Cost-effective multiplication with enhanced adders for multimedia applications

Cost-sensitive consumer multimedia devices based on MPEG and JPEG type algorithms tend to have multiplications by constants, rather than by variables. In this paper, we show how slightly enhanced adders may be used to perform these constant multiplications with higher performance than more expensive hardware multipliers, using low-cost preshift_add instructions. We were able to find the shortest instruction sequences for all 8-bit integer constants and nearly shortest sequences for 12-bit constants and 15-bit constants. We have achieved an average instruction length of 3.055 for 8-bit integer case, 4.2643 and 4.2782 for the two 12-bit constant cases and 5.07673 for the 15-bit constant case. Based on our preshifter design, we evaluate the area and delay of a 16-bit preshift_adder and compare it with a 16×16 multiplier. We show that the simpler preshift_adders achieve a speedup of more than 2X compared to multipliers with similar area cost for typical algorithms like DCT and IDCT.