/** Returns the best move to make from here during a playout. */
short bestSearchMove(SearchNode node, McRunnable runnable) {
final Board runnableBoard = runnable.getBoard();
final MersenneTwisterFast random = runnable.getRandom();
short result = node.getWinningMove();
if (result != NO_POINT && runnableBoard.isLegal(result)) {
// The isLegal() check is necessary to avoid superko violations
return result;
}
float bestSearchValue = searchValue(node, PASS);
result = PASS;
final ShortSet vacantPoints = runnableBoard.getVacantPoints();
int start;
start = random.nextInt(vacantPoints.size());
int i = start;
final int skip = PRIMES[random.nextInt(PRIMES.length)];
do {
final short move = vacantPoints.get(i);
final float searchValue = searchValue(node, move);
if (searchValue > bestSearchValue) {
if (runnable.isFeasible(move) && runnableBoard.isLegal(move)) {
bestSearchValue = searchValue;
result = move;
} else {
node.exclude(move);
}
}
// Advancing by a random prime skips through the array
// in a manner analogous to double hashing.
i = (i + skip) % vacantPoints.size();
} while (i != start);
return result;
}
/** Some nodes may have their biases updated. */
@Override
public void descend(McRunnable runnable) {
SearchNode node = getRoot();
assert node != null : "Fancy hash code: " + board.getFancyHash();
while (runnable.getBoard().getPasses() < 2) {
selectAndPlayMove(node, runnable);
final SearchNode child = table.findIfPresent(runnable.getBoard().getFancyHash());
if (child == null) {
return; // No child
}
if (child.getTotalRuns() > biasDelay && !child.biasUpdated()) {
child.updateBias(runnable);
}
node = child;
}
}
@Override
public void fakeDescend(McRunnable runnable, short... moves) {
runnable.copyDataFrom(board);
final SearchNode node = getRoot();
assert node != null : "Fancy hash code: " + board.getFancyHash();
for (final short move : moves) {
System.out.println("Passing " + move + " to runnable");
runnable.acceptMove(move);
final SearchNode child = table.findIfPresent(runnable.getBoard().getFancyHash());
if (child == null) {
return; // No child
}
if (child.getTotalRuns() > biasDelay && !child.biasUpdated()) {
child.updateBias(runnable);
}
}
}
/** Selects and plays one move in the search tree. */
short selectAndPlayMove(SearchNode node, McRunnable runnable) {
final short move = bestSearchMove(node, runnable);
runnable.acceptMove(move);
return move;
}