MAC (multiply and accumulate) operations are heavily involved in many DSP applications. To improve the performance of MAC operations, it is very crucial to make multiplication fast. In this paper, we propose a set of novel MAC operator designs with constant coefficients. It is well-known that shifting can replace a constant multiplication if the constant is a power of 2. We extend this idea in such a way that by employing more than 2 barrel shifters and a supplementary multiplier we can design a very efficient constant multiplier for general constants. To enhance the applicability of our design for a wide range of constants, a support for variable precision computations has been implemented. Experimental results show that our designs achieve consistent enhancement in terms of power consumption when our design is compared with other existing optimized designs.