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
+ Copyright (C) 2015-2017 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
#include "misc.h"
#include "movegen.h"
#include "movepick.h"
+#include "position.h"
#include "search.h"
#include "timeman.h"
#include "thread.h"
namespace Tablebases {
int Cardinality;
- uint64_t Hits;
bool RootInTB;
bool UseRule50;
Depth ProbeDepth;
// Different node types, used as a template parameter
enum NodeType { NonPV, PV };
+ // Sizes and phases of the skip-blocks, used for distributing search depths across the threads
+ const int skipSize[] = { 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4 };
+ 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
- const int razor_margin[4] = { 483, 570, 603, 554 };
+ // razor_margin[0] is unused as long as depth >= ONE_PLY in search
+ const int razor_margin[] = { 0, 570, 603, 554 };
Value futility_margin(Depth d) { return Value(150 * d / ONE_PLY); }
// Futility and reductions lookup tables, initialized at startup
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 ;
+ return d > 17 ? 0 : d * d + 2 * d - 2;
+ }
+
// Skill structure is used to implement strength limit
struct Skill {
Skill(int l) : level(l) {}
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.
+ // 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() {
std::copy(newPv.begin(), newPv.begin() + 3, pv);
StateInfo st[2];
- pos.do_move(newPv[0], st[0], pos.gives_check(newPv[0]));
- pos.do_move(newPv[1], st[1], pos.gives_check(newPv[1]));
+ 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]);
Move pv[3];
};
- // Set of rows with half bits set to 1 and half to 0. It is used to allocate
- // the search depths across the threads.
- typedef std::vector<int> Row;
-
- const Row HalfDensity[] = {
- {0, 1},
- {1, 0},
- {0, 0, 1, 1},
- {0, 1, 1, 0},
- {1, 1, 0, 0},
- {1, 0, 0, 1},
- {0, 0, 0, 1, 1, 1},
- {0, 0, 1, 1, 1, 0},
- {0, 1, 1, 1, 0, 0},
- {1, 1, 1, 0, 0, 0},
- {1, 1, 0, 0, 0, 1},
- {1, 0, 0, 0, 1, 1},
- {0, 0, 0, 0, 1, 1, 1, 1},
- {0, 0, 0, 1, 1, 1, 1, 0},
- {0, 0, 1, 1, 1, 1, 0 ,0},
- {0, 1, 1, 1, 1, 0, 0 ,0},
- {1, 1, 1, 1, 0, 0, 0 ,0},
- {1, 1, 1, 0, 0, 0, 0 ,1},
- {1, 1, 0, 0, 0, 0, 1 ,1},
- {1, 0, 0, 0, 0, 1, 1 ,1},
- };
-
- const size_t HalfDensitySize = std::extent<decltype(HalfDensity)>::value;
-
EasyMoveManager EasyMove;
Value DrawValue[COLOR_NB];
- CounterMoveHistoryStats CounterMoveHistory;
template <NodeType NT>
- Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
+ Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning);
template <NodeType NT, bool InCheck>
- Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
+ Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = DEPTH_ZERO);
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, Value bonus);
- void update_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, Value bonus);
+ void update_cm_stats(Stack* ss, Piece pc, Square s, int bonus);
+ void update_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, int bonus);
void check_time();
} // namespace
for (int d = 1; d < 64; ++d)
for (int mc = 1; mc < 64; ++mc)
{
- double r = log(d) * log(mc) / 2;
- if (r < 0.80)
- continue;
+ double r = log(d) * log(mc) / 1.95;
Reductions[NonPV][imp][d][mc] = int(std::round(r));
Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - 1, 0);
for (int d = 0; d < 16; ++d)
{
- FutilityMoveCounts[0][d] = int(2.4 + 0.773 * pow(d + 0.00, 1.8));
- FutilityMoveCounts[1][d] = int(2.9 + 1.045 * pow(d + 0.49, 1.8));
+ FutilityMoveCounts[0][d] = int(2.4 + 0.74 * pow(d, 1.78));
+ FutilityMoveCounts[1][d] = int(5.0 + 1.00 * pow(d, 2.00));
}
}
-/// Search::clear() resets search state to zero, to obtain reproducible results
+/// Search::clear() resets search state to its initial value, to obtain reproducible results
void Search::clear() {
TT.clear();
- CounterMoveHistory.clear();
for (Thread* th : Threads)
{
- th->history.clear();
th->counterMoves.clear();
- th->fromTo.clear();
+ th->history.clear();
+ th->counterMoveHistory.clear();
+ th->resetCalls = true;
+
+ CounterMoveStats& cm = th->counterMoveHistory[NO_PIECE][0];
+ auto* t = &cm[NO_PIECE][0];
+ std::fill(t, t + sizeof(cm)/sizeof(*t), CounterMovePruneThreshold - 1);
}
Threads.main()->previousScore = VALUE_INFINITE;
cnt = 1, nodes++;
else
{
- pos.do_move(m, st, pos.gives_check(m));
+ pos.do_move(m, st);
cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
nodes += cnt;
pos.undo_move(m);
&& rootMoves[0].pv[0] != MOVE_NONE)
{
for (Thread* th : Threads)
- if ( th->completedDepth > bestThread->completedDepth
- && th->rootMoves[0].score > bestThread->rootMoves[0].score)
+ {
+ Depth depthDiff = th->completedDepth - bestThread->completedDepth;
+ Value scoreDiff = th->rootMoves[0].score - bestThread->rootMoves[0].score;
+
+ if (scoreDiff > 0 && depthDiff >= 0)
bestThread = th;
+ }
}
previousScore = bestThread->rootMoves[0].score;
}
-// Thread::search() is the main iterative deepening loop. It calls search()
-// repeatedly with increasing depth until the allocated thinking time has been
-// consumed, the user stops the search, or the maximum search depth is reached.
+/// Thread::search() is the main iterative deepening loop. It calls search()
+/// repeatedly with increasing depth until the allocated thinking time has been
+/// consumed, the user stops the search, or the maximum search depth is reached.
void Thread::search() {
- Stack stack[MAX_PLY+7], *ss = stack+5; // To allow referencing (ss-5) and (ss+2)
+ Stack stack[MAX_PLY+7], *ss = stack+4; // To allow referencing (ss-4) and (ss+2)
Value bestValue, alpha, beta, delta;
Move easyMove = MOVE_NONE;
MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
- std::memset(ss-5, 0, 8 * sizeof(Stack));
+ 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
bestValue = delta = alpha = -VALUE_INFINITE;
beta = VALUE_INFINITE;
&& !Signals.stop
&& (!Limits.depth || Threads.main()->rootDepth / ONE_PLY <= Limits.depth))
{
- // Set up the new depths for the helper threads skipping on average every
- // 2nd ply (using a half-density matrix).
- if (!mainThread)
+ // Distribute search depths across the threads
+ if (idx)
{
- const Row& row = HalfDensity[(idx - 1) % HalfDensitySize];
- if (row[(rootDepth / ONE_PLY + rootPos.game_ply()) % row.size()])
- continue;
+ int i = (idx - 1) % 20;
+ if (((rootDepth / ONE_PLY + rootPos.game_ply() + skipPhase[i]) / skipSize[i]) % 2)
+ continue;
}
// Age out PV variability metric
// high/low anymore.
while (true)
{
- bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, false);
+ bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, false, false);
// Bring the best move to the front. It is critical that sorting
// is done with a stable algorithm because all the values but the
// search the already searched PV lines are preserved.
std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end());
- // If search has been stopped, break immediately. Sorting and
+ // 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 (!mainThread)
continue;
- if (Signals.stop)
- sync_cout << "info nodes " << Threads.nodes_searched()
- << " time " << Time.elapsed() << sync_endl;
-
- else if (PVIdx + 1 == multiPV || Time.elapsed() > 3000)
+ if (Signals.stop || PVIdx + 1 == multiPV || Time.elapsed() > 3000)
sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
}
bool doEasyMove = rootMoves[0].pv[0] == easyMove
&& mainThread->bestMoveChanges < 0.03
- && Time.elapsed() > Time.optimum() * 5 / 42;
+ && Time.elapsed() > Time.optimum() * 5 / 44;
if ( rootMoves.size() == 1
|| Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 628
- || (mainThread->easyMovePlayed = doEasyMove))
+ || (mainThread->easyMovePlayed = doEasyMove, doEasyMove))
{
// If we are allowed to ponder do not stop the search now but
// keep pondering until the GUI sends "ponderhit" or "stop".
// search<>() is the main search function for both PV and non-PV nodes
template <NodeType NT>
- Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
+ 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;
TTEntry* tte;
Key posKey;
Move ttMove, move, excludedMove, bestMove;
- Depth extension, newDepth, predictedDepth;
- Value bestValue, value, ttValue, eval, nullValue;
+ Depth extension, newDepth;
+ Value bestValue, value, ttValue, eval;
bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
- bool captureOrPromotion, doFullDepthSearch, moveCountPruning;
+ bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets;
Piece moved_piece;
int moveCount, quietCount;
// Step 1. Initialize node
Thread* thisThread = pos.this_thread();
inCheck = pos.checkers();
- moveCount = quietCount = ss->moveCount = 0;
+ moveCount = quietCount = ss->moveCount = 0;
+ ss->history = 0;
bestValue = -VALUE_INFINITE;
ss->ply = (ss-1)->ply + 1;
if (thisThread->resetCalls.load(std::memory_order_relaxed))
{
thisThread->resetCalls = false;
- thisThread->callsCnt = 0;
+
+ // 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 > 4096)
+
+ if (--thisThread->callsCnt <= 0)
{
for (Thread* th : Threads)
th->resetCalls = true;
if (!rootNode)
{
// Step 2. Check for aborted search and immediate draw
- if (Signals.stop.load(std::memory_order_relaxed) || pos.is_draw() || ss->ply >= MAX_PLY)
+ 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()];
assert(0 <= ss->ply && ss->ply < MAX_PLY);
ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
- ss->counterMoves = nullptr;
- (ss+1)->skipEarlyPruning = false;
+ ss->counterMoves = &thisThread->counterMoveHistory[NO_PIECE][0];
(ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
+ Square prevSq = to_sq((ss-1)->currentMove);
// Step 4. Transposition table lookup. We don't want the score of a partial
// 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 = excludedMove ? pos.exclusion_key() : pos.key();
+ posKey = pos.key() ^ Key(excludedMove);
tte = TT.probe(posKey, ttHit);
ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
ttMove = rootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
&& (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
: (tte->bound() & BOUND_UPPER)))
{
- ss->currentMove = ttMove; // Can be MOVE_NONE
-
- // If ttMove is quiet, update killers, history, counter move on TT hit
- if (ttValue >= beta && ttMove)
+ // If ttMove is quiet, update move sorting heuristics on TT hit
+ if (ttMove)
{
- int d = depth / ONE_PLY;
-
- if (!pos.capture_or_promotion(ttMove))
+ if (ttValue >= beta)
{
- Value bonus = Value(d * d + 2 * d - 2);
- update_stats(pos, ss, ttMove, nullptr, 0, bonus);
- }
+ if (!pos.capture_or_promotion(ttMove))
+ update_stats(pos, ss, ttMove, nullptr, 0, 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_type())
+ // 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));
+ }
+ // Penalty for a quiet ttMove that fails low
+ else if (!pos.capture_or_promotion(ttMove))
{
- Value penalty = Value(d * d + 4 * d + 1);
- Square prevSq = to_sq((ss-1)->currentMove);
- update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, -penalty);
+ 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);
}
}
return ttValue;
// Step 4a. Tablebase probe
if (!rootNode && TB::Cardinality)
{
- int piecesCnt = pos.count<ALL_PIECES>(WHITE) + pos.count<ALL_PIECES>(BLACK);
+ int piecesCount = pos.count<ALL_PIECES>();
- if ( piecesCnt <= TB::Cardinality
- && (piecesCnt < TB::Cardinality || depth >= TB::ProbeDepth)
+ if ( piecesCount <= TB::Cardinality
+ && (piecesCount < TB::Cardinality || depth >= TB::ProbeDepth)
&& pos.rule50_count() == 0
&& !pos.can_castle(ANY_CASTLING))
{
- int found, v = Tablebases::probe_wdl(pos, &found);
+ TB::ProbeState err;
+ TB::WDLScore v = Tablebases::probe_wdl(pos, &err);
- if (found)
+ if (err != TB::ProbeState::FAIL)
{
- TB::Hits++;
+ thisThread->tbHits++;
int drawScore = TB::UseRule50 ? 1 : 0;
ss->staticEval, TT.generation());
}
- if (ss->skipEarlyPruning)
+ if (skipEarlyPruning)
goto moves_loop;
// Step 6. Razoring (skipped when in check)
if ( !PvNode
&& depth < 4 * ONE_PLY
- && eval + razor_margin[depth / ONE_PLY] <= alpha
- && ttMove == MOVE_NONE)
+ && eval + razor_margin[depth / ONE_PLY] <= alpha)
{
- if ( depth <= ONE_PLY
- && eval + razor_margin[3 * ONE_PLY] <= alpha)
- return qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO);
+ if (depth <= ONE_PLY)
+ return qsearch<NonPV, false>(pos, ss, alpha, alpha+1);
Value ralpha = alpha - razor_margin[depth / ONE_PLY];
- Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
+ Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1);
if (v <= ralpha)
return v;
}
&& eval - futility_margin(depth) >= beta
&& eval < VALUE_KNOWN_WIN // Do not return unproven wins
&& pos.non_pawn_material(pos.side_to_move()))
- return eval - futility_margin(depth);
+ return eval;
// Step 8. Null move search with verification search (is omitted in PV nodes)
if ( !PvNode
&& (ss->staticEval >= beta - 35 * (depth / ONE_PLY - 6) || depth >= 13 * ONE_PLY)
&& pos.non_pawn_material(pos.side_to_move()))
{
- ss->currentMove = MOVE_NULL;
- ss->counterMoves = nullptr;
assert(eval - beta >= 0);
// Null move dynamic reduction based on depth and value
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];
+
pos.do_null_move(st);
- (ss+1)->skipEarlyPruning = true;
- nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
- : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
- (ss+1)->skipEarlyPruning = false;
+ Value nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1)
+ : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode, true);
pos.undo_null_move();
if (nullValue >= beta)
return nullValue;
// Do verification search at high depths
- ss->skipEarlyPruning = true;
- Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
- : search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
- ss->skipEarlyPruning = false;
+ 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);
if (v >= beta)
return nullValue;
Depth rdepth = depth - 4 * ONE_PLY;
assert(rdepth >= ONE_PLY);
- assert((ss-1)->currentMove != MOVE_NONE);
- assert((ss-1)->currentMove != MOVE_NULL);
+ assert(is_ok((ss-1)->currentMove));
MovePicker mp(pos, ttMove, rbeta - ss->staticEval);
if (pos.legal(move))
{
ss->currentMove = move;
- ss->counterMoves = &CounterMoveHistory[pos.moved_piece(move)][to_sq(move)];
- pos.do_move(move, st, pos.gives_check(move));
- value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
+ ss->counterMoves = &thisThread->counterMoveHistory[pos.moved_piece(move)][to_sq(move)];
+
+ pos.do_move(move, st);
+ value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode, false);
pos.undo_move(move);
if (value >= rbeta)
return value;
&& (PvNode || ss->staticEval + 256 >= beta))
{
Depth d = (3 * depth / (4 * ONE_PLY) - 2) * ONE_PLY;
- ss->skipEarlyPruning = true;
- search<NT>(pos, ss, alpha, beta, d, cutNode);
- ss->skipEarlyPruning = false;
+ search<NT>(pos, ss, alpha, beta, d, cutNode, true);
tte = TT.probe(posKey, ttHit);
ttMove = ttHit ? tte->move() : MOVE_NONE;
moves_loop: // When in check search starts from here
- const CounterMoveStats* cmh = (ss-1)->counterMoves;
- const CounterMoveStats* fmh = (ss-2)->counterMoves;
- const CounterMoveStats* fmh2 = (ss-4)->counterMoves;
+ const CounterMoveStats& cmh = *(ss-1)->counterMoves;
+ const CounterMoveStats& fmh = *(ss-2)->counterMoves;
+ const CounterMoveStats& fm2 = *(ss-4)->counterMoves;
MovePicker mp(pos, ttMove, depth, ss);
value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
singularExtensionNode = !rootNode
&& depth >= 8 * ONE_PLY
&& ttMove != MOVE_NONE
- /* && ttValue != VALUE_NONE Already implicit in the next condition */
- && abs(ttValue) < VALUE_KNOWN_WIN
+ && ttValue != VALUE_NONE
&& !excludedMove // Recursive singular search is not allowed
&& (tte->bound() & BOUND_LOWER)
&& tte->depth() >= depth - 3 * ONE_PLY;
+ skipQuiets = false;
// Step 11. Loop through moves
// Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
- while ((move = mp.next_move()) != MOVE_NONE)
+ while ((move = mp.next_move(skipQuiets)) != MOVE_NONE)
{
assert(is_ok(move));
moveCountPruning = depth < 16 * ONE_PLY
&& moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY];
- // Step 12. Extend checks
- if ( givesCheck
- && !moveCountPruning
- && pos.see_sign(move) >= VALUE_ZERO)
- extension = ONE_PLY;
+ // Step 12. Singular and Gives Check Extensions
// Singular extension search. If all moves but one fail low on a search of
// (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
// is singular and should be extended. To verify this we do a reduced search
// on all the other moves but the ttMove and if the result is lower than
- // ttValue minus a margin then we extend the ttMove.
+ // ttValue minus a margin then we will extend the ttMove.
if ( singularExtensionNode
&& move == ttMove
- && !extension
&& pos.legal(move))
{
- Value rBeta = ttValue - 2 * depth / ONE_PLY;
+ Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
Depth d = (depth / (2 * ONE_PLY)) * ONE_PLY;
ss->excludedMove = move;
- ss->skipEarlyPruning = true;
- value = search<NonPV>(pos, ss, rBeta - 1, rBeta, d, cutNode);
- ss->skipEarlyPruning = false;
+ value = search<NonPV>(pos, ss, rBeta - 1, rBeta, d, cutNode, true);
ss->excludedMove = MOVE_NONE;
if (value < rBeta)
extension = ONE_PLY;
}
+ else if ( givesCheck
+ && !moveCountPruning
+ && pos.see_ge(move))
+ extension = ONE_PLY;
- // Update the current move (this must be done after singular extension search)
+ // Calculate new depth for this move
newDepth = depth - ONE_PLY + extension;
// Step 13. Pruning at shallow depth
- if ( !rootNode
- && !captureOrPromotion
- && !inCheck
- && !givesCheck
- && !pos.advanced_pawn_push(move)
- && bestValue > VALUE_MATED_IN_MAX_PLY)
+ if ( !rootNode
+ && pos.non_pawn_material(pos.side_to_move())
+ && bestValue > VALUE_MATED_IN_MAX_PLY)
{
- // Move count based pruning
- if (moveCountPruning)
- continue;
+ if ( !captureOrPromotion
+ && !givesCheck
+ && (!pos.advanced_pawn_push(move) || pos.non_pawn_material() >= Value(5000)))
+ {
+ // Move count based pruning
+ if (moveCountPruning)
+ {
+ skipQuiets = true;
+ continue;
+ }
- predictedDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO);
+ // Reduced depth of the next LMR search
+ int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;
- // Countermoves based pruning
- if ( predictedDepth < 3 * ONE_PLY
- && move != ss->killers[0]
- && (!cmh || (*cmh )[moved_piece][to_sq(move)] < VALUE_ZERO)
- && (!fmh || (*fmh )[moved_piece][to_sq(move)] < VALUE_ZERO)
- && (!fmh2 || (*fmh2)[moved_piece][to_sq(move)] < VALUE_ZERO || (cmh && fmh)))
- continue;
-
- // Futility pruning: parent node
- if ( predictedDepth < 7 * ONE_PLY
- && ss->staticEval + 256 + 200 * predictedDepth / ONE_PLY <= alpha)
- continue;
+ // Countermoves based pruning
+ if ( lmrDepth < 3
+ && (cmh[moved_piece][to_sq(move)] < CounterMovePruneThreshold)
+ && (fmh[moved_piece][to_sq(move)] < CounterMovePruneThreshold))
+ continue;
- // Prune moves with negative SEE at low depths and below a decreasing
- // threshold at higher depths.
- if (predictedDepth < 8 * ONE_PLY)
- {
- Value see_v = predictedDepth < 4 * ONE_PLY ? VALUE_ZERO
- : -PawnValueMg * 2 * int(predictedDepth - 3 * ONE_PLY) / ONE_PLY;
+ // Futility pruning: parent node
+ if ( lmrDepth < 7
+ && !inCheck
+ && ss->staticEval + 256 + 200 * lmrDepth <= alpha)
+ continue;
- if (pos.see_sign(move) < see_v)
+ // Prune moves with negative SEE
+ if ( lmrDepth < 8
+ && !pos.see_ge(move, Value(-35 * lmrDepth * lmrDepth)))
continue;
}
+ else if ( depth < 7 * ONE_PLY
+ && !extension
+ && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY)))
+ continue;
}
// Speculative prefetch as early as possible
continue;
}
+ // Update the current move (this must be done after singular extension search)
ss->currentMove = move;
- ss->counterMoves = &CounterMoveHistory[moved_piece][to_sq(move)];
+ ss->counterMoves = &thisThread->counterMoveHistory[moved_piece][to_sq(move)];
// Step 14. Make the move
pos.do_move(move, st, givesCheck);
// 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.
- else if ( 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)
+ // hence break make_move().
+ 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
+
+ // Decrease/increase reduction by comparing opponent's stat score
+ if (ss->history > 0 && (ss-1)->history < 0)
+ r -= ONE_PLY;
+
+ else if (ss->history < 0 && (ss-1)->history > 0)
+ r += ONE_PLY;
+
// Decrease/increase reduction for moves with a good/bad history
- Value val = thisThread->history[moved_piece][to_sq(move)]
- + (cmh ? (*cmh )[moved_piece][to_sq(move)] : VALUE_ZERO)
- + (fmh ? (*fmh )[moved_piece][to_sq(move)] : VALUE_ZERO)
- + (fmh2 ? (*fmh2)[moved_piece][to_sq(move)] : VALUE_ZERO)
- + thisThread->fromTo.get(~pos.side_to_move(), move);
- int rHist = (val - 8000) / 20000;
- r = std::max(DEPTH_ZERO, (r / ONE_PLY - rHist) * ONE_PLY);
+ r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->history / 20000) * ONE_PLY);
}
Depth d = std::max(newDepth - r, ONE_PLY);
- value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
+ value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true, false);
doFullDepthSearch = (value > alpha && d != newDepth);
}
// 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)
- : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
- : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
+ givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha)
+ : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha)
+ : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode, false);
// 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
(ss+1)->pv[0] = MOVE_NONE;
value = newDepth < ONE_PLY ?
- givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
- : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
- : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
+ givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha)
+ : -qsearch<PV, false>(pos, ss+1, -beta, -alpha)
+ : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, false);
}
// Step 17. Undo move
if (value > alpha)
{
- // If there is an easy move for this position, clear it if unstable
- if ( PvNode
- && thisThread == Threads.main()
- && EasyMove.get(pos.key())
- && (move != EasyMove.get(pos.key()) || moveCount > 1))
- EasyMove.clear();
-
bestMove = move;
if (PvNode && !rootNode) // Update pv even in fail-high case
// All legal moves have been searched and if there are no legal moves, it
// must be a mate or a stalemate. If we are in a singular extension search then
// return a fail low score.
+
+ assert(moveCount || !inCheck || excludedMove || !MoveList<LEGAL>(pos).size());
+
if (!moveCount)
bestValue = excludedMove ? alpha
: inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
else if (bestMove)
{
- int d = depth / ONE_PLY;
-
- // Quiet best move: update killers, history and countermoves
+ // Quiet best move: update move sorting heuristics
if (!pos.capture_or_promotion(bestMove))
- {
- Value bonus = Value(d * d + 2 * d - 2);
- update_stats(pos, ss, bestMove, quietsSearched, quietCount, bonus);
- }
+ update_stats(pos, ss, bestMove, quietsSearched, quietCount, 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_type())
- {
- Value penalty = Value(d * d + 4 * d + 1);
- Square prevSq = to_sq((ss-1)->currentMove);
- update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, -penalty);
- }
+ if ((ss-1)->moveCount == 1 && !pos.captured_piece())
+ update_cm_stats(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_type()
+ && !pos.captured_piece()
&& is_ok((ss-1)->currentMove))
- {
- int d = depth / ONE_PLY;
- Value bonus = Value(d * d + 2 * d - 2);
- Square prevSq = to_sq((ss-1)->currentMove);
- update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, bonus);
- }
+ update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));
- tte->save(posKey, value_to_tt(bestValue, ss->ply),
- bestValue >= beta ? BOUND_LOWER :
- PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
- depth, bestMove, ss->staticEval, TT.generation());
+ if (!excludedMove)
+ tte->save(posKey, value_to_tt(bestValue, ss->ply),
+ bestValue >= beta ? BOUND_LOWER :
+ PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
+ depth, bestMove, ss->staticEval, TT.generation());
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
// qsearch() is the quiescence search function, which is called by the main
- // search function when the remaining depth is zero (or, to be more precise,
- // less than ONE_PLY).
+ // search function with depth zero, or recursively with depth less than ONE_PLY.
template <NodeType NT, bool InCheck>
Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
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;
+ moveCount = 0;
// Check for an instant draw or if the maximum ply has been reached
- if (pos.is_draw() || ss->ply >= MAX_PLY)
+ if (pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos)
: DrawValue[pos.side_to_move()];
&& ttValue != VALUE_NONE // Only in case of TT access race
&& (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
: (tte->bound() & BOUND_UPPER)))
- {
- ss->currentMove = ttMove; // Can be MOVE_NONE
return ttValue;
- }
// Evaluate the position statically
if (InCheck)
? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
: pos.gives_check(move);
+ moveCount++;
+
// Futility pruning
if ( !InCheck
&& !givesCheck
continue;
}
- if (futilityBase <= alpha && pos.see(move) <= VALUE_ZERO)
+ if (futilityBase <= alpha && !pos.see_ge(move, VALUE_ZERO + 1))
{
bestValue = std::max(bestValue, futilityBase);
continue;
// Detect non-capture evasions that are candidates to be pruned
evasionPrunable = InCheck
+ && (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_sign(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
- void update_cm_stats(Stack* ss, Piece pc, Square s, Value bonus) {
+ void update_cm_stats(Stack* ss, Piece pc, Square s, int bonus) {
- CounterMoveStats* cmh = (ss-1)->counterMoves;
- CounterMoveStats* fmh1 = (ss-2)->counterMoves;
- CounterMoveStats* fmh2 = (ss-4)->counterMoves;
-
- if (cmh)
- cmh->update(pc, s, bonus);
-
- if (fmh1)
- fmh1->update(pc, s, bonus);
-
- if (fmh2)
- fmh2->update(pc, s, bonus);
+ for (int i : {1, 2, 4})
+ if (is_ok((ss-i)->currentMove))
+ (ss-i)->counterMoves->update(pc, s, bonus);
}
- // update_stats() updates killers, history, countermove and countermove plus
- // follow-up move history when a new quiet best move is found.
+ // update_stats() updates move sorting heuristics when a new quiet best move is found
void update_stats(const Position& pos, Stack* ss, Move move,
- Move* quiets, int quietsCnt, Value bonus) {
+ Move* quiets, int quietsCnt, int bonus) {
if (ss->killers[0] != move)
{
Color c = pos.side_to_move();
Thread* thisThread = pos.this_thread();
- thisThread->fromTo.update(c, move, bonus);
- thisThread->history.update(pos.moved_piece(move), to_sq(move), bonus);
+ thisThread->history.update(c, move, bonus);
update_cm_stats(ss, pos.moved_piece(move), to_sq(move), bonus);
- if ((ss-1)->counterMoves)
+ if (is_ok((ss-1)->currentMove))
{
Square prevSq = to_sq((ss-1)->currentMove);
thisThread->counterMoves.update(pos.piece_on(prevSq), prevSq, move);
// Decrease all the other played quiet moves
for (int i = 0; i < quietsCnt; ++i)
{
- thisThread->fromTo.update(c, quiets[i], -bonus);
- thisThread->history.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
+ thisThread->history.update(c, quiets[i], -bonus);
update_cm_stats(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
}
}
if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10)
|| (Limits.movetime && elapsed >= Limits.movetime)
- || (Limits.nodes && Threads.nodes_searched() >= Limits.nodes))
+ || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
Signals.stop = true;
}
const RootMoves& rootMoves = pos.this_thread()->rootMoves;
size_t PVIdx = pos.this_thread()->PVIdx;
size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
- uint64_t nodes_searched = Threads.nodes_searched();
+ uint64_t nodesSearched = Threads.nodes_searched();
+ uint64_t tbHits = Threads.tb_hits() + (TB::RootInTB ? rootMoves.size() : 0);
for (size_t i = 0; i < multiPV; ++i)
{
- bool updated = (i <= PVIdx);
+ bool updated = (i <= PVIdx && rootMoves[i].score != -VALUE_INFINITE);
if (depth == ONE_PLY && !updated)
continue;
if (!tb && i == PVIdx)
ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
- ss << " nodes " << nodes_searched
- << " nps " << nodes_searched * 1000 / elapsed;
+ ss << " nodes " << nodesSearched
+ << " nps " << nodesSearched * 1000 / elapsed;
if (elapsed > 1000) // Earlier makes little sense
ss << " hashfull " << TT.hashfull();
- ss << " tbhits " << TB::Hits
+ ss << " tbhits " << tbHits
<< " time " << elapsed
<< " pv";
/// 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.
-bool RootMove::extract_ponder_from_tt(Position& pos)
-{
+bool RootMove::extract_ponder_from_tt(Position& pos) {
+
StateInfo st;
bool ttHit;
assert(pv.size() == 1);
- pos.do_move(pv[0], st, pos.gives_check(pv[0]));
+ if (!pv[0])
+ return false;
+
+ pos.do_move(pv[0], st);
TTEntry* tte = TT.probe(pos.key(), ttHit);
if (ttHit)
void Tablebases::filter_root_moves(Position& pos, Search::RootMoves& rootMoves) {
- Hits = 0;
RootInTB = false;
UseRule50 = Options["Syzygy50MoveRule"];
ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
RootInTB = root_probe_wdl(pos, rootMoves, TB::Score);
// Only probe during search if winning
- if (TB::Score <= VALUE_DRAW)
+ if (RootInTB && TB::Score <= VALUE_DRAW)
Cardinality = 0;
}
- if (RootInTB)
- {
- Hits = rootMoves.size();
-
- if (!UseRule50)
- TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1
- : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1
- : VALUE_DRAW;
- }
+ if (RootInTB && !UseRule50)
+ TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1
+ : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1
+ : VALUE_DRAW;
}
projects / stockfish / blobdiff