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1 ----------------------------------------------------------------
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2 -- ZLib for Ada thick binding. --
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3 -- --
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4 -- Copyright (C) 2002-2004 Dmitriy Anisimkov --
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5 -- --
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6 -- Open source license information is in the zlib.ads file. --
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7 ----------------------------------------------------------------
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8 --
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9 -- $Id: buffer_demo.adb,v 1.3 2004/09/06 06:55:35 vagul Exp $
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10
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11 -- This demo program provided by Dr Steve Sangwine <sjs@essex.ac.uk>
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12 --
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13 -- Demonstration of a problem with Zlib-Ada (already fixed) when a buffer
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14 -- of exactly the correct size is used for decompressed data, and the last
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15 -- few bytes passed in to Zlib are checksum bytes.
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16
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17 -- This program compresses a string of text, and then decompresses the
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18 -- compressed text into a buffer of the same size as the original text.
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19
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20 with Ada.Streams; use Ada.Streams;
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21 with Ada.Text_IO;
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22
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23 with ZLib; use ZLib;
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24
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25 procedure Buffer_Demo is
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26 EOL : Character renames ASCII.LF;
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27 Text : constant String
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28 := "Four score and seven years ago our fathers brought forth," & EOL &
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29 "upon this continent, a new nation, conceived in liberty," & EOL &
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30 "and dedicated to the proposition that `all men are created equal'.";
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31
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32 Source : Stream_Element_Array (1 .. Text'Length);
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33 for Source'Address use Text'Address;
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34
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35 begin
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36 Ada.Text_IO.Put (Text);
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37 Ada.Text_IO.New_Line;
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38 Ada.Text_IO.Put_Line
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39 ("Uncompressed size : " & Positive'Image (Text'Length) & " bytes");
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40
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41 declare
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42 Compressed_Data : Stream_Element_Array (1 .. Text'Length);
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43 L : Stream_Element_Offset;
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44 begin
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45 Compress : declare
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46 Compressor : Filter_Type;
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47 I : Stream_Element_Offset;
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48 begin
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49 Deflate_Init (Compressor);
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50
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51 -- Compress the whole of T at once.
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52
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53 Translate (Compressor, Source, I, Compressed_Data, L, Finish);
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54 pragma Assert (I = Source'Last);
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55
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56 Close (Compressor);
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57
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58 Ada.Text_IO.Put_Line
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59 ("Compressed size : "
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60 & Stream_Element_Offset'Image (L) & " bytes");
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61 end Compress;
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62
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63 -- Now we decompress the data, passing short blocks of data to Zlib
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64 -- (because this demonstrates the problem - the last block passed will
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65 -- contain checksum information and there will be no output, only a
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66 -- check inside Zlib that the checksum is correct).
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67
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68 Decompress : declare
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69 Decompressor : Filter_Type;
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70
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71 Uncompressed_Data : Stream_Element_Array (1 .. Text'Length);
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72
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73 Block_Size : constant := 4;
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74 -- This makes sure that the last block contains
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75 -- only Adler checksum data.
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76
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77 P : Stream_Element_Offset := Compressed_Data'First - 1;
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78 O : Stream_Element_Offset;
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79 begin
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80 Inflate_Init (Decompressor);
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81
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82 loop
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83 Translate
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84 (Decompressor,
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85 Compressed_Data
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86 (P + 1 .. Stream_Element_Offset'Min (P + Block_Size, L)),
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87 P,
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88 Uncompressed_Data
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89 (Total_Out (Decompressor) + 1 .. Uncompressed_Data'Last),
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90 O,
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91 No_Flush);
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92
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93 Ada.Text_IO.Put_Line
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94 ("Total in : " & Count'Image (Total_In (Decompressor)) &
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95 ", out : " & Count'Image (Total_Out (Decompressor)));
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96
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97 exit when P = L;
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98 end loop;
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99
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100 Ada.Text_IO.New_Line;
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101 Ada.Text_IO.Put_Line
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102 ("Decompressed text matches original text : "
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103 & Boolean'Image (Uncompressed_Data = Source));
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104 end Decompress;
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105 end;
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106 end Buffer_Demo;
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