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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  * BITS_LEFT(name, gb)
117  * Return the number of bits left
118  *
119  * For examples see get_bits, show_bits, skip_bits, get_vlc.
120  */
121 
122 #ifdef LONG_BITSTREAM_READER
123 # define MIN_CACHE_BITS 32
124 #else
125 # define MIN_CACHE_BITS 25
126 #endif
127 
128 #define OPEN_READER_NOSIZE(name, gb) \
129  unsigned int name ## _index = (gb)->index; \
130  unsigned int av_unused name ## _cache
131 
132 #if UNCHECKED_BITSTREAM_READER
133 #define OPEN_READER(name, gb) OPEN_READER_NOSIZE(name, gb)
134 
135 #define BITS_AVAILABLE(name, gb) 1
136 #else
137 #define OPEN_READER(name, gb) \
138  OPEN_READER_NOSIZE(name, gb); \
139  unsigned int name ## _size_plus8 = (gb)->size_in_bits_plus8
140 
141 #define BITS_AVAILABLE(name, gb) name ## _index < name ## _size_plus8
142 #endif
143 
144 #define CLOSE_READER(name, gb) (gb)->index = name ## _index
145 
146 # ifdef LONG_BITSTREAM_READER
147 
148 # define UPDATE_CACHE_LE(name, gb) name ## _cache = \
149  AV_RL64((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)
150 
151 # define UPDATE_CACHE_BE(name, gb) name ## _cache = \
152  AV_RB64((gb)->buffer + (name ## _index >> 3)) >> (32 - (name ## _index & 7))
153 
154 #else
155 
156 # define UPDATE_CACHE_LE(name, gb) name ## _cache = \
157  AV_RL32((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)
158 
159 # define UPDATE_CACHE_BE(name, gb) name ## _cache = \
160  AV_RB32((gb)->buffer + (name ## _index >> 3)) << (name ## _index & 7)
161 
162 #endif
163 
164 
165 #ifdef BITSTREAM_READER_LE
166 
167 # define UPDATE_CACHE(name, gb) UPDATE_CACHE_LE(name, gb)
168 
169 # define SKIP_CACHE(name, gb, num) name ## _cache >>= (num)
170 
171 #else
172 
173 # define UPDATE_CACHE(name, gb) UPDATE_CACHE_BE(name, gb)
174 
175 # define SKIP_CACHE(name, gb, num) name ## _cache <<= (num)
176 
177 #endif
178 
179 #if UNCHECKED_BITSTREAM_READER
180 # define SKIP_COUNTER(name, gb, num) name ## _index += (num)
181 #else
182 # define SKIP_COUNTER(name, gb, num) \
183  name ## _index = FFMIN(name ## _size_plus8, name ## _index + (num))
184 #endif
185 
186 #define BITS_LEFT(name, gb) ((int)((gb)->size_in_bits - name ## _index))
187 
188 #define SKIP_BITS(name, gb, num) \
189  do { \
190  SKIP_CACHE(name, gb, num); \
191  SKIP_COUNTER(name, gb, num); \
192  } while (0)
193 
194 #define LAST_SKIP_BITS(name, gb, num) SKIP_COUNTER(name, gb, num)
195 
196 #define SHOW_UBITS_LE(name, gb, num) zero_extend(name ## _cache, num)
197 #define SHOW_SBITS_LE(name, gb, num) sign_extend(name ## _cache, num)
198 
199 #define SHOW_UBITS_BE(name, gb, num) NEG_USR32(name ## _cache, num)
200 #define SHOW_SBITS_BE(name, gb, num) NEG_SSR32(name ## _cache, num)
201 
202 #ifdef BITSTREAM_READER_LE
203 # define SHOW_UBITS(name, gb, num) SHOW_UBITS_LE(name, gb, num)
204 # define SHOW_SBITS(name, gb, num) SHOW_SBITS_LE(name, gb, num)
205 #else
206 # define SHOW_UBITS(name, gb, num) SHOW_UBITS_BE(name, gb, num)
207 # define SHOW_SBITS(name, gb, num) SHOW_SBITS_BE(name, gb, num)
208 #endif
209 
210 #define GET_CACHE(name, gb) ((uint32_t) name ## _cache)
211 
212 static inline int get_bits_count(const GetBitContext *s)
213 {
214  return s->index;
215 }
216 
217 static inline void skip_bits_long(GetBitContext *s, int n)
218 {
219 #if UNCHECKED_BITSTREAM_READER
220  s->index += n;
221 #else
222  s->index += av_clip(n, -s->index, s->size_in_bits_plus8 - s->index);
223 #endif
224 }
225 
226 /**
227  * read mpeg1 dc style vlc (sign bit + mantissa with no MSB).
228  * if MSB not set it is negative
229  * @param n length in bits
230  */
231 static inline int get_xbits(GetBitContext *s, int n)
232 {
233  register int sign;
234  register int32_t cache;
235  OPEN_READER(re, s);
236  av_assert2(n>0 && n<=25);
237  UPDATE_CACHE(re, s);
238  cache = GET_CACHE(re, s);
239  sign = ~cache >> 31;
240  LAST_SKIP_BITS(re, s, n);
241  CLOSE_READER(re, s);
242  return (NEG_USR32(sign ^ cache, n) ^ sign) - sign;
243 }
244 
245 static inline int get_sbits(GetBitContext *s, int n)
246 {
247  register int tmp;
248  OPEN_READER(re, s);
249  av_assert2(n>0 && n<=25);
250  UPDATE_CACHE(re, s);
251  tmp = SHOW_SBITS(re, s, n);
252  LAST_SKIP_BITS(re, s, n);
253  CLOSE_READER(re, s);
254  return tmp;
255 }
256 
257 /**
258  * Read 1-25 bits.
259  */
260 static inline unsigned int get_bits(GetBitContext *s, int n)
261 {
262  register int tmp;
263  OPEN_READER(re, s);
264  av_assert2(n>0 && n<=25);
265  UPDATE_CACHE(re, s);
266  tmp = SHOW_UBITS(re, s, n);
267  LAST_SKIP_BITS(re, s, n);
268  CLOSE_READER(re, s);
269  return tmp;
270 }
271 
272 static inline unsigned int get_bits_le(GetBitContext *s, int n)
273 {
274  register int tmp;
275  OPEN_READER(re, s);
276  av_assert2(n>0 && n<=25);
277  UPDATE_CACHE_LE(re, s);
278  tmp = SHOW_UBITS_LE(re, s, n);
279  LAST_SKIP_BITS(re, s, n);
280  CLOSE_READER(re, s);
281  return tmp;
282 }
283 
284 /**
285  * Show 1-25 bits.
286  */
287 static inline unsigned int show_bits(GetBitContext *s, int n)
288 {
289  register int tmp;
291  av_assert2(n>0 && n<=25);
292  UPDATE_CACHE(re, s);
293  tmp = SHOW_UBITS(re, s, n);
294  return tmp;
295 }
296 
297 static inline void skip_bits(GetBitContext *s, int n)
298 {
299  OPEN_READER(re, s);
300  LAST_SKIP_BITS(re, s, n);
301  CLOSE_READER(re, s);
302 }
303 
304 static inline unsigned int get_bits1(GetBitContext *s)
305 {
306  unsigned int index = s->index;
307  uint8_t result = s->buffer[index >> 3];
308 #ifdef BITSTREAM_READER_LE
309  result >>= index & 7;
310  result &= 1;
311 #else
312  result <<= index & 7;
313  result >>= 8 - 1;
314 #endif
315 #if !UNCHECKED_BITSTREAM_READER
316  if (s->index < s->size_in_bits_plus8)
317 #endif
318  index++;
319  s->index = index;
320 
321  return result;
322 }
323 
324 static inline unsigned int show_bits1(GetBitContext *s)
325 {
326  return show_bits(s, 1);
327 }
328 
329 static inline void skip_bits1(GetBitContext *s)
330 {
331  skip_bits(s, 1);
332 }
333 
334 /**
335  * Read 0-32 bits.
336  */
337 static inline unsigned int get_bits_long(GetBitContext *s, int n)
338 {
339  if (!n) {
340  return 0;
341  } else if (n <= MIN_CACHE_BITS) {
342  return get_bits(s, n);
343  } else {
344 #ifdef BITSTREAM_READER_LE
345  unsigned ret = get_bits(s, 16);
346  return ret | (get_bits(s, n - 16) << 16);
347 #else
348  unsigned ret = get_bits(s, 16) << (n - 16);
349  return ret | get_bits(s, n - 16);
350 #endif
351  }
352 }
353 
354 /**
355  * Read 0-64 bits.
356  */
357 static inline uint64_t get_bits64(GetBitContext *s, int n)
358 {
359  if (n <= 32) {
360  return get_bits_long(s, n);
361  } else {
362 #ifdef BITSTREAM_READER_LE
363  uint64_t ret = get_bits_long(s, 32);
364  return ret | (uint64_t) get_bits_long(s, n - 32) << 32;
365 #else
366  uint64_t ret = (uint64_t) get_bits_long(s, n - 32) << 32;
367  return ret | get_bits_long(s, 32);
368 #endif
369  }
370 }
371 
372 /**
373  * Read 0-32 bits as a signed integer.
374  */
375 static inline int get_sbits_long(GetBitContext *s, int n)
376 {
377  return sign_extend(get_bits_long(s, n), n);
378 }
379 
380 /**
381  * Show 0-32 bits.
382  */
383 static inline unsigned int show_bits_long(GetBitContext *s, int n)
384 {
385  if (n <= MIN_CACHE_BITS) {
386  return show_bits(s, n);
387  } else {
388  GetBitContext gb = *s;
389  return get_bits_long(&gb, n);
390  }
391 }
392 
393 static inline int check_marker(GetBitContext *s, const char *msg)
394 {
395  int bit = get_bits1(s);
396  if (!bit)
397  av_log(NULL, AV_LOG_INFO, "Marker bit missing at %d of %d %s\n", get_bits_count(s) - 1, s->size_in_bits, msg);
398 
399  return bit;
400 }
401 
402 /**
403  * Initialize GetBitContext.
404  * @param buffer bitstream buffer, must be FF_INPUT_BUFFER_PADDING_SIZE bytes
405  * larger than the actual read bits because some optimized bitstream
406  * readers read 32 or 64 bit at once and could read over the end
407  * @param bit_size the size of the buffer in bits
408  * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
409  */
410 static inline int init_get_bits(GetBitContext *s, const uint8_t *buffer,
411  int bit_size)
412 {
413  int buffer_size;
414  int ret = 0;
415 
416  if (bit_size >= INT_MAX - 7 || bit_size < 0 || !buffer) {
417  bit_size = 0;
418  buffer = NULL;
419  ret = AVERROR_INVALIDDATA;
420  }
421 
422  buffer_size = (bit_size + 7) >> 3;
423 
424  s->buffer = buffer;
425  s->size_in_bits = bit_size;
426  s->size_in_bits_plus8 = bit_size + 8;
427  s->buffer_end = buffer + buffer_size;
428  s->index = 0;
429 
430  return ret;
431 }
432 
433 /**
434  * Initialize GetBitContext.
435  * @param buffer bitstream buffer, must be FF_INPUT_BUFFER_PADDING_SIZE bytes
436  * larger than the actual read bits because some optimized bitstream
437  * readers read 32 or 64 bit at once and could read over the end
438  * @param byte_size the size of the buffer in bytes
439  * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
440  */
441 static inline int init_get_bits8(GetBitContext *s, const uint8_t *buffer,
442  int byte_size)
443 {
444  if (byte_size > INT_MAX / 8 || byte_size < 0)
445  byte_size = -1;
446  return init_get_bits(s, buffer, byte_size * 8);
447 }
448 
449 static inline const uint8_t *align_get_bits(GetBitContext *s)
450 {
451  int n = -get_bits_count(s) & 7;
452  if (n)
453  skip_bits(s, n);
454  return s->buffer + (s->index >> 3);
455 }
456 
457 #define init_vlc(vlc, nb_bits, nb_codes, \
458  bits, bits_wrap, bits_size, \
459  codes, codes_wrap, codes_size, \
460  flags) \
461  ff_init_vlc_sparse(vlc, nb_bits, nb_codes, \
462  bits, bits_wrap, bits_size, \
463  codes, codes_wrap, codes_size, \
464  NULL, 0, 0, flags)
465 
466 int ff_init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,
467  const void *bits, int bits_wrap, int bits_size,
468  const void *codes, int codes_wrap, int codes_size,
469  const void *symbols, int symbols_wrap, int symbols_size,
470  int flags);
471 void ff_free_vlc(VLC *vlc);
472 
473 #define INIT_VLC_LE 2
474 #define INIT_VLC_USE_NEW_STATIC 4
475 
476 #define INIT_VLC_STATIC(vlc, bits, a, b, c, d, e, f, g, static_size) \
477  do { \
478  static VLC_TYPE table[static_size][2]; \
479  (vlc)->table = table; \
480  (vlc)->table_allocated = static_size; \
481  init_vlc(vlc, bits, a, b, c, d, e, f, g, INIT_VLC_USE_NEW_STATIC); \
482  } while (0)
483 
484 /**
485  * If the vlc code is invalid and max_depth=1, then no bits will be removed.
486  * If the vlc code is invalid and max_depth>1, then the number of bits removed
487  * is undefined.
488  */
489 #define GET_VLC(code, name, gb, table, bits, max_depth) \
490  do { \
491  int n, nb_bits; \
492  unsigned int index; \
493  \
494  index = SHOW_UBITS(name, gb, bits); \
495  code = table[index][0]; \
496  n = table[index][1]; \
497  \
498  if (max_depth > 1 && n < 0) { \
499  LAST_SKIP_BITS(name, gb, bits); \
500  UPDATE_CACHE(name, gb); \
501  \
502  nb_bits = -n; \
503  \
504  index = SHOW_UBITS(name, gb, nb_bits) + code; \
505  code = table[index][0]; \
506  n = table[index][1]; \
507  if (max_depth > 2 && n < 0) { \
508  LAST_SKIP_BITS(name, gb, nb_bits); \
509  UPDATE_CACHE(name, gb); \
510  \
511  nb_bits = -n; \
512  \
513  index = SHOW_UBITS(name, gb, nb_bits) + code; \
514  code = table[index][0]; \
515  n = table[index][1]; \
516  } \
517  } \
518  SKIP_BITS(name, gb, n); \
519  } while (0)
520 
521 #define GET_RL_VLC_INTERNAL(level, run, name, gb, table, bits, \
522  max_depth, need_update) \
523  do { \
524  int n, nb_bits; \
525  unsigned int index; \
526  \
527  index = SHOW_UBITS(name, gb, bits); \
528  level = table[index].level; \
529  n = table[index].len; \
530  \
531  if (max_depth > 1 && n < 0) { \
532  SKIP_BITS(name, gb, bits); \
533  if (need_update) { \
534  UPDATE_CACHE(name, gb); \
535  } \
536  \
537  nb_bits = -n; \
538  \
539  index = SHOW_UBITS(name, gb, nb_bits) + level; \
540  level = table[index].level; \
541  n = table[index].len; \
542  } \
543  run = table[index].run; \
544  SKIP_BITS(name, gb, n); \
545  } while (0)
546 
547 /**
548  * Parse a vlc code.
549  * @param bits is the number of bits which will be read at once, must be
550  * identical to nb_bits in init_vlc()
551  * @param max_depth is the number of times bits bits must be read to completely
552  * read the longest vlc code
553  * = (max_vlc_length + bits - 1) / bits
554  */
556  int bits, int max_depth)
557 {
558  int code;
559 
560  OPEN_READER(re, s);
561  UPDATE_CACHE(re, s);
562 
563  GET_VLC(code, re, s, table, bits, max_depth);
564 
565  CLOSE_READER(re, s);
566 
567  return code;
568 }
569 
570 static inline int decode012(GetBitContext *gb)
571 {
572  int n;
573  n = get_bits1(gb);
574  if (n == 0)
575  return 0;
576  else
577  return get_bits1(gb) + 1;
578 }
579 
580 static inline int decode210(GetBitContext *gb)
581 {
582  if (get_bits1(gb))
583  return 0;
584  else
585  return 2 - get_bits1(gb);
586 }
587 
588 static inline int get_bits_left(GetBitContext *gb)
589 {
590  return gb->size_in_bits - get_bits_count(gb);
591 }
592 
593 static inline int skip_1stop_8data_bits(GetBitContext *gb)
594 {
595  if (get_bits_left(gb) <= 0)
596  return AVERROR_INVALIDDATA;
597 
598  while (get_bits1(gb)) {
599  skip_bits(gb, 8);
600  if (get_bits_left(gb) <= 0)
601  return AVERROR_INVALIDDATA;
602  }
603 
604  return 0;
605 }
606 
607 //#define TRACE
608 
609 #ifdef TRACE
610 static inline void print_bin(int bits, int n)
611 {
612  int i;
613 
614  for (i = n - 1; i >= 0; i--)
615  av_log(NULL, AV_LOG_DEBUG, "%d", (bits >> i) & 1);
616  for (i = n; i < 24; i++)
617  av_log(NULL, AV_LOG_DEBUG, " ");
618 }
619 
620 static inline int get_bits_trace(GetBitContext *s, int n, const char *file,
621  const char *func, int line)
622 {
623  int r = get_bits(s, n);
624 
625  print_bin(r, n);
626  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d bit @%5d in %s %s:%d\n",
627  r, n, r, get_bits_count(s) - n, file, func, line);
628 
629  return r;
630 }
631 
632 static inline int get_vlc_trace(GetBitContext *s, VLC_TYPE (*table)[2],
633  int bits, int max_depth, const char *file,
634  const char *func, int line)
635 {
636  int show = show_bits(s, 24);
637  int pos = get_bits_count(s);
638  int r = get_vlc2(s, table, bits, max_depth);
639  int len = get_bits_count(s) - pos;
640  int bits2 = show >> (24 - len);
641 
642  print_bin(bits2, len);
643 
644  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d vlc @%5d in %s %s:%d\n",
645  bits2, len, r, pos, file, func, line);
646 
647  return r;
648 }
649 
650 #define GET_RL_VLC(level, run, name, gb, table, bits, \
651  max_depth, need_update) \
652  do { \
653  int show = SHOW_UBITS(name, gb, 24); \
654  int len; \
655  int pos = name ## _index; \
656  \
657  GET_RL_VLC_INTERNAL(level, run, name, gb, table, bits,max_depth, need_update); \
658  \
659  len = name ## _index - pos + 1; \
660  show = show >> (24 - len); \
661  \
662  print_bin(show, len); \
663  \
664  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d/%-3d rlv @%5d in %s %s:%d\n",\
665  show, len, run-1, level, pos, __FILE__, __PRETTY_FUNCTION__, __LINE__);\
666  } while (0) \
667 
668 
669 static inline int get_xbits_trace(GetBitContext *s, int n, const char *file,
670  const char *func, int line)
671 {
672  int show = show_bits(s, n);
673  int r = get_xbits(s, n);
674 
675  print_bin(show, n);
676  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d xbt @%5d in %s %s:%d\n",
677  show, n, r, get_bits_count(s) - n, file, func, line);
678 
679  return r;
680 }
681 
682 #define get_bits(s, n) get_bits_trace(s , n, __FILE__, __PRETTY_FUNCTION__, __LINE__)
683 #define get_bits1(s) get_bits_trace(s, 1, __FILE__, __PRETTY_FUNCTION__, __LINE__)
684 #define get_xbits(s, n) get_xbits_trace(s, n, __FILE__, __PRETTY_FUNCTION__, __LINE__)
685 
686 #define get_vlc(s, vlc) get_vlc_trace(s, (vlc)->table, (vlc)->bits, 3, __FILE__, __PRETTY_FUNCTION__, __LINE__)
687 #define get_vlc2(s, tab, bits, max) get_vlc_trace(s, tab, bits, max, __FILE__, __PRETTY_FUNCTION__, __LINE__)
688 #else //TRACE
689 #define GET_RL_VLC GET_RL_VLC_INTERNAL
690 #endif
691 
692 #endif /* AVCODEC_GET_BITS_H */