Messages in this thread | | | Date | Tue, 8 Oct 2019 18:33:57 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v3 04/10] sched/fair: rework load_balance |
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On Tue, Oct 08, 2019 at 03:34:04PM +0100, Valentin Schneider wrote: > On 08/10/2019 15:16, Peter Zijlstra wrote: > > On Wed, Oct 02, 2019 at 11:47:59AM +0100, Valentin Schneider wrote: > > > >> Yeah, right shift on signed negative values are implementation defined. > > > > Seriously? Even under -fno-strict-overflow? There is a perfectly > > sensible operation for signed shift right, this stuff should not be > > undefined. > > > > Mmm good point. I didn't see anything relevant in the description of that > flag. All my copy of the C99 standard (draft) says at 6.5.7.5 is: > > """ > The result of E1 >> E2 [...] If E1 has a signed type and a negative value, > the resulting value is implementation-defined. > """ > > Arithmetic shift would make sense, but I think this stems from twos' > complement not being imposed: 6.2.6.2.2 says sign can be done with > sign + magnitude, twos complement or ones' complement...
But -fno-strict-overflow mandates 2s complement for all such signed issues.
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