Reliable Verification Using Symbolic Simulation with Scalar Values Chris Wilson and David L. Dill Computer Systems Laboratory Stanford University Stanford, CA, 94035 chriswi@leland.stanford.edu dill@cs.stanford.edu This paper presents an algorithm for hardware verification that uses simulation and satisfiability checking techniques to determine the correctness of a symbolic test case on a circuit. The goal is to have coverage greater than that of random testing, but with the ease of use and predictability of directed testing. The user uses symbolic variables in simple directed tests to increase the input space that is explored. The algorithm, which is called {\em quasi-symbolic simulation}, simulates these tests using only scalar (0,1,X) values internally causing potentially conservative values to be generated at the outputs. Divide and conquer of the symbolic input space is used to resolve this conservativeness. In the best case, this method is as efficient as symbolic simulation using BDDs and, in the worst case, gives coverage and predictability at least as good as directed testing.