77 lines
2.1 KiB
C
77 lines
2.1 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 Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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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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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If not,
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write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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Boston, MA 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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if (xe == 0)
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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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