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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 differ (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  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 implementa-
       tion-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 implemen-
       tations 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 Condi-
       tions 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,  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 .

IEEE/The Open Group                  2003                             FDIM(3P)