sub isInNetwork {
    my ($cidr_str, $ipaddress_str) = @_;
    my ($network_str, $netmask_str) = split ('/', $cidr_str);
    my ($network, $ip) = (ip_2_int ($network_str), 
        ip_2_int ($ipaddress_str));
    return ($network==($ip|(2**$network-1));
}

print "10.0.50.12 is in 10/8!\n"
    if isInNetwork ('10.0.0.0/8', '10.0.50.12');