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) 2006-2019, 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_Warning; 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