Hmm, paying a whole extra register for `nocross` is pretty expensive ... though representing it as a logarithm means it only needs to represent 62 values (2^1 is meaningless for both 1-byte and 2-byte allocations, 2^64 cannot be crossed regardless), which is 6 bits, so we could stuff it in the flags or even the high bits of the alignment on 32-bit-or-larger platforms. That seems like the way to do it ... unless it is instead specified as part of the allocator itself.

Anyway, added that and other flags in that paper to my central list at https://gist.github.com/o11c/6b08643335388bbab0228db763f9921...