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41bdb6e20c
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.
79 lines
2.2 KiB
C
79 lines
2.2 KiB
C
/* Compute cubic root of double value.
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Copyright (C) 1997 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Dirk Alboth <dirka@uni-paderborn.de> and
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Ulrich Drepper <drepper@cygnus.com>, 1997.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, write to the Free
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Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA. */
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#include "math.h"
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#include "math_private.h"
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#define CBRT2 1.2599210498948731648 /* 2^(1/3) */
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#define SQR_CBRT2 1.5874010519681994748 /* 2^(2/3) */
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/* We don't use long double values here since U need not be computed
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with full precision. */
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static const double factor[5] =
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{
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1.0 / SQR_CBRT2,
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1.0 / CBRT2,
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1.0,
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CBRT2,
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SQR_CBRT2
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};
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long double
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__cbrtl (long double x)
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{
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long double xm, ym, u, t2;
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int xe;
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/* Reduce X. XM now is an range 1.0 to 0.5. */
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xm = __frexpl (fabs (x), &xe);
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/* If X is not finite or is null return it (with raising exceptions
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if necessary.
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Note: *Our* version of `frexp' sets XE to zero if the argument is
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Inf or NaN. This is not portable but faster. */
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if (xe == 0 && fpclassify (x) <= FP_ZERO)
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return x + x;
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u = (0.338058687610520237
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+ (1.67595307700780102
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+ (-2.82414939754975962
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+ (4.09559907378707839 +
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(-4.11151425200350531
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+ (2.65298938441952296 +
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(-0.988553671195413709
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+ 0.161617097923756032 * xm)
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* xm)
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* xm)
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* xm)
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* xm)
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* xm)
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*xm);
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t2 = u * u * u;
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ym = u * (t2 + 2.0 * xm) / (2.0 * t2 + xm) * factor[2 + xe % 3];
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return __ldexpl (x > 0.0 ? ym : -ym, xe / 3);
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}
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weak_alias (__cbrtl, cbrtl)
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