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pineapple-src/externals/ffmpeg/libavcodec/get_bits.h

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early-access version 1432
2021-02-09 03:25:58 +00:00
/*
* Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
* Copyright (c) 2016 Alexandra Hájková
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file
* bitstream reader API header.
*/
#ifndef AVCODEC_GET_BITS_H
#define AVCODEC_GET_BITS_H
#include <stdint.h>
#include "libavutil/common.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/log.h"
#include "libavutil/avassert.h"
#include "avcodec.h"
#include "mathops.h"
#include "vlc.h"
/*
* Safe bitstream reading:
* optionally, the get_bits API can check to ensure that we
* don't read past input buffer boundaries. This is protected
* with CONFIG_SAFE_BITSTREAM_READER at the global level, and
* then below that with UNCHECKED_BITSTREAM_READER at the per-
* decoder level. This means that decoders that check internally
* can "#define UNCHECKED_BITSTREAM_READER 1" to disable
* overread checks.
* Boundary checking causes a minor performance penalty so for
* applications that won't want/need this, it can be disabled
* globally using "#define CONFIG_SAFE_BITSTREAM_READER 0".
*/
#ifndef UNCHECKED_BITSTREAM_READER
#define UNCHECKED_BITSTREAM_READER !CONFIG_SAFE_BITSTREAM_READER
#endif
#ifndef CACHED_BITSTREAM_READER
#define CACHED_BITSTREAM_READER 0
#endif
typedef struct GetBitContext {
const uint8_t *buffer, *buffer_end;
#if CACHED_BITSTREAM_READER
uint64_t cache;
unsigned bits_left;
#endif
int index;
int size_in_bits;
int size_in_bits_plus8;
} GetBitContext;
static inline unsigned int get_bits(GetBitContext *s, int n);
static inline void skip_bits(GetBitContext *s, int n);
static inline unsigned int show_bits(GetBitContext *s, int n);
/* Bitstream reader API docs:
* name
* arbitrary name which is used as prefix for the internal variables
*
* gb
* getbitcontext
*
* OPEN_READER(name, gb)
* load gb into local variables
*
* CLOSE_READER(name, gb)
* store local vars in gb
*
* UPDATE_CACHE(name, gb)
* Refill the internal cache from the bitstream.
* After this call at least MIN_CACHE_BITS will be available.
*
* GET_CACHE(name, gb)
* Will output the contents of the internal cache,
* next bit is MSB of 32 or 64 bits (FIXME 64 bits).
*
* SHOW_UBITS(name, gb, num)
* Will return the next num bits.
*
* SHOW_SBITS(name, gb, num)
* Will return the next num bits and do sign extension.
*
* SKIP_BITS(name, gb, num)
* Will skip over the next num bits.
* Note, this is equivalent to SKIP_CACHE; SKIP_COUNTER.
*
* SKIP_CACHE(name, gb, num)
* Will remove the next num bits from the cache (note SKIP_COUNTER
* MUST be called before UPDATE_CACHE / CLOSE_READER).
*
* SKIP_COUNTER(name, gb, num)
* Will increment the internal bit counter (see SKIP_CACHE & SKIP_BITS).
*
* LAST_SKIP_BITS(name, gb, num)
* Like SKIP_BITS, to be used if next call is UPDATE_CACHE or CLOSE_READER.
*
* BITS_LEFT(name, gb)
* Return the number of bits left
*
* For examples see get_bits, show_bits, skip_bits, get_vlc.
*/
#if CACHED_BITSTREAM_READER
# define MIN_CACHE_BITS 64
#elif defined LONG_BITSTREAM_READER
# define MIN_CACHE_BITS 32
#else
# define MIN_CACHE_BITS 25
#endif
#if !CACHED_BITSTREAM_READER
#define OPEN_READER_NOSIZE(name, gb) \
unsigned int name ## _index = (gb)->index; \
unsigned int av_unused name ## _cache
#if UNCHECKED_BITSTREAM_READER
#define OPEN_READER(name, gb) OPEN_READER_NOSIZE(name, gb)
#define BITS_AVAILABLE(name, gb) 1
#else
#define OPEN_READER(name, gb) \
OPEN_READER_NOSIZE(name, gb); \
unsigned int name ## _size_plus8 = (gb)->size_in_bits_plus8
#define BITS_AVAILABLE(name, gb) name ## _index < name ## _size_plus8
#endif
#define CLOSE_READER(name, gb) (gb)->index = name ## _index
# ifdef LONG_BITSTREAM_READER
# define UPDATE_CACHE_LE(name, gb) name ## _cache = \
AV_RL64((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)
# define UPDATE_CACHE_BE(name, gb) name ## _cache = \
AV_RB64((gb)->buffer + (name ## _index >> 3)) >> (32 - (name ## _index & 7))
#else
# define UPDATE_CACHE_LE(name, gb) name ## _cache = \
AV_RL32((gb)->buffer + (name ## _index >> 3)) >> (name ## _index & 7)
# define UPDATE_CACHE_BE(name, gb) name ## _cache = \
AV_RB32((gb)->buffer + (name ## _index >> 3)) << (name ## _index & 7)
#endif
#ifdef BITSTREAM_READER_LE
# define UPDATE_CACHE(name, gb) UPDATE_CACHE_LE(name, gb)
# define SKIP_CACHE(name, gb, num) name ## _cache >>= (num)
#else
# define UPDATE_CACHE(name, gb) UPDATE_CACHE_BE(name, gb)
# define SKIP_CACHE(name, gb, num) name ## _cache <<= (num)
#endif
#if UNCHECKED_BITSTREAM_READER
# define SKIP_COUNTER(name, gb, num) name ## _index += (num)
#else
# define SKIP_COUNTER(name, gb, num) \
name ## _index = FFMIN(name ## _size_plus8, name ## _index + (num))
#endif
#define BITS_LEFT(name, gb) ((int)((gb)->size_in_bits - name ## _index))
#define SKIP_BITS(name, gb, num) \
do { \
SKIP_CACHE(name, gb, num); \
SKIP_COUNTER(name, gb, num); \
} while (0)
#define LAST_SKIP_BITS(name, gb, num) SKIP_COUNTER(name, gb, num)
#define SHOW_UBITS_LE(name, gb, num) zero_extend(name ## _cache, num)
#define SHOW_SBITS_LE(name, gb, num) sign_extend(name ## _cache, num)
#define SHOW_UBITS_BE(name, gb, num) NEG_USR32(name ## _cache, num)
#define SHOW_SBITS_BE(name, gb, num) NEG_SSR32(name ## _cache, num)
#ifdef BITSTREAM_READER_LE
# define SHOW_UBITS(name, gb, num) SHOW_UBITS_LE(name, gb, num)
# define SHOW_SBITS(name, gb, num) SHOW_SBITS_LE(name, gb, num)
#else
# define SHOW_UBITS(name, gb, num) SHOW_UBITS_BE(name, gb, num)
# define SHOW_SBITS(name, gb, num) SHOW_SBITS_BE(name, gb, num)
#endif
#define GET_CACHE(name, gb) ((uint32_t) name ## _cache)
#endif
static inline int get_bits_count(const GetBitContext *s)
{
#if CACHED_BITSTREAM_READER
return s->index - s->bits_left;
#else
return s->index;
#endif
}
#if CACHED_BITSTREAM_READER
static inline void refill_32(GetBitContext *s, int is_le)
{
#if !UNCHECKED_BITSTREAM_READER
if (s->index >> 3 >= s->buffer_end - s->buffer)
return;
#endif
if (is_le)
s->cache = (uint64_t)AV_RL32(s->buffer + (s->index >> 3)) << s->bits_left | s->cache;
else
s->cache = s->cache | (uint64_t)AV_RB32(s->buffer + (s->index >> 3)) << (32 - s->bits_left);
s->index += 32;
s->bits_left += 32;
}
static inline void refill_64(GetBitContext *s, int is_le)
{
#if !UNCHECKED_BITSTREAM_READER
if (s->index >> 3 >= s->buffer_end - s->buffer)
return;
#endif
if (is_le)
s->cache = AV_RL64(s->buffer + (s->index >> 3));
else
s->cache = AV_RB64(s->buffer + (s->index >> 3));
s->index += 64;
s->bits_left = 64;
}
static inline uint64_t get_val(GetBitContext *s, unsigned n, int is_le)
{
uint64_t ret;
av_assert2(n>0 && n<=63);
if (is_le) {
ret = s->cache & ((UINT64_C(1) << n) - 1);
s->cache >>= n;
} else {
ret = s->cache >> (64 - n);
s->cache <<= n;
}
s->bits_left -= n;
return ret;
}
static inline unsigned show_val(const GetBitContext *s, unsigned n)
{
#ifdef BITSTREAM_READER_LE
return s->cache & ((UINT64_C(1) << n) - 1);
#else
return s->cache >> (64 - n);
#endif
}
#endif
/**
* Skips the specified number of bits.
* @param n the number of bits to skip,
* For the UNCHECKED_BITSTREAM_READER this must not cause the distance
* from the start to overflow int32_t. Staying within the bitstream + padding
* is sufficient, too.
*/
static inline void skip_bits_long(GetBitContext *s, int n)
{
#if CACHED_BITSTREAM_READER
skip_bits(s, n);
#else
#if UNCHECKED_BITSTREAM_READER
s->index += n;
#else
s->index += av_clip(n, -s->index, s->size_in_bits_plus8 - s->index);
#endif
#endif
}
#if CACHED_BITSTREAM_READER
static inline void skip_remaining(GetBitContext *s, unsigned n)
{
#ifdef BITSTREAM_READER_LE
s->cache >>= n;
#else
s->cache <<= n;
#endif
s->bits_left -= n;
}
#endif
/**
* Read MPEG-1 dc-style VLC (sign bit + mantissa with no MSB).
* if MSB not set it is negative
* @param n length in bits
*/
static inline int get_xbits(GetBitContext *s, int n)
{
#if CACHED_BITSTREAM_READER
int32_t cache = show_bits(s, 32);
int sign = ~cache >> 31;
skip_remaining(s, n);
return ((((uint32_t)(sign ^ cache)) >> (32 - n)) ^ sign) - sign;
#else
register int sign;
register int32_t cache;
OPEN_READER(re, s);
av_assert2(n>0 && n<=25);
UPDATE_CACHE(re, s);
cache = GET_CACHE(re, s);
sign = ~cache >> 31;
LAST_SKIP_BITS(re, s, n);
CLOSE_READER(re, s);
return (NEG_USR32(sign ^ cache, n) ^ sign) - sign;
#endif
}
#if !CACHED_BITSTREAM_READER
static inline int get_xbits_le(GetBitContext *s, int n)
{
register int sign;
register int32_t cache;
OPEN_READER(re, s);
av_assert2(n>0 && n<=25);
UPDATE_CACHE_LE(re, s);
cache = GET_CACHE(re, s);
sign = sign_extend(~cache, n) >> 31;
LAST_SKIP_BITS(re, s, n);
CLOSE_READER(re, s);
return (zero_extend(sign ^ cache, n) ^ sign) - sign;
}
#endif
static inline int get_sbits(GetBitContext *s, int n)
{
register int tmp;
#if CACHED_BITSTREAM_READER
av_assert2(n>0 && n<=25);
tmp = sign_extend(get_bits(s, n), n);
#else
OPEN_READER(re, s);
av_assert2(n>0 && n<=25);
UPDATE_CACHE(re, s);
tmp = SHOW_SBITS(re, s, n);
LAST_SKIP_BITS(re, s, n);
CLOSE_READER(re, s);
#endif
return tmp;
}
/**
* Read 1-25 bits.
*/
static inline unsigned int get_bits(GetBitContext *s, int n)
{
register unsigned int tmp;
#if CACHED_BITSTREAM_READER
av_assert2(n>0 && n<=32);
if (n > s->bits_left) {
#ifdef BITSTREAM_READER_LE
refill_32(s, 1);
#else
refill_32(s, 0);
#endif
if (s->bits_left < 32)
s->bits_left = n;
}
#ifdef BITSTREAM_READER_LE
tmp = get_val(s, n, 1);
#else
tmp = get_val(s, n, 0);
#endif
#else
OPEN_READER(re, s);
av_assert2(n>0 && n<=25);
UPDATE_CACHE(re, s);
tmp = SHOW_UBITS(re, s, n);
LAST_SKIP_BITS(re, s, n);
CLOSE_READER(re, s);
#endif
av_assert2(tmp < UINT64_C(1) << n);
return tmp;
}
/**
* Read 0-25 bits.
*/
static av_always_inline int get_bitsz(GetBitContext *s, int n)
{
return n ? get_bits(s, n) : 0;
}
static inline unsigned int get_bits_le(GetBitContext *s, int n)
{
#if CACHED_BITSTREAM_READER
av_assert2(n>0 && n<=32);
if (n > s->bits_left) {
refill_32(s, 1);
if (s->bits_left < 32)
s->bits_left = n;
}
return get_val(s, n, 1);
#else
register int tmp;
OPEN_READER(re, s);
av_assert2(n>0 && n<=25);
UPDATE_CACHE_LE(re, s);
tmp = SHOW_UBITS_LE(re, s, n);
LAST_SKIP_BITS(re, s, n);
CLOSE_READER(re, s);
return tmp;
#endif
}
/**
* Show 1-25 bits.
*/
static inline unsigned int show_bits(GetBitContext *s, int n)
{
register unsigned int tmp;
#if CACHED_BITSTREAM_READER
if (n > s->bits_left)
#ifdef BITSTREAM_READER_LE
refill_32(s, 1);
#else
refill_32(s, 0);
#endif
tmp = show_val(s, n);
#else
OPEN_READER_NOSIZE(re, s);
av_assert2(n>0 && n<=25);
UPDATE_CACHE(re, s);
tmp = SHOW_UBITS(re, s, n);
#endif
return tmp;
}
static inline void skip_bits(GetBitContext *s, int n)
{
#if CACHED_BITSTREAM_READER
if (n < s->bits_left)
skip_remaining(s, n);
else {
n -= s->bits_left;
s->cache = 0;
s->bits_left = 0;
if (n >= 64) {
unsigned skip = (n / 8) * 8;
n -= skip;
s->index += skip;
}
#ifdef BITSTREAM_READER_LE
refill_64(s, 1);
#else
refill_64(s, 0);
#endif
if (n)
skip_remaining(s, n);
}
#else
OPEN_READER(re, s);
LAST_SKIP_BITS(re, s, n);
CLOSE_READER(re, s);
#endif
}
static inline unsigned int get_bits1(GetBitContext *s)
{
#if CACHED_BITSTREAM_READER
if (!s->bits_left)
#ifdef BITSTREAM_READER_LE
refill_64(s, 1);
#else
refill_64(s, 0);
#endif
#ifdef BITSTREAM_READER_LE
return get_val(s, 1, 1);
#else
return get_val(s, 1, 0);
#endif
#else
unsigned int index = s->index;
uint8_t result = s->buffer[index >> 3];
#ifdef BITSTREAM_READER_LE
result >>= index & 7;
result &= 1;
#else
result <<= index & 7;
result >>= 8 - 1;
#endif
#if !UNCHECKED_BITSTREAM_READER
if (s->index < s->size_in_bits_plus8)
#endif
index++;
s->index = index;
return result;
#endif
}
static inline unsigned int show_bits1(GetBitContext *s)
{
return show_bits(s, 1);
}
static inline void skip_bits1(GetBitContext *s)
{
skip_bits(s, 1);
}
/**
* Read 0-32 bits.
*/
static inline unsigned int get_bits_long(GetBitContext *s, int n)
{
av_assert2(n>=0 && n<=32);
if (!n) {
return 0;
#if CACHED_BITSTREAM_READER
}
return get_bits(s, n);
#else
} else if (n <= MIN_CACHE_BITS) {
return get_bits(s, n);
} else {
#ifdef BITSTREAM_READER_LE
unsigned ret = get_bits(s, 16);
return ret | (get_bits(s, n - 16) << 16);
#else
unsigned ret = get_bits(s, 16) << (n - 16);
return ret | get_bits(s, n - 16);
#endif
}
#endif
}
/**
* Read 0-64 bits.
*/
static inline uint64_t get_bits64(GetBitContext *s, int n)
{
if (n <= 32) {
return get_bits_long(s, n);
} else {
#ifdef BITSTREAM_READER_LE
uint64_t ret = get_bits_long(s, 32);
return ret | (uint64_t) get_bits_long(s, n - 32) << 32;
#else
uint64_t ret = (uint64_t) get_bits_long(s, n - 32) << 32;
return ret | get_bits_long(s, 32);
#endif
}
}
/**
* Read 0-32 bits as a signed integer.
*/
static inline int get_sbits_long(GetBitContext *s, int n)
{
// sign_extend(x, 0) is undefined
if (!n)
return 0;
return sign_extend(get_bits_long(s, n), n);
}
/**
* Show 0-32 bits.
*/
static inline unsigned int show_bits_long(GetBitContext *s, int n)
{
if (n <= MIN_CACHE_BITS) {
return show_bits(s, n);
} else {
GetBitContext gb = *s;
return get_bits_long(&gb, n);
}
}
static inline int check_marker(void *logctx, GetBitContext *s, const char *msg)
{
int bit = get_bits1(s);
if (!bit)
av_log(logctx, AV_LOG_INFO, "Marker bit missing at %d of %d %s\n",
get_bits_count(s) - 1, s->size_in_bits, msg);
return bit;
}
static inline int init_get_bits_xe(GetBitContext *s, const uint8_t *buffer,
int bit_size, int is_le)
{
int buffer_size;
int ret = 0;
if (bit_size >= INT_MAX - FFMAX(7, AV_INPUT_BUFFER_PADDING_SIZE*8) || bit_size < 0 || !buffer) {
bit_size = 0;
buffer = NULL;
ret = AVERROR_INVALIDDATA;
}
buffer_size = (bit_size + 7) >> 3;
s->buffer = buffer;
s->size_in_bits = bit_size;
s->size_in_bits_plus8 = bit_size + 8;
s->buffer_end = buffer + buffer_size;
s->index = 0;
#if CACHED_BITSTREAM_READER
s->cache = 0;
s->bits_left = 0;
refill_64(s, is_le);
#endif
return ret;
}
/**
* Initialize GetBitContext.
* @param buffer bitstream buffer, must be AV_INPUT_BUFFER_PADDING_SIZE bytes
* larger than the actual read bits because some optimized bitstream
* readers read 32 or 64 bit at once and could read over the end
* @param bit_size the size of the buffer in bits
* @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
*/
static inline int init_get_bits(GetBitContext *s, const uint8_t *buffer,
int bit_size)
{
#ifdef BITSTREAM_READER_LE
return init_get_bits_xe(s, buffer, bit_size, 1);
#else
return init_get_bits_xe(s, buffer, bit_size, 0);
#endif
}
/**
* Initialize GetBitContext.
* @param buffer bitstream buffer, must be AV_INPUT_BUFFER_PADDING_SIZE bytes
* larger than the actual read bits because some optimized bitstream
* readers read 32 or 64 bit at once and could read over the end
* @param byte_size the size of the buffer in bytes
* @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
*/
static inline int init_get_bits8(GetBitContext *s, const uint8_t *buffer,
int byte_size)
{
if (byte_size > INT_MAX / 8 || byte_size < 0)
byte_size = -1;
return init_get_bits(s, buffer, byte_size * 8);
}
static inline int init_get_bits8_le(GetBitContext *s, const uint8_t *buffer,
int byte_size)
{
if (byte_size > INT_MAX / 8 || byte_size < 0)
byte_size = -1;
return init_get_bits_xe(s, buffer, byte_size * 8, 1);
}
static inline const uint8_t *align_get_bits(GetBitContext *s)
{
int n = -get_bits_count(s) & 7;
if (n)
skip_bits(s, n);
return s->buffer + (s->index >> 3);
}
/**
* If the vlc code is invalid and max_depth=1, then no bits will be removed.
* If the vlc code is invalid and max_depth>1, then the number of bits removed
* is undefined.
*/
#define GET_VLC(code, name, gb, table, bits, max_depth) \
do { \
int n, nb_bits; \
unsigned int index; \
\
index = SHOW_UBITS(name, gb, bits); \
code = table[index][0]; \
n = table[index][1]; \
\
if (max_depth > 1 && n < 0) { \
LAST_SKIP_BITS(name, gb, bits); \
UPDATE_CACHE(name, gb); \
\
nb_bits = -n; \
\
index = SHOW_UBITS(name, gb, nb_bits) + code; \
code = table[index][0]; \
n = table[index][1]; \
if (max_depth > 2 && n < 0) { \
LAST_SKIP_BITS(name, gb, nb_bits); \
UPDATE_CACHE(name, gb); \
\
nb_bits = -n; \
\
index = SHOW_UBITS(name, gb, nb_bits) + code; \
code = table[index][0]; \
n = table[index][1]; \
} \
} \
SKIP_BITS(name, gb, n); \
} while (0)
#define GET_RL_VLC(level, run, name, gb, table, bits, \
max_depth, need_update) \
do { \
int n, nb_bits; \
unsigned int index; \
\
index = SHOW_UBITS(name, gb, bits); \
level = table[index].level; \
n = table[index].len; \
\
if (max_depth > 1 && n < 0) { \
SKIP_BITS(name, gb, bits); \
if (need_update) { \
UPDATE_CACHE(name, gb); \
} \
\
nb_bits = -n; \
\
index = SHOW_UBITS(name, gb, nb_bits) + level; \
level = table[index].level; \
n = table[index].len; \
if (max_depth > 2 && n < 0) { \
LAST_SKIP_BITS(name, gb, nb_bits); \
if (need_update) { \
UPDATE_CACHE(name, gb); \
} \
nb_bits = -n; \
\
index = SHOW_UBITS(name, gb, nb_bits) + level; \
level = table[index].level; \
n = table[index].len; \
} \
} \
run = table[index].run; \
SKIP_BITS(name, gb, n); \
} while (0)
/* Return the LUT element for the given bitstream configuration. */
static inline int set_idx(GetBitContext *s, int code, int *n, int *nb_bits,
VLC_TYPE (*table)[2])
{
unsigned idx;
*nb_bits = -*n;
idx = show_bits(s, *nb_bits) + code;
*n = table[idx][1];
return table[idx][0];
}
/**
* Parse a vlc code.
* @param bits is the number of bits which will be read at once, must be
* identical to nb_bits in init_vlc()
* @param max_depth is the number of times bits bits must be read to completely
* read the longest vlc code
* = (max_vlc_length + bits - 1) / bits
* @returns the code parsed or -1 if no vlc matches
*/
static av_always_inline int get_vlc2(GetBitContext *s, VLC_TYPE (*table)[2],
int bits, int max_depth)
{
#if CACHED_BITSTREAM_READER
int nb_bits;
unsigned idx = show_bits(s, bits);
int code = table[idx][0];
int n = table[idx][1];
if (max_depth > 1 && n < 0) {
skip_remaining(s, bits);
code = set_idx(s, code, &n, &nb_bits, table);
if (max_depth > 2 && n < 0) {
skip_remaining(s, nb_bits);
code = set_idx(s, code, &n, &nb_bits, table);
}
}
skip_remaining(s, n);
return code;
#else
int code;
OPEN_READER(re, s);
UPDATE_CACHE(re, s);
GET_VLC(code, re, s, table, bits, max_depth);
CLOSE_READER(re, s);
return code;
#endif
}
static inline int decode012(GetBitContext *gb)
{
int n;
n = get_bits1(gb);
if (n == 0)
return 0;
else
return get_bits1(gb) + 1;
}
static inline int decode210(GetBitContext *gb)
{
if (get_bits1(gb))
return 0;
else
return 2 - get_bits1(gb);
}
static inline int get_bits_left(GetBitContext *gb)
{
return gb->size_in_bits - get_bits_count(gb);
}
static inline int skip_1stop_8data_bits(GetBitContext *gb)
{
if (get_bits_left(gb) <= 0)
return AVERROR_INVALIDDATA;
while (get_bits1(gb)) {
skip_bits(gb, 8);
if (get_bits_left(gb) <= 0)
return AVERROR_INVALIDDATA;
}
return 0;
}
#endif /* AVCODEC_GET_BITS_H */
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