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/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (the "License").
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* or http://www.opensolaris.org/os/licensing.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
#pragma ident "@(#)cbrtl.c 1.7 06/01/31 SMI"
#pragma weak cbrtl = __cbrtl
#include "libm.h"
#define n0 0
long double
cbrtl(long double x) {
long double s, t, r, w, y;
double dx, dy;
int *py = (int *) &dy;
int n, m, m3, sx;
if (!finitel(x))
return (x + x);
if (iszerol(x))
return (x);
sx = signbitl(x);
x = fabsl(x);
n = ilogbl(x);
m = n / 3;
m3 = m + m + m;
y = scalbnl(x, -m3);
dx = (double) y;
dy = cbrt(dx);
py[1 - n0] += 2;
if (py[1 - n0] == 0)
py[n0] += 1;
/* one step newton iteration to 113 bits with error < 0.667ulps */
t = (long double) dy;
t = scalbnl(t, m);
s = t * t;
r = x / s;
w = t + t;
r = (r - t) / (w + r);
t += t * r;
return (sx == 0 ? t : -t);
}
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