Logic simulation includes storing a first state to identify in a simulation of a logic design whether a node included in the logic design has a logic high value Logic simulation also includes storing a second state to identify in simulation of the logic design whether the node has a logic low value and storing a third state to identify in simulation of the logic design whether the node has an undefined state. The logic simulation determines an output of the node in simulation of the logic design based on the first state, the second state, and the third state.