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-- --
-- --
-- G N A T . B Y T E _ O R D E R _ M A R K --
-- --
-- S p e c --
-- --
-- Copyright (C) 2006-2021, 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 3, 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 --
-- --
-- As a special exception under Section 7 of GPL version 3, you are granted --
-- additional permissions described in the GCC Runtime Library Exception, --
-- version 3.1, as published by the Free Software Foundation. --
-- --
-- You should have received a copy of the GNU General Public License and --
-- a copy of the GCC Runtime Library Exception along with this program; --
-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
-- <>. --
-- --
-- GNAT was originally developed by the GNAT team at New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc. --
-- --
-- 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_Warning;
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;