Re: [PATCH] speed up on find_first_bit for i386 (let compiler dothe work)

From: Maciej W. Rozycki
Date: Thu Jul 28 2005 - 12:12:13 EST

On Thu, 28 Jul 2005, Steven Rostedt wrote:

> I've been playing with different approaches, (still all hot cache
> though), and inspecting the generated code. It's not that the gcc
> generated code is always better for the normal case. But since it sees
> more and everything is not hidden in asm, it can optimise what is being
> used, and how it's used.

Since you're considering GCC-generated code for ffs(), ffz() and friends,
how about trying __builtin_ffs(), __builtin_clz() and __builtin_ctz() as
apropriate? Reasonably recent GCC may actually be good enough to use the
fastest code depending on the processor submodel selected.

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