I love weird little tricks with popcnt/leading/trailing zero instructions.
I recently had a lot of fun getting Swift’s OptionSet bitset interface to iterate over active members.
(Unfortunately, because of weird specifics of Swift protocol associated types, I wasn’t able to actually conform OptionSet to Collection like I wanted to originally. I find it amusing that one of the first examples in the official documentation for Swift macros is to make OptionSet used an associated enum like it should.)