* Restore P2 at seedNode and guarantee that no new violations of P2 appeared.
*/
private void compressDownward(long seedNode) {
double threshold = Math.floor(size / compressionFactor);
// P2 check same as above but shorter and slower (and invoked rarely)
LongArrayFIFOQueue q = new LongArrayFIFOQueue();
q.enqueue(seedNode);
while (!q.isEmpty()) {
long node = q.dequeueLong();
long atNode = get(node);
long atSibling = get(sibling(node));
if (atNode == 0 && atSibling == 0) {
continue;
}
long atParent = get(parent(node));
if (atParent + atNode + atSibling > threshold) {
continue;
}
node2count.addTo(parent(node), atNode + atSibling);
node2count.remove(node);
node2count.remove(sibling(node));
// Now P2 could have vanished at the node's and sibling's subtrees since they decreased.
if (!isLeaf(node)) {
q.enqueue(leftChild(node));
q.enqueue(leftChild(sibling(node)));
}
}
}