Because it doesn't accept a single number as an argument? (It's for IP addresses)

I don't understand what you mean by this?

By way of recompense for my lack of understanding, you might find this bit from the 5.8 INSTALL doc interesting/useful?

=head2 64 bit support.

If your platform does not have 64 bits natively, but can simulate them with compiler flags and/or C<long long> or C<int64_t>, you can build a perl that uses 64 bits.

There are actually two modes of 64-bitness: the first one is achieved using Configure -Duse64bitint and the second one using Configure -Duse64bitall. The difference is that the first one is minimal and the second one maximal. The first works in more places than the second.

The C<use64bitint> does only as much as is required to get 64-bit integers into Perl (this may mean, for example, using "long longs") while your memory may still be limited to 2 gigabytes (because your pointers could still be 32-bit). Note that the name C<64bitint> does not imply that your C compiler will be using 64-bit C<int>s (it might, but it doesn't have to): the C<use64bitint> means that you will be able to have 64 bits wide scalar values.

The C<use64bitall> goes all the way by attempting to switch also integers (if it can), longs (and pointers) to being 64-bit. This may create an even more binary incompatible Perl than -Duse64bitint: the resulting executable may not run at all in a 32-bit box, or you may have to reboot/reconfigure/rebuild your operating system to be 64-bit aware.

Which if I read it right, indicates that you can get 64-integers in perl even on 32-bit platforms as of 5.8.

You would have to re-compile to get it of course.