Messages in this thread | | | Date | Mon, 26 Feb 2007 15:44:13 -0800 | From | Stephen Hemminger <> | Subject | Re: [RFC] div64_64 support |
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On Tue, 27 Feb 2007 00:02:50 +0100 (MET) Jan Engelhardt <jengelh@linux01.gwdg.de> wrote:
> > On Feb 26 2007 13:28, Stephen Hemminger wrote: > >> > >> ./arch/arm26/lib/udivdi3.c > >> ./arch/sh/lib/udivdi3.c > >> ./arch/sparc/lib/udivdi3.S > >> > >> should not this be consolidated too? > > > >Hmm. Those are the GCC internal versions, that are picked up but > >doing divide in place. Do we want to allow general 64 bit in kernel to > >be easily used? It could cause sloppy slow code, but it would look > >cleaner. > > Then our reviewers should catch it, and if not, the janitors will > (/me winks at R.P.J.Day and trivial@). > > >@@ -134,7 +112,7 @@ > > */ > > do { > > x1 = x; > >- x = (2 * x + (uint32_t) div64_64(a, x*x)) / 3; > >+ x = (2 * x + (u32) (a / x*x)) / 3; > > Eye see a bug. > > Previously there was div64_64(a, x*x) which is equivalent to > (a)/(x*x), or just: a/(x^2). But now you do a/x*x, which is > equivalent to a*x/x (in the domain of real numbers). Furthermore, > a/x*x is a-(a%x), which does not even remotely match a/(x^2). > > Please keep the math intact, thank you ;-)
Been there, done that, don't want to repeat it...
-- Stephen Hemminger <shemminger@linux-foundation.org> - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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