Out of range pointers

[mcdonald at uxe.cso.uiuc.edu]

>One problem with this is that on the segmented machines it is the act
>of computing such a pointer that is invalid, not the pointer itself.

I don't understand this. I can understand that on certain wacko
architectures that computing it IN A SEGMENT REGISTER would cause
a problem. But why not do the computation in an ordinary 
arithmetic register, presumably by casting to an integer type?

DougMcDonald