1/*
2 * Copyright (c) 1998, 2001, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26/* __ieee754_atanh(x)
27 * Method :
28 * 1.Reduced x to positive by atanh(-x) = -atanh(x)
29 * 2.For x>=0.5
30 * 1 2x x
31 * atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
32 * 2 1 - x 1 - x
33 *
34 * For x<0.5
35 * atanh(x) = 0.5*log1p(2x+2x*x/(1-x))
36 *
37 * Special cases:
38 * atanh(x) is NaN if |x| > 1 with signal;
39 * atanh(NaN) is that NaN with no signal;
40 * atanh(+-1) is +-INF with signal.
41 *
42 */
43
44#include "fdlibm.h"
45
46#ifdef __STDC__
47static const double one = 1.0, huge = 1e300;
48#else
49static double one = 1.0, huge = 1e300;
50#endif
51
52static double zero = 0.0;
53
54#ifdef __STDC__
55 double __ieee754_atanh(double x)
56#else
57 double __ieee754_atanh(x)
58 double x;
59#endif
60{
61 double t;
62 int hx,ix;
63 unsigned lx;
64 hx = __HI(x); /* high word */
65 lx = __LO(x); /* low word */
66 ix = hx&0x7fffffff;
67 if ((ix|((lx|(-lx))>>31))>0x3ff00000) /* |x|>1 */
68 return (x-x)/(x-x);
69 if(ix==0x3ff00000)
70 return x/zero;
71 if(ix<0x3e300000&&(huge+x)>zero) return x; /* x<2**-28 */
72 __HI(x) = ix; /* x <- |x| */
73 if(ix<0x3fe00000) { /* x < 0.5 */
74 t = x+x;
75 t = 0.5*log1p(t+t*x/(one-x));
76 } else
77 t = 0.5*log1p((x+x)/(one-x));
78 if(hx>=0) return t; else return -t;
79}
80