// --------------------------------------------------------------------------------------------
static void ProcessNode(PositionEvalCache cache, MCTSNode node, float weightEmpirical,
bool saveToCache, bool rewriteNodeInTree)
{
Span <MCTSNodeStructChild> children = node.Ref.Children;
// TODO: optimize this away if saveToCache is false
ushort[] probabilities = new ushort[node.NumPolicyMoves];
ushort[] indices = new ushort[node.NumPolicyMoves];
// Compute empirical visit distribution
float[] nodeFractions = new float[node.NumPolicyMoves];
for (int i = 0; i < node.NumChildrenExpanded; i++)
{
nodeFractions[i] = (float)node.ChildAtIndex(i).N / (float)node.N;
}
// Determine P of first unexpanded node
// We can't allow any child to have a new P less than this
// since we need to keep them in order by P and the resorting logic below
// can only operate over expanded nodes
float minP = 0;
if (node.NumChildrenExpanded < node.NumPolicyMoves)
{
minP = node.ChildAtIndexInfo(node.NumChildrenExpanded).p;
}
// Add each move to the policy vector with blend of prior and empirical values
for (int i = 0; i < node.NumChildrenExpanded; i++)
{
(MCTSNode node, EncodedMove move, FP16 p)info = node.ChildAtIndexInfo(i);
indices[i] = (ushort)info.move.IndexNeuralNet;
float newValue = (1.0f - weightEmpirical) * info.p
+ weightEmpirical * nodeFractions[i];
if (newValue < minP)
{
newValue = minP;
}
probabilities[i] = CompressedPolicyVector.EncodedProbability(newValue);
if (rewriteNodeInTree && weightEmpirical != 0)
{
MCTSNodeStructChild thisChild = children[i];
if (thisChild.IsExpanded)
{
ref MCTSNodeStruct childNodeRef = ref thisChild.ChildRef;
thisChild.ChildRef.P = (FP16)newValue;
}
else
{
node.Ref.ChildAtIndex(i).SetUnexpandedPolicyValues(thisChild.Move, (FP16)newValue);
}
}
}
internal static void Repack(MCTSNode node, ref CompressedPolicyVector policy)
{
Span <ushort> indicies = stackalloc ushort[node.NumPolicyMoves];
Span <ushort> probabilities = stackalloc ushort[node.NumPolicyMoves];
for (int i = 0; i < node.NumPolicyMoves; i++)
{
ref MCTSNodeStructChild childRef = ref node.ChildAtIndexRef(i);
indicies[i] = (ushort)childRef.Move.IndexNeuralNet;
probabilities[i] = CompressedPolicyVector.EncodedProbability(childRef.P);
}