Bounds on the OBDD-size of integer multiplication via universal hashing

  • Authors:
  • Philipp Woelfel

  • Affiliations:
  • Department of Computer Science, University Dortmund, D-44221 Dortmund, Germany

  • Venue:
  • Journal of Computer and System Sciences
  • Year:
  • 2005

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Abstract

Bryant [On the complexity of VLSI implementations and graph representations of boolean functions with applications to integer multiplication, IEEE Trans. Comput. 40 (1991) 205-213] has shown that any OBDD for the function MUL"n"-"1","n, i.e. the middle bit of the n-bit multiplication, requires at least 2^n^/^8 nodes. In this paper a stronger lower bound of essentially 2^n^/^2/61 is proven by a new technique, using a universal family of hash functions. As a consequence, one cannot hope anymore to verify e.g. 128-bit multiplication circuits using OBDD-techniques because the representation of the middle bit of such a multiplier requires more than 3.10^1^7OBDD-nodes. Further, a first non-trivial upper bound of 7/3.2^4^n^/^3 for the OBDD-size of MUL"n"-"1","n is provided.