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5b200ac2 FW |
1 | /* Support routines for the intrinsic power (**) operator. |
2 | Copyright 2004 Free Software Foundation, Inc. | |
3 | Contributed by Paul Brook | |
4 | ||
57dea9f6 | 5 | This file is part of the GNU Fortran 95 runtime library (libgfortran). |
5b200ac2 | 6 | |
57dea9f6 TM |
7 | Libgfortran is free software; you can redistribute it and/or |
8 | modify it under the terms of the GNU General Public | |
5b200ac2 | 9 | License as published by the Free Software Foundation; either |
57dea9f6 | 10 | version 2 of the License, or (at your option) any later version. |
5b200ac2 | 11 | |
57dea9f6 TM |
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, | |
5b200ac2 FW |
22 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
23 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
57dea9f6 | 24 | GNU General Public License for more details. |
5b200ac2 | 25 | |
57dea9f6 TM |
26 | You should have received a copy of the GNU General Public |
27 | License along with libgfortran; see the file COPYING. If not, | |
5b200ac2 FW |
28 | write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, |
29 | Boston, MA 02111-1307, USA. */ | |
30 | ||
31 | #include "config.h" | |
32 | #include "libgfortran.h" | |
33 | ||
7d7b8bfe | 34 | /* Use Binary Method to calculate the powi. This is not an optimal but |
5b200ac2 FW |
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 | ||
7d7b8bfe RH |
39 | GFC_COMPLEX_8 pow_c8_i8 (GFC_COMPLEX_8 a, GFC_INTEGER_8 b); |
40 | export_proto(pow_c8_i8); | |
41 | ||
5b200ac2 | 42 | GFC_COMPLEX_8 |
7d7b8bfe | 43 | pow_c8_i8 (GFC_COMPLEX_8 a, GFC_INTEGER_8 b) |
5b200ac2 FW |
44 | { |
45 | GFC_COMPLEX_8 pow, x; | |
46 | GFC_INTEGER_8 n, u; | |
47 | ||
48 | n = b; | |
49 | x = a; | |
50 | pow = 1; | |
51 | if (n != 0) | |
52 | { | |
53 | if (n < 0) | |
54 | { | |
55 | ||
56 | n = -n; | |
57 | x = pow / x; | |
58 | } | |
59 | u = n; | |
60 | for (;;) | |
61 | { | |
62 | if (u & 1) | |
63 | pow *= x; | |
64 | u >>= 1; | |
65 | if (u) | |
66 | x *= x; | |
67 | else | |
68 | break; | |
69 | } | |
70 | } | |
71 | return pow; | |
72 | } |