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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT COMPILER COMPONENTS --
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4 -- --
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5 -- S Y S T E M . W C H _ C O N --
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6 -- --
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7 -- S p e c --
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8 -- --
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131
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9 -- Copyright (C) 1992-2018, Free Software Foundation, Inc. --
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111
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10 -- --
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11 -- GNAT is free software; you can redistribute it and/or modify it under --
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12 -- terms of the GNU General Public License as published by the Free Soft- --
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13 -- ware Foundation; either version 3, or (at your option) any later ver- --
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14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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16 -- or FITNESS FOR A PARTICULAR PURPOSE. --
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17 -- --
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18 -- As a special exception under Section 7 of GPL version 3, you are granted --
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19 -- additional permissions described in the GCC Runtime Library Exception, --
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20 -- version 3.1, as published by the Free Software Foundation. --
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21 -- --
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22 -- You should have received a copy of the GNU General Public License and --
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23 -- a copy of the GCC Runtime Library Exception along with this program; --
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24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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25 -- <http://www.gnu.org/licenses/>. --
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26 -- --
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27 -- GNAT was originally developed by the GNAT team at New York University. --
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28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
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29 -- --
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30 ------------------------------------------------------------------------------
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31
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32 -- This package defines the codes used to identify the encoding method for
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33 -- wide characters in string and character constants. This is needed both
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34 -- at compile time and at runtime (for the wide character runtime routines)
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35
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36 -- This unit may be used directly from an application program by providing
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37 -- an appropriate WITH, and the interface can be expected to remain stable.
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38
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39 pragma Compiler_Unit_Warning;
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40
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41 package System.WCh_Con is
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42 pragma Pure;
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43
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44 -------------------------------------
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45 -- Wide_Character Encoding Methods --
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46 -------------------------------------
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47
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48 -- A wide character encoding method is a method for uniquely representing
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49 -- a Wide_Character or Wide_Wide_Character value using a one or more
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50 -- Character values. Three types of encoding method are supported by GNAT:
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51
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52 -- An escape encoding method uses ESC as the first character of the
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53 -- sequence, and subsequent characters determine the wide character
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54 -- value that is represented. Any character other than ESC stands
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55 -- for itself as a single byte (i.e. any character in Latin-1, other
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56 -- than ESC itself, is represented as a single character: itself).
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57
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58 -- An upper half encoding method uses a character in the upper half
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59 -- range (i.e. in the range 16#80# .. 16#FF#) as the first byte of
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60 -- a wide character encoding sequence. Subsequent characters are
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61 -- used to determine the wide character value that is represented.
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62 -- Any character in the lower half (16#00# .. 16#7F#) represents
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63 -- itself as a single character.
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64
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65 -- The brackets notation, where a wide character is represented by the
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66 -- sequence ["xx"] or ["xxxx"] or ["xxxxxx"] where xx are hexadecimal
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67 -- characters. Note that currently this is the only encoding that
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68 -- supports the full UTF-32 range.
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69
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70 -- Note that GNAT does not currently support escape-in, escape-out
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71 -- encoding methods, where an escape sequence is used to set a mode
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72 -- used to recognize subsequent characters. All encoding methods use
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73 -- individual character-by-character encodings, so that a sequence of
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74 -- wide characters is represented by a sequence of encodings.
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75
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76 -- To add new encoding methods, the following steps are required:
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77
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78 -- 1. Define a code for a new value of type WC_Encoding_Method
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79 -- 2. Adjust the definition of WC_Encoding_Method accordingly
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80 -- 3. Provide appropriate conversion routines in System.WCh_Cnv
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81 -- 4. Adjust definition of WC_Longest_Sequence if necessary
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82 -- 5. Add an entry in WC_Encoding_Letters for the new method
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83 -- 6. Add proper code to s-wchstw.adb, s-wchwts.adb, s-widwch.adb
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84 -- 7. Update documentation (remember section on form strings)
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85
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86 -- Note that the WC_Encoding_Method values must be kept ordered so that
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87 -- the definitions of the subtypes WC_Upper_Half_Encoding_Method and
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88 -- WC_ESC_Encoding_Method are still correct.
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89
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90 ---------------------------------
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91 -- Encoding Method Definitions --
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92 ---------------------------------
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93
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94 type WC_Encoding_Method is range 1 .. 6;
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95 -- Type covering the range of values used to represent wide character
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96 -- encoding methods. An enumeration type might be a little neater, but
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97 -- more trouble than it's worth, given the need to pass these values
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98 -- from the compiler to the backend, and to record them in the ALI file.
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99
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100 WCEM_Hex : constant WC_Encoding_Method := 1;
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101 -- The wide character with code 16#abcd# is represented by the escape
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102 -- sequence ESC a b c d (five characters, where abcd are ASCII hex
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103 -- characters, using upper case for letters). This method is easy
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104 -- to deal with in external environments that do not support wide
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105 -- characters, and covers the whole 16-bit BMP. Codes larger than
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106 -- 16#FFFF# are not representable using this encoding method.
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107
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108 WCEM_Upper : constant WC_Encoding_Method := 2;
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109 -- The wide character with encoding 16#abcd#, where the upper bit is on
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110 -- (i.e. a is in the range 8-F) is represented as two bytes 16#ab# and
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111 -- 16#cd#. The second byte may never be a format control character, but
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112 -- is not required to be in the upper half. This method can be also used
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113 -- for shift-JIS or EUC where the internal coding matches the external
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114 -- coding. Codes larger than 16#FFFF# are not representable using this
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115 -- encoding method.
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116
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117 WCEM_Shift_JIS : constant WC_Encoding_Method := 3;
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118 -- A wide character is represented by a two character sequence 16#ab#
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119 -- and 16#cd#, with the restrictions described for upper half encoding
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120 -- as described above. The internal character code is the corresponding
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121 -- JIS character according to the standard algorithm for Shift-JIS
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122 -- conversion. See the body of package System.JIS_Conversions for
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123 -- further details. Codes larger than 16#FFFF are not representable
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124 -- using this encoding method.
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125
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126 WCEM_EUC : constant WC_Encoding_Method := 4;
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127 -- A wide character is represented by a two character sequence 16#ab# and
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128 -- 16#cd#, with both characters being in the upper half set. The internal
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129 -- character code is the corresponding JIS character according to the EUC
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130 -- encoding algorithm. See the body of package System.JIS_Conversions for
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131 -- further details. Codes larger than 16#FFFF# are not representable using
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132 -- this encoding method.
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133
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134 WCEM_UTF8 : constant WC_Encoding_Method := 5;
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135 -- An ISO 10646-1 BMP/Unicode wide character is represented in UCS
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136 -- Transformation Format 8 (UTF-8), as defined in Annex R of ISO
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137 -- 10646-1/Am.2. Depending on the character value, a Unicode character
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138 -- is represented as the one to six byte sequence.
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139 --
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140 -- 16#0000_0000#-16#0000_007f#: 2#0xxxxxxx#
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141 -- 16#0000_0080#-16#0000_07ff#: 2#110xxxxx# 2#10xxxxxx#
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142 -- 16#0000_0800#-16#0000_ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
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143 -- 16#0001_0000#-16#001F_FFFF#: 2#11110xxx# 2#10xxxxxx# 2#10xxxxxx#
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144 -- 2#10xxxxxx#
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145 -- 16#0020_0000#-16#03FF_FFFF#: 2#111110xx# 2#10xxxxxx# 2#10xxxxxx#
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146 -- 2#10xxxxxx# 2#10xxxxxx#
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147 -- 16#0400_0000#-16#7FFF_FFFF#: 2#1111110x# 2#10xxxxxx# 2#10xxxxxx#
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148 -- 2#10xxxxxx# 2#10xxxxxx# 2#10xxxxxx#
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149 --
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150 -- where the xxx bits correspond to the left-padded bits of the
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151 -- 16-bit character value. Note that all lower half ASCII characters
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152 -- are represented as ASCII bytes and all upper half characters and
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153 -- other wide characters are represented as sequences of upper-half. This
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154 -- encoding method can represent the entire range of Wide_Wide_Character.
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155
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156 WCEM_Brackets : constant WC_Encoding_Method := 6;
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157 -- A wide character is represented using one of the following sequences:
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158 --
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159 -- ["xx"]
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160 -- ["xxxx"]
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161 -- ["xxxxxx"]
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162 -- ["xxxxxxxx"]
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163 --
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164 -- where xx are hexadecimal digits representing the character code. This
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165 -- encoding method can represent the entire range of Wide_Wide_Character
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166 -- but in the general case results in ambiguous representations (there is
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167 -- no ambiguity in Ada sources, since the above sequences are illegal Ada).
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168
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169 WC_Encoding_Letters : constant array (WC_Encoding_Method) of Character :=
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170 (WCEM_Hex => 'h',
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171 WCEM_Upper => 'u',
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172 WCEM_Shift_JIS => 's',
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173 WCEM_EUC => 'e',
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174 WCEM_UTF8 => '8',
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175 WCEM_Brackets => 'b');
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176 -- Letters used for selection of wide character encoding method in the
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177 -- compiler options (-gnatW? switch) and for Wide_Text_IO (WCEM parameter
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178 -- in the form string).
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179
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180 subtype WC_ESC_Encoding_Method is
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181 WC_Encoding_Method range WCEM_Hex .. WCEM_Hex;
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182 -- Encoding methods using an ESC character at the start of the sequence
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183
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184 subtype WC_Upper_Half_Encoding_Method is
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185 WC_Encoding_Method range WCEM_Upper .. WCEM_UTF8;
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186 -- Encoding methods using an upper half character (16#80#..16#FF) at
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187 -- the start of the sequence.
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188
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189 WC_Longest_Sequence : constant := 12;
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190 -- The longest number of characters that can be used for a wide character
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191 -- or wide wide character sequence for any of the active encoding methods.
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192
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193 WC_Longest_Sequences : constant array (WC_Encoding_Method) of Natural :=
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194 (WCEM_Hex => 5,
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195 WCEM_Upper => 2,
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196 WCEM_Shift_JIS => 2,
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197 WCEM_EUC => 2,
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198 WCEM_UTF8 => 6,
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199 WCEM_Brackets => 12);
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200 -- The longest number of characters that can be used for a wide character
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201 -- or wide wide character sequence using the given encoding method.
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202
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203 function Get_WC_Encoding_Method (C : Character) return WC_Encoding_Method;
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204 -- Given a character C, returns corresponding encoding method (see array
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205 -- WC_Encoding_Letters above). Raises Constraint_Error if not in list.
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206
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207 function Get_WC_Encoding_Method (S : String) return WC_Encoding_Method;
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208 -- Given a lower case string that is one of hex, upper, shift_jis, euc,
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209 -- utf8, brackets, return the corresponding encoding method. Raises
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210 -- Constraint_Error if not in list.
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211
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212 function Is_Start_Of_Encoding
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213 (C : Character;
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214 EM : WC_Encoding_Method) return Boolean;
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215 pragma Inline (Is_Start_Of_Encoding);
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216 -- Returns True if the Character C is the start of a multi-character
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217 -- encoding sequence for the given encoding method EM. If EM is set to
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218 -- WCEM_Brackets, this function always returns False.
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219
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220 end System.WCh_Con;
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