Re: Integers on 64-bit machines

anton@mips.complang.tuwien.ac.at (Anton Ertl) writes:




> What I meant with the connection between integers and pointers is that
> one can do pointer arithmetic and cast between pointers and integers.


Pointer arithmetic does not require pointers and integers to be of the
same size. All that is required is that an integer can hold the
number of elements in an allocated array, so the difference of two
pointers into the same array can fit in an integer. Since it makes
sense to have virtual addresses much larger than physical memory, it
also makes sense to have addresses larger than integers.


Casting pointers to integers is an abomination.


> I think that a zoo of types is worse than marshalling, and you have to
> marshal anyway if your structure involves pointers.


I think machine-dependent integers is a much worse impediment to
marshalling than subrange types. With machine-dependent integers, you
can't write machine-independent marshalling code. And with
marshalling/unmarshalling you can't even be sure that the unmarshaller
has the same size ints as the marshaller, so you can get into loads of
trouble if you are not careful (such as storing the size of the number
with each number).


When marshalling structures that use pointers, all you need is an
ability to find the offset between two pointers in the same allocated
array and to comapre two pointer that are not in the same allocated
array for equality. Noone in their right mind would marshal a pointer
as its bit pattern. What you need is information sufficient to
reconstruct an equivalent heap structure -- without keeping exact
addresses.


Torben

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