63 lines
1.6 KiB
C
63 lines
1.6 KiB
C
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/* Support routines for the intrinsic power (**) operator.
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Copyright 2004 Free Software Foundation, Inc.
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Contributed by Paul Brook
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This file is part of the GNU Fortran 95 runtime library (libgfor).
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Libgfor 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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Ligbfor 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
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GNU 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 libgfor; 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 "config.h"
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#include "libgfortran.h"
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/* Uuse Binary Method to calculate the powi. This is not an optimal but
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a simple and reasonable arithmetic. See section 4.6.3, "Evaluation of
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Powers" of Donald E. Knuth, "Seminumerical Algorithms", Vol. 2, "The Art
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of Computer Programming", 3rd Edition, 1998. */
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GFC_INTEGER_8
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prefix(pow_i8_i4) (GFC_INTEGER_8 a, GFC_INTEGER_4 b)
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{
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GFC_INTEGER_8 pow, x;
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GFC_INTEGER_4 n, u;
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n = b;
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x = a;
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pow = 1;
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if (n != 0)
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{
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if (n < 0)
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{
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if (x == 1)
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return 1;
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if (x == -1)
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return (n & 1) ? -1 : 1;
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return (x == 0) ? 1 / x : 0;
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}
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u = n;
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for (;;)
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{
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if (u & 1)
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pow *= x;
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u >>= 1;
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if (u)
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x *= x;
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else
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break;
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}
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}
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return pow;
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}
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