181 lines
4.7 KiB
Groff
181 lines
4.7 KiB
Groff
.\" Copyright (c) 1985, 1991 Regents of the University of California.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)infnan.3 6.5 (Berkeley) 4/19/91
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.\"
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.Dd April 19, 1991
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.Dt INFNAN 3
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.Os BSD 4.3
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.Sh NAME
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.Nm infnan
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.Nd signals invalid floating\-point operations on a
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.Tn VAX
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(temporary)
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.Sh SYNOPSIS
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.Fd #include <math.h>
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.Ft double
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.Fn infnan "int iarg"
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.Sh DESCRIPTION
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At some time in the future, some of the useful properties of
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the Infinities and \*(Nas in the
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.Tn IEEE
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standard 754 for Binary
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Floating\-Point Arithmetic will be simulated in
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.Tn UNIX
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on the
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.Tn DEC VAX
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by using its Reserved Operands. Meanwhile, the
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Invalid, Overflow and Divide\-by\-Zero exceptions of the
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.Tn IEEE
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standard are being approximated on a
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.Tn VAX
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by calls to a
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procedure
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.Fn infnan
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in appropriate places in
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.Xr libm 3 .
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When
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better exception\-handling is implemented in
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.Tn UNIX ,
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only
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.Fn infnan
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among the codes in
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.Xr libm
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will have to be changed.
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And users of
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.Xr libm
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can design their own
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.Fn infnan
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now to
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insulate themselves from future changes.
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.Pp
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Whenever an elementary function code in
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.Xr libm
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has to
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simulate one of the aforementioned
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.Tn IEEE
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exceptions, it calls
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.Fn infnan iarg
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with an appropriate value of
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.Fa iarg .
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Then a
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reserved operand fault stops computation. But
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.Fn infnan
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could
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be replaced by a function with the same name that returns
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some plausible value, assigns an apt value to the global
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variable
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.Va errno ,
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and allows computation to resume.
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Alternatively, the Reserved Operand Fault Handler could be
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changed to respond by returning that plausible value, etc.
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instead of aborting.
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.Pp
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In the table below, the first two columns show various
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exceptions signaled by the
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.Tn IEEE
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standard, and the default
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result it prescribes. The third column shows what value is
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given to
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.Fa iarg
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by functions in
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.Xr libm
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when they
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invoke
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.Fn infnan iarg
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under analogous circumstances on a
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.Tn VAX .
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Currently
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.Fn infnan
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stops computation under all those
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circumstances. The last two columns offer an alternative;
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they suggest a setting for
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.Va errno
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and a value for a
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revised
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.Fn infnan
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to return. And a C program to
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implement that suggestion follows.
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.sp 0.5
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.Bd -filled -offset indent
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.Bl -column "IEEE Signal" "IEEE Default" XXERANGE ERANGEXXorXXEDOM
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.It IEEE Signal IEEE Default Ta
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.Fa iarg Ta
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.Va errno Ta
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.Fn infnan
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.It Invalid \*(Na Ta
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.Dv EDOM EDOM 0
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.It Overflow \(+-\*(If Ta
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.Dv ERANGE ERANGE HUGE
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.It Div\-by\-0 \(+-Infinity Ta
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.Dv \(+-ERANGE ERANGE or EDOM \(+-HUGE
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.It ( Ns Dv HUGE No "= 1.7e38 ... nearly 2.0**127)"
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.El
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.Ed
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.Pp
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ALTERNATIVE
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.Fn infnan :
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.Bd -literal -offset indent
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#include <math.h>
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#include <errno.h>
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extern int errno ;
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double infnan(iarg)
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int iarg ;
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{
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switch(iarg) {
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case \0ERANGE: errno = ERANGE; return(HUGE);
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case \-ERANGE: errno = EDOM; return(\-HUGE);
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default: errno = EDOM; return(0);
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}
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}
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.Ed
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.Sh SEE ALSO
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.Xr math 3 ,
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.Xr intro 2 ,
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.Xr signal 3 .
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.Pp
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.Dv ERANGE
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and
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.Dv EDOM
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are defined in
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.Aq Pa errno.h .
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(See
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.Xr intro 2
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for explanation of
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.Dv EDOM
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and
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.Dv ERANGE . )
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.Sh HISTORY
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The
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.Fn infnan
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function appeared in
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.Bx 4.3 .
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