public static DoubleLinkedList <T> .Node MergeSort(DoubleLinkedList <T> .Node head, Func <T, T, bool> isFirstBefore)
{
int blockSize = 1, blockCount;
do
{
DoubleLinkedList <T> .Node left = head, right = head, tail = null;
head = null;
blockCount = 0;
while (!ReferenceEquals(left, null))
{
blockCount++;
int leftSize = 0, rightSize = blockSize;
for (; leftSize < blockSize && !ReferenceEquals(right, null); ++leftSize)
{
right = right.Next;
}
bool leftEmpty = leftSize == 0,
rightEmpty = rightSize == 0 || ReferenceEquals(right, null);
while (!leftEmpty || !rightEmpty)
{
DoubleLinkedList <T> .Node smaller;
if (rightEmpty || (!leftEmpty && isFirstBefore(left.Value, right.Value)))
{
smaller = left; left = left.Next; --leftSize;
leftEmpty = leftSize == 0;
}
else
{
smaller = right; right = right.Next; --rightSize;
rightEmpty = rightSize == 0 || ReferenceEquals(right, null);
}
if (!ReferenceEquals(tail, null))
{
tail.Next = smaller;
}
else
{
head = smaller;
}
tail = smaller;
}
left = right;
}
if (!ReferenceEquals(tail, null))
{
tail.Next = null;
}
blockSize *= 2;
} while (blockCount > 1);
return(head);
}
