Thank you very much, pryrt for these ideas.

Unfortunately,

perl -V:sizesize -V:sizetype
[download]

does not produce anything useful under VMS (just the same output as Perl -V)

Converting the negative output would work for the specific example I gave, but I am afraid it is probably not a reliable option because some other files are still significantly larger (10 GB, or so), so there is no way for me to know how many times I would need to add 2**32.

Thanks anyway for your answer.