Tighter Packed Bit-Parallel NFA for Approximate String Matching

We propose a new variant of the bit-parallel NFA of Baeza-Yates and Navarro (BPD) for approximate string matching [1]. Given a length-m pattern and an error threshold k, the original BPD uses (m−k)(k +2) bits of space. We decrease this to (m− k)(k +1), and also give a slightly more efficient simulation algorithm for the NFA. In experiments our modified NFA is often noticeably more efficient than the original algorithm under moderate values of k and m.