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1 745 jeremybenn
----------------------------------------------------------------
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--  ZLib for Ada thick binding.                               --
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--                                                            --
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--  Copyright (C) 2002-2004 Dmitriy Anisimkov                 --
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--                                                            --
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--  Open source license information is in the zlib.ads file.  --
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----------------------------------------------------------------
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--
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--  $Id: buffer_demo.adb,v 1.3 2004/09/06 06:55:35 vagul Exp $
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--  This demo program provided by Dr Steve Sangwine <sjs@essex.ac.uk>
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--
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--  Demonstration of a problem with Zlib-Ada (already fixed) when a buffer
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--  of exactly the correct size is used for decompressed data, and the last
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--  few bytes passed in to Zlib are checksum bytes.
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--  This program compresses a string of text, and then decompresses the
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--  compressed text into a buffer of the same size as the original text.
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with Ada.Streams; use Ada.Streams;
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with Ada.Text_IO;
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with ZLib; use ZLib;
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procedure Buffer_Demo is
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   EOL  : Character renames ASCII.LF;
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   Text : constant String
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     := "Four score and seven years ago our fathers brought forth," & EOL &
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        "upon this continent, a new nation, conceived in liberty," & EOL &
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        "and dedicated to the proposition that `all men are created equal'.";
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   Source : Stream_Element_Array (1 .. Text'Length);
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   for Source'Address use Text'Address;
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begin
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   Ada.Text_IO.Put (Text);
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   Ada.Text_IO.New_Line;
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   Ada.Text_IO.Put_Line
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     ("Uncompressed size : " & Positive'Image (Text'Length) & " bytes");
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   declare
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      Compressed_Data : Stream_Element_Array (1 .. Text'Length);
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      L               : Stream_Element_Offset;
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   begin
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      Compress : declare
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         Compressor : Filter_Type;
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         I : Stream_Element_Offset;
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      begin
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         Deflate_Init (Compressor);
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         --  Compress the whole of T at once.
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         Translate (Compressor, Source, I, Compressed_Data, L, Finish);
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         pragma Assert (I = Source'Last);
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         Close (Compressor);
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         Ada.Text_IO.Put_Line
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           ("Compressed size :   "
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            & Stream_Element_Offset'Image (L) & " bytes");
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      end Compress;
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      --  Now we decompress the data, passing short blocks of data to Zlib
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      --  (because this demonstrates the problem - the last block passed will
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      --  contain checksum information and there will be no output, only a
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      --  check inside Zlib that the checksum is correct).
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      Decompress : declare
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         Decompressor : Filter_Type;
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         Uncompressed_Data : Stream_Element_Array (1 .. Text'Length);
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         Block_Size : constant := 4;
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         --  This makes sure that the last block contains
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         --  only Adler checksum data.
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         P : Stream_Element_Offset := Compressed_Data'First - 1;
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         O : Stream_Element_Offset;
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      begin
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         Inflate_Init (Decompressor);
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         loop
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            Translate
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              (Decompressor,
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               Compressed_Data
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                 (P + 1 .. Stream_Element_Offset'Min (P + Block_Size, L)),
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               P,
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               Uncompressed_Data
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                 (Total_Out (Decompressor) + 1 .. Uncompressed_Data'Last),
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               O,
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               No_Flush);
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               Ada.Text_IO.Put_Line
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                 ("Total in : " & Count'Image (Total_In (Decompressor)) &
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                  ", out : " & Count'Image (Total_Out (Decompressor)));
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               exit when P = L;
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         end loop;
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         Ada.Text_IO.New_Line;
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         Ada.Text_IO.Put_Line
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           ("Decompressed text matches original text : "
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             & Boolean'Image (Uncompressed_Data = Source));
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      end Decompress;
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   end;
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end Buffer_Demo;

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