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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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|
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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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|
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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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|
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with Ada.Streams; use Ada.Streams; |
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with Ada.Text_IO; |
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|
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with ZLib; use ZLib; |
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|
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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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|
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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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|
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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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|
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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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|
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-- Compress the whole of T at once. |
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|
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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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|
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Close (Compressor); |
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|
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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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|
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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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|
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Decompress : declare |
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Decompressor : Filter_Type; |
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|
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Uncompressed_Data : Stream_Element_Array (1 .. Text'Length); |
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|
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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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|
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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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|
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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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|
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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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|
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exit when P = L; |
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end loop; |
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|
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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; |
