BLIM: A New Bit-Parallel Pattern Matching Algorithm Overcoming Computer Word Size Limitation

Bitwise operations are executed very fast in computer architecture. Algorithms aiming to benefit from this intrinsic property can be classified as bit-parallel algorithms. Bit-parallelism has been widely investigated in pattern matching area since the introduction of the Shift-Or algorithm. In the original idea, there were no shift mechanism, and the input pattern length is required to be less than the computer word size (W) to benefit from the full power of bit-parallelism. The lack of the shift mechanism was removed by the succeding algorithms of this genre, but W limitation has not been overcomed in an elegant way. This study proposes a new bit-parallel algorithm, given name BLIM (bit-parallel length independent matching), for exact pattern matching that does not restrict the input pattern to be shorter than the word size. Multiple pattern case is also addressed, and it is shown that up to computer word size number of patterns, whatever their lengths are, can be searched simultaneously in a single bit-parallel framework. Similar to other algorithms of this genre, BLIM is also capable of handling fixed-length gaps and character classes in the input strings as well. The proposed algorithm is compared with the other alternatives of its class, mainly the shift-or and BNDM variants. Experimental results indicate that BLIM is compatible with the previous bit-parallel algorithms with an additional gain of overcoming the word size limitation.