namespace {
- // Different node types, used as template parameter
+ // Different node types, used as a template parameter
enum NodeType { Root, PV, NonPV };
// Razoring and futility margin based on depth
return Reductions[PvNode][i][std::min(d, 63 * ONE_PLY)][std::min(mn, 63)];
}
- // Skill struct is used to implement strength limiting
+ // Skill structure is used to implement strength limit
struct Skill {
Skill(int l) : level(l) {}
bool enabled() const { return level < 20; }
Move best = MOVE_NONE;
};
- // EasyMoveManager struct is used to detect a so called 'easy move'; when PV is
- // stable across multiple search iterations we can fast return the best move.
+ // EasyMoveManager structure is used to detect an 'easy move'. When the PV is
+ // stable across multiple search iterations, we can quickly return the best move.
struct EasyMoveManager {
void clear() {
assert(newPv.size() >= 3);
- // Keep track of how many times in a row 3rd ply remains stable
+ // Keep track of how many times in a row the 3rd ply remains stable
stableCnt = (newPv[2] == pv[2]) ? stableCnt + 1 : 0;
if (!std::equal(newPv.begin(), newPv.begin() + 3, pv))
EasyMoveManager EasyMove;
Value DrawValue[COLOR_NB];
- CounterMovesHistoryStats CounterMovesHistory;
+ CounterMoveHistoryStats CounterMoveHistory;
template <NodeType NT>
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
}
-/// Search::clear() resets to zero search state, to obtain reproducible results
+/// Search::clear() resets search state to zero, to obtain reproducible results
void Search::clear() {
TT.clear();
- CounterMovesHistory.clear();
+ CounterMoveHistory.clear();
for (Thread* th : Threads)
{
/// Search::perft() is our utility to verify move generation. All the leaf nodes
-/// up to the given depth are generated and counted and the sum returned.
+/// up to the given depth are generated and counted, and the sum is returned.
template<bool Root>
uint64_t Search::perft(Position& pos, Depth depth) {
/// MainThread::search() is called by the main thread when the program receives
-/// the UCI 'go' command. It searches from root position and at the end prints
-/// the "bestmove" to output.
+/// the UCI 'go' command. It searches from the root position and outputs the "bestmove".
void MainThread::search() {
if (TB::Cardinality >= rootPos.count<ALL_PIECES>(WHITE)
+ rootPos.count<ALL_PIECES>(BLACK))
{
- // If the current root position is in the tablebases then RootMoves
- // contains only moves that preserve the draw or win.
+ // If the current root position is in the tablebases, then RootMoves
+ // contains only moves that preserve the draw or the win.
TB::RootInTB = Tablebases::root_probe(rootPos, rootMoves, TB::Score);
if (TB::RootInTB)
else // If DTZ tables are missing, use WDL tables as a fallback
{
- // Filter out moves that do not preserve a draw or win
+ // Filter out moves that do not preserve the draw or the win.
TB::RootInTB = Tablebases::root_probe_wdl(rootPos, rootMoves, TB::Score);
// Only probe during search if winning
}
// When playing in 'nodes as time' mode, subtract the searched nodes from
- // the available ones before to exit.
+ // the available ones before exiting.
if (Limits.npmsec)
Time.availableNodes += Limits.inc[us] - Threads.nodes_searched();
// Thread::search() is the main iterative deepening loop. It calls search()
// repeatedly with increasing depth until the allocated thinking time has been
-// consumed, user stops the search, or the maximum search depth is reached.
+// consumed, the user stops the search, or the maximum search depth is reached.
void Thread::search() {
multiPV = std::min(multiPV, rootMoves.size());
- // Iterative deepening loop until requested to stop or target depth reached
+ // Iterative deepening loop until requested to stop or the target depth is reached.
while (++rootDepth < DEPTH_MAX && !Signals.stop && (!Limits.depth || rootDepth <= Limits.depth))
{
- // Set up the new depth for the helper threads skipping in average each
- // 2nd ply (using a half density map similar to a Hadamard matrix).
+ // Set up the new depths for the helper threads skipping on average every
+ // 2nd ply (using a half-density map similar to a Hadamard matrix).
if (!mainThread)
{
int d = rootDepth + rootPos.game_ply();
// search the already searched PV lines are preserved.
std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end());
- // Write PV back to transposition table in case the relevant
+ // Write PV back to the transposition table in case the relevant
// entries have been overwritten during the search.
for (size_t i = 0; i <= PVIdx; ++i)
rootMoves[i].insert_pv_in_tt(rootPos);
- // If search has been stopped break immediately. Sorting and
+ // If search has been stopped, break immediately. Sorting and
// writing PV back to TT is safe because RootMoves is still
- // valid, although it refers to previous iteration.
+ // valid, although it refers to the previous iteration.
if (Signals.stop)
break;
if (rootDepth > 4 * ONE_PLY && multiPV == 1)
Time.pv_instability(mainThread->bestMoveChanges);
- // Stop the search if only one legal move is available or all
- // of the available time has been used or we matched an easyMove
+ // Stop the search if only one legal move is available, or if all
+ // of the available time has been used, or if we matched an easyMove
// from the previous search and just did a fast verification.
if ( rootMoves.size() == 1
- || Time.elapsed() > Time.available() * ( 640 - 160 * !mainThread->failedLow
- - 126 * (bestValue >= mainThread->previousMoveScore)
+ || Time.elapsed() > Time.available() * ( 640 - 160 * !mainThread->failedLow
+ - 126 * (bestValue >= mainThread->previousMoveScore)
- 124 * (bestValue >= mainThread->previousMoveScore && !mainThread->failedLow))/640
|| ( mainThread->easyMovePlayed = ( rootMoves[0].pv[0] == easyMove
&& mainThread->bestMoveChanges < 0.03
bestValue = -VALUE_INFINITE;
ss->ply = (ss-1)->ply + 1;
- // Check for available remaining time
+ // Check for the available remaining time
if (thisThread->resetCalls.load(std::memory_order_relaxed))
{
thisThread->resetCalls = false;
Square prevSq = to_sq((ss-1)->currentMove);
Move cm = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
- const CounterMovesStats& cmh = CounterMovesHistory[pos.piece_on(prevSq)][prevSq];
+ const CounterMoveStats& cmh = CounterMoveHistory[pos.piece_on(prevSq)][prevSq];
MovePicker mp(pos, ttMove, depth, thisThread->history, cmh, cm, ss);
CheckInfo ci(pos);
// Decrease reduction for moves with a good history and
// increase reduction for moves with a bad history
- int rDecrease = ( thisThread->history[pos.piece_on(to_sq(move))][to_sq(move)]
+ int rDecrease = ( thisThread->history[pos.piece_on(to_sq(move))][to_sq(move)]
+ cmh[pos.piece_on(to_sq(move))][to_sq(move)]) / 14980;
r = std::max(DEPTH_ZERO, r - rDecrease * ONE_PLY);
- // Decrease reduction for moves that escape a capture. Filter out castling
- // moves because are coded as "king captures rook" and break make_move().
- // Also use see() instead of see_sign() because destination square is empty.
+ // Decrease reduction for moves that escape a capture. Filter out
+ // castling moves, because they are coded as "king captures rook" and
+ // hence break make_move(). Also use see() instead of see_sign(),
+ // because the destination square is empty.
if ( r
&& type_of(move) == NORMAL
&& type_of(pos.piece_on(to_sq(move))) != PAWN
else
doFullDepthSearch = !PvNode || moveCount > 1;
- // Step 16. Full depth search, when LMR is skipped or fails high
+ // Step 16. Full depth search when LMR is skipped or fails high
if (doFullDepthSearch)
value = newDepth < ONE_PLY ?
givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
// For PV nodes only, do a full PV search on the first move or after a fail
// high (in the latter case search only if value < beta), otherwise let the
- // parent node fail low with value <= alpha and to try another move.
+ // parent node fail low with value <= alpha and try another move.
if (PvNode && (moveCount == 1 || (value > alpha && (RootNode || value < beta))))
{
(ss+1)->pv = pv;
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
- // Step 18. Check for new best move
+ // Step 18. Check for a new best move
// Finished searching the move. If a stop occurred, the return value of
// the search cannot be trusted, and we return immediately without
// updating best move, PV and TT.
quietsSearched[quietCount++] = move;
}
- // Following condition would detect a stop only after move loop has been
+ // The following condition would detect a stop only after move loop has been
// completed. But in this case bestValue is valid because we have fully
// searched our subtree, and we can anyhow save the result in TT.
/*
// Step 20. Check for mate and stalemate
// All legal moves have been searched and if there are no legal moves, it
- // must be mate or stalemate. If we are in a singular extension search then
+ // must be a mate or a stalemate. If we are in a singular extension search then
// return a fail low score.
if (!moveCount)
bestValue = excludedMove ? alpha
{
Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1);
Square prevPrevSq = to_sq((ss - 2)->currentMove);
- CounterMovesStats& prevCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
+ CounterMoveStats& prevCmh = CounterMoveHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
prevCmh.update(pos.piece_on(prevSq), prevSq, bonus);
}
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
- // Check for new best move
+ // Check for a new best move
if (value > bestValue)
{
bestValue = value;
Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1);
Square prevSq = to_sq((ss-1)->currentMove);
- CounterMovesStats& cmh = CounterMovesHistory[pos.piece_on(prevSq)][prevSq];
+ CounterMoveStats& cmh = CounterMoveHistory[pos.piece_on(prevSq)][prevSq];
Thread* thisThread = pos.this_thread();
thisThread->history.update(pos.moved_piece(move), to_sq(move), bonus);
&& is_ok((ss-2)->currentMove))
{
Square prevPrevSq = to_sq((ss-2)->currentMove);
- CounterMovesStats& prevCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
+ CounterMoveStats& prevCmh = CounterMoveHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
prevCmh.update(pos.piece_on(prevSq), prevSq, -bonus - 2 * (depth + 1) / ONE_PLY);
}
}
int maxScore = -VALUE_INFINITE;
// Choose best move. For each move score we add two terms, both dependent on
- // weakness. One deterministic and bigger for weaker levels, and one random,
- // then we choose the move with the resulting highest score.
+ // weakness. One is deterministic and bigger for weaker levels, and one is
+ // random. Then we choose the move with the resulting highest score.
for (size_t i = 0; i < multiPV; ++i)
{
// This is our magic formula
/// RootMove::extract_ponder_from_tt() is called in case we have no ponder move
-/// before exiting the search, for instance in case we stop the search during a
+/// before exiting the search, for instance, in case we stop the search during a
/// fail high at root. We try hard to have a ponder move to return to the GUI,
/// otherwise in case of 'ponder on' we have nothing to think on.
projects / stockfish / blobdiff