FDIM(3P)                                            POSIX Programmer's Manual                                           FDIM(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       fdim, fdimf, fdiml - compute positive difference between two floating-point 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 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 sup-
       ported),  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  inte-
       ger  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  inte-
       ger  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.

SEE ALSO
       feclearexcept(), fetestexcept(), fmax(), fmin(), the Base  Definitions  volume  of  IEEE Std 1003.1-2001,  Section  4.18,
       Treatment of Error Conditions for Mathematical Functions, <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,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                      FDIM(3P)