xref: /titanic_44/usr/src/lib/libm/common/C/atanh.c (revision a60349c89adffc0902b2353230891d8e7f2b24d9)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License (the "License").
6  * You may not use this file except in compliance with the License.
7  *
8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9  * or http://www.opensolaris.org/os/licensing.
10  * See the License for the specific language governing permissions
11  * and limitations under the License.
12  *
13  * When distributing Covered Code, include this CDDL HEADER in each
14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15  * If applicable, add the following below this CDDL HEADER, with the
16  * fields enclosed by brackets "[]" replaced with your own identifying
17  * information: Portions Copyright [yyyy] [name of copyright owner]
18  *
19  * CDDL HEADER END
20  */
21 
22 /*
23  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
24  */
25 /*
26  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
27  * Use is subject to license terms.
28  */
29 
30 #pragma weak __atanh = atanh
31 
32 /* INDENT OFF */
33 /*
34  * atanh(x)
35  * Code originated from 4.3bsd.
36  * Modified by K.C. Ng for SUN 4.0 libm.
37  * Method :
38  *                  1              2x                          x
39  *	atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
40  *                  2             1 - x                      1 - x
41  * Note: to guarantee atanh(-x) = -atanh(x), we use
42  *                 sign(x)             |x|
43  *	atanh(x) = ------- * log1p(2*-------).
44  *                    2              1 - |x|
45  *
46  * Special cases:
47  *	atanh(x) is NaN if |x| > 1 with signal;
48  *	atanh(NaN) is that NaN with no signal;
49  *	atanh(+-1) is +-INF with signal.
50  */
51 /* INDENT ON */
52 
53 #include "libm.h"
54 #include "libm_protos.h"
55 #include <math.h>
56 
57 double
58 atanh(double x) {
59 	double t;
60 
61 	if (isnan(x))
62 		return (x * x);		/* switched from x + x for Cheetah */
63 	t = fabs(x);
64 	if (t > 1.0)
65 		return (_SVID_libm_err(x, x, 30));	/* sNaN */
66 	if (t == 1.0)
67 		return (_SVID_libm_err(x, x, 31));	/* x/0; */
68 	t = t / (1.0 - t);
69 	return (copysign(0.5, x) * log1p(t + t));
70 }
71