Re: [boost] is_nan

From: Johan Råde (rade_at_[hidden])
Date: 2006-07-26 07:49:48

Joe Gottman wrote:
>    Several libraries have an is_nan() function buried deep in the code.  Are 
> there any plans to make a general is_nan function available?  This would be 
> quite useful, as well as similar functions like is_finite.
> 
> Joe Gottman 
> 
> 
> 
> _______________________________________________
> Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
> 

The date_time library contains the following is_nan function:

static bool is_nan(const T& x)
{
     return std::numeric_limits<T>::has_quiet_NaN && (x != x);
}

It has been pointed out by Martin Bonner that this is not safe,
for it requires strict IEEE 754 compliance and it may be optimized away 
by an over-eager optimizing compiler.

Here is the implementation I'm currently using:

//-------------------------------------------------------------------

#if defined(BOOST_MSVC)		// Microsoft Visual C++
        
template<class T> int is_nan(T t)
{
     return _isnan(t);
}

#elif defined(__GNUC__)		// GCC

template<class T> int is_nan(T t)
{
     return isnan(t);
}

#else		// generic

template<class T> int is_nan(T t)
{
     if(std::numeric_limits<T>::has_infinity)
         return !(t <= std::numeric_limits<T>::infinity());
     else
         return t != t;
}

#endif

//--------------------------------------------------------------------

Comments?
Anyone wants to add more #if's?

--Johan Råde