libavcodec/get_bits.h

Go to the documentation of this file.

/*
 * 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
 */

#ifndef AVCODEC_GET_BITS_H
#define AVCODEC_GET_BITS_H

#include <stdint.h>
#include <stdlib.h>
#include <assert.h>
#include "libavutil/bswap.h"
#include "libavutil/common.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/log.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

/* bit input */
/* buffer, buffer_end and size_in_bits must be present and used by every reader */
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]; 
    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)
    loads gb into local variables

CLOSE_READER(name, gb)
    stores local vars in gb

UPDATE_CACHE(name, gb)
    refills 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_CACHE(name, gb, num)
    will remove the next num bits from the cache if it is needed for UPDATE_CACHE otherwise it will do nothing

LAST_SKIP_BITS(name, gb, num)
    is equivalent to LAST_SKIP_CACHE; SKIP_COUNTER

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(name, gb)                \
    unsigned int name##_index = (gb)->index;    \
    av_unused unsigned int name##_cache

#   define CLOSE_READER(name, gb) (gb)->index = name##_index

# ifdef ALT_BITSTREAM_READER_LE
# ifdef LONG_BITSTREAM_READER
#   define UPDATE_CACHE(name, gb) \
    name##_cache = AV_RL64((gb)->buffer+(name##_index>>3)) >> (name##_index&0x07)
# else
#   define UPDATE_CACHE(name, gb) \
    name##_cache = AV_RL32(((const uint8_t *)(gb)->buffer)+(name##_index>>3)) >> (name##_index&0x07)
# endif

#   define SKIP_CACHE(name, gb, num) name##_cache >>= (num)
# else
# ifdef LONG_BITSTREAM_READER
#   define UPDATE_CACHE(name, gb) \
    name##_cache = AV_RB64((gb)->buffer+(name##_index >> 3)) >> (32 - (name##_index & 0x07))
# else
#   define UPDATE_CACHE(name, gb) \
    name##_cache = AV_RB32(((const uint8_t *)(gb)->buffer)+(name##_index>>3)) << (name##_index&0x07)
# endif

#   define SKIP_CACHE(name, gb, num) name##_cache <<= (num)
# endif

// FIXME name?
#if UNCHECKED_BITSTREAM_READER
#   define SKIP_COUNTER(name, gb, num) name##_index += (num)
#else
#   define SKIP_COUNTER(name, gb, num) \
    name##_index = FFMIN((gb)->size_in_bits_plus8, name##_index + (num))
#endif

#   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 LAST_SKIP_CACHE(name, gb, num)

# ifdef ALT_BITSTREAM_READER_LE
#   define SHOW_UBITS(name, gb, num) zero_extend(name##_cache, num)

#   define SHOW_SBITS(name, gb, num) sign_extend(name##_cache, num)
# else
#   define SHOW_UBITS(name, gb, num) NEG_USR32(name##_cache, num)

#   define SHOW_SBITS(name, gb, num) NEG_SSR32(name##_cache, 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
}

static inline int get_xbits(GetBitContext *s, int n){
    register int sign;
    register int32_t cache;
    OPEN_READER(re, s);
    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);
    UPDATE_CACHE(re, s);
    tmp = SHOW_SBITS(re, s, n);
    LAST_SKIP_BITS(re, s, n);
    CLOSE_READER(re, s);
    return tmp;
}

static inline unsigned int get_bits(GetBitContext *s, int n){
    register int tmp;
    OPEN_READER(re, s);
    UPDATE_CACHE(re, s);
    tmp = SHOW_UBITS(re, s, n);
    LAST_SKIP_BITS(re, s, n);
    CLOSE_READER(re, s);
    return tmp;
}

static inline unsigned int show_bits(GetBitContext *s, int n){
    register int tmp;
    OPEN_READER(re, s);
    UPDATE_CACHE(re, s);
    tmp = SHOW_UBITS(re, s, n);
    return tmp;
}

static inline void skip_bits(GetBitContext *s, int n){
 //Note gcc seems to optimize this to s->index+=n for the ALT_READER :))
    OPEN_READER(re, s);
    UPDATE_CACHE(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 ALT_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);
}

static inline unsigned int get_bits_long(GetBitContext *s, int n){
    if (n <= MIN_CACHE_BITS) return get_bits(s, n);
    else {
#ifdef ALT_BITSTREAM_READER_LE
        int ret = get_bits(s, 16);
        return ret | (get_bits(s, n-16) << 16);
#else
        int ret = get_bits(s, 16) << (n-16);
        return ret | get_bits(s, n-16);
#endif
    }
}

static inline int get_sbits_long(GetBitContext *s, int n) {
    return sign_extend(get_bits_long(s, n), n);
}

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 %s\n", msg);

    return bit;
}

static inline void init_get_bits(GetBitContext *s,
                   const uint8_t *buffer, int bit_size)
{
    int buffer_size = (bit_size+7)>>3;
    if (buffer_size < 0 || bit_size < 0) {
        buffer_size = bit_size = 0;
        buffer = NULL;
    }

    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;
}

static inline void align_get_bits(GetBitContext *s)
{
    int n = -get_bits_count(s) & 7;
    if (n) skip_bits(s, n);
}

#define init_vlc(vlc, nb_bits, nb_codes,                \
                 bits, bits_wrap, bits_size,            \
                 codes, codes_wrap, codes_size,         \
                 flags)                                 \
        init_vlc_sparse(vlc, nb_bits, nb_codes,         \
                        bits, bits_wrap, bits_size,     \
                        codes, codes_wrap, codes_size,  \
                        NULL, 0, 0, flags)

int 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);
#define INIT_VLC_LE         2
#define INIT_VLC_USE_NEW_STATIC 4
void free_vlc(VLC *vlc);

#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)


#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;                                   \
        }                                                               \
        run = table[index].run;                                         \
        SKIP_BITS(name, gb, n);                                         \
    } while (0)


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);
}

//#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, 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, 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;
}
static inline int get_xbits_trace(GetBitContext *s, int n, 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__)

#define tprintf(p, ...) av_log(p, AV_LOG_DEBUG, __VA_ARGS__)

#else //TRACE
#define tprintf(p, ...) {}
#endif

#endif /* AVCODEC_GET_BITS_H */

---