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--                                                                          --

--                         GNAT COMPILER COMPONENTS                         --

--                                                                          --

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

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--                     Copyright (C) 2006-2008, 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 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,  51  Franklin  Street,  Fifth  Floor, --

-- Boston, MA 02110-1301, 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.      --

--                                                                          --

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--  This package provides a procedure for reading and interpreting the BOM

--  (byte order mark) used to publish the encoding method for a string (for

--  example, a UTF-8 encoded file in windows will start with the appropriate

--  BOM sequence to signal UTF-8 encoding.

--  There are two cases

--    Case 1. UTF encodings for Unicode files

--      Here the convention is to have the first character of the file be a

--      non-breaking zero width space character (16#0000_FEFF#). For the UTF

--      encodings, the representation of this character can be used to uniquely

--      determine the encoding. Furthermore, the possibility of any confusion

--      with unencoded files is minimal, since for example the UTF-8 encoding

--      of this character looks like the sequence:

--        LC_I_Diaeresis

--        Right_Angle_Quotation

--        Fraction_One_Half

--      which is so unlikely to occur legitimately in normal use that it can

--      safely be ignored in most cases (for example, no legitimate Ada source

--      file could start with this sequence of characters).

--   Case 2. Specialized XML encodings

--     The XML standard defines a number of other possible encodings and also

--     defines standardized sequences for marking these encodings. This package

--     can also optionally handle these XML defined BOM sequences. These XML

--     cases depend on the first character of the XML file being < so that the

--     encoding of this character can be recognized.

pragma Compiler_Unit;

package GNAT.Byte_Order_Mark is

   type BOM_Kind is

     (UTF8_All,  --  UTF8-encoding

      UTF16_LE,  --  UTF16 little-endian encoding

      UTF16_BE,  --  UTF16 big-endian encoding

      UTF32_LE,  --  UTF32 little-endian encoding

      UTF32_BE,  --  UTF32 big-endian encoding

      --  The following cases are for XML only

      UCS4_BE,   --  UCS-4, big endian machine (1234 order)

      UCS4_LE,   --  UCS-4, little endian machine (4321 order)

      UCS4_2143, --  UCS-4, unusual byte order (2143 order)

      UCS4_3412, --  UCS-4, unusual byte order (3412 order)

      --  Value returned if no BOM recognized

      Unknown);  --  Unknown, assumed to be ASCII compatible

   procedure Read_BOM

     (Str         : String;

      Len         : out Natural;

      BOM         : out BOM_Kind;

      XML_Support : Boolean := False);

   --  This is the routine to read the BOM from the start of the given string

   --  Str. On return BOM is set to the appropriate BOM_Kind and Len is set to

   --  its length. The caller will typically skip the first Len characters in

   --  the string to ignore the BOM sequence. The special XML possibilities are

   --  recognized only if flag XML_Support is set to True. Note that for the

   --  XML cases, Len is always set to zero on return (not to the length of the

   --  relevant sequence) since in the XML cases, the sequence recognized is

   --  for the first real character in the file (<) which is not to be skipped.

end GNAT.Byte_Order_Mark;