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mercoledì, 24 luglio 2024

Rapporti Tecnici

Dettagli rapporto tecnico
Autori:Travis Gagie
Giovanni Manzini
Area Scientifica:Text Compression and Indexing
Titolo:Space-Conscious Compression
Apparso su:TR-INF-2007-06-02-UNIPMN
Editore:Computer Science Department, UPO
Sommario:Compression is most important when space is in short supply, so compression algorithms are often implemented in limited memory. Most analyses ignore memory constraints as an implementation detail, however, creating a gap between theory and practice. In this paper we consider the effect of memory limitations on compression algorithms. In the first part we assume the memory available is fixed and prove nearly tight upper and lower bounds on how much memory is needed to compress a string close to its $k$-th order entropy. In the second part we assume the memory available grows (slowly) as more and more characters are read. In this setting we show that the rate of growth of the available memory determines the speed at which the compression ratio approaches the entropy. In particular, we establish a relationship between the rate of growth of the sliding window in the LZ77 algorithm and its convergence rate.