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 __atanhl = atanhl
31
32 #include "libm.h"
33
34 #define GENERIC long double
35 #define ATANH atanhl
36
37 /* ATANH(x)
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 */
52
53 #define FABS fabsl
54 #define LOG1P log1pl
55 #define COPYSIGN copysignl
56
57
58 extern GENERIC FABS(),LOG1P(),COPYSIGN();
59
60 static GENERIC
61 zero = (GENERIC) 0.0,
62 half = (GENERIC) 0.5,
63 one = (GENERIC) 1.0;
64
ATANH(x)65 GENERIC ATANH(x)
66 GENERIC x;
67 {
68 GENERIC t;
69 t = FABS(x);
70 if (t == one) return x/zero;
71 t = t/(one-t);
72 return COPYSIGN(half,x)*LOG1P(t+t);
73 }
74