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Re: Question on performance

On 2010-10-15 06:37:54 -0400, Michel Hack wrote:
> Vincent Lef?vre a ?crit:
> > ...  It's strange that GCC doesn't replace isnan() by a test x != x
> 
> Perhaps because these are NOT equivalent?

I think they are on conforming code.

> They differ for SNaN.

sNaN is undefined behavior in ISO C99:

  F.2.1 Infinities, signed zeros, and NaNs

  This specification does not define the behavior of signaling NaNs.

So, the transformation is OK.

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Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <http://www.vinc17.net/>
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