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 #if defined(ELFOBJ)
31 #pragma weak tanhl = __tanhl
32 #endif
33
34 /*
35 * tanhl(x) returns the hyperbolic tangent of x
36 *
37 * Method :
38 * 1. reduce x to non-negative: tanhl(-x) = - tanhl(x).
39 * 2.
40 * 0 < x <= small : tanhl(x) := x
41 * -expm1l(-2x)
42 * small < x <= 1 : tanhl(x) := --------------
43 * expm1l(-2x) + 2
44 * 2
45 * 1 <= x <= threshold : tanhl(x) := 1 - ---------------
46 * expm1l(2x) + 2
47 * threshold < x <= INF : tanhl(x) := 1.
48 *
49 * where
50 * single : small = 1.e-5 threshold = 11.0
51 * double : small = 1.e-10 threshold = 22.0
52 * quad : small = 1.e-20 threshold = 45.0
53 *
54 * Note: threshold was chosen so that
55 * fl(1.0+2/(expm1(2*threshold)+2)) == 1.
56 *
57 * Special cases:
58 * tanhl(NaN) is NaN;
59 * only tanhl(0.0)=0.0 is exact for finite argument.
60 */
61
62 #include "libm.h"
63 #include "longdouble.h"
64
65 static const long double small = 1.0e-20L, one = 1.0, two = 2.0,
66 #ifndef lint
67 big = 1.0e+20L,
68 #endif
69 threshold = 45.0L;
70
71 long double
72 tanhl(long double x) {
73 long double t, y, z;
74 int signx;
75
76 if (isnanl(x))
77 return (x + x); /* x is NaN */
78 signx = signbitl(x);
79 t = fabsl(x);
80 z = one;
81 if (t <= threshold) {
82 if (t > one)
83 z = one - two / (expm1l(t + t) + two);
84 else if (t > small) {
85 y = expm1l(-t - t);
86 z = -y / (y + two);
87 } else {
88 #ifndef lint
89 volatile long double dummy = t + big;
90 /* inexact if t != 0 */
91 #endif
92 return (x);
93 }
94 } else if (!finitel(t))
95 return (copysignl(one, x));
96 else
97 return (signx ? -z + small * small : z - small * small);
98 return (signx ? -z : z);
99 }