+++ /dev/null
-------------------------------------------------------------------------------
--- --
--- GNAT RUNTIME COMPONENTS --
--- --
--- S Y S T E M . E X P _ M O D --
--- --
--- B o d y --
--- --
--- $Revision: 1.1.16.2 $
--- --
--- Copyright (C) 1992,1993,1994,1995 Free Software Foundation, Inc. --
--- --
--- GNAT is free software; you can redistribute it and/or modify it under --
--- terms of the GNU General Public License as published by the Free Soft- --
--- ware Foundation; either version 2, or (at your option) any later ver- --
--- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
--- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
--- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
--- for more details. You should have received a copy of the GNU General --
--- Public License distributed with GNAT; see file COPYING. If not, write --
--- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
--- MA 02111-1307, USA. --
--- --
--- As a special exception, if other files instantiate generics from this --
--- unit, or you link this unit with other files to produce an executable, --
--- this unit does not by itself cause the resulting executable to be --
--- covered by the GNU General Public License. This exception does not --
--- however invalidate any other reasons why the executable file might be --
--- covered by the GNU Public License. --
--- --
--- GNAT was originally developed by the GNAT team at New York University. --
--- Extensive contributions were provided by Ada Core Technologies Inc. --
--- --
-------------------------------------------------------------------------------
-
-package body System.Exp_Mod is
-
- -----------------
- -- Exp_Modular --
- -----------------
-
- function Exp_Modular
- (Left : Integer;
- Modulus : Integer;
- Right : Natural)
- return Integer
- is
- Result : Integer := 1;
- Factor : Integer := Left;
- Exp : Natural := Right;
-
- function Mult (X, Y : Integer) return Integer;
- pragma Inline (Mult);
- -- Modular multiplication. Note that we can't take advantage of the
- -- compiler's circuit, because the modulus is not known statically.
-
- function Mult (X, Y : Integer) return Integer is
- begin
- return Integer
- (Long_Long_Integer (X) * Long_Long_Integer (Y)
- mod Long_Long_Integer (Modulus));
- end Mult;
-
- -- Start of processing for Exp_Modular
-
- begin
- -- We use the standard logarithmic approach, Exp gets shifted right
- -- testing successive low order bits and Factor is the value of the
- -- base raised to the next power of 2.
-
- -- Note: it is not worth special casing the cases of base values -1,0,+1
- -- since the expander does this when the base is a literal, and other
- -- cases will be extremely rare.
-
- if Exp /= 0 then
- loop
- if Exp rem 2 /= 0 then
- Result := Mult (Result, Factor);
- end if;
-
- Exp := Exp / 2;
- exit when Exp = 0;
- Factor := Mult (Factor, Factor);
- end loop;
- end if;
-
- return Result;
-
- end Exp_Modular;
-
-end System.Exp_Mod;
projects / msp430-gcc.git / blobdiff