Is more than 63 bits needed for file sizes?
===========================================

Old SLUL had a fileoffs type, based on C `off_t`.

SLUL-try2 uses 63-bit integers.

That's a lot simpler, BUT is there any possibility that a file size would
go over 64 bits? E.g. in a disk image, a SAN, or similar?


Solution 1: Don't solve, and use separate APIs for huge files
-------------------------------------------------------------

For example, as an extension to some file class:

    class HugeFileOffset
        long low
        long high
    end

    func seek
        HugeFileOffset offs
    code
        ...
    end


Solution 2: Use the high bit to extend the long type
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Maybe the high bit could be use to pass a pointer instead? (That would
of course require that the whole 64-bit address space is not in use.)

But how to know whether a function supports this usage or not?
It would have to be declared (maybe with some kind of since-version
scheme?).


Problem
-------

Regardless of chosen solution, there's always the problem of type
conversions and arithmetic with larger-than-64-bits integers (unless
of course all integers are bigintegers).

So any larger-than-64-bits type will be inconvenient to use, and many
libraries might not support that.

Related topic: Biginteger support? Or allow the runtime to decide the
maximum integer type? Maybe that could use the high-order-bit hack?