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
46 static const long double zero = 0.0L, small = 1.0e-20L, half = 0.5L, one = 1.0L;
47 #ifndef lint
48 static const long double big = 1.0e+20L;
49 #endif
50
51 long double
asinl(long double x)52 asinl(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