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 .