File : s-exnint.adb
1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT RUN-TIME COMPONENTS --
4 -- --
5 -- S Y S T E M . E X N _ I N T --
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 package body System.Exn_Int is
33
34 -----------------
35 -- Exn_Integer --
36 -----------------
37
38 function Exn_Integer (Left : Integer; Right : Natural) return Integer is
39 pragma Suppress (Division_Check);
40 pragma Suppress (Overflow_Check);
41
42 Result : Integer := 1;
43 Factor : Integer := Left;
44 Exp : Natural := Right;
45
46 begin
47 -- We use the standard logarithmic approach, Exp gets shifted right
48 -- testing successive low order bits and Factor is the value of the
49 -- base raised to the next power of 2.
50
51 -- Note: it is not worth special casing base values -1, 0, +1 since
52 -- the expander does this when the base is a literal, and other cases
53 -- will be extremely rare.
54
55 if Exp /= 0 then
56 loop
57 if Exp rem 2 /= 0 then
58 Result := Result * Factor;
59 end if;
60
61 Exp := Exp / 2;
62 exit when Exp = 0;
63 Factor := Factor * Factor;
64 end loop;
65 end if;
66
67 return Result;
68 end Exn_Integer;
69
70 end System.Exn_Int;