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From: Johan Råde (rade_at_[hidden])
Date: 20060725 06:32:05
Paul Giaccone wrote:
> Johan Råde wrote:
>> Floating point numbers can be classified into four categories:
>>
>> 1. finite numbers
>> 2. infinity
>> 3. negative infinity
>> 4. notanumber (nan)
>>
>> So maybe we need functions:
>>
>> [snip]
>> template<class T> bool is_infinity(T a)
>> {
>> return std::numeric_limits<T>::has_infinity
>> && a == std::numeric_limits<T>::infinity();
>> }
>>
>> [snip]
>>
>> You test for negative infinity by calling is_infinity(a).
>>
>
> ....for which it would be easy enough to provide a convenience function
> (perhaps "is_minus_infinity"), which would just be a wrapper around
> "is_infinity".
>
> Another useful convenience function would be "is_infinite", which would
> return true if and only if the number was equal to plus or minus
> infinity (making use of either "is_finite" or both "is_infinity" and
> "is_minus_infinity")
>
> The similarity of the names of "is_infinity" and "is_infinite" might be
> a problem, but the former could be changed to "is_plus_infinity" to give
> symmetry with "is_minus_infinity".
>
> Paul
>
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>
I agree that having the three functions
is_infinite (or maybe is_infinity)
is_plus_infinity
is negative_infinity
is a good idea.
John's proposal has the function is_infinity, in the sense of both plus
and minus infinity, but not the functions is_plus_infinity and
is_negative_infinity.
Maybe John's intention is that one should test for plus infinity by writing
is_infinity(x) && x >= 0
That would work, but is probably inefficient.
Johan
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