Chen–Ho encoding
The traditional system of binary encoding for decimal digits, known as binary-coded decimal (BCD), uses four bits to encode each digit, resulting in significant wastage of binary data bandwidth (since four bits can store 16 states and are being used to store only 10),[1] even when using packed BCD.The encoding reduces the storage requirements of two decimal digits (100 states) from 8 to 7 bits, and those of three decimal digits (1000 states) from 12 to 10 bits using only simple Boolean transformations avoiding any complex arithmetic operations like a base conversion.In what appears to have been a multiple discovery, some of the concepts behind what later became known as Chen–Ho encoding were independently developed by Theodore M. Hertz in 1969[2] and by Tien Chi Chen (陳天機) (1928–)[3][4][5][6] in 1971.[14] With input from Joseph D. Rutledge and John C. McPherson,[15] the final version of the Chen–Ho encoding was circulated inside IBM in 1974[16] and published in 1975 in the journal Communications of the ACM.[2] The patents also discuss the possibility to adapt the scheme to digits encoded in any other decimal codes than 8-4-2-1 BCD,[2] like f.e.