projects / thirdparty / gcc.git / blame
| Commit | Line | Data |
|---|---|---|
| 644cb69f FXC |
1 | /* Support routines for the intrinsic power (**) operator. |
| 2 | Copyright 2004 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 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 | ||
| 31 | #include "config.h" | |
| 32 | #include "libgfortran.h" | |
| 33 | ||
| 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_INTEGER_16) && defined (HAVE_GFC_INTEGER_4) | |
| 40 | ||
| 41 | GFC_INTEGER_16 pow_i16_i4 (GFC_INTEGER_16 a, GFC_INTEGER_4 b); | |
| 42 | export_proto(pow_i16_i4); | |
| 43 | ||
| 44 | GFC_INTEGER_16 | |
| 45 | pow_i16_i4 (GFC_INTEGER_16 a, GFC_INTEGER_4 b) | |
| 46 | { | |
| 47 | GFC_INTEGER_16 pow, x; | |
| 48 | GFC_INTEGER_4 n, u; | |
| 49 | ||
| 50 | n = b; | |
| 51 | x = a; | |
| 52 | pow = 1; | |
| 53 | if (n != 0) | |
| 54 | { | |
| 55 | if (n < 0) | |
| 56 | { | |
| 57 | if (x == 1) | |
| 58 | return 1; | |
| 59 | if (x == -1) | |
| 60 | return (n & 1) ? -1 : 1; | |
| 61 | return (x == 0) ? 1 / x : 0; | |
| 62 | } | |
| 63 | u = n; | |
| 64 | for (;;) | |
| 65 | { | |
| 66 | if (u & 1) | |
| 67 | pow *= x; | |
| 68 | u >>= 1; | |
| 69 | if (u) | |
| 70 | x *= x; | |
| 71 | else | |
| 72 | break; | |
| 73 | } | |
| 74 | } | |
| 75 | return pow; | |
| 76 | } | |
| 77 | ||
| 78 | #endif |