The implementation of fast dedicated processor for block matching motion estimation based on cumulants matching criteria implies the optimization of all of its components. Special care should be spent with the multiply-accumulate unit that is the core of many digital signal processing systems. Therefore, its optimization may be of outmost importance, specially if a significative number of such units are present in the platform. In this paper, the minimization of the size of one such unit is provided for a specific application, although the results have relevance in other scenarios.