A Boyer-Moore-style algorithm for regular expression pattern matching

Richard E. Watson Dept. of Mathematics Simon Fraser University Burnaby B.C., Canada watsona@sfu. ca This paper presents a Boyer-Moore type algorithm for regular expression pattern matching, answering an open problem posed by A. V. Aho in 1980 [Aho80, p. 3421. The new algorithm handles patterns specified by regular expressions a generalization of the Boyer-Moore and Commentz-Walter algorithms (which deal with patterns that are single keywords and /inite sets of keywords, respectively). Like the Boyer-Moore and Com mentz-Walter algorithms, the new algorithm makes use of shift functions which can be precomputed and tabulated. The precomputation algorithms are derived, and it is shown that the required shift functions can be precomputed from Commentz-Walter's shift functions known as d, and d2 . In certain cases, the Boyer-Moore (Commentz-Walter) algorithm has greatly outperformed the Knuth-Morris-Pratt (Aho-Corasick) algorithm. In testing, the algorithm presented in this paper also frequently outperforms the regular expression generalization of the Aho-Corasick algorithm.