1 ----------------------------------------------------------------
2 -- ZLib for Ada thick binding. --
4 -- Copyright (C) 2002-2004 Dmitriy Anisimkov --
6 -- Open source license information is in the zlib.ads file. --
7 ----------------------------------------------------------------
9 -- $Id: buffer_demo.adb,v 1.3 2004/09/06 06:55:35 vagul Exp $
11 -- This demo program provided by Dr Steve Sangwine <sjs@essex.ac.uk>
13 -- Demonstration of a problem with Zlib-Ada (already fixed) when a buffer
14 -- of exactly the correct size is used for decompressed data, and the last
15 -- few bytes passed in to Zlib are checksum bytes.
17 -- This program compresses a string of text, and then decompresses the
18 -- compressed text into a buffer of the same size as the original text.
20 with Ada.Streams; use Ada.Streams;
25 procedure Buffer_Demo is
26 EOL : Character renames ASCII.LF;
27 Text : constant String
28 := "Four score and seven years ago our fathers brought forth," & EOL &
29 "upon this continent, a new nation, conceived in liberty," & EOL &
30 "and dedicated to the proposition that `all men are created equal'.";
32 Source : Stream_Element_Array (1 .. Text'Length);
33 for Source'Address use Text'Address;
36 Ada.Text_IO.Put (Text);
39 ("Uncompressed size : " & Positive'Image (Text'Length) & " bytes");
42 Compressed_Data : Stream_Element_Array (1 .. Text'Length);
43 L : Stream_Element_Offset;
46 Compressor : Filter_Type;
47 I : Stream_Element_Offset;
49 Deflate_Init (Compressor);
51 -- Compress the whole of T at once.
53 Translate (Compressor, Source, I, Compressed_Data, L, Finish);
54 pragma Assert (I = Source'Last);
60 & Stream_Element_Offset'Image (L) & " bytes");
63 -- Now we decompress the data, passing short blocks of data to Zlib
64 -- (because this demonstrates the problem - the last block passed will
65 -- contain checksum information and there will be no output, only a
66 -- check inside Zlib that the checksum is correct).
69 Decompressor : Filter_Type;
71 Uncompressed_Data : Stream_Element_Array (1 .. Text'Length);
73 Block_Size : constant := 4;
74 -- This makes sure that the last block contains
75 -- only Adler checksum data.
77 P : Stream_Element_Offset := Compressed_Data'First - 1;
78 O : Stream_Element_Offset;
80 Inflate_Init (Decompressor);
86 (P + 1 .. Stream_Element_Offset'Min (P + Block_Size, L)),
89 (Total_Out (Decompressor) + 1 .. Uncompressed_Data'Last),
94 ("Total in : " & Count'Image (Total_In (Decompressor)) &
95 ", out : " & Count'Image (Total_Out (Decompressor)));
100 Ada.Text_IO.New_Line;
102 ("Decompressed text matches original text : "
103 & Boolean'Image (Uncompressed_Data = Source));