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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT COMPILER COMPONENTS --
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4 -- --
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5 -- G N A T . B Y T E _ O R D E R _ M A R K --
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6 -- --
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7 -- S p e c --
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8 -- --
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145
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9 -- Copyright (C) 2006-2019, AdaCore --
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111
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10 -- --
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11 -- GNAT is free software; you can redistribute it and/or modify it under --
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12 -- terms of the GNU General Public License as published by the Free Soft- --
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13 -- ware Foundation; either version 3, or (at your option) any later ver- --
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14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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16 -- or FITNESS FOR A PARTICULAR PURPOSE. --
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17 -- --
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18 -- As a special exception under Section 7 of GPL version 3, you are granted --
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19 -- additional permissions described in the GCC Runtime Library Exception, --
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20 -- version 3.1, as published by the Free Software Foundation. --
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21 -- --
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22 -- You should have received a copy of the GNU General Public License and --
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23 -- a copy of the GCC Runtime Library Exception along with this program; --
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24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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25 -- <http://www.gnu.org/licenses/>. --
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26 -- --
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27 -- GNAT was originally developed by the GNAT team at New York University. --
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28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
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29 -- --
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30 ------------------------------------------------------------------------------
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31
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32 -- This package provides a procedure for reading and interpreting the BOM
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33 -- (byte order mark) used to publish the encoding method for a string (for
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34 -- example, a UTF-8 encoded file in windows will start with the appropriate
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35 -- BOM sequence to signal UTF-8 encoding).
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36
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37 -- There are two cases
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38
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39 -- Case 1. UTF encodings for Unicode files
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40
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41 -- Here the convention is to have the first character of the file be a
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42 -- non-breaking zero width space character (16#0000_FEFF#). For the UTF
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43 -- encodings, the representation of this character can be used to uniquely
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44 -- determine the encoding. Furthermore, the possibility of any confusion
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45 -- with unencoded files is minimal, since for example the UTF-8 encoding
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46 -- of this character looks like the sequence:
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47
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48 -- LC_I_Diaeresis
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49 -- Right_Angle_Quotation
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50 -- Fraction_One_Half
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51
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52 -- which is so unlikely to occur legitimately in normal use that it can
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53 -- safely be ignored in most cases (for example, no legitimate Ada source
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54 -- file could start with this sequence of characters).
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55
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56 -- Case 2. Specialized XML encodings
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57
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58 -- The XML standard defines a number of other possible encodings and also
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59 -- defines standardized sequences for marking these encodings. This package
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60 -- can also optionally handle these XML defined BOM sequences. These XML
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61 -- cases depend on the first character of the XML file being < so that the
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62 -- encoding of this character can be recognized.
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63
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64 pragma Compiler_Unit_Warning;
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65
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66 package GNAT.Byte_Order_Mark is
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67
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68 type BOM_Kind is
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69 (UTF8_All, -- UTF8-encoding
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70 UTF16_LE, -- UTF16 little-endian encoding
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71 UTF16_BE, -- UTF16 big-endian encoding
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72 UTF32_LE, -- UTF32 little-endian encoding
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73 UTF32_BE, -- UTF32 big-endian encoding
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74
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75 -- The following cases are for XML only
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76
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77 UCS4_BE, -- UCS-4, big endian machine (1234 order)
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78 UCS4_LE, -- UCS-4, little endian machine (4321 order)
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79 UCS4_2143, -- UCS-4, unusual byte order (2143 order)
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80 UCS4_3412, -- UCS-4, unusual byte order (3412 order)
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81
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82 -- Value returned if no BOM recognized
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83
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84 Unknown); -- Unknown, assumed to be ASCII compatible
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85
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86 procedure Read_BOM
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87 (Str : String;
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88 Len : out Natural;
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89 BOM : out BOM_Kind;
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90 XML_Support : Boolean := False);
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91 -- This is the routine to read the BOM from the start of the given string
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92 -- Str. On return BOM is set to the appropriate BOM_Kind and Len is set to
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93 -- its length. The caller will typically skip the first Len characters in
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94 -- the string to ignore the BOM sequence. The special XML possibilities are
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95 -- recognized only if flag XML_Support is set to True. Note that for the
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96 -- XML cases, Len is always set to zero on return (not to the length of the
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97 -- relevant sequence) since in the XML cases, the sequence recognized is
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98 -- for the first real character in the file (<) which is not to be skipped.
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99
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100 end GNAT.Byte_Order_Mark;
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