public void Sort(string[] entries, Int32 first, Int32 last)
{
var length = last + 1 - first;
while (length > 1)
{
if (length < InsertionLimit)
{
InsertionSort.Sort(entries, first, last);
return;
}
Left = first;
Right = last;
pivot(entries);
partition(entries);
//[Note]Right < Left
var leftLength = Right + 1 - first;
var rightLength = last + 1 - Left;
//
// First recurse over shorter partition, then loop
// on the longer partition to elide tail recursion.
//
if (leftLength < rightLength)
{
Sort(entries, first, Right);
first = Left;
length = rightLength;
}
else
{
Sort(entries, Left, last);
last = Right;
length = leftLength;
}
}
}
private void pivot(string[] entries)
{
//
// An odd sample size is chosen based on the log of the interval size.
// The median of a randomly chosen set of samples is then returned as
// an estimate of the true median.
//
var length = Right + 1 - Left;
var logLen = (Int32)Math.Log10(length);
var pivotSamples = 2 * logLen + 1;
var sampleSize = Math.Min(pivotSamples, length);
var last = Left + sampleSize - 1;
// Sample without replacement
for (var first = Left; first <= last; first++)
{
// Random sampling avoids pathological cases
var random = Random.Next(first, Right + 1);
Swap(entries, first, random);
}
InsertionSort.Sort(entries, Left, last);
Median = entries[Left + sampleSize / 2];
}
