| ------------------------------------------------------------------------------ |
| -- -- |
| -- GNAT COMPILER COMPONENTS -- |
| -- -- |
| -- G N A T . B Y T E _ O R D E R _ M A R K -- |
| -- -- |
| -- S p e c -- |
| -- -- |
| -- Copyright (C) 2006-2023, 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 -- |
| -- or FITNESS FOR A PARTICULAR PURPOSE. -- |
| -- -- |
| -- 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 -- |
| -- <http://www.gnu.org/licenses/>. -- |
| -- -- |
| -- 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. |
| |
| 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; |
