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