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SubjectRe: [RFC][PATCH] Faster generic_fls
Date
On Wed 30 Apr 03 15:17, Falk Hueffner wrote:
> Daniel Phillips <dphillips@sistina.com> writes:
> > It's somewhat annoying that __builtin_clz leaves the all-ones case
> > dangling instead of returning -1.
>
> I assume you mean all-zero...

:-)

> Well, the semantics of the corresponding
> instructions simply differ too much. clz(0) is 31 on some, 32 on some
> others, and undefined on some more architectures. So nailing it down
> would incur some performance penalty.

It would only penalize stupidly broken architectures; it would help the ones
that got it right. It's hard to imagine how a sane person could think the
result of clz((u32)0) should be other than 32.

Sigh.

Regards,

Daniel

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