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.\" Copyright (c) 2004 David Schultz <das@FreeBSD.org>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd March 16, 2005
.Dt FEENABLEEXCEPT 3
.Os
.Sh NAME
.Nm feenableexcept ,
.Nm fedisableexcept ,
.Nm fegetexcept
.Nd floating-point exception masking
.Sh LIBRARY
.Lb libm
.Sh SYNOPSIS
.In fenv.h
.Fd "#pragma STDC FENV_ACCESS ON"
.Ft int
.Fn feenableexcept "int excepts"
.Ft int
.Fn fedisableexcept "int excepts"
.Ft int
.Fn fegetexcept "void"
.Sh DESCRIPTION
The
.Fn feenableexcept
and
.Fn fedisableexcept
functions
unmask and mask (respectively) exceptions specified in
.Fa excepts .
The
.Fn fegetexcept
function
returns the current exception mask.
All exceptions are masked by default.
.Pp
Floating-point operations that produce unmasked exceptions will trap, and a
.Dv SIGFPE
will be delivered to the process.
By installing a signal handler for
.Dv SIGFPE ,
applications can take appropriate action immediately without
testing the exception flags after every operation.
Note that the trap may not be immediate, but it should occur
before the next floating-point instruction is executed.
.Pp
For all of these functions, the possible types of exceptions
include those described in
.Xr fenv 3 .
Some architectures may define other types of floating-point exceptions.
.Sh RETURN VALUES
The
.Fn feenableexcept ,
.Fn fedisableexcept ,
and
.Fn fegetexcept
functions return a bitmap of the exceptions that were unmasked
prior to the call.
.Sh SEE ALSO
.Xr sigaction 2 ,
.Xr feclearexcept 3 ,
.Xr feholdexcept 3 ,
.Xr fenv 3 ,
.Xr feupdateenv 3
.Sh BUGS
Functions in the standard library may trigger exceptions multiple
times as a result of intermediate computations;
however, they generally do not trigger spurious exceptions.
.Pp
No interface is provided to permit exceptions to be handled in
nontrivial ways.
There is no uniform way for an exception handler to access
information about the exception-causing instruction, or
to determine whether that instruction should be reexecuted
after returning from the handler.
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