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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 dif-
       fer (consult 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  feclearex-
       cept(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 excep-
       tion 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 indepen-
       dent 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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  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 Stan-
       dard,  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 .



IEEE/The Open Group                  2003                             FDIM(3P)