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
atanh(double x)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