libgfortran/generated/pow_i8_i4.c

   1 /* Support routines for the intrinsic power (**) operator.
   2    Copyright (C) 2004-2017 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_INTEGER_8) && defined (HAVE_GFC_INTEGER_4)
  35
  36 GFC_INTEGER_8 pow_i8_i4 (GFC_INTEGER_8 a, GFC_INTEGER_4 b);
  37 export_proto(pow_i8_i4);
  38
  39 GFC_INTEGER_8
  40 pow_i8_i4 (GFC_INTEGER_8 a, GFC_INTEGER_4 b)
  41 {
  42   GFC_INTEGER_8 pow, x;
  43   GFC_INTEGER_4 n;
  44   GFC_UINTEGER_4 u;
  45
  46   n = b;
  47   x = a;
  48   pow = 1;
  49   if (n != 0)
  50     {
  51       if (n < 0)
  52         {
  53           if (x == 1)
  54             return 1;
  55           if (x == -1)
  56             return (n & 1) ? -1 : 1;
  57           return (x == 0) ? 1 / x : 0;
  58         }
  59       else
  60         {
  61            u = n;
  62         }
  63       for (;;)
  64         {
  65           if (u & 1)
  66             pow *= x;
  67           u >>= 1;
  68           if (u)
  69             x *= x;
  70           else
  71             break;
  72         }
  73     }
  74   return pow;
  75 }
  76
  77 #endif