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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 #if UNCHECKED_BITSTREAM_READER
129 #define OPEN_READER(name, gb) \
130  unsigned int name ## _index = (gb)->index; \
131  unsigned int av_unused name ## _cache
132 
133 #define HAVE_BITS_REMAINING(name, gb) 1
134 #else
135 #define OPEN_READER(name, gb) \
136  unsigned int name ## _index = (gb)->index; \
137  unsigned int av_unused name ## _cache = 0; \
138  unsigned int av_unused name ## _size_plus8 = (gb)->size_in_bits_plus8
139 
140 #define HAVE_BITS_REMAINING(name, gb) name ## _index < name ## _size_plus8
141 #endif
142 
143 #define CLOSE_READER(name, gb) (gb)->index = name ## _index
144 
145 # ifdef LONG_BITSTREAM_READER
146 
147 # define UPDATE_CACHE_LE(name, gb) name ## _cache = \
148  AV_RL64((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)
149 
150 # define UPDATE_CACHE_BE(name, gb) name ## _cache = \
151  AV_RB64((gb)->buffer + (name ## _index >> 3)) >> (32 - (name ## _index & 7))
152 
153 #else
154 
155 # define UPDATE_CACHE_LE(name, gb) name ## _cache = \
156  AV_RL32((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)
157 
158 # define UPDATE_CACHE_BE(name, gb) name ## _cache = \
159  AV_RB32((gb)->buffer + (name ## _index >> 3)) << (name ## _index & 7)
160 
161 #endif
162 
163 
164 #ifdef BITSTREAM_READER_LE
165 
166 # define UPDATE_CACHE(name, gb) UPDATE_CACHE_LE(name, gb)
167 
168 # define SKIP_CACHE(name, gb, num) name ## _cache >>= (num)
169 
170 #else
171 
172 # define UPDATE_CACHE(name, gb) UPDATE_CACHE_BE(name, gb)
173 
174 # define SKIP_CACHE(name, gb, num) name ## _cache <<= (num)
175 
176 #endif
177 
178 #if UNCHECKED_BITSTREAM_READER
179 # define SKIP_COUNTER(name, gb, num) name ## _index += (num)
180 #else
181 # define SKIP_COUNTER(name, gb, num) \
182  name ## _index = FFMIN(name ## _size_plus8, name ## _index + (num))
183 #endif
184 
185 #define BITS_LEFT(name, gb) ((int)((gb)->size_in_bits - name ## _index))
186 
187 #define SKIP_BITS(name, gb, num) \
188  do { \
189  SKIP_CACHE(name, gb, num); \
190  SKIP_COUNTER(name, gb, num); \
191  } while (0)
192 
193 #define LAST_SKIP_BITS(name, gb, num) SKIP_COUNTER(name, gb, num)
194 
195 #define SHOW_UBITS_LE(name, gb, num) zero_extend(name ## _cache, num)
196 #define SHOW_SBITS_LE(name, gb, num) sign_extend(name ## _cache, num)
197 
198 #define SHOW_UBITS_BE(name, gb, num) NEG_USR32(name ## _cache, num)
199 #define SHOW_SBITS_BE(name, gb, num) NEG_SSR32(name ## _cache, num)
200 
201 #ifdef BITSTREAM_READER_LE
202 # define SHOW_UBITS(name, gb, num) SHOW_UBITS_LE(name, gb, num)
203 # define SHOW_SBITS(name, gb, num) SHOW_SBITS_LE(name, gb, num)
204 #else
205 # define SHOW_UBITS(name, gb, num) SHOW_UBITS_BE(name, gb, num)
206 # define SHOW_SBITS(name, gb, num) SHOW_SBITS_BE(name, gb, num)
207 #endif
208 
209 #define GET_CACHE(name, gb) ((uint32_t) name ## _cache)
210 
211 static inline int get_bits_count(const GetBitContext *s)
212 {
213  return s->index;
214 }
215 
216 static inline void skip_bits_long(GetBitContext *s, int n)
217 {
218 #if UNCHECKED_BITSTREAM_READER
219  s->index += n;
220 #else
221  s->index += av_clip(n, -s->index, s->size_in_bits_plus8 - s->index);
222 #endif
223 }
224 
225 /**
226  * read mpeg1 dc style vlc (sign bit + mantissa with no MSB).
227  * if MSB not set it is negative
228  * @param n length in bits
229  */
230 static inline int get_xbits(GetBitContext *s, int n)
231 {
232  register int sign;
233  register int32_t cache;
234  OPEN_READER(re, s);
235  av_assert2(n>0 && n<=25);
236  UPDATE_CACHE(re, s);
237  cache = GET_CACHE(re, s);
238  sign = ~cache >> 31;
239  LAST_SKIP_BITS(re, s, n);
240  CLOSE_READER(re, s);
241  return (NEG_USR32(sign ^ cache, n) ^ sign) - sign;
242 }
243 
244 static inline int get_sbits(GetBitContext *s, int n)
245 {
246  register int tmp;
247  OPEN_READER(re, s);
248  av_assert2(n>0 && n<=25);
249  UPDATE_CACHE(re, s);
250  tmp = SHOW_SBITS(re, s, n);
251  LAST_SKIP_BITS(re, s, n);
252  CLOSE_READER(re, s);
253  return tmp;
254 }
255 
256 /**
257  * Read 1-25 bits.
258  */
259 static inline unsigned int get_bits(GetBitContext *s, int n)
260 {
261  register int tmp;
262  OPEN_READER(re, s);
263  av_assert2(n>0 && n<=25);
264  UPDATE_CACHE(re, s);
265  tmp = SHOW_UBITS(re, s, n);
266  LAST_SKIP_BITS(re, s, n);
267  CLOSE_READER(re, s);
268  return tmp;
269 }
270 
271 static inline unsigned int get_bits_le(GetBitContext *s, int n)
272 {
273  register int tmp;
274  OPEN_READER(re, s);
275  av_assert2(n>0 && n<=25);
276  UPDATE_CACHE_LE(re, s);
277  tmp = SHOW_UBITS_LE(re, s, n);
278  LAST_SKIP_BITS(re, s, n);
279  CLOSE_READER(re, s);
280  return tmp;
281 }
282 
283 /**
284  * Show 1-25 bits.
285  */
286 static inline unsigned int show_bits(GetBitContext *s, int n)
287 {
288  register int tmp;
289  OPEN_READER(re, s);
290  av_assert2(n>0 && n<=25);
291  UPDATE_CACHE(re, s);
292  tmp = SHOW_UBITS(re, s, n);
293  return tmp;
294 }
295 
296 static inline void skip_bits(GetBitContext *s, int n)
297 {
298  OPEN_READER(re, s);
299  LAST_SKIP_BITS(re, s, n);
300  CLOSE_READER(re, s);
301 }
302 
303 static inline unsigned int get_bits1(GetBitContext *s)
304 {
305  unsigned int index = s->index;
306  uint8_t result = s->buffer[index >> 3];
307 #ifdef BITSTREAM_READER_LE
308  result >>= index & 7;
309  result &= 1;
310 #else
311  result <<= index & 7;
312  result >>= 8 - 1;
313 #endif
314 #if !UNCHECKED_BITSTREAM_READER
315  if (s->index < s->size_in_bits_plus8)
316 #endif
317  index++;
318  s->index = index;
319 
320  return result;
321 }
322 
323 static inline unsigned int show_bits1(GetBitContext *s)
324 {
325  return show_bits(s, 1);
326 }
327 
328 static inline void skip_bits1(GetBitContext *s)
329 {
330  skip_bits(s, 1);
331 }
332 
333 /**
334  * Read 0-32 bits.
335  */
336 static inline unsigned int get_bits_long(GetBitContext *s, int n)
337 {
338  if (!n) {
339  return 0;
340  } else if (n <= MIN_CACHE_BITS) {
341  return get_bits(s, n);
342  } else {
343 #ifdef BITSTREAM_READER_LE
344  unsigned ret = get_bits(s, 16);
345  return ret | (get_bits(s, n - 16) << 16);
346 #else
347  unsigned ret = get_bits(s, 16) << (n - 16);
348  return ret | get_bits(s, n - 16);
349 #endif
350  }
351 }
352 
353 /**
354  * Read 0-64 bits.
355  */
356 static inline uint64_t get_bits64(GetBitContext *s, int n)
357 {
358  if (n <= 32) {
359  return get_bits_long(s, n);
360  } else {
361 #ifdef BITSTREAM_READER_LE
362  uint64_t ret = get_bits_long(s, 32);
363  return ret | (uint64_t) get_bits_long(s, n - 32) << 32;
364 #else
365  uint64_t ret = (uint64_t) get_bits_long(s, n - 32) << 32;
366  return ret | get_bits_long(s, 32);
367 #endif
368  }
369 }
370 
371 /**
372  * Read 0-32 bits as a signed integer.
373  */
374 static inline int get_sbits_long(GetBitContext *s, int n)
375 {
376  return sign_extend(get_bits_long(s, n), n);
377 }
378 
379 /**
380  * Show 0-32 bits.
381  */
382 static inline unsigned int show_bits_long(GetBitContext *s, int n)
383 {
384  if (n <= MIN_CACHE_BITS) {
385  return show_bits(s, n);
386  } else {
387  GetBitContext gb = *s;
388  return get_bits_long(&gb, n);
389  }
390 }
391 
392 static inline int check_marker(GetBitContext *s, const char *msg)
393 {
394  int bit = get_bits1(s);
395  if (!bit)
396  av_log(NULL, AV_LOG_INFO, "Marker bit missing %s\n", msg);
397 
398  return bit;
399 }
400 
401 /**
402  * Initialize GetBitContext.
403  * @param buffer bitstream buffer, must be FF_INPUT_BUFFER_PADDING_SIZE bytes
404  * larger than the actual read bits because some optimized bitstream
405  * readers read 32 or 64 bit at once and could read over the end
406  * @param bit_size the size of the buffer in bits
407  * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
408  */
409 static inline int init_get_bits(GetBitContext *s, const uint8_t *buffer,
410  int bit_size)
411 {
412  int buffer_size;
413  int ret = 0;
414 
415  if (bit_size >= INT_MAX - 7 || bit_size < 0 || !buffer) {
416  bit_size = 0;
417  buffer = NULL;
418  ret = AVERROR_INVALIDDATA;
419  }
420 
421  buffer_size = (bit_size + 7) >> 3;
422 
423  s->buffer = buffer;
424  s->size_in_bits = bit_size;
425  s->size_in_bits_plus8 = bit_size + 8;
426  s->buffer_end = buffer + buffer_size;
427  s->index = 0;
428 
429  return ret;
430 }
431 
432 /**
433  * Initialize GetBitContext.
434  * @param buffer bitstream buffer, must be FF_INPUT_BUFFER_PADDING_SIZE bytes
435  * larger than the actual read bits because some optimized bitstream
436  * readers read 32 or 64 bit at once and could read over the end
437  * @param byte_size the size of the buffer in bytes
438  * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
439  */
440 static inline int init_get_bits8(GetBitContext *s, const uint8_t *buffer,
441  int byte_size)
442 {
443  if (byte_size > INT_MAX / 8 || byte_size < 0)
444  byte_size = -1;
445  return init_get_bits(s, buffer, byte_size * 8);
446 }
447 
448 static inline const uint8_t *align_get_bits(GetBitContext *s)
449 {
450  int n = -get_bits_count(s) & 7;
451  if (n)
452  skip_bits(s, n);
453  return s->buffer + (s->index >> 3);
454 }
455 
456 #define init_vlc(vlc, nb_bits, nb_codes, \
457  bits, bits_wrap, bits_size, \
458  codes, codes_wrap, codes_size, \
459  flags) \
460  ff_init_vlc_sparse(vlc, nb_bits, nb_codes, \
461  bits, bits_wrap, bits_size, \
462  codes, codes_wrap, codes_size, \
463  NULL, 0, 0, flags)
464 
465 int ff_init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,
466  const void *bits, int bits_wrap, int bits_size,
467  const void *codes, int codes_wrap, int codes_size,
468  const void *symbols, int symbols_wrap, int symbols_size,
469  int flags);
470 void ff_free_vlc(VLC *vlc);
471 
472 #define INIT_VLC_LE 2
473 #define INIT_VLC_USE_NEW_STATIC 4
474 
475 #define INIT_VLC_STATIC(vlc, bits, a, b, c, d, e, f, g, static_size) \
476  do { \
477  static VLC_TYPE table[static_size][2]; \
478  (vlc)->table = table; \
479  (vlc)->table_allocated = static_size; \
480  init_vlc(vlc, bits, a, b, c, d, e, f, g, INIT_VLC_USE_NEW_STATIC); \
481  } while (0)
482 
483 /**
484  * If the vlc code is invalid and max_depth=1, then no bits will be removed.
485  * If the vlc code is invalid and max_depth>1, then the number of bits removed
486  * is undefined.
487  */
488 #define GET_VLC(code, name, gb, table, bits, max_depth) \
489  do { \
490  int n, nb_bits; \
491  unsigned int index; \
492  \
493  index = SHOW_UBITS(name, gb, bits); \
494  code = table[index][0]; \
495  n = table[index][1]; \
496  \
497  if (max_depth > 1 && n < 0) { \
498  LAST_SKIP_BITS(name, gb, bits); \
499  UPDATE_CACHE(name, gb); \
500  \
501  nb_bits = -n; \
502  \
503  index = SHOW_UBITS(name, gb, nb_bits) + code; \
504  code = table[index][0]; \
505  n = table[index][1]; \
506  if (max_depth > 2 && n < 0) { \
507  LAST_SKIP_BITS(name, gb, nb_bits); \
508  UPDATE_CACHE(name, gb); \
509  \
510  nb_bits = -n; \
511  \
512  index = SHOW_UBITS(name, gb, nb_bits) + code; \
513  code = table[index][0]; \
514  n = table[index][1]; \
515  } \
516  } \
517  SKIP_BITS(name, gb, n); \
518  } while (0)
519 
520 #define GET_RL_VLC_INTERNAL(level, run, name, gb, table, bits, \
521  max_depth, need_update) \
522  do { \
523  int n, nb_bits; \
524  unsigned int index; \
525  \
526  index = SHOW_UBITS(name, gb, bits); \
527  level = table[index].level; \
528  n = table[index].len; \
529  \
530  if (max_depth > 1 && n < 0) { \
531  SKIP_BITS(name, gb, bits); \
532  if (need_update) { \
533  UPDATE_CACHE(name, gb); \
534  } \
535  \
536  nb_bits = -n; \
537  \
538  index = SHOW_UBITS(name, gb, nb_bits) + level; \
539  level = table[index].level; \
540  n = table[index].len; \
541  } \
542  run = table[index].run; \
543  SKIP_BITS(name, gb, n); \
544  } while (0)
545 
546 /**
547  * Parse a vlc code.
548  * @param bits is the number of bits which will be read at once, must be
549  * identical to nb_bits in init_vlc()
550  * @param max_depth is the number of times bits bits must be read to completely
551  * read the longest vlc code
552  * = (max_vlc_length + bits - 1) / bits
553  */
555  int bits, int max_depth)
556 {
557  int code;
558 
559  OPEN_READER(re, s);
560  UPDATE_CACHE(re, s);
561 
562  GET_VLC(code, re, s, table, bits, max_depth);
563 
564  CLOSE_READER(re, s);
565 
566  return code;
567 }
568 
569 static inline int decode012(GetBitContext *gb)
570 {
571  int n;
572  n = get_bits1(gb);
573  if (n == 0)
574  return 0;
575  else
576  return get_bits1(gb) + 1;
577 }
578 
579 static inline int decode210(GetBitContext *gb)
580 {
581  if (get_bits1(gb))
582  return 0;
583  else
584  return 2 - get_bits1(gb);
585 }
586 
587 static inline int get_bits_left(GetBitContext *gb)
588 {
589  return gb->size_in_bits - get_bits_count(gb);
590 }
591 
592 static inline int skip_1stop_8data_bits(GetBitContext *gb)
593 {
594  if (get_bits_left(gb) <= 0)
595  return AVERROR_INVALIDDATA;
596 
597  while (get_bits1(gb)) {
598  skip_bits(gb, 8);
599  if (get_bits_left(gb) <= 0)
600  return AVERROR_INVALIDDATA;
601  }
602 
603  return 0;
604 }
605 
606 //#define TRACE
607 
608 #ifdef TRACE
609 static inline void print_bin(int bits, int n)
610 {
611  int i;
612 
613  for (i = n - 1; i >= 0; i--)
614  av_log(NULL, AV_LOG_DEBUG, "%d", (bits >> i) & 1);
615  for (i = n; i < 24; i++)
616  av_log(NULL, AV_LOG_DEBUG, " ");
617 }
618 
619 static inline int get_bits_trace(GetBitContext *s, int n, const char *file,
620  const char *func, int line)
621 {
622  int r = get_bits(s, n);
623 
624  print_bin(r, n);
625  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d bit @%5d in %s %s:%d\n",
626  r, n, r, get_bits_count(s) - n, file, func, line);
627 
628  return r;
629 }
630 
631 static inline int get_vlc_trace(GetBitContext *s, VLC_TYPE (*table)[2],
632  int bits, int max_depth, const char *file,
633  const char *func, int line)
634 {
635  int show = show_bits(s, 24);
636  int pos = get_bits_count(s);
637  int r = get_vlc2(s, table, bits, max_depth);
638  int len = get_bits_count(s) - pos;
639  int bits2 = show >> (24 - len);
640 
641  print_bin(bits2, len);
642 
643  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d vlc @%5d in %s %s:%d\n",
644  bits2, len, r, pos, file, func, line);
645 
646  return r;
647 }
648 
649 #define GET_RL_VLC(level, run, name, gb, table, bits, \
650  max_depth, need_update) \
651  do { \
652  int show = SHOW_UBITS(name, gb, 24); \
653  int len; \
654  int pos = name ## _index; \
655  \
656  GET_RL_VLC_INTERNAL(level, run, name, gb, table, bits,max_depth, need_update); \
657  \
658  len = name ## _index - pos + 1; \
659  show = show >> (24 - len); \
660  \
661  print_bin(show, len); \
662  \
663  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d/%-3d rlv @%5d in %s %s:%d\n",\
664  show, len, run-1, level, pos, __FILE__, __PRETTY_FUNCTION__, __LINE__);\
665  } while (0) \
666 
667 
668 static inline int get_xbits_trace(GetBitContext *s, int n, const char *file,
669  const char *func, int line)
670 {
671  int show = show_bits(s, n);
672  int r = get_xbits(s, n);
673 
674  print_bin(show, n);
675  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d xbt @%5d in %s %s:%d\n",
676  show, n, r, get_bits_count(s) - n, file, func, line);
677 
678  return r;
679 }
680 
681 #define get_bits(s, n) get_bits_trace(s , n, __FILE__, __PRETTY_FUNCTION__, __LINE__)
682 #define get_bits1(s) get_bits_trace(s, 1, __FILE__, __PRETTY_FUNCTION__, __LINE__)
683 #define get_xbits(s, n) get_xbits_trace(s, n, __FILE__, __PRETTY_FUNCTION__, __LINE__)
684 
685 #define get_vlc(s, vlc) get_vlc_trace(s, (vlc)->table, (vlc)->bits, 3, __FILE__, __PRETTY_FUNCTION__, __LINE__)
686 #define get_vlc2(s, tab, bits, max) get_vlc_trace(s, tab, bits, max, __FILE__, __PRETTY_FUNCTION__, __LINE__)
687 
688 #define tprintf(p, ...) av_log(p, AV_LOG_DEBUG, __VA_ARGS__)
689 
690 #else //TRACE
691 #define tprintf(p, ...) { }
692 #define GET_RL_VLC GET_RL_VLC_INTERNAL
693 #endif
694 
695 #endif /* AVCODEC_GET_BITS_H */