An apparatus 8 for performing a selectable one of multi-element comparison and multi-element addition is formed from a carry propagate adders stage 12 supplied with four non-final intermediate operands formed from the input vector, a non-final limit value selecting stage 14, which when performing a multi-element comparison serves to select, in dependence upon at least carry save values generated by the carry propagate adder, limit values that are of a larger or a smaller value of a pair of elements. A final intermediate operand forming stage 16 forms final intermediate operands from two non-final intermediate sum values from the carry propagate adders stage 12 and supplies these to a final output adder stage 18 which forms a sum of these two final intermediate operands to generate an output operand which can be either one or more candidates for limit values that will be a maximum or minimum value, or a sum value, or partial sum values in the case of a multi-element addition.