NAME¶

std::sub_sat - std::sub_sat

Synopsis¶

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

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.

Parameters¶

x, y - integer values

Return value¶

Saturated x - y.

Exceptions¶

Throws no exceptions.

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

Possible implementation¶

See libstdc++ (gcc).

Example¶

Can be previewed on Compiler Explorer

// Run this code

#include <climits>
#include <numeric>

static_assert
(""
&& (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() {}

See also¶

add_sat saturating addition operation on two integers
(C++26) (function template)
mul_sat saturating multiplication operation on two integers
(C++26) (function template)
div_sat saturating division operation on two integers
(C++26) (function template)
saturate_cast returns an integer value clamped to the range of a another integer
(C++26) type
(function template)
clamp clamps a value between a pair of boundary values
(C++17) (function template)
in_range checks if an integer value is in the range of a given integer type
(C++20) (function template)
min returns the smallest finite value of the given type
[static] (public static member function of std::numeric_limits<T>)
max returns the largest finite value of the given type
[static] (public static member function of std::numeric_limits<T>)

External links¶

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