SagTree: Towards efficient mutation in evolutionary circuit approximation

•We thoroughly investigate the performance of various mutation operators for Cartesian Genetic Programming in the context of automated design of complex arithmetic circuits.•We propose a novel mutation operator, so-called SagTree, that is tailored to circuit approximation and combines the classical single active gene mutation with a node deactivation operation.•We perform an extensive experimental comparison with existing mutation operators—our results, grounded on a rigorous statistical evaluation including 39 approximation problems and over 14,000 approximation runs, clearly demonstrate that the SagTree operator significantly outperforms the other operators in CGP-based circuit approximation.•Using the SagTree operator, we obtain complex approximate circuits providing significantly better trade-offs between energy savings and the incurred error compared to existing circuits obtained using both evolutionary and non-evolutionary state-of-the-art techniques.