std:: sub_sat

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C++
Numerics library
Common mathematical functions
Mathematical special functions (C++17)
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Basic linear algebra algorithms (C++26)
Data-parallel types ( simd ) (C++26)
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Complex numbers
Numeric array ( valarray )
Pseudo-random number generation
Factor operations
(C++17)
(C++17)
Interpolations
(C++20)
(C++20)
Saturation arithmetic
(C++26)
sub_sat
(C++26)
(C++26)
(C++26)
(C++26)

Generic numeric operations
Bit operations
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
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

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