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------------------------------------------------------------------------------
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--                                                                          --
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--                         GNAT RUN-TIME COMPONENTS                         --
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--                                                                          --
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--                    G N A T . D E C O D E _ S T R I N G                   --
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--                                                                          --
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--                                 S p e c                                  --
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--                                                                          --
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--                       Copyright (C) 2007, AdaCore                        --
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--                                                                          --
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-- GNAT is free software;  you can  redistribute it  and/or modify it under --
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-- terms of the  GNU General Public License as published  by the Free Soft- --
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-- ware  Foundation;  either version 2,  or (at your option) any later ver- --
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-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
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-- for  more details.  You should have  received  a copy of the GNU General --
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-- Public License  distributed with GNAT;  see file COPYING.  If not, write --
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-- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
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-- Boston, MA 02110-1301, USA.                                              --
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--                                                                          --
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-- As a special exception,  if other files  instantiate  generics from this --
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-- unit, or you link  this unit with other files  to produce an executable, --
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-- this  unit  does not  by itself cause  the resulting  executable  to  be --
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-- covered  by the  GNU  General  Public  License.  This exception does not --
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-- however invalidate  any other reasons why  the executable file  might be --
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-- covered by the  GNU Public License.                                      --
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--                                                                          --
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-- GNAT was originally developed  by the GNAT team at  New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc.      --
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--                                                                          --
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------------------------------------------------------------------------------
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--  This generic package provides utility routines for converting from an
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--  encoded string to a corresponding Wide_String or Wide_Wide_String value
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--  using a specified encoding convention, which is supplied as the generic
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--  parameter. UTF-8 is handled especially efficiently, and if the encoding
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--  method is known at compile time to be WCEM_UTF8, then the instantiation
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--  is specialized to handle only the UTF-8 case and exclude code for the
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--  other encoding methods. The package also provides positioning routines
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--  for skipping encoded characters in either direction, and for validating
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--  strings for correct encodings.
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--  Note: this package is only about decoding sequences of 8-bit characters
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--  into corresponding 16-bit Wide_String or 32-bit Wide_Wide_String values.
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--  It knows nothing at all about the character encodings being used for the
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--  resulting Wide_Character and Wide_Wide_Character values. Most often this
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--  will be Unicode/ISO-10646 as specified by the Ada RM, but this package
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--  does not make any assumptions about the character coding. See also the
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--  packages Ada.Wide_[Wide_]Characters.Unicode for unicode specific functions.
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--  Note on the use of brackets encoding (WCEM_Brackets). The brackets encoding
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--  method is ambiguous in the context of this package, since there is no way
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--  to tell if ["1234"] is eight unencoded characters or one encoded character.
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--  In the context of Ada sources, any sequence starting [" must be the start
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--  of an encoding (since that sequence is not valid in Ada source otherwise).
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--  The routines in this package use the same approach. If the input string
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--  contains the sequence [" then this is assumed to be the start of a brackets
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--  encoding sequence, and if it does not match the syntax, an error is raised.
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--  In the case of the Prev functions, a sequence ending with "] is assumed to
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--  be a valid brackets sequence, and an error is raised if it is not.
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with System.WCh_Con;
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generic
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   Encoding_Method : System.WCh_Con.WC_Encoding_Method;
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package GNAT.Decode_String is
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   pragma Pure;
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   function Decode_Wide_String (S : String) return Wide_String;
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   pragma Inline (Decode_Wide_String);
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   --  Decode the given String, which is encoded using the indicated coding
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   --  method, returning the corresponding decoded Wide_String value. If S
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   --  contains a character code that cannot be represented with the given
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   --  encoding, then Constraint_Error is raised.
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   procedure Decode_Wide_String
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     (S      : String;
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      Result : out Wide_String;
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      Length : out Natural);
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   --  Similar to the above function except that the result is stored in the
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   --  given Wide_String variable Result, starting at Result (Result'First). On
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   --  return, Length is set to the number of characters stored in Result. The
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   --  caller must ensure that Result is long enough (an easy choice is to set
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   --  the length equal to the S'Length, since decoding can never increase the
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   --  string length). If the length of Result is insufficient Constraint_Error
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   --  will be raised.
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   function Decode_Wide_Wide_String (S : String) return Wide_Wide_String;
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   pragma Inline (Decode_Wide_Wide_String);
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   --  Same as above function but for Wide_Wide_String output
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   procedure Decode_Wide_Wide_String
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     (S      : String;
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      Result : out Wide_Wide_String;
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      Length : out Natural);
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   --  Same as above procedure, but for Wide_Wide_String output
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   function Validate_Wide_String (S : String) return Boolean;
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   --  This function inspects the string S to determine if it contains only
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   --  valid encodings corresponding to Wide_Character values using the
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   --  given encoding. If a call to Decode_Wide_String (S) would return
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   --  without raising Constraint_Error, then Validate_Wide_String will
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   --  return True. If the call would have raised Constraint_Error, then
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   --  Validate_Wide_String will return False.
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   function Validate_Wide_Wide_String (S : String) return Boolean;
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   --  Similar to Validate_Wide_String, except that it succeeds if the string
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   --  contains only encodings corresponding to Wide_Wide_Character values.
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   procedure Decode_Wide_Character
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     (Input  : String;
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      Ptr    : in out Natural;
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      Result : out Wide_Character);
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   pragma Inline (Decode_Wide_Character);
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   --  This is a lower level procedure that decodes a single character using
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   --  the given encoding method. The encoded character is stored in Input,
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   --  starting at Input (Ptr). The resulting output character is stored in
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   --  Result, and on return Ptr is updated past the input character or
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   --  encoding sequence. Constraint_Error will be raised if the input has
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   --  has a character that cannot be represented using the given encoding,
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   --  or if Ptr is outside the bounds of the Input string.
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   procedure Decode_Wide_Wide_Character
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     (Input  : String;
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      Ptr    : in out Natural;
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      Result : out Wide_Wide_Character);
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   --  Same as above procedure but with Wide_Wide_Character input
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   procedure Next_Wide_Character (Input : String; Ptr : in out Natural);
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   --  This procedure examines the input string starting at Input (Ptr), and
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   --  advances Ptr past one character in the encoded string, so that on return
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   --  Ptr points to the next encoded character. Constraint_Error is raised if
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   --  an invalid encoding is encountered, or the end of the string is reached
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   --  or if Ptr is less than String'First on entry, or if the character
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   --  skipped is not a valid Wide_Character code. This call may be more
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   --  efficient than calling Decode_Wide_Character and discarding the result.
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   procedure Prev_Wide_Character (Input : String; Ptr : in out Natural);
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   --  This procedure is similar to Next_Encoded_Character except that it moves
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   --  backwards in the string, so that on return, Ptr is set to point to the
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   --  previous encoded character. Constraint_Error is raised if the start of
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   --  the string is encountered. It is valid for Ptr to be one past the end
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   --  of the string for this call (in which case on return it will point to
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   --  the last encoded character).
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   --
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   --  Note: it is not generally possible to do this function efficiently with
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   --  all encodings, the current implementation is only efficient for the case
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   --  of UTF-8 (Encoding_Method = WCEM_UTF8) and Brackets (Encoding_Method =
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   --  WCEM_Brackets). For all other encodings, we work by starting at the
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   --  beginning of the string and moving forward till Ptr is reached, which
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   --  is correct but slow.
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   procedure Next_Wide_Wide_Character (Input : String; Ptr : in out Natural);
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   --  Similar to Next_Wide_Character except that codes skipped must be valid
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   --  Wide_Wide_Character codes.
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   procedure Prev_Wide_Wide_Character (Input : String; Ptr : in out Natural);
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   --  Similar to Prev_Wide_Character except that codes skipped must be valid
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   --  Wide_Wide_Character codes.
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end GNAT.Decode_String;

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