template< class T >
constexpr T add_sat( T x, T y ) noexcept;
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,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.
Saturated x + y.
[edit] NotesUnlike 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.
[edit] Possible implementationSee libstdc++ (gcc).
[edit] ExampleCan be previewed on Compiler Explorer.
#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
}[edit] See also saturating subtraction operation on two integers
std::numeric_limits<T>) [edit] returns the largest finite value of the given type
std::numeric_limits<T>) [edit] [edit] External links
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