Floating-Point Trigonometric Functions for FPGAs

Field-programmable circuits now have a capacity that allows them to accelerate floating-point computing, but are still missing core libraries for it. In particular, there is a need for an equivalent to the mathematical library (libm) available with every processor and providing implementations of standard elementary functions such as exponential, logarithm or sine. This is all the more important as FPGAs are able to outperform current processors for such elementary functions, for which no dedicated hardware exists in the processor. FPLibrary, freely available from www.ens-lyon.fr/LIP/Arenaire/, is a first attempt to address this need for a mathematical library for FPGAs. This article demonstrates the implementation, in this library, of high-quality operators for floating-point sine and cosine functions up to single-precision. Small size and high performance are obtained using a specific, hardware-oriented algorithm, and careful datapath optimisation and error analysis. Operators fully compatible with the standard software functions are first presented, followed by a study of several more cost-efficient variants.