static inline int mpeg2_fast_decode_block_intra(MpegEncContext *s, int16_t *block, int n)
{
    int level, dc, diff, j, run;
    int component;
    RLTable *rl;
    uint8_t * scantable = s->intra_scantable.permutated;
    const uint16_t *quant_matrix;
    const int qscale = s->qscale;

    /* DC coefficient */
    if (n < 4) {
        quant_matrix = s->intra_matrix;
        component = 0;
    } else {
        quant_matrix = s->chroma_intra_matrix;
        component = (n & 1) + 1;
    }
    diff = decode_dc(&s->gb, component);
    if (diff >= 0xffff)
        return -1;
    dc = s->last_dc[component];
    dc += diff;
    s->last_dc[component] = dc;
    block[0] = dc << (3 - s->intra_dc_precision);
    if (s->intra_vlc_format)
        rl = &ff_rl_mpeg2;
    else
        rl = &ff_rl_mpeg1;

    {
        OPEN_READER(re, &s->gb);
        /* now quantify & encode AC coefficients */
        for (;;) {
            UPDATE_CACHE(re, &s->gb);
            GET_RL_VLC(level, run, re, &s->gb, rl->rl_vlc[0], TEX_VLC_BITS, 2, 0);

            if (level >= 64) {
                break;
            } else if (level != 0) {
                scantable += run;
                j = *scantable;
                level = (level * qscale * quant_matrix[j]) >> 4;
                level = (level ^ SHOW_SBITS(re, &s->gb, 1)) - SHOW_SBITS(re, &s->gb, 1);
                LAST_SKIP_BITS(re, &s->gb, 1);
            } else {
                /* escape */
                run = SHOW_UBITS(re, &s->gb, 6) + 1; LAST_SKIP_BITS(re, &s->gb, 6);
                UPDATE_CACHE(re, &s->gb);
                level = SHOW_SBITS(re, &s->gb, 12); SKIP_BITS(re, &s->gb, 12);
                scantable += run;
                j = *scantable;
                if (level < 0) {
                    level = (-level * qscale * quant_matrix[j]) >> 4;
                    level = -level;
                } else {
                    level = (level * qscale * quant_matrix[j]) >> 4;
                }
            }

            block[j] = level;
        }
        CLOSE_READER(re, &s->gb);
    }

    s->block_last_index[n] = scantable - s->intra_scantable.permutated;
    return 0;
}