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Space Efficient Algorithms for the Burrows-Wheeler Backtransformation

  • Ulrich Lauther
  • Tamás Lukovszki
Part of the Lecture Notes in Computer Science book series (LNCS, volume 3669)

Abstract

The Burrows-Wheeler transformation is used for effective data compression, e.g., in the well known program bzip2. Compression and decompression are done in a block-wise fashion; larger blocks usually result in better compression rates. With the currently used algorithms for decompression, 4n bytes of auxiliary memory for processing a block of n bytes are needed, 0 < n < 232. This may pose a problem in embedded systems (e.g., mobile phones), where RAM is a scarce resource. In this paper we present algorithms that reduce the memory need without sacrificing speed too much.

The main results are: Assuming an input string of n characters, 0 < n < 232, the reverse Burrows-Wheeler transformation can be done with 1.625 n bytes of auxiliary memory and O(n) runtime, using just a few operations per input character. Alternatively, we can use n/t bytes and 256 tn operations. The theoretical results are backed up by experimental data showing the space-time tradeoff.

Keywords

Query Time Input String Input Character Computer Word Random Access Machine 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2005

Authors and Affiliations

  • Ulrich Lauther
    • 1
  • Tamás Lukovszki
    • 1
  1. 1.Siemens AG, Corporate TechnologyMunichGermany

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