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/*
35 *                   1              2x                           x
36 *	atanhl(x) = --- * LOG(1 + -------) = 0.5 * log1pl(2 * --------)
37 *                   2             1 - x                       1 - x
38 * Note: to guarantee atanhl(-x) = -atanhl(x), we use
39 *                  sign(x)              |x|
40 *	atanhl(x) = ------- * log1pl(2*-------).
41 *                     2               1 - |x|
42 *
43 * Special cases:
44 *	atanhl(x) is NaN if |x| > 1 with signal;
45 *	atanhl(NaN) is that NaN with no signal;
46 *	atanhl(+-1) is +-INF with signal.
47 *
48 */
49
50static const long double zero = 0.0L, half = 0.5L, one = 1.0L;
51
52long double
53atanhl(long double x) {
54	long double t;
55
56	t = fabsl(x);
57	if (t == one)
58		return (x / zero);
59	t = t / (one - t);
60	return (copysignl(half, x) * log1pl(t + t));
61}
62