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 /*
27 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
28 * Use is subject to license terms.
29 */
30
31 #pragma weak __tanh = tanh
32
33
34 /*
35 * TANH(X)
36 * RETURN THE HYPERBOLIC TANGENT OF X
37 * code based on 4.3bsd
38 * Modified by K.C. Ng for sun 4.0, Jan 31, 1987
39 *
40 * Method :
41 * 1. reduce x to non-negative by tanh(-x) = - tanh(x).
42 * 2.
43 * 0 < x <= 1.e-10 : tanh(x) := x
44 * -expm1(-2x)
45 * 1.e-10 < x <= 1 : tanh(x) := --------------
46 * expm1(-2x) + 2
47 * 2
48 * 1 <= x <= 22.0 : tanh(x) := 1 - ---------------
49 * expm1(2x) + 2
50 * 22.0 < x <= INF : tanh(x) := 1.
51 *
52 * Note: 22 was chosen so that fl(1.0+2/(expm1(2*22)+2)) == 1.
53 *
54 * Special cases:
55 * tanh(NaN) is NaN;
56 * only tanh(0)=0 is exact for finite argument.
57 */
58
59 #include "libm.h"
60 #include "libm_protos.h"
61 #include <math.h>
62
63 static const double one = 1.0, two = 2.0, small = 1.0e-10, big = 1.0e10;
64
65
66 double
67 tanh(double x)
68 {
69 double t, y, z;
70 int signx;
71 volatile double dummy __unused;
72
73 if (isnan(x))
74 return (x * x); /* + -> * for Cheetah */
75
76 signx = signbit(x);
77 t = fabs(x);
78 z = one;
79
80 if (t <= 22.0) {
81 if (t > one) {
82 z = one - two / (expm1(t + t) + two);
83 } else if (t > small) {
84 y = expm1(-t - t);
85 z = -y / (y + two);
86 } else {
87 /* raise the INEXACT flag for non-zero t */
88 dummy = t + big;
89 #ifdef lint
90 dummy = dummy;
91 #endif
92 return (x);
93 }
94 } else if (!finite(t)) {
95 return (copysign(1.0, x));
96 } else {
97 return ((signx != 0) ? -z + small * small : z - small * small);
98 }
99
100 return ((signx != 0) ? -z : z);
101 }