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----------------------------------------------------------------

--  ZLib for Ada thick binding.                               --

--                                                            --

--  Copyright (C) 2002-2004 Dmitriy Anisimkov                 --

--                                                            --

--  Open source license information is in the zlib.ads file.  --

----------------------------------------------------------------

--

--  $Id: buffer_demo.adb,v 1.3 2004/09/06 06:55:35 vagul Exp $

--  This demo program provided by Dr Steve Sangwine <sjs@essex.ac.uk>

--

--  Demonstration of a problem with Zlib-Ada (already fixed) when a buffer

--  of exactly the correct size is used for decompressed data, and the last

--  few bytes passed in to Zlib are checksum bytes.

--  This program compresses a string of text, and then decompresses the

--  compressed text into a buffer of the same size as the original text.

with Ada.Streams; use Ada.Streams;

with Ada.Text_IO;

with ZLib; use ZLib;

procedure Buffer_Demo is

   EOL  : Character renames ASCII.LF;

   Text : constant String

     := "Four score and seven years ago our fathers brought forth," & EOL &

        "upon this continent, a new nation, conceived in liberty," & EOL &

        "and dedicated to the proposition that `all men are created equal'.";

   Source : Stream_Element_Array (1 .. Text'Length);

   for Source'Address use Text'Address;

begin

   Ada.Text_IO.Put (Text);

   Ada.Text_IO.New_Line;

   Ada.Text_IO.Put_Line

     ("Uncompressed size : " & Positive'Image (Text'Length) & " bytes");

   declare

      Compressed_Data : Stream_Element_Array (1 .. Text'Length);

      L               : Stream_Element_Offset;

   begin

      Compress : declare

         Compressor : Filter_Type;

         I : Stream_Element_Offset;

      begin

         Deflate_Init (Compressor);

         --  Compress the whole of T at once.

         Translate (Compressor, Source, I, Compressed_Data, L, Finish);

         pragma Assert (I = Source'Last);

         Close (Compressor);

         Ada.Text_IO.Put_Line

           ("Compressed size :   "

            & Stream_Element_Offset'Image (L) & " bytes");

      end Compress;

      --  Now we decompress the data, passing short blocks of data to Zlib

      --  (because this demonstrates the problem - the last block passed will

      --  contain checksum information and there will be no output, only a

      --  check inside Zlib that the checksum is correct).

      Decompress : declare

         Decompressor : Filter_Type;

         Uncompressed_Data : Stream_Element_Array (1 .. Text'Length);

         Block_Size : constant := 4;

         --  This makes sure that the last block contains

         --  only Adler checksum data.

         P : Stream_Element_Offset := Compressed_Data'First - 1;

         O : Stream_Element_Offset;

      begin

         Inflate_Init (Decompressor);

         loop

            Translate

              (Decompressor,

               Compressed_Data

                 (P + 1 .. Stream_Element_Offset'Min (P + Block_Size, L)),

               P,

               Uncompressed_Data

                 (Total_Out (Decompressor) + 1 .. Uncompressed_Data'Last),

               O,

               No_Flush);

               Ada.Text_IO.Put_Line

                 ("Total in : " & Count'Image (Total_In (Decompressor)) &

                  ", out : " & Count'Image (Total_Out (Decompressor)));

               exit when P = L;

         end loop;

         Ada.Text_IO.New_Line;

         Ada.Text_IO.Put_Line

           ("Decompressed text matches original text : "

             & Boolean'Image (Uncompressed_Data = Source));

      end Decompress;

   end;

end Buffer_Demo;