1*da2e3ebdSchin #include "FEATURE/uwin"
2*da2e3ebdSchin
3*da2e3ebdSchin #if !_UWIN || _lib_atanh
4*da2e3ebdSchin
_STUB_atanh()5*da2e3ebdSchin void _STUB_atanh(){}
6*da2e3ebdSchin
7*da2e3ebdSchin #else
8*da2e3ebdSchin
9*da2e3ebdSchin /*
10*da2e3ebdSchin * Copyright (c) 1985, 1993
11*da2e3ebdSchin * The Regents of the University of California. All rights reserved.
12*da2e3ebdSchin *
13*da2e3ebdSchin * Redistribution and use in source and binary forms, with or without
14*da2e3ebdSchin * modification, are permitted provided that the following conditions
15*da2e3ebdSchin * are met:
16*da2e3ebdSchin * 1. Redistributions of source code must retain the above copyright
17*da2e3ebdSchin * notice, this list of conditions and the following disclaimer.
18*da2e3ebdSchin * 2. Redistributions in binary form must reproduce the above copyright
19*da2e3ebdSchin * notice, this list of conditions and the following disclaimer in the
20*da2e3ebdSchin * documentation and/or other materials provided with the distribution.
21*da2e3ebdSchin * 3. Neither the name of the University nor the names of its contributors
22*da2e3ebdSchin * may be used to endorse or promote products derived from this software
23*da2e3ebdSchin * without specific prior written permission.
24*da2e3ebdSchin *
25*da2e3ebdSchin * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
26*da2e3ebdSchin * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
27*da2e3ebdSchin * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
28*da2e3ebdSchin * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
29*da2e3ebdSchin * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
30*da2e3ebdSchin * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
31*da2e3ebdSchin * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
32*da2e3ebdSchin * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
33*da2e3ebdSchin * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
34*da2e3ebdSchin * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35*da2e3ebdSchin * SUCH DAMAGE.
36*da2e3ebdSchin */
37*da2e3ebdSchin
38*da2e3ebdSchin #ifndef lint
39*da2e3ebdSchin static char sccsid[] = "@(#)atanh.c 8.1 (Berkeley) 6/4/93";
40*da2e3ebdSchin #endif /* not lint */
41*da2e3ebdSchin
42*da2e3ebdSchin /* ATANH(X)
43*da2e3ebdSchin * RETURN THE HYPERBOLIC ARC TANGENT OF X
44*da2e3ebdSchin * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
45*da2e3ebdSchin * CODED IN C BY K.C. NG, 1/8/85;
46*da2e3ebdSchin * REVISED BY K.C. NG on 2/7/85, 3/7/85, 8/18/85.
47*da2e3ebdSchin *
48*da2e3ebdSchin * Required kernel function:
49*da2e3ebdSchin * log1p(x) ...return log(1+x)
50*da2e3ebdSchin *
51*da2e3ebdSchin * Method :
52*da2e3ebdSchin * Return
53*da2e3ebdSchin * 1 2x x
54*da2e3ebdSchin * atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
55*da2e3ebdSchin * 2 1 - x 1 - x
56*da2e3ebdSchin *
57*da2e3ebdSchin * Special cases:
58*da2e3ebdSchin * atanh(x) is NaN if |x| > 1 with signal;
59*da2e3ebdSchin * atanh(NaN) is that NaN with no signal;
60*da2e3ebdSchin * atanh(+-1) is +-INF with signal.
61*da2e3ebdSchin *
62*da2e3ebdSchin * Accuracy:
63*da2e3ebdSchin * atanh(x) returns the exact hyperbolic arc tangent of x nearly rounded.
64*da2e3ebdSchin * In a test run with 512,000 random arguments on a VAX, the maximum
65*da2e3ebdSchin * observed error was 1.87 ulps (units in the last place) at
66*da2e3ebdSchin * x= -3.8962076028810414000e-03.
67*da2e3ebdSchin */
68*da2e3ebdSchin #include "mathimpl.h"
69*da2e3ebdSchin
70*da2e3ebdSchin #if defined(vax)||defined(tahoe)
71*da2e3ebdSchin #include <errno.h>
72*da2e3ebdSchin #endif /* defined(vax)||defined(tahoe) */
73*da2e3ebdSchin
74*da2e3ebdSchin extern double atanh(x)
75*da2e3ebdSchin double x;
76*da2e3ebdSchin {
77*da2e3ebdSchin double z;
78*da2e3ebdSchin z = copysign(0.5,x);
79*da2e3ebdSchin x = copysign(x,1.0);
80*da2e3ebdSchin #if defined(vax)||defined(tahoe)
81*da2e3ebdSchin if (x == 1.0) {
82*da2e3ebdSchin return(copysign(1.0,z)*infnan(ERANGE)); /* sign(x)*INF */
83*da2e3ebdSchin }
84*da2e3ebdSchin #endif /* defined(vax)||defined(tahoe) */
85*da2e3ebdSchin x = x/(1.0-x);
86*da2e3ebdSchin return( z*log1p(x+x) );
87*da2e3ebdSchin }
88*da2e3ebdSchin
89*da2e3ebdSchin #endif
90