Exploring the energy efficiency of multispeculative adders

Variable Latency Adders are attracting strong interest for increasing performance at a low cost. However, most of the literature is focused on achieving a good area-delay tradeoff. In this paper we consider multispeculation as an alternative for designing adders with low energy consumption, while offering better performance than the corresponding non-speculative ones. Instead of introducing more logic to accelerate the computation, the adder is split into several fragments which operate in parallel, and whose carry-in signals are provided by predictor units. On the one hand, the critical path of the module is shortened, and on the other hand the frequent useless glitches produced in the carry propagation structure are diminished. Hence, this will be translated into an overall energy reduction. Several experiments have been performed with linear and logarithmic adders, and results show energy savings by up to 90% and 70%, respectively, while achieving an additional execution time decrease. Futhermore, when utilized in whole datapaths with current control techniques, it is possible to reduce execution time by 24.5% (34% best case) and energy by 32% (48% best case) on average.