< cpp‎ | numeric
Defined in header <numeric>
template< class T >
constexpr T sub_sat( T x, T y ) noexcept;
(since C++26)

Computes the saturating subtraction x - y. This operation (unlike built-in arithmetic operations on integers) behaves as-if it is a mathematical operation with an infinite range. Let q denote the result of such operation. Returns:

  • q, if q is representable as a value of type T. Otherwise,
  • the largest or smallest value of type T, whichever is closer to the q.

This overload participates in overload resolution only if T is an integer type, that is: signed char, short, int, long, long long, an extended signed integer type, or an unsigned version of such types. In particular, T must not be (possibly cv-qualified) bool, char, wchar_t, char8_t, char16_t, and char32_t, as these types are not intended for arithmetic.


[edit] Parameters

x, y - integer values

[edit] Return value

Saturated x - y.

[edit] Exceptions

Throws no exceptions.

[edit] Notes

Unlike the built-in arithmetic operators on integers, the integral promotion does not apply to the x and y arguments.

If two arguments of different type are passed, the call fails to compile, i.e. the behavior relative to template argument deduction is the same as for std::min or std::max.

Most modern hardware architectures have efficient support for saturation arithmetic on SIMD vectors, including SSE2 for x86 and NEON for ARM.

Feature-test macro Value Std Feature
__cpp_lib_saturation_arithmetic 202311L (C++26) Saturation arithmetic

[edit] Possible implementation

See libstdc++ (gcc).

[edit] Example

Can be previewed on Compiler Explorer

#include <climits>
#include <numeric>
    && (std::sub_sat<int>(INT_MIN + 4, 3) == INT_MIN + 1) // not saturated
    && (std::sub_sat<int>(INT_MIN + 4, 5) == INT_MIN) // saturated
    && (std::sub_sat<int>(INT_MAX - 4, -3) == INT_MAX - 1) // not saturated
    && (std::sub_sat<int>(INT_MAX - 4, -5) == INT_MAX) // saturated
    && (std::sub_sat<unsigned>(4, 3) == 1) // not saturated
    && (std::sub_sat<unsigned>(4, 5) == 0) // saturated
int main() {}

[edit] See also

saturating addition operation on two integers
(function template) [edit]
saturating multiplication operation on two integers
(function template) [edit]
saturating division operation on two integers
(function template) [edit]
returns an integer value clamped to the range of a another integer type
(function template) [edit]
clamps a value between a pair of boundary values
(function template) [edit]
checks if an integer value is in the range of a given integer type
(function template) [edit]
returns the smallest finite value of the given type
(public static member function of std::numeric_limits<T>) [edit]
returns the largest finite value of the given type
(public static member function of std::numeric_limits<T>) [edit]

[edit] External links

1.  A branch-free implementation of saturation arithmetic —, 2012