Low-cost design of reciprocal function units using shared multipliers and adders for polynomial approximation and Newton Raphson interpolation

A hybrid method of computing reciprocal is presented by combining the degree-two piecewise polynomial interpolation method and a Newton-Raphson iteration. The degree-two piecewise method is used to obtain an initial approximation for the subsequent Newton-Raphson operations. Architecture for the proposed hybrid method is designed considering the hardware sharing of the composing multipliers in the sub-word level, leading to significant improvement in area cost compared to conventional table-based designs and other hybrid approaches.