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/* Support routines for the intrinsic power (**) operator.

   Copyright 2004, 2007, 2009 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_4)

GFC_INTEGER_16 pow_i16_i4 (GFC_INTEGER_16 a, GFC_INTEGER_4 b);

export_proto(pow_i16_i4);

GFC_INTEGER_16

pow_i16_i4 (GFC_INTEGER_16 a, GFC_INTEGER_4 b)

{

  GFC_INTEGER_16 pow, x;

  GFC_INTEGER_4 n;

  GFC_UINTEGER_4 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