Improved cotransformation for LNS subtraction

Two co-transformations have been proposed previously to avoid interpolation difficulties for logarithmic subtraction: Arnold´s and Coleman´s. We show these two are closely related, but that Arnold´s is considerably more accurate in the worst case. Coleman´s hardware is more convenient than Arnold´s original method because it works with negative arguments. This paper gives a new variant of Arnold´s co-transformation that works with negative arguments using hardware similar to Coleman´s while maintaining superior accuracy. This reduces the need for input guard bits to an LNS interpolator, which in turn reduces the size of its multiplier(s)