FFmpeg/libavcodec/cabac.h

/*
 * H.26L/H.264/AVC/JVT/14496-10/... encoder/decoder
 * Copyright (c) 2003 Michael Niedermayer <michaelni@gmx.at>
 *
 * This file is part of Libav.
 *
 * Libav 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.
 *
 * Libav 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 Libav; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file
 * Context Adaptive Binary Arithmetic Coder.
 */

#ifndef AVCODEC_CABAC_H
#define AVCODEC_CABAC_H

#include <stddef.h>

#include "put_bits.h"

//#undef NDEBUG
#include <assert.h>

#define CABAC_BITS 16
#define CABAC_MASK ((1<<CABAC_BITS)-1)

typedef struct CABACContext{
    int low;
    int range;
    int outstanding_count;
    const uint8_t *bytestream_start;
    const uint8_t *bytestream;
    const uint8_t *bytestream_end;
    PutBitContext pb;
}CABACContext;

extern uint8_t ff_h264_mlps_state[4*64];
extern uint8_t ff_h264_lps_range[4*2*64];  ///< rangeTabLPS
extern uint8_t ff_h264_mps_state[2*64];     ///< transIdxMPS
extern uint8_t ff_h264_lps_state[2*64];     ///< transIdxLPS
extern const uint8_t ff_h264_norm_shift[512];

#if ARCH_X86
#   include "x86/cabac.h"
#endif

void ff_init_cabac_encoder(CABACContext *c, uint8_t *buf, int buf_size);
void ff_init_cabac_decoder(CABACContext *c, const uint8_t *buf, int buf_size);
void ff_init_cabac_states(CABACContext *c);


static void refill(CABACContext *c){
#if CABAC_BITS == 16
        c->low+= (c->bytestream[0]<<9) + (c->bytestream[1]<<1);
#else
        c->low+= c->bytestream[0]<<1;
#endif
    c->low -= CABAC_MASK;
    c->bytestream+= CABAC_BITS/8;
}

static inline void renorm_cabac_decoder_once(CABACContext *c){
    int shift= (uint32_t)(c->range - 0x100)>>31;
    c->range<<= shift;
    c->low  <<= shift;
    if(!(c->low & CABAC_MASK))
        refill(c);
}

#ifndef get_cabac_inline
static void refill2(CABACContext *c){
    int i, x;

    x= c->low ^ (c->low-1);
    i= 7 - ff_h264_norm_shift[x>>(CABAC_BITS-1)];

    x= -CABAC_MASK;

#if CABAC_BITS == 16
        x+= (c->bytestream[0]<<9) + (c->bytestream[1]<<1);
#else
        x+= c->bytestream[0]<<1;
#endif

    c->low += x<<i;
    c->bytestream+= CABAC_BITS/8;
}

static av_always_inline int get_cabac_inline(CABACContext *c, uint8_t * const state){
    int s = *state;
    int RangeLPS= ff_h264_lps_range[2*(c->range&0xC0) + s];
    int bit, lps_mask;

    c->range -= RangeLPS;
    lps_mask= ((c->range<<(CABAC_BITS+1)) - c->low)>>31;

    c->low -= (c->range<<(CABAC_BITS+1)) & lps_mask;
    c->range += (RangeLPS - c->range) & lps_mask;

    s^=lps_mask;
    *state= (ff_h264_mlps_state+128)[s];
    bit= s&1;

    lps_mask= ff_h264_norm_shift[c->range];
    c->range<<= lps_mask;
    c->low  <<= lps_mask;
    if(!(c->low & CABAC_MASK))
        refill2(c);
    return bit;
}
#endif

static int av_noinline av_unused get_cabac_noinline(CABACContext *c, uint8_t * const state){
    return get_cabac_inline(c,state);
}

static int av_unused get_cabac(CABACContext *c, uint8_t * const state){
    return get_cabac_inline(c,state);
}

static int av_unused get_cabac_bypass(CABACContext *c){
    int range;
    c->low += c->low;

    if(!(c->low & CABAC_MASK))
        refill(c);

    range= c->range<<(CABAC_BITS+1);
    if(c->low < range){
        return 0;
    }else{
        c->low -= range;
        return 1;
    }
}


#ifndef get_cabac_bypass_sign
static av_always_inline int get_cabac_bypass_sign(CABACContext *c, int val){
    int range, mask;
    c->low += c->low;

    if(!(c->low & CABAC_MASK))
        refill(c);

    range= c->range<<(CABAC_BITS+1);
    c->low -= range;
    mask= c->low >> 31;
    range &= mask;
    c->low += range;
    return (val^mask)-mask;
}
#endif

/**
 *
 * @return the number of bytes read or 0 if no end
 */
static int av_unused get_cabac_terminate(CABACContext *c){
    c->range -= 2;
    if(c->low < c->range<<(CABAC_BITS+1)){
        renorm_cabac_decoder_once(c);
        return 0;
    }else{
        return c->bytestream - c->bytestream_start;
    }
}

#endif /* AVCODEC_CABAC_H */