[llvm-dev] [FPEnv] FNEG instruction

[Cameron McInally via llvm-dev]

On Wed, Aug 29, 2018 at 3:13 PM, Cameron McInally <cameron.mcinally at nyu.edu>
wrote:

> On Wed, Aug 29, 2018 at 1:51 PM, Stephen Canon <scanon at apple.com> wrote:
>
>> On Aug 29, 2018, at 1:22 PM, Cameron McInally via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>
>> FSUB(-0.0,  NaN) = NaN
>> FSUB(-0.0, -NaN) = NaN
>>
>>
>> Some specific architecture may define this, or APFloat might, but IEEE
>> 754 does not interpret the sign of NaN except in four operations (copy,
>> abs, negate, copysign), so it doesn’t say anything about these.
>>
>
> Good point. I suppose one could argue that the behavior is undefined.
>

Apologies, I was wrong about this one. Just tested the FSUB hardware
instruction on all the targets I care about and they all respect the sign
on NaNs. I'm not sure how this got into my head...
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