Language and Automata Theory and Applications

Volume 8370 of the series Lecture Notes in Computer Science pp 236-247

Optimal Sorting Networks

  • Daniel BundalaAffiliated withDepartment of Computer Science, University of Oxford
  • , Jakub ZávodnýAffiliated withDepartment of Computer Science, University of Oxford

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This paper settles the optimality of sorting networks given in The Art of Computer Programming vol. 3 more than 40 years ago. The book lists efficient sorting networks with n ≤ 16 inputs. In this paper we give general combinatorial arguments showing that if a sorting network with a given depth exists then there exists one with a special form. We then construct propositional formulas whose satisfiability is necessary for the existence of such a network. Using a SAT solver we conclude that the listed networks have optimal depth. For n ≤ 10 inputs where optimality was known previously, our algorithm is four orders of magnitude faster than those in prior work.