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    SubjectRe: Runaway cron task on 2.5.63/4 bk?

    On Tue, 11 Mar 2003, Andrew Morton wrote:
    > gcc will generate 64bit * 64bit multiplies without resorting to
    > any library code

    However, gcc is unable to do-the-right-thing and generate 32x32->64
    multiplies, or 32x64->64 multiplies, even though those are both a _lot_
    faster than the full 64x64->64 case.

    And in quite a _lot_ of cases, that's actually what you want. It might
    actually make sense to add a "do_mul()" thing to allow architectures to do
    these cases right, since gcc doesn't.

    > and you can probably do the division with do_div().

    Yes. This is the same issue - gcc will always promote a 64-bit divide to
    be _fully_ 64-bit, even if the mixed-size 64/32 -> [64,32] case is much
    faster and simpler. Which is why do_div() exists in the first place.


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