std::fdim, std::fdimf, std::fdiml

Since C++23

Header: <cmath>

1-3) Returns the positive difference between x and y, that is, if x > y, returns x - y, otherwise (i.e. if x <= y) returns +0.The library provides overloads of std::fdim for all cv-unqualified floating-point types as the type of the parameters.(since C++23)

# Declarations

float fdim ( float x, float y );
double fdim ( double x, double y );
long double fdim ( long double x, long double y );

(until C++23)

constexpr /*floating-point-type*/
fdim ( /*floating-point-type*/ x,
/*floating-point-type*/ y );

(since C++23)

float fdimf( float x, float y );

(since C++11) (constexpr since C++23)

long double fdiml( long double x, long double y );

(since C++11) (constexpr since C++23)

SIMD overload (since C++26)

template< class V0, class V1 >
constexpr /*math-common-simd-t*/<V0, V1>
fdim ( const V0& v_x, const V1& v_y );

(since C++26)

Additional overloads (since C++11)

template< class Integer >
double fdim ( Integer x, Integer y );

(constexpr since C++23)

# Parameters

# Return value

If successful, returns the positive difference between x and y.

# Notes

Equivalent to std::fmax(x - y, 0), except for the NaN handling requirements.

The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their first argument num1 and second argument num2:

If num1 and num2 have arithmetic types, then std::fdim(num1, num2) has the same effect as std::fdim(static_cast</common-floating-point-type/>(num1),static_cast</common-floating-point-type/>(num2)), where /common-floating-point-type/ is the floating-point type with the greatest floating-point conversion rank and greatest floating-point conversion subrank between the types of num1 and num2, arguments of integer type are considered to have the same floating-point conversion rank as double.

If no such floating-point type with the greatest rank and subrank exists, then overload resolution does not result in a usable candidate from the overloads provided.

# Example

#include <cerrno>
#include <cfenv>
#include <cmath>
#include <cstring>
#include <iostream>
 
#ifndef __GNUC__
#pragma STDC FENV_ACCESS ON
#endif
 
int main()
{
    std::cout << "fdim(4, 1) = " << std::fdim(4, 1) << '\n'
              << "fdim(1, 4) = " << std::fdim(1, 4) << '\n'
              << "fdim(4,-1) = " << std::fdim(4, -1) << '\n'
              << "fdim(1,-4) = " << std::fdim(1, -4) << '\n';
 
    // error handling 
    errno = 0;
    std::feclearexcept(FE_ALL_EXCEPT);
 
    std::cout << "fdim(1e308, -1e308) = " << std::fdim(1e308, -1e308) << '\n';
 
    if (errno == ERANGE)
        std::cout << "    errno == ERANGE: " << std::strerror(errno) << '\n';
    if (std::fetestexcept(FE_OVERFLOW))
        std::cout << "    FE_OVERFLOW raised\n";
}

# See also