1 /* Support routines for the intrinsic power (**) operator. 2 Copyright (C) 2004-2020 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 3 of the License, or (at your option) any later version. 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 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/>. */ 25 26 #include "libgfortran.h" 27 28 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_INTEGER_8) && defined (HAVE_GFC_INTEGER_8) 35 36 GFC_INTEGER_8 pow_i8_i8 (GFC_INTEGER_8 a, GFC_INTEGER_8 b); 37 export_proto(pow_i8_i8); 38 39 GFC_INTEGER_8 40 pow_i8_i8 (GFC_INTEGER_8 a, GFC_INTEGER_8 b) 41 { 42 GFC_INTEGER_8 pow, x; 43 GFC_INTEGER_8 n; 44 GFC_UINTEGER_8 u; 45 46 n = b; 47 x = a; 48 pow = 1; 49 if (n != 0) 50 { 51 if (n < 0) 52 { 53 if (x == 1) 54 return 1; 55 if (x == -1) 56 return (n & 1) ? -1 : 1; 57 return (x == 0) ? 1 / x : 0; 58 } 59 else 60 { 61 u = n; 62 } 63 for (;;) 64 { 65 if (u & 1) 66 pow *= x; 67 u >>= 1; 68 if (u) 69 x *= x; 70 else 71 break; 72 } 73 } 74 return pow; 75 } 76 77 #endif 78