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Virtual-Memory Powersort

Authors Finn Moltmann , Tamio-Vesa Nakajima , Sebastian Wild

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Subject Classification

ACM Subject Classification
  • Theory of computation → Data structures design and analysis
Keywords
  • adaptive sorting
  • inplace sorting
  • inplace merging
  • library sort
  • virtual memory
  • internal buffering
  • Powersort
  • Timsort

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Abstract

We give a more space-efficient implementation of adaptive mergesort: Virtual-Memory Powersort. Using internal buffering techniques, we significantly reduce the memory consumption of the algorithm; specifically, for sorting n objects the required buffer area is reduced from space for n/2 objects to O(√{n log n}) objects. While this space-efficiency can be achieved (indeed reduced to O(1)) conceptually very easily with known inplace merging algorithms, using these as a drop-in replacement for the standard merge algorithm incurs a substantial slow-down. Virtual-Memory Powersort, by contrast, uses the same number of moves and comparisons as previous Powersort implementations up to an additive O(n) term. We report on an empirical running-time study comparing our implementation against other Powersort variants and state-of-the-art stable sorting methods, demonstrating that almost in-place stable sorting can be achieved with negligible overhead in many scenarios.

Cite As Get BibTex

Finn Moltmann, Tamio-Vesa Nakajima, and Sebastian Wild. Virtual-Memory Powersort. In 34th Annual European Symposium on Algorithms (ESA 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 388, pp. 14:1-14:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026) https://doi.org/10.4230/LIPIcs.ESA.2026.14

Author Details

Finn Moltmann
  • Philipps-Universität Marburg, Germany
Tamio-Vesa Nakajima
  • Philipps-Universität Marburg, Germany
Sebastian Wild
  • Philipps-Universität Marburg, Germany
  • University of Liverpool, UK

Funding

  • Wild, Sebastian: Supported by EPSRC grant EP/X039447/2.

Acknowledgements

Note: Where we were aware of both a conference and a full paper, we cite both to give credit to both the definitive version and the venue of first dissemination.

Supplementary Materials

References

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    Software Heritage Logo archived version
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