1. Center for Energy-Efficient Computing and Applications, Peking University, Beijing, China
2. Computer Science Department, University of California, Los Angeles, Los Angeles, USA
3. Center for Energy-Efficient Computing and Applications, Peking University & PKU/UCLA Joint Research Institute in Science and Engineering, Beijing, China
4. Computer Science Department, University of California, Los Angeles, Los Angeles, USA & Center for Energy-Efficient Computing and Applications, Peking University & PKU/UCLA Joint Research Institute in Science and Engineering, Beijing, China