The case for a redundant format in floating point arithmetic

Abstract

We use a partially redundant number system as an internal format for floating point arithmetic operations. The redundant number system enables carry free arithmetic operations to improve performance. Conversion from the proposed internal format back to the standard IEEE format is done only when an operand is written to memory. A detailed discussion of an adder using the proposed format is presented and the specific challenges of the design are explained. A brief description of a multiplier and divider using the proposed format is also presented. The proposed internal format and arithmetic units comply with all the rounding modes of the IEEE 754 floating point standard. Transistor simulation of the adder and multiplier confirm the performance advantage predicted by the analytical model.