A new European research project aims to develop a microprocessor based on t
he logarithmic number system, in which a real number is represented as a fi
xed-point logarithm. Multiplication and division therefore proceed in minim
al time with no rounding error. However, the system can only offer an overa
ll advantage over floating-point if addition and subtraction can be perform
ed with speed and accuracy at least equal to that of floating-point, but th
ese operations require the interpolation of a nonlinear function which has
hitherto been either time-consuming or inaccurate. We present a procedure b
y 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 o
f both speed and accuracy.