File : s-expllu.adb
1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT RUN-TIME COMPONENTS --
4 -- --
5 -- S Y S T E M . X P _ B M L --
6 -- --
7 -- B o d y --
8 -- --
9 -- Copyright (C) 1992-2014, Free Software Foundation, Inc. --
10 -- --
11 -- GNAT is free software; you can redistribute it and/or modify it under --
12 -- terms of the GNU General Public License as published by the Free Soft- --
13 -- ware Foundation; either version 3, or (at your option) any later ver- --
14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
16 -- or FITNESS FOR A PARTICULAR PURPOSE. --
17 -- --
18 -- --
19 -- --
20 -- --
21 -- --
22 -- You should have received a copy of the GNU General Public License and --
23 -- a copy of the GCC Runtime Library Exception along with this program; --
24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
25 -- <http://www.gnu.org/licenses/>. --
26 -- --
27 -- GNAT was originally developed by the GNAT team at New York University. --
28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
29 -- --
30 ------------------------------------------------------------------------------
31
32 with System.Unsigned_Types; use System.Unsigned_Types;
33
34 package body System.Exp_LLU is
35
36 ----------------------------
37 -- Exp_Long_Long_Unsigned --
38 ----------------------------
39
40 function Exp_Long_Long_Unsigned
41 (Left : Long_Long_Unsigned;
42 Right : Natural)
43 return Long_Long_Unsigned
44 is
45 Result : Long_Long_Unsigned := 1;
46 Factor : Long_Long_Unsigned := Left;
47 Exp : Natural := Right;
48
49 begin
50 -- We use the standard logarithmic approach, Exp gets shifted right
51 -- testing successive low order bits and Factor is the value of the
52 -- base raised to the next power of 2.
53
54 -- Note: it is not worth special casing the cases of base values -1,0,+1
55 -- since the expander does this when the base is a literal, and other
56 -- cases will be extremely rare.
57
58 if Exp /= 0 then
59 loop
60 if Exp rem 2 /= 0 then
61 Result := Result * Factor;
62 end if;
63
64 Exp := Exp / 2;
65 exit when Exp = 0;
66 Factor := Factor * Factor;
67 end loop;
68 end if;
69
70 return Result;
71
72 end Exp_Long_Long_Unsigned;
73
74 end System.Exp_LLU;