1 #include "FEATURE/uwin"
2
3 #if !_UWIN || _lib_atanh
4
_STUB_atanh()5 void _STUB_atanh(){}
6
7 #else
8
9 /*
10 * Copyright (c) 1985, 1993
11 * The Regents of the University of California. All rights reserved.
12 *
13 * Redistribution and use in source and binary forms, with or without
14 * modification, are permitted provided that the following conditions
15 * are met:
16 * 1. Redistributions of source code must retain the above copyright
17 * notice, this list of conditions and the following disclaimer.
18 * 2. Redistributions in binary form must reproduce the above copyright
19 * notice, this list of conditions and the following disclaimer in the
20 * documentation and/or other materials provided with the distribution.
21 * 3. Neither the name of the University nor the names of its contributors
22 * may be used to endorse or promote products derived from this software
23 * without specific prior written permission.
24 *
25 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
26 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
27 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
28 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
29 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
30 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
31 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
32 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
33 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
34 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35 * SUCH DAMAGE.
36 */
37
38 #ifndef lint
39 static char sccsid[] = "@(#)atanh.c 8.1 (Berkeley) 6/4/93";
40 #endif /* not lint */
41
42 /* ATANH(X)
43 * RETURN THE HYPERBOLIC ARC TANGENT OF X
44 * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
45 * CODED IN C BY K.C. NG, 1/8/85;
46 * REVISED BY K.C. NG on 2/7/85, 3/7/85, 8/18/85.
47 *
48 * Required kernel function:
49 * log1p(x) ...return log(1+x)
50 *
51 * Method :
52 * Return
53 * 1 2x x
54 * atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
55 * 2 1 - x 1 - x
56 *
57 * Special cases:
58 * atanh(x) is NaN if |x| > 1 with signal;
59 * atanh(NaN) is that NaN with no signal;
60 * atanh(+-1) is +-INF with signal.
61 *
62 * Accuracy:
63 * atanh(x) returns the exact hyperbolic arc tangent of x nearly rounded.
64 * In a test run with 512,000 random arguments on a VAX, the maximum
65 * observed error was 1.87 ulps (units in the last place) at
66 * x= -3.8962076028810414000e-03.
67 */
68 #include "mathimpl.h"
69
70 #if defined(vax)||defined(tahoe)
71 #include <errno.h>
72 #endif /* defined(vax)||defined(tahoe) */
73
74 extern double atanh(x)
75 double x;
76 {
77 double z;
78 z = copysign(0.5,x);
79 x = copysign(x,1.0);
80 #if defined(vax)||defined(tahoe)
81 if (x == 1.0) {
82 return(copysign(1.0,z)*infnan(ERANGE)); /* sign(x)*INF */
83 }
84 #endif /* defined(vax)||defined(tahoe) */
85 x = x/(1.0-x);
86 return( z*log1p(x+x) );
87 }
88
89 #endif
90