We consider the classical exact multiple string matching problem. The proposed solution is based on a combination of a few ideas: using q-grams instead of single characters, pattern superimposition, bit-parallelism an...
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We consider the classical exact multiple string matching problem. The proposed solution is based on a combination of a few ideas: using q-grams instead of single characters, pattern superimposition, bit-parallelism and alphabet size reduction. We discuss the pros and cons of various alternatives to achieve the possibly best combination of techniques. The main contribution of this paper are different alphabet mapping methods that allow to reduce memory requirements and use larger q-grams. The experimental results show that the presented algorithm is competitive in most practical cases. One of the tests shows also that tailoring our scheme to search over a byte-encoded text results in speedups in comparison to searching over a plain text.
Searching for all occurrences of a pattern in a text is a fundamental problem in computer science with applications in many other fields, like natural language processing, information retrieval and computational biolo...
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Searching for all occurrences of a pattern in a text is a fundamental problem in computer science with applications in many other fields, like natural language processing, information retrieval and computational biology. In the last two decades a general trend has appeared trying to exploit the power of the word RAM model to speed-up the performances of classical string matching algorithms. In this model an algorithm operates on words of length w, grouping blocks of characters, and arithmetic and logic operations on the words take one unit of time. In this paper we use specialized word-size packed string matching instructions, based on the Intel streaming SIMD extensions (SSE) technology, to design a very fast string matching algorithm. We evaluate our solution in terms of efficiency, stability and flexibility, where we propose to use the deviation in running time of an algorithm on distinct equal length patterns as a measure of stability. From our experimental results it turns out that, despite their quadratic worst case time complexity, the new presented algorithm becomes the clear winner on the average in many cases, when compared against the most recent and effective algorithms known in literature. (C) 2014 Elsevier B.V. All rights reserved.
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