share/man/man3/fpgetround.3

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.\"     @(#)fpgetround.3        1.0 (Berkeley) 9/23/93
.\"
.Dd August 23, 1993
.Dt FPGETROUND 3
.Os
.Sh NAME
.Nm fpgetround ,
.Nm fpsetround ,
.Nm fpgetmask ,
.Nm fpsetmask ,
.Nm fpgetsticky ,
.Nm fpresetsticky
.Nd IEEE floating point interface
.Sh SYNOPSIS
.Fd #include <floatingpoint.h>
.Ft typedef enum {
.br
.Ft     FP_RN,
.Li             /* round to nearest */
.br
.Ft     FP_RM,
.Li             /* round to minus infinity */
.br
.Ft     FP_RP,
.Li             /* round to plus inifinity */
.br
.Ft     FP_RZ,
.Li             /* truncate */
.br
.Ft } fp_rnd;
.Pp
.Ft fp_rnd
.Fn fpgetround ""
.Ft fp_rnd
.Fn fpsetround "fp_rnd direction"
.Fd #define fp_except int
.Fd #define FP_X_INV    0x01            /* invalid */
.Fd #define FP_X_OFL    0x08            /* overflow */
.Fd #define FP_X_UFL    0x10            /* underflow */
.Fd #define FP_X_DZ     0x04            /* divide-by-zero */
.Fd #define FP_X_IMP    0x20            /* loss of precision */
.Fd #define FP_X_DNML   0x02            /* denormal */
.Ft fp_except
.Fn fpgetmask ""
.Ft fp_except
.Fn fpsetmask "fp_except mask"
.Ft fp_except
.Fn fpgetsticky ""
.Ft fp_except
.Fn fpresetsticky "fp_except sticky"
.Sh DESCRIPTION
When a floating point exception is detected, the exception sticky flag is
set and the exception mask is tested. If the mask is set, then a trap
occurs.  These routines allow both setting the floating point exception
masks, and  resetting the exception sticky flags after an exception is
detected.  In addition, they allow setting the floating point rounding mode.
.Pp
The
.Fn fpgetround
function
returns the current floating point rounding mode.
.Pp
The
.Fn fpsetround
function
sets the floating point rounding mode and returns
the previous mode.
.Pp
The
.Fn fpgetmask
function
returns the current floating point exception masks.
.Pp
The
.Fn fpsetmask
function
sets the floating point exception masks and returns the
previous masks.
.Pp
The
.Fn fpgetsticky
function
returns the current floating point sticky flags.
.Pp
The
.Fn fpresetsticky
function
clears the floating point sticky flags and returns
the previous flags.
.Pp
Sample code which prevents a trap on divide-by-zero:
.Bd -literal -offset indent
fpsetmask(~FP_X_DZ);
a = 1.0;
b = 0;
c = a / b;
fpresetsticky(FP_X_DZ);
fpsetmask(FP_X_DZ);
.Ed
.Sh SEE ALSO
.Xr isnan 3
.Sh CAVEAT
After a floating point exception and before a mask is set, the sticky
flags must be reset.  If another exception occurs before the sticky
flags are reset, then a wrong exception type may be signaled.
.Sh HISTORY
These routines are based on SysV/386 routines of the same name.