(gb) <= 0)
590  return AVERROR_INVALIDDATA;
591 
592  while (get_bits1(gb)) {
593  skip_bits(gb, 8);
594  if (get_bits_left(gb) <= 0)
595  return AVERROR_INVALIDDATA;
596  }
597 
598  return 0;
599 }
600 
601 //#define TRACE
602 
603 #ifdef TRACE
604 static inline void print_bin(int bits, int n)
605 {
606  int i;
607 
608  for (i = n - 1; i >= 0; i--)
609  av_log(NULL, AV_LOG_DEBUG, "%d", (bits >> i) & 1);
610  for (i = n; i < 24; i++)
611  av_log(NULL, AV_LOG_DEBUG, " ");
612 }
613 
614 static inline int get_bits_trace(GetBitContext *s, int n, const char *file,
615  const char *func, int line)
616 {
617  int r = get_bits(s, n);
618 
619  print_bin(r, n);
620  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d bit @%5d in %s %s:%d\n",
621  r, n, r, get_bits_count(s) - n, file, func, line);
622 
623  return r;
624 }
625 
626 static inline int get_vlc_trace(GetBitContext *s, VLC_TYPE (*table)[2],
627  int bits, int max_depth, const char *file,
628  const char *func, int line)
629 {
630  int show = show_bits(s, 24);
631  int pos = get_bits_count(s);
632  int r = get_vlc2(s, table, bits, max_depth);
633  int len = get_bits_count(s) - pos;
634  int bits2 = show >> (24 - len);
635 
636  print_bin(bits2, len);
637 
638  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d vlc @%5d in %s %s:%d\n",
639  bits2, len, r, pos, file, func, line);
640 
641  return r;
642 }
643 
644 #define GET_RL_VLC(level, run, name, gb, table, bits, \
645  max_depth, need_update) \
646  do { \
647  int show = SHOW_UBITS(name, gb, 24); \
648  int len; \
649  int pos = name ## _index; \
650  \
651  GET_RL_VLC_INTERNAL(level, run, name, gb, table, bits,max_depth, need_update); \
652  \
653  len = name ## _index - pos + 1; \
654  show = show >> (24 - len); \
655  \
656  print_bin(show, len); \
657  \
658  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d/%-3d rlv @%5d in %s %s:%d\n",\
659  show, len, run-1, level, pos, __FILE__, __PRETTY_FUNCTION__, __LINE__);\
660  } while (0) \
661 
662 
663 static inline int get_xbits_trace(GetBitContext *s, int n, const char *file,
664  const char *func, int line)
665 {
666  int show = show_bits(s, n);
667  int r = get_xbits(s, n);
668 
669  print_bin(show, n);
670  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d xbt @%5d in %s %s:%d\n",
671  show, n, r, get_bits_count(s) - n, file, func, line);
672 
673  return r;
674 }
675 
676 #define get_bits(s, n) get_bits_trace(s , n, __FILE__, __PRETTY_FUNCTION__, __LINE__)
677 #define get_bits1(s) get_bits_trace(s, 1, __FILE__, __PRETTY_FUNCTION__, __LINE__)
678 #define get_xbits(s, n) get_xbits_trace(s, n, __FILE__, __PRETTY_FUNCTION__, __LINE__)
679 
680 #define get_vlc(s, vlc) get_vlc_trace(s, (vlc)->table, (vlc)->bits, 3, __FILE__, __PRETTY_FUNCTION__, __LINE__)
681 #define get_vlc2(s, tab, bits, max) get_vlc_trace(s, tab, bits, max, __FILE__, __PRETTY_FUNCTION__, __LINE__)
682 
683 #define tprintf(p, ...) av_log(p, AV_LOG_DEBUG, __VA_ARGS__)
684 
685 #else //TRACE
686 #define tprintf(p, ...) { }
687 #define GET_RL_VLC GET_RL_VLC_INTERNAL
688 #endif
689 
690 #endif /* AVCODEC_GET_BITS_H */