[Python-Dev] Why is nan != nan?

[Curt Hagenlocher]

On Thu, Mar 25, 2010 at 7:08 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:

> Jesus Cea wrote:
> > But IEEE 754 was created by pretty clever guys and sure they had a
> > reason for define things in the way they are. Probably we are missing
> > something.
>
> Yes, this is where their "implementable in a hardware circuit" focus
> comes in. They were primarily thinking of a floating point
> representation where the 32/64 bits are *it* - you can't have "multiple
> NaNs" because you don't have the bits available to describe them.
>
Wait, what? I haven't been paying much attention, but this is backwards.
There are multiple representations of NaN in the IEEE encoding; that's
actually part of the problem with saying that NaN = NaN or NaN != NaN. If
you want to ignore the "payload" in the NaN, then you're not just comparing
bits any more.

--
Curt Hagenlocher
curt at hagenlocher.org
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