1 /* Support routines for the intrinsic power (**) operator.
2 Copyright (C) 2004-2013 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_COMPLEX_10) && defined (HAVE_GFC_INTEGER_16)
35
36 GFC_COMPLEX_10 pow_c10_i16 (GFC_COMPLEX_10 a, GFC_INTEGER_16 b);
37 export_proto(pow_c10_i16);
38
39 GFC_COMPLEX_10
pow_c10_i16(GFC_COMPLEX_10 a,GFC_INTEGER_16 b)40 pow_c10_i16 (GFC_COMPLEX_10 a, GFC_INTEGER_16 b)
41 {
42 GFC_COMPLEX_10 pow, x;
43 GFC_INTEGER_16 n;
44 GFC_UINTEGER_16 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
76