Hierarchical segmentation schemes for function evaluation

This paper presents a method for evaluating functions based on piecewise polynomial approximation with a novel hierarchical segmentation scheme. The use of a novel hierarchy scheme of uniform segments and segments with size varying by powers of two enables us to approximate nonlinear regions of a function particularly well. This partitioning is automated: efficient look-up tables and their coefficients are generated for a given function, input range, order of the polynomials, desired accuracy and finite precision constraints. We describe an algorithm to find the optimum number of segments and the placement of their boundaries, which is used to analyze the properties of a function and to benchmark our approach. Our method is illustrated using three non-linear compound functions, √ − log(x), x log(x) and a high order rational function. We present results for various operand sizes between 8 and 24 bits for first and second order polynomial approximations.