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Non-linear address spaces shouldn't affect pointer arithmetic though, unless I'm misunderstanding something. Otherwise, I guess the implication is that there are systems or implementations that rely on negative pointers; in which case I would think it should be up to the implementation.

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Consider a system where an address consists of a segment identifier combined with a byte offset within the segment. The relationship between different segments is unspecified. Pointer equality has to consider both parts of the address, but "<", "<=", ">", and ">=" can ignore the segment identifier and compare only the offsets.

Given two distinct objects, x and y, (&x == &y) is meaningful, but (&x < &y) isn't particularly. (Except that sometimes it would be convenient to have a consistent total ordering on addresses, something that C doesn't define.)

I can see that a non-linear address space doesn't imply a strict weak ordering, but this still seems to be an implementation defined detail. It doesn't imply anything about pointer arithmetic overflow.

For example, consider x86 segments. Is there a reason why you would use negative offsets? Given a segment address, the number of representable values is identical whether the offset is strictly positive, or negative with a shifted segment address (assuming two's compliment).

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