[andersa]

But in that case, it's not going to be wrapping either. We'll just read beyond the end of the buffer, which a bounds check should catch.

Or perhaps I'm not thinking of the specific sequence that would 1) not wrap during modifying index and 2) not hit bounds check after.

It would need to be a requirement that compilers can't upcast all your ints to 64 bit ones, do all the math, and then write them back - would need specific instructions for each size.