I'm not inclined to change anything here. It's a trivial point, and by "primitive" I had in mind a dedicated hardware instruction, blazing fast. Yes, I was aware of long-winded ways of doing it for specific fixed integer widths. But that's not what `O(1)` means. A dead obvious loop testing each bit, one at a time, starting with the MSB, until finding the first bit set, is also O(1) for any fixed-width int size.

So I'm not doing anything here. If someone else creates a PR with text they want to see instead, I'll review it, and if it's not unbearably pedantic ;-) I'll merge it.