Note: Minimization of circuit registers: Retiming revisited

  • Authors:
  • Bruno Gaujal;Jean Mairesse

  • Affiliations:
  • INRIA, LIG (CNRS, UJF, INPG), 51 Av. J. Kuntzmann, 38330 Montbonnot, France;CNRS, LIAFA (Université Paris 7), Case 7014, 2 place Jussieu, 75251 Paris Cedex 05, France

  • Venue:
  • Discrete Applied Mathematics
  • Year:
  • 2008

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Abstract

We address the following problem: given a synchronous digital circuit, is it possible to construct a new circuit computing the same function as the original one but using a minimal number of registers? We show that the minimal number of registers is the size of the minimal cut on a bi-infinite graph, namely the unfolding of the dependencies in the digital circuit. Furthermore, the construction of such a cut and the corresponding circuit can be done in polynomial time, using a max-flow min-cut result of Orlin for one-periodic bi-infinite graphs. Finally, we show the relation between this construction and the retiming technique introduced by Leiserson and Saxe.