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------------------------------------------------------------------------------

--                                                                          --

--                    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;