Re: [Boost-users] min and max preferring NaN

Subject: Re: [Boost-users] min and max preferring NaN
From: Krzysztof Czainski (1czajnik_at_[hidden])
Date: 2011-03-09 17:02:58

>
> On 03/08/2011 11:03 AM, Rhys Ulerich wrote:
>
>> The usual std::min and std::max prefer numbers over NaNs per
>> http://en.wikipedia.org/wiki/IEEE_754_revision#min_and_max.  POSIX's
>> fmin(3)
>> does as well.
>>
>> Can anyone suggest a better implementation (chained ternary complaints
>> aside)
>> for a NaN-preferring min or max than brute force things akin to
>>
>>     template<class T>
>>     inline
>>     const T&  minnan(const T&  a, const T&  b)
>>     {
>>         return UNLIKELY((boost::math::isnan)(a)) ? a :
>>                (a<  b)                           ? a : b;
>>     }
>>
>> where UNLIKELY is a small macro telling the compiler to generate code
>> expecting
>> that the boost::math::isnan test fails?
>>
>> The need arises in a numerical simulation where I want to gradually
>> accumulate
>> a global minimum where throwing away NaNs ("windowing" in IEEE 754
>> revision-speak) is the unacceptable.
>>
> 2011/3/9 Steven Watanabe <watanabesj_at_[hidden]>

> How about:
>
> template<class T>
> inline const T& minnan(const T& a, const T& b)
> {
>    return !(b <= a)? a : b;
> }
>

What if b is NaN, and a is a number?

Anyway, how about:
template < class T >
inline const %& minnan( const T& a, const T& b )
{
  return a < b || is_nan(a) ? a : b;
}

Regards,
Kris