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 __cbrtl = cbrtl
31
32 #include "libm.h"
33 #include "longdouble.h"
34
35 static const double d_one = 1.0;
36
37 long double
cbrtl(long double x)38 cbrtl(long double x) {
39 long double s, t, r, w, y;
40 double dx, dy;
41 int *py = (int *) &dy;
42 int n, m, m3, n0, sx;
43
44 if (!finitel(x))
45 return (x + x);
46 if (iszerol(x))
47 return (x);
48 n0 = 0;
49 if (*((int *) &d_one) == 0)
50 n0 = 1;
51 sx = signbitl(x);
52 x = fabsl(x);
53 n = ilogbl(x);
54 m = n / 3;
55 m3 = m + m + m;
56 y = scalbnl(x, -m3);
57 dx = (double) y;
58 dy = cbrt(dx);
59 py[1 - n0] += 2;
60 if (py[1 - n0] == 0)
61 py[n0] += 1;
62
63 /* one step newton iteration to 113 bits with error < 0.667ulps */
64 t = (long double) dy;
65 t = scalbnl(t, m);
66 s = t * t;
67 r = x / s;
68 w = t + t;
69 r = (r - t) / (w + r);
70 t += t * r;
71
72 return (sx == 0 ? t : -t);
73 }
74