1. Center for Energy-Efficient Computing and Applications, School of Electronics Engineering and Computer Science, Peking University, Beijing 100871, China
2. Department of Computer Engineering, University of California at Santa Cruz, Santa Cruz, CA 95064, USA
3. Advanced Micro Devices, Inc., Sunnyvale, CA 94085, USA
4. Hewlett Packard Lab, Palo Alto, CA 94304, USA
5. Department of Electrical and Computer Engineering, University of California at Santa Barbara, Santa Barbara, CA 93106, USA