libgfortran/generated/pow_r8_i8.c

   1 /* Support routines for the intrinsic power (**) operator.
   2    Copyright 2004 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 2 of the License, or (at your option) any later version.
  11
  12 In addition to the permissions in the GNU General Public License, the
  13 Free Software Foundation gives you unlimited permission to link the
  14 compiled version of this file into combinations with other programs,
  15 and to distribute those combinations without any restriction coming
  16 from the use of this file.  (The General Public License restrictions
  17 do apply in other respects; for example, they cover modification of
  18 the file, and distribution when not linked into a combine
  19 executable.)
  20
  21 Libgfortran is distributed in the hope that it will be useful,
  22 but WITHOUT ANY WARRANTY; without even the implied warranty of
  23 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  24 GNU General Public License for more details.
  25
  26 You should have received a copy of the GNU General Public
  27 License along with libgfortran; see the file COPYING.  If not,
  28 write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  29 Boston, MA 02110-1301, USA.  */
  30
  31 #include "config.h"
  32 #include "libgfortran.h"
  33
  34 /* Use Binary Method to calculate the powi. This is not an optimal but
  35    a simple and reasonable arithmetic. See section 4.6.3, "Evaluation of
  36    Powers" of Donald E. Knuth, "Seminumerical Algorithms", Vol. 2, "The Art
  37    of Computer Programming", 3rd Edition, 1998.  */
  38
  39 #if defined (HAVE_GFC_REAL_8) && defined (HAVE_GFC_INTEGER_8)
  40
  41 GFC_REAL_8 pow_r8_i8 (GFC_REAL_8 a, GFC_INTEGER_8 b);
  42 export_proto(pow_r8_i8);
  43
  44 GFC_REAL_8
  45 pow_r8_i8 (GFC_REAL_8 a, GFC_INTEGER_8 b)
  46 {
  47   GFC_REAL_8 pow, x;
  48   GFC_INTEGER_8 n, u;
  49
  50   n = b;
  51   x = a;
  52   pow = 1;
  53   if (n != 0)
  54     {
  55       if (n < 0)
  56         {
  57
  58           n = -n;
  59           x = pow / x;
  60         }
  61       u = n;
  62       for (;;)
  63         {
  64           if (u & 1)
  65             pow *= x;
  66           u >>= 1;
  67           if (u)
  68             x *= x;
  69           else
  70             break;
  71         }
  72     }
  73   return pow;
  74 }
  75
  76 #endif