A powering unit for an OpenGL lighting engine

The OpenGL geometry pipeline lighting stage requires raising a number in the range [0, 1] to a power between [1, 128] to compute specular reflections and spotlights. The result need only be accurate to a number of bits related to the color depth of the output device. This paper describes a hardware implementation of such a powering unit based on a logarithm lookup table, a multiplier, and an inverse log table. The log lookup table is partitioned into subintervals to reduce table size. A synthesized design uses 84 k gates to achieve 10-bit accuracy with a latency of 9.62 ns in a 180 nm process. Although the system is tailored for the OpenGL application, the same principles can be applied to the design of other powering units.