[Hu, Jianqiang] Hunan Agr Univ, Sch Informat Sci & Technol, Changsha 410128, Hunan, Peoples R China.^[Hu, Jianqiang;Wu, Gang;Zhong, Qian] Tsinghua Univ, Dept Comp Sci & Technol, Beijing 100084, Peoples R China.^[Hu, Jianqiang] Wuhan Univ, State Key Lab Software Engn, Wuhan 430072, Peoples R China.