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/* Support routines for the intrinsic power (**) operator.
Copyright 2004 Free Software Foundation, Inc.
Contributed by Paul Brook
This file is part of the GNU Fortran 95 runtime library (libgfor).
Libgfor 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.
Ligbfor 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 libgfor; see the file COPYING.LIB. If not,
write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */
#include "config.h"
#include "libgfortran.h"
/* Uuse Binary Method to calculate the powi. This is not an optimal but
a simple and reasonable arithmetic. See section 4.6.3, "Evaluation of
Powers" of Donald E. Knuth, "Seminumerical Algorithms", Vol. 2, "The Art
of Computer Programming", 3rd Edition, 1998. */
GFC_REAL_8
prefix(pow_r8_i8) (GFC_REAL_8 a, GFC_INTEGER_8 b)
{
GFC_REAL_8 pow, x;
GFC_INTEGER_8 n, u;
n = b;
x = a;
pow = 1;
if (n != 0)
{
if (n < 0)
{
n = -n;
x = pow / x;
}
u = n;
for (;;)
{
if (u & 1)
pow *= x;
u >>= 1;
if (u)
x *= x;
else
break;
}
}
return pow;
}
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