A processor includes a register, a non-zero weight value selector and a multiplier. The register holds a first group of weight values and a second group of weight values. Each group of weight values includes at least one weight value, and each weight value in the first group of weight values corresponding to a weight value in the second group of weight values. The non-zero weight value selector selects a non-zero weight value from a weight value in the first group of weight values or a non-zero weight value in the second group of weight values that corresponds to the weight value in the first group of weight values. The multiplier multiplies the selected non-zero weight value and an activation value that corresponds to the selected non-zero weight value to form an output product value.