http://d.puremagic.com/issues/show_bug.cgi?id=3632



--- Comment #15 from Walter Bright <bugzi...@digitalmars.com> 2011-06-28 
02:17:47 PDT ---
(In reply to comment #14)
> I use it all the time, mainly for distinguishing between +0.0 and -0.0

'is' does distinguish between +0 and -0. Just not -Nan and +Nan, nor the Nan
payloads.

> But it's reasonable to argue that '+0.0 is -0.0' should return true, and if 
> you
> do that, then 'NaN is NaN' should also return true, regardless of the payload.

I believe those are entirely different situations. The sign of 0 has a
mathematical meaning to fp arithmetic, the sign/payload of Nan does not.

> NaN payloads were used extensively in Apple's SANE, to distinguish different
> error types. Eg,
> http://doc.4d.com/4D-Language-Reference-11.6/Error-Codes/SANE-NaN-Errors-1-255.300-206143.en.html

I didn't know that. But it's worth noting that SANE has been dropped.

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