Complements and signed digit representations: Analysis of a   multi-exponentiation-algorithm of Wu, Lou, Lai and Chang
  Wu, Lou, Lai and Chang proposed a multi-exponentiation algorithm using binary complements and the non-adjacent form. The purpose of this paper is to show that neither the analysis of the algorithm given by its original proposers nor that by other authors are correct. In fact it turns out that the complement operation does not have significant influence on the performance of the algorithm and can therefore be omitted. 
Clemens Heuberger and Helmut Prodinger