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/* Support routines for the intrinsic power (**) operator.
Copyright (C) 2004-2021 Free Software Foundation, Inc.
Contributed by Paul Brook
This file is part of the GNU Fortran 95 runtime library (libgfortran).
Libgfortran is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public
License as published by the Free Software Foundation; either
version 3 of the License, or (at your option) any later version.
Libgfortran 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 General Public License for more details.
Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.
You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
<http://www.gnu.org/licenses/>. */
#include "libgfortran.h"
/* Use 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. */
#if defined (HAVE_GFC_INTEGER_16) && defined (HAVE_GFC_INTEGER_16)
GFC_INTEGER_16 pow_i16_i16 (GFC_INTEGER_16 a, GFC_INTEGER_16 b);
export_proto(pow_i16_i16);
GFC_INTEGER_16
pow_i16_i16 (GFC_INTEGER_16 a, GFC_INTEGER_16 b)
{
GFC_INTEGER_16 pow, x;
GFC_INTEGER_16 n;
GFC_UINTEGER_16 u;
n = b;
x = a;
pow = 1;
if (n != 0)
{
if (n < 0)
{
if (x == 1)
return 1;
if (x == -1)
return (n & 1) ? -1 : 1;
return (x == 0) ? 1 / x : 0;
}
else
{
u = n;
}
for (;;)
{
if (u & 1)
pow *= x;
u >>= 1;
if (u)
x *= x;
else
break;
}
}
return pow;
}
#endif
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