# This function takes a number in paramater (eg 24) and
# returns the corresponding mask in longer format 
# (eg 255.255.0.0)

sub mask_short_to_long
{
        my $short_mask = shift;
        my ($bin, $num, @mask);

        $bin = "1" x $short_mask . "0" x (32 - $short_mask);

        for my $i (0..31) {
                $num += substr($bin,31 - $i,1) * (2 ** $i);
        }

        for my $i (0..3) {
                unshift @mask, (($num >> ($i * 8)) & 0xFF);
        }
        return join('.',@mask);
}