How to Determine the Kind of a Number From std::numeric_limits

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##### How to Determine the Kind of a Number From `std::numeric_limits`

Based on the information above, one can see that different kinds of numbers can be differentiated based on the information stored in `std::numeric_limits`. This is in addition to the traits class number_category provided by this library.

##### Integer Types

For an integer type T, all of the following conditions hold:

    std::numeric_limits<T>::is_specialized == true
    std::numeric_limits<T>::is_integer == true
    std::numeric_limits<T>::is_exact == true
    std::numeric_limits<T>::min_exponent == 0
    std::numeric_limits<T>::max_exponent == 0
    std::numeric_limits<T>::min_exponent10 == 0
    std::numeric_limits<T>::max_exponent10 == 0

In addition the type is signed if:

    std::numeric_limits<T>::is_signed == true

If the type is arbitrary precision then:

    std::numeric_limits<T>::is_bounded == false

Otherwise the type is bounded, and returns a non zero value from:

    std::numeric_limits<T>::max()

and has:

    std::numeric_limits<T>::is_modulo == true

if the type implements modulo arithmetic on overflow.

##### Rational Types

Rational types are just like integers except that:

    std::numeric_limits<T>::is_integer == false

##### Fixed Precision Types

There appears to be no way to tell these apart from rational types, unless they set:

    std::numeric_limits<T>::is_exact == false

This is because these types are in essence a rational type with a fixed denominator.

##### floating-point Types

For a floating-point type T, all of the following conditions hold:

    std::numeric_limits<T>::is_specialized == true
    std::numeric_limits<T>::is_integer == false
    std::numeric_limits<T>::is_exact == false
    std::numeric_limits<T>::min_exponent != 0
    std::numeric_limits<T>::max_exponent != 0
    std::numeric_limits<T>::min_exponent10 != 0
    std::numeric_limits<T>::max_exponent10 != 0

In addition the type is signed if:

    std::numeric_limits<T>::is_signed == true

And the type may be decimal or binary depending on the value of:

    std::numeric_limits<T>::radix

In general, there are no arbitrary precision floating-point types, and so:

    std::numeric_limits<T>::is_bounded == false

##### Exact floating-point Types

Exact floating-point types are a field composed of an arbitrary precision integer scaled by an exponent. Such types have no division operator and are the same as floating-point types except:

    std::numeric_limits<T>::is_exact == true

##### Complex Numbers

For historical reasons, complex numbers do not specialize `std::numeric_limits`, instead you must inspect `std::numeric_limits<typename T::value_type>`.