Gapped code clone detection with lightweight source code analysis

A variety of methods detecting code clones has been proposed before. In order to detect gapped code clones, AST-based technique, PDG-based technique, metric-based technique and text-based technique using the LCS algorithm have been proposed. However, each of those techniques has limitations. For example, existing AST-based techniques and PDG-based techniques require costs for transforming source files into intermediate representations such as ASTs or PDGs and comparing them. Existing metric-based techniques and text-based techniques using the LCS algorithm cannot detect code clones if methods or blocks are partially duplicated. This paper proposes a new method that detects gapped code clones using the Smith-Waterman algorithm to resolve those limitations. The Smith-Waterman algorithm is an algorithm for identifying similar alignments between two sequences even if they include some gaps. The authors developed the proposed method as a software tool named CDSW, and confirmed that the proposed method could resolve the limitations by conducting a quantitative evaluation with Bellon's benchmark.