Other Alias

fdim, fdimf## SYNOPSIS

**#include <math.h>
**

double fdim(double *x***, double** *y***);
float fdimf(float**

*x*

**, float**

*y*

**);**

long double fdiml(long double

long double fdiml(long double

*x*

**, long double**

*y*

**);**

## DESCRIPTION

These functions shall determine the positive difference between their
arguments. If *x* is greater than *y*, *x*-
*y* is returned. If *x* is less than or equal to *y*,
+0 is returned.

An application wishing to check for error situations should set *errno*
to zero and call
*feclearexcept*(FE_ALL_EXCEPT) before calling these functions.
On return, if *errno* is non-zero or
*fetestexcept*(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
is non-zero, an error has occurred.

## RETURN VALUE

Upon successful completion, these functions shall return the positive difference value.

If *x*- *y* is positive and overflows, a range error shall
occur and *fdim*(), *fdimf*(), and *fdiml*()
shall return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL,
respectively.

If *x*- *y* is positive and underflows, a range error may
occur, and either ( *x*- *y*) (if representable),
or 0.0 (if supported), or an implementation-defined value
shall be returned.

If
*x* or *y* is NaN, a NaN shall be returned.

## ERRORS

The *fdim*() function shall fail if:

- Range Error
- The result overflows.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then *errno* shall be set to [ERANGE]. If the
integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
then the overflow floating-point exception shall be
raised.

The *fdim*() function may fail if:

- Range Error
- The result underflows.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then *errno* shall be set to [ERANGE]. If the
integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
then the underflow floating-point exception shall be
raised.

*The following sections are informative.*

## EXAMPLES

None.

## APPLICATION USAGE

On implementations supporting IEEE Std 754-1985, *x*- *y*
cannot underflow, and hence the 0.0 return value
is shaded as an extension for implementations supporting the XSI extension
rather than an MX extension.

On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

## RATIONALE

None.

## FUTURE DIRECTIONS

None.

## COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .