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arXiv · 2107.08824

Verifying a Realistic Mutable Hash Table

Samuel Chassot·Viktor Kunčak
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Abstract

In this work, we verify the mutable LongMap from the Scala standard library, a hash table using open addressing within a single array, using the Stainless program verifier. As a reference implementation, we write an immutable map based on a list of tuples. We then show that LongMap's operations correspond to operations of this association list. To express the resizing of the hash table array, we introduce a new reference swapping construct in Stainless. This allows us to apply the decorator pattern without introducing aliasing. Our verification effort led us to find and fix a bug in the original implementation that manifests for large hash tables. Our performance analysis shows the verified version to be within a 1.5 factor of the original data structure.

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Samuel Chassot, Viktor Kunčak. 2021-07-16. Verifying a Realistic Mutable Hash Table. https://arxiv.org/abs/2107.08824

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