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Groups > linux.kernel > #1692728
| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH] Optimize int_sqrt for small values for faster idle |
| Date | 2017-07-20 12:20 +0200 |
| Message-ID | <u5gIO-5VF-19@gated-at.bofh.it> (permalink) |
| References | <qW2BY-13z-9@gated-at.bofh.it> <qXucO-qs-11@gated-at.bofh.it> <qXumu-vl-13@gated-at.bofh.it> <qXvLz-1Cx-1@gated-at.bofh.it> <qXxaF-2zt-9@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Mon, Feb 01, 2016 at 04:36:38PM -0800, Eric Dumazet wrote:
> On Tue, 2016-02-02 at 00:08 +0100, Rasmus Villemoes wrote:
>
> > Thanks. (Is there a good way to tell gcc that avg*avg is actually a
> > 32x32->64 multiplication?)
>
> If avg is 32bit, compiler does that for you.
>
> u32 avg = ...
>
> u64 result = (u64)avg * avg;
It does not in fact do that :/ See commit:
9e3d6223d209 ("math64, timers: Fix 32bit mul_u64_u32_shr() and friends")
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Re: [PATCH] Optimize int_sqrt for small values for faster idle Peter Zijlstra <peterz@infradead.org> - 2017-07-20 12:20 +0200 Re: [PATCH] Optimize int_sqrt for small values for faster idle Eric Dumazet <eric.dumazet@gmail.com> - 2017-07-24 15:30 +0200
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