1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
|
------------------------------------------------------------------------------
-- --
-- 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 Warnings (Off);
pragma Compiler_Unit;
pragma Warnings (On);
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;
|
