2 * copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
4 * This file is part of FFmpeg.
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.
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.
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
23 * bitstream reader API header.
26 #ifndef AVCODEC_GET_BITS_H
27 #define AVCODEC_GET_BITS_H
31 #include "libavutil/common.h"
32 #include "libavutil/intreadwrite.h"
33 #include "libavutil/log.h"
34 #include "libavutil/avassert.h"
40 * Safe bitstream reading:
41 * optionally, the get_bits API can check to ensure that we
42 * don't read past input buffer boundaries. This is protected
43 * with CONFIG_SAFE_BITSTREAM_READER at the global level, and
44 * then below that with UNCHECKED_BITSTREAM_READER at the per-
45 * decoder level. This means that decoders that check internally
46 * can "#define UNCHECKED_BITSTREAM_READER 1" to disable
48 * Boundary checking causes a minor performance penalty so for
49 * applications that won't want/need this, it can be disabled
50 * globally using "#define CONFIG_SAFE_BITSTREAM_READER 0".
52 #ifndef UNCHECKED_BITSTREAM_READER
53 #define UNCHECKED_BITSTREAM_READER !CONFIG_SAFE_BITSTREAM_READER
56 typedef struct GetBitContext {
57 const uint8_t *buffer, *buffer_end;
60 int size_in_bits_plus8;
63 /* Bitstream reader API docs:
65 * arbitrary name which is used as prefix for the internal variables
70 * OPEN_READER(name, gb)
71 * load gb into local variables
73 * CLOSE_READER(name, gb)
74 * store local vars in gb
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.
81 * Will output the contents of the internal cache,
82 * next bit is MSB of 32 or 64 bits (FIXME 64 bits).
84 * SHOW_UBITS(name, gb, num)
85 * Will return the next num bits.
87 * SHOW_SBITS(name, gb, num)
88 * Will return the next num bits and do sign extension.
90 * SKIP_BITS(name, gb, num)
91 * Will skip over the next num bits.
92 * Note, this is equivalent to SKIP_CACHE; SKIP_COUNTER.
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).
98 * SKIP_COUNTER(name, gb, num)
99 * Will increment the internal bit counter (see SKIP_CACHE & SKIP_BITS).
101 * LAST_SKIP_BITS(name, gb, num)
102 * Like SKIP_BITS, to be used if next call is UPDATE_CACHE or CLOSE_READER.
104 * BITS_LEFT(name, gb)
105 * Return the number of bits left
107 * For examples see get_bits, show_bits, skip_bits, get_vlc.
110 #ifdef LONG_BITSTREAM_READER
111 # define MIN_CACHE_BITS 32
113 # define MIN_CACHE_BITS 25
116 #define OPEN_READER_NOSIZE(name, gb) \
117 unsigned int name ## _index = (gb)->index; \
118 unsigned int av_unused name ## _cache
120 #if UNCHECKED_BITSTREAM_READER
121 #define OPEN_READER(name, gb) OPEN_READER_NOSIZE(name, gb)
123 #define BITS_AVAILABLE(name, gb) 1
125 #define OPEN_READER(name, gb) \
126 OPEN_READER_NOSIZE(name, gb); \
127 unsigned int name ## _size_plus8 = (gb)->size_in_bits_plus8
129 #define BITS_AVAILABLE(name, gb) name ## _index < name ## _size_plus8
132 #define CLOSE_READER(name, gb) (gb)->index = name ## _index
134 # ifdef LONG_BITSTREAM_READER
136 # define UPDATE_CACHE_LE(name, gb) name ## _cache = \
137 AV_RL64((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)
139 # define UPDATE_CACHE_BE(name, gb) name ## _cache = \
140 AV_RB64((gb)->buffer + (name ## _index >> 3)) >> (32 - (name ## _index & 7))
144 # define UPDATE_CACHE_LE(name, gb) name ## _cache = \
145 AV_RL32((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)
147 # define UPDATE_CACHE_BE(name, gb) name ## _cache = \
148 AV_RB32((gb)->buffer + (name ## _index >> 3)) << (name ## _index & 7)
153 #ifdef BITSTREAM_READER_LE
155 # define UPDATE_CACHE(name, gb) UPDATE_CACHE_LE(name, gb)
157 # define SKIP_CACHE(name, gb, num) name ## _cache >>= (num)
161 # define UPDATE_CACHE(name, gb) UPDATE_CACHE_BE(name, gb)
163 # define SKIP_CACHE(name, gb, num) name ## _cache <<= (num)
167 #if UNCHECKED_BITSTREAM_READER
168 # define SKIP_COUNTER(name, gb, num) name ## _index += (num)
170 # define SKIP_COUNTER(name, gb, num) \
171 name ## _index = FFMIN(name ## _size_plus8, name ## _index + (num))
174 #define BITS_LEFT(name, gb) ((int)((gb)->size_in_bits - name ## _index))
176 #define SKIP_BITS(name, gb, num) \
178 SKIP_CACHE(name, gb, num); \
179 SKIP_COUNTER(name, gb, num); \
182 #define LAST_SKIP_BITS(name, gb, num) SKIP_COUNTER(name, gb, num)
184 #define SHOW_UBITS_LE(name, gb, num) zero_extend(name ## _cache, num)
185 #define SHOW_SBITS_LE(name, gb, num) sign_extend(name ## _cache, num)
187 #define SHOW_UBITS_BE(name, gb, num) NEG_USR32(name ## _cache, num)
188 #define SHOW_SBITS_BE(name, gb, num) NEG_SSR32(name ## _cache, num)
190 #ifdef BITSTREAM_READER_LE
191 # define SHOW_UBITS(name, gb, num) SHOW_UBITS_LE(name, gb, num)
192 # define SHOW_SBITS(name, gb, num) SHOW_SBITS_LE(name, gb, num)
194 # define SHOW_UBITS(name, gb, num) SHOW_UBITS_BE(name, gb, num)
195 # define SHOW_SBITS(name, gb, num) SHOW_SBITS_BE(name, gb, num)
198 #define GET_CACHE(name, gb) ((uint32_t) name ## _cache)
200 static inline int get_bits_count(const GetBitContext *s)
206 * Skips the specified number of bits.
207 * @param n the number of bits to skip,
208 * For the UNCHECKED_BITSTREAM_READER this must not cause the distance
209 * from the start to overflow int32_t. Staying within the bitstream + padding
210 * is sufficient, too.
212 static inline void skip_bits_long(GetBitContext *s, int n)
214 #if UNCHECKED_BITSTREAM_READER
217 s->index += av_clip(n, -s->index, s->size_in_bits_plus8 - s->index);
222 * Read MPEG-1 dc-style VLC (sign bit + mantissa with no MSB).
223 * if MSB not set it is negative
224 * @param n length in bits
226 static inline int get_xbits(GetBitContext *s, int n)
229 register int32_t cache;
231 av_assert2(n>0 && n<=25);
233 cache = GET_CACHE(re, s);
235 LAST_SKIP_BITS(re, s, n);
237 return (NEG_USR32(sign ^ cache, n) ^ sign) - sign;
240 static inline int get_xbits_le(GetBitContext *s, int n)
243 register int32_t cache;
245 av_assert2(n>0 && n<=25);
246 UPDATE_CACHE_LE(re, s);
247 cache = GET_CACHE(re, s);
248 sign = sign_extend(~cache, n) >> 31;
249 LAST_SKIP_BITS(re, s, n);
251 return (zero_extend(sign ^ cache, n) ^ sign) - sign;
254 static inline int get_sbits(GetBitContext *s, int n)
258 av_assert2(n>0 && n<=25);
260 tmp = SHOW_SBITS(re, s, n);
261 LAST_SKIP_BITS(re, s, n);
269 static inline unsigned int get_bits(GetBitContext *s, int n)
273 av_assert2(n>0 && n<=25);
275 tmp = SHOW_UBITS(re, s, n);
276 LAST_SKIP_BITS(re, s, n);
284 static av_always_inline int get_bitsz(GetBitContext *s, int n)
286 return n ? get_bits(s, n) : 0;
289 static inline unsigned int get_bits_le(GetBitContext *s, int n)
293 av_assert2(n>0 && n<=25);
294 UPDATE_CACHE_LE(re, s);
295 tmp = SHOW_UBITS_LE(re, s, n);
296 LAST_SKIP_BITS(re, s, n);
304 static inline unsigned int show_bits(GetBitContext *s, int n)
307 OPEN_READER_NOSIZE(re, s);
308 av_assert2(n>0 && n<=25);
310 tmp = SHOW_UBITS(re, s, n);
314 static inline void skip_bits(GetBitContext *s, int n)
317 LAST_SKIP_BITS(re, s, n);
321 static inline unsigned int get_bits1(GetBitContext *s)
323 unsigned int index = s->index;
324 uint8_t result = s->buffer[index >> 3];
325 #ifdef BITSTREAM_READER_LE
326 result >>= index & 7;
329 result <<= index & 7;
332 #if !UNCHECKED_BITSTREAM_READER
333 if (s->index < s->size_in_bits_plus8)
341 static inline unsigned int show_bits1(GetBitContext *s)
343 return show_bits(s, 1);
346 static inline void skip_bits1(GetBitContext *s)
354 static inline unsigned int get_bits_long(GetBitContext *s, int n)
356 av_assert2(n>=0 && n<=32);
359 } else if (n <= MIN_CACHE_BITS) {
360 return get_bits(s, n);
362 #ifdef BITSTREAM_READER_LE
363 unsigned ret = get_bits(s, 16);
364 return ret | (get_bits(s, n - 16) << 16);
366 unsigned ret = get_bits(s, 16) << (n - 16);
367 return ret | get_bits(s, n - 16);
375 static inline uint64_t get_bits64(GetBitContext *s, int n)
378 return get_bits_long(s, n);
380 #ifdef BITSTREAM_READER_LE
381 uint64_t ret = get_bits_long(s, 32);
382 return ret | (uint64_t) get_bits_long(s, n - 32) << 32;
384 uint64_t ret = (uint64_t) get_bits_long(s, n - 32) << 32;
385 return ret | get_bits_long(s, 32);
391 * Read 0-32 bits as a signed integer.
393 static inline int get_sbits_long(GetBitContext *s, int n)
395 // sign_extend(x, 0) is undefined
399 return sign_extend(get_bits_long(s, n), n);
405 static inline unsigned int show_bits_long(GetBitContext *s, int n)
407 if (n <= MIN_CACHE_BITS) {
408 return show_bits(s, n);
410 GetBitContext gb = *s;
411 return get_bits_long(&gb, n);
415 static inline int check_marker(void *logctx, GetBitContext *s, const char *msg)
417 int bit = get_bits1(s);
419 av_log(logctx, AV_LOG_INFO, "Marker bit missing at %d of %d %s\n",
420 get_bits_count(s) - 1, s->size_in_bits, msg);
426 * Initialize GetBitContext.
427 * @param buffer bitstream buffer, must be AV_INPUT_BUFFER_PADDING_SIZE bytes
428 * larger than the actual read bits because some optimized bitstream
429 * readers read 32 or 64 bit at once and could read over the end
430 * @param bit_size the size of the buffer in bits
431 * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
433 static inline int init_get_bits(GetBitContext *s, const uint8_t *buffer,
439 if (bit_size >= INT_MAX - FFMAX(7, AV_INPUT_BUFFER_PADDING_SIZE*8) || bit_size < 0 || !buffer) {
442 ret = AVERROR_INVALIDDATA;
445 buffer_size = (bit_size + 7) >> 3;
448 s->size_in_bits = bit_size;
449 s->size_in_bits_plus8 = bit_size + 8;
450 s->buffer_end = buffer + buffer_size;
457 * Initialize GetBitContext.
458 * @param buffer bitstream buffer, must be AV_INPUT_BUFFER_PADDING_SIZE bytes
459 * larger than the actual read bits because some optimized bitstream
460 * readers read 32 or 64 bit at once and could read over the end
461 * @param byte_size the size of the buffer in bytes
462 * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
464 static inline int init_get_bits8(GetBitContext *s, const uint8_t *buffer,
467 if (byte_size > INT_MAX / 8 || byte_size < 0)
469 return init_get_bits(s, buffer, byte_size * 8);
472 static inline const uint8_t *align_get_bits(GetBitContext *s)
474 int n = -get_bits_count(s) & 7;
477 return s->buffer + (s->index >> 3);
481 * If the vlc code is invalid and max_depth=1, then no bits will be removed.
482 * If the vlc code is invalid and max_depth>1, then the number of bits removed
485 #define GET_VLC(code, name, gb, table, bits, max_depth) \
488 unsigned int index; \
490 index = SHOW_UBITS(name, gb, bits); \
491 code = table[index][0]; \
492 n = table[index][1]; \
494 if (max_depth > 1 && n < 0) { \
495 LAST_SKIP_BITS(name, gb, bits); \
496 UPDATE_CACHE(name, gb); \
500 index = SHOW_UBITS(name, gb, nb_bits) + code; \
501 code = table[index][0]; \
502 n = table[index][1]; \
503 if (max_depth > 2 && n < 0) { \
504 LAST_SKIP_BITS(name, gb, nb_bits); \
505 UPDATE_CACHE(name, gb); \
509 index = SHOW_UBITS(name, gb, nb_bits) + code; \
510 code = table[index][0]; \
511 n = table[index][1]; \
514 SKIP_BITS(name, gb, n); \
517 #define GET_RL_VLC(level, run, name, gb, table, bits, \
518 max_depth, need_update) \
521 unsigned int index; \
523 index = SHOW_UBITS(name, gb, bits); \
524 level = table[index].level; \
525 n = table[index].len; \
527 if (max_depth > 1 && n < 0) { \
528 SKIP_BITS(name, gb, bits); \
530 UPDATE_CACHE(name, gb); \
535 index = SHOW_UBITS(name, gb, nb_bits) + level; \
536 level = table[index].level; \
537 n = table[index].len; \
538 if (max_depth > 2 && n < 0) { \
539 LAST_SKIP_BITS(name, gb, nb_bits); \
541 UPDATE_CACHE(name, gb); \
545 index = SHOW_UBITS(name, gb, nb_bits) + level; \
546 level = table[index].level; \
547 n = table[index].len; \
550 run = table[index].run; \
551 SKIP_BITS(name, gb, n); \
556 * @param bits is the number of bits which will be read at once, must be
557 * identical to nb_bits in init_vlc()
558 * @param max_depth is the number of times bits bits must be read to completely
559 * read the longest vlc code
560 * = (max_vlc_length + bits - 1) / bits
561 * @returns the code parsed or -1 if no vlc matches
563 static av_always_inline int get_vlc2(GetBitContext *s, VLC_TYPE (*table)[2],
564 int bits, int max_depth)
571 GET_VLC(code, re, s, table, bits, max_depth);
578 static inline int decode012(GetBitContext *gb)
585 return get_bits1(gb) + 1;
588 static inline int decode210(GetBitContext *gb)
593 return 2 - get_bits1(gb);
596 static inline int get_bits_left(GetBitContext *gb)
598 return gb->size_in_bits - get_bits_count(gb);
601 static inline int skip_1stop_8data_bits(GetBitContext *gb)
603 if (get_bits_left(gb) <= 0)
604 return AVERROR_INVALIDDATA;
606 while (get_bits1(gb)) {
608 if (get_bits_left(gb) <= 0)
609 return AVERROR_INVALIDDATA;
615 #endif /* AVCODEC_GET_BITS_H */