
FDIM(P) POSIX Programmer's Manual FDIM(P)
NAME
fdim, fdimf, fdiml  compute positive difference between two floatingpoint numbers
SYNOPSIS
#include <math.h>
double fdim(double x, double y);
float fdimf(float x, float y);
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 nonzero,
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, respec
tively.
If x y is positive and underflows, a range error may occur, and either ( x y) (if repre
sentable), or 0.0 (if supported), or an implementationdefined 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 nonzero, then errno shall be
set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non
zero, then the overflow floatingpoint exception shall be raised.
The fdim() function may fail if:
Range Error
The result underflows.
If the integer expression (math_errhandling & MATH_ERRNO) is nonzero, then errno shall be
set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non
zero, then the underflow floatingpoint exception shall be raised.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
On implementations supporting IEEE Std 7541985, 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 nonzero.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
feclearexcept() , fetestexcept() , fmax() , fmin() , the Base Definitions volume of
IEEE Std 1003.12001, Section 4.18, Treatment of Error Conditions for Mathematical Func
tions, <math.h>
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) 20012003 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 orig
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 FDIM(P) 
