Even if you follow broomdusters advice, you still have a big problem. The internal numbers presentation automatically changes a number to floating point if it gets too big. Anding floating point numbers is quite useless as you can see here:

$maskResult = 4000000000000000 & 4000000000000000;
print $maskResult,"\n";
####prints
4294967295

$maskResult = 1000000000000000 & 4000000000000000;
print $maskResult,"\n";
####prints
4294967295
[download]

If you want to use really large integers you need bigint or Math:BigInt