DouKaku?

#! /usr/bin/perl

package Modular;

sub modular {
    my    ($pkg,$n,$low,$high) = @_;
    $low + ($n + $high - $low + 1) % ($high - $low + 1);
}

package main;

printf("%d -> %d\n",$_,Modular->modular($_,-1,2)) foreach (-10..10);

1;