------------------------------------------------------------------------------ -- -- -- 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. -- -- 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;