Chris@4: ----------------------------------------------------------------
Chris@4: --  ZLib for Ada thick binding.                               --
Chris@4: --                                                            --
Chris@4: --  Copyright (C) 2002-2004 Dmitriy Anisimkov                 --
Chris@4: --                                                            --
Chris@4: --  Open source license information is in the zlib.ads file.  --
Chris@4: ----------------------------------------------------------------
Chris@4: --
Chris@4: --  $Id: buffer_demo.adb,v 1.3 2004/09/06 06:55:35 vagul Exp $
Chris@4: 
Chris@4: --  This demo program provided by Dr Steve Sangwine <sjs@essex.ac.uk>
Chris@4: --
Chris@4: --  Demonstration of a problem with Zlib-Ada (already fixed) when a buffer
Chris@4: --  of exactly the correct size is used for decompressed data, and the last
Chris@4: --  few bytes passed in to Zlib are checksum bytes.
Chris@4: 
Chris@4: --  This program compresses a string of text, and then decompresses the
Chris@4: --  compressed text into a buffer of the same size as the original text.
Chris@4: 
Chris@4: with Ada.Streams; use Ada.Streams;
Chris@4: with Ada.Text_IO;
Chris@4: 
Chris@4: with ZLib; use ZLib;
Chris@4: 
Chris@4: procedure Buffer_Demo is
Chris@4:    EOL  : Character renames ASCII.LF;
Chris@4:    Text : constant String
Chris@4:      := "Four score and seven years ago our fathers brought forth," & EOL &
Chris@4:         "upon this continent, a new nation, conceived in liberty," & EOL &
Chris@4:         "and dedicated to the proposition that `all men are created equal'.";
Chris@4: 
Chris@4:    Source : Stream_Element_Array (1 .. Text'Length);
Chris@4:    for Source'Address use Text'Address;
Chris@4: 
Chris@4: begin
Chris@4:    Ada.Text_IO.Put (Text);
Chris@4:    Ada.Text_IO.New_Line;
Chris@4:    Ada.Text_IO.Put_Line
Chris@4:      ("Uncompressed size : " & Positive'Image (Text'Length) & " bytes");
Chris@4: 
Chris@4:    declare
Chris@4:       Compressed_Data : Stream_Element_Array (1 .. Text'Length);
Chris@4:       L               : Stream_Element_Offset;
Chris@4:    begin
Chris@4:       Compress : declare
Chris@4:          Compressor : Filter_Type;
Chris@4:          I : Stream_Element_Offset;
Chris@4:       begin
Chris@4:          Deflate_Init (Compressor);
Chris@4: 
Chris@4:          --  Compress the whole of T at once.
Chris@4: 
Chris@4:          Translate (Compressor, Source, I, Compressed_Data, L, Finish);
Chris@4:          pragma Assert (I = Source'Last);
Chris@4: 
Chris@4:          Close (Compressor);
Chris@4: 
Chris@4:          Ada.Text_IO.Put_Line
Chris@4:            ("Compressed size :   "
Chris@4:             & Stream_Element_Offset'Image (L) & " bytes");
Chris@4:       end Compress;
Chris@4: 
Chris@4:       --  Now we decompress the data, passing short blocks of data to Zlib
Chris@4:       --  (because this demonstrates the problem - the last block passed will
Chris@4:       --  contain checksum information and there will be no output, only a
Chris@4:       --  check inside Zlib that the checksum is correct).
Chris@4: 
Chris@4:       Decompress : declare
Chris@4:          Decompressor : Filter_Type;
Chris@4: 
Chris@4:          Uncompressed_Data : Stream_Element_Array (1 .. Text'Length);
Chris@4: 
Chris@4:          Block_Size : constant := 4;
Chris@4:          --  This makes sure that the last block contains
Chris@4:          --  only Adler checksum data.
Chris@4: 
Chris@4:          P : Stream_Element_Offset := Compressed_Data'First - 1;
Chris@4:          O : Stream_Element_Offset;
Chris@4:       begin
Chris@4:          Inflate_Init (Decompressor);
Chris@4: 
Chris@4:          loop
Chris@4:             Translate
Chris@4:               (Decompressor,
Chris@4:                Compressed_Data
Chris@4:                  (P + 1 .. Stream_Element_Offset'Min (P + Block_Size, L)),
Chris@4:                P,
Chris@4:                Uncompressed_Data
Chris@4:                  (Total_Out (Decompressor) + 1 .. Uncompressed_Data'Last),
Chris@4:                O,
Chris@4:                No_Flush);
Chris@4: 
Chris@4:                Ada.Text_IO.Put_Line
Chris@4:                  ("Total in : " & Count'Image (Total_In (Decompressor)) &
Chris@4:                   ", out : " & Count'Image (Total_Out (Decompressor)));
Chris@4: 
Chris@4:                exit when P = L;
Chris@4:          end loop;
Chris@4: 
Chris@4:          Ada.Text_IO.New_Line;
Chris@4:          Ada.Text_IO.Put_Line
Chris@4:            ("Decompressed text matches original text : "
Chris@4:              & Boolean'Image (Uncompressed_Data = Source));
Chris@4:       end Decompress;
Chris@4:    end;
Chris@4: end Buffer_Demo;