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1 281 jeremybenn
------------------------------------------------------------------------------
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--                                                                          --
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--                         GNAT COMPILER COMPONENTS                         --
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--                                                                          --
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--                 G N A T . B Y T E _ O R D E R _ M A R K                  --
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--                                                                          --
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--                                 S p e c                                  --
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--                                                                          --
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--                     Copyright (C) 2006-2008, AdaCore                     --
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--                                                                          --
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-- GNAT is free software;  you can  redistribute it  and/or modify it under --
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-- terms of the  GNU General Public License as published  by the Free Soft- --
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-- ware  Foundation;  either version 2,  or (at your option) any later ver- --
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-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
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-- for  more details.  You should have  received  a copy of the GNU General --
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-- Public License  distributed with GNAT;  see file COPYING.  If not, write --
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-- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
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-- Boston, MA 02110-1301, USA.                                              --
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--                                                                          --
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-- As a special exception,  if other files  instantiate  generics from this --
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-- unit, or you link  this unit with other files  to produce an executable, --
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-- this  unit  does not  by itself cause  the resulting  executable  to  be --
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-- covered  by the  GNU  General  Public  License.  This exception does not --
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-- however invalidate  any other reasons why  the executable file  might be --
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-- covered by the  GNU Public License.                                      --
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--                                                                          --
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-- GNAT was originally developed  by the GNAT team at  New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc.      --
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--                                                                          --
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------------------------------------------------------------------------------
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--  This package provides a procedure for reading and interpreting the BOM
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--  (byte order mark) used to publish the encoding method for a string (for
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--  example, a UTF-8 encoded file in windows will start with the appropriate
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--  BOM sequence to signal UTF-8 encoding.
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--  There are two cases
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--    Case 1. UTF encodings for Unicode files
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--      Here the convention is to have the first character of the file be a
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--      non-breaking zero width space character (16#0000_FEFF#). For the UTF
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--      encodings, the representation of this character can be used to uniquely
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--      determine the encoding. Furthermore, the possibility of any confusion
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--      with unencoded files is minimal, since for example the UTF-8 encoding
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--      of this character looks like the sequence:
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--        LC_I_Diaeresis
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--        Right_Angle_Quotation
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--        Fraction_One_Half
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--      which is so unlikely to occur legitimately in normal use that it can
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--      safely be ignored in most cases (for example, no legitimate Ada source
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--      file could start with this sequence of characters).
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--   Case 2. Specialized XML encodings
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--     The XML standard defines a number of other possible encodings and also
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--     defines standardized sequences for marking these encodings. This package
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--     can also optionally handle these XML defined BOM sequences. These XML
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--     cases depend on the first character of the XML file being < so that the
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--     encoding of this character can be recognized.
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pragma Compiler_Unit;
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package GNAT.Byte_Order_Mark is
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   type BOM_Kind is
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     (UTF8_All,  --  UTF8-encoding
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      UTF16_LE,  --  UTF16 little-endian encoding
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      UTF16_BE,  --  UTF16 big-endian encoding
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      UTF32_LE,  --  UTF32 little-endian encoding
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      UTF32_BE,  --  UTF32 big-endian encoding
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      --  The following cases are for XML only
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      UCS4_BE,   --  UCS-4, big endian machine (1234 order)
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      UCS4_LE,   --  UCS-4, little endian machine (4321 order)
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      UCS4_2143, --  UCS-4, unusual byte order (2143 order)
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      UCS4_3412, --  UCS-4, unusual byte order (3412 order)
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      --  Value returned if no BOM recognized
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      Unknown);  --  Unknown, assumed to be ASCII compatible
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   procedure Read_BOM
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     (Str         : String;
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      Len         : out Natural;
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      BOM         : out BOM_Kind;
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      XML_Support : Boolean := False);
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   --  This is the routine to read the BOM from the start of the given string
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   --  Str. On return BOM is set to the appropriate BOM_Kind and Len is set to
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   --  its length. The caller will typically skip the first Len characters in
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   --  the string to ignore the BOM sequence. The special XML possibilities are
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   --  recognized only if flag XML_Support is set to True. Note that for the
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   --  XML cases, Len is always set to zero on return (not to the length of the
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   --  relevant sequence) since in the XML cases, the sequence recognized is
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   --  for the first real character in the file (<) which is not to be skipped.
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end GNAT.Byte_Order_Mark;

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