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
58extern GENERIC 	FABS(),LOG1P(),COPYSIGN();
59
60static GENERIC
61zero	= (GENERIC) 0.0,
62half 	= (GENERIC) 0.5,
63one	= (GENERIC) 1.0;
64
65GENERIC ATANH(x)
66GENERIC 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