static inline void interlaced_vertical_filter(int16_t *output, int16_t *low, int16_t *high,
                         int width)
{
    int i;
    for (i = 0; i < width; i++) {
      output[i] = (*low + *high)/2;
      output[i + width] = (*low - *high)/2;
      low++;
      high++;
    }
}

dst  = (int16_t *)pic->data[act_plane];
        low  = s->plane[plane].l_h[6];
        high = s->plane[plane].l_h[7];
        for (i = 0; i < lowpass_height; i++) {
            interlaced_vertical_filter(dst, low, high, lowpass_width * 2);
            low  += lowpass_width * 2;
            high += lowpass_width * 2;
            dst  += pic->linesize[act_plane];
        }