cannam@128: ----------------------------------------------------------------
cannam@128: --  ZLib for Ada thick binding.                               --
cannam@128: --                                                            --
cannam@128: --  Copyright (C) 2002-2004 Dmitriy Anisimkov                 --
cannam@128: --                                                            --
cannam@128: --  Open source license information is in the zlib.ads file.  --
cannam@128: ----------------------------------------------------------------
cannam@128: --
cannam@128: --  $Id: buffer_demo.adb,v 1.3 2004/09/06 06:55:35 vagul Exp $
cannam@128: 
cannam@128: --  This demo program provided by Dr Steve Sangwine <sjs@essex.ac.uk>
cannam@128: --
cannam@128: --  Demonstration of a problem with Zlib-Ada (already fixed) when a buffer
cannam@128: --  of exactly the correct size is used for decompressed data, and the last
cannam@128: --  few bytes passed in to Zlib are checksum bytes.
cannam@128: 
cannam@128: --  This program compresses a string of text, and then decompresses the
cannam@128: --  compressed text into a buffer of the same size as the original text.
cannam@128: 
cannam@128: with Ada.Streams; use Ada.Streams;
cannam@128: with Ada.Text_IO;
cannam@128: 
cannam@128: with ZLib; use ZLib;
cannam@128: 
cannam@128: procedure Buffer_Demo is
cannam@128:    EOL  : Character renames ASCII.LF;
cannam@128:    Text : constant String
cannam@128:      := "Four score and seven years ago our fathers brought forth," & EOL &
cannam@128:         "upon this continent, a new nation, conceived in liberty," & EOL &
cannam@128:         "and dedicated to the proposition that `all men are created equal'.";
cannam@128: 
cannam@128:    Source : Stream_Element_Array (1 .. Text'Length);
cannam@128:    for Source'Address use Text'Address;
cannam@128: 
cannam@128: begin
cannam@128:    Ada.Text_IO.Put (Text);
cannam@128:    Ada.Text_IO.New_Line;
cannam@128:    Ada.Text_IO.Put_Line
cannam@128:      ("Uncompressed size : " & Positive'Image (Text'Length) & " bytes");
cannam@128: 
cannam@128:    declare
cannam@128:       Compressed_Data : Stream_Element_Array (1 .. Text'Length);
cannam@128:       L               : Stream_Element_Offset;
cannam@128:    begin
cannam@128:       Compress : declare
cannam@128:          Compressor : Filter_Type;
cannam@128:          I : Stream_Element_Offset;
cannam@128:       begin
cannam@128:          Deflate_Init (Compressor);
cannam@128: 
cannam@128:          --  Compress the whole of T at once.
cannam@128: 
cannam@128:          Translate (Compressor, Source, I, Compressed_Data, L, Finish);
cannam@128:          pragma Assert (I = Source'Last);
cannam@128: 
cannam@128:          Close (Compressor);
cannam@128: 
cannam@128:          Ada.Text_IO.Put_Line
cannam@128:            ("Compressed size :   "
cannam@128:             & Stream_Element_Offset'Image (L) & " bytes");
cannam@128:       end Compress;
cannam@128: 
cannam@128:       --  Now we decompress the data, passing short blocks of data to Zlib
cannam@128:       --  (because this demonstrates the problem - the last block passed will
cannam@128:       --  contain checksum information and there will be no output, only a
cannam@128:       --  check inside Zlib that the checksum is correct).
cannam@128: 
cannam@128:       Decompress : declare
cannam@128:          Decompressor : Filter_Type;
cannam@128: 
cannam@128:          Uncompressed_Data : Stream_Element_Array (1 .. Text'Length);
cannam@128: 
cannam@128:          Block_Size : constant := 4;
cannam@128:          --  This makes sure that the last block contains
cannam@128:          --  only Adler checksum data.
cannam@128: 
cannam@128:          P : Stream_Element_Offset := Compressed_Data'First - 1;
cannam@128:          O : Stream_Element_Offset;
cannam@128:       begin
cannam@128:          Inflate_Init (Decompressor);
cannam@128: 
cannam@128:          loop
cannam@128:             Translate
cannam@128:               (Decompressor,
cannam@128:                Compressed_Data
cannam@128:                  (P + 1 .. Stream_Element_Offset'Min (P + Block_Size, L)),
cannam@128:                P,
cannam@128:                Uncompressed_Data
cannam@128:                  (Total_Out (Decompressor) + 1 .. Uncompressed_Data'Last),
cannam@128:                O,
cannam@128:                No_Flush);
cannam@128: 
cannam@128:                Ada.Text_IO.Put_Line
cannam@128:                  ("Total in : " & Count'Image (Total_In (Decompressor)) &
cannam@128:                   ", out : " & Count'Image (Total_Out (Decompressor)));
cannam@128: 
cannam@128:                exit when P = L;
cannam@128:          end loop;
cannam@128: 
cannam@128:          Ada.Text_IO.New_Line;
cannam@128:          Ada.Text_IO.Put_Line
cannam@128:            ("Decompressed text matches original text : "
cannam@128:              & Boolean'Image (Uncompressed_Data = Source));
cannam@128:       end Decompress;
cannam@128:    end;
cannam@128: end Buffer_Demo;