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106 | ----------------------------------------------------------------
-- 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;
|