A higher-radix algebra for full-addition of two numbers is described and realised by combining multi-valued logic min, max, literal and cyclic operators in terms disjoint terms. The latter operator is designed by using a current-mode threshold circuit while the other operator is realised by only voltage-mode switching circuits. The threshold circuit employed allows for much higher radices compared to architetures employing voltage-mode binary logic switching circuits as well as better mismatch properties compared to previous threshold circuits. Due to disjoint terms involved, multi-valued logic min and max operators can be replaced with ordinary ordinary transmission operation and addtion, respectively. Resultant a single-digit, radix-8 full-adder and its 3-bit counterpart voltage-mode circuits are realised and compared. The algorithm is also exploited for a multi-digit case and its HSPice simulation results are presented.