freebsd-skq/share/man/man3/fpgetround.3

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.\"     @(#)fpgetround.3	1.0 (Berkeley) 9/23/93
.\" $FreeBSD$
.\"
.Dd December 3, 2010
.Dt FPGETROUND 3
.Os
.Sh NAME
.Nm fpgetround ,
.Nm fpsetround ,
.Nm fpsetprec ,
.Nm fpgetprec ,
.Nm fpgetmask ,
.Nm fpsetmask ,
.Nm fpgetsticky ,
.Nm fpresetsticky
.Nd IEEE floating point interface
.Sh SYNOPSIS
.In ieeefp.h
.Bd -literal
typedef enum {
	FP_RN,		/* round to nearest */
	FP_RM,		/* round down to minus infinity */
	FP_RP,		/* round up to plus infinity */
	FP_RZ		/* truncate */
} fp_rnd_t;
.Ed
.Ft fp_rnd_t
.Fn fpgetround void
.Ft fp_rnd_t
.Fn fpsetround "fp_rnd_t direction"
.Bd -literal
typedef enum {
	FP_PS,		/* 24 bit (single-precision) */
	FP_PRS,		/* reserved */
	FP_PD,		/* 53 bit (double-precision) */
	FP_PE		/* 64 bit (extended-precision) */
} fp_prec_t;
.Ed
.Ft fp_prec_t
.Fn fpgetprec void
.Ft fp_prec_t
.Fn fpsetprec "fp_prec_t precision"
.Bd -literal
#define fp_except_t	int
#define FP_X_INV	0x01	/* invalid operation */
#define FP_X_DNML	0x02	/* denormal */
#define FP_X_DZ		0x04	/* zero divide */
#define FP_X_OFL	0x08	/* overflow */
#define FP_X_UFL	0x10	/* underflow */
#define FP_X_IMP	0x20	/* (im)precision */
#define FP_X_STK	0x40	/* stack fault */
.Ed
.Ft fp_except_t
.Fn fpgetmask void
.Ft fp_except_t
.Fn fpsetmask "fp_except_t mask"
.Ft fp_except_t
.Fn fpgetsticky void
.Ft fp_except_t
.Fn fpresetsticky "fp_except_t sticky"
.Sh DESCRIPTION
The routines described herein are deprecated.
New code should use the functionality provided by
.Xr fenv 3 .
.Pp
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
and precision.
.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 fpgetprec
function
returns the current floating point precision.
.Pp
The
.Fn fpsetprec
function
sets the floating point precision and returns
the previous precision.
.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 IMPLEMENTATION NOTES
The
.Fn fpgetprec
and
.Fn fpsetprec
functions provide functionality unavailable on many platforms.
At present, they are implemented only on the i386 and amd64 platforms.
Changing precision isn't a supported feature:
it may be ineffective when code is compiled to take advantage of SSE,
and many library functions and compiler optimizations depend upon the
default precision for correct behavior.
.Sh SEE ALSO
.Xr fenv 3 ,
.Xr isnan 3
.Sh HISTORY
These routines are based on SysV/386 routines of the same name.
.Sh CAVEATS
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.