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99d8158635
git-svn-id: file:///srv/svn/repos/haiku/buildtools/trunk@29042 a95241bf-73f2-0310-859d-f6bbb57e9c96
96 lines
2.8 KiB
C
96 lines
2.8 KiB
C
/* mpfr_ui_pow_ui -- compute the power beetween two machine integer
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Copyright 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
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Contributed by the Arenaire and Cacao projects, INRIA.
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This file is part of the MPFR Library.
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The MPFR Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or (at your
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option) any later version.
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The MPFR Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the MPFR Library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
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MA 02110-1301, USA. */
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#include "mpfr-impl.h"
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int
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mpfr_ui_pow_ui (mpfr_ptr x, unsigned long int y, unsigned long int n,
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mp_rnd_t rnd)
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{
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mp_exp_t err;
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unsigned long m;
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mpfr_t res;
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mp_prec_t prec;
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int size_n;
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int inexact;
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MPFR_ZIV_DECL (loop);
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MPFR_SAVE_EXPO_DECL (expo);
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if (MPFR_UNLIKELY (n <= 1))
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{
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if (n == 1)
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return mpfr_set_ui (x, y, rnd); /* y^1 = y */
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else
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return mpfr_set_ui (x, 1, rnd); /* y^0 = 1 for any y */
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}
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else if (MPFR_UNLIKELY (y <= 1))
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{
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if (y == 1)
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return mpfr_set_ui (x, 1, rnd); /* 1^n = 1 for any n > 0 */
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else
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return mpfr_set_ui (x, 0, rnd); /* 0^n = 0 for any n > 0 */
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}
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for (size_n = 0, m = n; m; size_n++, m >>= 1);
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MPFR_SAVE_EXPO_MARK (expo);
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prec = MPFR_PREC (x) + 3 + size_n;
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mpfr_init2 (res, prec);
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MPFR_ZIV_INIT (loop, prec);
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for (;;)
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{
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int i = size_n;
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inexact = mpfr_set_ui (res, y, GMP_RNDU);
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err = 1;
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/* now 2^(i-1) <= n < 2^i: i=1+floor(log2(n)) */
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for (i -= 2; i >= 0; i--)
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{
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inexact |= mpfr_mul (res, res, res, GMP_RNDU);
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err++;
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if (n & (1UL << i))
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inexact |= mpfr_mul_ui (res, res, y, GMP_RNDU);
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}
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/* since the loop is executed floor(log2(n)) times,
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we have err = 1+floor(log2(n)).
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Since prec >= MPFR_PREC(x) + 4 + floor(log2(n)), prec > err */
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err = prec - err;
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if (MPFR_LIKELY (inexact == 0
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|| MPFR_CAN_ROUND (res, err, MPFR_PREC (x), rnd)))
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break;
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/* Actualisation of the precision */
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MPFR_ZIV_NEXT (loop, prec);
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mpfr_set_prec (res, prec);
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}
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MPFR_ZIV_FREE (loop);
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inexact = mpfr_set (x, res, rnd);
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mpfr_clear (res);
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MPFR_SAVE_EXPO_FREE (expo);
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return mpfr_check_range (x, inexact, rnd);
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}
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