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) 2015-2017 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
+ Copyright (C) 2015-2018 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 Search {
- SignalsType Signals;
LimitsType Limits;
}
int FutilityMoveCounts[2][16]; // [improving][depth]
int Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
- // Threshold used for countermoves based pruning
- const int CounterMovePruneThreshold = 0;
-
template <bool PvNode> Depth reduction(bool i, Depth d, int mn) {
return Reductions[PvNode][i][std::min(d / ONE_PLY, 63)][std::min(mn, 63)] * ONE_PLY;
}
// History and stats update bonus, based on depth
int stat_bonus(Depth depth) {
- int d = depth / ONE_PLY ;
+ int d = depth / ONE_PLY;
return d > 17 ? 0 : d * d + 2 * d - 2;
}
// Skill structure is used to implement strength limit
struct Skill {
- Skill(int l) : level(l) {}
+ explicit Skill(int l) : level(l) {}
bool enabled() const { return level < 20; }
bool time_to_pick(Depth depth) const { return depth / ONE_PLY == 1 + level; }
- Move best_move(size_t multiPV) { return best ? best : pick_best(multiPV); }
Move pick_best(size_t multiPV);
int level;
Move best = MOVE_NONE;
};
- // 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() {
- stableCnt = 0;
- expectedPosKey = 0;
- pv[0] = pv[1] = pv[2] = MOVE_NONE;
- }
-
- Move get(Key key) const {
- return expectedPosKey == key ? pv[2] : MOVE_NONE;
- }
-
- void update(Position& pos, const std::vector<Move>& newPv) {
-
- assert(newPv.size() >= 3);
-
- // 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))
- {
- std::copy(newPv.begin(), newPv.begin() + 3, pv);
-
- StateInfo st[2];
- pos.do_move(newPv[0], st[0]);
- pos.do_move(newPv[1], st[1]);
- expectedPosKey = pos.key();
- pos.undo_move(newPv[1]);
- pos.undo_move(newPv[0]);
- }
- }
-
- int stableCnt;
- Key expectedPosKey;
- Move pv[3];
- };
-
- EasyMoveManager EasyMove;
- Value DrawValue[COLOR_NB];
-
template <NodeType NT>
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning);
Value value_to_tt(Value v, int ply);
Value value_from_tt(Value v, int ply);
void update_pv(Move* pv, Move move, Move* childPv);
- void update_cm_stats(Stack* ss, Piece pc, Square s, int bonus);
+ void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus);
void update_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, int bonus);
- void check_time();
+ void update_capture_stats(const Position& pos, Move move, Move* captures, int captureCnt, int bonus);
+ bool pv_is_draw(Position& pos);
+
+ // perft() is our utility to verify move generation. All the leaf nodes up
+ // to the given depth are generated and counted, and the sum is returned.
+ template<bool Root>
+ uint64_t perft(Position& pos, Depth depth) {
+
+ StateInfo st;
+ uint64_t cnt, nodes = 0;
+ const bool leaf = (depth == 2 * ONE_PLY);
+
+ for (const auto& m : MoveList<LEGAL>(pos))
+ {
+ if (Root && depth <= ONE_PLY)
+ cnt = 1, nodes++;
+ else
+ {
+ pos.do_move(m, st);
+ cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
+ nodes += cnt;
+ pos.undo_move(m);
+ }
+ if (Root)
+ sync_cout << UCI::move(m, pos.is_chess960()) << ": " << cnt << sync_endl;
+ }
+ return nodes;
+ }
} // namespace
}
-/// Search::clear() resets search state to zero, to obtain reproducible results
+/// Search::clear() resets search state to its initial value
void Search::clear() {
- TT.clear();
-
- for (Thread* th : Threads)
- {
- th->counterMoves.clear();
- th->history.clear();
- th->counterMoveHistory.clear();
- th->resetCalls = true;
- CounterMoveStats& cm = th->counterMoveHistory[NO_PIECE][0];
- int* t = &cm[NO_PIECE][0];
- std::fill(t, t + sizeof(cm), CounterMovePruneThreshold - 1);
- }
-
- 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 is returned.
-template<bool Root>
-uint64_t Search::perft(Position& pos, Depth depth) {
-
- StateInfo st;
- uint64_t cnt, nodes = 0;
- const bool leaf = (depth == 2 * ONE_PLY);
+ Threads.main()->wait_for_search_finished();
- for (const auto& m : MoveList<LEGAL>(pos))
- {
- if (Root && depth <= ONE_PLY)
- cnt = 1, nodes++;
- else
- {
- pos.do_move(m, st);
- cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
- nodes += cnt;
- pos.undo_move(m);
- }
- if (Root)
- sync_cout << UCI::move(m, pos.is_chess960()) << ": " << cnt << sync_endl;
- }
- return nodes;
+ Time.availableNodes = 0;
+ TT.clear();
+ Threads.clear();
}
-template uint64_t Search::perft<true>(Position&, Depth);
-
/// MainThread::search() is called by the main thread when the program receives
/// the UCI 'go' command. It searches from the root position and outputs the "bestmove".
void MainThread::search() {
+ if (Limits.perft)
+ {
+ nodes = perft<true>(rootPos, Limits.perft * ONE_PLY);
+ sync_cout << "\nNodes searched: " << nodes << "\n" << sync_endl;
+ return;
+ }
+
Color us = rootPos.side_to_move();
Time.init(Limits, us, rootPos.game_ply());
+ TT.new_search();
int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns
- DrawValue[ us] = VALUE_DRAW - Value(contempt);
- DrawValue[~us] = VALUE_DRAW + Value(contempt);
+
+ Eval::Contempt = (us == WHITE ? make_score(contempt, contempt / 2)
+ : -make_score(contempt, contempt / 2));
if (rootMoves.empty())
{
- rootMoves.push_back(RootMove(MOVE_NONE));
+ rootMoves.emplace_back(MOVE_NONE);
sync_cout << "info depth 0 score "
<< UCI::value(rootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
<< sync_endl;
Thread::search(); // Let's start searching!
}
- // When playing in 'nodes as time' mode, subtract the searched nodes from
- // the available ones before exiting.
- if (Limits.npmsec)
- Time.availableNodes += Limits.inc[us] - Threads.nodes_searched();
-
// When we reach the maximum depth, we can arrive here without a raise of
- // Signals.stop. However, if we are pondering or in an infinite search,
+ // Threads.stop. However, if we are pondering or in an infinite search,
// the UCI protocol states that we shouldn't print the best move before the
// GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
- // until the GUI sends one of those commands (which also raises Signals.stop).
- if (!Signals.stop && (Limits.ponder || Limits.infinite))
- {
- Signals.stopOnPonderhit = true;
- wait(Signals.stop);
- }
+ // until the GUI sends one of those commands (which also raises Threads.stop).
+ Threads.stopOnPonderhit = true;
+
+ while (!Threads.stop && (Threads.ponder || Limits.infinite))
+ {} // Busy wait for a stop or a ponder reset
- // Stop the threads if not already stopped
- Signals.stop = true;
+ // Stop the threads if not already stopped (also raise the stop if
+ // "ponderhit" just reset Threads.ponder).
+ Threads.stop = true;
// Wait until all threads have finished
for (Thread* th : Threads)
if (th != this)
th->wait_for_search_finished();
+ // When playing in 'nodes as time' mode, subtract the searched nodes from
+ // the available ones before exiting.
+ if (Limits.npmsec)
+ Time.availableNodes += Limits.inc[us] - Threads.nodes_searched();
+
// Check if there are threads with a better score than main thread
Thread* bestThread = this;
- if ( !this->easyMovePlayed
- && Options["MultiPV"] == 1
+ if ( Options["MultiPV"] == 1
&& !Limits.depth
&& !Skill(Options["Skill Level"]).enabled()
&& rootMoves[0].pv[0] != MOVE_NONE)
Depth depthDiff = th->completedDepth - bestThread->completedDepth;
Value scoreDiff = th->rootMoves[0].score - bestThread->rootMoves[0].score;
- if (scoreDiff > 0 && depthDiff >= 0)
+ // Select the thread with the best score, always if it is a mate
+ if ( scoreDiff > 0
+ && (depthDiff >= 0 || th->rootMoves[0].score >= VALUE_MATE_IN_MAX_PLY))
bestThread = th;
}
}
void Thread::search() {
- Stack stack[MAX_PLY+7], *ss = stack+4; // To allow referencing (ss-4) and (ss+2)
+ Stack stack[MAX_PLY+7], *ss = stack+4; // To reference from (ss-4) to (ss+2)
Value bestValue, alpha, beta, delta;
- Move easyMove = MOVE_NONE;
+ Move lastBestMove = MOVE_NONE;
+ Depth lastBestMoveDepth = DEPTH_ZERO;
MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
+ double timeReduction = 1.0;
std::memset(ss-4, 0, 7 * sizeof(Stack));
- for(int i = 4; i > 0; i--)
- (ss-i)->counterMoves = &this->counterMoveHistory[NO_PIECE][0]; // Use as sentinel
+ for (int i = 4; i > 0; i--)
+ (ss-i)->contHistory = &this->contHistory[NO_PIECE][0]; // Use as sentinel
bestValue = delta = alpha = -VALUE_INFINITE;
beta = VALUE_INFINITE;
- completedDepth = DEPTH_ZERO;
if (mainThread)
{
- easyMove = EasyMove.get(rootPos.key());
- EasyMove.clear();
- mainThread->easyMovePlayed = mainThread->failedLow = false;
+ mainThread->failedLow = false;
mainThread->bestMoveChanges = 0;
- TT.new_search();
}
size_t multiPV = Options["MultiPV"];
// Iterative deepening loop until requested to stop or the target depth is reached
while ( (rootDepth += ONE_PLY) < DEPTH_MAX
- && !Signals.stop
- && (!Limits.depth || Threads.main()->rootDepth / ONE_PLY <= Limits.depth))
+ && !Threads.stop
+ && !(Limits.depth && mainThread && rootDepth / ONE_PLY > Limits.depth))
{
// Distribute search depths across the threads
if (idx)
rm.previousScore = rm.score;
// MultiPV loop. We perform a full root search for each PV line
- for (PVIdx = 0; PVIdx < multiPV && !Signals.stop; ++PVIdx)
+ for (PVIdx = 0; PVIdx < multiPV && !Threads.stop; ++PVIdx)
{
+ // Reset UCI info selDepth for each depth and each PV line
+ selDepth = 0;
+
// Reset aspiration window starting size
if (rootDepth >= 5 * ONE_PLY)
{
// If search has been stopped, we break immediately. Sorting and
// writing PV back to TT is safe because RootMoves is still
// valid, although it refers to the previous iteration.
- if (Signals.stop)
+ if (Threads.stop)
break;
// When failing high/low give some update (without cluttering
if (mainThread)
{
mainThread->failedLow = true;
- Signals.stopOnPonderhit = false;
+ Threads.stopOnPonderhit = false;
}
}
else if (bestValue >= beta)
- {
- alpha = (alpha + beta) / 2;
beta = std::min(bestValue + delta, VALUE_INFINITE);
- }
else
break;
// Sort the PV lines searched so far and update the GUI
std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1);
- if (!mainThread)
- continue;
-
- if (Signals.stop || PVIdx + 1 == multiPV || Time.elapsed() > 3000)
+ if ( mainThread
+ && (Threads.stop || PVIdx + 1 == multiPV || Time.elapsed() > 3000))
sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
}
- if (!Signals.stop)
+ if (!Threads.stop)
completedDepth = rootDepth;
+ if (rootMoves[0].pv[0] != lastBestMove) {
+ lastBestMove = rootMoves[0].pv[0];
+ lastBestMoveDepth = rootDepth;
+ }
+
+ // Have we found a "mate in x"?
+ if ( Limits.mate
+ && bestValue >= VALUE_MATE_IN_MAX_PLY
+ && VALUE_MATE - bestValue <= 2 * Limits.mate)
+ Threads.stop = true;
+
if (!mainThread)
continue;
if (skill.enabled() && skill.time_to_pick(rootDepth))
skill.pick_best(multiPV);
- // Have we found a "mate in x"?
- if ( Limits.mate
- && bestValue >= VALUE_MATE_IN_MAX_PLY
- && VALUE_MATE - bestValue <= 2 * Limits.mate)
- Signals.stop = true;
-
// Do we have time for the next iteration? Can we stop searching now?
if (Limits.use_time_management())
{
- if (!Signals.stop && !Signals.stopOnPonderhit)
+ if (!Threads.stop && !Threads.stopOnPonderhit)
{
// 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.
+ // of the available time has been used
const int F[] = { mainThread->failedLow,
bestValue - mainThread->previousScore };
-
int improvingFactor = std::max(229, std::min(715, 357 + 119 * F[0] - 6 * F[1]));
- double unstablePvFactor = 1 + mainThread->bestMoveChanges;
- bool doEasyMove = rootMoves[0].pv[0] == easyMove
- && mainThread->bestMoveChanges < 0.03
- && Time.elapsed() > Time.optimum() * 5 / 44;
+ Color us = rootPos.side_to_move();
+ bool thinkHard = bestValue == VALUE_DRAW
+ && Limits.time[us] - Time.elapsed() > Limits.time[~us]
+ && ::pv_is_draw(rootPos);
+
+ double unstablePvFactor = 1 + mainThread->bestMoveChanges + thinkHard;
+
+ // if the bestMove is stable over several iterations, reduce time for this move,
+ // the longer the move has been stable, the more.
+ // Use part of the gained time from a previous stable move for the current move.
+ timeReduction = 1;
+ for (int i : {3, 4, 5})
+ if (lastBestMoveDepth * i < completedDepth && !thinkHard)
+ timeReduction *= 1.3;
+ unstablePvFactor *= std::pow(mainThread->previousTimeReduction, 0.51) / timeReduction;
if ( rootMoves.size() == 1
- || Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 628
- || (mainThread->easyMovePlayed = doEasyMove, doEasyMove))
+ || Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 628)
{
// If we are allowed to ponder do not stop the search now but
// keep pondering until the GUI sends "ponderhit" or "stop".
- if (Limits.ponder)
- Signals.stopOnPonderhit = true;
+ if (Threads.ponder)
+ Threads.stopOnPonderhit = true;
else
- Signals.stop = true;
+ Threads.stop = true;
}
}
-
- if (rootMoves[0].pv.size() >= 3)
- EasyMove.update(rootPos, rootMoves[0].pv);
- else
- EasyMove.clear();
}
}
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 || mainThread->easyMovePlayed)
- EasyMove.clear();
+ mainThread->previousTimeReduction = timeReduction;
// If skill level is enabled, swap best PV line with the sub-optimal one
if (skill.enabled())
- std::swap(rootMoves[0], *std::find(rootMoves.begin(),
- rootMoves.end(), skill.best_move(multiPV)));
+ std::swap(rootMoves[0], *std::find(rootMoves.begin(), rootMoves.end(),
+ skill.best ? skill.best : skill.pick_best(multiPV)));
}
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning) {
const bool PvNode = NT == PV;
- const bool rootNode = PvNode && (ss-1)->ply == 0;
+ const bool rootNode = PvNode && ss->ply == 0;
assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
assert(PvNode || (alpha == beta - 1));
assert(!(PvNode && cutNode));
assert(depth / ONE_PLY * ONE_PLY == depth);
- Move pv[MAX_PLY+1], quietsSearched[64];
+ Move pv[MAX_PLY+1], capturesSearched[32], quietsSearched[64];
StateInfo st;
TTEntry* tte;
Key posKey;
Depth extension, newDepth;
Value bestValue, value, ttValue, eval;
bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
- bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets;
- Piece moved_piece;
- int moveCount, quietCount;
+ bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture, pvExact;
+ Piece movedPiece;
+ int moveCount, captureCount, quietCount;
// Step 1. Initialize node
Thread* thisThread = pos.this_thread();
inCheck = pos.checkers();
- moveCount = quietCount = ss->moveCount = 0;
- ss->history = 0;
+ moveCount = captureCount = quietCount = ss->moveCount = 0;
+ ss->statScore = 0;
bestValue = -VALUE_INFINITE;
- ss->ply = (ss-1)->ply + 1;
// Check for the available remaining time
- if (thisThread->resetCalls.load(std::memory_order_relaxed))
- {
- thisThread->resetCalls = false;
-
- // At low node count increase the checking rate to about 0.1% of nodes
- // otherwise use a default value.
- thisThread->callsCnt = Limits.nodes ? std::min(4096, int(Limits.nodes / 1024))
- : 4096;
- }
-
- if (--thisThread->callsCnt <= 0)
- {
- for (Thread* th : Threads)
- th->resetCalls = true;
+ if (thisThread == Threads.main())
+ static_cast<MainThread*>(thisThread)->check_time();
- check_time();
- }
-
- // Used to send selDepth info to GUI
- if (PvNode && thisThread->maxPly < ss->ply)
- thisThread->maxPly = ss->ply;
+ // Used to send selDepth info to GUI (selDepth counts from 1, ply from 0)
+ if (PvNode && thisThread->selDepth < ss->ply + 1)
+ thisThread->selDepth = ss->ply + 1;
if (!rootNode)
{
// Step 2. Check for aborted search and immediate draw
- if (Signals.stop.load(std::memory_order_relaxed) || pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
- return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos)
- : DrawValue[pos.side_to_move()];
+ if (Threads.stop.load(std::memory_order_relaxed) || pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
+ return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos) : VALUE_DRAW;
// Step 3. Mate distance pruning. Even if we mate at the next move our score
// would be at best mate_in(ss->ply+1), but if alpha is already bigger because
assert(0 <= ss->ply && ss->ply < MAX_PLY);
+ (ss+1)->ply = ss->ply + 1;
ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
- ss->counterMoves = &thisThread->counterMoveHistory[NO_PIECE][0];
+ ss->contHistory = &thisThread->contHistory[NO_PIECE][0];
(ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
Square prevSq = to_sq((ss-1)->currentMove);
// search to overwrite a previous full search TT value, so we use a different
// position key in case of an excluded move.
excludedMove = ss->excludedMove;
- posKey = pos.key() ^ Key(excludedMove);
+ posKey = pos.key() ^ Key(excludedMove << 16); // isn't a very good hash
tte = TT.probe(posKey, ttHit);
ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
ttMove = rootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
// Extra penalty for a quiet TT move in previous ply when it gets refuted
if ((ss-1)->moveCount == 1 && !pos.captured_piece())
- update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
+ update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
}
// Penalty for a quiet ttMove that fails low
else if (!pos.capture_or_promotion(ttMove))
{
int penalty = -stat_bonus(depth);
- thisThread->history.update(pos.side_to_move(), ttMove, penalty);
- update_cm_stats(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty);
+ thisThread->mainHistory.update(pos.side_to_move(), ttMove, penalty);
+ update_continuation_histories(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty);
}
}
return ttValue;
if (err != TB::ProbeState::FAIL)
{
- thisThread->tbHits++;
+ thisThread->tbHits.fetch_add(1, std::memory_order_relaxed);
int drawScore = TB::UseRule50 ? 1 : 0;
- value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply
- : v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply
+ value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply + 1
+ : v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply - 1
: VALUE_DRAW + 2 * v * drawScore;
tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT,
eval = ss->staticEval = evaluate(pos);
// Can ttValue be used as a better position evaluation?
- if (ttValue != VALUE_NONE)
- if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
- eval = ttValue;
+ if ( ttValue != VALUE_NONE
+ && (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER)))
+ eval = ttValue;
}
else
{
ss->staticEval, TT.generation());
}
- if (skipEarlyPruning)
+ if (skipEarlyPruning || !pos.non_pawn_material(pos.side_to_move()))
goto moves_loop;
// Step 6. Razoring (skipped when in check)
if ( !rootNode
&& depth < 7 * ONE_PLY
&& eval - futility_margin(depth) >= beta
- && eval < VALUE_KNOWN_WIN // Do not return unproven wins
- && pos.non_pawn_material(pos.side_to_move()))
+ && eval < VALUE_KNOWN_WIN) // Do not return unproven wins
return eval;
// Step 8. Null move search with verification search (is omitted in PV nodes)
if ( !PvNode
&& eval >= beta
- && (ss->staticEval >= beta - 35 * (depth / ONE_PLY - 6) || depth >= 13 * ONE_PLY)
- && pos.non_pawn_material(pos.side_to_move()))
+ && ss->staticEval >= beta - 36 * depth / ONE_PLY + 225
+ && (ss->ply >= thisThread->nmp_ply || ss->ply % 2 == thisThread->pair))
{
assert(eval - beta >= 0);
Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
ss->currentMove = MOVE_NULL;
- ss->counterMoves = &thisThread->counterMoveHistory[NO_PIECE][0];
+ ss->contHistory = &thisThread->contHistory[NO_PIECE][0];
pos.do_null_move(st);
Value nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1)
return nullValue;
// Do verification search at high depths
+ R += ONE_PLY;
+ // disable null move pruning for side to move for the first part of the remaining search tree
+ int nmp_ply = thisThread->nmp_ply;
+ int pair = thisThread->pair;
+ thisThread->nmp_ply = ss->ply + 3 * (depth-R) / 4;
+ thisThread->pair = (ss->ply % 2) == 0;
+
Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta)
: search<NonPV>(pos, ss, beta-1, beta, depth-R, false, true);
+ thisThread->pair = pair;
+ thisThread->nmp_ply = nmp_ply;
if (v >= beta)
return nullValue;
&& abs(beta) < VALUE_MATE_IN_MAX_PLY)
{
Value rbeta = std::min(beta + 200, VALUE_INFINITE);
- Depth rdepth = depth - 4 * ONE_PLY;
- assert(rdepth >= ONE_PLY);
assert(is_ok((ss-1)->currentMove));
- MovePicker mp(pos, ttMove, rbeta - ss->staticEval);
+ MovePicker mp(pos, ttMove, rbeta - ss->staticEval, &thisThread->captureHistory);
while ((move = mp.next_move()) != MOVE_NONE)
if (pos.legal(move))
{
ss->currentMove = move;
- ss->counterMoves = &thisThread->counterMoveHistory[pos.moved_piece(move)][to_sq(move)];
+ ss->contHistory = &thisThread->contHistory[pos.moved_piece(move)][to_sq(move)];
+ assert(depth >= 5 * ONE_PLY);
pos.do_move(move, st);
- value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode, false);
+ value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false);
pos.undo_move(move);
if (value >= rbeta)
return value;
moves_loop: // When in check search starts from here
- const CounterMoveStats& cmh = *(ss-1)->counterMoves;
- const CounterMoveStats& fmh = *(ss-2)->counterMoves;
- const CounterMoveStats& fm2 = *(ss-4)->counterMoves;
+ const PieceToHistory* contHist[] = { (ss-1)->contHistory, (ss-2)->contHistory, nullptr, (ss-4)->contHistory };
+ Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
- MovePicker mp(pos, ttMove, depth, ss);
+ MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, &thisThread->captureHistory, contHist, countermove, ss->killers);
value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
improving = ss->staticEval >= (ss-2)->staticEval
/* || ss->staticEval == VALUE_NONE Already implicit in the previous condition */
&& (tte->bound() & BOUND_LOWER)
&& tte->depth() >= depth - 3 * ONE_PLY;
skipQuiets = false;
+ ttCapture = false;
+ pvExact = PvNode && ttHit && tte->bound() == BOUND_EXACT;
// Step 11. Loop through moves
// Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
extension = DEPTH_ZERO;
captureOrPromotion = pos.capture_or_promotion(move);
- moved_piece = pos.moved_piece(move);
+ movedPiece = pos.moved_piece(move);
givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates()
- ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
+ ? pos.check_squares(type_of(movedPiece)) & to_sq(move)
: pos.gives_check(move);
moveCountPruning = depth < 16 * ONE_PLY
}
else if ( givesCheck
&& !moveCountPruning
- && pos.see_ge(move, VALUE_ZERO))
+ && pos.see_ge(move))
extension = ONE_PLY;
// Calculate new depth for this move
// Countermoves based pruning
if ( lmrDepth < 3
- && (cmh[moved_piece][to_sq(move)] < CounterMovePruneThreshold)
- && (fmh[moved_piece][to_sq(move)] < CounterMovePruneThreshold))
+ && (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
+ && (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
continue;
// Futility pruning: parent node
continue;
}
+ if (move == ttMove && captureOrPromotion)
+ ttCapture = true;
+
// Update the current move (this must be done after singular extension search)
ss->currentMove = move;
- ss->counterMoves = &thisThread->counterMoveHistory[moved_piece][to_sq(move)];
+ ss->contHistory = &thisThread->contHistory[movedPiece][to_sq(move)];
// Step 14. Make the move
pos.do_move(move, st, givesCheck);
r -= r ? ONE_PLY : DEPTH_ZERO;
else
{
+ // Decrease reduction if opponent's move count is high
+ if ((ss-1)->moveCount > 15)
+ r -= ONE_PLY;
+
+ // Decrease reduction for exact PV nodes
+ if (pvExact)
+ r -= ONE_PLY;
+
+ // Increase reduction if ttMove is a capture
+ if (ttCapture)
+ r += ONE_PLY;
+
// Increase reduction for cut nodes
if (cutNode)
r += 2 * 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().
- else if ( type_of(move) == NORMAL
- && !pos.see_ge(make_move(to_sq(move), from_sq(move)), VALUE_ZERO))
+ else if ( type_of(move) == NORMAL
+ && !pos.see_ge(make_move(to_sq(move), from_sq(move))))
r -= 2 * ONE_PLY;
- ss->history = cmh[moved_piece][to_sq(move)]
- + fmh[moved_piece][to_sq(move)]
- + fm2[moved_piece][to_sq(move)]
- + thisThread->history.get(~pos.side_to_move(), move)
- - 4000; // Correction factor
+ ss->statScore = thisThread->mainHistory[~pos.side_to_move()][from_to(move)]
+ + (*contHist[0])[movedPiece][to_sq(move)]
+ + (*contHist[1])[movedPiece][to_sq(move)]
+ + (*contHist[3])[movedPiece][to_sq(move)]
+ - 4000;
// Decrease/increase reduction by comparing opponent's stat score
- if (ss->history > 0 && (ss-1)->history < 0)
+ if (ss->statScore >= 0 && (ss-1)->statScore < 0)
r -= ONE_PLY;
- else if (ss->history < 0 && (ss-1)->history > 0)
+ else if ((ss-1)->statScore >= 0 && ss->statScore < 0)
r += ONE_PLY;
// Decrease/increase reduction for moves with a good/bad history
- r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->history / 20000) * ONE_PLY);
+ r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->statScore / 20000) * ONE_PLY);
}
Depth d = std::max(newDepth - r, ONE_PLY);
// 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.
- if (Signals.stop.load(std::memory_order_relaxed))
+ if (Threads.stop.load(std::memory_order_relaxed))
return VALUE_ZERO;
if (rootNode)
if (moveCount == 1 || value > alpha)
{
rm.score = value;
+ rm.selDepth = thisThread->selDepth;
rm.pv.resize(1);
assert((ss+1)->pv);
++static_cast<MainThread*>(thisThread)->bestMoveChanges;
}
else
- // All other moves but the PV are set to the lowest value: this is
- // not a problem when sorting because the sort is stable and the
+ // All other moves but the PV are set to the lowest value: this
+ // is not a problem when sorting because the sort is stable and the
// move position in the list is preserved - just the PV is pushed up.
rm.score = -VALUE_INFINITE;
}
if (!captureOrPromotion && move != bestMove && quietCount < 64)
quietsSearched[quietCount++] = move;
+ else if (captureOrPromotion && move != bestMove && captureCount < 32)
+ capturesSearched[captureCount++] = move;
}
// 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.
/*
- if (Signals.stop)
+ if (Threads.stop)
return VALUE_DRAW;
*/
if (!moveCount)
bestValue = excludedMove ? alpha
- : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
+ : inCheck ? mated_in(ss->ply) : VALUE_DRAW;
else if (bestMove)
{
-
// Quiet best move: update move sorting heuristics
if (!pos.capture_or_promotion(bestMove))
update_stats(pos, ss, bestMove, quietsSearched, quietCount, stat_bonus(depth));
+ else
+ update_capture_stats(pos, bestMove, capturesSearched, captureCount, stat_bonus(depth));
// Extra penalty for a quiet TT move in previous ply when it gets refuted
if ((ss-1)->moveCount == 1 && !pos.captured_piece())
- update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
+ update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
}
// Bonus for prior countermove that caused the fail low
else if ( depth >= 3 * ONE_PLY
&& !pos.captured_piece()
&& is_ok((ss-1)->currentMove))
- update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));
+ update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));
if (!excludedMove)
tte->save(posKey, value_to_tt(bestValue, ss->ply),
const bool PvNode = NT == PV;
- assert(InCheck == !!pos.checkers());
+ assert(InCheck == bool(pos.checkers()));
assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
assert(PvNode || (alpha == beta - 1));
assert(depth <= DEPTH_ZERO);
Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
bool ttHit, givesCheck, evasionPrunable;
Depth ttDepth;
+ int moveCount;
if (PvNode)
{
}
ss->currentMove = bestMove = MOVE_NONE;
- ss->ply = (ss-1)->ply + 1;
+ (ss+1)->ply = ss->ply + 1;
+ moveCount = 0;
// Check for an instant draw or if the maximum ply has been reached
if (pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
- return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos)
- : DrawValue[pos.side_to_move()];
+ return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos) : VALUE_DRAW;
assert(0 <= ss->ply && ss->ply < MAX_PLY);
// only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
: DEPTH_QS_NO_CHECKS;
-
// Transposition table lookup
posKey = pos.key();
tte = TT.probe(posKey, ttHit);
ss->staticEval = bestValue = evaluate(pos);
// Can ttValue be used as a better position evaluation?
- if (ttValue != VALUE_NONE)
- if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
- bestValue = ttValue;
+ if ( ttValue != VALUE_NONE
+ && (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER)))
+ bestValue = ttValue;
}
else
ss->staticEval = bestValue =
if (bestValue >= beta)
{
if (!ttHit)
- tte->save(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
+ tte->save(posKey, value_to_tt(bestValue, ss->ply), BOUND_LOWER,
DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
return bestValue;
// to search the moves. Because the depth is <= 0 here, only captures,
// queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
// be generated.
- MovePicker mp(pos, ttMove, depth, to_sq((ss-1)->currentMove));
+ MovePicker mp(pos, ttMove, depth, &pos.this_thread()->mainHistory, &pos.this_thread()->captureHistory, to_sq((ss-1)->currentMove));
// Loop through the moves until no moves remain or a beta cutoff occurs
while ((move = mp.next_move()) != MOVE_NONE)
assert(is_ok(move));
givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates()
- ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
+ ? pos.check_squares(type_of(pos.moved_piece(move))) & to_sq(move)
: pos.gives_check(move);
+ moveCount++;
+
// Futility pruning
if ( !InCheck
&& !givesCheck
// Detect non-capture evasions that are candidates to be pruned
evasionPrunable = InCheck
- && depth != DEPTH_ZERO
+ && (depth != DEPTH_ZERO || moveCount > 2)
&& bestValue > VALUE_MATED_IN_MAX_PLY
&& !pos.capture(move);
// Don't search moves with negative SEE values
if ( (!InCheck || evasionPrunable)
&& type_of(move) != PROMOTION
- && !pos.see_ge(move, VALUE_ZERO))
+ && !pos.see_ge(move))
continue;
// Speculative prefetch as early as possible
// Check for legality just before making the move
if (!pos.legal(move))
+ {
+ moveCount--;
continue;
+ }
ss->currentMove = move;
}
- // update_cm_stats() updates countermove and follow-up move history
+ // update_continuation_histories() updates histories of the move pairs formed
+ // by moves at ply -1, -2, and -4 with current move.
- void update_cm_stats(Stack* ss, Piece pc, Square s, int bonus) {
+ void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus) {
for (int i : {1, 2, 4})
if (is_ok((ss-i)->currentMove))
- (ss-i)->counterMoves->update(pc, s, bonus);
+ (ss-i)->contHistory->update(pc, to, bonus);
+ }
+
+
+ // update_capture_stats() updates move sorting heuristics when a new capture best move is found
+
+ void update_capture_stats(const Position& pos, Move move,
+ Move* captures, int captureCnt, int bonus) {
+
+ CapturePieceToHistory& captureHistory = pos.this_thread()->captureHistory;
+ Piece moved_piece = pos.moved_piece(move);
+ PieceType captured = type_of(pos.piece_on(to_sq(move)));
+ captureHistory.update(moved_piece, to_sq(move), captured, bonus);
+
+ // Decrease all the other played capture moves
+ for (int i = 0; i < captureCnt; ++i)
+ {
+ moved_piece = pos.moved_piece(captures[i]);
+ captured = type_of(pos.piece_on(to_sq(captures[i])));
+ captureHistory.update(moved_piece, to_sq(captures[i]), captured, -bonus);
+ }
}
Color c = pos.side_to_move();
Thread* thisThread = pos.this_thread();
- thisThread->history.update(c, move, bonus);
- update_cm_stats(ss, pos.moved_piece(move), to_sq(move), bonus);
+ thisThread->mainHistory.update(c, move, bonus);
+ update_continuation_histories(ss, pos.moved_piece(move), to_sq(move), bonus);
if (is_ok((ss-1)->currentMove))
{
Square prevSq = to_sq((ss-1)->currentMove);
- thisThread->counterMoves.update(pos.piece_on(prevSq), prevSq, move);
+ thisThread->counterMoves[pos.piece_on(prevSq)][prevSq] = move;
}
// Decrease all the other played quiet moves
for (int i = 0; i < quietsCnt; ++i)
{
- thisThread->history.update(c, quiets[i], -bonus);
- update_cm_stats(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
+ thisThread->mainHistory.update(c, quiets[i], -bonus);
+ update_continuation_histories(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
}
}
+ // Is the PV leading to a draw position? Assumes all pv moves are legal
+ bool pv_is_draw(Position& pos) {
+
+ StateInfo st[MAX_PLY];
+ auto& pv = pos.this_thread()->rootMoves[0].pv;
+
+ for (size_t i = 0; i < pv.size(); ++i)
+ pos.do_move(pv[i], st[i]);
+
+ bool isDraw = pos.is_draw(pv.size());
+
+ for (size_t i = pv.size(); i > 0; --i)
+ pos.undo_move(pv[i-1]);
+
+ return isDraw;
+ }
+
+
// When playing with strength handicap, choose best move among a set of RootMoves
// using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
int push = ( weakness * int(topScore - rootMoves[i].score)
+ delta * (rng.rand<unsigned>() % weakness)) / 128;
- if (rootMoves[i].score + push > maxScore)
+ if (rootMoves[i].score + push >= maxScore)
{
maxScore = rootMoves[i].score + push;
best = rootMoves[i].pv[0];
return best;
}
+} // namespace
// check_time() is used to print debug info and, more importantly, to detect
// when we are out of available time and thus stop the search.
- void check_time() {
+ void MainThread::check_time() {
+
+ if (--callsCnt > 0)
+ return;
+
+ // At low node count increase the checking rate to about 0.1% of nodes
+ // otherwise use a default value.
+ callsCnt = Limits.nodes ? std::min(4096, int(Limits.nodes / 1024)) : 4096;
static TimePoint lastInfoTime = now();
}
// An engine may not stop pondering until told so by the GUI
- if (Limits.ponder)
+ if (Threads.ponder)
return;
if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10)
|| (Limits.movetime && elapsed >= Limits.movetime)
|| (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
- Signals.stop = true;
+ Threads.stop = true;
}
-} // namespace
-
/// UCI::pv() formats PV information according to the UCI protocol. UCI requires
/// that all (if any) unsearched PV lines are sent using a previous search score.
ss << "info"
<< " depth " << d / ONE_PLY
- << " seldepth " << pos.this_thread()->maxPly
+ << " seldepth " << rootMoves[i].selDepth
<< " multipv " << i + 1
<< " score " << UCI::value(v);
if (Cardinality < popcount(pos.pieces()) || pos.can_castle(ANY_CASTLING))
return;
+ // Don't filter any moves if the user requested analysis on multiple
+ if (Options["MultiPV"] != 1)
+ return;
+
// If the current root position is in the tablebases, then RootMoves
// contains only moves that preserve the draw or the win.
RootInTB = root_probe(pos, rootMoves, TB::Score);
projects / stockfish / blobdiff