/// <summary>
/// Creates a tree from the given chunks. Children are grouped to increase the likelihood of node reuse.
/// </summary>
private static DedupNode CreateRollingHashTree(IReadOnlyList <DedupNode> chunks)
{
// If we do need to make a tree, then we'll want to use a rolling hash function to ensure
// that we get consistent groupings of children nodes even with insertions/removals
// of children (i.e. changes to the underlying file).
var rolling = new RollingHash(
windowLength: 4,
bitMask: VariableChildCountBitMask,
minCount: MinVariableChildCount);
var thisLevel = new Queue <DedupNode>(chunks);
while (thisLevel.Count > DedupNode.MaxDirectChildrenPerNode)
{
var nextLevel = new Queue <DedupNode>();
while (thisLevel.Any())
{
rolling.Reset();
var nodesForChild = new List <DedupNode>();
while (thisLevel.Any() && nodesForChild.Count < DedupNode.MaxDirectChildrenPerNode && !rolling.IsAtBoundary)
{
var node = thisLevel.Dequeue();
ulong nodeHash = 0;
nodeHash ^= BitConverter.ToUInt64(node.Hash, 0);
nodeHash ^= BitConverter.ToUInt64(node.Hash, 8);
nodeHash ^= BitConverter.ToUInt64(node.Hash, 16);
nodeHash ^= BitConverter.ToUInt64(node.Hash, 24);
rolling.Add(nodeHash);
nodesForChild.Add(node);
}
var newNode = new DedupNode(nodesForChild);
nextLevel.Enqueue(newNode);
}
thisLevel = nextLevel;
}
var root = new DedupNode(thisLevel.ToList());
return(root);
}
