sub divides1 { 
    my($d, $n) = @_; 
    $d < $n ? 
        $d & 1 ? 
            $n & 1 ? divides($d, $n - $d) : divides($d, $n >> 1) : 
            $n & 1 ? 0 : divides($d >> 1, $n >> 1) :
        $d == $n; 
} 
sub divides { 
    0 == $_[1] || divides1(abs $_[0], abs $_[1]) 
}