US Patent 4,560,976

Number:	4,560,976
Title:	Data compression
Filed:	05-Jun-1984
Granted:	24-Dec-1985
Inventor:	Steven G. Finn, Framingham, MA
Assignee:	Codex Corporation, Mansfield MA

Comment by FAQ:A stream of source characters, which occur with varying relative frequencies, is encoded into a compressed stream of codewords, each having one, two or three subwords, by ranking the source characters by their current frequency of appearance, encoding the source characters having ranks no higher than a first number as one subword codewords, source characters having ranks higher than the first number but no higher than a second number as two subword codewords, and the remaining source characters as three subword codewords.