1*4887Schin #include "FEATURE/uwin"
2*4887Schin
3*4887Schin #if !_UWIN || _lib_atanh
4*4887Schin
_STUB_atanh()5*4887Schin void _STUB_atanh(){}
6*4887Schin
7*4887Schin #else
8*4887Schin
9*4887Schin /*
10*4887Schin * Copyright (c) 1985, 1993
11*4887Schin * The Regents of the University of California. All rights reserved.
12*4887Schin *
13*4887Schin * Redistribution and use in source and binary forms, with or without
14*4887Schin * modification, are permitted provided that the following conditions
15*4887Schin * are met:
16*4887Schin * 1. Redistributions of source code must retain the above copyright
17*4887Schin * notice, this list of conditions and the following disclaimer.
18*4887Schin * 2. Redistributions in binary form must reproduce the above copyright
19*4887Schin * notice, this list of conditions and the following disclaimer in the
20*4887Schin * documentation and/or other materials provided with the distribution.
21*4887Schin * 3. Neither the name of the University nor the names of its contributors
22*4887Schin * may be used to endorse or promote products derived from this software
23*4887Schin * without specific prior written permission.
24*4887Schin *
25*4887Schin * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
26*4887Schin * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
27*4887Schin * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
28*4887Schin * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
29*4887Schin * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
30*4887Schin * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
31*4887Schin * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
32*4887Schin * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
33*4887Schin * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
34*4887Schin * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35*4887Schin * SUCH DAMAGE.
36*4887Schin */
37*4887Schin
38*4887Schin #ifndef lint
39*4887Schin static char sccsid[] = "@(#)atanh.c 8.1 (Berkeley) 6/4/93";
40*4887Schin #endif /* not lint */
41*4887Schin
42*4887Schin /* ATANH(X)
43*4887Schin * RETURN THE HYPERBOLIC ARC TANGENT OF X
44*4887Schin * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
45*4887Schin * CODED IN C BY K.C. NG, 1/8/85;
46*4887Schin * REVISED BY K.C. NG on 2/7/85, 3/7/85, 8/18/85.
47*4887Schin *
48*4887Schin * Required kernel function:
49*4887Schin * log1p(x) ...return log(1+x)
50*4887Schin *
51*4887Schin * Method :
52*4887Schin * Return
53*4887Schin * 1 2x x
54*4887Schin * atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
55*4887Schin * 2 1 - x 1 - x
56*4887Schin *
57*4887Schin * Special cases:
58*4887Schin * atanh(x) is NaN if |x| > 1 with signal;
59*4887Schin * atanh(NaN) is that NaN with no signal;
60*4887Schin * atanh(+-1) is +-INF with signal.
61*4887Schin *
62*4887Schin * Accuracy:
63*4887Schin * atanh(x) returns the exact hyperbolic arc tangent of x nearly rounded.
64*4887Schin * In a test run with 512,000 random arguments on a VAX, the maximum
65*4887Schin * observed error was 1.87 ulps (units in the last place) at
66*4887Schin * x= -3.8962076028810414000e-03.
67*4887Schin */
68*4887Schin #include "mathimpl.h"
69*4887Schin
70*4887Schin #if defined(vax)||defined(tahoe)
71*4887Schin #include <errno.h>
72*4887Schin #endif /* defined(vax)||defined(tahoe) */
73*4887Schin
74*4887Schin extern double atanh(x)
75*4887Schin double x;
76*4887Schin {
77*4887Schin double z;
78*4887Schin z = copysign(0.5,x);
79*4887Schin x = copysign(x,1.0);
80*4887Schin #if defined(vax)||defined(tahoe)
81*4887Schin if (x == 1.0) {
82*4887Schin return(copysign(1.0,z)*infnan(ERANGE)); /* sign(x)*INF */
83*4887Schin }
84*4887Schin #endif /* defined(vax)||defined(tahoe) */
85*4887Schin x = x/(1.0-x);
86*4887Schin return( z*log1p(x+x) );
87*4887Schin }
88*4887Schin
89*4887Schin #endif
90