fpsetround(3C)

NAME

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

SYNOPSIS

     #include <ieeefp.h>

     fp_rnd fpgetround(void);

     fp_rnd fpsetround(fp_rnd rnd_dir);

     fp_except fpgetmask(void);

     fp_except fpsetmask(fp_except mask);

     fp_except fpgetsticky(void);

     fp_except fpsetsticky(fp_except sticky);

DESCRIPTION

     There are five floating-point exceptions:

        o  divide-by-zero,

        o  overflow,

        o  underflow,

        o  imprecise (inexact) result, and

        o  invalid operation.

     When a floating-point exception  occurs,  the  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.

     The mask argument is formed by the logical OR  operation  of
     the following floating-point exception masks:

     FP_X_INV       /* invalid operation exception */
     FP_X_OFL       /* overflow exception */
     FP_X_UFL       /* underflow exception */
     FP_X_DZ        /* divide-by-zero exception */
     FP_X_IMP       /* imprecise (loss of precision) */

     The following floating-point rounding modes  are  passed  to
     fpsetround and returned by  fpgetround().

     FP_RN       /* round to nearest representative number */
     FP_RP       /* round to plus infinity */
     FP_RM       /* round to minus infinity */
     FP_RZ       /* round to zero (truncate) */

     The default environment is  rounding  mode  set  to  nearest
     (FP_RN) and all traps disabled.

     The fpsetsticky() function modifies all  sticky  flags.  The
     fpsetmask()  function changes all mask bits. The fpsetmask()
     function clears the sticky bit corresponding to  any  excep-
     tion being enabled.

RETURN VALUES

     The fpgetround() function returns the current rounding mode.

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

     The  fpgetmask()  function  returns  the  current  exception
     masks.

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

     The fpgetsticky() function  returns  the  current  exception
     sticky flags.

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

USAGE

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

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

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

ATTRIBUTES

     See attributes(5) for descriptions of the  following  attri-
     butes:

     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | MT-Level                    | MT-Safe                     |
    |_____________________________|_____________________________|

SEE ALSO

     isnan(3C), attributes(5)