.\" $OpenBSD: infnan.3,v 1.5 2000/11/08 20:43:38 deraadt Exp $ .\" .\" Copyright (c) 1985, 1991, 1993 .\" The Regents of the University of California. 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. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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. .\" .\" @(#)infnan.3 8.1 (Berkeley) 6/4/93 .\" .Dd June 4, 1993 .Dt INFNAN 3 .Os .Sh NAME .Nm infnan .Nd signals invalid floating\-point operations on a .Tn VAX (temporary) .Sh SYNOPSIS .Fd #include .Ft double .Fn infnan "int iarg" .Sh DESCRIPTION At some time in the future, some of the useful properties of the Infinities and \*(Nas in the .Tn IEEE standard 754 for Binary Floating\-Point Arithmetic will be simulated in .Tn UNIX on the .Tn DEC VAX by using its Reserved Operands. Meanwhile, the Invalid, Overflow and Divide\-by\-Zero exceptions of the .Tn IEEE standard are being approximated on a .Tn VAX by calls to a procedure .Fn infnan in appropriate places in .Xr libm 3 . When better exception\-handling is implemented in .Tn UNIX , only .Fn infnan among the codes in .Xr libm will have to be changed. And users of .Xr libm can design their own .Fn infnan now to insulate themselves from future changes. .Pp Whenever an elementary function code in .Xr libm has to simulate one of the aforementioned .Tn IEEE exceptions, it calls .Fn infnan iarg with an appropriate value of .Fa iarg . Then a reserved operand fault stops computation. But .Fn infnan could be replaced by a function with the same name that returns some plausible value, assigns an apt value to the global variable .Va errno , and allows computation to resume. Alternatively, the Reserved Operand Fault Handler could be changed to respond by returning that plausible value, etc. instead of aborting. .Pp In the table below, the first two columns show various exceptions signaled by the .Tn IEEE standard, and the default result it prescribes. The third column shows what value is given to .Fa iarg by functions in .Xr libm when they invoke .Fn infnan iarg under analogous circumstances on a .Tn VAX . Currently .Fn infnan stops computation under all those circumstances. The last two columns offer an alternative; they suggest a setting for .Va errno and a value for a revised .Fn infnan to return. And a C program to implement that suggestion follows. .sp 0.5 .Bd -filled -offset indent .Bl -column "IEEE Sig" "IEEE Default" XXERANGE ERANGExEDOM .It IEEE Signal IEEE Default Ta .Fa iarg Ta .Va errno Ta .Fn infnan .It Invalid \*(Na Ta .Dv EDOM EDOM 0 .It Overflow \(+-\*(If Ta .Dv ERANGE ERANGE HUGE .It Div\-by\-0 \(+-Infinity Ta .Dv \(+-ERANGE ERANGE/EDOM \(+-HUGE .It ( Ns Dv HUGE No "= 1.7e38 ... nearly 2.0**127)" .El .Ed .Pp ALTERNATIVE .Fn infnan : .Bd -literal -offset indent #include #include double infnan(iarg) int iarg; { switch (iarg) { case \0ERANGE: errno = ERANGE; return (HUGE); case \-ERANGE: errno = EDOM; return (\-HUGE); default: errno = EDOM; return (0); } } .Ed .Sh SEE ALSO .Xr intro 2 , .Xr math 3 , .Xr signal 3 .Pp .Dv ERANGE and .Dv EDOM are defined in .Aq Pa errno.h . (See .Xr intro 2 for explanation of .Dv EDOM and .Dv ERANGE . ) .Sh HISTORY The .Fn infnan function appeared in .Bx 4.3 .