Messages in this thread | | | Date | Tue, 27 Feb 2007 00:02:50 +0100 (MET) | From | Jan Engelhardt <> | Subject | Re: [RFC] div64_64 support |
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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 ;-)
Jan -- - 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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