/C

# fdim, fdimf, fdiml

Defined in header `<math.h>`
`float       fdimf( float x, float y );`
(1) (since C99)
`double      fdim( double x, double y );`
(2) (since C99)
`long double fdiml( long double x, long double y );`
(3) (since C99)
Defined in header `<tgmath.h>`
`#define fdim( x, y )`
(4) (since C99)
1-3) Returns the positive difference between `x` and `y`, that is, if `x>y`, returns `x-y`, otherwise (if `x≤y`), returns +0.
4) Type-generic macro: If any argument has type `long double`, `fdiml` is called. Otherwise, if any argument has integer type or has type `double`, `fdim` is called. Otherwise, `fdimf` is called.

### Parameters

 x, y - floating point value

### 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 `fmax(x-y, 0)` except for the NaN handling requirements.

### Example

```#include <stdio.h>
#include <math.h>
#include <errno.h>
#include <fenv.h>
// #pragma STDC FENV_ACCESS ON
int main(void)
{
printf("fdim(4, 1) = %f, fdim(1, 4)=%f\n", fdim(4,1), fdim(1,4));
printf("fdim(4,-1) = %f, fdim(1,-4)=%f\n", fdim(4,-1), fdim(1,-4));
//error handling
errno = 0; feclearexcept(FE_ALL_EXCEPT);
printf("fdim(1e308, -1e308) = %f\n", fdim(1e308, -1e308));
if(errno == ERANGE) perror("    errno == ERANGE");
if(fetestexcept(FE_OVERFLOW)) puts("    FE_OVERFLOW raised");
}```

Possible output:

```fdim(4, 1) = 3.000000, fdim(1, 4)=0.000000
fdim(4,-1) = 5.000000, fdim(1,-4)=5.000000
fdim(1e308, -1e308) = inf
errno == ERANGE: Numerical result out of range
FE_OVERFLOW raised```

### References

• C17 standard (ISO/IEC 9899:2018):
• 7.12.12.1 The fdim functions (p: 187-188)
• 7.25 Type-generic math <tgmath.h> (p: 272-273)
• F.10.9.1 The fdim functions (p: 386)
• C11 standard (ISO/IEC 9899:2011):
• 7.12.12.1 The fdim functions (p: 257)
• 7.25 Type-generic math <tgmath.h> (p: 373-375)
• F.10.9.1 The fdim functions (p: 530)
• C99 standard (ISO/IEC 9899:1999):
• 7.12.12.1 The fdim functions (p: 238)
• 7.22 Type-generic math <tgmath.h> (p: 335-337)
• F.9.9.1 The fdim functions (p: 466)

 abslabsllabs (C99) computes absolute value of an integral value (\(\small{|x|}\)|x|) (function) fmaxfmaxffmaxl (C99)(C99)(C99) determines larger of two floating-point values (function) C++ documentation for `fdim`