CPAN is, as ever, your friend. I would use the Net::IPv4Addr module. From the synopsis:

use Net::IPv4Addr qw( :all );
my ($broadcast) = ipv4_broadcast($ip_str, $msk_str);
[download]

Where $ip_str and $msk_str in this case (assuming you have (0..255) in your arrays) would be:

$ip_str = join('.', @ip);
$msk_str = join('.', @netmask);
[download]

If you want to know how your problem is solved in the module, then download it and use the source luke.