107 lines
3.6 KiB
Ada
107 lines
3.6 KiB
Ada
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----------------------------------------------------------------
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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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