Fast, Efficient Floating-Point Adders and Multipliers for FPGAs

Abstract

Floating-point applications are a growing trend in the FPGA community. As such, it has become critical to create floating-point units optimized for standard FPGA technology. Unfortunately, the FPGA design space is very different from the VLSI design space; thus, optimizations for FPGAs can differ significantly from optimizations for VLSI. In particular, the FPGA environment constrains the design space such that only limited parallelism can be effectively exploited to reduce latency. Obtaining the right balances between clock speed, latency, and area in FPGAs can be particularly challenging. This article presents implementation details for an IEEE-754 standard floating-point adder and multiplier for FPGAs. The designs presented here enable a Xilinx Virtex4 FPGA (-11 speed grade) to achieve 270 MHz IEEE compliant double precision floating-point performance with a 9-stage adder pipeline and 14-stage multiplier pipeline. The area requirement is approximately 500 slices for the adder and under 750 slices for the multiplier.