1.\" $NetBSD: feenableexcept.3,v 1.1 2010/07/31 21:47:53 joerg Exp $ 2.\" Copyright (c) 2004 David Schultz <das@FreeBSD.org> 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.Dd March 16, 2005 27.Dt FEENABLEEXCEPT 3 28.Os 29.Sh NAME 30.Nm feenableexcept , 31.Nm fedisableexcept , 32.Nm fegetexcept 33.Nd floating-point exception masking 34.Sh LIBRARY 35.Lb libm 36.Sh SYNOPSIS 37.In fenv.h 38.Fd "#pragma STDC FENV_ACCESS ON" 39.Ft int 40.Fn feenableexcept "int excepts" 41.Ft int 42.Fn fedisableexcept "int excepts" 43.Ft int 44.Fn fegetexcept "void" 45.Sh DESCRIPTION 46The 47.Fn feenableexcept 48and 49.Fn fedisableexcept 50functions 51unmask and mask (respectively) exceptions specified in 52.Fa excepts . 53The 54.Fn fegetexcept 55function 56returns the current exception mask. 57All exceptions are masked by default. 58.Pp 59Floating-point operations that produce unmasked exceptions will trap, and a 60.Dv SIGFPE 61will be delivered to the process. 62By installing a signal handler for 63.Dv SIGFPE , 64applications can take appropriate action immediately without 65testing the exception flags after every operation. 66Note that the trap may not be immediate, but it should occur 67before the next floating-point instruction is executed. 68.Pp 69For all of these functions, the possible types of exceptions 70include those described in 71.Xr fenv 3 . 72Some architectures may define other types of floating-point exceptions. 73.Sh RETURN VALUES 74The 75.Fn feenableexcept , 76.Fn fedisableexcept , 77and 78.Fn fegetexcept 79functions return a bitmap of the exceptions that were unmasked 80prior to the call. 81.Sh SEE ALSO 82.Xr sigaction 2 , 83.Xr feclearexcept 3 , 84.Xr feholdexcept 3 , 85.Xr fenv 3 , 86.Xr feupdateenv 3 87.Sh BUGS 88Functions in the standard library may trigger exceptions multiple 89times as a result of intermediate computations; 90however, they generally do not trigger spurious exceptions. 91.Pp 92No interface is provided to permit exceptions to be handled in 93nontrivial ways. 94There is no uniform way for an exception handler to access 95information about the exception-causing instruction, or 96to determine whether that instruction should be reexecuted 97after returning from the handler. 98