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
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Floating point numbers can be classified into four categories: 1. finite numbers 2. infinity 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) { return std::numeric_limits<T>::has_infinity && 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). Three issues: 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.) --Johan Råde