.\"	$OpenBSD: feclearexcept.3,v 1.3 2011/12/23 17:00:47 jmc Exp $
.\"
.\" Copyright (c) 2011 Martynas Venckus <martynas@openbsd.org>
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.Dd $Mdocdate: December 23 2011 $
.Dt FECLEAREXCEPT 3
.Os
.Sh NAME
.Nm feclearexcept ,
.Nm fegetexceptflag ,
.Nm feraiseexcept ,
.Nm fesetexceptflag ,
.Nm fetestexcept
.Nd access floating-point status flags
.Sh SYNOPSIS
.Fd #include <fenv.h>
.Ft int
.Fn feclearexcept "int excepts"
.Ft int
.Fn fegetexceptflag "fexcept_t *flagp" "int excepts"
.Ft int
.Fn feraiseexcept "int excepts"
.Ft int
.Fn fesetexceptflag "const fexcept_t *flagp" "int excepts"
.Ft int
.Fn fetestexcept "int excepts"
.Sh DESCRIPTION
These functions provide access to the floating-point status flags.
The
.Fa excepts
input argument is a bitmask specifying an exception type and
containing any of the values listed below.
.Bl -tag -width ".Dv FE_DIVBYZERO"
.It Dv FE_DIVBYZERO
A divide-by-zero exception occurs when the program attempts to
divide a finite non-zero number by zero.
.It Dv FE_INEXACT
An inexact exception is raised whenever there is a loss of precision
due to rounding.
.It Dv FE_INVALID
Invalid operation exceptions occur when a program attempts to
perform calculations for which there is no reasonable representable
answer.
.Pp
For instance, subtraction of infinities, division of zero by zero,
ordered comparison involving \*(Nas, and taking the square root of a
negative number are all invalid operations.
.It Dv FE_OVERFLOW
An overflow exception occurs when the magnitude of the result of a
computation is too large to fit in the destination type.
.It Dv FE_UNDERFLOW
Underflow occurs when the result of a computation is too close to zero
to be represented as a non-zero value in the destination type.
.It Dv FE_DENORMAL
Denormalization exception occurs when the result of a floating-point
expression is a denormalized number.
.Pp
This is available only on the floating-point implementations of
amd64 and i386 processors.
.El
.Pp
Additionally, the macro
.Dv FE_ALL_EXCEPT
is simply the bitwise OR of all floating-point exception macros
listed above.
.Pp
The
.Fn feclearexcept
function clears the floating-point exceptions represented by
.Fa excepts .
.Pp
The
.Fn fegetexceptflag
function stores a representation of the states of the floating-point
flags indicated by
.Pa excepts
in the object pointed to by
.Pa flagp .
.Pp
The
.Fn feraiseexcept
function raises floating-point exceptions represented by
.Pa excepts .
.Pp
The
.Fn fesetexceptflag
function sets the floating-point status flags indicated by
.Pa excepts
to the states stored in the object pointed to by
.Pa flagp .
The value of
.Pa flagp
shall have been set by a previous call to
.Fn fegetexceptflag
whose second argument represented at least those floating-point
exceptions represented by
.Pa excepts .
This function does not raise floating-point exceptions, but only
sets the state of the flags.
.Pp
The
.Fn fetesteexcept
function determines which of a specified subset of the floating-point
exception flags are currently set.
The
.Pa excepts
specifies the floating-point status flags to be queried.
.Sh RETURN VALUES
The
.Fn feclearexcept ,
.Fn fegetexceptflag ,
.Fn feraiseexcept ,
and
.Fn fesetexceptflag
functions return zero on success, and non-zero if an error occurred.
The
.Fn fetestexcept
function returns a bitmask of a specified subset of the floating-point
exception flags which are currently set.
.Sh SEE ALSO
.Xr feenableexcept 3 ,
.Xr fegetenv 3 ,
.Xr fegetround 3
.Sh STANDARDS
The
.Fn feclearexcept ,
.Fn fegetexceptflag ,
.Fn feraiseexcept ,
.Fn fesetexceptflag ,
and
.Fn fetestexcept
functions conform to
.St -isoC-99 .
.Pp
The return types for
.Fn feclearexcept ,
.Fn fegetexceptflag ,
.Fn feraiseexcept ,
and
.Fn fesetexceptflag
are
.Vt int
for alignment with
.St -isoC-99
Defect Report #202.
.Sh HISTORY
These functions first appeared in
.Ox 5.0 .
.Sh CAVEATS
On some architectures,
.Fn feraiseexcept
additionally raises the
.Dq inexact
floating-point exception whenever it raises the
.Dq overflow
or
.Dq underflow
floating-point exception.