1`/* Support routines for the intrinsic power (**) operator.
2   Copyright (C) 2004-2014 Free Software Foundation, Inc.
3   Contributed by Paul Brook
4
5This file is part of the GNU Fortran 95 runtime library (libgfortran).
6
7Libgfortran is free software; you can redistribute it and/or
8modify it under the terms of the GNU General Public
9License as published by the Free Software Foundation; either
10version 3 of the License, or (at your option) any later version.
11
12Libgfortran is distributed in the hope that it will be useful,
13but WITHOUT ANY WARRANTY; without even the implied warranty of
14MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15GNU General Public License for more details.
16
17Under Section 7 of GPL version 3, you are granted additional
18permissions described in the GCC Runtime Library Exception, version
193.1, as published by the Free Software Foundation.
20
21You should have received a copy of the GNU General Public License and
22a copy of the GCC Runtime Library Exception along with this program;
23see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
24<http://www.gnu.org/licenses/>.  */
25
26#include "libgfortran.h"'
27
28include(iparm.m4)dnl
29
30/* Use Binary Method to calculate the powi. This is not an optimal but
31   a simple and reasonable arithmetic. See section 4.6.3, "Evaluation of
32   Powers" of Donald E. Knuth, "Seminumerical Algorithms", Vol. 2, "The Art
33   of Computer Programming", 3rd Edition, 1998.  */
34
35`#if defined (HAVE_'rtype_name`) && defined (HAVE_'atype_name`)'
36
37rtype_name `pow_'rtype_code`_'atype_code` ('rtype_name` a, 'atype_name` b);
38export_proto(pow_'rtype_code`_'atype_code`);
39
40'rtype_name`
41pow_'rtype_code`_'atype_code` ('rtype_name` a, 'atype_name` b)
42{
43  'rtype_name` pow, x;
44  'atype_name` n;
45  GFC_UINTEGER_'atype_kind` u;
46
47  n = b;
48  x = a;
49  pow = 1;
50  if (n != 0)
51    {
52      if (n < 0)
53	{
54'ifelse(rtype_letter,i,`dnl
55	  if (x == 1)
56	    return 1;
57	  if (x == -1)
58	    return (n & 1) ? -1 : 1;
59	  return (x == 0) ? 1 / x : 0;
60',`
61	  u = -n;
62	  x = pow / x;
63')dnl
64`	}
65      else
66	{
67	   u = n;
68	}
69      for (;;)
70	{
71	  if (u & 1)
72	    pow *= x;
73	  u >>= 1;
74	  if (u)
75	    x *= x;
76	  else
77	    break;
78	}
79    }
80  return pow;
81}
82
83#endif'
84