A Carry-Select Adder structure comprising a carry generation network and a multiplexer to select a particular pre-calculatad sum of a bit-group via orthogonal signal levels of a Hot-Carry signal provided by said carry generation network (21), wherein in order to provide orthogonal signal levels of said Hot-Carry signal, the carry generation network (21) comprises two carry lookahead trees (22, 23) working in parallel to each other, wherein a first carry lookahead tree (22) provides a first signal level of the Hot-Carry signal, and a second carry lookahead tree (23) provides a second, compared to the first signal level inverse signal level of the Hot-Carry signal. Furthermore a method to operate such a Carry-Select Adder is described.