glibc/sysdeps/ieee754/dbl-64/s_cbrt.c
Andreas Jaeger 41bdb6e20c Update to LGPL v2.1.
2001-07-06  Paul Eggert  <eggert@twinsun.com>

	* manual/argp.texi: Remove ignored LGPL copyright notice; it's
	not appropriate for documentation anyway.
	* manual/libc-texinfo.sh: "Library General Public License" ->
	"Lesser General Public License".

2001-07-06  Andreas Jaeger  <aj@suse.de>

	* All files under GPL/LGPL version 2: Place under LGPL version
	2.1.
2001-07-06 04:58:11 +00:00

77 lines
2.1 KiB
C

/* Compute cubic root of double value.
Copyright (C) 1997 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Dirk Alboth <dirka@uni-paderborn.de> and
Ulrich Drepper <drepper@cygnus.com>, 1997.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
#include "math.h"
#include "math_private.h"
#define CBRT2 1.2599210498948731648 /* 2^(1/3) */
#define SQR_CBRT2 1.5874010519681994748 /* 2^(2/3) */
static const double factor[5] =
{
1.0 / SQR_CBRT2,
1.0 / CBRT2,
1.0,
CBRT2,
SQR_CBRT2
};
double
__cbrt (double x)
{
double xm, ym, u, t2;
int xe;
/* Reduce X. XM now is an range 1.0 to 0.5. */
xm = __frexp (fabs (x), &xe);
/* If X is not finite or is null return it (with raising exceptions
if necessary.
Note: *Our* version of `frexp' sets XE to zero if the argument is
Inf or NaN. This is not portable but faster. */
if (xe == 0 && fpclassify (x) <= FP_ZERO)
return x + x;
u = (0.354895765043919860
+ ((1.50819193781584896
+ ((-2.11499494167371287
+ ((2.44693122563534430
+ ((-1.83469277483613086
+ (0.784932344976639262 - 0.145263899385486377 * xm) * xm)
* xm))
* xm))
* xm))
* xm));
t2 = u * u * u;
ym = u * (t2 + 2.0 * xm) / (2.0 * t2 + xm) * factor[2 + xe % 3];
return __ldexp (x > 0.0 ? ym : -ym, xe / 3);
}
weak_alias (__cbrt, cbrt)
#ifdef NO_LONG_DOUBLE
strong_alias (__cbrt, __cbrtl)
weak_alias (__cbrt, cbrtl)
#endif