std:: add_sat

Computes the saturating addition 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

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.

Possible implementation

See libstdc++ (gcc) .

Example

#include <climits>
#include <limits>
#include <numeric>
 
static_assert(CHAR_BIT == 8);
static_assert(UCHAR_MAX == 255);
 
int main()
{
    constexpr int a = std::add_sat(3, 4); // no saturation occurs, T = int
    static_assert(a == 7);
 
    constexpr unsigned char b = std::add_sat<unsigned char>(UCHAR_MAX, 4); // saturated
    static_assert(b == UCHAR_MAX);
 
    constexpr unsigned char c = std::add_sat(UCHAR_MAX, 4); // not saturated, T = int
        // add_sat(int, int) returns int tmp == 259,
        // then assignment truncates 259 % 256 == 3
    static_assert(c == 3);
 
//  unsigned char d = std::add_sat(252, c); // Error: inconsistent deductions for T
 
    constexpr unsigned char e = std::add_sat<unsigned char>(251, a); // saturated
    static_assert(e == UCHAR_MAX);
        // 251 is of type T = unsigned char, `a` is converted to unsigned char value;
        // might yield an int -> unsigned char conversion warning for `a`
 
    constexpr signed char f = std::add_sat<signed char>(-123, -3); // not saturated
    static_assert(f == -126);
 
    constexpr signed char g = std::add_sat<signed char>(-123, -13); // saturated
    static_assert(g == std::numeric_limits<signed char>::min()); // g == -128
}

See also

External links