In 2000 we described a proposal for a logarithmic arithmetic unit, which we suggested would offer a faster, more accurate alternative to floating-point procedures. Would it in fact do so, and could it feasibly be integrated into a microprocessor so that the intended benefits might be realized? Here, we describe the European logarithmic microprocessor, a device designed around that unit, and compare its performance with that of a commercial superscalar pipelined floating-point processor. We conclude that the experiment has been successful, and that for 32-bit work, logarithmic arithmetic may now be the technique of choice.

A new European research project aims to develop a microprocessor based on the logarithmic number system, in which a real number is represented as a fixed-point logarithm. Multiplication and division therefore proceed in minimal time with no rounding error. However, the system can only offer an overall advantage over floating-point if addition and subtraction can be performed with speed and accuracy at least equal to that of floating-point, but these operations require the interpolation of a nonlinear function which has hitherto been either time-consuming or inaccurate. We present a procedure by which additions and subtractions can be performed rapidly and accurately and show that these operations are thereby competitive with their floating-point equivalents. We then present some large-scale case studies which show that the average performance of the LNS exceeds floating-point, in terms of both speed and accuracy.