std::numeric_limits::is_modulo

From cppreference.com


static const bool is_modulo		(until C++11)

static constexpr bool is_modulo		(since C++11)

The value of std::numeric_limits<T>::is_modulo is true for all arithmetic types T that handle overflows with modulo arithmetic, that is, if the result of addition, subtraction, multiplication, or division of this type would fall outside the range [min(), max()], the value returned by such operation differs from the expected value by a multiple of max()-min()+1.


`T`	value of std::numeric_limits<T>::is_modulo

/* non-specialized */	false

bool	false

char	implementation-defined

signed char	implementation-defined

unsigned char	true

wchar_t	implementation-defined

char16_t	implementation-defined

char32_t	implementation-defined

short	implementation-defined

unsigned short	true

int	implementation-defined

unsigned int	true

long	implementation-defined

unsigned long	true

long long	implementation-defined

unsigned long long	true

float	false

double	false

long double	false

[edit] Notes

Although the C++11 standard still says "On most machines, this is true for signed integers.", the exact wording changed from C++03 to C++11 in such a way that the true value is no longer compatible with undefined behavior on signed integer overflow (it changed from "possible" to a strict requirement). Because of that, the implementations that rely on signed overflow being undefined (for optimization opportunities) now set is_modulo to false for signed integers. See for example GCC PR 22200.

[edit] Example

Demonstrates the behavior of modulo types

run this code

#include <iostream>
#include <type_traits>
#include <limits>
 
template<class T>
typename std::enable_if<std::numeric_limits<T>::is_modulo>::type
    check_overflow()
{
    std::cout << "\nmax value is " << std::numeric_limits<T>::max() << '\n'
              << "min value is " << std::numeric_limits<T>::min() << '\n'
              << "max value + 1 is " << std::numeric_limits<T>::max()+1 << '\n';
}
 
int main()
{
    check_overflow<int>();
    check_overflow<unsigned long>();
    // check_overflow<float>(); // compile-time error, not a modulo type
}

Possible output:

max value is 2147483647
min value is -2147483648
max value + 1 is -2147483648
 
max value is 18446744073709551615
min value is 0
max value + 1 is 0

[edit] See also


is_integer [static]	identifies integer types (public static member constant)

is_iec559 [static]	identifies the IEC 559/IEEE 754 floating-point types (public static member constant)

is_exact [static]	identifies exact types (public static member constant)

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)

std::numeric_limits::is_modulo

Contents

[edit] Standard specializations

[edit] Notes

[edit] Example

[edit] See also