Subject: Re: [boost] [ICL] #6853: boost::icl::contains(NaN) returns true
From: Thomas Klimpel (Thomas.Klimpel_at_[hidden])
Date: 2012-05-04 16:10:33
Jeffrey Lee Hellrung, Jr. wrote:
> > On Fri, May 04, 2012 at 11:48:30AM -0700, Jeffrey Lee Hellrung, Jr. wrote:
> > > On Fri, May 4, 2012 at 8:14 AM, Andrew Hundt <ahundt_at_[hidden]>
> wrote:
> > > How well does std::set/std::map interact with NaN when floating point
> > > types are used as keys?
> >
> > Undefinedly, most usually explodedly.
> >
> > For libraries that have sanity checks on the comparator, hard asserts.
> > For the rest (or NDEBUG), amusing loss of elements and general
> > malfunction.
> >
>
> Then it seems reasonable to me for ICL to also opt not to support NaN's in
> favor of a simpler implementation, better performance, etc.
I want to add that for recent gcc (at least for gcc 4.5.2), even the built-in "isnan" functions stops working when the compiler flag "-ffast-math" is used. That broke some of my code, and I had to debug quite a while before I found the reason. It took me so long since I couldn't believe that the built-in "isnan" would go wrong. My conclusion from this is that NaN can't be used portably, so there is no point for Boost.ICL to try to support it.
Regards,
Thomas