Affiliations: Department of Computer Science, University of Western
Ontario, N6A 5B7, London, Ontario, Canada. ilie@csd.uwo.ca
Note: [] Address for correspondence: Department of Computer Science,
University of Western Ontario, N6A 5B7, London, Ontario, Canada
Abstract: We consider the data compression using antidictionaries and give
algorithms for faster compression and decompression. While the original method
of Crochemore et al. uses finite transducers with ε-moves, we
(de)compress using ε-free transducers. This is provably faster, assuming
data non-negligibly compressible, but we have to consider the overhead due to
building the new ma-chines. In general, they can be quadratic in size compared
to the ones allowing ε-moves; we prove this bound optimal as it is
reached for de Bruijn words. However, in practice, the size of the ε-free
machines turns out to be close to the size of the ones allowing ε-moves
and therefore we can achieve significantly faster (de)compression. We show our
results for the files in Calgary corpus.
Keywords: Text compression, antidictionaries, finite transducers, ε-free transducers, de Bruijn words
