This is an issue with Perl, not with this module. Huge numbers get converted to floats automatically by Perl. You can't convert back, as you suggest, because you've lost accuracy:

$ perl -e 'print 10000000000000001, $/'
1e+16
$ perl -e 'print 10000000000000005, $/'
1e+16
$ perl -e 'print 10000000000000000, $/'
1e+16
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You will find that every module on CPAN that needs to deal with integers this big either (A) requires you to pass the number as a string, or (B) uses Math::BigInt or similar, to prevent Perl from converting the integer to a float. Even notice from Math::BigInt's pod:

Scalars holding numbers may also be passed, but note that non-integer 
+numbers
may already have lost precision due to the conversation to float. Quot
+e your
input if you want BigInt to see all the digits:

        $x = Math::BigInt->new(12345678890123456789);   # bad
        $x = Math::BigInt->new('12345678901234567890'); # good
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