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Got it, thanks. I suck at x86, even more than I thought. :/

Edit: it's CLZ on Arm [1], probably what I was looking for.

[1]: https://developer.arm.com/documentation/100069/0610/A32-and-...

In that case, I suck at POSIX—I could’ve sworn clz() was a standard or at least a conventional function, but no, that’s fls(), which is furthermore not universal across Unices. Either way, if you don’t feel your knowledge of the x86 instruction set is adequate, there’s always an option of taking an instruction listing and looking up anything that seems unfamilliar. It’s surprisingly effective. (You can either use an old listing[1] or skip all the vector stuff in a new one[2].)

[1] https://web.archive.org/web/20000819070651/http://www.quanta...

[2] https://www.felixcloutier.com/x86/

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