Yeah "it's actually xoring array indices" is the standard solution

Or you can go Deep on memory models and try to apply Ralf's Xor Provenance Hack and claim that, well, provenance is stored in bytes, but it doesn't have to be a pointer-sized range of bytes, so let me have some horrible way to express "the high half has provenance 1, the low half has provenance 2" and handwave magic problem solved.

This is of course horrible and also not at all a portable notion to CHERI which tracks provenance at the granularity of "aligned pointer-sized region of memory". But hey, if it helps you sleep at night.