n..times..times..times. ##EQU00007## where L is a number of stored values, k indicates a current instance of the values, j is an integer from 0 to p-1, p is a number of values in the periodic sequence, y.sub.k-i is a previous confined value instance, and each x is a periodicsequence instance of the plurality of instances of the periodic sequence, and where the selected instance of the periodic seq