cabac.h

This the source release kit for the following system configuration(s): - AMD Alchemy(TM) DBAu1200(

/*
 * H.26L/H.264/AVC/JVT/14496-10/... encoder/decoder
 * Copyright (c) 2003 Michael Niedermayer <[e-mail]>
 *
 * 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 cabac.h
 * Context Adaptive Binary Arithmetic Coder.
 */



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

typedef struct CABACContext{
    int low;
    int range;
    int outstanding_count;
#ifdef STRICT_LIMITS
    int symCount;
#endif
    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];


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 inline void put_cabac_bit(CABACContext *c, int b){
    put_bits(&c->pb, 1, b);
    for(;c->outstanding_count; c->outstanding_count--){
        put_bits(&c->pb, 1, 1-b);
    }
}

static inline void renorm_cabac_encoder(CABACContext *c){
    while(c->range < 0x100){
        //FIXME optimize
        if(c->low<0x100){
            put_cabac_bit(c, 0);
        }else if(c->low<0x200){
            c->outstanding_count++;
            c->low -= 0x100;
        }else{
            put_cabac_bit(c, 1);
            c->low -= 0x200;
        }

        c->range+= c->range;
        c->low += c->low;
    }
}

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

    if(bit == ((*state)&1)){
        c->range -= RangeLPS;
        *state= ff_h264_mps_state[*state];
    }else{
        c->low += c->range - RangeLPS;
        c->range = RangeLPS;
        *state= ff_h264_lps_state[*state];
    }

    renorm_cabac_encoder(c);

#ifdef STRICT_LIMITS
    c->symCount++;
#endif
}

/**
 * @param bit 0 -> write zero bit, !=0 write one bit
 */
static void put_cabac_bypass(CABACContext *c, int bit){
    c->low += c->low;

    if(bit){
        c->low += c->range;
    }
//FIXME optimize
    if(c->low<0x200){
        put_cabac_bit(c, 0);
    }else if(c->low<0x400){
        c->outstanding_count++;
        c->low -= 0x200;
    }else{
        put_cabac_bit(c, 1);
        c->low -= 0x400;
    }

#ifdef STRICT_LIMITS
    c->symCount++;
#endif
}

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>>3);
}

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>>3);
}

static inline void renorm_cabac_decoder_once(CABACContext *c){
    //P3:675    athlon:476
    int shift= (uint32_t)(c->range - 0x100)>>31;
    c->range<<= shift;
    c->low  <<= shift;
    if(!(c->low & CABAC_MASK))
        refill(c);
}

static int always_inline get_cabac_inline(CABACContext *c, uint8_t * const state){
    //FIXME gcc generates duplicate load/stores for c->low and c->range
#define LOW          "0"
#define RANGE        "4"
#define BYTESTART   "12"
#define BYTE        "16"
#define BYTEEND     "20"
    int s = *state;
    int RangeLPS= ff_h264_lps_range[2*(c->range&0xC0) + s];
    int bit, lps_mask attribute_unused;

    c->range -= RangeLPS;
#ifndef BRANCHLESS_CABAC_DECODER
    if(c->low < (c->range<<17)){
        bit= s&1;
        *state= ff_h264_mps_state[s];
        renorm_cabac_decoder_once(c);
    }else{
        bit= ff_h264_norm_shift[RangeLPS];
        c->low -= (c->range<<17);
        *state= ff_h264_lps_state[s];
        c->range = RangeLPS<<bit;
        c->low <<= bit;
        bit= (s&1)^1;

        if(!(c->low & 0xFFFF)){
            refill2(c);
        }
    }
#else /* BRANCHLESS_CABAC_DECODER */
    lps_mask= ((c->range<<17) - c->low)>>31;

    c->low -= (c->range<<17) & 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);
#endif /* BRANCHLESS_CABAC_DECODER */
    return bit;
}

extern int __attribute((noinline)) get_cabac_noinline(CABACContext *c, uint8_t * const state);

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

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

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

    range= c->range<<17;
    if(c->low < range){
        return 0;
    }else{
        c->low -= range;
        return 1;
    }
}


static 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<<17;
    c->low -= range;
    mask= c->low >> 31;
    range &= mask;
    c->low += range;
    return (val^mask)-mask;
}

/**
 *
 * @return the number of bytes read or 0 if no end
 */
static int get_cabac_terminate(CABACContext *c){
    c->range -= 2;
    if(c->low < c->range<<17){
        renorm_cabac_decoder_once(c);
        return 0;
    }else{
        return c->bytestream - c->bytestream_start;
    }
}