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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT RUN-TIME COMPONENTS --
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4 -- --
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5 -- G N A T . D E C O D E _ S T R I N G --
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6 -- --
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7 -- S p e c --
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8 -- --
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9 -- Copyright (C) 2007-2017, AdaCore --
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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 generic package provides utility routines for converting from an
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33 -- encoded string to a corresponding Wide_String or Wide_Wide_String value
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34 -- using a specified encoding convention, which is supplied as the generic
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35 -- parameter. UTF-8 is handled especially efficiently, and if the encoding
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36 -- method is known at compile time to be WCEM_UTF8, then the instantiation
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37 -- is specialized to handle only the UTF-8 case and exclude code for the
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38 -- other encoding methods. The package also provides positioning routines
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39 -- for skipping encoded characters in either direction, and for validating
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40 -- strings for correct encodings.
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41
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42 -- Note: this package is only about decoding sequences of 8-bit characters
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43 -- into corresponding 16-bit Wide_String or 32-bit Wide_Wide_String values.
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44 -- It knows nothing at all about the character encodings being used for the
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45 -- resulting Wide_Character and Wide_Wide_Character values. Most often this
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46 -- will be Unicode/ISO-10646 as specified by the Ada RM, but this package
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47 -- does not make any assumptions about the character coding. See also the
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48 -- packages Ada.Wide_[Wide_]Characters.Unicode for unicode specific functions.
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49
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50 -- In particular, in the case of UTF-8, all valid UTF-8 encodings, as listed
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51 -- in table 3.6 of the Unicode Standard, version 6.2.0, are recognized as
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52 -- legitimate. This includes the full range 16#0000_0000# .. 16#03FF_FFFF#.
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53 -- This includes codes in the range 16#D800# - 16#DFFF#. These codes all
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54 -- have UTF-8 encoding sequences that are well-defined (e.g. the encoding for
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55 -- 16#D800# is ED A0 80). But these codes do not correspond to defined Unicode
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56 -- characters and are thus considered to be "not well-formed" (see table 3.7
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57 -- of the Unicode Standard). If you need to exclude these codes, you must do
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58 -- that manually, e.g. use Decode_Wide_Character/Decode_Wide_String and check
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59 -- that the resulting code(s) are not in this range.
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60
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61 -- Note on the use of brackets encoding (WCEM_Brackets). The brackets encoding
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62 -- method is ambiguous in the context of this package, since there is no way
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63 -- to tell if ["1234"] is eight unencoded characters or one encoded character.
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64 -- In the context of Ada sources, any sequence starting [" must be the start
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65 -- of an encoding (since that sequence is not valid in Ada source otherwise).
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66 -- The routines in this package use the same approach. If the input string
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67 -- contains the sequence [" then this is assumed to be the start of a brackets
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68 -- encoding sequence, and if it does not match the syntax, an error is raised.
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69 -- In the case of the Prev functions, a sequence ending with "] is assumed to
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70 -- be a valid brackets sequence, and an error is raised if it is not.
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71
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72 with System.WCh_Con;
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73
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74 generic
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75 Encoding_Method : System.WCh_Con.WC_Encoding_Method;
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76
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77 package GNAT.Decode_String is
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78 pragma Pure;
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79
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80 function Decode_Wide_String (S : String) return Wide_String;
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81 pragma Inline (Decode_Wide_String);
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82 -- Decode the given String, which is encoded using the indicated coding
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83 -- method, returning the corresponding decoded Wide_String value. If S
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84 -- contains a character code that cannot be represented with the given
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85 -- encoding, then Constraint_Error is raised.
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86
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87 procedure Decode_Wide_String
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88 (S : String;
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89 Result : out Wide_String;
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90 Length : out Natural);
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91 -- Similar to the above function except that the result is stored in the
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92 -- given Wide_String variable Result, starting at Result (Result'First). On
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93 -- return, Length is set to the number of characters stored in Result. The
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94 -- caller must ensure that Result is long enough (an easy choice is to set
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95 -- the length equal to the S'Length, since decoding can never increase the
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96 -- string length). If the length of Result is insufficient Constraint_Error
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97 -- will be raised.
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98
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99 function Decode_Wide_Wide_String (S : String) return Wide_Wide_String;
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100 -- Same as above function but for Wide_Wide_String output
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101
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102 procedure Decode_Wide_Wide_String
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103 (S : String;
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104 Result : out Wide_Wide_String;
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105 Length : out Natural);
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106 -- Same as above procedure, but for Wide_Wide_String output
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107
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108 function Validate_Wide_String (S : String) return Boolean;
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109 -- This function inspects the string S to determine if it contains only
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110 -- valid encodings corresponding to Wide_Character values using the
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111 -- given encoding. If a call to Decode_Wide_String (S) would return
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112 -- without raising Constraint_Error, then Validate_Wide_String will
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113 -- return True. If the call would have raised Constraint_Error, then
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114 -- Validate_Wide_String will return False.
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115
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116 function Validate_Wide_Wide_String (S : String) return Boolean;
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117 -- Similar to Validate_Wide_String, except that it succeeds if the string
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118 -- contains only encodings corresponding to Wide_Wide_Character values.
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119
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120 procedure Decode_Wide_Character
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121 (Input : String;
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122 Ptr : in out Natural;
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123 Result : out Wide_Character);
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124 pragma Inline (Decode_Wide_Character);
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125 -- This is a lower level procedure that decodes a single character using
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126 -- the given encoding method. The encoded character is stored in Input,
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127 -- starting at Input (Ptr). The resulting output character is stored in
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128 -- Result, and on return Ptr is updated past the input character or
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129 -- encoding sequence. Constraint_Error will be raised if the input has
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130 -- has a character that cannot be represented using the given encoding,
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131 -- or if Ptr is outside the bounds of the Input string.
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132
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133 procedure Decode_Wide_Wide_Character
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134 (Input : String;
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135 Ptr : in out Natural;
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136 Result : out Wide_Wide_Character);
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137 pragma Inline (Decode_Wide_Wide_Character);
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138 -- Same as above procedure but with Wide_Wide_Character input
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139
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140 procedure Next_Wide_Character (Input : String; Ptr : in out Natural);
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141 pragma Inline (Next_Wide_Character);
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142 -- This procedure examines the input string starting at Input (Ptr), and
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143 -- advances Ptr past one character in the encoded string, so that on return
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144 -- Ptr points to the next encoded character. Constraint_Error is raised if
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145 -- an invalid encoding is encountered, or the end of the string is reached
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146 -- or if Ptr is less than String'First on entry, or if the character
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147 -- skipped is not a valid Wide_Character code.
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148
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149 procedure Prev_Wide_Character (Input : String; Ptr : in out Natural);
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150 -- This procedure is similar to Next_Encoded_Character except that it moves
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151 -- backwards in the string, so that on return, Ptr is set to point to the
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152 -- previous encoded character. Constraint_Error is raised if the start of
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153 -- the string is encountered. It is valid for Ptr to be one past the end
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154 -- of the string for this call (in which case on return it will point to
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155 -- the last encoded character).
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156 --
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157 -- Note: it is not generally possible to do this function efficiently with
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158 -- all encodings, the current implementation is only efficient for the case
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159 -- of UTF-8 (Encoding_Method = WCEM_UTF8) and Brackets (Encoding_Method =
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160 -- WCEM_Brackets). For all other encodings, we work by starting at the
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161 -- beginning of the string and moving forward till Ptr is reached, which
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162 -- is correct but slow.
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163 --
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164 -- Note: this routine assumes that the sequence prior to Ptr is correctly
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165 -- encoded, it does not have a defined behavior if this is not the case.
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166
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167 procedure Next_Wide_Wide_Character (Input : String; Ptr : in out Natural);
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168 pragma Inline (Next_Wide_Wide_Character);
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169 -- Similar to Next_Wide_Character except that codes skipped must be valid
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170 -- Wide_Wide_Character codes.
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171
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172 procedure Prev_Wide_Wide_Character (Input : String; Ptr : in out Natural);
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173 -- Similar to Prev_Wide_Character except that codes skipped must be valid
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174 -- Wide_Wide_Character codes.
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175
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176 end GNAT.Decode_String;
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