n_atanhf.c revision 1.1 
1/*      $NetBSD: n_atanhf.c,v 1.1 2016/09/21 14:11:40 christos Exp $ */
2/*
3 * Copyright (c) 1985, 1993
4 *	The Regents of the University of California.  All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 *    notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 *    notice, this list of conditions and the following disclaimer in the
13 *    documentation and/or other materials provided with the distribution.
14 * 3. Neither the name of the University nor the names of its contributors
15 *    may be used to endorse or promote products derived from this software
16 *    without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 * SUCH DAMAGE.
29 */
30#include <sys/cdefs.h>
31__RCSID("$NetBSD: n_atanhf.c,v 1.1 2016/09/21 14:11:40 christos Exp $");
32
33#ifndef lint
34#if 0
35static char sccsid[] = "@(#)atanh.c	8.1 (Berkeley) 6/4/93";
36#endif
37#endif /* not lint */
38
39/* ATANH(X)
40 * RETURN THE HYPERBOLIC ARC TANGENT OF X
41 * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
42 * CODED IN C BY K.C. NG, 1/8/85;
43 * REVISED BY K.C. NG on 2/7/85, 3/7/85, 8/18/85.
44 *
45 * Required kernel function:
46 *	log1p(x) 	...return log(1+x)
47 *
48 * Method :
49 *	Return
50 *                          1              2x                          x
51 *		atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
52 *                          2             1 - x                      1 - x
53 *
54 * Special cases:
55 *	atanh(x) is NaN if |x| > 1 with signal;
56 *	atanh(NaN) is that NaN with no signal;
57 *	atanh(+-1) is +-INF with signal.
58 *
59 * Accuracy:
60 *	atanh(x) returns the exact hyperbolic arc tangent of x nearly rounded.
61 *	In a test run with 512,000 random arguments on a VAX, the maximum
62 *	observed error was 1.87 ulps (units in the last place) at
63 *	x= -3.8962076028810414000e-03.
64 */
65#include "mathimpl.h"
66
67#if defined(__vax__)||defined(tahoe)
68#include <errno.h>
69#endif	/* defined(__vax__)||defined(tahoe) */
70
71float
72atanhf(float x)
73{
74	float z;
75	z = copysignf(0.5,x);
76	x = copysignf(x,1.0);
77#if defined(__vax__)||defined(tahoe)
78	if (x == 1.0) {
79	    return(copysignf(1.0,z)*infnan(ERANGE));	/* sign(x)*INF */
80	}
81#endif	/* defined(__vax__)||defined(tahoe) */
82	x = x/(1.0-x);
83	return( z*log1pf(x+x) );
84}
85