GZDoom lightmode calculation

int gl_CalcLightLevel(int lightlevel, int rellight, bool weapon)
{
    int light;

    if (lightlevel == 0) return 0;

    if ((glset.lightmode & 2) && lightlevel < 192 && !weapon)
    {
        light = xs_CRoundToInt(192.f - (192-lightlevel)* 1.95f);
    }
    else
    {
        light=lightlevel;
    }

    if (light<gl_light_ambient && glset.lightmode != 8)     // ambient clipping only if not using software lighting model.
    {
        light = gl_light_ambient;
        if (rellight<0) rellight>>=1;
    }
    return clamp(light+rellight, 0, 255);
}