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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  void * volatile init_state;
68 } VLC;
69 
70 typedef struct RL_VLC_ELEM {
71  int16_t level;
72  int8_t len;
74 } RL_VLC_ELEM;
75 
76 /* Bitstream reader API docs:
77  * name
78  * arbitrary name which is used as prefix for the internal variables
79  *
80  * gb
81  * getbitcontext
82  *
83  * OPEN_READER(name, gb)
84  * load gb into local variables
85  *
86  * CLOSE_READER(name, gb)
87  * store local vars in gb
88  *
89  * UPDATE_CACHE(name, gb)
90  * Refill the internal cache from the bitstream.
91  * After this call at least MIN_CACHE_BITS will be available.
92  *
93  * GET_CACHE(name, gb)
94  * Will output the contents of the internal cache,
95  * next bit is MSB of 32 or 64 bit (FIXME 64bit).
96  *
97  * SHOW_UBITS(name, gb, num)
98  * Will return the next num bits.
99  *
100  * SHOW_SBITS(name, gb, num)
101  * Will return the next num bits and do sign extension.
102  *
103  * SKIP_BITS(name, gb, num)
104  * Will skip over the next num bits.
105  * Note, this is equivalent to SKIP_CACHE; SKIP_COUNTER.
106  *
107  * SKIP_CACHE(name, gb, num)
108  * Will remove the next num bits from the cache (note SKIP_COUNTER
109  * MUST be called before UPDATE_CACHE / CLOSE_READER).
110  *
111  * SKIP_COUNTER(name, gb, num)
112  * Will increment the internal bit counter (see SKIP_CACHE & SKIP_BITS).
113  *
114  * LAST_SKIP_BITS(name, gb, num)
115  * Like SKIP_BITS, to be used if next call is UPDATE_CACHE or CLOSE_READER.
116  *
117  * For examples see get_bits, show_bits, skip_bits, get_vlc.
118  */
119 
120 #ifdef LONG_BITSTREAM_READER
121 # define MIN_CACHE_BITS 32
122 #else
123 # define MIN_CACHE_BITS 25
124 #endif
125 
126 #if UNCHECKED_BITSTREAM_READER
127 #define OPEN_READER(name, gb) \
128  unsigned int name ## _index = (gb)->index; \
129  unsigned int av_unused name ## _cache
130 
131 #define HAVE_BITS_REMAINING(name, gb) 1
132 #else
133 #define OPEN_READER(name, gb) \
134  unsigned int name ## _index = (gb)->index; \
135  unsigned int av_unused name ## _cache = 0; \
136  unsigned int av_unused name ## _size_plus8 = (gb)->size_in_bits_plus8
137 
138 #define HAVE_BITS_REMAINING(name, gb) name ## _index < name ## _size_plus8
139 #endif
140 
141 #define CLOSE_READER(name, gb) (gb)->index = name ## _index
142 
143 # ifdef LONG_BITSTREAM_READER
144 
145 # define UPDATE_CACHE_LE(name, gb) name ## _cache = \
146  AV_RL64((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)
147 
148 # define UPDATE_CACHE_BE(name, gb) name ## _cache = \
149  AV_RB64((gb)->buffer + (name ## _index >> 3)) >> (32 - (name ## _index & 7))
150 
151 #else
152 
153 # define UPDATE_CACHE_LE(name, gb) name ## _cache = \
154  AV_RL32((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)
155 
156 # define UPDATE_CACHE_BE(name, gb) name ## _cache = \
157  AV_RB32((gb)->buffer + (name ## _index >> 3)) << (name ## _index & 7)
158 
159 #endif
160 
161 
162 #ifdef BITSTREAM_READER_LE
163 
164 # define UPDATE_CACHE(name, gb) UPDATE_CACHE_LE(name, gb)
165 
166 # define SKIP_CACHE(name, gb, num) name ## _cache >>= (num)
167 
168 #else
169 
170 # define UPDATE_CACHE(name, gb) UPDATE_CACHE_BE(name, gb)
171 
172 # define SKIP_CACHE(name, gb, num) name ## _cache <<= (num)
173 
174 #endif
175 
176 #if UNCHECKED_BITSTREAM_READER
177 # define SKIP_COUNTER(name, gb, num) name ## _index += (num)
178 #else
179 # define SKIP_COUNTER(name, gb, num) \
180  name ## _index = FFMIN(name ## _size_plus8, name ## _index + (num))
181 #endif
182 
183 #define SKIP_BITS(name, gb, num) \
184  do { \
185  SKIP_CACHE(name, gb, num); \
186  SKIP_COUNTER(name, gb, num); \
187  } while (0)
188 
189 #define LAST_SKIP_BITS(name, gb, num) SKIP_COUNTER(name, gb, num)
190 
191 #define SHOW_UBITS_LE(name, gb, num) zero_extend(name ## _cache, num)
192 #define SHOW_SBITS_LE(name, gb, num) sign_extend(name ## _cache, num)
193 
194 #define SHOW_UBITS_BE(name, gb, num) NEG_USR32(name ## _cache, num)
195 #define SHOW_SBITS_BE(name, gb, num) NEG_SSR32(name ## _cache, num)
196 
197 #ifdef BITSTREAM_READER_LE
198 # define SHOW_UBITS(name, gb, num) SHOW_UBITS_LE(name, gb, num)
199 # define SHOW_SBITS(name, gb, num) SHOW_SBITS_LE(name, gb, num)
200 #else
201 # define SHOW_UBITS(name, gb, num) SHOW_UBITS_BE(name, gb, num)
202 # define SHOW_SBITS(name, gb, num) SHOW_SBITS_BE(name, gb, num)
203 #endif
204 
205 #define GET_CACHE(name, gb) ((uint32_t) name ## _cache)
206 
207 static inline int get_bits_count(const GetBitContext *s)
208 {
209  return s->index;
210 }
211 
212 static inline void skip_bits_long(GetBitContext *s, int n)
213 {
214 #if UNCHECKED_BITSTREAM_READER
215  s->index += n;
216 #else
217  s->index += av_clip(n, -s->index, s->size_in_bits_plus8 - s->index);
218 #endif
219 }
220 
221 /**
222  * read mpeg1 dc style vlc (sign bit + mantisse with no MSB).
223  * if MSB not set it is negative
224  * @param n length in bits
225  */
226 static inline int get_xbits(GetBitContext *s, int n)
227 {
228  register int sign;
229  register int32_t cache;
230  OPEN_READER(re, s);
231  av_assert2(n>0 && n<=25);
232  UPDATE_CACHE(re, s);
233  cache = GET_CACHE(re, s);
234  sign = ~cache >> 31;
235  LAST_SKIP_BITS(re, s, n);
236  CLOSE_READER(re, s);
237  return (NEG_USR32(sign ^ cache, n) ^ sign) - sign;
238 }
239 
240 static inline int get_sbits(GetBitContext *s, int n)
241 {
242  register int tmp;
243  OPEN_READER(re, s);
244  av_assert2(n>0 && n<=25);
245  UPDATE_CACHE(re, s);
246  tmp = SHOW_SBITS(re, s, n);
247  LAST_SKIP_BITS(re, s, n);
248  CLOSE_READER(re, s);
249  return tmp;
250 }
251 
252 /**
253  * Read 1-25 bits.
254  */
255 static inline unsigned int get_bits(GetBitContext *s, int n)
256 {
257  register int tmp;
258  OPEN_READER(re, s);
259  av_assert2(n>0 && n<=25);
260  UPDATE_CACHE(re, s);
261  tmp = SHOW_UBITS(re, s, n);
262  LAST_SKIP_BITS(re, s, n);
263  CLOSE_READER(re, s);
264  return tmp;
265 }
266 
267 static inline unsigned int get_bits_le(GetBitContext *s, int n)
268 {
269  register int tmp;
270  OPEN_READER(re, s);
271  av_assert2(n>0 && n<=25);
272  UPDATE_CACHE_LE(re, s);
273  tmp = SHOW_UBITS_LE(re, s, n);
274  LAST_SKIP_BITS(re, s, n);
275  CLOSE_READER(re, s);
276  return tmp;
277 }
278 
279 /**
280  * Show 1-25 bits.
281  */
282 static inline unsigned int show_bits(GetBitContext *s, int n)
283 {
284  register int tmp;
285  OPEN_READER(re, s);
286  av_assert2(n>0 && n<=25);
287  UPDATE_CACHE(re, s);
288  tmp = SHOW_UBITS(re, s, n);
289  return tmp;
290 }
291 
292 static inline void skip_bits(GetBitContext *s, int n)
293 {
294  OPEN_READER(re, s);
295  LAST_SKIP_BITS(re, s, n);
296  CLOSE_READER(re, s);
297 }
298 
299 static inline unsigned int get_bits1(GetBitContext *s)
300 {
301  unsigned int index = s->index;
302  uint8_t result = s->buffer[index >> 3];
303 #ifdef BITSTREAM_READER_LE
304  result >>= index & 7;
305  result &= 1;
306 #else
307  result <<= index & 7;
308  result >>= 8 - 1;
309 #endif
310 #if !UNCHECKED_BITSTREAM_READER
311  if (s->index < s->size_in_bits_plus8)
312 #endif
313  index++;
314  s->index = index;
315 
316  return result;
317 }
318 
319 static inline unsigned int show_bits1(GetBitContext *s)
320 {
321  return show_bits(s, 1);
322 }
323 
324 static inline void skip_bits1(GetBitContext *s)
325 {
326  skip_bits(s, 1);
327 }
328 
329 /**
330  * Read 0-32 bits.
331  */
332 static inline unsigned int get_bits_long(GetBitContext *s, int n)
333 {
334  if (!n) {
335  return 0;
336  } else if (n <= MIN_CACHE_BITS) {
337  return get_bits(s, n);
338  } else {
339 #ifdef BITSTREAM_READER_LE
340  unsigned ret = get_bits(s, 16);
341  return ret | (get_bits(s, n - 16) << 16);
342 #else
343  unsigned ret = get_bits(s, 16) << (n - 16);
344  return ret | get_bits(s, n - 16);
345 #endif
346  }
347 }
348 
349 /**
350  * Read 0-64 bits.
351  */
352 static inline uint64_t get_bits64(GetBitContext *s, int n)
353 {
354  if (n <= 32) {
355  return get_bits_long(s, n);
356  } else {
357 #ifdef BITSTREAM_READER_LE
358  uint64_t ret = get_bits_long(s, 32);
359  return ret | (uint64_t) get_bits_long(s, n - 32) << 32;
360 #else
361  uint64_t ret = (uint64_t) get_bits_long(s, n - 32) << 32;
362  return ret | get_bits_long(s, 32);
363 #endif
364  }
365 }
366 
367 /**
368  * Read 0-32 bits as a signed integer.
369  */
370 static inline int get_sbits_long(GetBitContext *s, int n)
371 {
372  return sign_extend(get_bits_long(s, n), n);
373 }
374 
375 /**
376  * Show 0-32 bits.
377  */
378 static inline unsigned int show_bits_long(GetBitContext *s, int n)
379 {
380  if (n <= MIN_CACHE_BITS) {
381  return show_bits(s, n);
382  } else {
383  GetBitContext gb = *s;
384  return get_bits_long(&gb, n);
385  }
386 }
387 
388 static inline int check_marker(GetBitContext *s, const char *msg)
389 {
390  int bit = get_bits1(s);
391  if (!bit)
392  av_log(NULL, AV_LOG_INFO, "Marker bit missing %s\n", msg);
393 
394  return bit;
395 }
396 
397 /**
398  * Initialize GetBitContext.
399  * @param buffer bitstream buffer, must be FF_INPUT_BUFFER_PADDING_SIZE bytes
400  * larger than the actual read bits because some optimized bitstream
401  * readers read 32 or 64 bit at once and could read over the end
402  * @param bit_size the size of the buffer in bits
403  * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
404  */
405 static inline int init_get_bits(GetBitContext *s, const uint8_t *buffer,
406  int bit_size)
407 {
408  int buffer_size;
409  int ret = 0;
410 
411  if (bit_size >= INT_MAX - 7 || bit_size < 0 || !buffer) {
412  buffer_size = bit_size = 0;
413  buffer = NULL;
414  ret = AVERROR_INVALIDDATA;
415  }
416 
417  buffer_size = (bit_size + 7) >> 3;
418 
419  s->buffer = buffer;
420  s->size_in_bits = bit_size;
421  s->size_in_bits_plus8 = bit_size + 8;
422  s->buffer_end = buffer + buffer_size;
423  s->index = 0;
424 
425  return ret;
426 }
427 
428 /**
429  * Initialize GetBitContext.
430  * @param buffer bitstream buffer, must be FF_INPUT_BUFFER_PADDING_SIZE bytes
431  * larger than the actual read bits because some optimized bitstream
432  * readers read 32 or 64 bit at once and could read over the end
433  * @param byte_size the size of the buffer in bytes
434  * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
435  */
436 static inline int init_get_bits8(GetBitContext *s, const uint8_t *buffer,
437  int byte_size)
438 {
439  if (byte_size > INT_MAX / 8 || byte_size < 0)
440  byte_size = -1;
441  return init_get_bits(s, buffer, byte_size * 8);
442 }
443 
444 static inline const uint8_t *align_get_bits(GetBitContext *s)
445 {
446  int n = -get_bits_count(s) & 7;
447  if (n)
448  skip_bits(s, n);
449  return s->buffer + (s->index >> 3);
450 }
451 
452 #define init_vlc(vlc, nb_bits, nb_codes, \
453  bits, bits_wrap, bits_size, \
454  codes, codes_wrap, codes_size, \
455  flags) \
456  ff_init_vlc_sparse(vlc, nb_bits, nb_codes, \
457  bits, bits_wrap, bits_size, \
458  codes, codes_wrap, codes_size, \
459  NULL, 0, 0, flags)
460 
461 int ff_init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,
462  const void *bits, int bits_wrap, int bits_size,
463  const void *codes, int codes_wrap, int codes_size,
464  const void *symbols, int symbols_wrap, int symbols_size,
465  int flags);
466 void ff_free_vlc(VLC *vlc);
467 
468 #define INIT_VLC_LE 2
469 #define INIT_VLC_USE_NEW_STATIC 4
470 
471 #define INIT_VLC_STATIC(vlc, bits, a, b, c, d, e, f, g, static_size) \
472  do { \
473  static VLC_TYPE table[static_size][2]; \
474  (vlc)->table = table; \
475  (vlc)->table_allocated = static_size; \
476  init_vlc(vlc, bits, a, b, c, d, e, f, g, INIT_VLC_USE_NEW_STATIC); \
477  } while (0)
478 
479 /**
480  * If the vlc code is invalid and max_depth=1, then no bits will be removed.
481  * If the vlc code is invalid and max_depth>1, then the number of bits removed
482  * is undefined.
483  */
484 #define GET_VLC(code, name, gb, table, bits, max_depth) \
485  do { \
486  int n, nb_bits; \
487  unsigned int index; \
488  \
489  index = SHOW_UBITS(name, gb, bits); \
490  code = table[index][0]; \
491  n = table[index][1]; \
492  \
493  if (max_depth > 1 && n < 0) { \
494  LAST_SKIP_BITS(name, gb, bits); \
495  UPDATE_CACHE(name, gb); \
496  \
497  nb_bits = -n; \
498  \
499  index = SHOW_UBITS(name, gb, nb_bits) + code; \
500  code = table[index][0]; \
501  n = table[index][1]; \
502  if (max_depth > 2 && n < 0) { \
503  LAST_SKIP_BITS(name, gb, nb_bits); \
504  UPDATE_CACHE(name, gb); \
505  \
506  nb_bits = -n; \
507  \
508  index = SHOW_UBITS(name, gb, nb_bits) + code; \
509  code = table[index][0]; \
510  n = table[index][1]; \
511  } \
512  } \
513  SKIP_BITS(name, gb, n); \
514  } while (0)
515 
516 #define GET_RL_VLC(level, run, name, gb, table, bits, \
517  max_depth, need_update) \
518  do { \
519  int n, nb_bits; \
520  unsigned int index; \
521  \
522  index = SHOW_UBITS(name, gb, bits); \
523  level = table[index].level; \
524  n = table[index].len; \
525  \
526  if (max_depth > 1 && n < 0) { \
527  SKIP_BITS(name, gb, bits); \
528  if (need_update) { \
529  UPDATE_CACHE(name, gb); \
530  } \
531  \
532  nb_bits = -n; \
533  \
534  index = SHOW_UBITS(name, gb, nb_bits) + level; \
535  level = table[index].level; \
536  n = table[index].len; \
537  } \
538  run = table[index].run; \
539  SKIP_BITS(name, gb, n); \
540  } while (0)
541 
542 /**
543  * Parse a vlc code.
544  * @param bits is the number of bits which will be read at once, must be
545  * identical to nb_bits in init_vlc()
546  * @param max_depth is the number of times bits bits must be read to completely
547  * read the longest vlc code
548  * = (max_vlc_length + bits - 1) / bits
549  */
551  int bits, int max_depth)
552 {
553  int code;
554 
555  OPEN_READER(re, s);
556  UPDATE_CACHE(re, s);
557 
558  GET_VLC(code, re, s, table, bits, max_depth);
559 
560  CLOSE_READER(re, s);
561 
562  return code;
563 }
564 
565 static inline int decode012(GetBitContext *gb)
566 {
567  int n;
568  n = get_bits1(gb);
569  if (n == 0)
570  return 0;
571  else
572  return get_bits1(gb) + 1;
573 }
574 
575 static inline int decode210(GetBitContext *gb)
576 {
577  if (get_bits1(gb))
578  return 0;
579  else
580  return 2 - get_bits1(gb);
581 }
582 
583 static inline int get_bits_left(GetBitContext *gb)
584 {
585  return gb->size_in_bits - get_bits_count(gb);
586 }
587 
588 //#define TRACE
589 
590 #ifdef TRACE
591 static inline void print_bin(int bits, int n)
592 {
593  int i;
594 
595  for (i = n - 1; i >= 0; i--)
596  av_log(NULL, AV_LOG_DEBUG, "%d", (bits >> i) & 1);
597  for (i = n; i < 24; i++)
598  av_log(NULL, AV_LOG_DEBUG, " ");
599 }
600 
601 static inline int get_bits_trace(GetBitContext *s, int n, const char *file,
602  const char *func, int line)
603 {
604  int r = get_bits(s, n);
605 
606  print_bin(r, n);
607  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d bit @%5d in %s %s:%d\n",
608  r, n, r, get_bits_count(s) - n, file, func, line);
609 
610  return r;
611 }
612 
613 static inline int get_vlc_trace(GetBitContext *s, VLC_TYPE (*table)[2],
614  int bits, int max_depth, const char *file,
615  const char *func, int line)
616 {
617  int show = show_bits(s, 24);
618  int pos = get_bits_count(s);
619  int r = get_vlc2(s, table, bits, max_depth);
620  int len = get_bits_count(s) - pos;
621  int bits2 = show >> (24 - len);
622 
623  print_bin(bits2, len);
624 
625  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d vlc @%5d in %s %s:%d\n",
626  bits2, len, r, pos, file, func, line);
627 
628  return r;
629 }
630 
631 static inline int get_xbits_trace(GetBitContext *s, int n, const char *file,
632  const char *func, int line)
633 {
634  int show = show_bits(s, n);
635  int r = get_xbits(s, n);
636 
637  print_bin(show, n);
638  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d xbt @%5d in %s %s:%d\n",
639  show, n, r, get_bits_count(s) - n, file, func, line);
640 
641  return r;
642 }
643 
644 #define get_bits(s, n) get_bits_trace(s , n, __FILE__, __PRETTY_FUNCTION__, __LINE__)
645 #define get_bits1(s) get_bits_trace(s, 1, __FILE__, __PRETTY_FUNCTION__, __LINE__)
646 #define get_xbits(s, n) get_xbits_trace(s, n, __FILE__, __PRETTY_FUNCTION__, __LINE__)
647 
648 #define get_vlc(s, vlc) get_vlc_trace(s, (vlc)->table, (vlc)->bits, 3, __FILE__, __PRETTY_FUNCTION__, __LINE__)
649 #define get_vlc2(s, tab, bits, max) get_vlc_trace(s, tab, bits, max, __FILE__, __PRETTY_FUNCTION__, __LINE__)
650 
651 #define tprintf(p, ...) av_log(p, AV_LOG_DEBUG, __VA_ARGS__)
652 
653 #else //TRACE
654 #define tprintf(p, ...) { }
655 #endif
656 
657 #endif /* AVCODEC_GET_BITS_H */