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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
       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 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
       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,  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 .