Messages in this thread | | | Date | Fri, 29 Jul 2005 16:09:25 +0100 (BST) | From | "Maciej W. Rozycki" <> | Subject | Re: [PATCH] speed up on find_first_bit for i386 (let compiler do the work) |
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On Thu, 28 Jul 2005, Linus Torvalds wrote:
> > Since you're considering GCC-generated code for ffs(), ffz() and friends, > > how about trying __builtin_ffs(), __builtin_clz() and __builtin_ctz() as > > apropriate? > > Please don't. Try again in three years when everybody has them.
Well, __builtin_ffs() has been there since at least gcc 2.95. The two others are quite recent, indeed -- apparently only since GCC 3.4. They may still be considered to be used conditionally if there is justified benefit.
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