Accelerating Equation (3) is needed to accelerate a compressed DNN. We perform the indexing S[Iij] and the multiply-add only for those columns for which both Wij and aj are non-zero, so that both the sparsity of the matrix and the vector are exploited. This results in a dynamically irregular computation. Performing the indexing itself involves bit manipulations to extract four-bit Iij and an extra load (which is almost assured a cache hit).