1------------------------------------------------------------------------------ 2-- -- 3-- GNAT COMPILER COMPONENTS -- 4-- -- 5-- S Y S T E M . W C H _ C O N -- 6-- -- 7-- S p e c -- 8-- -- 9-- Copyright (C) 1992-2019, Free Software Foundation, Inc. -- 10-- -- 11-- GNAT is free software; you can redistribute it and/or modify it under -- 12-- terms of the GNU General Public License as published by the Free Soft- -- 13-- ware Foundation; either version 3, or (at your option) any later ver- -- 14-- sion. GNAT is distributed in the hope that it will be useful, but WITH- -- 15-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY -- 16-- or FITNESS FOR A PARTICULAR PURPOSE. -- 17-- -- 18-- As a special exception under Section 7 of GPL version 3, you are granted -- 19-- additional permissions described in the GCC Runtime Library Exception, -- 20-- version 3.1, as published by the Free Software Foundation. -- 21-- -- 22-- You should have received a copy of the GNU General Public License and -- 23-- a copy of the GCC Runtime Library Exception along with this program; -- 24-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see -- 25-- <http://www.gnu.org/licenses/>. -- 26-- -- 27-- GNAT was originally developed by the GNAT team at New York University. -- 28-- Extensive contributions were provided by Ada Core Technologies Inc. -- 29-- -- 30------------------------------------------------------------------------------ 31 32-- This package defines the codes used to identify the encoding method for 33-- wide characters in string and character constants. This is needed both 34-- at compile time and at runtime (for the wide character runtime routines) 35 36-- This unit may be used directly from an application program by providing 37-- an appropriate WITH, and the interface can be expected to remain stable. 38 39pragma Compiler_Unit_Warning; 40 41package System.WCh_Con is 42 pragma Pure; 43 44 ------------------------------------- 45 -- Wide_Character Encoding Methods -- 46 ------------------------------------- 47 48 -- A wide character encoding method is a method for uniquely representing 49 -- a Wide_Character or Wide_Wide_Character value using a one or more 50 -- Character values. Three types of encoding method are supported by GNAT: 51 52 -- An escape encoding method uses ESC as the first character of the 53 -- sequence, and subsequent characters determine the wide character 54 -- value that is represented. Any character other than ESC stands 55 -- for itself as a single byte (i.e. any character in Latin-1, other 56 -- than ESC itself, is represented as a single character: itself). 57 58 -- An upper half encoding method uses a character in the upper half 59 -- range (i.e. in the range 16#80# .. 16#FF#) as the first byte of 60 -- a wide character encoding sequence. Subsequent characters are 61 -- used to determine the wide character value that is represented. 62 -- Any character in the lower half (16#00# .. 16#7F#) represents 63 -- itself as a single character. 64 65 -- The brackets notation, where a wide character is represented by the 66 -- sequence ["xx"] or ["xxxx"] or ["xxxxxx"] where xx are hexadecimal 67 -- characters. Note that currently this is the only encoding that 68 -- supports the full UTF-32 range. 69 70 -- Note that GNAT does not currently support escape-in, escape-out 71 -- encoding methods, where an escape sequence is used to set a mode 72 -- used to recognize subsequent characters. All encoding methods use 73 -- individual character-by-character encodings, so that a sequence of 74 -- wide characters is represented by a sequence of encodings. 75 76 -- To add new encoding methods, the following steps are required: 77 78 -- 1. Define a code for a new value of type WC_Encoding_Method 79 -- 2. Adjust the definition of WC_Encoding_Method accordingly 80 -- 3. Provide appropriate conversion routines in System.WCh_Cnv 81 -- 4. Adjust definition of WC_Longest_Sequence if necessary 82 -- 5. Add an entry in WC_Encoding_Letters for the new method 83 -- 6. Add proper code to s-wchstw.adb, s-wchwts.adb, s-widwch.adb 84 -- 7. Update documentation (remember section on form strings) 85 86 -- Note that the WC_Encoding_Method values must be kept ordered so that 87 -- the definitions of the subtypes WC_Upper_Half_Encoding_Method and 88 -- WC_ESC_Encoding_Method are still correct. 89 90 --------------------------------- 91 -- Encoding Method Definitions -- 92 --------------------------------- 93 94 type WC_Encoding_Method is range 1 .. 6; 95 -- Type covering the range of values used to represent wide character 96 -- encoding methods. An enumeration type might be a little neater, but 97 -- more trouble than it's worth, given the need to pass these values 98 -- from the compiler to the backend, and to record them in the ALI file. 99 100 WCEM_Hex : constant WC_Encoding_Method := 1; 101 -- The wide character with code 16#abcd# is represented by the escape 102 -- sequence ESC a b c d (five characters, where abcd are ASCII hex 103 -- characters, using upper case for letters). This method is easy 104 -- to deal with in external environments that do not support wide 105 -- characters, and covers the whole 16-bit BMP. Codes larger than 106 -- 16#FFFF# are not representable using this encoding method. 107 108 WCEM_Upper : constant WC_Encoding_Method := 2; 109 -- The wide character with encoding 16#abcd#, where the upper bit is on 110 -- (i.e. a is in the range 8-F) is represented as two bytes 16#ab# and 111 -- 16#cd#. The second byte may never be a format control character, but 112 -- is not required to be in the upper half. This method can be also used 113 -- for shift-JIS or EUC where the internal coding matches the external 114 -- coding. Codes larger than 16#FFFF# are not representable using this 115 -- encoding method. 116 117 WCEM_Shift_JIS : constant WC_Encoding_Method := 3; 118 -- A wide character is represented by a two character sequence 16#ab# 119 -- and 16#cd#, with the restrictions described for upper half encoding 120 -- as described above. The internal character code is the corresponding 121 -- JIS character according to the standard algorithm for Shift-JIS 122 -- conversion. See the body of package System.JIS_Conversions for 123 -- further details. Codes larger than 16#FFFF are not representable 124 -- using this encoding method. 125 126 WCEM_EUC : constant WC_Encoding_Method := 4; 127 -- A wide character is represented by a two character sequence 16#ab# and 128 -- 16#cd#, with both characters being in the upper half set. The internal 129 -- character code is the corresponding JIS character according to the EUC 130 -- encoding algorithm. See the body of package System.JIS_Conversions for 131 -- further details. Codes larger than 16#FFFF# are not representable using 132 -- this encoding method. 133 134 WCEM_UTF8 : constant WC_Encoding_Method := 5; 135 -- An ISO 10646-1 BMP/Unicode wide character is represented in UCS 136 -- Transformation Format 8 (UTF-8), as defined in Annex R of ISO 137 -- 10646-1/Am.2. Depending on the character value, a Unicode character 138 -- is represented as the one to six byte sequence. 139 -- 140 -- 16#0000_0000#-16#0000_007f#: 2#0xxxxxxx# 141 -- 16#0000_0080#-16#0000_07ff#: 2#110xxxxx# 2#10xxxxxx# 142 -- 16#0000_0800#-16#0000_ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx# 143 -- 16#0001_0000#-16#001F_FFFF#: 2#11110xxx# 2#10xxxxxx# 2#10xxxxxx# 144 -- 2#10xxxxxx# 145 -- 16#0020_0000#-16#03FF_FFFF#: 2#111110xx# 2#10xxxxxx# 2#10xxxxxx# 146 -- 2#10xxxxxx# 2#10xxxxxx# 147 -- 16#0400_0000#-16#7FFF_FFFF#: 2#1111110x# 2#10xxxxxx# 2#10xxxxxx# 148 -- 2#10xxxxxx# 2#10xxxxxx# 2#10xxxxxx# 149 -- 150 -- where the xxx bits correspond to the left-padded bits of the 151 -- 16-bit character value. Note that all lower half ASCII characters 152 -- are represented as ASCII bytes and all upper half characters and 153 -- other wide characters are represented as sequences of upper-half. This 154 -- encoding method can represent the entire range of Wide_Wide_Character. 155 156 WCEM_Brackets : constant WC_Encoding_Method := 6; 157 -- A wide character is represented using one of the following sequences: 158 -- 159 -- ["xx"] 160 -- ["xxxx"] 161 -- ["xxxxxx"] 162 -- ["xxxxxxxx"] 163 -- 164 -- where xx are hexadecimal digits representing the character code. This 165 -- encoding method can represent the entire range of Wide_Wide_Character 166 -- but in the general case results in ambiguous representations (there is 167 -- no ambiguity in Ada sources, since the above sequences are illegal Ada). 168 169 WC_Encoding_Letters : constant array (WC_Encoding_Method) of Character := 170 (WCEM_Hex => 'h', 171 WCEM_Upper => 'u', 172 WCEM_Shift_JIS => 's', 173 WCEM_EUC => 'e', 174 WCEM_UTF8 => '8', 175 WCEM_Brackets => 'b'); 176 -- Letters used for selection of wide character encoding method in the 177 -- compiler options (-gnatW? switch) and for Wide_Text_IO (WCEM parameter 178 -- in the form string). 179 180 subtype WC_ESC_Encoding_Method is 181 WC_Encoding_Method range WCEM_Hex .. WCEM_Hex; 182 -- Encoding methods using an ESC character at the start of the sequence 183 184 subtype WC_Upper_Half_Encoding_Method is 185 WC_Encoding_Method range WCEM_Upper .. WCEM_UTF8; 186 -- Encoding methods using an upper half character (16#80#..16#FF) at 187 -- the start of the sequence. 188 189 WC_Longest_Sequence : constant := 12; 190 -- The longest number of characters that can be used for a wide character 191 -- or wide wide character sequence for any of the active encoding methods. 192 193 WC_Longest_Sequences : constant array (WC_Encoding_Method) of Natural := 194 (WCEM_Hex => 5, 195 WCEM_Upper => 2, 196 WCEM_Shift_JIS => 2, 197 WCEM_EUC => 2, 198 WCEM_UTF8 => 6, 199 WCEM_Brackets => 12); 200 -- The longest number of characters that can be used for a wide character 201 -- or wide wide character sequence using the given encoding method. 202 203 function Get_WC_Encoding_Method (C : Character) return WC_Encoding_Method; 204 -- Given a character C, returns corresponding encoding method (see array 205 -- WC_Encoding_Letters above). Raises Constraint_Error if not in list. 206 207 function Get_WC_Encoding_Method (S : String) return WC_Encoding_Method; 208 -- Given a lower case string that is one of hex, upper, shift_jis, euc, 209 -- utf8, brackets, return the corresponding encoding method. Raises 210 -- Constraint_Error if not in list. 211 212 function Is_Start_Of_Encoding 213 (C : Character; 214 EM : WC_Encoding_Method) return Boolean; 215 pragma Inline (Is_Start_Of_Encoding); 216 -- Returns True if the Character C is the start of a multi-character 217 -- encoding sequence for the given encoding method EM. If EM is set to 218 -- WCEM_Brackets, this function always returns False. 219 220end System.WCh_Con; 221