Messages in this thread | | | Date | Fri, 15 Jun 2007 14:28:16 -0400 (EDT) | From | "Robert P. J. Day" <> | Subject | Re: [PATCH] Optimize is_power_of_2(). |
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On Fri, 15 Jun 2007, H. Peter Anvin wrote:
> Vegard Nossum wrote: > > From: Vegard Nossum <vegard@peltkore.net> > > Date: Fri, 15 Jun 2007 18:35:49 +0200 > > Subject: [PATCH] Optimize is_power_of_2(). > > > > Rationale: Removes one conditional branch and reduces icache > > footprint. Proof: If n is false, the product of n and any value is > > false. If n is true, the truth of (n * x) is the truth of x. > > You realize that on a lot of platforms, multiplication is done by an > out-of-line subroutine, and that even on those that aren't, it's > generally a long-pipeline operation, right?
i was *just* about to mention somthing of the sort, but probably not as succinctly.
rday -- ======================================================================== Robert P. J. Day Linux Consulting, Training and Annoying Kernel Pedantry Waterloo, Ontario, CANADA
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