Area and Perimeter Computation of the Union of a Set of Iso-Rectangles in Parallel

Finding the area and perimeter of the union/intersection of a set of iso-rectangles is a very important part of circuit extraction in VLSI design. We combine two techniques, the uniform grid and the vertex neighborhoods, to develop a new parallel algorithm for the area and perimeter problems which has an average linear time performance but is not worst-case optimal. The uniform grid technique has been used to generate the candidate vertices of the union or intersection of the rectangles. An efficient point-in-rectangles inclusion test filters the candidate set to obtain the relevant vertices of the union or intersection. Finally, the vertex neighborhood technique is used to compute the mass properties from these vertices. This algorithm has an average time complexity of O(((n + k)/p) + log p) where n is the number of input rectangle edges with k intersections on p processors assuming a PRAM model of computation. The analysis of the algorithm on a SIMD architecture is also presented. This algorithm requires very simple data structures which makes the implementation easy. We have implemented the algorithm on a Sun 4/280 workstation and a Connection Machine. The sequential implementation performs better than the optimal algorithm for large datasets. The parallel implementation on a Connection Machine CM-2 with 32K processors also shows good results.