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644cb69f | 1 | /* Support routines for the intrinsic power (**) operator. |
36ae8a61 | 2 | Copyright 2004, 2007 Free Software Foundation, Inc. |
644cb69f FXC |
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 | ||
644cb69f FXC |
31 | #include "libgfortran.h" |
32 | ||
36ae8a61 | 33 | |
644cb69f FXC |
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_COMPLEX_16) && defined (HAVE_GFC_INTEGER_4) | |
40 | ||
41 | GFC_COMPLEX_16 pow_c16_i4 (GFC_COMPLEX_16 a, GFC_INTEGER_4 b); | |
42 | export_proto(pow_c16_i4); | |
43 | ||
44 | GFC_COMPLEX_16 | |
45 | pow_c16_i4 (GFC_COMPLEX_16 a, GFC_INTEGER_4 b) | |
46 | { | |
47 | GFC_COMPLEX_16 pow, x; | |
3d1f465a TK |
48 | GFC_INTEGER_4 n; |
49 | GFC_UINTEGER_4 u; | |
644cb69f FXC |
50 | |
51 | n = b; | |
52 | x = a; | |
53 | pow = 1; | |
54 | if (n != 0) | |
55 | { | |
56 | if (n < 0) | |
57 | { | |
58 | ||
3d1f465a | 59 | u = -n; |
644cb69f FXC |
60 | x = pow / x; |
61 | } | |
3d1f465a TK |
62 | else |
63 | { | |
64 | u = n; | |
65 | } | |
644cb69f FXC |
66 | for (;;) |
67 | { | |
68 | if (u & 1) | |
69 | pow *= x; | |
70 | u >>= 1; | |
71 | if (u) | |
72 | x *= x; | |
73 | else | |
74 | break; | |
75 | } | |
76 | } | |
77 | return pow; | |
78 | } | |
79 | ||
80 | #endif |