Messages in this thread | | | Date | Wed, 7 Sep 2022 10:50:47 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v5 2/2] x86/asm/bitops: __ffs,ffz: use __builtin_ctzl to evaluate constant expressions |
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On Wed, Sep 07, 2022 at 02:35:41PM +0900, Vincent MAILHOL wrote: > I rephrased the beginning of the commit message as below: > > > If x is not 0, __ffs(x) is equivalent to: > (unsigned long)__builtin_ctzl(x) > And if x is not ~0UL, ffz(x) is equivalent to: > (unsigned long)__builtin_ctzl(~x) > Because __builting_ctzl() returns an int, a cast to (unsigned long) is > necessary to avoid potential warnings on implicit casts. > > Concerning the edge cases, __builtin_ctzl(0) is always undefined, > whereas __ffs(0) and ffz(~0UL) may or may not be defined, depending on > the processor. Regardless, for both functions, developers are asked to > check against 0 or ~0UL so replacing __ffs() or ffz() by > __builting_ctzl() is safe. > > > > Does this solve the issue?
Yes, that sounds better.
Thx.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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