| /* Support routines for the intrinsic power (**) operator. |
| Copyright (C) 2004-2021 Free Software Foundation, Inc. |
| Contributed by Paul Brook |
| |
| This file is part of the GNU Fortran 95 runtime library (libgfortran). |
| |
| Libgfortran is free software; you can redistribute it and/or |
| modify it under the terms of the GNU General Public |
| License as published by the Free Software Foundation; either |
| version 3 of the License, or (at your option) any later version. |
| |
| Libgfortran is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| GNU General Public License for more details. |
| |
| Under Section 7 of GPL version 3, you are granted additional |
| permissions described in the GCC Runtime Library Exception, version |
| 3.1, as published by the Free Software Foundation. |
| |
| You should have received a copy of the GNU General Public License and |
| a copy of the GCC Runtime Library Exception along with this program; |
| see the files COPYING3 and COPYING.RUNTIME respectively. If not, see |
| <http://www.gnu.org/licenses/>. */ |
| |
| #include "libgfortran.h" |
| |
| |
| /* Use Binary Method to calculate the powi. This is not an optimal but |
| a simple and reasonable arithmetic. See section 4.6.3, "Evaluation of |
| Powers" of Donald E. Knuth, "Seminumerical Algorithms", Vol. 2, "The Art |
| of Computer Programming", 3rd Edition, 1998. */ |
| |
| #if defined (HAVE_GFC_INTEGER_4) && defined (HAVE_GFC_INTEGER_16) |
| |
| GFC_INTEGER_4 pow_i4_i16 (GFC_INTEGER_4 a, GFC_INTEGER_16 b); |
| export_proto(pow_i4_i16); |
| |
| GFC_INTEGER_4 |
| pow_i4_i16 (GFC_INTEGER_4 a, GFC_INTEGER_16 b) |
| { |
| GFC_INTEGER_4 pow, x; |
| GFC_INTEGER_16 n; |
| GFC_UINTEGER_16 u; |
| |
| n = b; |
| x = a; |
| pow = 1; |
| if (n != 0) |
| { |
| if (n < 0) |
| { |
| if (x == 1) |
| return 1; |
| if (x == -1) |
| return (n & 1) ? -1 : 1; |
| return (x == 0) ? 1 / x : 0; |
| } |
| else |
| { |
| u = n; |
| } |
| for (;;) |
| { |
| if (u & 1) |
| pow *= x; |
| u >>= 1; |
| if (u) |
| x *= x; |
| else |
| break; |
| } |
| } |
| return pow; |
| } |
| |
| #endif |