Case Branching Backward Simulator for Integer Factorization

To verify the safety of a system, it is desirable to test all the situation, at least, by simulation. However, it is difficult to test the entire situation because the number of situations is almost uncountable. As a promising method, backward simulation which traces back from the undesirable result to causal input(s) is proposed. For such backward simulation, we have to transform the forward model into a backward model. This paper shows an example of transformation in the case of mathematical model of integer factorization, and shows the effectiveness of the backward simulation. Such backward simulation would require case branch processing. And the practicality of the simulation result will be influenced by the efficiency of the case division. We show an effective case branch processing by using stack and threaded actors which are promising schemes applicable to distributed processing.