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1 | ---------------------------------------------------------------- |
2 | -- ZLib for Ada thick binding. -- |
3 | -- -- |
4 | -- Copyright (C) 2002-2004 Dmitriy Anisimkov -- |
5 | -- -- |
6 | -- Open source license information is in the zlib.ads file. -- |
7 | ---------------------------------------------------------------- |
8 | -- |
9 | -- $Id: buffer_demo.adb,v 1.3 2004/09/06 06:55:35 vagul Exp $ |
10 | |
11 | -- This demo program provided by Dr Steve Sangwine <sjs@essex.ac.uk> |
12 | -- |
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. |
16 | |
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. |
19 | |
20 | with Ada.Streams; use Ada.Streams; |
21 | with Ada.Text_IO; |
22 | |
23 | with ZLib; use ZLib; |
24 | |
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'."; |
31 | |
32 | Source : Stream_Element_Array (1 .. Text'Length); |
33 | for Source'Address use Text'Address; |
34 | |
35 | begin |
36 | Ada.Text_IO.Put (Text); |
37 | Ada.Text_IO.New_Line; |
38 | Ada.Text_IO.Put_Line |
39 | ("Uncompressed size : " & Positive'Image (Text'Length) & " bytes"); |
40 | |
41 | declare |
42 | Compressed_Data : Stream_Element_Array (1 .. Text'Length); |
43 | L : Stream_Element_Offset; |
44 | begin |
45 | Compress : declare |
46 | Compressor : Filter_Type; |
47 | I : Stream_Element_Offset; |
48 | begin |
49 | Deflate_Init (Compressor); |
50 | |
51 | -- Compress the whole of T at once. |
52 | |
53 | Translate (Compressor, Source, I, Compressed_Data, L, Finish); |
54 | pragma Assert (I = Source'Last); |
55 | |
56 | Close (Compressor); |
57 | |
58 | Ada.Text_IO.Put_Line |
59 | ("Compressed size : " |
60 | & Stream_Element_Offset'Image (L) & " bytes"); |
61 | end Compress; |
62 | |
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). |
67 | |
68 | Decompress : declare |
69 | Decompressor : Filter_Type; |
70 | |
71 | Uncompressed_Data : Stream_Element_Array (1 .. Text'Length); |
72 | |
73 | Block_Size : constant := 4; |
74 | -- This makes sure that the last block contains |
75 | -- only Adler checksum data. |
76 | |
77 | P : Stream_Element_Offset := Compressed_Data'First - 1; |
78 | O : Stream_Element_Offset; |
79 | begin |
80 | Inflate_Init (Decompressor); |
81 | |
82 | loop |
83 | Translate |
84 | (Decompressor, |
85 | Compressed_Data |
86 | (P + 1 .. Stream_Element_Offset'Min (P + Block_Size, L)), |
87 | P, |
88 | Uncompressed_Data |
89 | (Total_Out (Decompressor) + 1 .. Uncompressed_Data'Last), |
90 | O, |
91 | No_Flush); |
92 | |
93 | Ada.Text_IO.Put_Line |
94 | ("Total in : " & Count'Image (Total_In (Decompressor)) & |
95 | ", out : " & Count'Image (Total_Out (Decompressor))); |
96 | |
97 | exit when P = L; |
98 | end loop; |
99 | |
100 | Ada.Text_IO.New_Line; |
101 | Ada.Text_IO.Put_Line |
102 | ("Decompressed text matches original text : " |
103 | & Boolean'Image (Uncompressed_Data = Source)); |
104 | end Decompress; |
105 | end; |
106 | end Buffer_Demo; |