Abstract: Optimization of reversible circuits is one of key problems of reversible logic synthesis．To solve the problem of high algorithm complexity and poor scalability of reversible Toffoli circuits,the paper analyzed and summarized relationship between adjacent Toffoli gates,proposed and proven the moving and simplification rules of sub-sequence of reversible circuit cascaded by Toffoli gates,and gave the optimization algorithm based on these rules．The algorithm exami-nes the circuit bidirectionally according to the moving rules,searches the sub-sequence satisfying simplification rules,performs corresponding optimization,and the process is repeated until the circuit does’t change．The algorithm is irrelevant to the number of input lines,does’t need to store extra information,is suitable to different Toffoli circuit synthesis methods,and its algorithm complexity is O(s³),which is superior to O(n!t^2s3) of generally used template optimization technique．Results of examples and experiments on all 3-bit reversible functions show that the number of gates and the control bits can be reduced effectively and the cost of reversible circuit is decreased.

Key words: Reversible logic synthesis,Reversible function,Toffoli gate,Optimization of reversible circuit