801684620b
Add NonZeroUn::is_power_of_two This saves instructions on both new and old machines <https://rust.godbolt.org/z/4fjTMz> - On the default x64 target (with no fancy instructions available) it saves a few instructions by not needing to also check for zero. - On newer targets (with BMI1) it uses `BLSR` for super-short assembly. This can be used for things like checks against alignments stored in `NonZeroUsize`.