Size-time complexity of Boolean networks for prefix computations

  • Authors:
  • G. Bilardi;F. P. Preparata

  • Affiliations:
  • Cornell Univ., Ithaca, NY;Univ. of Illinois at Urbana-Champaign, Urbana

  • Venue:
  • Journal of the ACM (JACM)
  • Year:
  • 1989

Quantified Score

Hi-index 0.00

Visualization

Abstract

The prefix problem consists of computing all the products x0x1 … xj (j = 0, … , N - 1), given a sequence x = (x0, x1, … , xN-1) of elements in a semigroup. In this paper we completely characterize the size-time complexity of computing prefixes with Boolean networks, which are synchronized interconnections of Boolean gates and one-bit storage devices. This complexity crucially depends upon two properties of the underlying semigroup, which we call cycle-freedom (no cycle of length greater than one in the Cayley graph of the semigroup), and memory-induciveness (arbitrarily long products of semigroup elements are true functions of all their factors). A nontrivial characterization is given of non-memory-inducive semigroups as those whose recurrent subsemigroup (formed by the elements with self-loops in the Cayley graph) is the direct product of a left-zero semigroup and a right-zero semigroup. Denoting by S and T size and computation time, respectively, we have S = &THgr;((N/T)log(N/T)) for memory-inducive non-cycle-free semigroups, and S = &THgr;(N/T) for all other semigroups. We have T &egr; [&OHgr;(log N), &Ogr;(N)] for all semigroups, with the exception of those whose recurrent subsemigroup is a right-zero semigroup, for which T &egr; [&OHgr;(1), &Ogr;(N)]. The preceding results are also extended to the VLSI model of computation. Area-time optimal circuits are obtained for both boundary and nonboundary I/O protocols.