X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=src%2Fsearch.cpp;h=2d5fb6305b8d84dde21795edd409d2af2d88285c;hb=28dcd700a9dd3c776b66b2032cf0cf6df88b671d;hp=cfa737dbd6773bf72cd460a19eb71f9b143232e1;hpb=76f1807baa90eb69f66001d25df2a28533f9406f;p=stockfish
diff --git a/src/search.cpp b/src/search.cpp
index cfa737db..2d5fb630 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -18,6 +18,7 @@
along with this program. If not, see .
*/
+#include
#include
#include
#include // For std::memset
@@ -61,17 +62,17 @@ namespace {
enum NodeType { NonPV, PV };
// Razor and futility margins
- constexpr int RazorMargin = 600;
+ constexpr int RazorMargin = 661;
Value futility_margin(Depth d, bool improving) {
- return Value((175 - 50 * improving) * d / ONE_PLY);
+ return Value(198 * (d / ONE_PLY - improving));
}
// Reductions lookup table, initialized at startup
- int Reductions[64]; // [depth or moveNumber]
+ int Reductions[MAX_MOVES]; // [depth or moveNumber]
- template Depth reduction(bool i, Depth d, int mn) {
- int r = Reductions[std::min(d / ONE_PLY, 63)] * Reductions[std::min(mn, 63)] / 1024;
- return ((r + 512) / 1024 + (!i && r > 1024) - PvNode) * ONE_PLY;
+ Depth reduction(bool i, Depth d, int mn) {
+ int r = Reductions[d / ONE_PLY] * Reductions[mn];
+ return ((r + 520) / 1024 + (!i && r > 999)) * ONE_PLY;
}
constexpr int futility_move_count(bool improving, int depth) {
@@ -81,14 +82,13 @@ namespace {
// History and stats update bonus, based on depth
int stat_bonus(Depth depth) {
int d = depth / ONE_PLY;
- return d > 17 ? 0 : 29 * d * d + 138 * d - 134;
+ return d > 17 ? -8 : 22 * d * d + 151 * d - 140;
}
- // Add a small random component to draw evaluations to keep search dynamic
- // and to avoid 3fold-blindness.
+ // Add a small random component to draw evaluations to avoid 3fold-blindness
Value value_draw(Depth depth, Thread* thisThread) {
- return depth < 4 ? VALUE_DRAW
- : VALUE_DRAW + Value(2 * (thisThread->nodes.load(std::memory_order_relaxed) % 2) - 1);
+ return depth < 4 * ONE_PLY ? VALUE_DRAW
+ : VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1);
}
// Skill structure is used to implement strength limit
@@ -102,6 +102,49 @@ namespace {
Move best = MOVE_NONE;
};
+ // Breadcrumbs are used to mark nodes as being searched by a given thread
+ struct Breadcrumb {
+ std::atomic thread;
+ std::atomic key;
+ };
+ std::array 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
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
@@ -148,8 +191,8 @@ namespace {
void Search::init() {
- for (int i = 1; i < 64; ++i)
- Reductions[i] = int(1024 * std::log(i) / std::sqrt(1.95));
+ for (int i = 1; i < MAX_MOVES; ++i)
+ Reductions[i] = int(23.4 * std::log(i));
}
@@ -162,12 +205,12 @@ void Search::clear() {
Time.availableNodes = 0;
TT.clear();
Threads.clear();
- Tablebases::init(Options["SyzygyPath"]); // Free up mapped files
+ Tablebases::init(Options["SyzygyPath"]); // Free mapped files
}
-/// 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".
+/// MainThread::search() is started when the program receives the UCI 'go'
+/// command. It searches from the root position and outputs the "bestmove".
void MainThread::search() {
@@ -192,8 +235,11 @@ void MainThread::search() {
else
{
for (Thread* th : Threads)
+ {
+ th->bestMoveChanges = 0;
if (th != this)
th->start_searching();
+ }
Thread::search(); // Let's start searching!
}
@@ -221,35 +267,37 @@ void MainThread::search() {
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;
+
+ // Check if there are threads with a better score than main thread
if ( Options["MultiPV"] == 1
&& !Limits.depth
- && !Skill(Options["Skill Level"]).enabled()
+ && !(Skill(Options["Skill Level"]).enabled() || Options["UCI_LimitStrength"])
&& rootMoves[0].pv[0] != MOVE_NONE)
{
std::map votes;
Value minScore = this->rootMoves[0].score;
- // Find out minimum score and reset votes for moves which can be voted
+ // Find out minimum score
for (Thread* th: Threads)
minScore = std::min(minScore, th->rootMoves[0].score);
- // Vote according to score and depth
+ // Vote according to score and depth, and select the best thread
for (Thread* th : Threads)
{
- int64_t s = th->rootMoves[0].score - minScore + 1;
- votes[th->rootMoves[0].pv[0]] += 200 + s * s * int(th->completedDepth);
- }
+ votes[th->rootMoves[0].pv[0]] +=
+ (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth);
- // Select best thread
- auto bestVote = votes[this->rootMoves[0].pv[0]];
- for (Thread* th : Threads)
- if (votes[th->rootMoves[0].pv[0]] > bestVote)
+ if (bestThread->rootMoves[0].score >= VALUE_MATE_IN_MAX_PLY)
{
- bestVote = votes[th->rootMoves[0].pv[0]];
- bestThread = th;
+ // Make sure we pick the shortest mate
+ if (th->rootMoves[0].score > bestThread->rootMoves[0].score)
+ bestThread = th;
}
+ else if ( th->rootMoves[0].score >= VALUE_MATE_IN_MAX_PLY
+ || votes[th->rootMoves[0].pv[0]] > votes[bestThread->rootMoves[0].pv[0]])
+ bestThread = th;
+ }
}
previousScore = bestThread->rootMoves[0].score;
@@ -273,9 +321,9 @@ void MainThread::search() {
void Thread::search() {
- // To allow access to (ss-5) up to (ss+2), the stack must be oversized.
+ // 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-4, also near the root.
+ // which accesses its argument at ss-6, also near the root.
// The latter is needed for statScores and killer initialization.
Stack stack[MAX_PLY+10], *ss = stack+7;
Move pv[MAX_PLY+1];
@@ -283,7 +331,7 @@ void Thread::search() {
Move lastBestMove = MOVE_NONE;
Depth lastBestMoveDepth = DEPTH_ZERO;
MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
- double timeReduction = 1.0;
+ double timeReduction = 1, totBestMoveChanges = 0;
Color us = rootPos.side_to_move();
std::memset(ss-7, 0, 10 * sizeof(Stack));
@@ -294,11 +342,20 @@ void Thread::search() {
bestValue = delta = alpha = -VALUE_INFINITE;
beta = VALUE_INFINITE;
- if (mainThread)
- mainThread->bestMoveChanges = 0;
-
size_t multiPV = Options["MultiPV"];
- Skill skill(Options["Skill Level"]);
+
+ // Pick integer skill levels, but non-deterministically round up or down
+ // such that the average integer skill corresponds to the input floating point one.
+ // UCI_Elo is converted to a suitable fractional skill level, using anchoring
+ // to CCRL Elo (goldfish 1.13 = 2000) and a fit through Ordo derived Elo
+ // for match (TC 60+0.6) results spanning a wide range of k values.
+ PRNG rng(now());
+ double floatLevel = Options["UCI_LimitStrength"] ?
+ clamp(std::pow((Options["UCI_Elo"] - 1346.6) / 143.4, 1 / 0.806), 0.0, 20.0) :
+ double(Options["Skill Level"]);
+ int intLevel = int(floatLevel) +
+ ((floatLevel - int(floatLevel)) * 1024 > rng.rand() % 1024 ? 1 : 0);
+ Skill skill(intLevel);
// When playing with strength handicap enable MultiPV search that we will
// use behind the scenes to retrieve a set of possible moves.
@@ -317,7 +374,7 @@ void Thread::search() {
: Options["Analysis Contempt"] == "Black" && us == WHITE ? -ct
: ct;
- // In evaluate.cpp the evaluation is from the white point of view
+ // Evaluation score is from the white point of view
contempt = (us == WHITE ? make_score(ct, ct / 2)
: -make_score(ct, ct / 2));
@@ -328,7 +385,7 @@ void Thread::search() {
{
// Age out PV variability metric
if (mainThread)
- mainThread->bestMoveChanges *= 0.517;
+ totBestMoveChanges /= 2;
// Save the last iteration's scores before first PV line is searched and
// all the move scores except the (new) PV are set to -VALUE_INFINITE.
@@ -353,15 +410,15 @@ void Thread::search() {
selDepth = 0;
// Reset aspiration window starting size
- if (rootDepth >= 5 * ONE_PLY)
+ if (rootDepth >= 4 * ONE_PLY)
{
Value previousScore = rootMoves[pvIdx].previousScore;
- delta = Value(20);
+ delta = Value(23);
alpha = std::max(previousScore - delta,-VALUE_INFINITE);
beta = std::min(previousScore + delta, VALUE_INFINITE);
// Adjust contempt based on root move's previousScore (dynamic contempt)
- int dct = ct + 88 * previousScore / (abs(previousScore) + 200);
+ int dct = ct + 86 * previousScore / (abs(previousScore) + 176);
contempt = (us == WHITE ? make_score(dct, dct / 2)
: -make_score(dct, dct / 2));
@@ -405,20 +462,20 @@ void Thread::search() {
beta = (alpha + beta) / 2;
alpha = std::max(bestValue - delta, -VALUE_INFINITE);
+ failedHighCnt = 0;
if (mainThread)
- {
- failedHighCnt = 0;
mainThread->stopOnPonderhit = false;
- }
}
else if (bestValue >= beta)
{
beta = std::min(bestValue + delta, VALUE_INFINITE);
- if (mainThread)
- ++failedHighCnt;
+ ++failedHighCnt;
}
else
+ {
+ ++rootMoves[pvIdx].bestMoveCount;
break;
+ }
delta += delta / 4 + 5;
@@ -459,15 +516,20 @@ void Thread::search() {
&& !Threads.stop
&& !mainThread->stopOnPonderhit)
{
- double fallingEval = (306 + 9 * (mainThread->previousScore - bestValue)) / 581.0;
+ double fallingEval = (354 + 10 * (mainThread->previousScore - bestValue)) / 692.0;
fallingEval = clamp(fallingEval, 0.5, 1.5);
// If the bestMove is stable over several iterations, reduce time accordingly
- timeReduction = lastBestMoveDepth + 10 * ONE_PLY < completedDepth ? 1.95 : 1.0;
- double reduction = std::pow(mainThread->previousTimeReduction, 0.528) / timeReduction;
+ timeReduction = lastBestMoveDepth + 9 * ONE_PLY < completedDepth ? 1.97 : 0.98;
+ double reduction = (1.36 + mainThread->previousTimeReduction) / (2.29 * timeReduction);
// Use part of the gained time from a previous stable move for the current move
- double bestMoveInstability = 1.0 + mainThread->bestMoveChanges;
+ for (Thread* th : Threads)
+ {
+ totBestMoveChanges += th->bestMoveChanges;
+ th->bestMoveChanges = 0;
+ }
+ double bestMoveInstability = 1 + totBestMoveChanges / Threads.size();
// Stop the search if we have only one legal move, or if available time elapsed
if ( rootMoves.size() == 1
@@ -533,17 +595,17 @@ namespace {
Key posKey;
Move ttMove, move, excludedMove, bestMove;
Depth extension, newDepth;
- Value bestValue, value, ttValue, eval, maxValue, pureStaticEval;
- bool ttHit, ttPv, inCheck, givesCheck, improving;
+ Value bestValue, value, ttValue, eval, maxValue;
+ bool ttHit, ttPv, inCheck, givesCheck, improving, doLMR;
bool captureOrPromotion, doFullDepthSearch, moveCountPruning, ttCapture;
Piece movedPiece;
- int moveCount, captureCount, quietCount;
+ int moveCount, captureCount, quietCount, singularLMR;
// Step 1. Initialize node
Thread* thisThread = pos.this_thread();
inCheck = pos.checkers();
Color us = pos.side_to_move();
- moveCount = captureCount = quietCount = ss->moveCount = 0;
+ moveCount = captureCount = quietCount = singularLMR = ss->moveCount = 0;
bestValue = -VALUE_INFINITE;
maxValue = VALUE_INFINITE;
@@ -579,8 +641,7 @@ namespace {
assert(0 <= ss->ply && ss->ply < MAX_PLY);
(ss+1)->ply = ss->ply + 1;
- ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
- ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
+ (ss+1)->excludedMove = bestMove = MOVE_NONE;
(ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
Square prevSq = to_sq((ss-1)->currentMove);
@@ -589,7 +650,10 @@ namespace {
// starts with statScore = 0. Later grandchildren start with the last calculated
// statScore of the previous grandchild. This influences the reduction rules in
// LMR which are based on the statScore of parent position.
- (ss+2)->statScore = 0;
+ if (rootNode)
+ (ss+4)->statScore = 0;
+ else
+ (ss+2)->statScore = 0;
// 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
@@ -600,16 +664,7 @@ namespace {
ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
ttMove = rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0]
: ttHit ? tte->move() : MOVE_NONE;
- ttPv = (ttHit && tte->is_pv()) || (PvNode && depth > 4 * ONE_PLY);
-
- // if position has been searched at higher depths and we are shuffling, return value_draw
- if (pos.rule50_count() > 36
- && ss->ply > 36
- && depth < 3 * ONE_PLY
- && ttHit
- && tte->depth() > depth
- && pos.count() > 0)
- return VALUE_DRAW;
+ ttPv = PvNode || (ttHit && tte->is_pv());
// At non-PV nodes we check for an early TT cutoff
if ( !PvNode
@@ -627,10 +682,9 @@ namespace {
if (!pos.capture_or_promotion(ttMove))
update_quiet_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth));
- // Extra penalty for a quiet TT or main killer move in previous ply when it gets refuted
- if ( ((ss-1)->moveCount == 1 || (ss-1)->currentMove == (ss-1)->killers[0])
- && !pos.captured_piece())
- update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
+ // Extra penalty for early quiet moves of the previous ply
+ if ((ss-1)->moveCount <= 2 && !pos.captured_piece())
+ 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))
@@ -697,16 +751,19 @@ namespace {
// Step 6. Static evaluation of the position
if (inCheck)
{
- ss->staticEval = eval = pureStaticEval = VALUE_NONE;
+ ss->staticEval = eval = VALUE_NONE;
improving = false;
goto moves_loop; // Skip early pruning when in check
}
else if (ttHit)
{
- // Never assume anything on values stored in TT
- ss->staticEval = eval = pureStaticEval = tte->eval();
+ // Never assume anything about values stored in TT
+ ss->staticEval = eval = tte->eval();
if (eval == VALUE_NONE)
- ss->staticEval = eval = pureStaticEval = evaluate(pos);
+ ss->staticEval = eval = evaluate(pos);
+
+ if (eval == VALUE_DRAW)
+ eval = value_draw(depth, thisThread);
// Can ttValue be used as a better position evaluation?
if ( ttValue != VALUE_NONE
@@ -719,13 +776,12 @@ namespace {
{
int bonus = -(ss-1)->statScore / 512;
- pureStaticEval = evaluate(pos);
- ss->staticEval = eval = pureStaticEval + bonus;
+ ss->staticEval = eval = evaluate(pos) + bonus;
}
else
- ss->staticEval = eval = pureStaticEval = -(ss-1)->staticEval + 2 * Eval::Tempo;
+ ss->staticEval = eval = -(ss-1)->staticEval + 2 * Eval::Tempo;
- tte->save(posKey, VALUE_NONE, ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, pureStaticEval);
+ tte->save(posKey, VALUE_NONE, ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
}
// Step 7. Razoring (~2 Elo)
@@ -747,9 +803,10 @@ namespace {
// Step 9. Null move search with verification search (~40 Elo)
if ( !PvNode
&& (ss-1)->currentMove != MOVE_NULL
- && (ss-1)->statScore < 23200
+ && (ss-1)->statScore < 22661
&& eval >= beta
- && pureStaticEval >= beta - 36 * depth / ONE_PLY + 225
+ && eval >= ss->staticEval
+ && ss->staticEval >= beta - 33 * depth / ONE_PLY + 299 - improving * 30
&& !excludedMove
&& pos.non_pawn_material(us)
&& (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
@@ -757,7 +814,7 @@ namespace {
assert(eval - beta >= 0);
// Null move dynamic reduction based on depth and value
- Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min(int(eval - beta) / 200, 3)) * ONE_PLY;
+ Depth R = ((835 + 70 * depth / ONE_PLY) / 256 + std::min(int(eval - beta) / 185, 3)) * ONE_PLY;
ss->currentMove = MOVE_NULL;
ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
@@ -774,14 +831,14 @@ namespace {
if (nullValue >= VALUE_MATE_IN_MAX_PLY)
nullValue = beta;
- if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 12 * ONE_PLY))
+ if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 13 * ONE_PLY))
return nullValue;
assert(!thisThread->nmpMinPly); // Recursive verification is not allowed
// Do verification search at high depths, with null move pruning disabled
// for us, until ply exceeds nmpMinPly.
- thisThread->nmpMinPly = ss->ply + 3 * (depth-R) / 4;
+ thisThread->nmpMinPly = ss->ply + 3 * (depth-R) / (4 * ONE_PLY);
thisThread->nmpColor = us;
Value v = search(pos, ss, beta-1, beta, depth-R, false);
@@ -800,7 +857,7 @@ namespace {
&& depth >= 5 * ONE_PLY
&& abs(beta) < VALUE_MATE_IN_MAX_PLY)
{
- Value raisedBeta = std::min(beta + 216 - 48 * improving, VALUE_INFINITE);
+ Value raisedBeta = std::min(beta + 191 - 46 * improving, VALUE_INFINITE);
MovePicker mp(pos, ttMove, raisedBeta - ss->staticEval, &thisThread->captureHistory);
int probCutCount = 0;
@@ -832,8 +889,7 @@ namespace {
}
// Step 11. Internal iterative deepening (~2 Elo)
- if ( depth >= 8 * ONE_PLY
- && !ttMove)
+ if (depth >= 7 * ONE_PLY && !ttMove)
{
search(pos, ss, alpha, beta, depth - 7 * ONE_PLY, cutNode);
@@ -847,6 +903,7 @@ moves_loop: // When in check, search starts from here
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
nullptr, (ss-4)->continuationHistory,
nullptr, (ss-6)->continuationHistory };
+
Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
@@ -854,11 +911,14 @@ moves_loop: // When in check, search starts from here
contHist,
countermove,
ss->killers);
- value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
+ value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
moveCountPruning = false;
ttCapture = ttMove && pos.capture_or_promotion(ttMove);
+ // Mark this node as being searched
+ ThreadHolding th(thisThread, posKey, ss->ply);
+
// 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)
@@ -897,44 +957,61 @@ moves_loop: // When in check, search starts from here
// 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 >= 8 * ONE_PLY
+ if ( depth >= 6 * ONE_PLY
&& move == ttMove
&& !rootNode
&& !excludedMove // Avoid recursive singular search
- /* && ttValue != VALUE_NONE Already implicit in the next condition */
+ /* && ttValue != VALUE_NONE Already implicit in the next condition */
&& abs(ttValue) < VALUE_KNOWN_WIN
&& (tte->bound() & BOUND_LOWER)
&& tte->depth() >= depth - 3 * ONE_PLY
&& pos.legal(move))
{
Value singularBeta = ttValue - 2 * depth / ONE_PLY;
+ Depth halfDepth = depth / (2 * ONE_PLY) * ONE_PLY; // ONE_PLY invariant
ss->excludedMove = move;
- value = search(pos, ss, singularBeta - 1, singularBeta, depth / 2, cutNode);
+ value = search(pos, ss, singularBeta - 1, singularBeta, halfDepth, cutNode);
ss->excludedMove = MOVE_NONE;
if (value < singularBeta)
+ {
extension = ONE_PLY;
+ singularLMR++;
+
+ if (value < singularBeta - std::min(4 * depth / ONE_PLY, 36))
+ singularLMR++;
+ }
// Multi-cut pruning
// Our ttMove is assumed to fail high, and now we failed high also on a reduced
// search without the ttMove. So we assume this expected Cut-node is not singular,
- // that is multiple moves fail high, and we can prune the whole subtree by returning
- // the hard beta bound.
- else if (cutNode && singularBeta > beta)
- return beta;
+ // that multiple moves fail high, and we can prune the whole subtree by returning
+ // a soft bound.
+ else if ( eval >= beta
+ && singularBeta >= beta)
+ return singularBeta;
}
// Check extension (~2 Elo)
else if ( givesCheck
- && (pos.blockers_for_king(~us) & from_sq(move) || pos.see_ge(move)))
+ && (pos.is_discovery_check_on_king(~us, move) || pos.see_ge(move)))
+ extension = ONE_PLY;
+
+ // Castling extension
+ else if (type_of(move) == CASTLING)
extension = ONE_PLY;
// Shuffle extension
- else if(pos.rule50_count() > 14 && ss->ply > 14 && depth < 3 * ONE_PLY && PvNode)
+ else if ( PvNode
+ && pos.rule50_count() > 18
+ && depth < 3 * ONE_PLY
+ && ++thisThread->shuffleExts < thisThread->nodes.load(std::memory_order_relaxed) / 4) // To avoid too many extensions
extension = ONE_PLY;
- // Castling extension
- else if (type_of(move) == CASTLING)
+ // Passed pawn extension
+ else if ( move == ss->killers[0]
+ && pos.advanced_pawn_push(move)
+ && pos.pawn_passed(us, to_sq(move)))
extension = ONE_PLY;
// Calculate new depth for this move
@@ -946,36 +1023,38 @@ moves_loop: // When in check, search starts from here
&& bestValue > VALUE_MATED_IN_MAX_PLY)
{
// Skip quiet moves if movecount exceeds our FutilityMoveCount threshold
- moveCountPruning = moveCount >= futility_move_count(improving,depth / ONE_PLY);
+ moveCountPruning = moveCount >= futility_move_count(improving, depth / ONE_PLY);
if ( !captureOrPromotion
&& !givesCheck
- && !pos.advanced_pawn_push(move))
+ && (!pos.advanced_pawn_push(move) || pos.non_pawn_material(~us) > BishopValueMg))
{
- // Move count based pruning (~30 Elo)
+ // Move count based pruning
if (moveCountPruning)
continue;
// Reduced depth of the next LMR search
- int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;
+ int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), DEPTH_ZERO);
+ lmrDepth /= ONE_PLY;
// Countermoves based pruning (~20 Elo)
- if ( lmrDepth < 3 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1)
+ 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)
continue;
// Futility pruning: parent node (~2 Elo)
- if ( lmrDepth < 7
+ if ( lmrDepth < 6
&& !inCheck
- && ss->staticEval + 256 + 200 * lmrDepth <= alpha)
+ && ss->staticEval + 250 + 211 * lmrDepth <= alpha)
continue;
// Prune moves with negative SEE (~10 Elo)
- if (!pos.see_ge(move, Value(-29 * lmrDepth * lmrDepth)))
+ if (!pos.see_ge(move, Value(-(31 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
continue;
}
- else if (!pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY))) // (~20 Elo)
+ else if ( !(givesCheck && extension)
+ && !pos.see_ge(move, Value(-199) * (depth / ONE_PLY))) // (~20 Elo)
continue;
}
@@ -999,19 +1078,30 @@ moves_loop: // When in check, search starts from here
// Step 16. Reduced depth search (LMR). If the move fails high it will be
// re-searched at full depth.
if ( depth >= 3 * ONE_PLY
- && moveCount > 1
- && (!captureOrPromotion || moveCountPruning))
+ && moveCount > 1 + 2 * rootNode
+ && (!rootNode || thisThread->best_move_count(move) == 0)
+ && ( !captureOrPromotion
+ || moveCountPruning
+ || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha
+ || cutNode))
{
- Depth r = reduction(improving, depth, moveCount);
+ Depth r = reduction(improving, depth, moveCount);
+
+ // Reduction if other threads are searching this position.
+ if (th.marked())
+ r += ONE_PLY;
// Decrease reduction if position is or has been on the PV
if (ttPv)
- r -= ONE_PLY;
+ r -= 2 * ONE_PLY;
// Decrease reduction if opponent's move count is high (~10 Elo)
if ((ss-1)->moveCount > 15)
r -= ONE_PLY;
+ // Decrease reduction if ttMove has been singularly extended
+ r -= singularLMR * ONE_PLY;
+
if (!captureOrPromotion)
{
// Increase reduction if ttMove is a capture (~0 Elo)
@@ -1026,39 +1116,59 @@ moves_loop: // When in check, search starts from here
// castling moves, because they are coded as "king captures rook" and
// hence break make_move(). (~5 Elo)
else if ( type_of(move) == NORMAL
- && !pos.see_ge(make_move(to_sq(move), from_sq(move))))
+ && !pos.see_ge(reverse_move(move)))
r -= 2 * ONE_PLY;
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)]
- - 4000;
+ - 4729;
+
+ // Reset statScore to zero if negative and most stats shows >= 0
+ if ( ss->statScore < 0
+ && (*contHist[0])[movedPiece][to_sq(move)] >= 0
+ && (*contHist[1])[movedPiece][to_sq(move)] >= 0
+ && thisThread->mainHistory[us][from_to(move)] >= 0)
+ ss->statScore = 0;
// Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
- if (ss->statScore >= 0 && (ss-1)->statScore < 0)
+ if (ss->statScore >= -99 && (ss-1)->statScore < -116)
r -= ONE_PLY;
- else if ((ss-1)->statScore >= 0 && ss->statScore < 0)
+ else if ((ss-1)->statScore >= -117 && ss->statScore < -144)
r += ONE_PLY;
// Decrease/increase reduction for moves with a good/bad history (~30 Elo)
- r -= ss->statScore / 20000 * ONE_PLY;
+ r -= ss->statScore / 16384 * ONE_PLY;
}
- Depth d = std::max(newDepth - std::max(r, DEPTH_ZERO), ONE_PLY);
+ Depth d = clamp(newDepth - r, ONE_PLY, newDepth);
value = -search(pos, ss+1, -(alpha+1), -alpha, d, true);
- doFullDepthSearch = (value > alpha && d != newDepth);
+ doFullDepthSearch = (value > alpha && d != newDepth), doLMR = true;
}
else
- doFullDepthSearch = !PvNode || moveCount > 1;
+ doFullDepthSearch = !PvNode || moveCount > 1, doLMR = false;
// Step 17. Full depth search when LMR is skipped or fails high
if (doFullDepthSearch)
+ {
value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
+ if (doLMR && !captureOrPromotion)
+ {
+ int bonus = value > alpha ? stat_bonus(newDepth)
+ : -stat_bonus(newDepth);
+
+ if (move == ss->killers[0])
+ bonus += bonus / 4;
+
+ update_continuation_histories(ss, movedPiece, to_sq(move), bonus);
+ }
+ }
+
// For PV nodes only, do a full PV search on the first move or after a fail
// high (in the latter case search only if value < beta), otherwise let the
// parent node fail low with value <= alpha and try another move.
@@ -1102,8 +1212,8 @@ moves_loop: // When in check, search starts from here
// We record how often the best move has been changed in each
// iteration. This information is used for time management: When
// the best move changes frequently, we allocate some more time.
- if (moveCount > 1 && thisThread == Threads.main())
- ++static_cast(thisThread)->bestMoveChanges;
+ if (moveCount > 1)
+ ++thisThread->bestMoveChanges;
}
else
// All other moves but the PV are set to the lowest value: this
@@ -1189,7 +1299,7 @@ moves_loop: // When in check, search starts from here
tte->save(posKey, value_to_tt(bestValue, ss->ply), ttPv,
bestValue >= beta ? BOUND_LOWER :
PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
- depth, bestMove, pureStaticEval);
+ depth, bestMove, ss->staticEval);
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
@@ -1197,8 +1307,8 @@ moves_loop: // When in check, search starts from here
}
- // qsearch() is the quiescence search function, which is called by the main
- // search function with depth zero, or recursively with depth less than ONE_PLY.
+ // 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
Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
@@ -1228,8 +1338,7 @@ moves_loop: // When in check, search starts from here
Thread* thisThread = pos.this_thread();
(ss+1)->ply = ss->ply + 1;
- ss->currentMove = bestMove = MOVE_NONE;
- ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
+ bestMove = MOVE_NONE;
inCheck = pos.checkers();
moveCount = 0;
@@ -1270,7 +1379,7 @@ moves_loop: // When in check, search starts from here
{
if (ttHit)
{
- // Never assume anything on values stored in TT
+ // Never assume anything about values stored in TT
if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
ss->staticEval = bestValue = evaluate(pos);
@@ -1297,7 +1406,7 @@ moves_loop: // When in check, search starts from here
if (PvNode && bestValue > alpha)
alpha = bestValue;
- futilityBase = bestValue + 128;
+ futilityBase = bestValue + 153;
}
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
@@ -1353,6 +1462,7 @@ moves_loop: // When in check, search starts from here
// Don't search moves with negative SEE values
if ( (!inCheck || evasionPrunable)
+ && (!givesCheck || !(pos.blockers_for_king(~pos.side_to_move()) & from_sq(move)))
&& !pos.see_ge(move))
continue;
@@ -1463,7 +1573,7 @@ moves_loop: // When in check, search starts from here
void update_capture_stats(const Position& pos, Move move,
Move* captures, int captureCount, int bonus) {
- CapturePieceToHistory& captureHistory = pos.this_thread()->captureHistory;
+ CapturePieceToHistory& captureHistory = pos.this_thread()->captureHistory;
Piece moved_piece = pos.moved_piece(move);
PieceType captured = type_of(pos.piece_on(to_sq(move)));
@@ -1496,6 +1606,9 @@ moves_loop: // When in check, search starts from here
thisThread->mainHistory[us][from_to(move)] << bonus;
update_continuation_histories(ss, pos.moved_piece(move), to_sq(move), bonus);
+ if (type_of(pos.moved_piece(move)) != PAWN)
+ thisThread->mainHistory[us][from_to(reverse_move(move))] << -bonus;
+
if (is_ok((ss-1)->currentMove))
{
Square prevSq = to_sq((ss-1)->currentMove);
@@ -1704,7 +1817,7 @@ void Tablebases::rank_root_moves(Position& pos, Search::RootMoves& rootMoves) {
}
else
{
- // Assign the same rank to all moves
+ // Clean up if root_probe() and root_probe_wdl() have failed
for (auto& m : rootMoves)
m.tbRank = 0;
}