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Fast Partial Evaluation of Pattern Matching in Strings
Mads Sig Ager
May 2003 |
Abstract:
We show how to obtain all of Knuth, Morris, and Pratt's
linear-time string matcher by partial evaluation of a quadratic-time string
matcher with respect to a pattern string. Although it has been known for 15
years how to obtain this linear matcher by partial evaluation of a quadratic
one, how to obtain it in linear time has remained an open
problem.
Obtaining a linear matcher by partial evaluation of a quadratic one is achieved by performing its backtracking at specialization time and memoizing its results. We show (1) how to rewrite the source matcher such that its static intermediate computations can be shared at specialization time and (2) how to extend the memoization capabilities of a partial evaluator to static functions. Such an extended partial evaluator, if its memoization is implemented efficiently, specializes the rewritten source matcher in linear time Available as PostScript, PDF. |