// sequential variant (deeper levels)
void TopDownSplitMergeSeq(int *src, int begin, int end, int *dest) {
if (end - begin < 2)
return;
int middle = (end + begin)/2;
TopDownSplitMergeSeq(src, begin, middle, dest);
TopDownSplitMergeSeq(src, middle, end, dest);
TopDownMerge(src, begin, middle, end, dest);
memcpy(src + begin, dest + begin, sizeof(int) * (end - begin));
}
TopDownSplitMerge(A[], iBegin, iEnd, B[])
{
if(iEnd - iBegin < 2) // if run size == 1
return; // consider it sorted
// recursively split runs into two halves until run size == 1,
// then merge them and return back up the call chain
iMiddle = (iEnd + iBegin) / 2; // iMiddle = mid point
TopDownSplitMerge(A, iBegin, iMiddle, B); // split / merge left half
TopDownSplitMerge(A, iMiddle, iEnd, B); // split / merge right half
TopDownMerge(A, iBegin, iMiddle, iEnd, B); // merge the two half runs
CopyArray(B, iBegin, iEnd, A); // copy the merged runs back to A
}
// parallelized variant (highest levels)
void TopDownSplitMerge(int *src, int begin, int end, int *dest, int depth) {
if (end - begin < 2)
return;
// Once we've reached the desired depth, move to the sequential version.
if (depth > max_depth) {
TopDownSplitMergeSeq(src, begin, end, dest);
return;
}
int middle = (end + begin)/2;
#pragma omp parallel sections num_threads(2)
{
#pragma omp section
TopDownSplitMerge(src, begin, middle, dest, depth + 1);
#pragma omp section
TopDownSplitMerge(src, middle, end, dest, depth + 1);
}
// Merge the two sorted array into a sorted section of the temporary buffer,
// then copy that temporary buffer back to our main results array.
TopDownMerge(src, begin, middle, end, dest);
memcpy(src + begin, dest + begin, sizeof(int) * (end - begin));
}
