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#pragma weak __asinl = asinl
31
32/*
33 *	asinl(x) = atan2l(x,sqrt(1-x*x));
34 *
35 * For better accuracy, 1-x*x is computed as follows
36 *	1-x*x                     if x <  0.5,
37 *	2*(1-|x|)-(1-|x|)*(1-|x|) if x >= 0.5.
38 *
39 * Special cases:
40 *	if x is NaN, return x itself;
41 *	if |x|>1, return NaN with invalid signal.
42 */
43
44#include "libm.h"
45
46static const long double zero = 0.0L, small = 1.0e-20L, half = 0.5L, one = 1.0L;
47#ifndef lint
48static const long double big = 1.0e+20L;
49#endif
50
51long double
52asinl(long double x) {
53	long double t, w;
54#ifndef lint
55	volatile long double dummy;
56#endif
57
58	w = fabsl(x);
59	if (isnanl(x))
60		return (x + x);
61	else if (w <= half) {
62		if (w < small) {
63#ifndef lint
64			dummy = w + big;
65							/* inexact if w != 0 */
66#endif
67			return (x);
68		} else
69			return (atanl(x / sqrtl(one - x * x)));
70	} else if (w < one) {
71		t = one - w;
72		w = t + t;
73		return (atanl(x / sqrtl(w - t * t)));
74	} else if (w == one)
75		return (atan2l(x, zero));	/* asin(+-1) =  +- PI/2 */
76	else
77		return (zero / zero);		/* |x| > 1: invalid */
78}
79