std::add_sat

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Numerics library

Common mathematical functions
Mathematical special functions (C++17)
Mathematical constants (C++20)
Basic linear algebra algorithms (C++26)
Floating-point environment (C++11)
Complex numbers
Numeric array (valarray)
Pseudo-random number generation
Factor operations
gcd (C++17)	lcm (C++17)
Interpolations
midpoint (C++20)	lerp (C++20)
Saturation arithmetic
add_sat (C++26) sub_sat (C++26) saturate_cast (C++26)	mul_sat (C++26) div_sat (C++26)
Generic numeric operations
iota (C++11) ranges::iota (C++23) accumulate inner_product adjacent_difference partial_sum	reduce (C++17) transform_reduce (C++17) inclusive_scan (C++17) exclusive_scan (C++17) transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
Bit operations
has_single_bit (C++20)     bit_cast (C++20) bit_ceil (C++20) bit_floor (C++20) bit_width (C++20) rotl (C++20) rotr (C++20)	popcount (C++20) countl_zero (C++20) countl_one (C++20) countr_zero (C++20) countr_one (C++20) byteswap (C++23) endian (C++20)

 

Defined in header <numeric>
template< class T > constexpr T add_sat( T x, T y ) noexcept;		(since C++26)

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.

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

Run this code

#include <climits>
#include <limits>
#include <numeric>
 
static_assert(CHAR_BIT == 8);
 
int main()
{
    constexpr int a = std::add_sat(3, 4);
    static_assert(a == 7);
 
    constexpr unsigned char b = std::add_sat(255, 4);
    static_assert(b == 3);
        // add_sat(int, int) returns int tmp == 259
        // then assignment truncates 259 % 256 == 3
 
    constexpr unsigned char c = std::add_sat<unsigned char>(255, 4);
    static_assert(c == 255);
 
    constexpr unsigned char d = std::add_sat<unsigned char>(251, a);
    static_assert(255);
        // 251 is of T == `unsigned char`
        // might yield an `int` -> `unsigned char` conversion warning for a
 
//  unsigned char e = std::add_sat(252, b); // Error: inconsistent deductions for T
 
    constexpr signed char f = std::add_sat<signed char>(-250, -4);
    static_assert(f == -254);
 
    constexpr signed char g = std::add_sat<signed char>(-250, -7);
    static_assert(g == -256 && g == std::numeric_limits<signed char>::min());
}

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