A high performance floating-point special function unit using constrained piecewise quadratic approximation

A special function unit, able to compute square root, reciprocal square root, logarithm and exponential functions is presented in this paper. The system supports single precision IEEE-754 floating-point standard and uses a novel constrained piecewise quadratic interpolation technique to approximate the implemented functions. The proposed approach allows to reduce look-up table size of 40% with respect to previously proposed techniques. The SFU has been implemented in a test chip in 0.18μm CMOS. A maximum clock frequency of 420MHz and a power dissipation of 160mW@420MHz have been measured.