D-class computation requires multiplication of three Boolean matrices for each of all possible triples of $n{ imes}n$ Boolean matrices and search for equivalent $n{ imes}n$ Boolean matrices according to a specific equivalence relation. It is easy to see that even multiplying all $n{ imes}n$ Boolean matrices with themselves shows exponential time complexity and D-Class computation was left an unsolved problem due to its computational complexity. The vector-based multiplication theory shows that the multiplication of three Boolean matrices for each of all possible triples of $n{ imes}n$ Boolean matrices can be done much more efficiently. However, D-Class computation requires computation of equivalent classes in addition to the efficient multiplication. The paper discusses a theory and an algorithm for efficient D-class computation, and shows execution results of the algorithm.