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Main features


Original method of sliding window was designed in 1977 by Abrahamem Lempel and Jacob Ziv. It forms a basis for LZ variations.


This method uses window divided to search buffer and look-ahead buffer. Size of the search buffer is usually 8 192 bits and size of the look-ahead buffer about 10 to 20 bits. In demonstration both parameters can be set.

The algorithm can be described as follows. First the longest prefix of a look-ahead buffer that starts in search buffer is found. This prefix is encoded as triplet (i, j, X) where i is the distance of the begining of the found prefix from the end of the search buffer, j is the length of the found prefix and X is the first character after the prefix in look-ahead buffer. The following applet visualizes this algorithm. The number of bits written to the output depends on used encoding of numbers.


 1:  begin
 2:     fill view from input
 3:     while (view not empty) do 
 4:      begin
 5:        find longest prefix p of view starting in coded part
 6:        i := position of p in window
 7:        j := length of p
 8:        X := first char after p in view
 9:        output(i,j,X)
10:        add j+1 chars
11:      end
12:  end