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  FPGETROUND(3C)  (C Programming Language Utilities) FPGETROUND(3C)



  NAME
       fpgetround, fpsetround, fpgetmask, fpsetmask, fpgetsticky,
       fpsetsticky - IEEE floating point environment control

  SYNOPSIS
       #include <ieeefp.h>

       typedef enum {
            FPRN=0,   /* round to nearest */
            FPRP,     /* round to plus */
            FPRM,     /* round to minus */
            FPRZ,     /* round to zero (truncate) */
            } fprnd;

            fprnd fpgetround();

            fprnd fpsetround(rnddir)
            fprnd rnddir;

            #define   fpexcept int
            #define   FPXINV  0x10 /* invalid operation exception*/
            #define   FPXOFL  0x08 /* overflow exception*/
            #define   FPXUFL  0x04 /* underflow exception*/
            #define   FPXDZ   0x02 /* divide-by-zero exception*/
            #define   FPXIMP  0x01 /* imprecise (loss of precision)*/

            fpexcept fpgetmask();

            fpexcept fpsetmask(mask);
            fpexcept mask;

            fpexcept fpgetsticky();

            fpexcept fpsetsticky(sticky);
            fpexcept sticky;

  DESCRIPTION
       There are five floating point exceptions: divide-by-zero,
       overflow, underflow, imprecise (inexact) result, and invalid
       operation.  When a floating point exception occurs, the


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  FPGETROUND(3C)  (C Programming Language Utilities) FPGETROUND(3C)



       corresponding sticky bit is set (1), and if the mask bit is
       enabled (1), the trap takes place.  These routines let the
       user change the behavior on occurrence of any of these
       exceptions, as well as change the rounding mode for floating
       point operations.

       fpgetround() returns the current rounding mode.

       fpsetround() sets the rounding mode and returns the previous
       rounding mode.

       fpgetmask() returns the current exception masks.

       fpsetmask() sets the exception masks and returns the
       previous setting.

       fpgetsticky() returns the current exception sticky flags.

       fpsetsticky() sets (clears) the exception sticky flags and
       returns the previous setting.

       The default environment on the 3B computer family is:

            Rounding mode set to nearest(FP_RN),
            Divide-by-zero,
            Floating point overflow, and
            Invalid  operation traps enabled.

  SEE ALSO
       isnan(3C).

  WARNINGS
       fpsetsticky() modifies all sticky flags. fpsetmask() changes
       all mask bits.

       Both C and F77 require truncation (round to zero) for
       floating point to integral conversions.  The current
       rounding mode has no effect on these conversions.

  CAVEATS


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  FPGETROUND(3C)  (C Programming Language Utilities) FPGETROUND(3C)



       One must clear the sticky bit to recover from the trap and
       to proceed.  If the sticky bit is not cleared before the
       next trap occurs, a wrong exception type may be signaled.

       For the same reason, when calling fpsetmask() the user
       should make sure that the sticky bit corresponding to the
       exception being enabled is cleared.



































  Page 3                                                   May 1989