static double clip(void *opaque, double val)
{
    LutContext *s = opaque;
    double minval = s->var_values[VAR_MINVAL];
    double maxval = s->var_values[VAR_MAXVAL];

    return av_clip(val, minval, maxval);
}
static double clip(void *opaque, double val)
{
    LutContext *s = opaque;
    double minval = s->var_values[VAR_MINVAL];
    double maxval = s->var_values[VAR_MAXVAL];

    return av_clip(val, minval, maxval);
}