Design of a versatile and cost-effective hybrid floating-point/LNS arithmetic processor

LNS (logarithmic number system) arithmetic has the advantages of high-precision and high performance in complex function computation. However, the large hardware problem in LNS addition/subtraction computation has made the large word-length LNS arithmetic implementation impractical. In this research, we proposed a hybrid floating-point (FLP)/LNS processor that can utilize the FLP multiplication-addition-fused (MAF) unit and the FLP division unit for implementing the computation of LNS addition/subtraction. With unified representation format in FLP and LNS numbers, this hybrid processor is versatile because it can execute the FLP-to-LNS and LNS-to-FLP conversions easily, without any extra hardware cost, in addition to the FLP multiplication-addition/subtraction, FLP division, and LNS addition/subtraction instructions. It is cost-effective because the FLP hardware is shared by the LNS unit. A 32-bit hybrid FLP/LNS processor is implemented on the Xilinx Virtex II multimedia FF896 development board. From the synthesis results, the hardware of the 32-bit hybrid processor is at most three times that of a 32-bit pure FLP processor. Our proposed hybrid FLP/LNS approach has made the design of very large word-length LNS arithmetic processors become practical.