Messages in this thread | ![/](/images/icornerl.gif) | | Date | Tue, 11 Mar 2003 15:35:56 -0800 | From | george anzinger <> | Subject | Re: Runaway cron task on 2.5.63/4 bk? |
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Linus Torvalds wrote: > > 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.
Often the 64/32 -> [32,32] is all that is needed and that is even faster if we could get to it. > > Linus > > - > 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/ >
-- George Anzinger george@mvista.com High-res-timers: http://sourceforge.net/projects/high-res-timers/ Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml
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