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    SubjectRe: [RFC] div64_64 support

    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

    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 ;-)

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