If you get a Perl warning about non-portable numbers like this:

Hexadecimal number > 0xffffffff non-portable at /tmp/x.pl line 19.

It means that you are using a hex number greater than 2^32. I dunno why this is a warning when everything is 64bit these days, but it is. There have been a couple of times I needed this in my code so you can disable these warnings with:

no warnings 'portable';