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

--                                                                          --

--                         GNAT COMPILER COMPONENTS                         --

--                                                                          --

--                 G N A T . B Y T E _ O R D E R _ M A R K                  --

--                                                                          --

--                                 B o d y                                  --

--                                                                          --

--                     Copyright (C) 2006-2010, AdaCore                     --

--                                                                          --

-- 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;

package body GNAT.Byte_Order_Mark is

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

   -- Read_BOM --

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

   procedure Read_BOM

     (Str         : String;

      Len         : out Natural;

      BOM         : out BOM_Kind;

      XML_Support : Boolean := False)

   is

   begin

      --  Note: the order of these tests is important, because in some cases

      --  one sequence is a prefix of a longer sequence, and we must test for

      --  the longer sequence first

      --  UTF-32 (big-endian)

      if Str'Length >= 4

        and then Str (Str'First)     = Character'Val (16#00#)

        and then Str (Str'First + 1) = Character'Val (16#00#)

        and then Str (Str'First + 2) = Character'Val (16#FE#)

        and then Str (Str'First + 3) = Character'Val (16#FF#)

      then

         Len := 4;

         BOM := UTF32_BE;

      --  UTF-32 (little-endian)

      elsif Str'Length >= 4

        and then Str (Str'First)     = Character'Val (16#FF#)

        and then Str (Str'First + 1) = Character'Val (16#FE#)

        and then Str (Str'First + 2) = Character'Val (16#00#)

        and then Str (Str'First + 3) = Character'Val (16#00#)

      then

         Len := 4;

         BOM := UTF32_LE;

      --  UTF-16 (big-endian)

      elsif Str'Length >= 2

        and then Str (Str'First) = Character'Val (16#FE#)

        and then Str (Str'First + 1) = Character'Val (16#FF#)

      then

         Len := 2;

         BOM := UTF16_BE;

      --  UTF-16 (little-endian)

      elsif Str'Length >= 2

        and then Str (Str'First) = Character'Val (16#FF#)

        and then Str (Str'First + 1) = Character'Val (16#FE#)

      then

         Len := 2;

         BOM := UTF16_LE;

      --  UTF-8 (endian-independent)

      elsif Str'Length >= 3

        and then Str (Str'First)     = Character'Val (16#EF#)

        and then Str (Str'First + 1) = Character'Val (16#BB#)

        and then Str (Str'First + 2) = Character'Val (16#BF#)

      then

         Len := 3;

         BOM := UTF8_All;

      --  UCS-4 (big-endian) XML only

      elsif XML_Support

        and then Str'Length >= 4

        and then Str (Str'First)     = Character'Val (16#00#)

        and then Str (Str'First + 1) = Character'Val (16#00#)

        and then Str (Str'First + 2) = Character'Val (16#00#)

        and then Str (Str'First + 3) = Character'Val (16#3C#)

      then

         Len := 0;

         BOM := UCS4_BE;

      --  UCS-4 (little-endian) XML case

      elsif XML_Support

        and then Str'Length >= 4

        and then Str (Str'First)     = Character'Val (16#3C#)

        and then Str (Str'First + 1) = Character'Val (16#00#)

        and then Str (Str'First + 2) = Character'Val (16#00#)

        and then Str (Str'First + 3) = Character'Val (16#00#)

      then

         Len := 0;

         BOM := UCS4_LE;

      --  UCS-4 (unusual byte order 2143) XML case

      elsif XML_Support

        and then Str'Length >= 4

        and then Str (Str'First)     = Character'Val (16#00#)

        and then Str (Str'First + 1) = Character'Val (16#00#)

        and then Str (Str'First + 2) = Character'Val (16#3C#)

        and then Str (Str'First + 3) = Character'Val (16#00#)

      then

         Len := 0;

         BOM := UCS4_2143;

      --  UCS-4 (unusual byte order 3412) XML case

      elsif XML_Support

        and then Str'Length >= 4

        and then Str (Str'First)     = Character'Val (16#00#)

        and then Str (Str'First + 1) = Character'Val (16#3C#)

        and then Str (Str'First + 2) = Character'Val (16#00#)

        and then Str (Str'First + 3) = Character'Val (16#00#)

      then

         Len := 0;

         BOM := UCS4_3412;

      --  UTF-16 (big-endian) XML case

      elsif XML_Support

        and then Str'Length >= 4

        and then Str (Str'First)     = Character'Val (16#00#)

        and then Str (Str'First + 1) = Character'Val (16#3C#)

        and then Str (Str'First + 2) = Character'Val (16#00#)

        and then Str (Str'First + 3) = Character'Val (16#3F#)

      then

         Len := 0;

         BOM := UTF16_BE;

      --  UTF-32 (little-endian) XML case

      elsif XML_Support

        and then Str'Length >= 4

        and then Str (Str'First)     = Character'Val (16#3C#)

        and then Str (Str'First + 1) = Character'Val (16#00#)

        and then Str (Str'First + 2) = Character'Val (16#3F#)

        and then Str (Str'First + 3) = Character'Val (16#00#)

      then

         Len := 0;

         BOM := UTF16_LE;

      --  Unrecognized special encodings XML only

      elsif XML_Support

        and then Str'Length >= 4

        and then Str (Str'First)     = Character'Val (16#3C#)

        and then Str (Str'First + 1) = Character'Val (16#3F#)

        and then Str (Str'First + 2) = Character'Val (16#78#)

        and then Str (Str'First + 3) = Character'Val (16#6D#)

      then

         --  UTF-8, ASCII, some part of ISO8859, Shift-JIS, EUC,...

         Len := 0;

         BOM := Unknown;

      --  No BOM recognized

      else

         Len := 0;

         BOM := Unknown;

      end if;

   end Read_BOM;

end GNAT.Byte_Order_Mark;