xref: /titanic_44/usr/src/lib/libast/common/uwin/atanh.c (revision 45405cce0657d01714b3d014a0facf3bdce45736)
1 #include "FEATURE/uwin"
2 
3 #if !_UWIN || _lib_atanh
4 
5 void _STUB_atanh(){}
6 
7 #else
8 
9 /*
10  * Copyright (c) 1985, 1993
11  *	The Regents of the University of California.  All rights reserved.
12  *
13  * Redistribution and use in source and binary forms, with or without
14  * modification, are permitted provided that the following conditions
15  * are met:
16  * 1. Redistributions of source code must retain the above copyright
17  *    notice, this list of conditions and the following disclaimer.
18  * 2. Redistributions in binary form must reproduce the above copyright
19  *    notice, this list of conditions and the following disclaimer in the
20  *    documentation and/or other materials provided with the distribution.
21  * 3. Neither the name of the University nor the names of its contributors
22  *    may be used to endorse or promote products derived from this software
23  *    without specific prior written permission.
24  *
25  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
26  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
27  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
28  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
29  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
30  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
31  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
32  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
33  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
34  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35  * SUCH DAMAGE.
36  */
37 
38 #ifndef lint
39 static char sccsid[] = "@(#)atanh.c	8.1 (Berkeley) 6/4/93";
40 #endif /* not lint */
41 
42 /* ATANH(X)
43  * RETURN THE HYPERBOLIC ARC TANGENT OF X
44  * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
45  * CODED IN C BY K.C. NG, 1/8/85;
46  * REVISED BY K.C. NG on 2/7/85, 3/7/85, 8/18/85.
47  *
48  * Required kernel function:
49  *	log1p(x) 	...return log(1+x)
50  *
51  * Method :
52  *	Return
53  *                          1              2x                          x
54  *		atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
55  *                          2             1 - x                      1 - x
56  *
57  * Special cases:
58  *	atanh(x) is NaN if |x| > 1 with signal;
59  *	atanh(NaN) is that NaN with no signal;
60  *	atanh(+-1) is +-INF with signal.
61  *
62  * Accuracy:
63  *	atanh(x) returns the exact hyperbolic arc tangent of x nearly rounded.
64  *	In a test run with 512,000 random arguments on a VAX, the maximum
65  *	observed error was 1.87 ulps (units in the last place) at
66  *	x= -3.8962076028810414000e-03.
67  */
68 #include "mathimpl.h"
69 
70 #if defined(vax)||defined(tahoe)
71 #include <errno.h>
72 #endif	/* defined(vax)||defined(tahoe) */
73 
74 extern double atanh(x)
75 double x;
76 {
77 	double z;
78 	z = copysign(0.5,x);
79 	x = copysign(x,1.0);
80 #if defined(vax)||defined(tahoe)
81 	if (x == 1.0) {
82 	    return(copysign(1.0,z)*infnan(ERANGE));	/* sign(x)*INF */
83 	}
84 #endif	/* defined(vax)||defined(tahoe) */
85 	x = x/(1.0-x);
86 	return( z*log1p(x+x) );
87 }
88 
89 #endif
90