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Text File | 1995-10-17 | 8.2 KB | 155 lines

------------------------------------------------------------------------------ -- -- -- GNAT COMPILER COMPONENTS -- -- -- -- S Y S T E M . W C H _ C O N -- -- -- -- S p e c -- -- -- -- $Revision: 1.5 $ -- -- -- -- Copyright (c) 1992,1993,1994 NYU, All Rights Reserved -- -- -- -- The GNAT library is free software; you can redistribute it and/or modify -- -- it under terms of the GNU Library General Public License as published by -- -- the Free Software Foundation; either version 2, or (at your option) any -- -- later version. The GNAT library is distributed in the hope that it will -- -- be useful, but WITHOUT ANY WARRANTY; without even the implied warranty -- -- of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU -- -- Library General Public License for more details. You should have -- -- received a copy of the GNU Library General Public License along with -- -- the GNAT library; see the file COPYING.LIB. If not, write to the Free -- -- Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. -- -- -- ------------------------------------------------------------------------------ -- 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. Two 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. -- 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 -- 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. -------------------------------- -- Compatibility Requirements -- -------------------------------- -- When a unit is compiled with a particular option, any units that it -- with's are compiled with the same setting. Basically this means that -- all units in a program which contain wide character encodings must -- use a consistent encoding method. At bind time, the binder checks -- that all units in the program are either compiled in WCEM_None mode, -- meaning that they have no wide character encodings, or that they are -- compiled in a consistent mode. It is not permitted to mix two modes -- (other than WCEM_None) in a single program. --------------------------------- -- Encoding Method Definitions -- --------------------------------- type WC_Encoding_Method is range 0 .. 4; -- 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_None : constant WC_Encoding_Method := 0; -- No wide character encoding is permitted in the source program. -- This is the default. A unit compiled with this option can be -- used with units compiled with any other option. 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. -- 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. WC_Encoding_Letters : constant array (WC_Encoding_Method) of Character := (WCEM_None => 'n', WCEM_Hex => 'h', WCEM_Upper => 'u', WCEM_Shift_JIS => 's', WCEM_EUC => 'e'); -- Letters used for selection of wide character encoding method in the -- compiler options (-gnatj? 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_EUC; -- Encoding methods using an upper half character (16#80#..16#FF) at -- the start of the sequence. WC_Longest_Sequence : constant := 5; -- 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;