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1 /* Support routines for the intrinsic power (**) operator.
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145
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2 Copyright (C) 2004-2020 Free Software Foundation, Inc.
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3 Contributed by Paul Brook
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4
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5 This file is part of the GNU Fortran 95 runtime library (libgfortran).
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6
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7 Libgfortran is free software; you can redistribute it and/or
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8 modify it under the terms of the GNU General Public
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9 License as published by the Free Software Foundation; either
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10 version 3 of the License, or (at your option) any later version.
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11
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12 Libgfortran is distributed in the hope that it will be useful,
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13 but WITHOUT ANY WARRANTY; without even the implied warranty of
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14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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15 GNU General Public License for more details.
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16
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17 Under Section 7 of GPL version 3, you are granted additional
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18 permissions described in the GCC Runtime Library Exception, version
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19 3.1, as published by the Free Software Foundation.
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20
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21 You should have received a copy of the GNU General Public License and
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22 a copy of the GCC Runtime Library Exception along with this program;
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23 see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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24 <http://www.gnu.org/licenses/>. */
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25
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26 #include "libgfortran.h"
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27
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28
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29 /* Use Binary Method to calculate the powi. This is not an optimal but
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30 a simple and reasonable arithmetic. See section 4.6.3, "Evaluation of
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31 Powers" of Donald E. Knuth, "Seminumerical Algorithms", Vol. 2, "The Art
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32 of Computer Programming", 3rd Edition, 1998. */
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33
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34 #if defined (HAVE_GFC_REAL_8) && defined (HAVE_GFC_INTEGER_16)
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35
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36 GFC_REAL_8 pow_r8_i16 (GFC_REAL_8 a, GFC_INTEGER_16 b);
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37 export_proto(pow_r8_i16);
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38
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39 GFC_REAL_8
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40 pow_r8_i16 (GFC_REAL_8 a, GFC_INTEGER_16 b)
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41 {
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42 GFC_REAL_8 pow, x;
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43 GFC_INTEGER_16 n;
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44 GFC_UINTEGER_16 u;
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45
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46 n = b;
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47 x = a;
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48 pow = 1;
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49 if (n != 0)
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50 {
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51 if (n < 0)
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52 {
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53
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54 u = -n;
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55 x = pow / x;
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56 }
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57 else
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58 {
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59 u = n;
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60 }
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61 for (;;)
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62 {
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63 if (u & 1)
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64 pow *= x;
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65 u >>= 1;
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66 if (u)
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67 x *= x;
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68 else
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69 break;
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70 }
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71 }
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72 return pow;
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73 }
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74
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75 #endif
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