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FFmpeg/libavcodec/get_bits.h
Andreas Cadhalpun 713654d9d3 get_bits: add get_bitsz for reading 0-25 bits 
This can be used to simplify code in a couple of places.

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
2016-01-03 21:12:43 +01:00

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/*
* copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
*
* 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 "mathops.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
typedef struct GetBitContext {
const uint8_t *buffer, *buffer_end;
int index;
int size_in_bits;
int size_in_bits_plus8;
} GetBitContext;
#define VLC_TYPE int16_t
typedef struct VLC {
int bits;
VLC_TYPE (*table)[2]; ///< code, bits
int table_size, table_allocated;
} VLC;
typedef struct RL_VLC_ELEM {
int16_t level;
int8_t len;
uint8_t run;
} RL_VLC_ELEM;
/* 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 bit (FIXME 64bit).
*
* 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.
*/
#ifdef LONG_BITSTREAM_READER
# define MIN_CACHE_BITS 32
#else
# define MIN_CACHE_BITS 25
#endif
#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)
static inline int get_bits_count(const GetBitContext *s)
{
return s->index;
}
static inline void skip_bits_long(GetBitContext *s, int n)
{
#if UNCHECKED_BITSTREAM_READER
s->index += n;
#else
s->index += av_clip(n, -s->index, s->size_in_bits_plus8 - s->index);
#endif
}
/**
* read mpeg1 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)
{
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;
}
static inline int get_sbits(GetBitContext *s, int n)
{
register int tmp;
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);
return tmp;
}
/**
* Read 1-25 bits.
*/
static inline unsigned int get_bits(GetBitContext *s, int n)
{
register int tmp;
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);
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)
{
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;
}
/**
* Show 1-25 bits.
*/
static inline unsigned int show_bits(GetBitContext *s, int n)
{
register int tmp;
OPEN_READER_NOSIZE(re, s);
av_assert2(n>0 && n<=25);
UPDATE_CACHE(re, s);
tmp = SHOW_UBITS(re, s, n);
return tmp;
}
static inline void skip_bits(GetBitContext *s, int n)
{
OPEN_READER(re, s);
LAST_SKIP_BITS(re, s, n);
CLOSE_READER(re, s);
}
static inline unsigned int get_bits1(GetBitContext *s)
{
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;
}
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)
{
if (!n) {
return 0;
} 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
}
}
/**
* 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)
{
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(GetBitContext *s, const char *msg)
{
int bit = get_bits1(s);
if (!bit)
av_log(NULL, AV_LOG_INFO, "Marker bit missing at %d of %d %s\n", get_bits_count(s) - 1, s->size_in_bits, msg);
return bit;
}
/**
* 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)
{
int buffer_size;
int ret = 0;
if (bit_size >= INT_MAX - 7 || 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;
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 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 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);
}
#define init_vlc(vlc, nb_bits, nb_codes, \
bits, bits_wrap, bits_size, \
codes, codes_wrap, codes_size, \
flags) \
ff_init_vlc_sparse(vlc, nb_bits, nb_codes, \
bits, bits_wrap, bits_size, \
codes, codes_wrap, codes_size, \
NULL, 0, 0, flags)
int ff_init_vlc_sparse(VLC *vlc, int nb_bits, int nb_codes,
const void *bits, int bits_wrap, int bits_size,
const void *codes, int codes_wrap, int codes_size,
const void *symbols, int symbols_wrap, int symbols_size,
int flags);
void ff_free_vlc(VLC *vlc);
#define INIT_VLC_LE 2
#define INIT_VLC_USE_NEW_STATIC 4
#define INIT_VLC_STATIC(vlc, bits, a, b, c, d, e, f, g, static_size) \
do { \
static VLC_TYPE table[static_size][2]; \
(vlc)->table = table; \
(vlc)->table_allocated = static_size; \
init_vlc(vlc, bits, a, b, c, d, e, f, g, INIT_VLC_USE_NEW_STATIC); \
} while (0)
/**
* 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_INTERNAL(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)
/**
* 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
*/
static av_always_inline int get_vlc2(GetBitContext *s, VLC_TYPE (*table)[2],
int bits, int max_depth)
{
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;
}
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;
}
//#define TRACE
#ifdef TRACE
static inline void print_bin(int bits, int n)
{
int i;
for (i = n - 1; i >= 0; i--)
av_log(NULL, AV_LOG_DEBUG, "%d", (bits >> i) & 1);
for (i = n; i < 24; i++)
av_log(NULL, AV_LOG_DEBUG, " ");
}
static inline int get_bits_trace(GetBitContext *s, int n, const char *file,
const char *func, int line)
{
int r = get_bits(s, n);
print_bin(r, n);
av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d bit @%5d in %s %s:%d\n",
r, n, r, get_bits_count(s) - n, file, func, line);
return r;
}
static inline int get_vlc_trace(GetBitContext *s, VLC_TYPE (*table)[2],
int bits, int max_depth, const char *file,
const char *func, int line)
{
int show = show_bits(s, 24);
int pos = get_bits_count(s);
int r = get_vlc2(s, table, bits, max_depth);
int len = get_bits_count(s) - pos;
int bits2 = show >> (24 - len);
print_bin(bits2, len);
av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d vlc @%5d in %s %s:%d\n",
bits2, len, r, pos, file, func, line);
return r;
}
#define GET_RL_VLC(level, run, name, gb, table, bits, \
max_depth, need_update) \
do { \
int show = SHOW_UBITS(name, gb, 24); \
int len; \
int pos = name ## _index; \
\
GET_RL_VLC_INTERNAL(level, run, name, gb, table, bits,max_depth, need_update); \
\
len = name ## _index - pos + 1; \
show = show >> (24 - len); \
\
print_bin(show, len); \
\
av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d/%-3d rlv @%5d in %s %s:%d\n",\
show, len, run-1, level, pos, __FILE__, __PRETTY_FUNCTION__, __LINE__);\
} while (0) \
static inline int get_xbits_trace(GetBitContext *s, int n, const char *file,
const char *func, int line)
{
int show = show_bits(s, n);
int r = get_xbits(s, n);
print_bin(show, n);
av_log(NULL, AV_LOG_DEBUG, "%5d %2d %3d xbt @%5d in %s %s:%d\n",
show, n, r, get_bits_count(s) - n, file, func, line);
return r;
}
#define get_bits(s, n) get_bits_trace(s , n, __FILE__, __PRETTY_FUNCTION__, __LINE__)
#define get_bits1(s) get_bits_trace(s, 1, __FILE__, __PRETTY_FUNCTION__, __LINE__)
#define get_xbits(s, n) get_xbits_trace(s, n, __FILE__, __PRETTY_FUNCTION__, __LINE__)
#define get_vlc(s, vlc) get_vlc_trace(s, (vlc)->table, (vlc)->bits, 3, __FILE__, __PRETTY_FUNCTION__, __LINE__)
#define get_vlc2(s, tab, bits, max) get_vlc_trace(s, tab, bits, max, __FILE__, __PRETTY_FUNCTION__, __LINE__)
#else //TRACE
#define GET_RL_VLC GET_RL_VLC_INTERNAL
#endif
#endif /* AVCODEC_GET_BITS_H */
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