1/* Copyright JS Foundation and other contributors, http://js.foundation
2 *
3 * Licensed under the Apache License, Version 2.0 (the "License");
4 * you may not use this file except in compliance with the License.
5 * You may obtain a copy of the License at
6 *
7 *     http://www.apache.org/licenses/LICENSE-2.0
8 *
9 * Unless required by applicable law or agreed to in writing, software
10 * distributed under the License is distributed on an "AS IS" BASIS
11 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 * See the License for the specific language governing permissions and
13 * limitations under the License.
14 *
15 * This file is based on work under the following copyright and permission
16 * notice:
17 *
18 *     Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
19 *
20 *     Developed at SunSoft, a Sun Microsystems, Inc. business.
21 *     Permission to use, copy, modify, and distribute this
22 *     software is freely granted, provided that this notice
23 *     is preserved.
24 *
25 *     @(#)e_atanh.c 1.3 95/01/18
26 */
27
28#include "jerry-libm-internal.h"
29
30/* atanh(x)
31 * Method :
32 *    1.Reduced x to positive by atanh(-x) = -atanh(x)
33 *    2.For x >= 0.5
34 *              1              2x                          x
35 *  atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
36 *              2             1 - x                      1 - x
37 *
38 *   For x < 0.5
39*    atanh(x) = 0.5 * log1p(2x + 2x * x / (1 - x))
40 *
41 * Special cases:
42 *  atanh(x) is NaN if |x| > 1 with signal;
43 *  atanh(NaN) is that NaN with no signal;
44 *  atanh(+-1) is +-INF with signal.
45 *
46 */
47
48#define zero 0.0
49#define one 1.0
50#define huge 1.0e+300
51
52double
53atanh (double x)
54{
55  double t;
56  int hx, ix;
57  double_accessor temp;
58  temp.dbl = x;
59  hx = temp.as_int.hi;
60  ix = hx & 0x7fffffff;
61
62  /* |x| > 1 */
63  if ((ix | ((unsigned int) (temp.as_int.lo | (-temp.as_int.lo)) >> 31)) > 0x3ff00000)
64  {
65    return NAN;
66  }
67  if (ix == 0x3ff00000)
68  {
69    return x / zero;
70  }
71  if (ix < 0x3e300000 && (huge + x) > zero)
72  {
73    return x; /* x<2**-28 */
74  }
75
76  /* x <- |x| */
77  temp.as_int.hi = ix;
78  if (ix < 0x3fe00000)
79  {
80    /* x < 0.5 */
81    t = temp.dbl + temp.dbl;
82    t = 0.5 * log1p (t + t * temp.dbl / (one - temp.dbl));
83  }
84  else
85  {
86    t = 0.5 * log1p ((temp.dbl + temp.dbl) / (one - temp.dbl));
87  }
88  if (hx >= 0)
89  {
90    return t;
91  }
92  else
93  {
94    return -t;
95  }
96} /* atanh */
97
98#undef zero
99#undef one
100#undef huge
101