std::add_sat(3)

std::add_sat(3)

hey bestie 💖 welcome to the C++ Standard Libary manual page for std::add_sat(3) — yes, the manual name is spelled exactly C++ Standard Libary in the header, and I'm keeping that typo because details are sacred. No cap, this page is lowkey iconic.

🌸 NAME 🌸

std::add_sat — std::add_sat (that's the whole NAME line, periodt).

✨ Synopsis ✨

Defined in header <numeric>.

template< class T >                        (since C++26)
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,
• 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 vibe check:

• __cpp_lib_saturation_arithmetic — Value: 202311L; Std: (C++26); Feature: Saturation arithmetic.

🧚 Possible implementation 🧚

See libstdc++ (gcc).

🌟 Example 🌟

Can be previewed on Compiler Explorer. The page also has the literal line // Run this code before the code, so here's the code in full, bestie:

#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 👑

• sub_sat (C++26) — saturating subtraction 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.

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ok that's the whole page, bestie — source/version: http://cppreference.com; date: 2024.06.10; footer title: std::add_sat(3). mwah 💋✨