private List <File> SortPhase(File sourceFile, uint bufferSize, int nSortRuns)
{
SortBuffer sortBuffer = new SortBuffer(
nBlocks: bufferSize,
blockSize: sourceFile.blockSize);
List <File> runFiles = new List <File>();
for (int runIndex = 0; runIndex < nSortRuns; runIndex++)
{
var outFile = SortPass(sourceFile, bufferSize, sortBuffer, runIndex);
runFiles.Add(outFile);
}
return(runFiles);
}
private File SortPass(File sourceFile, uint bufferSize, SortBuffer sortBuffer, int runIndex = 0)
{
sortBuffer.loadBlocks(
sourceFile: sourceFile,
startingBlock: (int)(runIndex * bufferSize)
);
sortBuffer.Sort();
File outFile = new File(
nBlocks: bufferSize,
blockSize: sourceFile.blockSize,
initializer: 0);
sortBuffer.writeBack(outFile);
return(outFile);
}
//TODO: add block transfer counting to evaluate performance
public File ExternalMergeSort(File sourceFile, uint bufferSize)
{
//Check wether there is enough blocks in the buffer?
File sortedFile;
int nSortRuns = (int)Math.Ceiling((decimal)(sourceFile.nBlocks / bufferSize));
if (nSortRuns > 1)
{
var runFiles = SortPhase(sourceFile, bufferSize, nSortRuns);
sortedFile = MergePhase(sourceFile, bufferSize, runFiles);
}
else
{
SortBuffer sortBuffer = new SortBuffer(
nBlocks: bufferSize,
blockSize: sourceFile.blockSize);
sortedFile = SortPass(sourceFile, bufferSize, sortBuffer);
}
return(sortedFile);
}