Libav
get_bits.h
Go to the documentation of this file.
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 
31 #include "libavutil/common.h"
32 #include "libavutil/intreadwrite.h"
33 #include "libavutil/log.h"
34 #include "mathops.h"
35 #include "vlc.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;
58 #if !UNCHECKED_BITSTREAM_READER
59  int size_in_bits_plus8;
60 #endif
62 
63 /* Bitstream reader API docs:
64  * name
65  * arbitrary name which is used as prefix for the internal variables
66  *
67  * gb
68  * getbitcontext
69  *
70  * OPEN_READER(name, gb)
71  * load gb into local variables
72  *
73  * CLOSE_READER(name, gb)
74  * store local vars in gb
75  *
76  * UPDATE_CACHE(name, gb)
77  * Refill the internal cache from the bitstream.
78  * After this call at least MIN_CACHE_BITS will be available.
79  *
80  * GET_CACHE(name, gb)
81  * Will output the contents of the internal cache,
82  * next bit is MSB of 32 or 64 bits (FIXME 64 bits).
83  *
84  * SHOW_UBITS(name, gb, num)
85  * Will return the next num bits.
86  *
87  * SHOW_SBITS(name, gb, num)
88  * Will return the next num bits and do sign extension.
89  *
90  * SKIP_BITS(name, gb, num)
91  * Will skip over the next num bits.
92  * Note, this is equivalent to SKIP_CACHE; SKIP_COUNTER.
93  *
94  * SKIP_CACHE(name, gb, num)
95  * Will remove the next num bits from the cache (note SKIP_COUNTER
96  * MUST be called before UPDATE_CACHE / CLOSE_READER).
97  *
98  * SKIP_COUNTER(name, gb, num)
99  * Will increment the internal bit counter (see SKIP_CACHE & SKIP_BITS).
100  *
101  * LAST_SKIP_BITS(name, gb, num)
102  * Like SKIP_BITS, to be used if next call is UPDATE_CACHE or CLOSE_READER.
103  *
104  * For examples see get_bits, show_bits, skip_bits, get_vlc.
105  */
106 
107 #ifdef LONG_BITSTREAM_READER
108 # define MIN_CACHE_BITS 32
109 #else
110 # define MIN_CACHE_BITS 25
111 #endif
112 
113 #define OPEN_READER_NOSIZE(name, gb) \
114  unsigned int name ## _index = (gb)->index; \
115  unsigned int av_unused name ## _cache = 0
116 
117 #if UNCHECKED_BITSTREAM_READER
118 #define OPEN_READER(name, gb) OPEN_READER_NOSIZE(name, gb)
119 
120 #define BITS_AVAILABLE(name, gb) 1
121 #else
122 #define OPEN_READER(name, gb) \
123  OPEN_READER_NOSIZE(name, gb); \
124  unsigned int name ## _size_plus8 = (gb)->size_in_bits_plus8
125 
126 #define BITS_AVAILABLE(name, gb) name ## _index < name ## _size_plus8
127 #endif
128 
129 #define CLOSE_READER(name, gb) (gb)->index = name ## _index
130 
131 #ifdef BITSTREAM_READER_LE
132 
133 # ifdef LONG_BITSTREAM_READER
134 # define UPDATE_CACHE(name, gb) name ## _cache = \
135  AV_RL64((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)
136 # else
137 # define UPDATE_CACHE(name, gb) name ## _cache = \
138  AV_RL32((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)
139 # endif
140 
141 # define SKIP_CACHE(name, gb, num) name ## _cache >>= (num)
142 
143 #else
144 
145 # ifdef LONG_BITSTREAM_READER
146 # define UPDATE_CACHE(name, gb) name ## _cache = \
147  AV_RB64((gb)->buffer + (name ## _index >> 3)) >> (32 - (name ## _index & 7))
148 # else
149 # define UPDATE_CACHE(name, gb) name ## _cache = \
150  AV_RB32((gb)->buffer + (name ## _index >> 3)) << (name ## _index & 7)
151 # endif
152 
153 # define SKIP_CACHE(name, gb, num) name ## _cache <<= (num)
154 
155 #endif
156 
157 #if UNCHECKED_BITSTREAM_READER
158 # define SKIP_COUNTER(name, gb, num) name ## _index += (num)
159 #else
160 # define SKIP_COUNTER(name, gb, num) \
161  name ## _index = FFMIN(name ## _size_plus8, name ## _index + (num))
162 #endif
163 
164 #define SKIP_BITS(name, gb, num) \
165  do { \
166  SKIP_CACHE(name, gb, num); \
167  SKIP_COUNTER(name, gb, num); \
168  } while (0)
169 
170 #define LAST_SKIP_BITS(name, gb, num) SKIP_COUNTER(name, gb, num)
171 
172 #ifdef BITSTREAM_READER_LE
173 # define SHOW_UBITS(name, gb, num) zero_extend(name ## _cache, num)
174 # define SHOW_SBITS(name, gb, num) sign_extend(name ## _cache, num)
175 #else
176 # define SHOW_UBITS(name, gb, num) NEG_USR32(name ## _cache, num)
177 # define SHOW_SBITS(name, gb, num) NEG_SSR32(name ## _cache, num)
178 #endif
179 
180 #define GET_CACHE(name, gb) ((uint32_t) name ## _cache)
181 
182 static inline int get_bits_count(const GetBitContext *s)
183 {
184  return s->index;
185 }
186 
187 static inline void skip_bits_long(GetBitContext *s, int n)
188 {
189 #if UNCHECKED_BITSTREAM_READER
190  s->index += n;
191 #else
192  s->index += av_clip(n, -s->index, s->size_in_bits_plus8 - s->index);
193 #endif
194 }
195 
201 static inline int get_xbits(GetBitContext *s, int n)
202 {
203  register int sign;
204  register int32_t cache;
205  OPEN_READER(re, s);
206  UPDATE_CACHE(re, s);
207  cache = GET_CACHE(re, s);
208  sign = ~cache >> 31;
209  LAST_SKIP_BITS(re, s, n);
210  CLOSE_READER(re, s);
211  return (NEG_USR32(sign ^ cache, n) ^ sign) - sign;
212 }
213 
214 static inline int get_sbits(GetBitContext *s, int n)
215 {
216  register int tmp;
217  OPEN_READER(re, s);
218  UPDATE_CACHE(re, s);
219  tmp = SHOW_SBITS(re, s, n);
220  LAST_SKIP_BITS(re, s, n);
221  CLOSE_READER(re, s);
222  return tmp;
223 }
224 
228 static inline unsigned int get_bits(GetBitContext *s, int n)
229 {
230  register int tmp;
231  OPEN_READER(re, s);
232  UPDATE_CACHE(re, s);
233  tmp = SHOW_UBITS(re, s, n);
234  LAST_SKIP_BITS(re, s, n);
235  CLOSE_READER(re, s);
236  return tmp;
237 }
238 
243 {
244  return n ? get_bits(s, n) : 0;
245 }
246 
250 static inline unsigned int show_bits(GetBitContext *s, int n)
251 {
252  register int tmp;
254  UPDATE_CACHE(re, s);
255  tmp = SHOW_UBITS(re, s, n);
256  return tmp;
257 }
258 
259 static inline void skip_bits(GetBitContext *s, int n)
260 {
261  OPEN_READER(re, s);
262  UPDATE_CACHE(re, s);
263  LAST_SKIP_BITS(re, s, n);
264  CLOSE_READER(re, s);
265 }
266 
267 static inline unsigned int get_bits1(GetBitContext *s)
268 {
269  unsigned int index = s->index;
270  uint8_t result = s->buffer[index >> 3];
271 #ifdef BITSTREAM_READER_LE
272  result >>= index & 7;
273  result &= 1;
274 #else
275  result <<= index & 7;
276  result >>= 8 - 1;
277 #endif
278 #if !UNCHECKED_BITSTREAM_READER
279  if (s->index < s->size_in_bits_plus8)
280 #endif
281  index++;
282  s->index = index;
283 
284  return result;
285 }
286 
287 static inline unsigned int show_bits1(GetBitContext *s)
288 {
289  return show_bits(s, 1);
290 }
291 
292 static inline void skip_bits1(GetBitContext *s)
293 {
294  skip_bits(s, 1);
295 }
296 
300 static inline unsigned int get_bits_long(GetBitContext *s, int n)
301 {
302  if (n <= MIN_CACHE_BITS) {
303  return get_bits(s, n);
304  } else {
305 #ifdef BITSTREAM_READER_LE
306  int ret = get_bits(s, 16);
307  return ret | (get_bits(s, n - 16) << 16);
308 #else
309  int ret = get_bits(s, 16) << (n - 16);
310  return ret | get_bits(s, n - 16);
311 #endif
312  }
313 }
314 
315 /*
316  * Read 0-64 bits.
317  */
318 static inline uint64_t get_bits64(GetBitContext *s, int n)
319 {
320  if (n <= 32) {
321  return get_bits_long(s, n);
322  } else {
323 #ifdef BITSTREAM_READER_LE
324  uint64_t ret = get_bits_long(s, 32);
325  return ret | (uint64_t) get_bits_long(s, n - 32) << 32;
326 #else
327  uint64_t ret = (uint64_t) get_bits_long(s, n - 32) << 32;
328  return ret | get_bits_long(s, 32);
329 #endif
330  }
331 }
332 
336 static inline int get_sbits_long(GetBitContext *s, int n)
337 {
338  return sign_extend(get_bits_long(s, n), n);
339 }
340 
344 static inline unsigned int show_bits_long(GetBitContext *s, int n)
345 {
346  if (n <= MIN_CACHE_BITS) {
347  return show_bits(s, n);
348  } else {
349  GetBitContext gb = *s;
350  return get_bits_long(&gb, n);
351  }
352 }
353 
362 static inline int init_get_bits(GetBitContext *s, const uint8_t *buffer,
363  int bit_size)
364 {
365  int buffer_size;
366  int ret = 0;
367 
368  if (bit_size > INT_MAX - 7 || bit_size < 0 || !buffer) {
369  bit_size = 0;
370  buffer = NULL;
371  ret = AVERROR_INVALIDDATA;
372  }
373 
374  buffer_size = (bit_size + 7) >> 3;
375 
376  s->buffer = buffer;
377  s->size_in_bits = bit_size;
378 #if !UNCHECKED_BITSTREAM_READER
379  s->size_in_bits_plus8 = bit_size + 8;
380 #endif
381  s->buffer_end = buffer + buffer_size;
382  s->index = 0;
383 
384  return ret;
385 }
386 
395 static inline int init_get_bits8(GetBitContext *s, const uint8_t *buffer,
396  int byte_size)
397 {
398  if (byte_size > INT_MAX / 8)
399  return AVERROR_INVALIDDATA;
400  return init_get_bits(s, buffer, byte_size * 8);
401 }
402 
403 static inline const uint8_t *align_get_bits(GetBitContext *s)
404 {
405  int n = -get_bits_count(s) & 7;
406  if (n)
407  skip_bits(s, n);
408  return s->buffer + (s->index >> 3);
409 }
410 
416 #define GET_VLC(code, name, gb, table, bits, max_depth) \
417  do { \
418  int n, nb_bits; \
419  unsigned int index; \
420  \
421  index = SHOW_UBITS(name, gb, bits); \
422  code = table[index][0]; \
423  n = table[index][1]; \
424  \
425  if (max_depth > 1 && n < 0) { \
426  LAST_SKIP_BITS(name, gb, bits); \
427  UPDATE_CACHE(name, gb); \
428  \
429  nb_bits = -n; \
430  \
431  index = SHOW_UBITS(name, gb, nb_bits) + code; \
432  code = table[index][0]; \
433  n = table[index][1]; \
434  if (max_depth > 2 && n < 0) { \
435  LAST_SKIP_BITS(name, gb, nb_bits); \
436  UPDATE_CACHE(name, gb); \
437  \
438  nb_bits = -n; \
439  \
440  index = SHOW_UBITS(name, gb, nb_bits) + code; \
441  code = table[index][0]; \
442  n = table[index][1]; \
443  } \
444  } \
445  SKIP_BITS(name, gb, n); \
446  } while (0)
447 
448 #define GET_RL_VLC(level, run, name, gb, table, bits, \
449  max_depth, need_update) \
450  do { \
451  int n, nb_bits; \
452  unsigned int index; \
453  \
454  index = SHOW_UBITS(name, gb, bits); \
455  level = table[index].level; \
456  n = table[index].len; \
457  \
458  if (max_depth > 1 && n < 0) { \
459  SKIP_BITS(name, gb, bits); \
460  if (need_update) { \
461  UPDATE_CACHE(name, gb); \
462  } \
463  \
464  nb_bits = -n; \
465  \
466  index = SHOW_UBITS(name, gb, nb_bits) + level; \
467  level = table[index].level; \
468  n = table[index].len; \
469  if (max_depth > 2 && n < 0) { \
470  LAST_SKIP_BITS(name, gb, nb_bits); \
471  if (need_update) { \
472  UPDATE_CACHE(name, gb); \
473  } \
474  nb_bits = -n; \
475  \
476  index = SHOW_UBITS(name, gb, nb_bits) + level; \
477  level = table[index].level; \
478  n = table[index].len; \
479  } \
480  } \
481  run = table[index].run; \
482  SKIP_BITS(name, gb, n); \
483  } while (0)
484 
493 static av_always_inline int get_vlc2(GetBitContext *s, VLC_TYPE (*table)[2],
494  int bits, int max_depth)
495 {
496  int code;
497 
498  OPEN_READER(re, s);
499  UPDATE_CACHE(re, s);
500 
501  GET_VLC(code, re, s, table, bits, max_depth);
502 
503  CLOSE_READER(re, s);
504 
505  return code;
506 }
507 
508 static inline int decode012(GetBitContext *gb)
509 {
510  int n;
511  n = get_bits1(gb);
512  if (n == 0)
513  return 0;
514  else
515  return get_bits1(gb) + 1;
516 }
517 
518 static inline int decode210(GetBitContext *gb)
519 {
520  if (get_bits1(gb))
521  return 0;
522  else
523  return 2 - get_bits1(gb);
524 }
525 
526 static inline int get_bits_left(GetBitContext *gb)
527 {
528  return gb->size_in_bits - get_bits_count(gb);
529 }
530 
531 #endif /* AVCODEC_GET_BITS_H */
static unsigned int show_bits_long(GetBitContext *s, int n)
Show 0-32 bits.
Definition: get_bits.h:344
static unsigned int show_bits1(GetBitContext *s)
Definition: get_bits.h:287
#define AVERROR_INVALIDDATA
Invalid data found when processing input.
Definition: error.h:54
float re
Definition: fft.c:69
static unsigned int get_bits(GetBitContext *s, int n)
Read 1-25 bits.
Definition: get_bits.h:228
static void skip_bits_long(GetBitContext *s, int n)
Definition: get_bits.h:187
const uint8_t * buffer
Definition: get_bits.h:55
static int get_sbits(GetBitContext *s, int n)
Definition: get_bits.h:214
static int get_sbits_long(GetBitContext *s, int n)
Read 0-32 bits as a signed integer.
Definition: get_bits.h:336
uint8_t bits
Definition: crc.c:252
uint8_t
static int get_bits_count(const GetBitContext *s)
Definition: get_bits.h:182
static int get_bits_left(GetBitContext *gb)
Definition: get_bits.h:526
static uint64_t get_bits64(GetBitContext *s, int n)
Definition: get_bits.h:318
#define UPDATE_CACHE(name, gb)
Definition: get_bits.h:149
#define CLOSE_READER(name, gb)
Definition: get_bits.h:129
#define NEG_USR32(a, s)
Definition: mathops.h:154
int size_in_bits
Definition: get_bits.h:57
int32_t
static unsigned int show_bits(GetBitContext *s, int n)
Show 1-25 bits.
Definition: get_bits.h:250
#define LAST_SKIP_BITS(name, gb, num)
Definition: get_bits.h:170
static av_always_inline int get_vlc2(GetBitContext *s, VLC_TYPE(*table)[2], int bits, int max_depth)
Parse a vlc code.
Definition: get_bits.h:493
#define GET_VLC(code, name, gb, table, bits, max_depth)
If the vlc code is invalid and max_depth=1, then no bits will be removed.
Definition: get_bits.h:416
#define SHOW_UBITS(name, gb, num)
Definition: get_bits.h:176
static int decode210(GetBitContext *gb)
Definition: get_bits.h:518
NULL
Definition: eval.c:55
static int init_get_bits8(GetBitContext *s, const uint8_t *buffer, int byte_size)
Initialize GetBitContext.
Definition: get_bits.h:395
static int get_xbits(GetBitContext *s, int n)
Read MPEG-1 dc-style VLC (sign bit + mantisse with no MSB).
Definition: get_bits.h:201
#define OPEN_READER(name, gb)
Definition: get_bits.h:118
static unsigned int get_bits1(GetBitContext *s)
Definition: get_bits.h:267
static void skip_bits1(GetBitContext *s)
Definition: get_bits.h:292
static void skip_bits(GetBitContext *s, int n)
Definition: get_bits.h:259
static int init_get_bits(GetBitContext *s, const uint8_t *buffer, int bit_size)
Initialize GetBitContext.
Definition: get_bits.h:362
#define GET_CACHE(name, gb)
Definition: get_bits.h:180
static unsigned int get_bits_long(GetBitContext *s, int n)
Read 0-32 bits.
Definition: get_bits.h:300
#define MIN_CACHE_BITS
Definition: get_bits.h:110
static av_const int sign_extend(int val, unsigned bits)
Definition: mathops.h:118
#define SHOW_SBITS(name, gb, num)
Definition: get_bits.h:177
#define OPEN_READER_NOSIZE(name, gb)
Definition: get_bits.h:113
common internal and external API header
const uint8_t * buffer_end
Definition: get_bits.h:55
static uint8_t tmp[8]
Definition: des.c:38
static int decode012(GetBitContext *gb)
Definition: get_bits.h:508
static const uint8_t * align_get_bits(GetBitContext *s)
Definition: get_bits.h:403
#define av_always_inline
Definition: attributes.h:40
#define VLC_TYPE
Definition: vlc.h:24
static av_always_inline int get_bitsz(GetBitContext *s, int n)
Read 0-25 bits.
Definition: get_bits.h:242