Re: [boost] Floating Point Utilities Review starts today

From: John Maddock (john_at_[hidden])
Date: 2008-02-26 04:31:12

Johan Råde wrote:
> If I enable SSE2 on VC71 and optimize the code for speed (/O2), then
>
>    -std::numeric_limits<double>::quiet_nan()
>
> returns a positive NaN (binary expansion 7ff8000000000000), while
>
>    boost::math::changesign(std::numeric_limits<double>::quiet_nan())
>
> returns a negative NaN (binary expansion fff8000000000000).
>
> If I turn off the compiler optimization, then both return a negative
> NaN.
>
> Conclusion: boost::math::changesign is useful.

Well, if that's the only use, then personally I won't be using it, what use 
is a negative NaN over a positive one?  This feels like a very borderline 
use case to me, but maybe I'm missing something?

John.