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
const int skipPhase[] = { 0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 7 };
// Razoring and futility margin based on depth
- // razor_margin[0] is unused as long as depth >= ONE_PLY in search
- const int razor_margin[] = { 0, 570, 603, 554 };
+ const int razor_margin = 600;
Value futility_margin(Depth d) { return Value(150 * d / ONE_PLY); }
// Futility and reductions lookup tables, initialized at startup
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]);
- }
- }
-
- Key expectedPosKey;
- int stableCnt;
- 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);
void update_pv(Move* pv, Move move, Move* childPv);
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 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.
Time.availableNodes = 0;
TT.clear();
-
- for (Thread* th : Threads)
- th->clear();
-
- Threads.main()->callsCnt = 0;
- Threads.main()->previousScore = VALUE_INFINITE;
+ Threads.clear();
}
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())
{
// 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)
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--)
if (mainThread)
{
- easyMove = EasyMove.get(rootPos.key());
- EasyMove.clear();
- mainThread->easyMovePlayed = mainThread->failedLow = false;
+ mainThread->failedLow = false;
mainThread->bestMoveChanges = 0;
}
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
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".
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())
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;
bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture, pvExact;
Piece movedPiece;
- int moveCount, quietCount;
+ int moveCount, captureCount, quietCount;
// Step 1. Initialize node
Thread* thisThread = pos.this_thread();
inCheck = pos.checkers();
- moveCount = quietCount = ss->moveCount = 0;
+ moveCount = captureCount = quietCount = ss->moveCount = 0;
ss->statScore = 0;
bestValue = -VALUE_INFINITE;
{
// Step 2. Check for aborted search and immediate draw
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)
- : DrawValue[pos.side_to_move()];
+ 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
// 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]
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 ( !PvNode
&& depth < 4 * ONE_PLY
- && eval + razor_margin[depth / ONE_PLY] <= alpha)
+ && eval + razor_margin <= alpha)
{
if (depth <= ONE_PLY)
return qsearch<NonPV, false>(pos, ss, alpha, alpha+1);
- Value ralpha = alpha - razor_margin[depth / ONE_PLY];
+ Value ralpha = alpha - razor_margin;
Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1);
if (v <= ralpha)
return v;
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->nmp_odd))
{
assert(eval - beta >= 0);
if (nullValue >= VALUE_MATE_IN_MAX_PLY)
nullValue = beta;
- if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
+ if (abs(beta) < VALUE_KNOWN_WIN && (depth < 12 * ONE_PLY || thisThread->nmp_ply))
return nullValue;
// Do verification search at high depths
+ // disable null move pruning for side to move for the first part of the remaining search tree
+ thisThread->nmp_ply = ss->ply + 3 * (depth-R) / 4;
+ thisThread->nmp_odd = ss->ply % 2;
+
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->nmp_odd = thisThread->nmp_ply = 0;
+
if (v >= beta)
return nullValue;
}
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))
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, &thisThread->mainHistory, contHist, countermove, ss->killers);
+ 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 */
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
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
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())
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);
// 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);
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, &pos.this_thread()->mainHistory, 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++;
// Don't search moves with negative SEE values
if ( (!InCheck || evasionPrunable)
- && type_of(move) != PROMOTION
&& !pos.see_ge(move))
continue;
}
+ // 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);
+ }
+ }
+
+
// update_stats() updates move sorting heuristics when a new quiet best move is found
void update_stats(const Position& pos, Stack* ss, Move move,
}
+ // 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.
if (Threads.ponder)
return;
- if ( (Limits.use_time_management() && elapsed > Time.maximum())
+ if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10)
|| (Limits.movetime && elapsed >= Limits.movetime)
|| (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
Threads.stop = true;
ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
Cardinality = Options["SyzygyProbeLimit"];
- // Don't filter any moves if the user requested analysis on multiple
- if (Options["MultiPV"] != 1)
- return;
-
// Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
if (Cardinality > MaxCardinality)
{
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