+++ /dev/null
-------------------------------------------------------------------------------
--- --
--- GNAT COMPILER COMPONENTS --
--- --
--- S Y S T E M . W C H _ C O N --
--- --
--- S p e c --
--- --
--- $Revision: 1.1.16.2 $
--- --
--- 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. --
--- Extensive contributions were provided by Ada Core Technologies Inc. --
--- --
-------------------------------------------------------------------------------
-
--- 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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