1/*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21
22/*
23 * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
24 */
25/*
26 * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
27 * Use is subject to license terms.
28 */
29
30/*
31 * arccosin function
32 *			      ________
33 *                           / 1 - x
34 *	acos(x) = 2*atan2(  / -------- , 1 )
35 *                        \/   1 + x
36 *
37 *			      ________
38 *                           / 1 - x
39 *		= 2*atan (  / -------- ) for non-exceptional x.
40 *                        \/   1 + x
41 *
42 * Special cases:
43 *	if x is NaN, return x itself;
44 *	if |x|>1, return NaN with invalid signal.
45 */
46
47#pragma weak __acosl = acosl
48
49#include "libm.h"
50
51static const long double zero = 0.0L, one = 1.0L;
52
53long double
54acosl(long double x) {
55	if (isnanl(x))
56		return (x + x);
57	else if (fabsl(x) < one)
58		x = atanl(sqrtl((one - x) / (one + x)));
59	else if (x == -one)
60		x = atan2l(one, zero);	/* x <- PI */
61	else if (x == one)
62		x = zero;
63	else {		/* |x| > 1  create invalid signal */
64		return (zero / zero);
65	}
66	return (x + x);
67}
68