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)
205 static inline void skip_bits_long(GetBitContext *s, int n)
207 #if UNCHECKED_BITSTREAM_READER
210 s->index += av_clip(n, -s->index, s->size_in_bits_plus8 - s->index);
215 * Read MPEG-1 dc-style VLC (sign bit + mantissa with no MSB).
216 * if MSB not set it is negative
217 * @param n length in bits
219 static inline int get_xbits(GetBitContext *s, int n)
222 register int32_t cache;
224 av_assert2(n>0 && n<=25);
226 cache = GET_CACHE(re, s);
228 LAST_SKIP_BITS(re, s, n);
230 return (NEG_USR32(sign ^ cache, n) ^ sign) - sign;
233 static inline int get_xbits_le(GetBitContext *s, int n)
236 register int32_t cache;
238 av_assert2(n>0 && n<=25);
239 UPDATE_CACHE_LE(re, s);
240 cache = GET_CACHE(re, s);
241 sign = sign_extend(~cache, n) >> 31;
242 LAST_SKIP_BITS(re, s, n);
244 return (zero_extend(sign ^ cache, n) ^ sign) - sign;
247 static inline int get_sbits(GetBitContext *s, int n)
251 av_assert2(n>0 && n<=25);
253 tmp = SHOW_SBITS(re, s, n);
254 LAST_SKIP_BITS(re, s, n);
262 static inline unsigned int get_bits(GetBitContext *s, int n)
266 av_assert2(n>0 && n<=25);
268 tmp = SHOW_UBITS(re, s, n);
269 LAST_SKIP_BITS(re, s, n);
277 static av_always_inline int get_bitsz(GetBitContext *s, int n)
279 return n ? get_bits(s, n) : 0;
282 static inline unsigned int get_bits_le(GetBitContext *s, int n)
286 av_assert2(n>0 && n<=25);
287 UPDATE_CACHE_LE(re, s);
288 tmp = SHOW_UBITS_LE(re, s, n);
289 LAST_SKIP_BITS(re, s, n);
297 static inline unsigned int show_bits(GetBitContext *s, int n)
300 OPEN_READER_NOSIZE(re, s);
301 av_assert2(n>0 && n<=25);
303 tmp = SHOW_UBITS(re, s, n);
307 static inline void skip_bits(GetBitContext *s, int n)
310 LAST_SKIP_BITS(re, s, n);
314 static inline unsigned int get_bits1(GetBitContext *s)
316 unsigned int index = s->index;
317 uint8_t result = s->buffer[index >> 3];
318 #ifdef BITSTREAM_READER_LE
319 result >>= index & 7;
322 result <<= index & 7;
325 #if !UNCHECKED_BITSTREAM_READER
326 if (s->index < s->size_in_bits_plus8)
334 static inline unsigned int show_bits1(GetBitContext *s)
336 return show_bits(s, 1);
339 static inline void skip_bits1(GetBitContext *s)
347 static inline unsigned int get_bits_long(GetBitContext *s, int n)
349 av_assert2(n>=0 && n<=32);
352 } else if (n <= MIN_CACHE_BITS) {
353 return get_bits(s, n);
355 #ifdef BITSTREAM_READER_LE
356 unsigned ret = get_bits(s, 16);
357 return ret | (get_bits(s, n - 16) << 16);
359 unsigned ret = get_bits(s, 16) << (n - 16);
360 return ret | get_bits(s, n - 16);
368 static inline uint64_t get_bits64(GetBitContext *s, int n)
371 return get_bits_long(s, n);
373 #ifdef BITSTREAM_READER_LE
374 uint64_t ret = get_bits_long(s, 32);
375 return ret | (uint64_t) get_bits_long(s, n - 32) << 32;
377 uint64_t ret = (uint64_t) get_bits_long(s, n - 32) << 32;
378 return ret | get_bits_long(s, 32);
384 * Read 0-32 bits as a signed integer.
386 static inline int get_sbits_long(GetBitContext *s, int n)
388 // sign_extend(x, 0) is undefined
392 return sign_extend(get_bits_long(s, n), n);
398 static inline unsigned int show_bits_long(GetBitContext *s, int n)
400 if (n <= MIN_CACHE_BITS) {
401 return show_bits(s, n);
403 GetBitContext gb = *s;
404 return get_bits_long(&gb, n);
408 static inline int check_marker(void *logctx, GetBitContext *s, const char *msg)
410 int bit = get_bits1(s);
412 av_log(logctx, AV_LOG_INFO, "Marker bit missing at %d of %d %s\n",
413 get_bits_count(s) - 1, s->size_in_bits, msg);
419 * Initialize GetBitContext.
420 * @param buffer bitstream buffer, must be AV_INPUT_BUFFER_PADDING_SIZE bytes
421 * larger than the actual read bits because some optimized bitstream
422 * readers read 32 or 64 bit at once and could read over the end
423 * @param bit_size the size of the buffer in bits
424 * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
426 static inline int init_get_bits(GetBitContext *s, const uint8_t *buffer,
432 if (bit_size >= INT_MAX - FFMAX(7, AV_INPUT_BUFFER_PADDING_SIZE*8) || bit_size < 0 || !buffer) {
435 ret = AVERROR_INVALIDDATA;
438 buffer_size = (bit_size + 7) >> 3;
441 s->size_in_bits = bit_size;
442 s->size_in_bits_plus8 = bit_size + 8;
443 s->buffer_end = buffer + buffer_size;
450 * Initialize GetBitContext.
451 * @param buffer bitstream buffer, must be AV_INPUT_BUFFER_PADDING_SIZE bytes
452 * larger than the actual read bits because some optimized bitstream
453 * readers read 32 or 64 bit at once and could read over the end
454 * @param byte_size the size of the buffer in bytes
455 * @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
457 static inline int init_get_bits8(GetBitContext *s, const uint8_t *buffer,
460 if (byte_size > INT_MAX / 8 || byte_size < 0)
462 return init_get_bits(s, buffer, byte_size * 8);
465 static inline const uint8_t *align_get_bits(GetBitContext *s)
467 int n = -get_bits_count(s) & 7;
470 return s->buffer + (s->index >> 3);
474 * If the vlc code is invalid and max_depth=1, then no bits will be removed.
475 * If the vlc code is invalid and max_depth>1, then the number of bits removed
478 #define GET_VLC(code, name, gb, table, bits, max_depth) \
481 unsigned int index; \
483 index = SHOW_UBITS(name, gb, bits); \
484 code = table[index][0]; \
485 n = table[index][1]; \
487 if (max_depth > 1 && n < 0) { \
488 LAST_SKIP_BITS(name, gb, bits); \
489 UPDATE_CACHE(name, gb); \
493 index = SHOW_UBITS(name, gb, nb_bits) + code; \
494 code = table[index][0]; \
495 n = table[index][1]; \
496 if (max_depth > 2 && n < 0) { \
497 LAST_SKIP_BITS(name, gb, nb_bits); \
498 UPDATE_CACHE(name, gb); \
502 index = SHOW_UBITS(name, gb, nb_bits) + code; \
503 code = table[index][0]; \
504 n = table[index][1]; \
507 SKIP_BITS(name, gb, n); \
510 #define GET_RL_VLC(level, run, name, gb, table, bits, \
511 max_depth, need_update) \
514 unsigned int index; \
516 index = SHOW_UBITS(name, gb, bits); \
517 level = table[index].level; \
518 n = table[index].len; \
520 if (max_depth > 1 && n < 0) { \
521 SKIP_BITS(name, gb, bits); \
523 UPDATE_CACHE(name, gb); \
528 index = SHOW_UBITS(name, gb, nb_bits) + level; \
529 level = table[index].level; \
530 n = table[index].len; \
531 if (max_depth > 2 && n < 0) { \
532 LAST_SKIP_BITS(name, gb, nb_bits); \
534 UPDATE_CACHE(name, gb); \
538 index = SHOW_UBITS(name, gb, nb_bits) + level; \
539 level = table[index].level; \
540 n = table[index].len; \
543 run = table[index].run; \
544 SKIP_BITS(name, gb, n); \
549 * @param bits is the number of bits which will be read at once, must be
550 * identical to nb_bits in init_vlc()
551 * @param max_depth is the number of times bits bits must be read to completely
552 * read the longest vlc code
553 * = (max_vlc_length + bits - 1) / bits
554 * @returns the code parsed or -1 if no vlc matches
556 static av_always_inline int get_vlc2(GetBitContext *s, VLC_TYPE (*table)[2],
557 int bits, int max_depth)
564 GET_VLC(code, re, s, table, bits, max_depth);
571 static inline int decode012(GetBitContext *gb)
578 return get_bits1(gb) + 1;
581 static inline int decode210(GetBitContext *gb)
586 return 2 - get_bits1(gb);
589 static inline int get_bits_left(GetBitContext *gb)
591 return gb->size_in_bits - get_bits_count(gb);
594 static inline int skip_1stop_8data_bits(GetBitContext *gb)
596 if (get_bits_left(gb) <= 0)
597 return AVERROR_INVALIDDATA;
599 while (get_bits1(gb)) {
601 if (get_bits_left(gb) <= 0)
602 return AVERROR_INVALIDDATA;
608 #endif /* AVCODEC_GET_BITS_H */