std::sub_sat

 

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add_sat (C++26) sub_sat (C++26) saturate_cast (C++26)	mul_sat (C++26) div_sat (C++26)
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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.

Parameters

x, y

-

integer values

Return value

Saturated x - y.

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

External links

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