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 tanh = __tanh
31
32 /* INDENT OFF */
33 /* TANH(X)
34 * RETURN THE HYPERBOLIC TANGENT OF X
35 * code based on 4.3bsd
36 * Modified by K.C. Ng for sun 4.0, Jan 31, 1987
37 *
38 * Method :
39 * 1. reduce x to non-negative by tanh(-x) = - tanh(x).
40 * 2.
41 * 0 < x <= 1.e-10 : tanh(x) := x
42 * -expm1(-2x)
43 * 1.e-10 < x <= 1 : tanh(x) := --------------
44 * expm1(-2x) + 2
45 * 2
46 * 1 <= x <= 22.0 : tanh(x) := 1 - ---------------
47 * expm1(2x) + 2
48 * 22.0 < x <= INF : tanh(x) := 1.
49 *
50 * Note: 22 was chosen so that fl(1.0+2/(expm1(2*22)+2)) == 1.
51 *
52 * Special cases:
53 * tanh(NaN) is NaN;
54 * only tanh(0)=0 is exact for finite argument.
55 */
56
57 #include "libm.h"
58 #include "libm_synonyms.h"
59 #include "libm_protos.h"
60 #include <math.h>
61
62 static const double
63 one = 1.0,
64 two = 2.0,
65 small = 1.0e-10,
66 big = 1.0e10;
67 /* INDENT ON */
68
69 double
70 tanh(double x) {
71 double t, y, z;
72 int signx;
73 volatile double dummy;
74
75 if (isnan(x))
76 return x * x; /* + -> * for Cheetah */
77 signx = signbit(x);
78 t = fabs(x);
79 z = one;
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 }
87 else { /* 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 }
95 else if (!finite(t))
96 return copysign(1.0, x);
97 else
98 return signx == 1 ? -z + small * small : z - small * small;
99
100 return signx == 1 ? -z : z;
101 }