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Message-ID: <18441.50147.324276.27512@harpo.it.uu.se> Date: Sat, 19 Apr 2008 12:05:23 +0200 From: Mikael Pettersson <mikpe@...uu.se> To: dean gaudet <dean@...tic.org> Cc: Joe Perches <joe@...ches.com>, Harvey Harrison <harvey.harrison@...il.com>, Alexander van Heukelum <heukelum@...lshack.com>, Alexander van Heukelum <heukelum@...tmail.fm>, Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: Alternative implementation of the generic __ffs dean gaudet writes: > On Fri, 18 Apr 2008, Joe Perches wrote: > > > On Fri, 2008-04-18 at 18:11 -0700, dean gaudet wrote: > > > have you benchmarked it? > > > > I modified Alexander's benchmark: > > http://lkml.org/lkml/2008/4/18/267 > > to include 32 and 64 bit variants called smallest. > > > > On an old ARM: > > i'm guessing the 32-bit constants suck :( > > the code could be modified to use 16-bit constants only 16-bit immediates don't help, as ARMs express immediate operands in arithmetic instructions as 8-bit values plus a 4-bit rotation count (which is multiplied by 2). Very new ARMs can construct full 16-bit immediates, but that still takes an additional instruction and an additional register. -- 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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