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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) 1992-2009, 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 3, 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. -- -- -- -- As a special exception under Section 7 of GPL version 3, you are granted -- -- additional permissions described in the GCC Runtime Library Exception, -- -- version 3.1, as published by the Free Software Foundation. -- -- -- -- You should have received a copy of the GNU General Public License and -- -- a copy of the GCC Runtime Library Exception along with this program; -- -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see -- -- <http://www.gnu.org/licenses/>. -- -- -- -- 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) -- This unit may be used directly from an application program by providing -- an appropriate WITH, and the interface can be expected to remain stable. pragma Compiler_Unit; package System.WCh_Con is pragma Pure; ------------------------------------- -- Wide_Character Encoding Methods -- ------------------------------------- -- A wide character encoding method is a method for uniquely representing -- a Wide_Character or Wide_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"] or ["xxxxxx"] where xx are hexadecimal -- characters. Note that currently this is the only encoding that -- supports the full UTF-32 range. -- 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 -- 7. Update documentation (remember section on form strings) -- 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 16-bit BMP. Codes larger than -- 16#FFFF# are not representable using this 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. Codes larger than 16#FFFF# are not representable using this -- encoding method. 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. Codes larger than 16#FFFF are not representable -- using this encoding method. 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. Codes larger than 16#FFFF# are not representable using -- this encoding method. 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 to six byte sequence. -- -- 16#0000_0000#-16#0000_007f#: 2#0xxxxxxx# -- 16#0000_0080#-16#0000_07ff#: 2#110xxxxx# 2#10xxxxxx# -- 16#0000_0800#-16#0000_ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx# -- 16#0001_0000#-16#001F_FFFF#: 2#11110xxx# 2#10xxxxxx# 2#10xxxxxx# -- 2#10xxxxxx# -- 16#0020_0000#-16#03FF_FFFF#: 2#111110xx# 2#10xxxxxx# 2#10xxxxxx# -- 2#10xxxxxx# 2#10xxxxxx# -- 16#0400_0000#-16#7FFF_FFFF#: 2#1111110x# 2#10xxxxxx# 2#10xxxxxx# -- 2#10xxxxxx# 2#10xxxxxx# 2#10xxxxxx# -- -- where the xxx bits correspond to the left-padded bits of 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. This -- encoding method can represent the entire range of Wide_Wide_Character. WCEM_Brackets : constant WC_Encoding_Method := 6; -- A wide character is represented using one of the following sequences: -- -- ["xx"] -- ["xxxx"] -- ["xxxxxx"] -- ["xxxxxxxx"] -- -- where xx are hexadecimal digits representing the character code. This -- encoding method can represent the entire range of Wide_Wide_Character -- but in the general case results in ambiguous representations (there is -- no ambiguity in Ada sources, since the above sequences are illegal Ada). 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 := 12; -- The longest number of characters that can be used for a wide character -- or wide wide character sequence for any of the active encoding methods. WC_Longest_Sequences : constant array (WC_Encoding_Method) of Natural := (WCEM_Hex => 5, WCEM_Upper => 2, WCEM_Shift_JIS => 2, WCEM_EUC => 2, WCEM_UTF8 => 6, WCEM_Brackets => 12); -- The longest number of characters that can be used for a wide character -- or wide wide character sequence using the given encoding method. function Get_WC_Encoding_Method (C : Character) return WC_Encoding_Method; -- Given a character C, returns corresponding encoding method (see array -- WC_Encoding_Letters above). Raises Constraint_Error if not in list. function Get_WC_Encoding_Method (S : String) return WC_Encoding_Method; -- Given a lower case string that is one of hex, upper, shift_jis, euc, -- utf8, brackets, return the corresponding encoding method. Raises -- Constraint_Error if not in list. function Is_Start_Of_Encoding (C : Character; EM : WC_Encoding_Method) return Boolean; pragma Inline (Is_Start_Of_Encoding); -- Returns True if the Character C is the start of a multi-character -- encoding sequence for the given encoding method EM. If EM is set to -- WCEM_Brackets, this function always returns False. end System.WCh_Con;
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