A Novel Carry-Look Ahead Approach to a Unified BCD and Binary Adder/Subtractor

Increasing prominence of commercial, financial and Internet-based applications, which process decimal data, there is an increasing interest in providing hardware support for such data. In this paper, new architecture for efficient binary and binary coded decimal (BCD) adder/subtracter is presented. This employs a new method of subtraction unlike the existing designs which mostly use 10's complements, to obtain a much lower latency. Though there is a necessity of correction in some cases, the delay overhead is minimal. A complete discussion about such cases and the required logic to process is presented. The architecture is run-time reconfigurable to facilitate both BCD and binary operations, including signed and unsigned numbers. The proposed circuits are compared (both qualitatively as well as quantitatively) with the existing circuits in literature and are shown to perform better. Simulation results show that the proposed architecture is at least 11% faster than the existing designs.