#include "uci.h"
#include "syzygy/tbprobe.h"
+namespace Stockfish {
+
namespace Search {
LimitsType Limits;
namespace {
// Different node types, used as a template parameter
- enum NodeType { NonPV, PV };
-
- constexpr uint64_t TtHitAverageWindow = 4096;
- constexpr uint64_t TtHitAverageResolution = 1024;
+ enum NodeType { NonPV, PV, Root };
// Futility margin
Value futility_margin(Depth d, bool improving) {
- return Value(234 * (d - improving));
+ return Value(214 * (d - improving));
}
// Reductions lookup table, initialized at startup
int Reductions[MAX_MOVES]; // [depth or moveNumber]
- Depth reduction(bool i, Depth d, int mn) {
+ Depth reduction(bool i, Depth d, int mn, bool rangeReduction) {
int r = Reductions[d] * Reductions[mn];
- return (r + 503) / 1024 + (!i && r > 915);
+ return (r + 534) / 1024 + (!i && r > 904) + rangeReduction;
}
constexpr int futility_move_count(bool improving, Depth depth) {
// History and stats update bonus, based on depth
int stat_bonus(Depth d) {
- return d > 14 ? 29 : 8 * d * d + 224 * d - 215;
+ return std::min((6 * d + 229) * d - 215 , 2000);
}
// Add a small random component to draw evaluations to avoid 3-fold blindness
return VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1);
}
+ // Check if the current thread is in a search explosion
+ ExplosionState search_explosion(Thread* thisThread) {
+
+ uint64_t nodesNow = thisThread->nodes;
+ bool explosive = thisThread->doubleExtensionAverage[WHITE].is_greater(2, 100)
+ || thisThread->doubleExtensionAverage[BLACK].is_greater(2, 100);
+
+ if (explosive)
+ thisThread->nodesLastExplosive = nodesNow;
+ else
+ thisThread->nodesLastNormal = nodesNow;
+
+ if ( explosive
+ && thisThread->state == EXPLOSION_NONE
+ && nodesNow - thisThread->nodesLastNormal > 6000000)
+ thisThread->state = MUST_CALM_DOWN;
+
+ if ( thisThread->state == MUST_CALM_DOWN
+ && nodesNow - thisThread->nodesLastExplosive > 6000000)
+ thisThread->state = EXPLOSION_NONE;
+
+ return thisThread->state;
+ }
+
// Skill structure is used to implement strength limit
struct Skill {
explicit Skill(int l) : level(l) {}
Move best = MOVE_NONE;
};
- // Breadcrumbs are used to mark nodes as being searched by a given thread
- struct Breadcrumb {
- std::atomic<Thread*> thread;
- std::atomic<Key> key;
- };
- std::array<Breadcrumb, 1024> breadcrumbs;
-
- // ThreadHolding structure keeps track of which thread left breadcrumbs at the given
- // node for potential reductions. A free node will be marked upon entering the moves
- // loop by the constructor, and unmarked upon leaving that loop by the destructor.
- struct ThreadHolding {
- explicit ThreadHolding(Thread* thisThread, Key posKey, int ply) {
- location = ply < 8 ? &breadcrumbs[posKey & (breadcrumbs.size() - 1)] : nullptr;
- otherThread = false;
- owning = false;
- if (location)
- {
- // See if another already marked this location, if not, mark it ourselves
- Thread* tmp = (*location).thread.load(std::memory_order_relaxed);
- if (tmp == nullptr)
- {
- (*location).thread.store(thisThread, std::memory_order_relaxed);
- (*location).key.store(posKey, std::memory_order_relaxed);
- owning = true;
- }
- else if ( tmp != thisThread
- && (*location).key.load(std::memory_order_relaxed) == posKey)
- otherThread = true;
- }
- }
-
- ~ThreadHolding() {
- if (owning) // Free the marked location
- (*location).thread.store(nullptr, std::memory_order_relaxed);
- }
-
- bool marked() { return otherThread; }
-
- private:
- Breadcrumb* location;
- bool otherThread, owning;
- };
-
- template <NodeType NT>
+ template <NodeType nodeType>
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
- template <NodeType NT>
+ template <NodeType nodeType>
Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = 0);
Value value_to_tt(Value v, int ply);
uint64_t perft(Position& pos, Depth depth) {
StateInfo st;
- ASSERT_ALIGNED(&st, Eval::NNUE::kCacheLineSize);
+ ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize);
uint64_t cnt, nodes = 0;
const bool leaf = (depth == 2);
void Search::init() {
for (int i = 1; i < MAX_MOVES; ++i)
- Reductions[i] = int((21.3 + 2 * std::log(Threads.size())) * std::log(i + 0.25 * std::log(i)));
+ Reductions[i] = int((21.9 + std::log(Threads.size()) / 2) * std::log(i));
}
// To allow access to (ss-7) up to (ss+2), the stack must be oversized.
// The former is needed to allow update_continuation_histories(ss-1, ...),
// which accesses its argument at ss-6, also near the root.
- // The latter is needed for statScores and killer initialization.
+ // The latter is needed for statScore and killer initialization.
Stack stack[MAX_PLY+10], *ss = stack+7;
Move pv[MAX_PLY+1];
Value bestValue, alpha, beta, delta;
for (int i = 7; i > 0; i--)
(ss-i)->continuationHistory = &this->continuationHistory[0][0][NO_PIECE][0]; // Use as a sentinel
+ for (int i = 0; i <= MAX_PLY + 2; ++i)
+ (ss+i)->ply = i;
+
ss->pv = pv;
bestValue = delta = alpha = -VALUE_INFINITE;
multiPV = std::max(multiPV, (size_t)4);
multiPV = std::min(multiPV, rootMoves.size());
- ttHitAverage = TtHitAverageWindow * TtHitAverageResolution / 2;
-
- int ct = int(Options["Contempt"]) * PawnValueEg / 100; // From centipawns
- // In analysis mode, adjust contempt in accordance with user preference
- if (Limits.infinite || Options["UCI_AnalyseMode"])
- ct = Options["Analysis Contempt"] == "Off" ? 0
- : Options["Analysis Contempt"] == "Both" ? ct
- : Options["Analysis Contempt"] == "White" && us == BLACK ? -ct
- : Options["Analysis Contempt"] == "Black" && us == WHITE ? -ct
- : ct;
+ doubleExtensionAverage[WHITE].set(0, 100); // initialize the running average at 0%
+ doubleExtensionAverage[BLACK].set(0, 100); // initialize the running average at 0%
- // Evaluation score is from the white point of view
- contempt = (us == WHITE ? make_score(ct, ct / 2)
- : -make_score(ct, ct / 2));
+ nodesLastExplosive = nodes;
+ nodesLastNormal = nodes;
+ state = EXPLOSION_NONE;
+ trend = SCORE_ZERO;
int searchAgainCounter = 0;
alpha = std::max(prev - delta,-VALUE_INFINITE);
beta = std::min(prev + delta, VALUE_INFINITE);
- // Adjust contempt based on root move's previousScore (dynamic contempt)
- int dct = ct + (113 - ct / 2) * prev / (abs(prev) + 147);
+ // Adjust trend based on root move's previousScore (dynamic contempt)
+ int tr = 113 * prev / (abs(prev) + 147);
- contempt = (us == WHITE ? make_score(dct, dct / 2)
- : -make_score(dct, dct / 2));
+ trend = (us == WHITE ? make_score(tr, tr / 2)
+ : -make_score(tr, tr / 2));
}
// Start with a small aspiration window and, in the case of a fail
// high/low, re-search with a bigger window until we don't fail
// high/low anymore.
- failedHighCnt = 0;
+ int failedHighCnt = 0;
while (true)
{
Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - searchAgainCounter);
- bestValue = ::search<PV>(rootPos, ss, alpha, beta, adjustedDepth, false);
+ bestValue = Stockfish::search<Root>(rootPos, ss, alpha, beta, adjustedDepth, 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
totBestMoveChanges += th->bestMoveChanges;
th->bestMoveChanges = 0;
}
- double bestMoveInstability = 1 + 2 * totBestMoveChanges / Threads.size();
-
+ double bestMoveInstability = 1.073 + std::max(1.0, 2.25 - 9.9 / rootDepth)
+ * totBestMoveChanges / Threads.size();
double totalTime = Time.optimum() * fallingEval * reduction * bestMoveInstability;
// Cap used time in case of a single legal move for a better viewer experience in tournaments
// search<>() is the main search function for both PV and non-PV nodes
- template <NodeType NT>
+ template <NodeType nodeType>
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
- constexpr bool PvNode = NT == PV;
- const bool rootNode = PvNode && ss->ply == 0;
+ Thread* thisThread = pos.this_thread();
+
+ // Step 0. Limit search explosion
+ if ( ss->ply > 10
+ && search_explosion(thisThread) == MUST_CALM_DOWN
+ && depth > (ss-1)->depth)
+ depth = (ss-1)->depth;
+
+ constexpr bool PvNode = nodeType != NonPV;
+ constexpr bool rootNode = nodeType == Root;
const Depth maxNextDepth = rootNode ? depth : depth + 1;
// Check if we have an upcoming move which draws by repetition, or
// if the opponent had an alternative move earlier to this position.
- if ( pos.rule50_count() >= 3
+ if ( !rootNode
+ && pos.rule50_count() >= 3
&& alpha < VALUE_DRAW
- && !rootNode
&& pos.has_game_cycle(ss->ply))
{
alpha = value_draw(pos.this_thread());
// Dive into quiescence search when the depth reaches zero
if (depth <= 0)
- return qsearch<NT>(pos, ss, alpha, beta);
+ return qsearch<PvNode ? PV : NonPV>(pos, ss, alpha, beta);
assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
assert(PvNode || (alpha == beta - 1));
Move pv[MAX_PLY+1], capturesSearched[32], quietsSearched[64];
StateInfo st;
- ASSERT_ALIGNED(&st, Eval::NNUE::kCacheLineSize);
+ ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize);
TTEntry* tte;
Key posKey;
Move ttMove, move, excludedMove, bestMove;
Depth extension, newDepth;
Value bestValue, value, ttValue, eval, maxValue, probCutBeta;
- bool formerPv, givesCheck, improving, didLMR, priorCapture;
+ bool givesCheck, improving, didLMR, priorCapture;
bool captureOrPromotion, doFullDepthSearch, moveCountPruning,
- ttCapture, singularQuietLMR;
+ ttCapture, singularQuietLMR, noLMRExtension;
Piece movedPiece;
- int moveCount, captureCount, quietCount;
+ int moveCount, captureCount, quietCount, bestMoveCount, improvement;
// Step 1. Initialize node
- Thread* thisThread = pos.this_thread();
- ss->inCheck = pos.checkers();
- priorCapture = pos.captured_piece();
- Color us = pos.side_to_move();
- moveCount = captureCount = quietCount = ss->moveCount = 0;
- bestValue = -VALUE_INFINITE;
- maxValue = VALUE_INFINITE;
+ ss->inCheck = pos.checkers();
+ priorCapture = pos.captured_piece();
+ Color us = pos.side_to_move();
+ moveCount = bestMoveCount = captureCount = quietCount = ss->moveCount = 0;
+ bestValue = -VALUE_INFINITE;
+ maxValue = VALUE_INFINITE;
// Check for the available remaining time
if (thisThread == Threads.main())
assert(0 <= ss->ply && ss->ply < MAX_PLY);
- (ss+1)->ply = ss->ply + 1;
- (ss+1)->ttPv = false;
+ (ss+1)->ttPv = false;
(ss+1)->excludedMove = bestMove = MOVE_NONE;
- (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
- Square prevSq = to_sq((ss-1)->currentMove);
+ (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
+ ss->doubleExtensions = (ss-1)->doubleExtensions;
+ ss->depth = depth;
+ Square prevSq = to_sq((ss-1)->currentMove);
+
+ // Update the running average statistics for double extensions
+ thisThread->doubleExtensionAverage[us].update(ss->depth > (ss-1)->depth);
// Initialize statScore to zero for the grandchildren of the current position.
// So statScore is shared between all grandchildren and only the first grandchild
ttValue = ss->ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE;
ttMove = rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0]
: ss->ttHit ? tte->move() : MOVE_NONE;
+ ttCapture = ttMove && pos.capture_or_promotion(ttMove);
if (!excludedMove)
ss->ttPv = PvNode || (ss->ttHit && tte->is_pv());
- formerPv = ss->ttPv && !PvNode;
// Update low ply history for previous move if we are near root and position is or has been in PV
if ( ss->ttPv
&& is_ok((ss-1)->currentMove))
thisThread->lowPlyHistory[ss->ply - 1][from_to((ss-1)->currentMove)] << stat_bonus(depth - 5);
- // thisThread->ttHitAverage can be used to approximate the running average of ttHit
- thisThread->ttHitAverage = (TtHitAverageWindow - 1) * thisThread->ttHitAverage / TtHitAverageWindow
- + TtHitAverageResolution * ss->ttHit;
-
// At non-PV nodes we check for an early TT cutoff
if ( !PvNode
&& ss->ttHit
if (ttValue >= beta)
{
// Bonus for a quiet ttMove that fails high
- if (!pos.capture_or_promotion(ttMove))
+ if (!ttCapture)
update_quiet_stats(pos, ss, ttMove, stat_bonus(depth), depth);
// Extra penalty for early quiet moves of the previous ply
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + 1));
}
// Penalty for a quiet ttMove that fails low
- else if (!pos.capture_or_promotion(ttMove))
+ else if (!ttCapture)
{
int penalty = -stat_bonus(depth);
thisThread->mainHistory[us][from_to(ttMove)] << penalty;
// Skip early pruning when in check
ss->staticEval = eval = VALUE_NONE;
improving = false;
+ improvement = 0;
goto moves_loop;
}
else if (ss->ttHit)
else
{
// In case of null move search use previous static eval with a different sign
- // and addition of two tempos
if ((ss-1)->currentMove != MOVE_NULL)
ss->staticEval = eval = evaluate(pos);
else
- ss->staticEval = eval = -(ss-1)->staticEval + 2 * Tempo;
+ ss->staticEval = eval = -(ss-1)->staticEval;
// Save static evaluation into transposition table
+ if(!excludedMove)
tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
}
// Use static evaluation difference to improve quiet move ordering
if (is_ok((ss-1)->currentMove) && !(ss-1)->inCheck && !priorCapture)
{
- int bonus = std::clamp(-depth * 4 * int((ss-1)->staticEval + ss->staticEval - 2 * Tempo), -1000, 1000);
+ int bonus = std::clamp(-depth * 4 * int((ss-1)->staticEval + ss->staticEval), -1000, 1000);
thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus;
}
- // Set up improving flag that is used in various pruning heuristics
- // We define position as improving if static evaluation of position is better
- // Than the previous static evaluation at our turn
- // In case of us being in check at our previous move we look at move prior to it
- improving = (ss-2)->staticEval == VALUE_NONE
- ? ss->staticEval > (ss-4)->staticEval || (ss-4)->staticEval == VALUE_NONE
- : ss->staticEval > (ss-2)->staticEval;
+ // Set up the improvement variable, which is the difference between the current
+ // static evaluation and the previous static evaluation at our turn (if we were
+ // in check at our previous move we look at the move prior to it). The improvement
+ // margin and the improving flag are used in various pruning heuristics.
+ improvement = (ss-2)->staticEval != VALUE_NONE ? ss->staticEval - (ss-2)->staticEval
+ : (ss-4)->staticEval != VALUE_NONE ? ss->staticEval - (ss-4)->staticEval
+ : 200;
- // Step 7. Futility pruning: child node (~50 Elo)
+ improving = improvement > 0;
+
+ // Step 7. Futility pruning: child node (~50 Elo).
+ // The depth condition is important for mate finding.
if ( !PvNode
&& depth < 9
&& eval - futility_margin(depth, improving) >= beta
// Step 8. Null move search with verification search (~40 Elo)
if ( !PvNode
&& (ss-1)->currentMove != MOVE_NULL
- && (ss-1)->statScore < 22977
+ && (ss-1)->statScore < 23767
&& eval >= beta
&& eval >= ss->staticEval
- && ss->staticEval >= beta - 30 * depth - 28 * improving + 84 * ss->ttPv + 168
+ && ss->staticEval >= beta - 20 * depth - improvement / 15 + 168 * ss->ttPv + 177
&& !excludedMove
&& pos.non_pawn_material(us)
&& (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
assert(eval - beta >= 0);
// Null move dynamic reduction based on depth and value
- Depth R = (1015 + 85 * depth) / 256 + std::min(int(eval - beta) / 191, 3);
+ Depth R = std::min(int(eval - beta) / 205, 3) + depth / 3 + 4;
ss->currentMove = MOVE_NULL;
ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0];
}
}
- probCutBeta = beta + 194 - 49 * improving;
+ probCutBeta = beta + 209 - 44 * improving;
- // Step 9. ProbCut (~10 Elo)
+ // Step 9. ProbCut (~4 Elo)
// If we have a good enough capture and a reduced search returns a value
// much above beta, we can (almost) safely prune the previous move.
if ( !PvNode
&& ttValue != VALUE_NONE
&& ttValue < probCutBeta))
{
- // if ttMove is a capture and value from transposition table is good enough produce probCut
- // cutoff without digging into actual probCut search
- if ( ss->ttHit
- && tte->depth() >= depth - 3
- && ttValue != VALUE_NONE
- && ttValue >= probCutBeta
- && ttMove
- && pos.capture_or_promotion(ttMove))
- return probCutBeta;
-
assert(probCutBeta < VALUE_INFINITE);
+
MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &captureHistory);
int probCutCount = 0;
bool ttPv = ss->ttPv;
ss->ttPv = ttPv;
}
- // Step 10. If the position is not in TT, decrease depth by 2
+ // Step 10. If the position is not in TT, decrease depth by 2 or 1 depending on node type
if ( PvNode
&& depth >= 6
&& !ttMove)
depth -= 2;
-moves_loop: // When in check, search starts from here
+ if ( cutNode
+ && depth >= 9
+ && !ttMove)
+ depth--;
+
+moves_loop: // When in check, search starts here
+
+ int rangeReduction = 0;
+
+ // Step 11. A small Probcut idea, when we are in check
+ probCutBeta = beta + 409;
+ if ( ss->inCheck
+ && !PvNode
+ && depth >= 4
+ && ttCapture
+ && (tte->bound() & BOUND_LOWER)
+ && tte->depth() >= depth - 3
+ && ttValue >= probCutBeta
+ && abs(ttValue) <= VALUE_KNOWN_WIN
+ && abs(beta) <= VALUE_KNOWN_WIN
+ )
+ return probCutBeta;
+
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
nullptr , (ss-4)->continuationHistory,
ss->ply);
value = bestValue;
- singularQuietLMR = moveCountPruning = false;
- ttCapture = ttMove && pos.capture_or_promotion(ttMove);
+ singularQuietLMR = moveCountPruning = noLMRExtension = false;
- // Mark this node as being searched
- ThreadHolding th(thisThread, posKey, ss->ply);
+ // Indicate PvNodes that will probably fail low if the node was searched
+ // at a depth equal or greater than the current depth, and the result of this search was a fail low.
+ bool likelyFailLow = PvNode
+ && ttMove
+ && (tte->bound() & BOUND_UPPER)
+ && tte->depth() >= depth;
- // Step 11. Loop through all pseudo-legal moves until no moves remain
+ // Step 12. Loop through all pseudo-legal moves until no moves remain
// or a beta cutoff occurs.
while ((move = mp.next_move(moveCountPruning)) != MOVE_NONE)
{
// Calculate new depth for this move
newDepth = depth - 1;
- // Step 12. Pruning at shallow depth (~200 Elo)
+ // Step 13. Pruning at shallow depth (~200 Elo). Depth conditions are important for mate finding.
if ( !rootNode
&& pos.non_pawn_material(us)
&& bestValue > VALUE_TB_LOSS_IN_MAX_PLY)
moveCountPruning = moveCount >= futility_move_count(improving, depth);
// Reduced depth of the next LMR search
- int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), 0);
+ int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount, rangeReduction > 2), 0);
if ( captureOrPromotion
|| givesCheck)
}
else
{
- // Countermoves based pruning (~20 Elo)
- if ( lmrDepth < 4 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1)
- && (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
- && (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
+ // Continuation history based pruning (~20 Elo)
+ if (lmrDepth < 5
+ && (*contHist[0])[movedPiece][to_sq(move)]
+ + (*contHist[1])[movedPiece][to_sq(move)]
+ + (*contHist[3])[movedPiece][to_sq(move)] < -3000 * depth + 3000)
continue;
// Futility pruning: parent node (~5 Elo)
- if ( lmrDepth < 7
- && !ss->inCheck
- && ss->staticEval + 254 + 159 * lmrDepth <= alpha
- && (*contHist[0])[movedPiece][to_sq(move)]
- + (*contHist[1])[movedPiece][to_sq(move)]
- + (*contHist[3])[movedPiece][to_sq(move)]
- + (*contHist[5])[movedPiece][to_sq(move)] / 2 < 26394)
+ if ( !ss->inCheck
+ && lmrDepth < 8
+ && ss->staticEval + 172 + 145 * lmrDepth <= alpha)
continue;
// Prune moves with negative SEE (~20 Elo)
- if (!pos.see_ge(move, Value(-(30 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
+ if (!pos.see_ge(move, Value(-21 * lmrDepth * lmrDepth - 21 * lmrDepth)))
continue;
}
}
- // Step 13. Extensions (~75 Elo)
+ // Step 14. Extensions (~75 Elo)
// Singular extension search (~70 Elo). 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 will extend the ttMove.
- if ( depth >= 7
+ if ( !rootNode
+ && depth >= 7
&& move == ttMove
- && !rootNode
&& !excludedMove // Avoid recursive singular search
/* && ttValue != VALUE_NONE Already implicit in the next condition */
&& abs(ttValue) < VALUE_KNOWN_WIN
&& (tte->bound() & BOUND_LOWER)
&& tte->depth() >= depth - 3)
{
- Value singularBeta = ttValue - ((formerPv + 4) * depth) / 2;
- Depth singularDepth = (depth - 1 + 3 * formerPv) / 2;
+ Value singularBeta = ttValue - 3 * depth;
+ Depth singularDepth = (depth - 1) / 2;
+
ss->excludedMove = move;
value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode);
ss->excludedMove = MOVE_NONE;
{
extension = 1;
singularQuietLMR = !ttCapture;
+
+ // Avoid search explosion by limiting the number of double extensions
+ if ( !PvNode
+ && value < singularBeta - 75
+ && ss->doubleExtensions <= 6)
+ {
+ extension = 2;
+ noLMRExtension = true;
+ }
}
// Multi-cut pruning
else if (singularBeta >= beta)
return singularBeta;
- // If the eval of ttMove is greater than beta we try also if there is another
- // move that pushes it over beta, if so also produce a cutoff.
+ // If the eval of ttMove is greater than beta, we reduce it (negative extension)
else if (ttValue >= beta)
- {
- ss->excludedMove = move;
- value = search<NonPV>(pos, ss, beta - 1, beta, (depth + 3) / 2, cutNode);
- ss->excludedMove = MOVE_NONE;
-
- if (value >= beta)
- return beta;
- }
+ extension = -2;
}
- // Check extension (~2 Elo)
- else if ( givesCheck
- && (pos.is_discovered_check_on_king(~us, move) || pos.see_ge(move)))
+ // Capture extensions for PvNodes and cutNodes
+ else if ( (PvNode || cutNode)
+ && captureOrPromotion
+ && moveCount != 1)
+ extension = 1;
+
+ // Check extensions
+ else if ( givesCheck
+ && depth > 6
+ && abs(ss->staticEval) > 100)
extension = 1;
- // Last captures extension
- else if ( PieceValue[EG][pos.captured_piece()] > PawnValueEg
- && pos.non_pawn_material() <= 2 * RookValueMg)
+ // Quiet ttMove extensions
+ else if ( PvNode
+ && move == ttMove
+ && move == ss->killers[0]
+ && (*contHist[0])[movedPiece][to_sq(move)] >= 10000)
extension = 1;
// Add extension to new depth
newDepth += extension;
+ ss->doubleExtensions = (ss-1)->doubleExtensions + (extension == 2);
// Speculative prefetch as early as possible
prefetch(TT.first_entry(pos.key_after(move)));
[movedPiece]
[to_sq(move)];
- // Step 14. Make the move
+ // Step 15. Make the move
pos.do_move(move, st, givesCheck);
- // Step 15. Reduced depth search (LMR, ~200 Elo). If the move fails high it will be
- // re-searched at full depth.
+ // Step 16. Late moves reduction / extension (LMR, ~200 Elo)
+ // We use various heuristics for the sons of a node after the first son has
+ // been searched. In general we would like to reduce them, but there are many
+ // cases where we extend a son if it has good chances to be "interesting".
if ( depth >= 3
&& moveCount > 1 + 2 * rootNode
&& ( !captureOrPromotion
- || moveCountPruning
- || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha
- || cutNode
- || (!PvNode && !formerPv && captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 4506)
- || thisThread->ttHitAverage < 432 * TtHitAverageResolution * TtHitAverageWindow / 1024))
+ || (cutNode && (ss-1)->moveCount > 1)
+ || !ss->ttPv)
+ && (!PvNode || ss->ply > 1 || thisThread->id() % 4 != 3))
{
- Depth r = reduction(improving, depth, moveCount);
+ Depth r = reduction(improving, depth, moveCount, rangeReduction > 2);
- // Decrease reduction if the ttHit running average is large
- if (thisThread->ttHitAverage > 537 * TtHitAverageResolution * TtHitAverageWindow / 1024)
+ // Decrease reduction if on the PV (~2 Elo)
+ if ( PvNode
+ && bestMoveCount <= 3)
r--;
- // Increase reduction if other threads are searching this position
- if (th.marked())
- r++;
-
- // Decrease reduction if position is or has been on the PV (~10 Elo)
- if (ss->ttPv)
+ // Decrease reduction if position is or has been on the PV
+ // and node is not likely to fail low. (~3 Elo)
+ if ( ss->ttPv
+ && !likelyFailLow)
r -= 2;
// Increase reduction at root and non-PV nodes when the best move does not change frequently
- if ((rootNode || !PvNode) && thisThread->rootDepth > 10 && thisThread->bestMoveChanges <= 2)
- r++;
-
- // More reductions for late moves if position was not in previous PV
- if (moveCountPruning && !formerPv)
+ if ( (rootNode || !PvNode)
+ && thisThread->bestMoveChanges <= 2)
r++;
- // Decrease reduction if opponent's move count is high (~5 Elo)
+ // Decrease reduction if opponent's move count is high (~1 Elo)
if ((ss-1)->moveCount > 13)
r--;
- // Decrease reduction if ttMove has been singularly extended (~3 Elo)
+ // Decrease reduction if ttMove has been singularly extended (~1 Elo)
if (singularQuietLMR)
r--;
- if (captureOrPromotion)
- {
- // Unless giving check, this capture is likely bad
- if ( !givesCheck
- && ss->staticEval + PieceValue[EG][pos.captured_piece()] + 210 * depth <= alpha)
- r++;
- }
- else
- {
- // Increase reduction if ttMove is a capture (~5 Elo)
- if (ttCapture)
- r++;
-
- // Increase reduction at root if failing high
- r += rootNode ? thisThread->failedHighCnt * thisThread->failedHighCnt * moveCount / 512 : 0;
-
- // Increase reduction for cut nodes (~10 Elo)
- if (cutNode)
- r += 2;
-
- // 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(). (~2 Elo)
- else if ( type_of(move) == NORMAL
- && !pos.see_ge(reverse_move(move)))
- r -= 2 + ss->ttPv - (type_of(movedPiece) == PAWN);
-
- ss->statScore = thisThread->mainHistory[us][from_to(move)]
- + (*contHist[0])[movedPiece][to_sq(move)]
- + (*contHist[1])[movedPiece][to_sq(move)]
- + (*contHist[3])[movedPiece][to_sq(move)]
- - 5287;
-
- // Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
- if (ss->statScore >= -105 && (ss-1)->statScore < -103)
- r--;
-
- else if ((ss-1)->statScore >= -122 && ss->statScore < -129)
- r++;
-
- // Decrease/increase reduction for moves with a good/bad history (~30 Elo)
- // If we are not in check use statScore, if we are in check
- // use sum of main history and first continuation history with an offset
- if (ss->inCheck)
- r -= (thisThread->mainHistory[us][from_to(move)]
- + (*contHist[0])[movedPiece][to_sq(move)] - 4333) / 16384;
- else
- r -= ss->statScore / 14884;
- }
+ // Increase reduction for cut nodes (~3 Elo)
+ if (cutNode && move != ss->killers[0])
+ r += 2;
+
+ // Increase reduction if ttMove is a capture (~3 Elo)
+ if (ttCapture)
+ r++;
+
+ ss->statScore = thisThread->mainHistory[us][from_to(move)]
+ + (*contHist[0])[movedPiece][to_sq(move)]
+ + (*contHist[1])[movedPiece][to_sq(move)]
+ + (*contHist[3])[movedPiece][to_sq(move)]
+ - 4923;
- Depth d = std::clamp(newDepth - r, 1, newDepth);
+ // Decrease/increase reduction for moves with a good/bad history (~30 Elo)
+ r -= ss->statScore / 14721;
+
+ // In general we want to cap the LMR depth search at newDepth. But if reductions
+ // are really negative and movecount is low, we allow this move to be searched
+ // deeper than the first move (this may lead to hidden double extensions if
+ // newDepth got its own extension before).
+ int deeper = r >= -1 ? 0
+ : noLMRExtension ? 0
+ : moveCount <= 5 ? 1
+ : (depth > 6 && PvNode) ? 1
+ : 0;
+
+ Depth d = std::clamp(newDepth - r, 1, newDepth + deeper);
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
- doFullDepthSearch = value > alpha && d != newDepth;
+ // Range reductions (~3 Elo)
+ if (ss->staticEval - value < 30 && depth > 7)
+ rangeReduction++;
+ // If the son is reduced and fails high it will be re-searched at full depth
+ doFullDepthSearch = value > alpha && d < newDepth;
didLMR = true;
}
else
{
doFullDepthSearch = !PvNode || moveCount > 1;
-
didLMR = false;
}
- // Step 16. Full depth search when LMR is skipped or fails high
+ // Step 17. Full depth search when LMR is skipped or fails high
if (doFullDepthSearch)
{
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
std::min(maxNextDepth, newDepth), false);
}
- // Step 17. Undo move
+ // Step 18. Undo move
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
- // Step 18. Check for a new best move
+ // Step 19. 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.
for (Move* m = (ss+1)->pv; *m != MOVE_NONE; ++m)
rm.pv.push_back(*m);
- // We record how often the best move has been changed in each
- // iteration. This information is used for time management and LMR
- if (moveCount > 1)
+ // We record how often the best move has been changed in each iteration.
+ // This information is used for time management and LMR. In MultiPV mode,
+ // we must take care to only do this for the first PV line.
+ if ( moveCount > 1
+ && !thisThread->pvIdx)
++thisThread->bestMoveChanges;
}
else
update_pv(ss->pv, move, (ss+1)->pv);
if (PvNode && value < beta) // Update alpha! Always alpha < beta
+ {
alpha = value;
+ bestMoveCount++;
+ }
else
{
assert(value >= beta); // Fail high
- ss->statScore = 0;
break;
}
}
return VALUE_DRAW;
*/
- // Step 19. Check for mate and stalemate
+ // Step 20. Check for mate and stalemate
// 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 || !ss->inCheck || excludedMove || !MoveList<LEGAL>(pos).size());
if (!moveCount)
- bestValue = excludedMove ? alpha
- : ss->inCheck ? mated_in(ss->ply) : VALUE_DRAW;
+ bestValue = excludedMove ? alpha :
+ ss->inCheck ? mated_in(ss->ply)
+ : VALUE_DRAW;
// If there is a move which produces search value greater than alpha we update stats of searched moves
else if (bestMove)
// Bonus for prior countermove that caused the fail low
else if ( (depth >= 3 || PvNode)
&& !priorCapture)
- update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));
+ update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * (1 + (PvNode || cutNode)));
if (PvNode)
bestValue = std::min(bestValue, maxValue);
// qsearch() is the quiescence search function, which is called by the main search
// function with zero depth, or recursively with further decreasing depth per call.
- template <NodeType NT>
+ template <NodeType nodeType>
Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
- constexpr bool PvNode = NT == PV;
+ static_assert(nodeType != Root);
+ constexpr bool PvNode = nodeType == PV;
assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
assert(PvNode || (alpha == beta - 1));
Move pv[MAX_PLY+1];
StateInfo st;
- ASSERT_ALIGNED(&st, Eval::NNUE::kCacheLineSize);
+ ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize);
TTEntry* tte;
Key posKey;
}
Thread* thisThread = pos.this_thread();
- (ss+1)->ply = ss->ply + 1;
bestMove = MOVE_NONE;
ss->inCheck = pos.checkers();
moveCount = 0;
}
else
// In case of null move search use previous static eval with a different sign
- // and addition of two tempos
ss->staticEval = bestValue =
(ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
- : -(ss-1)->staticEval + 2 * Tempo;
+ : -(ss-1)->staticEval;
// Stand pat. Return immediately if static value is at least beta
if (bestValue >= beta)
// Initialize a MovePicker object for the current position, and prepare
// to search the moves. Because the depth is <= 0 here, only captures,
- // queen and checking knight promotions, and other checks(only if depth >= DEPTH_QS_CHECKS)
+ // queen promotions, and other checks (only if depth >= DEPTH_QS_CHECKS)
// will be generated.
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
&thisThread->captureHistory,
{
assert(is_ok(move));
+ // Check for legality
+ if (!pos.legal(move))
+ continue;
+
givesCheck = pos.gives_check(move);
captureOrPromotion = pos.capture_or_promotion(move);
moveCount++;
- // Futility pruning
+ // Futility pruning and moveCount pruning
if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
&& !givesCheck
&& futilityBase > -VALUE_KNOWN_WIN
- && !pos.advanced_pawn_push(move))
+ && type_of(move) != PROMOTION)
{
- assert(type_of(move) != EN_PASSANT); // Due to !pos.advanced_pawn_push
- // moveCount pruning
if (moveCount > 2)
continue;
// Speculative prefetch as early as possible
prefetch(TT.first_entry(pos.key_after(move)));
- // Check for legality just before making the move
- if (!pos.legal(move))
- {
- moveCount--;
- continue;
- }
-
ss->currentMove = move;
ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck]
[captureOrPromotion]
[pos.moved_piece(move)]
[to_sq(move)];
- // CounterMove based pruning
+ // Continuation history based pruning
if ( !captureOrPromotion
&& bestValue > VALUE_TB_LOSS_IN_MAX_PLY
&& (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold
// Make and search the move
pos.do_move(move, st, givesCheck);
- value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth - 1);
+ value = -qsearch<nodeType>(pos, ss+1, -beta, -alpha, depth - 1);
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
bool RootMove::extract_ponder_from_tt(Position& pos) {
StateInfo st;
- ASSERT_ALIGNED(&st, Eval::NNUE::kCacheLineSize);
+ ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize);
bool ttHit;
m.tbRank = 0;
}
}
+
+} // namespace Stockfish
projects / stockfish / blobdiff