next up previous contents index
Next: 12.7.2 The Bitonic Algorithm Up: 12.7 Sorting Previous: 12.7 Sorting

12.7.1 The Merge Strategy

In the merging strategy to be used by our sorting algorithms, the first step is for each processor to sort its own sublist using some fast algorithm. We take for this a combined quicksort/insertion sort which is described in detail as Algorithm Q by Knuth ([Knuth:73a, pp. 118-9]). Once the local (processor) sort is complete, it must be decided how to merge all of the sorted lists in order to form one globally sorted list. This is done in a series of compare-exchange steps. In each step, two neighboring processors exchange items so that each processor ends up with a sorted list and all of the items in one processor are greater than all of the items in the other. Thus, two sorted lists of m items each are merged into a sorted list of 2m items (stored collectively in the memory of the two processors). The compare-exchange algorithm is interesting in its own right, but we do not have the space here to discuss it. The reader is referred to Chapter 18 of [Fox:88a] for the details.

Guy Robinson
Wed Mar 1 10:19:35 EST 1995