cabac.c

另一个版本的x264的decoder

     0, 0, 1, 2, 2, 4, 4, 5, 6, 7, 8, 9, 9,11,11,12,
    13,13,15,15,16,16,18,18,19,19,21,21,22,22,23,24,
    24,25,26,26,27,27,28,29,29,30,30,30,31,32,32,33,
    33,33,34,34,35,35,35,36,36,36,37,37,37,38,38,63
};
static const int x264_transition_mps[64] =
{
     1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12,13,14,15,16,
    17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,
    33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,
    49,50,51,52,53,54,55,56,57,58,59,60,61,62,62,63,
};

#define FIX8(f) ((int)(f*(1<<8)))
static int x264_cabac_probability[128] =
{
    FIX8(0.9812), FIX8(0.9802), FIX8(0.9792), FIX8(0.9781),
    FIX8(0.9769), FIX8(0.9757), FIX8(0.9744), FIX8(0.9730),
    FIX8(0.9716), FIX8(0.9700), FIX8(0.9684), FIX8(0.9667),
    FIX8(0.9650), FIX8(0.9631), FIX8(0.9611), FIX8(0.9590),
    FIX8(0.9568), FIX8(0.9545), FIX8(0.9521), FIX8(0.9495),
    FIX8(0.9468), FIX8(0.9440), FIX8(0.9410), FIX8(0.9378),
    FIX8(0.9345), FIX8(0.9310), FIX8(0.9273), FIX8(0.9234),
    FIX8(0.9193), FIX8(0.9150), FIX8(0.9105), FIX8(0.9057),
    FIX8(0.9006), FIX8(0.8953), FIX8(0.8897), FIX8(0.8838),
    FIX8(0.8776), FIX8(0.8710), FIX8(0.8641), FIX8(0.8569),
    FIX8(0.8492), FIX8(0.8411), FIX8(0.8326), FIX8(0.8237),
    FIX8(0.8143), FIX8(0.8043), FIX8(0.7938), FIX8(0.7828),
    FIX8(0.7712), FIX8(0.7590), FIX8(0.7461), FIX8(0.7325),
    FIX8(0.7182), FIX8(0.7031), FIX8(0.6872), FIX8(0.6705),
    FIX8(0.6528), FIX8(0.6343), FIX8(0.6147), FIX8(0.5941),
    FIX8(0.5724), FIX8(0.5495), FIX8(0.5254), FIX8(0.5000),
    FIX8(0.5000), FIX8(0.4746), FIX8(0.4505), FIX8(0.4276),
    FIX8(0.4059), FIX8(0.3853), FIX8(0.3657), FIX8(0.3472),
    FIX8(0.3295), FIX8(0.3128), FIX8(0.2969), FIX8(0.2818),
    FIX8(0.2675), FIX8(0.2539), FIX8(0.2410), FIX8(0.2288),
    FIX8(0.2172), FIX8(0.2062), FIX8(0.1957), FIX8(0.1857),
    FIX8(0.1763), FIX8(0.1674), FIX8(0.1589), FIX8(0.1508),
    FIX8(0.1431), FIX8(0.1359), FIX8(0.1290), FIX8(0.1224),
    FIX8(0.1162), FIX8(0.1103), FIX8(0.1047), FIX8(0.0994),
    FIX8(0.0943), FIX8(0.0895), FIX8(0.0850), FIX8(0.0807),
    FIX8(0.0766), FIX8(0.0727), FIX8(0.0690), FIX8(0.0655),
    FIX8(0.0622), FIX8(0.0590), FIX8(0.0560), FIX8(0.0532),
    FIX8(0.0505), FIX8(0.0479), FIX8(0.0455), FIX8(0.0432),
    FIX8(0.0410), FIX8(0.0389), FIX8(0.0369), FIX8(0.0350),
    FIX8(0.0333), FIX8(0.0316), FIX8(0.0300), FIX8(0.0284),
    FIX8(0.0270), FIX8(0.0256), FIX8(0.0243), FIX8(0.0231),
    FIX8(0.0219), FIX8(0.0208), FIX8(0.0198), FIX8(0.0187)
};
/* -ln2(probability) */
static int x264_cabac_entropy[128] =
{
    FIX8(0.0273), FIX8(0.0288), FIX8(0.0303), FIX8(0.0320),
    FIX8(0.0337), FIX8(0.0355), FIX8(0.0375), FIX8(0.0395),
    FIX8(0.0416), FIX8(0.0439), FIX8(0.0463), FIX8(0.0488),
    FIX8(0.0515), FIX8(0.0543), FIX8(0.0572), FIX8(0.0604),
    FIX8(0.0637), FIX8(0.0671), FIX8(0.0708), FIX8(0.0747),
    FIX8(0.0788), FIX8(0.0832), FIX8(0.0878), FIX8(0.0926),
    FIX8(0.0977), FIX8(0.1032), FIX8(0.1089), FIX8(0.1149),
    FIX8(0.1214), FIX8(0.1282), FIX8(0.1353), FIX8(0.1429),
    FIX8(0.1510), FIX8(0.1596), FIX8(0.1686), FIX8(0.1782),
    FIX8(0.1884), FIX8(0.1992), FIX8(0.2107), FIX8(0.2229),
    FIX8(0.2358), FIX8(0.2496), FIX8(0.2642), FIX8(0.2798),
    FIX8(0.2964), FIX8(0.3142), FIX8(0.3331), FIX8(0.3532),
    FIX8(0.3748), FIX8(0.3979), FIX8(0.4226), FIX8(0.4491),
    FIX8(0.4776), FIX8(0.5082), FIX8(0.5412), FIX8(0.5768),
    FIX8(0.6152), FIX8(0.6568), FIX8(0.7020), FIX8(0.7513),
    FIX8(0.8050), FIX8(0.8638), FIX8(0.9285), FIX8(1.0000),
    FIX8(1.0000), FIX8(1.0752), FIX8(1.1504), FIX8(1.2256),
    FIX8(1.3008), FIX8(1.3759), FIX8(1.4511), FIX8(1.5263),
    FIX8(1.6015), FIX8(1.6767), FIX8(1.7519), FIX8(1.8271),
    FIX8(1.9023), FIX8(1.9775), FIX8(2.0527), FIX8(2.1278),
    FIX8(2.2030), FIX8(2.2782), FIX8(2.3534), FIX8(2.4286),
    FIX8(2.5038), FIX8(2.5790), FIX8(2.6542), FIX8(2.7294),
    FIX8(2.8046), FIX8(2.8797), FIX8(2.9549), FIX8(3.0301),
    FIX8(3.1053), FIX8(3.1805), FIX8(3.2557), FIX8(3.3309),
    FIX8(3.4061), FIX8(3.4813), FIX8(3.5565), FIX8(3.6316),
    FIX8(3.7068), FIX8(3.7820), FIX8(3.8572), FIX8(3.9324),
    FIX8(4.0076), FIX8(4.0828), FIX8(4.1580), FIX8(4.2332),
    FIX8(4.3083), FIX8(4.3836), FIX8(4.4588), FIX8(4.5339),
    FIX8(4.6091), FIX8(4.6843), FIX8(4.7595), FIX8(4.8347),
    FIX8(4.9099), FIX8(4.9851), FIX8(5.0602), FIX8(5.1354),
    FIX8(5.2106), FIX8(5.2859), FIX8(5.3610), FIX8(5.4362),
    FIX8(5.5114), FIX8(5.5866), FIX8(5.6618), FIX8(5.7370)
};

#undef FIX8


/*****************************************************************************
 *
 *****************************************************************************/
void x264_cabac_context_init( x264_cabac_t *cb, int i_slice_type, int i_qp, int i_model )
{
    const int (*cabac_context_init)[399][2];
    int i;

    if( i_slice_type == SLICE_TYPE_I )
    {
        cabac_context_init = &x264_cabac_context_init_I;
    }
    else
    {
        cabac_context_init = &x264_cabac_context_init_PB[i_model];
    }

    for( i = 0; i < 399; i++ )
    {
        int i_pre_state;

        i_pre_state = x264_clip3( (((*cabac_context_init)[i][0] * i_qp) >> 4) + (*cabac_context_init)[i][1], 1, 126 );
        if( i_pre_state <= 63 )
        {
            cb->ctxstate[i].i_state = 63 - i_pre_state;
            cb->ctxstate[i].i_mps = 0;
        }
        else
        {
            cb->ctxstate[i].i_state = i_pre_state - 64;
            cb->ctxstate[i].i_mps = 1;
        }
        cb->ctxstate[i].i_count = 0;
    }
}

/*****************************************************************************
 *
 *****************************************************************************/
void x264_cabac_decode_init( x264_cabac_t *cb, bs_t *s )
{
    cb->i_range = 0x01fe;
    cb->i_low   = bs_read( s, 9 );
    cb->s       = s;
}

static inline void x264_cabac_decode_renorm( x264_cabac_t *cb )
{

	//printf(" \nbefore renorm  %d  %d",*cb->s->p,cb->s->i_left);

    while( cb->i_range < 0x0100 )
    {
        cb->i_range <<= 1;
        cb->i_low   = ( cb->i_low << 1 )|bs_read( cb->s, 1 );
    }
	//printf(" \nafter renorm  %d  %d",*cb->s->p,cb->s->i_left);
}

/*static inline void x264_cabac_decode_renorm( x264_cabac_t *cb )
{
    while( cb->i_range < 0x0100 )
    {
        cb->i_range <<= 1;
		if (--cb->s->i_left< 0) 
			{
			//	get_byte();   
			cb->s->p = cb->s->p_start++;
			cb->s->i_left = 7;
			}		
	
		cb->i_low = (cb->i_low << 1) | (((*cb->s->p)>>(cb->s->i_left)) & 0x01);
		
    	}
}*/



int  x264_cabac_decode_decision( x264_cabac_t *cb, int i_ctx )
{
    int i_state = cb->ctxstate[i_ctx].i_state;
    int i_mps   = cb->ctxstate[i_ctx].i_mps;
		int count = cb->ctxstate[i_ctx].i_count;
	
    int i_range_lps = x264_cabac_range_lps[i_state][(cb->i_range>>6)&0x03];

    int val;
	//	printf("\n count %d", count); 


    cb->i_range -= i_range_lps;

    if( cb->i_low >= cb->i_range )
    {
        val = 1 - i_mps;

        cb->i_low -= cb->i_range;
        cb->i_range= i_range_lps;

        if( i_state == 0 )
        {
            cb->ctxstate[i_ctx].i_mps ^= 0x01;
        }
        cb->ctxstate[i_ctx].i_state = x264_transition_lps[i_state];
    }
    else
    {
        val = i_mps;

        cb->ctxstate[i_ctx].i_state = x264_transition_mps[i_state];
    }
	//printf("\n before renorm %d  %d",cb->s->i_left,*cb->s->p);

    x264_cabac_decode_renorm( cb );
	//printf("\n after renorm %d  %d",cb->s->i_left,*cb->s->p);

    return val;
}
int  x264_cabac_decode_bypass( x264_cabac_t *cb )
{
    cb->i_low = (cb->i_low << 1)|bs_read( cb->s, 1 );

    if( cb->i_low >= cb->i_range )
    {
        cb->i_low -= cb->i_range;
        return 1;
    }
    return 0;
}
int  x264_cabac_decode_terminal( x264_cabac_t *cb )
{
    if( cb->i_low >= cb->i_range - 2 )
    {
        return 1;
    }

    cb->i_range -= 2;
    x264_cabac_decode_renorm( cb );
    return 0;
}

void x264_cabac_model_init( x264_cabac_t *cb )
{
    int i;

    for( i = 0; i < 3; i++ )
    {
        cb->slice[i].i_model = 0;
        cb->slice[i].i_cost  = -1;
    }
}

int  x264_cabac_model_get ( x264_cabac_t *cb, int i_slice_type )
{
    return cb->slice[i_slice_type].i_model;
}

void x264_cabac_model_update( x264_cabac_t *cb, int i_slice_type, int i_qp )
{
    int i;

    if( i_slice_type == SLICE_TYPE_I )
    {
        return;
    }
    cb->slice[i_slice_type].i_cost = -1;

    for( i = 0; i < 3; i++ )
    {
        int i_ctx;
        int i_cost;

        i_cost = 0; /* fix8 */

        for( i_ctx = 0; i_ctx < 399; i_ctx++ )
        {
            int i_weight;
            int i_model_state;
            int i_ctx_state;

            i_weight = X264_MIN( (1<<8), (cb->ctxstate[i_ctx].i_count<<8) / 32 );
            i_model_state = x264_clip3( ((x264_cabac_context_init_PB[i][i_ctx][0] * i_qp)>>4) +
                                          x264_cabac_context_init_PB[i][i_ctx][1], 0, 127 );
            i_ctx_state   = cb->ctxstate[i_ctx].i_mps ? 64 + cb->ctxstate[i_ctx].i_state : 63 - cb->ctxstate[i_ctx].i_state;

            i_cost += (i_weight * (( x264_cabac_probability[      i_ctx_state] * x264_cabac_entropy[      i_model_state] +
                                     x264_cabac_probability[127 - i_ctx_state] * x264_cabac_entropy[127 - i_model_state] ) >> 8))>>8;
        }

        if( cb->slice[i_slice_type].i_cost == -1 || cb->slice[i_slice_type].i_cost > i_cost )
        {
            cb->slice[i_slice_type].i_model= i;
            cb->slice[i_slice_type].i_cost = i_cost;
        }
    }
}


static inline void x264_cabac_putbit( x264_cabac_t *cb, int b )
{
    if( cb->b_first_bit )
    {
        cb->b_first_bit = 0;
    }
    else
    {
        bs_write1( cb->s, b );
    }

    while( cb->i_bits_outstanding > 0 )
    {
        bs_write1( cb->s, 1 - b );
        cb->i_bits_outstanding--;
    }
}


/*****************************************************************************
 *
 *****************************************************************************/