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An Improved Algorithm to Accelerate

Regular Expression Evaluation

Authors: Michela Becchi and Patrick Crowley

Publisher: ANCS’07Present: Kia-Tso Chang

Date: January 8 2008

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outline

D2FA The proposal Reducing the alphabet Experimental evaluation

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Default transition

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D2FA(diameter bound of 4)

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D2FA(diameter bound of 4)

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D2FA(diameter bound of 2)

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Lemma

we define its depth as the minimum number of states visited when moving from s0 to s in the DFA.

Lemma: If none of the default transitions in a D2FA lead from a state with depth di to a state of depth dj with dj ≥ di, then any string of length N will require at most 2N state traversals to be processed.

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The proposal

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Reducing the alphabet

Two symbols ci and cj will fall into the same class if they are treated the same way in all DFA states. In other words, given the transition function δ(states, Σ)→states,δ(s,ci)= δ(s,cj) for each state s belonging to the DFA

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Two observations

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Experimental evaluation

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Experimental evaluation