get_bits.h
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1 /*
2  * copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
3  *
4  * This file is part of Libav.
5  *
6  * Libav 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  * Libav 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 Libav; if not, write to the Free Software
18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
19  */
20 
26 #ifndef AVCODEC_GET_BITS_H
27 #define AVCODEC_GET_BITS_H
28 
29 #include <stdint.h>
30 #include "libavutil/common.h"
31 #include "libavutil/intreadwrite.h"
32 #include "libavutil/log.h"
33 #include "mathops.h"
34 
35 /*
36  * Safe bitstream reading:
37  * optionally, the get_bits API can check to ensure that we
38  * don't read past input buffer boundaries. This is protected
39  * with CONFIG_SAFE_BITSTREAM_READER at the global level, and
40  * then below that with UNCHECKED_BITSTREAM_READER at the per-
41  * decoder level. This means that decoders that check internally
42  * can "#define UNCHECKED_BITSTREAM_READER 1" to disable
43  * overread checks.
44  * Boundary checking causes a minor performance penalty so for
45  * applications that won't want/need this, it can be disabled
46  * globally using "#define CONFIG_SAFE_BITSTREAM_READER 0".
47  */
48 #ifndef UNCHECKED_BITSTREAM_READER
49 #define UNCHECKED_BITSTREAM_READER !CONFIG_SAFE_BITSTREAM_READER
50 #endif
51 
52 typedef struct GetBitContext {
53  const uint8_t *buffer, *buffer_end;
54  int index;
56 #if !UNCHECKED_BITSTREAM_READER
57  int size_in_bits_plus8;
58 #endif
60 
61 #define VLC_TYPE int16_t
62 
63 typedef struct VLC {
64  int bits;
65  VLC_TYPE (*table)[2];
67 } VLC;
68 
69 typedef struct RL_VLC_ELEM {
70  int16_t level;
71  int8_t len;
72  uint8_t run;
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, next bit is MSB of 32 or 64 bit (FIXME 64bit)
94 
95 SHOW_UBITS(name, gb, num)
96  will return the next num bits
97 
98 SHOW_SBITS(name, gb, num)
99  will return the next num bits and do sign extension
100 
101 SKIP_BITS(name, gb, num)
102  will skip over the next num bits
103  note, this is equivalent to SKIP_CACHE; SKIP_COUNTER
104 
105 SKIP_CACHE(name, gb, num)
106  will remove the next num bits from the cache (note SKIP_COUNTER MUST be called before UPDATE_CACHE / CLOSE_READER)
107 
108 SKIP_COUNTER(name, gb, num)
109  will increment the internal bit counter (see SKIP_CACHE & SKIP_BITS)
110 
111 LAST_SKIP_BITS(name, gb, num)
112  like SKIP_BITS, to be used if next call is UPDATE_CACHE or CLOSE_READER
113 
114 for examples see get_bits, show_bits, skip_bits, get_vlc
115 */
116 
117 #ifdef LONG_BITSTREAM_READER
118 # define MIN_CACHE_BITS 32
119 #else
120 # define MIN_CACHE_BITS 25
121 #endif
122 
123 #if UNCHECKED_BITSTREAM_READER
124 #define OPEN_READER(name, gb) \
125  unsigned int name##_index = (gb)->index; \
126  unsigned int av_unused name##_cache = 0
127 
128 #define HAVE_BITS_REMAINING(name, gb) 1
129 #else
130 #define OPEN_READER(name, gb) \
131  unsigned int name##_index = (gb)->index; \
132  unsigned int av_unused name##_cache = 0; \
133  unsigned int av_unused name##_size_plus8 = \
134  (gb)->size_in_bits_plus8
135 
136 #define HAVE_BITS_REMAINING(name, gb) \
137  name##_index < name##_size_plus8
138 #endif
139 
140 #define CLOSE_READER(name, gb) (gb)->index = name##_index
141 
142 #ifdef BITSTREAM_READER_LE
143 
144 # ifdef LONG_BITSTREAM_READER
145 # define UPDATE_CACHE(name, gb) name##_cache = \
146  AV_RL64((gb)->buffer + (name##_index >> 3)) >> (name##_index & 7)
147 # else
148 # define UPDATE_CACHE(name, gb) name##_cache = \
149  AV_RL32((gb)->buffer + (name##_index >> 3)) >> (name##_index & 7)
150 # endif
151 
152 # define SKIP_CACHE(name, gb, num) name##_cache >>= (num)
153 
154 #else
155 
156 # ifdef LONG_BITSTREAM_READER
157 # define UPDATE_CACHE(name, gb) name##_cache = \
158  AV_RB64((gb)->buffer + (name##_index >> 3)) >> (32 - (name##_index & 7))
159 # else
160 # define UPDATE_CACHE(name, gb) name##_cache = \
161  AV_RB32((gb)->buffer + (name##_index >> 3)) << (name##_index & 7)
162 # endif
163 
164 # define SKIP_CACHE(name, gb, num) name##_cache <<= (num)
165 
166 #endif
167 
168 #if UNCHECKED_BITSTREAM_READER
169 # define SKIP_COUNTER(name, gb, num) name##_index += (num)
170 #else
171 # define SKIP_COUNTER(name, gb, num) \
172  name##_index = FFMIN(name##_size_plus8, name##_index + (num))
173 #endif
174 
175 #define SKIP_BITS(name, gb, num) do { \
176  SKIP_CACHE(name, gb, num); \
177  SKIP_COUNTER(name, gb, num); \
178  } while (0)
179 
180 #define LAST_SKIP_BITS(name, gb, num) SKIP_COUNTER(name, gb, num)
181 
182 #ifdef BITSTREAM_READER_LE
183 # define SHOW_UBITS(name, gb, num) zero_extend(name##_cache, num)
184 # define SHOW_SBITS(name, gb, num) sign_extend(name##_cache, num)
185 #else
186 # define SHOW_UBITS(name, gb, num) NEG_USR32(name##_cache, num)
187 # define SHOW_SBITS(name, gb, num) NEG_SSR32(name##_cache, num)
188 #endif
189 
190 #define GET_CACHE(name, gb) ((uint32_t)name##_cache)
191 
192 static inline int get_bits_count(const GetBitContext *s)
193 {
194  return s->index;
195 }
196 
197 static inline void skip_bits_long(GetBitContext *s, int n){
198 #if UNCHECKED_BITSTREAM_READER
199  s->index += n;
200 #else
201  s->index += av_clip(n, -s->index, s->size_in_bits_plus8 - s->index);
202 #endif
203 }
204 
210 static inline int get_xbits(GetBitContext *s, int n)
211 {
212  register int sign;
213  register int32_t cache;
214  OPEN_READER(re, s);
215  UPDATE_CACHE(re, s);
216  cache = GET_CACHE(re, s);
217  sign = ~cache >> 31;
218  LAST_SKIP_BITS(re, s, n);
219  CLOSE_READER(re, s);
220  return (NEG_USR32(sign ^ cache, n) ^ sign) - sign;
221 }
222 
223 static inline int get_sbits(GetBitContext *s, int n)
224 {
225  register int tmp;
226  OPEN_READER(re, s);
227  UPDATE_CACHE(re, s);
228  tmp = SHOW_SBITS(re, s, n);
229  LAST_SKIP_BITS(re, s, n);
230  CLOSE_READER(re, s);
231  return tmp;
232 }
233 
237 static inline unsigned int get_bits(GetBitContext *s, int n)
238 {
239  register int tmp;
240  OPEN_READER(re, s);
241  UPDATE_CACHE(re, s);
242  tmp = SHOW_UBITS(re, s, n);
243  LAST_SKIP_BITS(re, s, n);
244  CLOSE_READER(re, s);
245  return tmp;
246 }
247 
251 static inline unsigned int show_bits(GetBitContext *s, int n)
252 {
253  register int tmp;
254  OPEN_READER(re, s);
255  UPDATE_CACHE(re, s);
256  tmp = SHOW_UBITS(re, s, n);
257  return tmp;
258 }
259 
260 static inline void skip_bits(GetBitContext *s, int n)
261 {
262  OPEN_READER(re, s);
263  UPDATE_CACHE(re, s);
264  LAST_SKIP_BITS(re, s, n);
265  CLOSE_READER(re, s);
266 }
267 
268 static inline unsigned int get_bits1(GetBitContext *s)
269 {
270  unsigned int index = s->index;
271  uint8_t result = s->buffer[index>>3];
272 #ifdef BITSTREAM_READER_LE
273  result >>= index & 7;
274  result &= 1;
275 #else
276  result <<= index & 7;
277  result >>= 8 - 1;
278 #endif
279 #if !UNCHECKED_BITSTREAM_READER
280  if (s->index < s->size_in_bits_plus8)
281 #endif
282  index++;
283  s->index = index;
284 
285  return result;
286 }
287 
288 static inline unsigned int show_bits1(GetBitContext *s)
289 {
290  return show_bits(s, 1);
291 }
292 
293 static inline void skip_bits1(GetBitContext *s)
294 {
295  skip_bits(s, 1);
296 }
297 
301 static inline unsigned int get_bits_long(GetBitContext *s, int n)
302 {
303  if (n <= MIN_CACHE_BITS)
304  return get_bits(s, n);
305  else {
306 #ifdef BITSTREAM_READER_LE
307  int ret = get_bits(s, 16);
308  return ret | (get_bits(s, n-16) << 16);
309 #else
310  int ret = get_bits(s, 16) << (n-16);
311  return ret | get_bits(s, n-16);
312 #endif
313  }
314 }
315 
319 static inline int get_sbits_long(GetBitContext *s, int n)
320 {
321  return sign_extend(get_bits_long(s, n), n);
322 }
323 
327 static inline unsigned int show_bits_long(GetBitContext *s, int n)
328 {
329  if (n <= MIN_CACHE_BITS)
330  return show_bits(s, n);
331  else {
332  GetBitContext gb = *s;
333  return get_bits_long(&gb, n);
334  }
335 }
336 
337 static inline int check_marker(GetBitContext *s, const char *msg)
338 {
339  int bit = get_bits1(s);
340  if (!bit)
341  av_log(NULL, AV_LOG_INFO, "Marker bit missing %s\n", msg);
342 
343  return bit;
344 }
345 
354 static inline int init_get_bits(GetBitContext *s, const uint8_t *buffer,
355  int bit_size)
356 {
357  int buffer_size;
358  int ret = 0;
359 
360  if (bit_size > INT_MAX - 7 || bit_size < 0 || !buffer) {
361  buffer_size = bit_size = 0;
362  buffer = NULL;
363  ret = AVERROR_INVALIDDATA;
364  }
365 
366  buffer_size = (bit_size + 7) >> 3;
367 
368  s->buffer = buffer;
369  s->size_in_bits = bit_size;
370 #if !UNCHECKED_BITSTREAM_READER
371  s->size_in_bits_plus8 = bit_size + 8;
372 #endif
373  s->buffer_end = buffer + buffer_size;
374  s->index = 0;
375  return ret;
376 }
377 
378 static inline void align_get_bits(GetBitContext *s)
379 {
380  int n = -get_bits_count(s) & 7;
381  if (n) skip_bits(s, n);
382 }
383 
384 #define init_vlc(vlc, nb_bits, nb_codes, \
385  bits, bits_wrap, bits_size, \
386  codes, codes_wrap, codes_size, \
387  flags) \
388  ff_init_vlc_sparse(vlc, nb_bits, nb_codes, \
389  bits, bits_wrap, bits_size, \
390  codes, codes_wrap, codes_size, \
391  NULL, 0, 0, flags)
392 
393 int ff_init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,
394  const void *bits, int bits_wrap, int bits_size,
395  const void *codes, int codes_wrap, int codes_size,
396  const void *symbols, int symbols_wrap, int symbols_size,
397  int flags);
398 #define INIT_VLC_LE 2
399 #define INIT_VLC_USE_NEW_STATIC 4
400 void ff_free_vlc(VLC *vlc);
401 
402 #define INIT_VLC_STATIC(vlc, bits, a,b,c,d,e,f,g, static_size) do { \
403  static VLC_TYPE table[static_size][2]; \
404  (vlc)->table = table; \
405  (vlc)->table_allocated = static_size; \
406  init_vlc(vlc, bits, a,b,c,d,e,f,g, INIT_VLC_USE_NEW_STATIC); \
407  } while (0)
408 
409 
415 #define GET_VLC(code, name, gb, table, bits, max_depth) \
416  do { \
417  int n, nb_bits; \
418  unsigned int index; \
419  \
420  index = SHOW_UBITS(name, gb, bits); \
421  code = table[index][0]; \
422  n = table[index][1]; \
423  \
424  if (max_depth > 1 && n < 0) { \
425  LAST_SKIP_BITS(name, gb, bits); \
426  UPDATE_CACHE(name, gb); \
427  \
428  nb_bits = -n; \
429  \
430  index = SHOW_UBITS(name, gb, nb_bits) + code; \
431  code = table[index][0]; \
432  n = table[index][1]; \
433  if (max_depth > 2 && n < 0) { \
434  LAST_SKIP_BITS(name, gb, nb_bits); \
435  UPDATE_CACHE(name, gb); \
436  \
437  nb_bits = -n; \
438  \
439  index = SHOW_UBITS(name, gb, nb_bits) + code; \
440  code = table[index][0]; \
441  n = table[index][1]; \
442  } \
443  } \
444  SKIP_BITS(name, gb, n); \
445  } while (0)
446 
447 #define GET_RL_VLC(level, run, name, gb, table, bits, max_depth, need_update) \
448  do { \
449  int n, nb_bits; \
450  unsigned int index; \
451  \
452  index = SHOW_UBITS(name, gb, bits); \
453  level = table[index].level; \
454  n = table[index].len; \
455  \
456  if (max_depth > 1 && n < 0) { \
457  SKIP_BITS(name, gb, bits); \
458  if (need_update) { \
459  UPDATE_CACHE(name, gb); \
460  } \
461  \
462  nb_bits = -n; \
463  \
464  index = SHOW_UBITS(name, gb, nb_bits) + level; \
465  level = table[index].level; \
466  n = table[index].len; \
467  } \
468  run = table[index].run; \
469  SKIP_BITS(name, gb, n); \
470  } while (0)
471 
472 
481 static av_always_inline int get_vlc2(GetBitContext *s, VLC_TYPE (*table)[2],
482  int bits, int max_depth)
483 {
484  int code;
485 
486  OPEN_READER(re, s);
487  UPDATE_CACHE(re, s);
488 
489  GET_VLC(code, re, s, table, bits, max_depth);
490 
491  CLOSE_READER(re, s);
492  return code;
493 }
494 
495 static inline int decode012(GetBitContext *gb)
496 {
497  int n;
498  n = get_bits1(gb);
499  if (n == 0)
500  return 0;
501  else
502  return get_bits1(gb) + 1;
503 }
504 
505 static inline int decode210(GetBitContext *gb)
506 {
507  if (get_bits1(gb))
508  return 0;
509  else
510  return 2 - get_bits1(gb);
511 }
512 
513 static inline int get_bits_left(GetBitContext *gb)
514 {
515  return gb->size_in_bits - get_bits_count(gb);
516 }
517 
518 //#define TRACE
519 
520 #ifdef TRACE
521 static inline void print_bin(int bits, int n)
522 {
523  int i;
524 
525  for (i = n-1; i >= 0; i--) {
526  av_log(NULL, AV_LOG_DEBUG, "%d", (bits>>i)&1);
527  }
528  for (i = n; i < 24; i++)
529  av_log(NULL, AV_LOG_DEBUG, " ");
530 }
531 
532 static inline int get_bits_trace(GetBitContext *s, int n, char *file,
533  const char *func, int line)
534 {
535  int r = get_bits(s, n);
536 
537  print_bin(r, n);
538  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d bit @%5d in %s %s:%d\n",
539  r, n, r, get_bits_count(s)-n, file, func, line);
540  return r;
541 }
542 static inline int get_vlc_trace(GetBitContext *s, VLC_TYPE (*table)[2],
543  int bits, int max_depth, char *file,
544  const char *func, int line)
545 {
546  int show = show_bits(s, 24);
547  int pos = get_bits_count(s);
548  int r = get_vlc2(s, table, bits, max_depth);
549  int len = get_bits_count(s) - pos;
550  int bits2 = show >> (24-len);
551 
552  print_bin(bits2, len);
553 
554  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d vlc @%5d in %s %s:%d\n",
555  bits2, len, r, pos, file, func, line);
556  return r;
557 }
558 static inline int get_xbits_trace(GetBitContext *s, int n, char *file,
559  const char *func, int line)
560 {
561  int show = show_bits(s, n);
562  int r = get_xbits(s, n);
563 
564  print_bin(show, n);
565  av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d xbt @%5d in %s %s:%d\n",
566  show, n, r, get_bits_count(s)-n, file, func, line);
567  return r;
568 }
569 
570 #define get_bits(s, n) get_bits_trace(s, n, __FILE__, __PRETTY_FUNCTION__, __LINE__)
571 #define get_bits1(s) get_bits_trace(s, 1, __FILE__, __PRETTY_FUNCTION__, __LINE__)
572 #define get_xbits(s, n) get_xbits_trace(s, n, __FILE__, __PRETTY_FUNCTION__, __LINE__)
573 #define get_vlc(s, vlc) get_vlc_trace(s, (vlc)->table, (vlc)->bits, 3, __FILE__, __PRETTY_FUNCTION__, __LINE__)
574 #define get_vlc2(s, tab, bits, max) get_vlc_trace(s, tab, bits, max, __FILE__, __PRETTY_FUNCTION__, __LINE__)
575 
576 #define tprintf(p, ...) av_log(p, AV_LOG_DEBUG, __VA_ARGS__)
577 
578 #else //TRACE
579 #define tprintf(p, ...) {}
580 #endif
581 
582 #endif /* AVCODEC_GET_BITS_H */