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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; |