An efficient algorithm for optimal PLA folding

A three-step heuristic algorithm for PLA column folding and row folding of column-folded PLA is presented. The algorithm is significantly faster than earlier algorithms and provides nearly optimal results. The three steps are min-cut partition of vertices in the column (or row) intersection graph, determination of product order using Fiduccia's min-net cut algorithm, and head-tail pairing for column folding (some heuristics are proposed for deciding row folding pairs). The time complexity of this algorithm is O(n/sup 2/ log n), compared to the O(n/sup 3/) to O(n/sup 4/) of the earlier algorithms. For a test PLA with 23 inputs, 19 outputs, and 52 products, the number of column folding pairs obtained using this algorithm is 20, which is optimal compared to the 17 obtained previously.<>