Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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;
- double BestMoveChanges;
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)
{
th->history.clear();
th->counterMoves.clear();
}
+
+ Threads.main()->previousScore = VALUE_INFINITE;
}
/// 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();
if (th != this)
th->wait_for_search_finished();
- // Check if there are threads with a better score than main thread.
+ // Check if there are threads with a better score than main thread
Thread* bestThread = this;
- if (Options["MultiPV"] == 1 && !Skill(Options["Skill Level"]).enabled())
+ if ( !this->easyMovePlayed
+ && Options["MultiPV"] == 1
+ && !Skill(Options["Skill Level"]).enabled())
+ {
for (Thread* th : Threads)
if ( th->completedDepth > bestThread->completedDepth
&& th->rootMoves[0].score > bestThread->rootMoves[0].score)
- bestThread = th;
+ bestThread = th;
+ }
+
+ previousScore = bestThread->rootMoves[0].score;
- // Send new PV when needed.
- // FIXME: Breaks multiPV, and skill levels
+ // Send new PV when needed
if (bestThread != this)
sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl;
// 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() {
Stack stack[MAX_PLY+4], *ss = stack+2; // To allow referencing (ss-2) and (ss+2)
Value bestValue, alpha, beta, delta;
Move easyMove = MOVE_NONE;
- bool isMainThread = (this == Threads.main());
+ MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
std::memset(ss-2, 0, 5 * sizeof(Stack));
beta = VALUE_INFINITE;
completedDepth = DEPTH_ZERO;
- if (isMainThread)
+ if (mainThread)
{
easyMove = EasyMove.get(rootPos.key());
EasyMove.clear();
- BestMoveChanges = 0;
+ mainThread->easyMovePlayed = mainThread->failedLow = false;
+ mainThread->bestMoveChanges = 0;
TT.new_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
- if (!isMainThread)
- rootDepth = std::min(DEPTH_MAX - ONE_PLY, Threads.main()->rootDepth + Depth(int(2.2 * log(1 + this->idx))));
+ // 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();
+
+ if (idx <= 6 || idx > 24)
+ {
+ if (((d + idx) >> (msb(idx + 1) - 1)) % 2)
+ continue;
+ }
+ else
+ {
+ // Table of values of 6 bits with 3 of them set
+ static const int HalfDensityMap[] = {
+ 0x07, 0x0b, 0x0d, 0x0e, 0x13, 0x16, 0x19, 0x1a, 0x1c,
+ 0x23, 0x25, 0x26, 0x29, 0x2c, 0x31, 0x32, 0x34, 0x38
+ };
+
+ if ((HalfDensityMap[idx - 7] >> (d % 6)) & 1)
+ continue;
+ }
+ }
// Age out PV variability metric
- if (isMainThread)
- BestMoveChanges *= 0.5;
+ if (mainThread)
+ mainThread->bestMoveChanges *= 0.505, mainThread->failedLow = false;
// Save the last iteration's scores before first PV line is searched and
// all the move scores except the (new) PV are set to -VALUE_INFINITE.
// 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;
// When failing high/low give some update (without cluttering
// the UI) before a re-search.
- if ( isMainThread
+ if ( mainThread
&& multiPV == 1
&& (bestValue <= alpha || bestValue >= beta)
&& Time.elapsed() > 3000)
beta = (alpha + beta) / 2;
alpha = std::max(bestValue - delta, -VALUE_INFINITE);
- if (isMainThread)
+ if (mainThread)
{
- Signals.failedLowAtRoot = true;
+ mainThread->failedLow = true;
Signals.stopOnPonderhit = false;
}
}
// Sort the PV lines searched so far and update the GUI
std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1);
- if (!isMainThread)
+ if (!mainThread)
break;
if (Signals.stop)
if (!Signals.stop)
completedDepth = rootDepth;
- if (!isMainThread)
+ if (!mainThread)
continue;
// If skill level is enabled and time is up, pick a sub-optimal best move
{
// Take some extra time if the best move has changed
if (rootDepth > 4 * ONE_PLY && multiPV == 1)
- Time.pv_instability(BestMoveChanges);
+ 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.
+ const bool F[] = { !mainThread->failedLow,
+ bestValue >= mainThread->previousScore };
+
+ int improvingFactor = 640 - 160*F[0] - 126*F[1] - 124*F[0]*F[1];
+
+ bool doEasyMove = rootMoves[0].pv[0] == easyMove
+ && mainThread->bestMoveChanges < 0.03
+ && Time.elapsed() > Time.available() * 25 / 206;
+
if ( rootMoves.size() == 1
- || Time.elapsed() > Time.available()
- || ( rootMoves[0].pv[0] == easyMove
- && BestMoveChanges < 0.03
- && Time.elapsed() > Time.available() / 10))
+ || Time.elapsed() > Time.available() * improvingFactor / 640
+ || (mainThread->easyMovePlayed = doEasyMove))
{
// If we are allowed to ponder do not stop the search now but
// keep pondering until the GUI sends "ponderhit" or "stop".
}
}
- if (!isMainThread)
+ if (!mainThread)
return;
// Clear any candidate easy move that wasn't stable for the last search
// iterations; the second condition prevents consecutive fast moves.
- if (EasyMove.stableCnt < 6 || Time.elapsed() < Time.available())
+ if (EasyMove.stableCnt < 6 || mainThread->easyMovePlayed)
EasyMove.clear();
// If skill level is enabled, swap best PV line with the sub-optimal one
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;
assert(0 <= ss->ply && ss->ply < MAX_PLY);
- ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
- (ss+1)->skipEarlyPruning = false; (ss+1)->reduction = DEPTH_ZERO;
+ ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
+ (ss+1)->skipEarlyPruning = false;
(ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
// Step 4. Transposition table lookup. We don't want the score of a partial
posKey = excludedMove ? pos.exclusion_key() : pos.key();
tte = TT.probe(posKey, ttHit);
ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
- ss->ttMove = ttMove = RootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
- : ttHit ? tte->move() : MOVE_NONE;
+ ttMove = RootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
+ : ttHit ? tte->move() : MOVE_NONE;
// At non-PV nodes we check for an early TT cutoff
if ( !PvNode
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);
ss->moveCount = ++moveCount;
- if (RootNode && thisThread == Threads.main())
- {
- Signals.firstRootMove = (moveCount == 1);
-
- if (Time.elapsed() > 3000)
- sync_cout << "info depth " << depth / ONE_PLY
- << " currmove " << UCI::move(move, pos.is_chess960())
- << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl;
- }
+ if (RootNode && thisThread == Threads.main() && Time.elapsed() > 3000)
+ sync_cout << "info depth " << depth / ONE_PLY
+ << " currmove " << UCI::move(move, pos.is_chess960())
+ << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl;
if (PvNode)
(ss+1)->pv = nullptr;
// re-searched at full depth.
if ( depth >= 3 * ONE_PLY
&& moveCount > 1
- && !captureOrPromotion
- && move != ss->killers[0]
- && move != ss->killers[1])
+ && !captureOrPromotion)
{
-
ss->reduction = reduction<PvNode>(improving, depth, moveCount);
+
Depth r = reduction<PvNode>(improving, depth, moveCount);
// Increase reduction for cut nodes and moves with a bad history
if ( (!PvNode && cutNode)
|| ( thisThread->history[pos.piece_on(to_sq(move))][to_sq(move)] < VALUE_ZERO
&& cmh[pos.piece_on(to_sq(move))][to_sq(move)] <= VALUE_ZERO))
- ss->reduction += ONE_PLY;
-
- // Decrease reduction for moves with a good history
- if ( thisThread->history[pos.piece_on(to_sq(move))][to_sq(move)] > VALUE_ZERO
- && cmh[pos.piece_on(to_sq(move))][to_sq(move)] > VALUE_ZERO)
- ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
-
- // Decrease reduction for moves that escape a capture
- if ( ss->reduction
+ r += ONE_PLY;
+
+ // Decrease/increase reduction for moves with a good/bad history
+ int rHist = ( 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 - rHist * ONE_PLY);
+
+ // 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
&& pos.see(make_move(to_sq(move), from_sq(move))) < VALUE_ZERO)
- ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
+ r = std::max(DEPTH_ZERO, r - ONE_PLY);
- Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
+ Depth d = std::max(newDepth - r, ONE_PLY);
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
- doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
- ss->reduction = DEPTH_ZERO;
+ doFullDepthSearch = (value > alpha && r != DEPTH_ZERO);
}
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.
// iteration. This information is used for time management: When
// the best move changes frequently, we allocate some more time.
if (moveCount > 1 && thisThread == Threads.main())
- ++BestMoveChanges;
+ ++static_cast<MainThread*>(thisThread)->bestMoveChanges;
}
else
// All other moves but the PV are set to the lowest value: this is
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
if (Limits.ponder)
return;
- if (Limits.use_time_management())
- {
- bool stillAtFirstMove = Signals.firstRootMove.load(std::memory_order_relaxed)
- && !Signals.failedLowAtRoot.load(std::memory_order_relaxed)
- && elapsed > Time.available() * 3 / 4;
-
- if (stillAtFirstMove || elapsed > Time.maximum() - 10)
- Signals.stop = true;
- }
- else if (Limits.movetime && elapsed >= Limits.movetime)
- Signals.stop = true;
-
- else if (Limits.nodes && Threads.nodes_searched() >= Limits.nodes)
+ if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10)
+ || (Limits.movetime && elapsed >= Limits.movetime)
+ || (Limits.nodes && Threads.nodes_searched() >= Limits.nodes))
Signals.stop = true;
}
/// 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