| ------------------------------------------------------------------------------ |
| -- -- |
| -- GNAT COMPILER COMPONENTS -- |
| -- -- |
| -- S Y S T E M . W C H _ C O N -- |
| -- -- |
| -- S p e c -- |
| -- -- |
| -- $Revision: 1.10 $ -- |
| -- -- |
| -- 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; |
