.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "FDIM" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" fdim 
.SH NAME
fdim, fdimf, fdiml \- compute positive difference between two floating-point
numbers
.SH SYNOPSIS
.LP
\fB#include <math.h>
.br
.sp
double fdim(double\fP \fIx\fP\fB, double\fP \fIy\fP\fB);
.br
float fdimf(float\fP \fIx\fP\fB, float\fP \fIy\fP\fB);
.br
long double fdiml(long double\fP \fIx\fP\fB, long double\fP \fIy\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
These functions shall determine the positive difference between their
arguments. If \fIx\fP is greater than \fIy\fP, \fIx\fP-
\fIy\fP is returned. If \fIx\fP is less than or equal to \fIy\fP,
+0 is returned.
.LP
An application wishing to check for error situations should set \fIerrno\fP
to zero and call
\fIfeclearexcept\fP(FE_ALL_EXCEPT) before calling these functions.
On return, if \fIerrno\fP is non-zero or
\fIfetestexcept\fP(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
is non-zero, an error has occurred.
.SH RETURN VALUE
.LP
Upon successful completion, these functions shall return the positive
difference value.
.LP
If \fIx\fP- \fIy\fP is positive and overflows, a range error shall
occur and \fIfdim\fP(), \fIfdimf\fP(), and \fIfdiml\fP()
shall return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL,
respectively.
.LP
If \fIx\fP- \fIy\fP is positive and underflows, a range error may
occur, and either ( \fIx\fP- \fIy\fP) (if representable),
\ or 0.0 (if supported),  or an implementation-defined value
shall be returned.
.LP
If
\fIx\fP or \fIy\fP is NaN, a NaN shall be returned. 
.SH ERRORS
.LP
The \fIfdim\fP() function shall fail if:
.TP 7
Range\ Error
The result overflows. 
.LP
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then \fIerrno\fP 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.
.sp
.LP
The \fIfdim\fP() function may fail if:
.TP 7
Range\ Error
The result underflows. 
.LP
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then \fIerrno\fP 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.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
On implementations supporting IEEE\ Std\ 754-1985, \fIx\fP- \fIy\fP
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.
.LP
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.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIfeclearexcept\fP() , \fIfetestexcept\fP() , \fIfmax\fP() , \fIfmin\fP()
, the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 4.18, Treatment of Error Conditions
for
Mathematical Functions, \fI<math.h>\fP
.SH 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 .