Patent ID: 8711944

Claim:
A method of compressing digital data for storage or transmission, comprising the steps of: (i) reading digital data as series of binary coded words representing a context and a codeword to be compressed; (ii) calculating distribution output data for the input data and generating variable length prefix codewords for each combination of context and input codeword so as to form a respective sorted transition table of local codewords for each context, in a manner which reserves logical codeword space at the long end to represent any new input codewords, which have not yet occurred with that context, as they occur for the first time; and (iii) repeating the process of step (ii) from time to time; (iv) whereby the input data can be subsequently replayed by recalculating the codeword tables at corresponding times in the input data, wherein the codewords are recalculated each time the number of codewords has doubled.