internal ImmutableStack <RopeCacheEntry> FindNodeUsingCache(int index)
{
Debug.Assert(index >= 0 && index < this.Length);
// thread safety: fetch stack into local variable
ImmutableStack <RopeCacheEntry> stack = lastUsedNodeStack;
ImmutableStack <RopeCacheEntry> oldStack = stack;
if (stack == null)
{
stack = ImmutableStack <RopeCacheEntry> .Empty.Push(new RopeCacheEntry(root, 0));
}
while (!stack.PeekOrDefault().IsInside(index))
{
stack = stack.Pop();
}
while (true)
{
RopeCacheEntry entry = stack.PeekOrDefault();
// check if we've reached a leaf or function node
if (entry.node.height == 0)
{
if (entry.node.contents == null)
{
// this is a function node - go down into its subtree
entry = new RopeCacheEntry(entry.node.GetContentNode(), entry.nodeStartIndex);
// entry is now guaranteed NOT to be another function node
}
if (entry.node.contents != null)
{
// this is a node containing actual content, so we're done
break;
}
}
// go down towards leaves
if (index - entry.nodeStartIndex >= entry.node.left.length)
{
stack = stack.Push(new RopeCacheEntry(entry.node.right, entry.nodeStartIndex + entry.node.left.length));
}
else
{
stack = stack.Push(new RopeCacheEntry(entry.node.left, entry.nodeStartIndex));
}
}
// write back stack to volatile cache variable
// (in multithreaded access, it doesn't matter which of the threads wins - it's just a cache)
if (oldStack != stack)
{
// no need to write when we the cache variable didn't change
lastUsedNodeStack = stack;
}
// this method guarantees that it finds a leaf node
Debug.Assert(stack.Peek().node.contents != null);
return(stack);
}