1  /* Support routines for the intrinsic power (**) operator.
       2     Copyright (C) 2004-2023 Free Software Foundation, Inc.
       3     Contributed by Paul Brook
       4  
       5  This file is part of the GNU Fortran 95 runtime library (libgfortran).
       6  
       7  Libgfortran is free software; you can redistribute it and/or
       8  modify it under the terms of the GNU General Public
       9  License as published by the Free Software Foundation; either
      10  version 3 of the License, or (at your option) any later version.
      11  
      12  Libgfortran is distributed in the hope that it will be useful,
      13  but WITHOUT ANY WARRANTY; without even the implied warranty of
      14  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      15  GNU General Public License for more details.
      16  
      17  Under Section 7 of GPL version 3, you are granted additional
      18  permissions described in the GCC Runtime Library Exception, version
      19  3.1, as published by the Free Software Foundation.
      20  
      21  You should have received a copy of the GNU General Public License and
      22  a copy of the GCC Runtime Library Exception along with this program;
      23  see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
      24  <http://www.gnu.org/licenses/>.  */
      25  
      26  #include "libgfortran.h"
      27  
      28  
      29  /* Use Binary Method to calculate the powi. This is not an optimal but
      30     a simple and reasonable arithmetic. See section 4.6.3, "Evaluation of
      31     Powers" of Donald E. Knuth, "Seminumerical Algorithms", Vol. 2, "The Art
      32     of Computer Programming", 3rd Edition, 1998.  */
      33  
      34  #if defined (HAVE_GFC_REAL_4) && defined (HAVE_GFC_INTEGER_8)
      35  
      36  GFC_REAL_4 pow_r4_i8 (GFC_REAL_4 a, GFC_INTEGER_8 b);
      37  export_proto(pow_r4_i8);
      38  
      39  GFC_REAL_4
      40  pow_r4_i8 (GFC_REAL_4 a, GFC_INTEGER_8 b)
      41  {
      42    GFC_REAL_4 pow, x;
      43    GFC_INTEGER_8 n;
      44    GFC_UINTEGER_8 u;
      45    
      46    n = b;
      47    x = a;
      48    pow = 1;
      49    if (n != 0)
      50      {
      51        if (n < 0)
      52  	{
      53  
      54  	  u = -n;
      55  	  x = pow / x;
      56  	}
      57        else
      58  	{
      59  	   u = n;
      60  	}
      61        for (;;)
      62  	{
      63  	  if (u & 1)
      64  	    pow *= x;
      65  	  u >>= 1;
      66  	  if (u)
      67  	    x *= x;
      68  	  else
      69  	    break;
      70  	}
      71      }
      72    return pow;
      73  }
      74  
      75  #endif