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