Towards Polynomial Formal Verification of Complex Arithmetic Circuits

With the growing demands for highly area-efficient, delay-optimized, and low-power designs, the complexity of digital circuits is increasing as well. Especially, a wide variety of arithmetic circuits, including different types of adders, multipliers, and dividers have been proposed to meet the demands in applications such as cryptography and Artificial Intelligence (AI). Some of these arithmetic circuits have highly parallel architectures and contain millions of gates; as a result, they are extremely error-prone. In the last 30 years, several formal verification methods have been proposed to verify arithmetic circuits. These methods report very good results when it comes to the verification of adders and structurally simple multipliers. Moreover, their space and time complexities are polynomial, i.e, they are scalable. However, when it comes to the verification of structurally complex multipliers, the story is different.In this paper, we investigate the space and time complexity of verifying a structurally complex multiplier using a word-level verification method. We prove that the space and time complexity is always exponential. Then, we introduce a new verification strategy that takes advantage of several verification engines. We show that the polynomial formal verification of the complex multiplier becomes possible if the correctness of each stage is verified using the proper verification method. Our verification strategy can be applied to other complex digital circuits.