if (s->first_gob_line && ((n < 2) || (n > 3))) c = 1024;
void h263_pred_acdc(MpegEncContext * s, INT16 *block, int n){    int x, y, wrap, a, c, pred_dc, scale, i;    INT16 *dc_val, *ac_val, *ac_val1;    /* find prediction */    if (n < 4) {        x = 2 * s->mb_x + 1 + (n & 1);        y = 2 * s->mb_y + 1 + ((n & 2) >> 1);        wrap = s->mb_width * 2 + 2;        dc_val = s->dc_val[0];        ac_val = s->ac_val[0][0];        scale = s->y_dc_scale;    } else {        x = s->mb_x + 1;        y = s->mb_y + 1;        wrap = s->mb_width + 2;        dc_val = s->dc_val[n - 4 + 1];        ac_val = s->ac_val[n - 4 + 1][0];        scale = s->c_dc_scale;    }        ac_val += ((y) * wrap + (x)) * 16;    ac_val1 = ac_val;        /* B C     * A X      */    a = dc_val[(x - 1) + (y) * wrap];    c = dc_val[(x) + (y - 1) * wrap];        pred_dc = 1024;    if (s->ac_pred) {        if (s->h263_aic_dir) {            /* left prediction */            if (a != 1024) {                ac_val -= 16;                for(i=1;i<8;i++) {                    block[block_permute_op(i*8)] += ac_val[i];                }                pred_dc = a;            }        } else {            /* top prediction */            if (c != 1024) {                ac_val -= 16 * wrap;                for(i=1;i<8;i++) {                    block[block_permute_op(i)] += ac_val[i + 8];                }                pred_dc = c;            }        }    } else {        /* just DC prediction */        if (a != 1024 && c != 1024)            pred_dc = (a + c) >> 1;        else if (a != 1024)            pred_dc = a;        else            pred_dc = c;    }        /* we assume pred is positive */    block[0]=block[0]*scale + pred_dc;        if (block[0] < 0)        block[0] = 0;    else if (!(block[0] & 1))        block[0]++;        /* Update AC/DC tables */    dc_val[(x) + (y) * wrap] = block[0];        /* left copy */    for(i=1;i<8;i++)        ac_val1[i] = block[block_permute_op(i * 8)];    /* top copy */    for(i=1;i<8;i++)        ac_val1[8 + i] = block[block_permute_op(i)];}