In this work, the design of the diminished-1 modulo [Formula: see text] adders, subtractors and adders/subtractors are examined. Some of the existing modulo [Formula: see text] adders, subtractors and adder/subtractors are redesigned and improved. Compared to other existing implementations, the proposed subtractor and adder/subtractors offer reduced area complexity and lower power consumption, while operating at the same speed. All the considered architectures are modified parallel-prefix adders with fast input carry processing. The totally parallel-prefix and carry look ahead implementation of the proposed arithmetic units are also discussed.