static int decode_plane(UtvideoContext *c, int plane_no,
                        uint8_t *dst, int step, int stride,
                        int width, int height,
                        const uint8_t *src, int use_pred)
{
    int i, j, slice, pix;
    int sstart, send;
    VLC vlc;
    GetBitContext gb;
    int prev, fsym;
    const int cmask = ~(!plane_no && c->avctx->pix_fmt == AV_PIX_FMT_YUV420P);

    if (build_huff(src, &vlc, &fsym)) {
        av_log(c->avctx, AV_LOG_ERROR, "Cannot build Huffman codes\n");
        return AVERROR_INVALIDDATA;
    }
    if (fsym >= 0) { // build_huff reported a symbol to fill slices with
        send = 0;
        for (slice = 0; slice < c->slices; slice++) {
            uint8_t *dest;

            sstart = send;
            send   = (height * (slice + 1) / c->slices) & cmask;
            dest   = dst + sstart * stride;

            prev = 0x80;
            for (j = sstart; j < send; j++) {
                for (i = 0; i < width * step; i += step) {
                    pix = fsym;
                    if (use_pred) {
                        prev += pix;
                        pix   = prev;
                    }
                    dest[i] = pix;
                }
                dest += stride;
            }
        }
        return 0;
    }

    src      += 256;

    send = 0;
    for (slice = 0; slice < c->slices; slice++) {
        uint8_t *dest;
        int slice_data_start, slice_data_end, slice_size;

        sstart = send;
        send   = (height * (slice + 1) / c->slices) & cmask;
        dest   = dst + sstart * stride;

        // slice offset and size validation was done earlier
        slice_data_start = slice ? AV_RL32(src + slice * 4 - 4) : 0;
        slice_data_end   = AV_RL32(src + slice * 4);
        slice_size       = slice_data_end - slice_data_start;

        if (!slice_size) {
            av_log(c->avctx, AV_LOG_ERROR, "Plane has more than one symbol "
                   "yet a slice has a length of zero.\n");
            goto fail;
        }

        memcpy(c->slice_bits, src + slice_data_start + c->slices * 4,
               slice_size);
        memset(c->slice_bits + slice_size, 0, AV_INPUT_BUFFER_PADDING_SIZE);
        c->bdsp.bswap_buf((uint32_t *) c->slice_bits,
                          (uint32_t *) c->slice_bits,
                          (slice_data_end - slice_data_start + 3) >> 2);
        init_get_bits(&gb, c->slice_bits, slice_size * 8);

        prev = 0x80;
        for (j = sstart; j < send; j++) {
            for (i = 0; i < width * step; i += step) {
                if (get_bits_left(&gb) <= 0) {
                    av_log(c->avctx, AV_LOG_ERROR,
                           "Slice decoding ran out of bits\n");
                    goto fail;
                }
                pix = get_vlc2(&gb, vlc.table, vlc.bits, 3);
                if (pix < 0) {
                    av_log(c->avctx, AV_LOG_ERROR, "Decoding error\n");
                    goto fail;
                }
                if (use_pred) {
                    prev += pix;
                    pix   = prev;
                }
                dest[i] = pix;
            }
            dest += stride;
        }
        if (get_bits_left(&gb) > 32)
            av_log(c->avctx, AV_LOG_WARNING,
                   "%d bits left after decoding slice\n", get_bits_left(&gb));
    }

    ff_free_vlc(&vlc);

    return 0;
fail:
    ff_free_vlc(&vlc);
    return AVERROR_INVALIDDATA;
}
static int decode_plane(UtvideoContext *c, int plane_no,
                        uint8_t *dst, int step, int stride,
                        int width, int height,
                        const uint8_t *src, int use_pred)
{
    int i, j, slice, pix;
    int sstart, send;
    VLC vlc;
    GetBitContext gb;
    int prev, fsym;
    const int cmask = ~(!plane_no && c->avctx->pix_fmt == AV_PIX_FMT_YUV420P);

    if (build_huff(src, &vlc, &fsym)) {
        av_log(c->avctx, AV_LOG_ERROR, "Cannot build Huffman codes\n");
        return AVERROR_INVALIDDATA;
    }
    if (fsym >= 0) {  
        send = 0;
        for (slice = 0; slice < c->slices; slice++) {
            uint8_t *dest;

            sstart = send;
            send   = (height * (slice + 1) / c->slices) & cmask;
            dest   = dst + sstart * stride;

            prev = 0x80;
            for (j = sstart; j < send; j++) {
                for (i = 0; i < width * step; i += step) {
                    pix = fsym;
                    if (use_pred) {
                        prev += pix;
                        pix   = prev;
                    }
                    dest[i] = pix;
                }
                dest += stride;
            }
        }
        return 0;
    }

    src      += 256;

    send = 0;
    for (slice = 0; slice < c->slices; slice++) {
        uint8_t *dest;
        int slice_data_start, slice_data_end, slice_size;

        sstart = send;
        send   = (height * (slice + 1) / c->slices) & cmask;
        dest   = dst + sstart * stride;

         
        slice_data_start = slice ? AV_RL32(src + slice * 4 - 4) : 0;
        slice_data_end   = AV_RL32(src + slice * 4);
        slice_size       = slice_data_end - slice_data_start;

        if (!slice_size) {
            av_log(c->avctx, AV_LOG_ERROR, "Plane has more than one symbol "
                   "yet a slice has a length of zero.\n");
            goto fail;
        }

        memcpy(c->slice_bits, src + slice_data_start + c->slices * 4,
               slice_size);
        memset(c->slice_bits + slice_size, 0, AV_INPUT_BUFFER_PADDING_SIZE);
        c->bdsp.bswap_buf((uint32_t *) c->slice_bits,
                          (uint32_t *) c->slice_bits,
                          (slice_data_end - slice_data_start + 3) >> 2);
        init_get_bits(&gb, c->slice_bits, slice_size * 8);

        prev = 0x80;
        for (j = sstart; j < send; j++) {
            for (i = 0; i < width * step; i += step) {
                if (get_bits_left(&gb) <= 0) {
                    av_log(c->avctx, AV_LOG_ERROR,
                           "Slice decoding ran out of bits\n");
                    goto fail;
                }
                pix = get_vlc2(&gb, vlc.table, vlc.bits, 3);
                if (pix < 0) {
                    av_log(c->avctx, AV_LOG_ERROR, "Decoding error\n");
                    goto fail;
                }
                if (use_pred) {
                    prev += pix;
                    pix   = prev;
                }
                dest[i] = pix;
            }
            dest += stride;
        }
        if (get_bits_left(&gb) > 32)
            av_log(c->avctx, AV_LOG_WARNING,
                   "%d bits left after decoding slice\n", get_bits_left(&gb));
    }

    ff_free_vlc(&vlc);

    return 0;
fail:
    ff_free_vlc(&vlc);
    return AVERROR_INVALIDDATA;
}