static void qtrle_decode_8bpp(QtrleContext *s, int stream_ptr, int row_ptr, int lines_to_change)
{
    int rle_code;
    int pixel_ptr;
    int row_inc = s->frame.linesize[0];
    unsigned char pi1, pi2, pi3, pi4;  /* 4 palette indexes */
    unsigned char *rgb = s->frame.data[0];
    int pixel_limit = s->frame.linesize[0] * s->avctx->height;

    while (lines_to_change--) {
        CHECK_STREAM_PTR(2);
        pixel_ptr = row_ptr + (4 * (s->buf[stream_ptr++] - 1));

        while ((rle_code = (signed char)s->buf[stream_ptr++]) != -1) {
            if (rle_code == 0) {
                /* there's another skip code in the stream */
                CHECK_STREAM_PTR(1);
                pixel_ptr += (4 * (s->buf[stream_ptr++] - 1));
                CHECK_PIXEL_PTR(0);  /* make sure pixel_ptr is positive */
            } else if (rle_code < 0) {
                /* decode the run length code */
                rle_code = -rle_code;
                /* get the next 4 bytes from the stream, treat them as palette
                 * indexes, and output them rle_code times */
                CHECK_STREAM_PTR(4);
                pi1 = s->buf[stream_ptr++];
                pi2 = s->buf[stream_ptr++];
                pi3 = s->buf[stream_ptr++];
                pi4 = s->buf[stream_ptr++];

                CHECK_PIXEL_PTR(rle_code * 4);

                while (rle_code--) {
                    rgb[pixel_ptr++] = pi1;
                    rgb[pixel_ptr++] = pi2;
                    rgb[pixel_ptr++] = pi3;
                    rgb[pixel_ptr++] = pi4;
                }
            } else {
                /* copy the same pixel directly to output 4 times */
                rle_code *= 4;
                CHECK_STREAM_PTR(rle_code);
                CHECK_PIXEL_PTR(rle_code);

                while (rle_code--) {
                    rgb[pixel_ptr++] = s->buf[stream_ptr++];
                }
            }
        }
        row_ptr += row_inc;
    }
}