static inline int mdec_decode_block_intra(MDECContext *a, int16_t *block, int n)

{

    int level, diff, i, j, run;

    int component;

    RLTable *rl = &ff_rl_mpeg1;

    uint8_t * const scantable = a->scantable.permutated;

    const uint16_t *quant_matrix = ff_mpeg1_default_intra_matrix;

    const int qscale = a->qscale;



    /* DC coefficient */

    if (a->version == 2) {

        block[0] = 2 * get_sbits(&a->gb, 10) + 1024;

    } else {

        component = (n <= 3 ? 0 : n - 4 + 1);

        diff = decode_dc(&a->gb, component);

        if (diff >= 0xffff)

            return AVERROR_INVALIDDATA;

        a->last_dc[component] += diff;

        block[0] = a->last_dc[component] << 3;

    }



    i = 0;

    {

        OPEN_READER(re, &a->gb);

        /* now quantify & encode AC coefficients */

        for (;;) {

            UPDATE_CACHE(re, &a->gb);

            GET_RL_VLC(level, run, re, &a->gb, rl->rl_vlc[0], TEX_VLC_BITS, 2, 0);



            if (level == 127) {

                break;

            } else if (level != 0) {

                i += run;

                if (i > 63) {

                    av_log(a->avctx, AV_LOG_ERROR,

                           "ac-tex damaged at %d %d\n", a->mb_x, a->mb_y);

                    return AVERROR_INVALIDDATA;

                }

                j     = scantable[i];

                level = (level * qscale * quant_matrix[j]) >> 3;

                level = (level ^ SHOW_SBITS(re, &a->gb, 1)) - SHOW_SBITS(re, &a->gb, 1);

                LAST_SKIP_BITS(re, &a->gb, 1);

            } else {

                /* escape */

                run = SHOW_UBITS(re, &a->gb, 6)+1; LAST_SKIP_BITS(re, &a->gb, 6);

                UPDATE_CACHE(re, &a->gb);

                level = SHOW_SBITS(re, &a->gb, 10); SKIP_BITS(re, &a->gb, 10);

                i += run;

                if (i > 63) {

                    av_log(a->avctx, AV_LOG_ERROR,

                           "ac-tex damaged at %d %d\n", a->mb_x, a->mb_y);

                    return AVERROR_INVALIDDATA;

                }

                j = scantable[i];

                if (level < 0) {

                    level = -level;

                    level = (level * qscale * quant_matrix[j]) >> 3;

                    level = (level - 1) | 1;

                    level = -level;

                } else {

                    level = (level * qscale * quant_matrix[j]) >> 3;

                    level = (level - 1) | 1;

                }

            }



            block[j] = level;

        }

        CLOSE_READER(re, &a->gb);

    }

    a->block_last_index[n] = i;

    return 0;

}
