COMPUTING ON RECONFIGURABLE BUSES—A NEW COMPUTATIONAL PARADIGM

Abstract

Up to now, buses have been used exclusively to ferry data around. The contribution of this work is to show that buses can be used both as topological descriptors and as powerful computational devices. We illustrate the power of this paradigm by designing two fast algorithms for image segmentation and parallel visibility. Our algorithm for image segmentation uses a novel technique invol ving building a bus around every region of interest in the image. With a binary image pretiled in the natural way on a reconfigurable mesh of size N×N our segmentation algorithm runs in O( log N) time, improving by a factor of O( log N) over the state of the art. Next, we exhibit a very simple algorithm to solve the parallel visibility problem on an image of size N×N. Our algorithm runs in O( log N) time. The only previously-known algorithm for this problem runs in O( log N) time on a hypercube with N processors. To support these algorithms, a set of basic building blocks are developed which are of independent interest. These include solutions to the following problems on a bus on length N: (1) computing the prefix maxima of items stored by the processors on the bus, even if none of the processors knows its rank on the bus; (2) computing the rank of every processor on the bus; (3) electing a leader on a closed bus.