------------------------------------------------------------------------------
--                                                                          --
--                    GNAT RUN-TIME LIBRARY COMPONENTS                      --
--                                                                          --
--                S Y S T E M . S T R I N G _ C O M P A R E                 --
--                                                                          --
--                                 B o d y                                  --
--                                                                          --
--          Copyright (C) 2002-2009, 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 3,  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.                                     --
--                                                                          --
-- As a special exception under Section 7 of GPL version 3, you are granted --
-- additional permissions described in the GCC Runtime Library Exception,   --
-- version 3.1, as published by the Free Software Foundation.               --
--                                                                          --
-- You should have received a copy of the GNU General Public License and    --
-- a copy of the GCC Runtime Library Exception along with this program;     --
-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
-- <http://www.gnu.org/licenses/>.                                          --
--                                                                          --
-- GNAT was originally developed  by the GNAT team at  New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc.      --
--                                                                          --
------------------------------------------------------------------------------

pragma Compiler_Unit;

with Ada.Unchecked_Conversion;

package body System.String_Compare is

   type Word is mod 2 ** 32;
   --  Used to process operands by words

   type Big_Words is array (Natural) of Word;
   type Big_Words_Ptr is access Big_Words;
   for Big_Words_Ptr'Storage_Size use 0;
   --  Array type used to access by words

   type Byte is mod 2 ** 8;
   --  Used to process operands by bytes

   type Big_Bytes is array (Natural) of Byte;
   type Big_Bytes_Ptr is access Big_Bytes;
   for Big_Bytes_Ptr'Storage_Size use 0;
   --  Array type used to access by bytes

   function To_Big_Words is new
     Ada.Unchecked_Conversion (System.Address, Big_Words_Ptr);

   function To_Big_Bytes is new
     Ada.Unchecked_Conversion (System.Address, Big_Bytes_Ptr);

   -----------------
   -- Str_Compare --
   -----------------

   function Str_Compare
     (Left      : System.Address;
      Right     : System.Address;
      Left_Len  : Natural;
      Right_Len : Natural) return Integer
   is
      Compare_Len : constant Natural := Natural'Min (Left_Len, Right_Len);

   begin
      --  If operands are non-aligned, or length is too short, go by bytes

      if (((Left or Right) and 2#11#) /= 0) or else Compare_Len < 4 then
         return Str_Compare_Bytes (Left, Right, Left_Len, Right_Len);
      end if;

      --  Here we can go by words

      declare
         LeftP  : constant Big_Words_Ptr := To_Big_Words (Left);
         RightP : constant Big_Words_Ptr := To_Big_Words (Right);
         Clen4  : constant Natural       := Compare_Len / 4 - 1;
         Clen4F : constant Natural       := Clen4 * 4;

      begin
         for J in 0 .. Clen4 loop
            if LeftP (J) /= RightP (J) then
               return Str_Compare_Bytes
                        (Left  + Address (4 * J),
                         Right + Address (4 * J),
                         4, 4);
            end if;
         end loop;

         return Str_Compare_Bytes
                  (Left      + Address (Clen4F),
                   Right     + Address (Clen4F),
                   Left_Len  - Clen4F,
                   Right_Len - Clen4F);
      end;
   end Str_Compare;

   -----------------------
   -- Str_Compare_Bytes --
   -----------------------

   function Str_Compare_Bytes
     (Left      : System.Address;
      Right     : System.Address;
      Left_Len  : Natural;
      Right_Len : Natural) return Integer
   is
      Compare_Len : constant Natural := Natural'Min (Left_Len, Right_Len);

      LeftP  : constant Big_Bytes_Ptr := To_Big_Bytes (Left);
      RightP : constant Big_Bytes_Ptr := To_Big_Bytes (Right);

   begin
      for J in 0 .. Compare_Len - 1 loop
         if LeftP (J) /= RightP (J) then
            if LeftP (J) > RightP (J) then
               return +1;
            else
               return -1;
            end if;
         end if;
      end loop;

      if Left_Len = Right_Len then
         return 0;
      elsif Left_Len > Right_Len then
         return +1;
      else
         return -1;
      end if;
   end Str_Compare_Bytes;

end System.String_Compare;
