1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT COMPILER COMPONENTS                         --
4--                                                                          --
5--                 G N A T . B Y T E _ O R D E R _ M A R K                  --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--                     Copyright (C) 2006-2010, AdaCore                     --
10--                                                                          --
11-- GNAT is free software;  you can  redistribute it  and/or modify it under --
12-- terms of the  GNU General Public License as published  by the Free Soft- --
13-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
14-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
15-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
16-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
17--                                                                          --
18-- As a special exception under Section 7 of GPL version 3, you are granted --
19-- additional permissions described in the GCC Runtime Library Exception,   --
20-- version 3.1, as published by the Free Software Foundation.               --
21--                                                                          --
22-- You should have received a copy of the GNU General Public License and    --
23-- a copy of the GCC Runtime Library Exception along with this program;     --
24-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
25-- <http://www.gnu.org/licenses/>.                                          --
26--                                                                          --
27-- GNAT was originally developed  by the GNAT team at  New York University. --
28-- Extensive contributions were provided by Ada Core Technologies Inc.      --
29--                                                                          --
30------------------------------------------------------------------------------
31
32--  This package provides a procedure for reading and interpreting the BOM
33--  (byte order mark) used to publish the encoding method for a string (for
34--  example, a UTF-8 encoded file in windows will start with the appropriate
35--  BOM sequence to signal UTF-8 encoding.
36
37--  There are two cases
38
39--    Case 1. UTF encodings for Unicode files
40
41--      Here the convention is to have the first character of the file be a
42--      non-breaking zero width space character (16#0000_FEFF#). For the UTF
43--      encodings, the representation of this character can be used to uniquely
44--      determine the encoding. Furthermore, the possibility of any confusion
45--      with unencoded files is minimal, since for example the UTF-8 encoding
46--      of this character looks like the sequence:
47
48--        LC_I_Diaeresis
49--        Right_Angle_Quotation
50--        Fraction_One_Half
51
52--      which is so unlikely to occur legitimately in normal use that it can
53--      safely be ignored in most cases (for example, no legitimate Ada source
54--      file could start with this sequence of characters).
55
56--   Case 2. Specialized XML encodings
57
58--     The XML standard defines a number of other possible encodings and also
59--     defines standardized sequences for marking these encodings. This package
60--     can also optionally handle these XML defined BOM sequences. These XML
61--     cases depend on the first character of the XML file being < so that the
62--     encoding of this character can be recognized.
63
64pragma Compiler_Unit;
65
66package GNAT.Byte_Order_Mark is
67
68   type BOM_Kind is
69     (UTF8_All,  --  UTF8-encoding
70      UTF16_LE,  --  UTF16 little-endian encoding
71      UTF16_BE,  --  UTF16 big-endian encoding
72      UTF32_LE,  --  UTF32 little-endian encoding
73      UTF32_BE,  --  UTF32 big-endian encoding
74
75      --  The following cases are for XML only
76
77      UCS4_BE,   --  UCS-4, big endian machine (1234 order)
78      UCS4_LE,   --  UCS-4, little endian machine (4321 order)
79      UCS4_2143, --  UCS-4, unusual byte order (2143 order)
80      UCS4_3412, --  UCS-4, unusual byte order (3412 order)
81
82      --  Value returned if no BOM recognized
83
84      Unknown);  --  Unknown, assumed to be ASCII compatible
85
86   procedure Read_BOM
87     (Str         : String;
88      Len         : out Natural;
89      BOM         : out BOM_Kind;
90      XML_Support : Boolean := False);
91   --  This is the routine to read the BOM from the start of the given string
92   --  Str. On return BOM is set to the appropriate BOM_Kind and Len is set to
93   --  its length. The caller will typically skip the first Len characters in
94   --  the string to ignore the BOM sequence. The special XML possibilities are
95   --  recognized only if flag XML_Support is set to True. Note that for the
96   --  XML cases, Len is always set to zero on return (not to the length of the
97   --  relevant sequence) since in the XML cases, the sequence recognized is
98   --  for the first real character in the file (<) which is not to be skipped.
99
100end GNAT.Byte_Order_Mark;
101