/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
- Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
- Copyright (C) 2015-2017 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
+ Copyright (C) 2004-2020 The Stockfish developers (see AUTHORS file)
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 "movepick.h"
#include "position.h"
#include "search.h"
-#include "timeman.h"
#include "thread.h"
+#include "timeman.h"
#include "tt.h"
#include "uci.h"
#include "syzygy/tbprobe.h"
bool RootInTB;
bool UseRule50;
Depth ProbeDepth;
- Value Score;
}
namespace TB = Tablebases;
// 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 };
+ constexpr uint64_t TtHitAverageWindow = 4096;
+ constexpr uint64_t TtHitAverageResolution = 1024;
- // Razoring and futility margin based on depth
- // razor_margin[0] is unused as long as depth >= ONE_PLY in search
- const int razor_margin[] = { 0, 570, 603, 554 };
- Value futility_margin(Depth d) { return Value(150 * d / ONE_PLY); }
+ // Razor and futility margins
+ constexpr int RazorMargin = 510;
+ Value futility_margin(Depth d, bool improving) {
+ return Value(223 * (d - improving));
+ }
- // Futility and reductions lookup tables, initialized at startup
- int FutilityMoveCounts[2][16]; // [improving][depth]
- int Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
+ // Reductions lookup table, initialized at startup
+ int Reductions[MAX_MOVES]; // [depth or moveNumber]
- // Threshold used for countermoves based pruning
- const int CounterMovePruneThreshold = 0;
+ Depth reduction(bool i, Depth d, int mn) {
+ int r = Reductions[d] * Reductions[mn];
+ return (r + 509) / 1024 + (!i && r > 894);
+ }
- 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;
+ constexpr int futility_move_count(bool improving, Depth depth) {
+ return (3 + depth * depth) / (2 - improving);
}
// 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;
+ int stat_bonus(Depth d) {
+ return d > 13 ? 29 : 17 * d * d + 134 * d - 134;
+ }
+
+ // Add a small random component to draw evaluations to avoid 3fold-blindness
+ Value value_draw(Thread* thisThread) {
+ return VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1);
}
// Skill structure is used to implement strength limit
struct Skill {
- Skill(int l) : level(l) {}
+ explicit Skill(int l) : level(l) {}
bool enabled() const { return level < 20; }
- bool time_to_pick(Depth depth) const { return depth / ONE_PLY == 1 + level; }
- Move best_move(size_t multiPV) { return best ? best : pick_best(multiPV); }
+ bool time_to_pick(Depth depth) const { return depth == 1 + level; }
Move pick_best(size_t multiPV);
int level;
Move best = MOVE_NONE;
};
- // EasyMoveManager structure is used to detect an 'easy move'. When the PV is stable
- // across multiple search iterations, we can quickly return the best move.
- struct EasyMoveManager {
-
- void clear() {
- stableCnt = 0;
- expectedPosKey = 0;
- pv[0] = pv[1] = pv[2] = MOVE_NONE;
+ // 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;
+ }
}
- Move get(Key key) const {
- return expectedPosKey == key ? pv[2] : MOVE_NONE;
+ ~ThreadHolding() {
+ if (owning) // Free the marked location
+ (*location).thread.store(nullptr, std::memory_order_relaxed);
}
- void update(Position& pos, const std::vector<Move>& newPv) {
-
- assert(newPv.size() >= 3);
-
- // Keep track of how many times in a row the 3rd ply remains stable
- stableCnt = (newPv[2] == pv[2]) ? stableCnt + 1 : 0;
-
- if (!std::equal(newPv.begin(), newPv.begin() + 3, pv))
- {
- std::copy(newPv.begin(), newPv.begin() + 3, pv);
-
- StateInfo st[2];
- pos.do_move(newPv[0], st[0]);
- pos.do_move(newPv[1], st[1]);
- expectedPosKey = pos.key();
- pos.undo_move(newPv[1]);
- pos.undo_move(newPv[0]);
- }
- }
+ bool marked() { return otherThread; }
- int stableCnt;
- Key expectedPosKey;
- Move pv[3];
+ private:
+ Breadcrumb* location;
+ bool otherThread, owning;
};
- EasyMoveManager EasyMove;
- Value DrawValue[COLOR_NB];
-
template <NodeType NT>
- Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning);
+ Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
- template <NodeType NT, bool InCheck>
- Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = DEPTH_ZERO);
+ template <NodeType NT>
+ Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = 0);
Value value_to_tt(Value v, int ply);
- Value value_from_tt(Value v, int ply);
+ Value value_from_tt(Value v, int ply, int r50c);
void update_pv(Move* pv, Move move, Move* childPv);
void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus);
- void update_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, int bonus);
+ void update_quiet_stats(const Position& pos, Stack* ss, Move move, int bonus, int depth);
+ void update_all_stats(const Position& pos, Stack* ss, Move bestMove, Value bestValue, Value beta, Square prevSq,
+ Move* quietsSearched, int quietCount, Move* capturesSearched, int captureCount, Depth depth);
-} // namespace
+ // perft() is our utility to verify move generation. All the leaf nodes up
+ // to the given depth are generated and counted, and the sum is returned.
+ template<bool Root>
+ uint64_t perft(Position& pos, Depth depth) {
+ StateInfo st;
+ uint64_t cnt, nodes = 0;
+ const bool leaf = (depth == 2);
-/// Search::init() is called during startup to initialize various lookup tables
+ for (const auto& m : MoveList<LEGAL>(pos))
+ {
+ if (Root && depth <= 1)
+ cnt = 1, nodes++;
+ else
+ {
+ pos.do_move(m, st);
+ cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - 1);
+ nodes += cnt;
+ pos.undo_move(m);
+ }
+ if (Root)
+ sync_cout << UCI::move(m, pos.is_chess960()) << ": " << cnt << sync_endl;
+ }
+ return nodes;
+ }
-void Search::init() {
+} // namespace
- for (int imp = 0; imp <= 1; ++imp)
- for (int d = 1; d < 64; ++d)
- for (int mc = 1; mc < 64; ++mc)
- {
- 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);
+/// Search::init() is called at startup to initialize various lookup tables
- // Increase reduction for non-PV nodes when eval is not improving
- if (!imp && Reductions[NonPV][imp][d][mc] >= 2)
- Reductions[NonPV][imp][d][mc]++;
- }
+void Search::init() {
- for (int d = 0; d < 16; ++d)
- {
- FutilityMoveCounts[0][d] = int(2.4 + 0.74 * pow(d, 1.78));
- FutilityMoveCounts[1][d] = int(5.0 + 1.00 * pow(d, 2.00));
- }
+ for (int i = 1; i < MAX_MOVES; ++i)
+ Reductions[i] = int((22.0 + std::log(Threads.size())) * std::log(i));
}
Time.availableNodes = 0;
TT.clear();
-
- for (Thread* th : Threads)
- {
- th->counterMoves.fill(MOVE_NONE);
- th->mainHistory.fill(0);
-
- for (auto& to : th->contHistory)
- for (auto& h : to)
- h.fill(0);
-
- th->contHistory[NO_PIECE][0].fill(CounterMovePruneThreshold - 1);
- }
-
- Threads.main()->callsCnt = 0;
- Threads.main()->previousScore = VALUE_INFINITE;
+ Threads.clear();
+ Tablebases::init(Options["SyzygyPath"]); // Free mapped files
}
-/// Search::perft() is our utility to verify move generation. All the leaf nodes
-/// up to the given depth are generated and counted, and the sum is returned.
-template<bool Root>
-uint64_t Search::perft(Position& pos, Depth depth) {
+/// MainThread::search() is started when the program receives the UCI 'go'
+/// command. It searches from the root position and outputs the "bestmove".
- StateInfo st;
- uint64_t cnt, nodes = 0;
- const bool leaf = (depth == 2 * ONE_PLY);
+void MainThread::search() {
- for (const auto& m : MoveList<LEGAL>(pos))
+ if (Limits.perft)
{
- if (Root && depth <= ONE_PLY)
- cnt = 1, nodes++;
- else
- {
- pos.do_move(m, st);
- cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
- nodes += cnt;
- pos.undo_move(m);
- }
- if (Root)
- sync_cout << UCI::move(m, pos.is_chess960()) << ": " << cnt << sync_endl;
+ nodes = perft<true>(rootPos, Limits.perft);
+ sync_cout << "\nNodes searched: " << nodes << "\n" << sync_endl;
+ return;
}
- return nodes;
-}
-
-template uint64_t Search::perft<true>(Position&, Depth);
-
-
-/// MainThread::search() is called by the main thread when the program receives
-/// the UCI 'go' command. It searches from the root position and outputs the "bestmove".
-
-void MainThread::search() {
Color us = rootPos.side_to_move();
Time.init(Limits, us, rootPos.game_ply());
TT.new_search();
- int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns
- DrawValue[ us] = VALUE_DRAW - Value(contempt);
- DrawValue[~us] = VALUE_DRAW + Value(contempt);
+ Eval::verify_NNUE();
if (rootMoves.empty())
{
- rootMoves.push_back(RootMove(MOVE_NONE));
+ rootMoves.emplace_back(MOVE_NONE);
sync_cout << "info depth 0 score "
<< UCI::value(rootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
<< sync_endl;
}
else
{
- for (Thread* th : Threads)
- if (th != this)
- th->start_searching();
-
- Thread::search(); // Let's start searching!
+ Threads.start_searching(); // start non-main threads
+ Thread::search(); // main thread start searching
}
- // When playing in 'nodes as time' mode, subtract the searched nodes from
- // the available ones before exiting.
- if (Limits.npmsec)
- Time.availableNodes += Limits.inc[us] - Threads.nodes_searched();
-
// When we reach the maximum depth, we can arrive here without a raise of
// Threads.stop. However, if we are pondering or in an infinite search,
// the UCI protocol states that we shouldn't print the best move before the
// GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
- // until the GUI sends one of those commands (which also raises Threads.stop).
- if (!Threads.stop && (Threads.ponder || Limits.infinite))
- {
- Threads.stopOnPonderhit = true;
- wait(Threads.stop);
- }
+ // until the GUI sends one of those commands.
+
+ while (!Threads.stop && (ponder || Limits.infinite))
+ {} // Busy wait for a stop or a ponder reset
- // Stop the threads if not already stopped
+ // Stop the threads if not already stopped (also raise the stop if
+ // "ponderhit" just reset Threads.ponder).
Threads.stop = true;
// Wait until all threads have finished
- for (Thread* th : Threads)
- if (th != this)
- th->wait_for_search_finished();
+ Threads.wait_for_search_finished();
+
+ // When playing in 'nodes as time' mode, subtract the searched nodes from
+ // the available ones before exiting.
+ if (Limits.npmsec)
+ Time.availableNodes += Limits.inc[us] - Threads.nodes_searched();
- // Check if there are threads with a better score than main thread
Thread* bestThread = this;
- if ( !this->easyMovePlayed
- && Options["MultiPV"] == 1
- && !Limits.depth
- && !Skill(Options["Skill Level"]).enabled()
- && rootMoves[0].pv[0] != MOVE_NONE)
- {
- for (Thread* th : Threads)
- {
- Depth depthDiff = th->completedDepth - bestThread->completedDepth;
- Value scoreDiff = th->rootMoves[0].score - bestThread->rootMoves[0].score;
- if (scoreDiff > 0 && depthDiff >= 0)
- bestThread = th;
- }
- }
+ if ( int(Options["MultiPV"]) == 1
+ && !Limits.depth
+ && !(Skill(Options["Skill Level"]).enabled() || int(Options["UCI_LimitStrength"]))
+ && rootMoves[0].pv[0] != MOVE_NONE)
+ bestThread = Threads.get_best_thread();
- previousScore = bestThread->rootMoves[0].score;
+ bestPreviousScore = bestThread->rootMoves[0].score;
- // Send new PV when needed
+ // Send again PV info if we have a new best thread
if (bestThread != this)
sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl;
void Thread::search() {
- Stack stack[MAX_PLY+7], *ss = stack+4; // To allow referencing (ss-4) and (ss+2)
+ // 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.
+ Stack stack[MAX_PLY+10], *ss = stack+7;
+ Move pv[MAX_PLY+1];
Value bestValue, alpha, beta, delta;
- Move easyMove = MOVE_NONE;
+ Move lastBestMove = MOVE_NONE;
+ Depth lastBestMoveDepth = 0;
MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
+ double timeReduction = 1, totBestMoveChanges = 0;
+ Color us = rootPos.side_to_move();
+ int iterIdx = 0;
+
+ std::memset(ss-7, 0, 10 * sizeof(Stack));
+ for (int i = 7; i > 0; i--)
+ (ss-i)->continuationHistory = &this->continuationHistory[0][0][NO_PIECE][0]; // Use as a sentinel
- std::memset(ss-4, 0, 7 * sizeof(Stack));
- for (int i = 4; i > 0; i--)
- (ss-i)->contHistory = &this->contHistory[NO_PIECE][0]; // Use as sentinel
+ ss->pv = pv;
bestValue = delta = alpha = -VALUE_INFINITE;
beta = VALUE_INFINITE;
- completedDepth = DEPTH_ZERO;
if (mainThread)
{
- easyMove = EasyMove.get(rootPos.key());
- EasyMove.clear();
- mainThread->easyMovePlayed = mainThread->failedLow = false;
- mainThread->bestMoveChanges = 0;
+ if (mainThread->bestPreviousScore == VALUE_INFINITE)
+ for (int i = 0; i < 4; ++i)
+ mainThread->iterValue[i] = VALUE_ZERO;
+ else
+ for (int i = 0; i < 4; ++i)
+ mainThread->iterValue[i] = mainThread->bestPreviousScore;
}
- size_t multiPV = Options["MultiPV"];
- Skill skill(Options["Skill Level"]);
+ std::copy(&lowPlyHistory[2][0], &lowPlyHistory.back().back() + 1, &lowPlyHistory[0][0]);
+ std::fill(&lowPlyHistory[MAX_LPH - 2][0], &lowPlyHistory.back().back() + 1, 0);
+
+ size_t multiPV = size_t(Options["MultiPV"]);
+
+ // 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"] ?
+ std::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<unsigned>() % 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.
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;
+
+ // Evaluation score is from the white point of view
+ contempt = (us == WHITE ? make_score(ct, ct / 2)
+ : -make_score(ct, ct / 2));
+
+ int searchAgainCounter = 0;
// Iterative deepening loop until requested to stop or the target depth is reached
- while ( (rootDepth += ONE_PLY) < DEPTH_MAX
+ while ( ++rootDepth < MAX_PLY
&& !Threads.stop
- && !(Limits.depth && mainThread && rootDepth / ONE_PLY > Limits.depth))
+ && !(Limits.depth && mainThread && rootDepth > Limits.depth))
{
- // Distribute search depths across the threads
- if (idx)
- {
- int i = (idx - 1) % 20;
- if (((rootDepth / ONE_PLY + rootPos.game_ply() + skipPhase[i]) / skipSize[i]) % 2)
- continue;
- }
-
// Age out PV variability metric
if (mainThread)
- mainThread->bestMoveChanges *= 0.505, mainThread->failedLow = false;
+ 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.
for (RootMove& rm : rootMoves)
rm.previousScore = rm.score;
+ size_t pvFirst = 0;
+ pvLast = 0;
+
+ if (!Threads.increaseDepth)
+ searchAgainCounter++;
+
// MultiPV loop. We perform a full root search for each PV line
- for (PVIdx = 0; PVIdx < multiPV && !Threads.stop; ++PVIdx)
+ for (pvIdx = 0; pvIdx < multiPV && !Threads.stop; ++pvIdx)
{
+ if (pvIdx == pvLast)
+ {
+ pvFirst = pvLast;
+ for (pvLast++; pvLast < rootMoves.size(); pvLast++)
+ if (rootMoves[pvLast].tbRank != rootMoves[pvFirst].tbRank)
+ break;
+ }
+
// Reset UCI info selDepth for each depth and each PV line
selDepth = 0;
// Reset aspiration window starting size
- if (rootDepth >= 5 * ONE_PLY)
+ if (rootDepth >= 4)
{
- delta = Value(18);
- alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE);
- beta = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE);
+ Value prev = rootMoves[pvIdx].previousScore;
+ delta = Value(17);
+ 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 + (105 - ct / 2) * prev / (abs(prev) + 149);
+
+ contempt = (us == WHITE ? make_score(dct, dct / 2)
+ : -make_score(dct, dct / 2));
}
// Start with a small aspiration window and, in the case of a fail
- // high/low, re-search with a bigger window until we're not failing
+ // high/low, re-search with a bigger window until we don't fail
// high/low anymore.
+ int failedHighCnt = 0;
while (true)
{
- bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, false, false);
+ Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - searchAgainCounter);
+ bestValue = ::search<PV>(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
// and we want to keep the same order for all the moves except the
// new PV that goes to the front. Note that in case of MultiPV
// search the already searched PV lines are preserved.
- std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end());
+ std::stable_sort(rootMoves.begin() + pvIdx, rootMoves.begin() + pvLast);
- // 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 search has been stopped, we break immediately. Sorting is
+ // safe because RootMoves is still valid, although it refers to
+ // the previous iteration.
if (Threads.stop)
break;
beta = (alpha + beta) / 2;
alpha = std::max(bestValue - delta, -VALUE_INFINITE);
+ failedHighCnt = 0;
if (mainThread)
- {
- mainThread->failedLow = true;
- Threads.stopOnPonderhit = false;
- }
+ mainThread->stopOnPonderhit = false;
}
else if (bestValue >= beta)
+ {
beta = std::min(bestValue + delta, VALUE_INFINITE);
+ ++failedHighCnt;
+ }
else
+ {
+ ++rootMoves[pvIdx].bestMoveCount;
break;
+ }
delta += delta / 4 + 5;
}
// Sort the PV lines searched so far and update the GUI
- std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1);
+ std::stable_sort(rootMoves.begin() + pvFirst, rootMoves.begin() + pvIdx + 1);
- if (!mainThread)
- continue;
-
- if (Threads.stop || PVIdx + 1 == multiPV || Time.elapsed() > 3000)
+ if ( mainThread
+ && (Threads.stop || pvIdx + 1 == multiPV || Time.elapsed() > 3000))
sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
}
if (!Threads.stop)
completedDepth = rootDepth;
- if (!mainThread)
- continue;
-
- // If skill level is enabled and time is up, pick a sub-optimal best move
- if (skill.enabled() && skill.time_to_pick(rootDepth))
- skill.pick_best(multiPV);
+ if (rootMoves[0].pv[0] != lastBestMove) {
+ lastBestMove = rootMoves[0].pv[0];
+ lastBestMoveDepth = rootDepth;
+ }
// Have we found a "mate in x"?
if ( Limits.mate
&& VALUE_MATE - bestValue <= 2 * Limits.mate)
Threads.stop = true;
+ if (!mainThread)
+ continue;
+
+ // If skill level is enabled and time is up, pick a sub-optimal best move
+ if (skill.enabled() && skill.time_to_pick(rootDepth))
+ skill.pick_best(multiPV);
+
// Do we have time for the next iteration? Can we stop searching now?
- if (Limits.use_time_management())
+ if ( Limits.use_time_management()
+ && !Threads.stop
+ && !mainThread->stopOnPonderhit)
{
- if (!Threads.stop && !Threads.stopOnPonderhit)
+ double fallingEval = (318 + 6 * (mainThread->bestPreviousScore - bestValue)
+ + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 825.0;
+ fallingEval = std::clamp(fallingEval, 0.5, 1.5);
+
+ // If the bestMove is stable over several iterations, reduce time accordingly
+ timeReduction = lastBestMoveDepth + 9 < completedDepth ? 1.92 : 0.95;
+ double reduction = (1.47 + mainThread->previousTimeReduction) / (2.32 * timeReduction);
+
+ // Use part of the gained time from a previous stable move for the current move
+ for (Thread* th : Threads)
{
- // Stop the search if only one legal move is available, or if all
- // of the available time has been used, or if we matched an easyMove
- // from the previous search and just did a fast verification.
- const int F[] = { mainThread->failedLow,
- bestValue - mainThread->previousScore };
-
- int improvingFactor = std::max(229, std::min(715, 357 + 119 * F[0] - 6 * F[1]));
- double unstablePvFactor = 1 + mainThread->bestMoveChanges;
-
- bool doEasyMove = rootMoves[0].pv[0] == easyMove
- && mainThread->bestMoveChanges < 0.03
- && Time.elapsed() > Time.optimum() * 5 / 44;
-
- if ( rootMoves.size() == 1
- || Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 628
- || (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".
- if (Threads.ponder)
- Threads.stopOnPonderhit = true;
- else
- Threads.stop = true;
- }
+ totBestMoveChanges += th->bestMoveChanges;
+ th->bestMoveChanges = 0;
}
+ double bestMoveInstability = 1 + totBestMoveChanges / Threads.size();
- if (rootMoves[0].pv.size() >= 3)
- EasyMove.update(rootPos, rootMoves[0].pv);
+ double totalTime = rootMoves.size() == 1 ? 0 :
+ Time.optimum() * fallingEval * reduction * bestMoveInstability;
+
+ // Stop the search if we have exceeded the totalTime, at least 1ms search
+ if (Time.elapsed() > totalTime)
+ {
+ // If we are allowed to ponder do not stop the search now but
+ // keep pondering until the GUI sends "ponderhit" or "stop".
+ if (mainThread->ponder)
+ mainThread->stopOnPonderhit = true;
+ else
+ Threads.stop = true;
+ }
+ else if ( Threads.increaseDepth
+ && !mainThread->ponder
+ && Time.elapsed() > totalTime * 0.58)
+ Threads.increaseDepth = false;
else
- EasyMove.clear();
+ Threads.increaseDepth = true;
}
+
+ mainThread->iterValue[iterIdx] = bestValue;
+ iterIdx = (iterIdx + 1) & 3;
}
if (!mainThread)
return;
- // Clear any candidate easy move that wasn't stable for the last search
- // iterations; the second condition prevents consecutive fast moves.
- if (EasyMove.stableCnt < 6 || mainThread->easyMovePlayed)
- EasyMove.clear();
+ mainThread->previousTimeReduction = timeReduction;
// If skill level is enabled, swap best PV line with the sub-optimal one
if (skill.enabled())
- std::swap(rootMoves[0], *std::find(rootMoves.begin(),
- rootMoves.end(), skill.best_move(multiPV)));
+ std::swap(rootMoves[0], *std::find(rootMoves.begin(), rootMoves.end(),
+ skill.best ? skill.best : skill.pick_best(multiPV)));
}
// 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, bool skipEarlyPruning) {
+ Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
- const bool PvNode = NT == PV;
- const bool rootNode = PvNode && (ss-1)->ply == 0;
+ constexpr bool PvNode = NT == PV;
+ const bool rootNode = PvNode && ss->ply == 0;
+
+ // 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
+ && alpha < VALUE_DRAW
+ && !rootNode
+ && pos.has_game_cycle(ss->ply))
+ {
+ alpha = value_draw(pos.this_thread());
+ if (alpha >= beta)
+ return alpha;
+ }
+
+ // Dive into quiescence search when the depth reaches zero
+ if (depth <= 0)
+ return qsearch<NT>(pos, ss, alpha, beta);
assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
assert(PvNode || (alpha == beta - 1));
- assert(DEPTH_ZERO < depth && depth < DEPTH_MAX);
+ assert(0 < depth && depth < MAX_PLY);
assert(!(PvNode && cutNode));
- assert(depth / ONE_PLY * ONE_PLY == depth);
- Move pv[MAX_PLY+1], quietsSearched[64];
+ Move pv[MAX_PLY+1], capturesSearched[32], quietsSearched[64];
StateInfo st;
TTEntry* tte;
Key posKey;
Move ttMove, move, excludedMove, bestMove;
Depth extension, newDepth;
- Value bestValue, value, ttValue, eval;
- bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
- bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture;
+ Value bestValue, value, ttValue, eval, maxValue, probCutBeta;
+ bool ttHit, ttPv, formerPv, givesCheck, improving, didLMR, priorCapture;
+ bool captureOrPromotion, doFullDepthSearch, moveCountPruning,
+ ttCapture, singularQuietLMR;
Piece movedPiece;
- int moveCount, quietCount;
+ int moveCount, captureCount, quietCount;
// Step 1. Initialize node
Thread* thisThread = pos.this_thread();
- inCheck = pos.checkers();
- moveCount = quietCount = ss->moveCount = 0;
- ss->statScore = 0;
+ ss->inCheck = pos.checkers();
+ priorCapture = pos.captured_piece();
+ Color us = pos.side_to_move();
+ moveCount = captureCount = quietCount = ss->moveCount = 0;
bestValue = -VALUE_INFINITE;
- ss->ply = (ss-1)->ply + 1;
+ maxValue = VALUE_INFINITE;
// Check for the available remaining time
if (thisThread == Threads.main())
static_cast<MainThread*>(thisThread)->check_time();
- // Used to send selDepth info to GUI
- if (PvNode && thisThread->selDepth < ss->ply)
- thisThread->selDepth = ss->ply;
+ // Used to send selDepth info to GUI (selDepth counts from 1, ply from 0)
+ if (PvNode && thisThread->selDepth < ss->ply + 1)
+ thisThread->selDepth = ss->ply + 1;
if (!rootNode)
{
// Step 2. Check for aborted search and immediate draw
- if (Threads.stop.load(std::memory_order_relaxed) || pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
- return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos)
- : DrawValue[pos.side_to_move()];
+ if ( Threads.stop.load(std::memory_order_relaxed)
+ || pos.is_draw(ss->ply)
+ || ss->ply >= MAX_PLY)
+ return (ss->ply >= MAX_PLY && !ss->inCheck) ? evaluate(pos)
+ : value_draw(pos.this_thread());
// Step 3. Mate distance pruning. Even if we mate at the next move our score
// would be at best mate_in(ss->ply+1), but if alpha is already bigger because
assert(0 <= ss->ply && ss->ply < MAX_PLY);
- ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
- ss->contHistory = &thisThread->contHistory[NO_PIECE][0];
+ (ss+1)->ply = ss->ply + 1;
+ (ss+1)->excludedMove = bestMove = MOVE_NONE;
(ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
Square prevSq = to_sq((ss-1)->currentMove);
+ // Initialize statScore to zero for the grandchildren of the current position.
+ // So statScore is shared between all grandchildren and only the first grandchild
+ // 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.
+ 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
// position key in case of an excluded move.
excludedMove = ss->excludedMove;
- posKey = pos.key() ^ Key(excludedMove);
+ posKey = excludedMove == MOVE_NONE ? pos.key() : pos.key() ^ make_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 = ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE;
+ ttMove = rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0]
: ttHit ? tte->move() : MOVE_NONE;
+ ttPv = PvNode || (ttHit && tte->is_pv());
+ formerPv = ttPv && !PvNode;
+
+ if ( ttPv
+ && depth > 12
+ && ss->ply - 1 < MAX_LPH
+ && !priorCapture
+ && 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 * ttHit;
// At non-PV nodes we check for an early TT cutoff
if ( !PvNode
if (ttValue >= beta)
{
if (!pos.capture_or_promotion(ttMove))
- update_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth));
+ update_quiet_stats(pos, ss, ttMove, stat_bonus(depth), depth);
- // Extra penalty for a quiet TT move in previous ply when it gets refuted
- if ((ss-1)->moveCount == 1 && !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 && !priorCapture)
+ 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))
{
int penalty = -stat_bonus(depth);
- thisThread->mainHistory.update(pos.side_to_move(), ttMove, penalty);
+ thisThread->mainHistory[us][from_to(ttMove)] << penalty;
update_continuation_histories(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty);
}
}
- return ttValue;
+
+ if (pos.rule50_count() < 90)
+ return ttValue;
}
- // Step 4a. Tablebase probe
+ // Step 5. Tablebases probe
if (!rootNode && TB::Cardinality)
{
int piecesCount = pos.count<ALL_PIECES>();
&& !pos.can_castle(ANY_CASTLING))
{
TB::ProbeState err;
- TB::WDLScore v = Tablebases::probe_wdl(pos, &err);
+ TB::WDLScore wdl = Tablebases::probe_wdl(pos, &err);
+
+ // Force check of time on the next occasion
+ if (thisThread == Threads.main())
+ static_cast<MainThread*>(thisThread)->callsCnt = 0;
if (err != TB::ProbeState::FAIL)
{
int drawScore = TB::UseRule50 ? 1 : 0;
- value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply
- : v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply
- : VALUE_DRAW + 2 * v * drawScore;
+ // use the range VALUE_MATE_IN_MAX_PLY to VALUE_TB_WIN_IN_MAX_PLY to score
+ value = wdl < -drawScore ? VALUE_MATED_IN_MAX_PLY + ss->ply + 1
+ : wdl > drawScore ? VALUE_MATE_IN_MAX_PLY - ss->ply - 1
+ : VALUE_DRAW + 2 * wdl * drawScore;
- tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT,
- std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
- MOVE_NONE, VALUE_NONE, TT.generation());
+ Bound b = wdl < -drawScore ? BOUND_UPPER
+ : wdl > drawScore ? BOUND_LOWER : BOUND_EXACT;
- return value;
+ if ( b == BOUND_EXACT
+ || (b == BOUND_LOWER ? value >= beta : value <= alpha))
+ {
+ tte->save(posKey, value_to_tt(value, ss->ply), ttPv, b,
+ std::min(MAX_PLY - 1, depth + 6),
+ MOVE_NONE, VALUE_NONE);
+
+ return value;
+ }
+
+ if (PvNode)
+ {
+ if (b == BOUND_LOWER)
+ bestValue = value, alpha = std::max(alpha, bestValue);
+ else
+ maxValue = value;
+ }
}
}
}
- // Step 5. Evaluate the position statically
- if (inCheck)
+ CapturePieceToHistory& captureHistory = thisThread->captureHistory;
+
+ // Step 6. Static evaluation of the position
+ if (ss->inCheck)
{
+ // Skip early pruning when in check
ss->staticEval = eval = VALUE_NONE;
+ improving = false;
goto moves_loop;
}
-
else if (ttHit)
{
- // Never assume anything on values stored in TT
- if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
- eval = ss->staticEval = evaluate(pos);
+ // Never assume anything about values stored in TT
+ ss->staticEval = eval = tte->eval();
+ if (eval == VALUE_NONE)
+ ss->staticEval = eval = evaluate(pos);
+
+ if (eval == VALUE_DRAW)
+ eval = value_draw(thisThread);
// Can ttValue be used as a better position evaluation?
- if ( ttValue != VALUE_NONE
+ if ( ttValue != VALUE_NONE
&& (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER)))
eval = ttValue;
}
else
{
- eval = ss->staticEval =
- (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
- : -(ss-1)->staticEval + 2 * Eval::Tempo;
+ if ((ss-1)->currentMove != MOVE_NULL)
+ ss->staticEval = eval = evaluate(pos);
+ else
+ ss->staticEval = eval = -(ss-1)->staticEval + 2 * Tempo;
- tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
- ss->staticEval, TT.generation());
+ tte->save(posKey, VALUE_NONE, ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
}
- if (skipEarlyPruning)
- goto moves_loop;
+ // Step 7. Razoring (~1 Elo)
+ if ( !rootNode // The required rootNode PV handling is not available in qsearch
+ && depth == 1
+ && eval <= alpha - RazorMargin)
+ return qsearch<NT>(pos, ss, alpha, beta);
- // Step 6. Razoring (skipped when in check)
- if ( !PvNode
- && depth < 4 * ONE_PLY
- && eval + razor_margin[depth / ONE_PLY] <= alpha)
- {
- if (depth <= ONE_PLY)
- return qsearch<NonPV, false>(pos, ss, alpha, alpha+1);
+ improving = (ss-2)->staticEval == VALUE_NONE
+ ? ss->staticEval > (ss-4)->staticEval || (ss-4)->staticEval == VALUE_NONE
+ : ss->staticEval > (ss-2)->staticEval;
- Value ralpha = alpha - razor_margin[depth / ONE_PLY];
- Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1);
- if (v <= ralpha)
- return v;
- }
-
- // Step 7. Futility pruning: child node (skipped when in check)
- if ( !rootNode
- && depth < 7 * ONE_PLY
- && eval - futility_margin(depth) >= beta
- && eval < VALUE_KNOWN_WIN // Do not return unproven wins
- && pos.non_pawn_material(pos.side_to_move()))
+ // Step 8. Futility pruning: child node (~50 Elo)
+ if ( !PvNode
+ && depth < 8
+ && eval - futility_margin(depth, improving) >= beta
+ && eval < VALUE_KNOWN_WIN) // Do not return unproven wins
return eval;
- // Step 8. Null move search with verification search (is omitted in PV nodes)
+ // Step 9. Null move search with verification search (~40 Elo)
if ( !PvNode
+ && (ss-1)->currentMove != MOVE_NULL
+ && (ss-1)->statScore < 22977
&& eval >= beta
- && (ss->staticEval >= beta - 35 * (depth / ONE_PLY - 6) || depth >= 13 * ONE_PLY)
- && pos.non_pawn_material(pos.side_to_move()))
+ && eval >= ss->staticEval
+ && ss->staticEval >= beta - 30 * depth - 28 * improving + 84 * ttPv + 182
+ && !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 = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
+ Depth R = (817 + 71 * depth) / 213 + std::min(int(eval - beta) / 192, 3);
ss->currentMove = MOVE_NULL;
- ss->contHistory = &thisThread->contHistory[NO_PIECE][0];
+ ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0];
pos.do_null_move(st);
- 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);
+
+ Value nullValue = -search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
+
pos.undo_null_move();
if (nullValue >= beta)
{
- // Do not return unproven mate scores
- if (nullValue >= VALUE_MATE_IN_MAX_PLY)
+ // Do not return unproven mate or TB scores
+ if (nullValue >= VALUE_TB_WIN_IN_MAX_PLY)
nullValue = beta;
- if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
+ if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 13))
return nullValue;
- // Do verification search at high depths
- 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);
+ 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->nmpColor = us;
+
+ Value v = search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
+
+ thisThread->nmpMinPly = 0;
if (v >= beta)
return nullValue;
}
}
- // Step 9. ProbCut (skipped when in check)
+ probCutBeta = beta + 176 - 49 * improving;
+
+ // Step 10. ProbCut (~10 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
- && depth >= 5 * ONE_PLY
- && abs(beta) < VALUE_MATE_IN_MAX_PLY)
+ && depth > 4
+ && abs(beta) < VALUE_TB_WIN_IN_MAX_PLY
+ // if value from transposition table is lower than probCutBeta, don't attempt probCut
+ // there and in further interactions with transposition table cutoff depth is set to depth - 3
+ // because probCut search has depth set to depth - 4 but we also do a move before it
+ // so effective depth is equal to depth - 3
+ && !( ttHit
+ && tte->depth() >= depth - 3
+ && ttValue != VALUE_NONE
+ && ttValue < probCutBeta))
{
- Value rbeta = std::min(beta + 200, VALUE_INFINITE);
-
- assert(is_ok((ss-1)->currentMove));
+ // if ttMove is a capture and value from transposition table is good enough produce probCut
+ // cutoff without digging into actual probCut search
+ if ( 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;
+
+ while ( (move = mp.next_move()) != MOVE_NONE
+ && probCutCount < 2 + 2 * cutNode)
+ if (move != excludedMove && pos.legal(move))
+ {
+ assert(pos.capture_or_promotion(move));
+ assert(depth >= 5);
- MovePicker mp(pos, ttMove, rbeta - ss->staticEval);
+ captureOrPromotion = true;
+ probCutCount++;
- while ((move = mp.next_move()) != MOVE_NONE)
- if (pos.legal(move))
- {
ss->currentMove = move;
- ss->contHistory = &thisThread->contHistory[pos.moved_piece(move)][to_sq(move)];
+ ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck]
+ [captureOrPromotion]
+ [pos.moved_piece(move)]
+ [to_sq(move)];
- assert(depth >= 5 * ONE_PLY);
pos.do_move(move, st);
- value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false);
+
+ // Perform a preliminary qsearch to verify that the move holds
+ value = -qsearch<NonPV>(pos, ss+1, -probCutBeta, -probCutBeta+1);
+
+ // If the qsearch held, perform the regular search
+ if (value >= probCutBeta)
+ value = -search<NonPV>(pos, ss+1, -probCutBeta, -probCutBeta+1, depth - 4, !cutNode);
+
pos.undo_move(move);
- if (value >= rbeta)
+
+ if (value >= probCutBeta)
+ {
+ // if transposition table doesn't have equal or more deep info write probCut data into it
+ if ( !(ttHit
+ && tte->depth() >= depth - 3
+ && ttValue != VALUE_NONE))
+ tte->save(posKey, value_to_tt(value, ss->ply), ttPv,
+ BOUND_LOWER,
+ depth - 3, move, ss->staticEval);
return value;
+ }
}
}
- // Step 10. Internal iterative deepening (skipped when in check)
- if ( depth >= 6 * ONE_PLY
- && !ttMove
- && (PvNode || ss->staticEval + 256 >= beta))
- {
- Depth d = (3 * depth / (4 * ONE_PLY) - 2) * ONE_PLY;
- search<NT>(pos, ss, alpha, beta, d, cutNode, true);
+ // Step 11. If the position is not in TT, decrease depth by 2
+ if ( PvNode
+ && depth >= 6
+ && !ttMove)
+ depth -= 2;
- tte = TT.probe(posKey, ttHit);
- ttMove = ttHit ? tte->move() : MOVE_NONE;
- }
+moves_loop: // When in check, search starts from here
-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 };
- const PieceToHistory* contHist[] = { (ss-1)->contHistory, (ss-2)->contHistory, nullptr, (ss-4)->contHistory };
Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
- MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, contHist, countermove, ss->killers);
- value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
- improving = ss->staticEval >= (ss-2)->staticEval
- /* || ss->staticEval == VALUE_NONE Already implicit in the previous condition */
- ||(ss-2)->staticEval == VALUE_NONE;
-
- singularExtensionNode = !rootNode
- && depth >= 8 * ONE_PLY
- && ttMove != MOVE_NONE
- && ttValue != VALUE_NONE
- && !excludedMove // Recursive singular search is not allowed
- && (tte->bound() & BOUND_LOWER)
- && tte->depth() >= depth - 3 * ONE_PLY;
- skipQuiets = false;
- ttCapture = 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(skipQuiets)) != MOVE_NONE)
+ MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
+ &thisThread->lowPlyHistory,
+ &captureHistory,
+ contHist,
+ countermove,
+ ss->killers,
+ ss->ply);
+
+ value = bestValue;
+ singularQuietLMR = 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)
{
assert(is_ok(move));
// At root obey the "searchmoves" option and skip moves not listed in Root
// Move List. As a consequence any illegal move is also skipped. In MultiPV
- // mode we also skip PV moves which have been already searched.
- if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx,
- thisThread->rootMoves.end(), move))
+ // mode we also skip PV moves which have been already searched and those
+ // of lower "TB rank" if we are in a TB root position.
+ if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->pvIdx,
+ thisThread->rootMoves.begin() + thisThread->pvLast, move))
+ continue;
+
+ // Check for legality
+ if (!rootNode && !pos.legal(move))
continue;
ss->moveCount = ++moveCount;
if (rootNode && thisThread == Threads.main() && Time.elapsed() > 3000)
- sync_cout << "info depth " << depth / ONE_PLY
+ sync_cout << "info depth " << depth
<< " currmove " << UCI::move(move, pos.is_chess960())
- << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl;
-
+ << " currmovenumber " << moveCount + thisThread->pvIdx << sync_endl;
if (PvNode)
(ss+1)->pv = nullptr;
- extension = DEPTH_ZERO;
+ extension = 0;
captureOrPromotion = pos.capture_or_promotion(move);
movedPiece = pos.moved_piece(move);
-
- givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates()
- ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
- : pos.gives_check(move);
-
- moveCountPruning = depth < 16 * ONE_PLY
- && moveCount >= FutilityMoveCounts[improving][depth / 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 will extend the ttMove.
- if ( singularExtensionNode
- && move == ttMove
- && pos.legal(move))
- {
- Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
- Depth d = (depth / (2 * ONE_PLY)) * ONE_PLY;
- ss->excludedMove = move;
- 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;
+ givesCheck = pos.gives_check(move);
// Calculate new depth for this move
- newDepth = depth - ONE_PLY + extension;
+ newDepth = depth - 1;
- // Step 13. Pruning at shallow depth
+ // Step 13. Pruning at shallow depth (~200 Elo)
if ( !rootNode
- && pos.non_pawn_material(pos.side_to_move())
- && bestValue > VALUE_MATED_IN_MAX_PLY)
+ && pos.non_pawn_material(us)
+ && bestValue > VALUE_TB_LOSS_IN_MAX_PLY)
{
- if ( !captureOrPromotion
- && !givesCheck
- && (!pos.advanced_pawn_push(move) || pos.non_pawn_material() >= Value(5000)))
- {
- // Move count based pruning
- if (moveCountPruning)
- {
- skipQuiets = true;
- continue;
- }
+ // Skip quiet moves if movecount exceeds our FutilityMoveCount threshold
+ moveCountPruning = moveCount >= futility_move_count(improving, depth);
- // Reduced depth of the next LMR search
- int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;
+ // Reduced depth of the next LMR search
+ int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), 0);
- // Countermoves based pruning
- if ( lmrDepth < 3
+ if ( !captureOrPromotion
+ && !givesCheck)
+ {
+ // 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)
continue;
- // Futility pruning: parent node
+ // Futility pruning: parent node (~5 Elo)
if ( lmrDepth < 7
- && !inCheck
- && ss->staticEval + 256 + 200 * lmrDepth <= alpha)
+ && !ss->inCheck
+ && ss->staticEval + 283 + 170 * 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 < 27376)
continue;
- // Prune moves with negative SEE
- if ( lmrDepth < 8
- && !pos.see_ge(move, Value(-35 * lmrDepth * lmrDepth)))
+ // Prune moves with negative SEE (~20 Elo)
+ if (!pos.see_ge(move, Value(-(29 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
continue;
}
- else if ( depth < 7 * ONE_PLY
- && !extension
- && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY)))
+ else
+ {
+ // Capture history based pruning when the move doesn't give check
+ if ( !givesCheck
+ && lmrDepth < 1
+ && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] < 0)
+ continue;
+
+ // Futility pruning for captures
+ if ( !givesCheck
+ && lmrDepth < 6
+ && !(PvNode && abs(bestValue) < 2)
+ && PieceValue[MG][type_of(movedPiece)] >= PieceValue[MG][type_of(pos.piece_on(to_sq(move)))]
+ && !ss->inCheck
+ && ss->staticEval + 169 + 244 * lmrDepth
+ + PieceValue[MG][type_of(pos.piece_on(to_sq(move)))] <= alpha)
+ continue;
+
+ // See based pruning
+ if (!pos.see_ge(move, Value(-221) * depth)) // (~25 Elo)
continue;
+ }
}
- // Speculative prefetch as early as possible
- prefetch(TT.first_entry(pos.key_after(move)));
+ // Step 14. Extensions (~75 Elo)
- // Check for legality just before making the move
- if (!rootNode && !pos.legal(move))
+ // 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
+ && 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)
{
- ss->moveCount = --moveCount;
- continue;
+ Value singularBeta = ttValue - ((formerPv + 4) * depth) / 2;
+ Depth singularDepth = (depth - 1 + 3 * formerPv) / 2;
+ ss->excludedMove = move;
+ value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode);
+ ss->excludedMove = MOVE_NONE;
+
+ if (value < singularBeta)
+ {
+ extension = 1;
+ singularQuietLMR = !ttCapture;
+ }
+
+ // 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 multiple moves fail high, and we can prune the whole subtree by returning
+ // a soft bound.
+ 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.
+ 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;
+ }
}
- if (move == ttMove && captureOrPromotion)
- ttCapture = true;
+ // Check extension (~2 Elo)
+ else if ( givesCheck
+ && (pos.is_discovery_check_on_king(~us, move) || pos.see_ge(move)))
+ extension = 1;
+
+ // Last captures extension
+ else if ( PieceValue[EG][pos.captured_piece()] > PawnValueEg
+ && pos.non_pawn_material() <= 2 * RookValueMg)
+ extension = 1;
+
+ // Castling extension
+ if ( type_of(move) == CASTLING
+ && popcount(pos.pieces(us) & ~pos.pieces(PAWN) & (to_sq(move) & KingSide ? KingSide : QueenSide)) <= 2)
+ extension = 1;
+
+ // Late irreversible move extension
+ if ( move == ttMove
+ && pos.rule50_count() > 80
+ && (captureOrPromotion || type_of(movedPiece) == PAWN))
+ extension = 2;
+
+ // Add extension to new depth
+ newDepth += extension;
+
+ // Speculative prefetch as early as possible
+ prefetch(TT.first_entry(pos.key_after(move)));
// Update the current move (this must be done after singular extension search)
ss->currentMove = move;
- ss->contHistory = &thisThread->contHistory[movedPiece][to_sq(move)];
+ ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck]
+ [captureOrPromotion]
+ [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). If the move fails high it will be
+ // Step 16. Reduced depth search (LMR, ~200 Elo). If the move fails high it will be
// re-searched at full depth.
- if ( depth >= 3 * ONE_PLY
- && moveCount > 1
- && (!captureOrPromotion || moveCountPruning))
+ if ( depth >= 3
+ && moveCount > 1 + 2 * rootNode + 2 * (PvNode && abs(bestValue) < 2)
+ && (!rootNode || thisThread->best_move_count(move) == 0)
+ && ( !captureOrPromotion
+ || moveCountPruning
+ || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha
+ || cutNode
+ || thisThread->ttHitAverage < 427 * TtHitAverageResolution * TtHitAverageWindow / 1024))
{
- Depth r = reduction<PvNode>(improving, depth, moveCount);
+ Depth r = reduction(improving, depth, moveCount);
- if (captureOrPromotion)
- r -= r ? ONE_PLY : DEPTH_ZERO;
- else
+ // Decrease reduction at non-check cut nodes for second move at low depths
+ if ( cutNode
+ && depth <= 10
+ && moveCount <= 2
+ && !ss->inCheck)
+ r--;
+
+ // Decrease reduction if the ttHit running average is large
+ if (thisThread->ttHitAverage > 509 * TtHitAverageResolution * TtHitAverageWindow / 1024)
+ r--;
+
+ // 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 (ttPv)
+ r -= 2;
+
+ if (moveCountPruning && !formerPv)
+ r++;
+
+ // Decrease reduction if opponent's move count is high (~5 Elo)
+ if ((ss-1)->moveCount > 13)
+ r--;
+
+ // Decrease reduction if ttMove has been singularly extended (~3 Elo)
+ if (singularQuietLMR)
+ r -= 1 + formerPv;
+
+ if (!captureOrPromotion)
{
- // Increase reduction if ttMove is a capture
+ // Increase reduction if ttMove is a capture (~5 Elo)
if (ttCapture)
- r += ONE_PLY;
+ r++;
- // Increase reduction for cut nodes
+ // Increase reduction for cut nodes (~10 Elo)
if (cutNode)
- r += 2 * ONE_PLY;
+ 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().
+ // hence break make_move(). (~2 Elo)
else if ( type_of(move) == NORMAL
- && !pos.see_ge(make_move(to_sq(move), from_sq(move))))
- r -= 2 * ONE_PLY;
+ && !pos.see_ge(reverse_move(move)))
+ r -= 2 + ttPv - (type_of(movedPiece) == PAWN);
- ss->statScore = thisThread->mainHistory[~pos.side_to_move()][from_to(move)]
+ 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;
+ - 5287;
- // Decrease/increase reduction by comparing opponent's stat score
- if (ss->statScore > 0 && (ss-1)->statScore < 0)
- r -= ONE_PLY;
+ // Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
+ if (ss->statScore >= -106 && (ss-1)->statScore < -104)
+ r--;
- else if (ss->statScore < 0 && (ss-1)->statScore > 0)
- r += ONE_PLY;
+ else if ((ss-1)->statScore >= -119 && ss->statScore < -140)
+ r++;
- // Decrease/increase reduction for moves with a good/bad history
- r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->statScore / 20000) * ONE_PLY);
+ // Decrease/increase reduction for moves with a good/bad history (~30 Elo)
+ r -= ss->statScore / 14884;
+ }
+ else
+ {
+ // Increase reduction for captures/promotions if late move and at low depth
+ if (depth < 8 && moveCount > 2)
+ r++;
+
+ // Unless giving check, this capture is likely bad
+ if ( !givesCheck
+ && ss->staticEval + PieceValue[EG][pos.captured_piece()] + 213 * depth <= alpha)
+ r++;
}
- Depth d = std::max(newDepth - r, ONE_PLY);
+ Depth d = std::clamp(newDepth - r, 1, newDepth);
- value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true, false);
+ value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
- doFullDepthSearch = (value > alpha && d != newDepth);
+ doFullDepthSearch = value > alpha && d != newDepth;
+
+ didLMR = true;
}
else
+ {
doFullDepthSearch = !PvNode || moveCount > 1;
- // Step 16. Full depth search when LMR is skipped or fails high
+ didLMR = false;
+ }
+
+ // Step 17. 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)
- : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha)
- : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode, false);
+ {
+ value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
+
+ if (didLMR && !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
(ss+1)->pv = pv;
(ss+1)->pv[0] = MOVE_NONE;
- value = newDepth < ONE_PLY ?
- 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);
+ value = -search<PV>(pos, ss+1, -beta, -alpha, 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.
RootMove& rm = *std::find(thisThread->rootMoves.begin(),
thisThread->rootMoves.end(), move);
- // PV move or new best move ?
+ // PV move or new best move?
if (moveCount == 1 || value > alpha)
{
rm.score = value;
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: When
+ // 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<MainThread*>(thisThread)->bestMoveChanges;
+ if (moveCount > 1)
+ ++thisThread->bestMoveChanges;
}
else
// All other moves but the PV are set to the lowest value: this
else
{
assert(value >= beta); // Fail high
+ ss->statScore = 0;
break;
}
}
}
- if (!captureOrPromotion && move != bestMove && quietCount < 64)
- quietsSearched[quietCount++] = move;
+ if (move != bestMove)
+ {
+ if (captureOrPromotion && captureCount < 32)
+ capturesSearched[captureCount++] = move;
+
+ else if (!captureOrPromotion && quietCount < 64)
+ quietsSearched[quietCount++] = move;
+ }
}
// The following condition would detect a stop only after move loop has been
// 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());
+ assert(moveCount || !ss->inCheck || excludedMove || !MoveList<LEGAL>(pos).size());
if (!moveCount)
bestValue = excludedMove ? alpha
- : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
+ : ss->inCheck ? mated_in(ss->ply) : VALUE_DRAW;
+
else if (bestMove)
- {
- // Quiet best move: update move sorting heuristics
- if (!pos.capture_or_promotion(bestMove))
- update_stats(pos, ss, bestMove, quietsSearched, quietCount, stat_bonus(depth));
+ update_all_stats(pos, ss, bestMove, bestValue, beta, prevSq,
+ quietsSearched, quietCount, capturesSearched, captureCount, depth);
- // Extra penalty for a quiet TT move in previous ply when it gets refuted
- if ((ss-1)->moveCount == 1 && !pos.captured_piece())
- update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
- }
// Bonus for prior countermove that caused the fail low
- else if ( depth >= 3 * ONE_PLY
- && !pos.captured_piece()
- && is_ok((ss-1)->currentMove))
+ else if ( (depth >= 3 || PvNode)
+ && !priorCapture)
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));
- if (!excludedMove)
- tte->save(posKey, value_to_tt(bestValue, ss->ply),
+ if (PvNode)
+ bestValue = std::min(bestValue, maxValue);
+
+ if (!excludedMove && !(rootNode && thisThread->pvIdx))
+ tte->save(posKey, value_to_tt(bestValue, ss->ply), ttPv,
bestValue >= beta ? BOUND_LOWER :
PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
- depth, bestMove, ss->staticEval, TT.generation());
+ depth, bestMove, ss->staticEval);
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
}
- // 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.
-
- template <NodeType NT, bool InCheck>
+ // 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>
Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
- const bool PvNode = NT == PV;
+ constexpr bool PvNode = NT == PV;
- assert(InCheck == !!pos.checkers());
assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
assert(PvNode || (alpha == beta - 1));
- assert(depth <= DEPTH_ZERO);
- assert(depth / ONE_PLY * ONE_PLY == depth);
+ assert(depth <= 0);
Move pv[MAX_PLY+1];
StateInfo st;
TTEntry* tte;
Key posKey;
Move ttMove, move, bestMove;
- Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
- bool ttHit, givesCheck, evasionPrunable;
Depth ttDepth;
+ Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
+ bool ttHit, pvHit, givesCheck, captureOrPromotion;
int moveCount;
if (PvNode)
ss->pv[0] = MOVE_NONE;
}
- ss->currentMove = bestMove = MOVE_NONE;
- ss->ply = (ss-1)->ply + 1;
+ Thread* thisThread = pos.this_thread();
+ (ss+1)->ply = ss->ply + 1;
+ bestMove = MOVE_NONE;
+ ss->inCheck = pos.checkers();
moveCount = 0;
- // Check for an instant draw or if the maximum ply has been reached
- if (pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
- return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos)
- : DrawValue[pos.side_to_move()];
+ // Check for an immediate draw or maximum ply reached
+ if ( pos.is_draw(ss->ply)
+ || ss->ply >= MAX_PLY)
+ return (ss->ply >= MAX_PLY && !ss->inCheck) ? evaluate(pos) : VALUE_DRAW;
assert(0 <= ss->ply && ss->ply < MAX_PLY);
// Decide whether or not to include checks: this fixes also the type of
// TT entry depth that we are going to use. Note that in qsearch we use
// only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
- ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
+ ttDepth = ss->inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
: DEPTH_QS_NO_CHECKS;
-
// Transposition table lookup
posKey = pos.key();
tte = TT.probe(posKey, ttHit);
+ ttValue = ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE;
ttMove = ttHit ? tte->move() : MOVE_NONE;
- ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
+ pvHit = ttHit && tte->is_pv();
if ( !PvNode
&& ttHit
&& tte->depth() >= ttDepth
&& ttValue != VALUE_NONE // Only in case of TT access race
- && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
- : (tte->bound() & BOUND_UPPER)))
+ && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
+ : (tte->bound() & BOUND_UPPER)))
return ttValue;
// Evaluate the position statically
- if (InCheck)
+ if (ss->inCheck)
{
ss->staticEval = VALUE_NONE;
bestValue = futilityBase = -VALUE_INFINITE;
{
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);
// Can ttValue be used as a better position evaluation?
- if ( ttValue != VALUE_NONE
+ if ( ttValue != VALUE_NONE
&& (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER)))
bestValue = ttValue;
}
else
ss->staticEval = bestValue =
(ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
- : -(ss-1)->staticEval + 2 * Eval::Tempo;
+ : -(ss-1)->staticEval + 2 * Tempo;
// Stand pat. Return immediately if static value is at least beta
if (bestValue >= beta)
{
if (!ttHit)
- tte->save(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
- DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
+ tte->save(posKey, value_to_tt(bestValue, ss->ply), false, BOUND_LOWER,
+ DEPTH_NONE, MOVE_NONE, ss->staticEval);
return bestValue;
}
if (PvNode && bestValue > alpha)
alpha = bestValue;
- futilityBase = bestValue + 128;
+ futilityBase = bestValue + 145;
}
+ const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
+ nullptr , (ss-4)->continuationHistory,
+ nullptr , (ss-6)->continuationHistory };
+
// Initialize a MovePicker object for the current position, and prepare
// to search the moves. Because the depth is <= 0 here, only captures,
- // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
- // be generated.
- const PieceToHistory* contHist[4] = {};
- MovePicker mp(pos, ttMove, depth, &pos.this_thread()->mainHistory, contHist, to_sq((ss-1)->currentMove));
+ // queen and checking knight promotions, and other checks(only if depth >= DEPTH_QS_CHECKS)
+ // will be generated.
+ MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
+ &thisThread->captureHistory,
+ contHist,
+ to_sq((ss-1)->currentMove));
// Loop through the moves until no moves remain or a beta cutoff occurs
while ((move = mp.next_move()) != MOVE_NONE)
{
assert(is_ok(move));
- givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates()
- ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
- : pos.gives_check(move);
+ givesCheck = pos.gives_check(move);
+ captureOrPromotion = pos.capture_or_promotion(move);
moveCount++;
// Futility pruning
- if ( !InCheck
+ if ( !ss->inCheck
&& !givesCheck
&& futilityBase > -VALUE_KNOWN_WIN
&& !pos.advanced_pawn_push(move))
}
}
- // 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_ge(move))
+ // Do not search moves with negative SEE values
+ if ( !ss->inCheck && !pos.see_ge(move))
continue;
// Speculative prefetch as early as possible
}
ss->currentMove = move;
+ ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck]
+ [captureOrPromotion]
+ [pos.moved_piece(move)]
+ [to_sq(move)];
// Make and search the move
pos.do_move(move, st, givesCheck);
- value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
- : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
+ value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth - 1);
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
if (value > alpha)
{
+ bestMove = move;
+
if (PvNode) // Update pv even in fail-high case
update_pv(ss->pv, move, (ss+1)->pv);
if (PvNode && value < beta) // Update alpha here!
- {
alpha = value;
- bestMove = move;
- }
- else // Fail high
- {
- tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
- ttDepth, move, ss->staticEval, TT.generation());
-
- return value;
- }
+ else
+ break; // Fail high
}
}
}
- // All legal moves have been searched. A special case: If we're in check
+ // All legal moves have been searched. A special case: if we're in check
// and no legal moves were found, it is checkmate.
- if (InCheck && bestValue == -VALUE_INFINITE)
+ if (ss->inCheck && bestValue == -VALUE_INFINITE)
return mated_in(ss->ply); // Plies to mate from the root
- tte->save(posKey, value_to_tt(bestValue, ss->ply),
- PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
- ttDepth, bestMove, ss->staticEval, TT.generation());
+ tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit,
+ bestValue >= beta ? BOUND_LOWER :
+ PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
+ ttDepth, bestMove, ss->staticEval);
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
}
- // value_to_tt() adjusts a mate score from "plies to mate from the root" to
- // "plies to mate from the current position". Non-mate scores are unchanged.
+ // value_to_tt() adjusts a mate or TB score from "plies to mate from the root" to
+ // "plies to mate from the current position". Standard scores are unchanged.
// The function is called before storing a value in the transposition table.
Value value_to_tt(Value v, int ply) {
assert(v != VALUE_NONE);
- return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
- : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
+ return v >= VALUE_TB_WIN_IN_MAX_PLY ? v + ply
+ : v <= VALUE_TB_LOSS_IN_MAX_PLY ? v - ply : v;
}
- // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
- // from the transposition table (which refers to the plies to mate/be mated
- // from current position) to "plies to mate/be mated from the root".
+ // value_from_tt() is the inverse of value_to_tt(): it adjusts a mate or TB score
+ // from the transposition table (which refers to the plies to mate/be mated from
+ // current position) to "plies to mate/be mated (TB win/loss) from the root". However,
+ // for mate scores, to avoid potentially false mate scores related to the 50 moves rule
+ // and the graph history interaction, we return an optimal TB score instead.
+
+ Value value_from_tt(Value v, int ply, int r50c) {
+
+ if (v == VALUE_NONE)
+ return VALUE_NONE;
+
+ if (v >= VALUE_TB_WIN_IN_MAX_PLY) // TB win or better
+ {
+ if (v >= VALUE_MATE_IN_MAX_PLY && VALUE_MATE - v > 99 - r50c)
+ return VALUE_MATE_IN_MAX_PLY - 1; // do not return a potentially false mate score
+
+ return v - ply;
+ }
+
+ if (v <= VALUE_TB_LOSS_IN_MAX_PLY) // TB loss or worse
+ {
+ if (v <= VALUE_MATED_IN_MAX_PLY && VALUE_MATE + v > 99 - r50c)
+ return VALUE_MATED_IN_MAX_PLY + 1; // do not return a potentially false mate score
- Value value_from_tt(Value v, int ply) {
+ return v + ply;
+ }
- return v == VALUE_NONE ? VALUE_NONE
- : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
- : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
+ return v;
}
}
+ // update_all_stats() updates stats at the end of search() when a bestMove is found
+
+ void update_all_stats(const Position& pos, Stack* ss, Move bestMove, Value bestValue, Value beta, Square prevSq,
+ Move* quietsSearched, int quietCount, Move* capturesSearched, int captureCount, Depth depth) {
+
+ int bonus1, bonus2;
+ Color us = pos.side_to_move();
+ Thread* thisThread = pos.this_thread();
+ CapturePieceToHistory& captureHistory = thisThread->captureHistory;
+ Piece moved_piece = pos.moved_piece(bestMove);
+ PieceType captured = type_of(pos.piece_on(to_sq(bestMove)));
+
+ bonus1 = stat_bonus(depth + 1);
+ bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus
+ : stat_bonus(depth); // smaller bonus
+
+ if (!pos.capture_or_promotion(bestMove))
+ {
+ update_quiet_stats(pos, ss, bestMove, bonus2, depth);
+
+ // Decrease all the non-best quiet moves
+ for (int i = 0; i < quietCount; ++i)
+ {
+ thisThread->mainHistory[us][from_to(quietsSearched[i])] << -bonus2;
+ update_continuation_histories(ss, pos.moved_piece(quietsSearched[i]), to_sq(quietsSearched[i]), -bonus2);
+ }
+ }
+ else
+ captureHistory[moved_piece][to_sq(bestMove)][captured] << bonus1;
+
+ // 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, -bonus1);
+
+ // Decrease all the non-best capture moves
+ for (int i = 0; i < captureCount; ++i)
+ {
+ moved_piece = pos.moved_piece(capturesSearched[i]);
+ captured = type_of(pos.piece_on(to_sq(capturesSearched[i])));
+ captureHistory[moved_piece][to_sq(capturesSearched[i])][captured] << -bonus1;
+ }
+ }
+
+
// update_continuation_histories() updates histories of the move pairs formed
- // by moves at ply -1, -2, and -4 with current move.
+ // by moves at ply -1, -2, -4, and -6 with current move.
void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus) {
- for (int i : {1, 2, 4})
+ for (int i : {1, 2, 4, 6})
+ {
+ if (ss->inCheck && i > 2)
+ break;
if (is_ok((ss-i)->currentMove))
- (ss-i)->contHistory->update(pc, to, bonus);
+ (*(ss-i)->continuationHistory)[pc][to] << bonus;
+ }
}
- // update_stats() updates move sorting heuristics when a new quiet best move is found
+ // update_quiet_stats() updates move sorting heuristics
- void update_stats(const Position& pos, Stack* ss, Move move,
- Move* quiets, int quietsCnt, int bonus) {
+ void update_quiet_stats(const Position& pos, Stack* ss, Move move, int bonus, int depth) {
if (ss->killers[0] != move)
{
ss->killers[0] = move;
}
- Color c = pos.side_to_move();
+ Color us = pos.side_to_move();
Thread* thisThread = pos.this_thread();
- thisThread->mainHistory.update(c, move, bonus);
+ 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);
thisThread->counterMoves[pos.piece_on(prevSq)][prevSq] = move;
}
- // Decrease all the other played quiet moves
- for (int i = 0; i < quietsCnt; ++i)
- {
- thisThread->mainHistory.update(c, quiets[i], -bonus);
- update_continuation_histories(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
- }
+ if (depth > 11 && ss->ply < MAX_LPH)
+ thisThread->lowPlyHistory[ss->ply][from_to(move)] << stat_bonus(depth - 7);
}
-
// When playing with strength handicap, choose best move among a set of RootMoves
// using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
int push = ( weakness * int(topScore - rootMoves[i].score)
+ delta * (rng.rand<unsigned>() % weakness)) / 128;
- if (rootMoves[i].score + push > maxScore)
+ if (rootMoves[i].score + push >= maxScore)
{
maxScore = rootMoves[i].score + push;
best = rootMoves[i].pv[0];
} // namespace
- // check_time() is used to print debug info and, more importantly, to detect
- // when we are out of available time and thus stop the search.
- void MainThread::check_time() {
+/// MainThread::check_time() is used to print debug info and, more importantly,
+/// to detect when we are out of available time and thus stop the search.
- if (--callsCnt > 0)
- return;
+void MainThread::check_time() {
- // At low node count increase the checking rate to about 0.1% of nodes
- // otherwise use a default value.
- callsCnt = Limits.nodes ? std::min(4096, int(Limits.nodes / 1024)) : 4096;
+ if (--callsCnt > 0)
+ return;
- static TimePoint lastInfoTime = now();
+ // When using nodes, ensure checking rate is not lower than 0.1% of nodes
+ callsCnt = Limits.nodes ? std::min(1024, int(Limits.nodes / 1024)) : 1024;
- int elapsed = Time.elapsed();
- TimePoint tick = Limits.startTime + elapsed;
+ static TimePoint lastInfoTime = now();
- if (tick - lastInfoTime >= 1000)
- {
- lastInfoTime = tick;
- dbg_print();
- }
+ TimePoint elapsed = Time.elapsed();
+ TimePoint tick = Limits.startTime + elapsed;
- // An engine may not stop pondering until told so by the GUI
- if (Threads.ponder)
- return;
-
- if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10)
- || (Limits.movetime && elapsed >= Limits.movetime)
- || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
- Threads.stop = true;
+ if (tick - lastInfoTime >= 1000)
+ {
+ lastInfoTime = tick;
+ dbg_print();
}
+ // We should not stop pondering until told so by the GUI
+ if (ponder)
+ return;
+
+ if ( (Limits.use_time_management() && (elapsed > Time.maximum() - 10 || stopOnPonderhit))
+ || (Limits.movetime && elapsed >= Limits.movetime)
+ || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
+ Threads.stop = true;
+}
+
/// UCI::pv() formats PV information according to the UCI protocol. UCI requires
/// that all (if any) unsearched PV lines are sent using a previous search score.
string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
std::stringstream ss;
- int elapsed = Time.elapsed() + 1;
+ TimePoint elapsed = Time.elapsed() + 1;
const RootMoves& rootMoves = pos.this_thread()->rootMoves;
- size_t PVIdx = pos.this_thread()->PVIdx;
+ size_t pvIdx = pos.this_thread()->pvIdx;
size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
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 && rootMoves[i].score != -VALUE_INFINITE);
+ bool updated = rootMoves[i].score != -VALUE_INFINITE;
- if (depth == ONE_PLY && !updated)
+ if (depth == 1 && !updated)
continue;
- Depth d = updated ? depth : depth - ONE_PLY;
+ Depth d = updated ? depth : depth - 1;
Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
- bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
- v = tb ? TB::Score : v;
+ bool tb = TB::RootInTB && abs(v) < VALUE_MATE_IN_MAX_PLY;
+ v = tb ? rootMoves[i].tbScore : v;
if (ss.rdbuf()->in_avail()) // Not at first line
ss << "\n";
ss << "info"
- << " depth " << d / ONE_PLY
+ << " depth " << d
<< " seldepth " << rootMoves[i].selDepth
<< " multipv " << i + 1
<< " score " << UCI::value(v);
- if (!tb && i == PVIdx)
+ if (Options["UCI_ShowWDL"])
+ ss << UCI::wdl(v, pos.game_ply());
+
+ if (!tb && i == pvIdx)
ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
ss << " nodes " << nodesSearched
assert(pv.size() == 1);
- if (!pv[0])
+ if (pv[0] == MOVE_NONE)
return false;
pos.do_move(pv[0], st);
return pv.size() > 1;
}
-void Tablebases::filter_root_moves(Position& pos, Search::RootMoves& rootMoves) {
+void Tablebases::rank_root_moves(Position& pos, Search::RootMoves& rootMoves) {
RootInTB = false;
- UseRule50 = Options["Syzygy50MoveRule"];
- ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
- Cardinality = Options["SyzygyProbeLimit"];
+ UseRule50 = bool(Options["Syzygy50MoveRule"]);
+ ProbeDepth = int(Options["SyzygyProbeDepth"]);
+ Cardinality = int(Options["SyzygyProbeLimit"]);
+ bool dtz_available = true;
- // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
+ // Tables with fewer pieces than SyzygyProbeLimit are searched with
+ // ProbeDepth == DEPTH_ZERO
if (Cardinality > MaxCardinality)
{
Cardinality = MaxCardinality;
- ProbeDepth = DEPTH_ZERO;
+ ProbeDepth = 0;
}
- if (Cardinality < popcount(pos.pieces()) || pos.can_castle(ANY_CASTLING))
- return;
+ if (Cardinality >= popcount(pos.pieces()) && !pos.can_castle(ANY_CASTLING))
+ {
+ // Rank moves using DTZ tables
+ RootInTB = root_probe(pos, rootMoves);
- // If the current root position is in the tablebases, then RootMoves
- // contains only moves that preserve the draw or the win.
- RootInTB = root_probe(pos, rootMoves, TB::Score);
+ if (!RootInTB)
+ {
+ // DTZ tables are missing; try to rank moves using WDL tables
+ dtz_available = false;
+ RootInTB = root_probe_wdl(pos, rootMoves);
+ }
+ }
if (RootInTB)
- Cardinality = 0; // Do not probe tablebases during the search
-
- else // If DTZ tables are missing, use WDL tables as a fallback
{
- // Filter out moves that do not preserve the draw or the win.
- RootInTB = root_probe_wdl(pos, rootMoves, TB::Score);
+ // Sort moves according to TB rank
+ std::sort(rootMoves.begin(), rootMoves.end(),
+ [](const RootMove &a, const RootMove &b) { return a.tbRank > b.tbRank; } );
- // Only probe during search if winning
- if (RootInTB && TB::Score <= VALUE_DRAW)
+ // Probe during search only if DTZ is not available and we are winning
+ if (dtz_available || rootMoves[0].tbScore <= VALUE_DRAW)
Cardinality = 0;
}
-
- 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;
+ else
+ {
+ // Clean up if root_probe() and root_probe_wdl() have failed
+ for (auto& m : rootMoves)
+ m.tbRank = 0;
+ }
}