std::sub_sat(3)

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