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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT RUN-TIME COMPONENTS --
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4 -- --
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5 -- S Y S T E M . E X P I N T --
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6 -- --
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7 -- B o d y --
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8 -- --
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131
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9 -- Copyright (C) 1992-2018, Free Software Foundation, Inc. --
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111
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10 -- --
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11 -- GNAT is free software; you can redistribute it and/or modify it under --
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12 -- terms of the GNU General Public License as published by the Free Soft- --
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13 -- ware Foundation; either version 3, or (at your option) any later ver- --
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14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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16 -- or FITNESS FOR A PARTICULAR PURPOSE. --
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17 -- --
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18 -- As a special exception under Section 7 of GPL version 3, you are granted --
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19 -- additional permissions described in the GCC Runtime Library Exception, --
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20 -- version 3.1, as published by the Free Software Foundation. --
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21 -- --
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22 -- You should have received a copy of the GNU General Public License and --
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23 -- a copy of the GCC Runtime Library Exception along with this program; --
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24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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25 -- <http://www.gnu.org/licenses/>. --
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26 -- --
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27 -- GNAT was originally developed by the GNAT team at New York University. --
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28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
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29 -- --
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30 ------------------------------------------------------------------------------
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31
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32 package body System.Exp_Int is
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33
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34 -----------------
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35 -- Exp_Integer --
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36 -----------------
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37
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38 -- Note that negative exponents get a constraint error because the
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39 -- subtype of the Right argument (the exponent) is Natural.
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40
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41 function Exp_Integer
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42 (Left : Integer;
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43 Right : Natural)
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44 return Integer
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45 is
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46 Result : Integer := 1;
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47 Factor : Integer := Left;
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48 Exp : Natural := Right;
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49
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50 begin
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51 -- We use the standard logarithmic approach, Exp gets shifted right
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52 -- testing successive low order bits and Factor is the value of the
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53 -- base raised to the next power of 2.
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54
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55 -- Note: it is not worth special casing base values -1, 0, +1 since
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56 -- the expander does this when the base is a literal, and other cases
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57 -- will be extremely rare.
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58
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59 if Exp /= 0 then
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60 loop
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61 if Exp rem 2 /= 0 then
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62 declare
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63 pragma Unsuppress (All_Checks);
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64 begin
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65 Result := Result * Factor;
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66 end;
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67 end if;
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68
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69 Exp := Exp / 2;
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70 exit when Exp = 0;
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71
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72 declare
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73 pragma Unsuppress (All_Checks);
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74 begin
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75 Factor := Factor * Factor;
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76 end;
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77 end loop;
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78 end if;
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79
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80 return Result;
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81 end Exp_Integer;
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82
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83 end System.Exp_Int;
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