static int decode_i_block(FourXContext *f, DCTELEM *block){
    int code, i, j, level, val;
    /* DC coef */
    val = get_vlc2(&f->pre_gb, f->pre_vlc.table, ACDC_VLC_BITS, 3);
    if (val>>4){
        av_log(f->avctx, AV_LOG_ERROR, "error dc run != 0\n");
    if(val)
        val = get_xbits(&f->gb, val);
    val = val * dequant_table[0] + f->last_dc;
    f->last_dc =
    block[0] = val;
    /* AC coefs */
    i = 1;
    for(;;) {
        code = get_vlc2(&f->pre_gb, f->pre_vlc.table, ACDC_VLC_BITS, 3);
        /* EOB */
        if (code == 0)
            break;
        if (code == 0xf0) {
            i += 16;
        } else {
            level = get_xbits(&f->gb, code & 0xf);
            i += code >> 4;
            if (i >= 64) {
                av_log(f->avctx, AV_LOG_ERROR, "run %d oveflow\n", i);
                return 0;
            j= ff_zigzag_direct[i];
            block[j] = level * dequant_table[j];
            i++;
            if (i >= 64)
                break;
    return 0;