A Regular Expression Matching Algorithm Using Transition Merging Department of Computer Science and Information Engineering National Cheng Kung University, Taiwan R.O.C. Author: Jiekun Zhang, Dafang Zhang, Kun Huang Publisher: IEEE Pacific Rim International Symposium on Dependable Computing (PRDC 2009) Presenter: Sih-An Pan Date: 2014/6/18

Computer & Internet Architecture Lab CSIE NCKU Introduction The authors in [1] propose a novel method to reduce the DFA memory requirement and still provide worst-case speed guarantees, called State Merging DFA (SM-DFA). SM-DFA results in large memory reductions. But this algorithm only considers the reduction of states, while adding auxiliary information on the transitions at the same time. But the transitions have not been reduced, which increase the memory requirement. 2

Computer & Internet Architecture Lab CSIE NCKU STATE MERGING DFA 3

Computer & Internet Architecture Lab CSIE NCKU STATE MERGING DFA 4 The transition [g-i]/0, j/1 indicates that the same next state, in this case state 5, is reached from state 3_4 upon receiving input characters g, h, i with label 0 or input character j with label 1.

Computer & Internet Architecture Lab CSIE NCKU STATE MERGING DFA The transition a.0/0,1 from state 3_4 to state 1_2 means: The transition carries with it a label 0 that tells its destination state, 1_2 that the transition is meant for underlying original state 1. The transition is taken when its source state 3_4 receives labels 0 or 1. 5

Computer & Internet Architecture Lab CSIE NCKU TRANSITION MERGING DFA 6 String:”acgacik” 0->1-2->3-4->5-> 1-2->3-4->5->6

Computer & Internet Architecture Lab CSIE NCKU EXPERIMENTAL RESULTS 7 TM-DFA matching algorithm ensures the speed of pattern matching, and reduces the memory consumption by 30% compared to SM-DFA, while compared to the original DFA, it reduces the memory consumption by 42%.

Computer & Internet Architecture Lab CSIE NCKU EXPERIMENTAL RESULTS TM-DFA continues reducing the memory consumptionand we can see from Fig. 8 and Fig. 9 that the performance of the proposed TM-DFA scheme is outperformed by the SM-DFA scheme when the rule length becomes larger. 8