1. Computer Science Department, University of California, Irvine, CA 92697-3425, USA
2. Department of Electrical and Computer Engineering, Northwestern University, Evasnton, IL 60201, USA
3. Synplicity Inc., 600 W California Ave, Sunnyvale, CA 94086, USA
4. Computer Science Department, University of California, Los Angeles (UCLA), 3531C Boelter Hall, Los Angeles, CA 90095, USA