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
50 static const long double zero = 0.0L, half = 0.5L, one = 1.0L;
51
52 long double
atanhl(long double x)53 atanhl(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