JANUS, an on-line multiplier/divider for manipulating large numbers

The authors deal with the detailed VLSI implementation of a fast bit-serial operator designed to perform very high precision (600 decimal digits) additions, multiplications, and divisions, and some of the applications of the circuit are discussed. Online arithmetic needs carry-free redundant number systems. Frequently, the radix chosen is different from 2, since a carry-free addition algorithm can be used in radix r≠2. In radix 2, carry-free addition is possible, but with two inconveniences: the algorithm seems more complicated, and the delay is larger. The authors show that the first inconvenience vanishes if good binary representation of the digits in radix-2 signed digit notation is chosen