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644cb69f | 1 | /* Support routines for the intrinsic power (**) operator. |
a5544970 | 2 | Copyright (C) 2004-2019 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 | |
748086b7 | 10 | version 3 of the License, or (at your option) any later version. |
644cb69f FXC |
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 | ||
748086b7 JJ |
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/>. */ | |
644cb69f | 25 | |
644cb69f FXC |
26 | #include "libgfortran.h" |
27 | ||
36ae8a61 | 28 | |
644cb69f FXC |
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_REAL_16) && defined (HAVE_GFC_INTEGER_16) | |
35 | ||
36 | GFC_REAL_16 pow_r16_i16 (GFC_REAL_16 a, GFC_INTEGER_16 b); | |
37 | export_proto(pow_r16_i16); | |
38 | ||
39 | GFC_REAL_16 | |
40 | pow_r16_i16 (GFC_REAL_16 a, GFC_INTEGER_16 b) | |
41 | { | |
42 | GFC_REAL_16 pow, x; | |
3d1f465a TK |
43 | GFC_INTEGER_16 n; |
44 | GFC_UINTEGER_16 u; | |
644cb69f FXC |
45 | |
46 | n = b; | |
47 | x = a; | |
48 | pow = 1; | |
49 | if (n != 0) | |
50 | { | |
51 | if (n < 0) | |
52 | { | |
53 | ||
3d1f465a | 54 | u = -n; |
644cb69f FXC |
55 | x = pow / x; |
56 | } | |
3d1f465a TK |
57 | else |
58 | { | |
59 | u = n; | |
60 | } | |
644cb69f FXC |
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 |