From: Johan Råde (rade_at_[hidden])
Date: 2006-07-25 05:27:02
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
Floating point numbers can be classified into four categories:
1. finite numbers
3. negative infinity
4. not-a-number (nan)
So maybe we need functions:
template<class T> bool is_finite(T a)
return a >= -std::numeric_limits<T>::min()
&& a <= std::numeric_limits<T>::max();
template<class T> bool is_infinity(T a)
&& a == std::numeric_limits<T>::infinity();
template<class T> bool is_nan(T a)
return a != a;
You test for negative infinity by calling is_infinity(-a).
1. Do these implementations work an all platforms?
2. The category not-a-number can be divided into the sub-categories
quite not-a-number and signalling not-a-number. Does anyone need to
distinguish between them?
3. Are these the most efficient implementations. (Important if you have
a large vector of numbers and need to verify that each element is finite.)
Boost list run by bdawes at acm.org, gregod at cs.rpi.edu, cpdaniel at pacbell.net, john at johnmaddock.co.uk