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Message-ID: <Pine.LNX.4.64.0706151427370.12949@localhost.localdomain> Date: Fri, 15 Jun 2007 14:28:16 -0400 (EDT) From: "Robert P. J. Day" <rpjday@...dspring.com> To: "H. Peter Anvin" <hpa@...or.com> cc: Vegard Nossum <vegard.nossum@...il.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH] Optimize is_power_of_2(). On Fri, 15 Jun 2007, H. Peter Anvin wrote: > Vegard Nossum wrote: > > From: Vegard Nossum <vegard@...tkore.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 http://fsdev.net/wiki/index.php?title=Main_Page ======================================================================== - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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