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1.1 root 1: .\" Copyright (c) 1985 Regents of the University of California.
2: .\" All rights reserved. The Berkeley software License Agreement
3: .\" specifies the terms and conditions for redistribution.
4: .\"
5: .\" @(#)infnan.3 6.4 (Berkeley) 5/27/86
6: .\"
7: .TH INFNAN 3M "May 27, 1986"
8: .UC 6
9: .ds nn \fINaN\fR
10: .SH NAME
11: infnan \- signals invalid floating-point operations on a VAX (temporary)
12: .SH SYNOPSIS
13: .nf
14: .B #include <math.h>
15: .PP
16: .B double infnan(iarg)
17: .B int iarg;
18: .SH DESCRIPTION
19: At some time in the future, some of the useful properties of
20: the Infinities and \*(nns in the IEEE standard 754 for Binary
21: Floating\-Point Arithmetic will be simulated in UNIX on the
22: DEC VAX by using its Reserved Operands. Meanwhile, the
23: Invalid, Overflow and Divide\-by\-Zero exceptions of the
24: IEEE standard are being approximated on a VAX by calls to a
25: procedure \fIinfnan\fR in appropriate places in \fIlibm\fR. When
26: better exception\-handling is implemented in UNIX, only
27: \fIinfnan\fR among the codes in \fIlibm\fR will have to be changed.
28: And users of \fIlibm\fR can design their own \fIinfnan\fR now to
29: insulate themselves from future changes.
30: .PP
31: Whenever an elementary function code in \fIlibm\fR has to
32: simulate one of the aforementioned IEEE exceptions, it calls
33: infnan(iarg) with an appropriate value of \fIiarg\fR. Then a
34: reserved operand fault stops computation. But \fIinfnan\fR could
35: be replaced by a function with the same name that returns
36: some plausible value, assigns an apt value to the global
37: variable \fIerrno\fR, and allows computation to resume.
38: Alternatively, the Reserved Operand Fault Handler could be
39: changed to respond by returning that plausible value, etc.
40: instead of aborting.
41: .PP
42: In the table below, the first two columns show various
43: exceptions signaled by the IEEE standard, and the default
44: result it prescribes. The third column shows what value is
45: given to \fIiarg\fR by functions in \fIlibm\fR when they
46: invoke infnan(iarg) under analogous circumstances on a VAX.
47: Currently \fIinfnan\fR stops computation under all those
48: circumstances. The last two columns offer an alternative;
49: they suggest a setting for \fIerrno\fR and a value for a
50: revised \fIinfnan\fR to return. And a C program to
51: implement that suggestion follows.
52: .sp 0.5
53: .RS
54: .nf
55: .ta \w'Div\-by\-0'u+2n +\w'+Infinity'u+1n +\w'+ERANGE'u+1n +\w'ERANGE or EDOM'u+4n +\w'+HUGE'u+1n
56: IEEE IEEE
57: Signal Default \fIiarg\fR \fIerrno\fR \fIinfnan\fR
58: .if t \{\
59: .sp -0.5
60: .ta \w'Div\-by\-0'u+2n+\w'+Infinity'u+1n+\w'+ERANGE'u+1n+\w'ERANGE or EDOM'u+4n+\w'+HUGE'u+1n
61: .tc \(ru
62:
63: .ta \w'Div\-by\-0'u+2n +\w'+Infinity'u+1n +\w'+ERANGE'u+1n +\w'ERANGE or EDOM'u+4n +\w'+HUGE'u+1n
64: .tc \}
65: .if n \
66: \l'5i'
67: Invalid \*(nn EDOM EDOM 0
68: .if n \{\
69: Overflow \(+-Infinity ERANGE ERANGE HUGE
70: Div\-by\-0 \(+-Infinity \(+-ERANGE ERANGE or EDOM \(+-HUGE \}
71: .if t \{\
72: Overflow \(+-\(if ERANGE ERANGE HUGE
73: Div\-by\-0 \(+-\(if \(+-ERANGE ERANGE or EDOM \(+-HUGE \}
74: .sp 0.5
75: (HUGE = 1.7e38 ... nearly 2.0**127)
76: .ta
77: .fi
78: .RE
79: .sp 0.5
80: .PP
81: .nf
82: .ta \w'\fBextern int\fR'u+1n +\w'\fBdefault:\fR'u+1n +\w'\fB\-ERANGE:\fR'u+1n +\w'\fBerrno = ERANGE;\fR'u+1n
83: ALTERNATIVE \fIinfnan\fR:\fB
84: .sp 0.5
85: #include <math.h>
86: #include <errno.h>
87: extern int errno ;
88: double infnan(iarg)
89: int iarg ;
90: {
91: switch(iarg) {
92: case \0ERANGE: errno = ERANGE; return(HUGE);
93: case \-ERANGE: errno = EDOM; return(\-HUGE);
94: default: errno = EDOM; return(0);
95: }
96: }\fR
97: .ta
98: .fi
99: .SH SEE ALSO
100: math(3M), intro(2), signal(3).
101: .PP
102: ERANGE and EDOM are defined in <errno.h>. See intro(2)
103: for explanation of EDOM and ERANGE.
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