fpgetround(3C)      (C Programming Language Utilities)       fpgetround(3C)


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

   SYNOPSIS
         #include <ieeefp.h>

         fprnd fpgetround (void);

         fprnd fpsetround (fprnd rnddir);

         fpexcept fpgetmask (void);

         fpexcept fpsetmask (fpexcept mask);

         fpexcept fpgetsticky (void);

         fpexcept fpsetsticky (fpexcept sticky);

   DESCRIPTION
         There are eight floating point exceptions: branch/set on unordered,
         signalling not a number, operand error, overflow, underflow, divide-
         by-zero, inexact operation, and inexact decimal input. When an
         exception occurs, the trap takes place if the corresponding mask bit
         is set(1), and the fact is noted by setting an associated accrued
         exception bit (sticky bit). There are five sticky bits: invalid
         operation, overflow, underflow, divide-by-zero, and inexact result.
         The following algorithm is used in setting the sticky bits:

               FPAIOP  |= FPEBSUN | FPESNAN | FPEOPERR
               FPAOVFL |= FPEOVFL
               FPAUNFL |= FPEUNFL & FPEINEX2
               FPADZ   |= FPEDZ
               FPAINEX |= FPEINEX1 | FPEINEX2 | FPEOVFL

         The fpexcept mask can take the following (not exclusive) values:

               /* exception enable */

               FPEBSUN   /* branch/set on unordered */
               FPESNAN   /* signalling not a number */
               FPEOPERR  /* operand error     */
               FPEOVFL   /* overflow          */
               FPEUNFL   /* underflow               */
               FPEDZ           /* divide-by-zero    */
               FPEINEX2  /* inexact operation       */
               FPEINEX1  /* inexact decimal input   */

               /* accrued exceptions */

               FPAIOP    /* invalid operation */


   7/91                                                                 Page 1

   fpgetround(3C)      (C Programming Language Utilities)       fpgetround(3C)


               FPAOVFL   /* overflow          */
               FPAUNFL   /* underflow           */
               FPADZ     /* divide-by-zero    */
               FPAINEX   /* inexact result    */

         The fprnd mask can take the following (exclusive) values to control
         the rounding mode:
               FPRN       /* round to nearest representative number */
               FPRZ       /* round to zero (truncate)           */
               FPRM       /* round to minus infinity            */
               FPRP       /* round to plus infinity             */

         The following 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 is rounding mode set to nearest(FPRN) and
         all traps disabled.

         Individual bits may be examined using the constants defined in
         <ieeefp.h>.

   SEE ALSO
         isnan(3C).

   NOTES
         fpsetsticky modifies all sticky flags. fpsetmask changes all mask
         bits.  fpsetmask clears the sticky bit associated with each exception
         being enabled according to the following table:
            sticky bit cleared  mask bit(s) set

               FPAIOP         FPEBSUN & FPESNAN & FPEOPERR
               FPAOVFL        FPEOVFL
               FPAUNFL        FPEUNFL | FPEINEX2
               FPADZ          FPEDZ
               FPAINEX        FPEINEX1 | FPEINEX2 | FPEOVFL



   Page 2                                                                 7/91

   fpgetround(3C)      (C Programming Language Utilities)       fpgetround(3C)


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

         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.














































   7/91                                                                 Page 3