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------------------------------------------------------------------------------
-- --
-- GNAT COMPILER COMPONENTS --
-- --
-- S Y S T E M . W C H _ C O N --
-- --
-- S p e c --
-- --
-- --
-- Copyright (C) 1992-1998 Free Software Foundation, Inc. --
-- --
-- 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 2, 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. See the GNU General Public License --
-- for more details. You should have received a copy of the GNU General --
-- Public License distributed with GNAT; see file COPYING. If not, write --
-- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
-- MA 02111-1307, USA. --
-- --
-- As a special exception, if other files instantiate generics from this --
-- unit, or you link this unit with other files to produce an executable, --
-- this unit does not by itself cause the resulting executable to be --
-- covered by the GNU General Public License. This exception does not --
-- however invalidate any other reasons why the executable file might be --
-- covered by the GNU Public License. --
-- --
-- GNAT was originally developed by the GNAT team at New York University. --
-- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
-- --
------------------------------------------------------------------------------
-- This package defines the codes used to identify the encoding method for
-- wide characters in string and character constants. This is needed both
-- at compile time and at runtime (for the wide character runtime routines)
package System.WCh_Con is
pragma Pure (WCh_Con);
-------------------------------------
-- Wide_Character Encoding Methods --
-------------------------------------
-- A wide character encoding method is a method for uniquely representing
-- a Wide_Character value using a one or more Character values. Three
-- types of encoding method are supported by GNAT:
-- An escape encoding method uses ESC as the first character of the
-- sequence, and subsequent characters determine the wide character
-- value that is represented. Any character other than ESC stands
-- for itself as a single byte (i.e. any character in Latin-1, other
-- than ESC itself, is represented as a single character: itself).
-- An upper half encoding method uses a character in the upper half
-- range (i.e. in the range 16#80# .. 16#FF#) as the first byte of
-- a wide character encoding sequence. Subsequent characters are
-- used to determine the wide character value that is represented.
-- Any character in the lower half (16#00# .. 16#7F#) represents
-- itself as a single character.
-- The brackets notation, where a wide character is represented
-- by the sequence ["xx"] or ["xxxx"] where xx are hexadecimal
-- characters.
-- Note that GNAT does not currently support escape-in, escape-out
-- encoding methods, where an escape sequence is used to set a mode
-- used to recognize subsequent characters. All encoding methods use
-- individual character-by-character encodings, so that a sequence of
-- wide characters is represented by a sequence of encodings.
-- To add new encoding methods, the following steps are required:
-- 1. Define a code for a new value of type WC_Encoding_Method
-- 2. Adjust the definition of WC_Encoding_Method accordingly
-- 3. Provide appropriate conversion routines in System.Wch_Cnv
-- 4. Adjust definition of WC_Longest_Sequence if necessary
-- 5. Add an entry in WC_Encoding_Letters for the new method
-- 6. Add proper code to s-wchstw.adb, s-wchwts.adb, s-widwch.adb
-- Note that the WC_Encoding_Method values must be kept ordered so that
-- the definitions of the subtypes WC_Upper_Half_Encoding_Method and
-- WC_ESC_Encoding_Method are still correct.
---------------------------------
-- Encoding Method Definitions --
---------------------------------
type WC_Encoding_Method is range 1 .. 6;
-- Type covering the range of values used to represent wide character
-- encoding methods. An enumeration type might be a little neater, but
-- more trouble than it's worth, given the need to pass these values
-- from the compiler to the backend, and to record them in the ALI file.
WCEM_Hex : constant WC_Encoding_Method := 1;
-- The wide character with code 16#abcd# is represented by the escape
-- sequence ESC a b c d (five characters, where abcd are ASCII hex
-- characters, using upper case for letters). This method is easy
-- to deal with in external environments that do not support wide
-- characters, and covers the whole BMP. This is the default encoding
-- method.
WCEM_Upper : constant WC_Encoding_Method := 2;
-- The wide character with encoding 16#abcd#, where the upper bit is on
-- (i.e. a is in the range 8-F) is represented as two bytes 16#ab# and
-- 16#cd#. The second byte may never be a format control character, but
-- is not required to be in the upper half. This method can be also used
-- for shift-JIS or EUC where the internal coding matches the external
-- coding.
WCEM_Shift_JIS : constant WC_Encoding_Method := 3;
-- A wide character is represented by a two character sequence 16#ab#
-- and 16#cd#, with the restrictions described for upper half encoding
-- as described above. The internal character code is the corresponding
-- JIS character according to the standard algorithm for Shift-JIS
-- conversion. See the body of package System.JIS_Conversions for
-- further details.
WCEM_EUC : constant WC_Encoding_Method := 4;
-- A wide character is represented by a two character sequence 16#ab# and
-- 16#cd#, with both characters being in the upper half set. The internal
-- character code is the corresponding JIS character according to the EUC
-- encoding algorithm. See the body of package System.JIS_Conversions for
-- further details.
WCEM_UTF8 : constant WC_Encoding_Method := 5;
-- An ISO 10646-1 BMP/Unicode wide character is represented in
-- UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
-- 10646-1/Am.2. Depending on the character value, a Unicode character
-- is represented as the one, two, or three byte sequence
--
-- 16#0000#-16#007f#: 2#0xxxxxxx#
-- 16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx#
-- 16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
--
-- where the xxx bits correspond to the left-padded bits of the the
-- 16-bit character value. Note that all lower half ASCII characters
-- are represented as ASCII bytes and all upper half characters and
-- other wide characters are represented as sequences of upper-half
-- (The full UTF-8 scheme allows for encoding 31-bit characters as
-- 6-byte sequences, but in this implementation, all UTF-8 sequences
-- of four or more bytes length will raise a Constraint_Error, as
-- will all illegal UTF-8 sequences.)
WCEM_Brackets : constant WC_Encoding_Method := 6;
-- A wide character is represented as the sequence ["abcd"] where abcd
-- are four hexadecimal characters. In this mode, the sequence ["ab"]
-- is also recognized for the case of character codes in the range 0-255.
WC_Encoding_Letters : constant array (WC_Encoding_Method) of Character :=
(WCEM_Hex => 'h',
WCEM_Upper => 'u',
WCEM_Shift_JIS => 's',
WCEM_EUC => 'e',
WCEM_UTF8 => '8',
WCEM_Brackets => 'b');
-- Letters used for selection of wide character encoding method in the
-- compiler options (-gnatW? switch) and for Wide_Text_IO (WCEM parameter
-- in the form string).
subtype WC_ESC_Encoding_Method is
WC_Encoding_Method range WCEM_Hex .. WCEM_Hex;
-- Encoding methods using an ESC character at the start of the sequence.
subtype WC_Upper_Half_Encoding_Method is
WC_Encoding_Method range WCEM_Upper .. WCEM_UTF8;
-- Encoding methods using an upper half character (16#80#..16#FF) at
-- the start of the sequence.
WC_Longest_Sequence : constant := 8;
-- The longest number of characters that can be used for a wide
-- character sequence for any of the active encoding methods.
end System.WCh_Con;
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