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

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Defined in header <cmath>
(1)
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 );
(2) (since C++11)
(constexpr since C++23)
long double fdiml( long double x, long double y ) ;
(3) (since C++11)
(constexpr since C++23)
SIMD overload (since C++26)
Defined in header <simd>
template < class V0, class V1 >

constexpr /*math-common-simd-t*/<V0, V1>

            fdim ( const V0& v_x, const V1& v_y ) ;
(S) (since C++26)
Additional overloads (since C++11)
Defined in header <cmath>
template < class Integer >
double      fdim ( Integer x, Integer y ) ;
(A) (constexpr since C++23)
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)
S) The SIMD overload performs an element-wise std::fdim on v_xand v_y
(See math-common-simd-t for its definition.)
(since C++26)
A) Additional overloads are provided for all integer types, which are treated as double.
 (since C++11)

Parameters

x, y - floating-point or integer values

Return value

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

If a range error due to overflow occurs, +HUGE_VAL, +HUGE_VALF, or +HUGE_VALL is returned.

If a range error due to underflow occurs, the correct value (after rounding) is returned.

Error handling

Errors are reported as specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

  • If either argument is NaN, NaN is returned.

Notes

Equivalent to std::fmax(x - y, 0)

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 or num2 has type long double, then std::fdim(num1, num2) has the same effect as std:: fdim ( static_cast < long double > (num1)
    static_cast < long double > (num2) )
  • Otherwise, if num1 and/or num2 has type double or an integer type, then std::fdim(num1, num2) has the same effect as std:: fdim ( static_cast < double > (num1)
    static_cast < double > (num2) )
  • Otherwise, if num1 or num2 has type float, then std::fdim(num1, num2) has the same effect as std:: fdim ( static_cast < float > (num1)
    static_cast < float > (num2) )
(until C++23)

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

(since C++23)

Example

Run this code
#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";
}

Output: 

fdim(4, 1) = 3
fdim(1, 4) = 0
fdim(4,-1) = 5
fdim(1,-4) = 5
fdim(1e308, -1e308) = inf
    errno == ERANGE: Numerical result out of range
    FE_OVERFLOW raised

See also

(C++11)
 computes absolute value of an integral value (|x|)
(function)
(C++11)(C++11)(C++11)
 larger of two floating-point values
(function)
C documentation for fdim
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