function eumod($a,$b)
{
    return (($a % $b)+$b)%$b;
}

function mirror($x,$min,$max)
{
    //Difference
    $diff = $max-$min;
    $sum = $max+$min;

    //Down
    if(eumod($x,$diff*2) > $diff)
        return $sum-($min+(($x)%$diff));
    //Up
        return $min+(($x)%$diff);
}