/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
#include <algorithm>
#include <cassert>
#include <cmath>
-#include <cstring>
+#include <cstring> // For std::memset
#include <iostream>
#include <sstream>
-#include "book.h"
#include "evaluate.h"
+#include "misc.h"
#include "movegen.h"
#include "movepick.h"
-#include "notation.h"
#include "search.h"
#include "timeman.h"
#include "thread.h"
#include "tt.h"
-#include "ucioption.h"
+#include "uci.h"
+#include "syzygy/tbprobe.h"
namespace Search {
- volatile SignalsType Signals;
+ SignalsType Signals;
LimitsType Limits;
- std::vector<RootMove> RootMoves;
- Position RootPos;
- Color RootColor;
- Time::point SearchTime;
- StateStackPtr SetupStates;
}
+namespace Tablebases {
+
+ int Cardinality;
+ uint64_t Hits;
+ bool RootInTB;
+ bool UseRule50;
+ Depth ProbeDepth;
+ Value Score;
+}
+
+namespace TB = Tablebases;
+
using std::string;
using Eval::evaluate;
using namespace Search;
namespace {
- // Set to true to force running with one thread. Used for debugging
- const bool FakeSplit = false;
+ // Different node types, used as a template parameter
+ enum NodeType { NonPV, PV };
- // This is the minimum interval in msec between two check_time() calls
- const int TimerResolution = 5;
+ // Razoring and futility margin based on depth
+ const int razor_margin[4] = { 483, 570, 603, 554 };
+ Value futility_margin(Depth d) { return Value(150 * d / ONE_PLY); }
- // Different node types, used as template parameter
- enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
+ // Futility and reductions lookup tables, initialized at startup
+ int FutilityMoveCounts[2][16]; // [improving][depth]
+ int Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
- // Dynamic razoring margin based on depth
- inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
+ 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;
+ }
- // Futility lookup tables (initialized at startup) and their access functions
- Value FutilityMargins[16][64]; // [depth][moveNumber]
- int FutilityMoveCounts[2][32]; // [improving][depth]
+ // Skill structure is used to implement strength limit
+ struct Skill {
+ 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); }
+ Move pick_best(size_t multiPV);
- inline Value futility_margin(Depth d, int mn) {
+ int level;
+ Move best = MOVE_NONE;
+ };
- return d < 7 * ONE_PLY ? FutilityMargins[std::max(int(d), 1)][std::min(mn, 63)]
- : 2 * VALUE_INFINITE;
- }
+ // 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 {
- // Reduction lookup tables (initialized at startup) and their access function
- int8_t Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
+ void clear() {
+ stableCnt = 0;
+ expectedPosKey = 0;
+ pv[0] = pv[1] = pv[2] = MOVE_NONE;
+ }
- template <bool PvNode> inline Depth reduction(bool i, Depth d, int mn) {
+ Move get(Key key) const {
+ return expectedPosKey == key ? pv[2] : MOVE_NONE;
+ }
- return (Depth) Reductions[PvNode][i][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
- }
+ 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.gives_check(newPv[0]));
+ pos.do_move(newPv[1], st[1], pos.gives_check(newPv[1]));
+ expectedPosKey = pos.key();
+ pos.undo_move(newPv[1]);
+ pos.undo_move(newPv[0]);
+ }
+ }
- size_t PVSize, PVIdx;
- TimeManager TimeMgr;
- double BestMoveChanges;
+ int stableCnt;
+ Key expectedPosKey;
+ Move pv[3];
+ };
+
+ // Set of rows with half bits set to 1 and half to 0. It is used to allocate
+ // the search depths across the threads.
+ typedef std::vector<int> Row;
+
+ const Row HalfDensity[] = {
+ {0, 1},
+ {1, 0},
+ {0, 0, 1, 1},
+ {0, 1, 1, 0},
+ {1, 1, 0, 0},
+ {1, 0, 0, 1},
+ {0, 0, 0, 1, 1, 1},
+ {0, 0, 1, 1, 1, 0},
+ {0, 1, 1, 1, 0, 0},
+ {1, 1, 1, 0, 0, 0},
+ {1, 1, 0, 0, 0, 1},
+ {1, 0, 0, 0, 1, 1},
+ {0, 0, 0, 0, 1, 1, 1, 1},
+ {0, 0, 0, 1, 1, 1, 1, 0},
+ {0, 0, 1, 1, 1, 1, 0 ,0},
+ {0, 1, 1, 1, 1, 0, 0 ,0},
+ {1, 1, 1, 1, 0, 0, 0 ,0},
+ {1, 1, 1, 0, 0, 0, 0 ,1},
+ {1, 1, 0, 0, 0, 0, 1 ,1},
+ {1, 0, 0, 0, 0, 1, 1 ,1},
+ };
+
+ const size_t HalfDensitySize = std::extent<decltype(HalfDensity)>::value;
+
+ EasyMoveManager EasyMove;
Value DrawValue[COLOR_NB];
- HistoryStats History;
- GainsStats Gains;
- CountermovesStats Countermoves;
+ CounterMoveHistoryStats CounterMoveHistory;
template <NodeType NT>
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);
- void id_loop(Position& pos);
Value value_to_tt(Value v, int ply);
Value value_from_tt(Value v, int ply);
- bool allows(const Position& pos, Move first, Move second);
- bool refutes(const Position& pos, Move first, Move second);
- string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
-
- struct Skill {
- Skill(int l) : level(l), best(MOVE_NONE) {}
- ~Skill() {
- if (enabled()) // Swap best PV line with the sub-optimal one
- std::swap(RootMoves[0], *std::find(RootMoves.begin(),
- RootMoves.end(), best ? best : pick_move()));
- }
-
- bool enabled() const { return level < 20; }
- bool time_to_pick(int depth) const { return depth == 1 + level; }
- Move pick_move();
-
- int level;
- Move best;
- };
+ void update_pv(Move* pv, Move move, Move* childPv);
+ void update_cm_stats(Stack* ss, Piece pc, Square s, Value bonus);
+ void update_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, Value bonus);
+ void check_time();
} // namespace
void Search::init() {
- int d; // depth (ONE_PLY == 2)
- int hd; // half depth (ONE_PLY == 1)
- int mc; // moveCount
+ 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) / 2;
+ if (r < 0.80)
+ continue;
+
+ Reductions[NonPV][imp][d][mc] = int(std::round(r));
+ Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - 1, 0);
- // Init reductions array
- for (hd = 1; hd < 64; ++hd) for (mc = 1; mc < 64; ++mc)
+ // Increase reduction for non-PV nodes when eval is not improving
+ if (!imp && Reductions[NonPV][imp][d][mc] >= 2)
+ Reductions[NonPV][imp][d][mc]++;
+ }
+
+ for (int d = 0; d < 16; ++d)
{
- double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
- double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
- Reductions[1][1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
- Reductions[0][1][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
+ FutilityMoveCounts[0][d] = int(2.4 + 0.773 * pow(d + 0.00, 1.8));
+ FutilityMoveCounts[1][d] = int(2.9 + 1.045 * pow(d + 0.49, 1.8));
+ }
+}
- Reductions[1][0][hd][mc] = Reductions[1][1][hd][mc];
- Reductions[0][0][hd][mc] = Reductions[0][1][hd][mc];
- if (Reductions[0][0][hd][mc] > 2 * ONE_PLY)
- Reductions[0][0][hd][mc] += ONE_PLY;
+/// Search::clear() resets search state to zero, to obtain reproducible results
- else if (Reductions[0][0][hd][mc] > 1 * ONE_PLY)
- Reductions[0][0][hd][mc] += ONE_PLY / 2;
- }
+void Search::clear() {
- // Init futility margins array
- for (d = 1; d < 16; ++d) for (mc = 0; mc < 64; ++mc)
- FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
+ TT.clear();
+ CounterMoveHistory.clear();
- // Init futility move count array
- for (d = 0; d < 32; ++d)
+ for (Thread* th : Threads)
{
- FutilityMoveCounts[0][d] = int(3 + 0.3 * pow(double(d ), 1.8)) * 3/4 + (2 < d && d < 5);
- FutilityMoveCounts[1][d] = int(3 + 0.3 * pow(double(d + 0.98), 1.8));
+ th->history.clear();
+ th->counterMoves.clear();
+ th->fromTo.clear();
}
+
+ Threads.main()->previousScore = VALUE_INFINITE;
}
/// 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 returned.
-
-static size_t perft(Position& pos, Depth depth) {
+/// 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) {
StateInfo st;
- size_t cnt = 0;
- CheckInfo ci(pos);
- const bool leaf = depth == 2 * ONE_PLY;
+ uint64_t cnt, nodes = 0;
+ const bool leaf = (depth == 2 * ONE_PLY);
- for (MoveList<LEGAL> it(pos); *it; ++it)
+ for (const auto& m : MoveList<LEGAL>(pos))
{
- pos.do_move(*it, st, ci, pos.gives_check(*it, ci));
- cnt += leaf ? MoveList<LEGAL>(pos).size() : ::perft(pos, depth - ONE_PLY);
- pos.undo_move(*it);
+ if (Root && depth <= ONE_PLY)
+ cnt = 1, nodes++;
+ else
+ {
+ pos.do_move(m, st, pos.gives_check(m));
+ 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;
}
- return cnt;
+ return nodes;
}
-size_t Search::perft(Position& pos, Depth depth) {
- return depth > ONE_PLY ? ::perft(pos, depth) : MoveList<LEGAL>(pos).size();
-}
+template uint64_t Search::perft<true>(Position&, Depth);
+
-/// Search::think() is the external interface to Stockfish's search, and is
-/// called by the main thread when the program receives the UCI 'go' command. It
-/// searches from RootPos and at the end prints the "bestmove" to output.
+/// 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 Search::think() {
+void MainThread::search() {
- static PolyglotBook book; // Defined static to initialize the PRNG only once
+ Color us = rootPos.side_to_move();
+ Time.init(Limits, us, rootPos.game_ply());
- RootColor = RootPos.side_to_move();
- TimeMgr.init(Limits, RootPos.game_ply(), RootColor);
+ int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns
+ DrawValue[ us] = VALUE_DRAW - Value(contempt);
+ DrawValue[~us] = VALUE_DRAW + Value(contempt);
- if (RootMoves.empty())
+ if (rootMoves.empty())
{
- RootMoves.push_back(MOVE_NONE);
+ rootMoves.push_back(RootMove(MOVE_NONE));
sync_cout << "info depth 0 score "
- << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
+ << UCI::value(rootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
<< sync_endl;
-
- goto finalize;
}
-
- if (Options["OwnBook"] && !Limits.infinite && !Limits.mate)
+ else
{
- Move bookMove = book.probe(RootPos, Options["Book File"], Options["Best Book Move"]);
+ for (Thread* th : Threads)
+ if (th != this)
+ th->start_searching();
- if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
- {
- std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
- goto finalize;
- }
+ Thread::search(); // Let's start searching!
}
- if (Options["Contempt Factor"] && !Options["UCI_AnalyseMode"])
+ // 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
+ // Signals.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 Signals.stop).
+ if (!Signals.stop && (Limits.ponder || Limits.infinite))
{
- int cf = Options["Contempt Factor"] * PawnValueMg / 100; // From centipawns
- cf = cf * Material::game_phase(RootPos) / PHASE_MIDGAME; // Scale down with phase
- DrawValue[ RootColor] = VALUE_DRAW - Value(cf);
- DrawValue[~RootColor] = VALUE_DRAW + Value(cf);
+ Signals.stopOnPonderhit = true;
+ wait(Signals.stop);
}
- else
- DrawValue[WHITE] = DrawValue[BLACK] = VALUE_DRAW;
- if (Options["Write Search Log"])
+ // Stop the threads if not already stopped
+ Signals.stop = true;
+
+ // Wait until all threads have finished
+ for (Thread* th : Threads)
+ if (th != this)
+ th->wait_for_search_finished();
+
+ // 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)
{
- Log log(Options["Search Log Filename"]);
- log << "\nSearching: " << RootPos.fen()
- << "\ninfinite: " << Limits.infinite
- << " ponder: " << Limits.ponder
- << " time: " << Limits.time[RootColor]
- << " increment: " << Limits.inc[RootColor]
- << " moves to go: " << Limits.movestogo
- << std::endl;
+ for (Thread* th : Threads)
+ if ( th->completedDepth > bestThread->completedDepth
+ && th->rootMoves[0].score > bestThread->rootMoves[0].score)
+ bestThread = th;
}
- // Reset the threads, still sleeping: will be wake up at split time
- for (size_t i = 0; i < Threads.size(); ++i)
- Threads[i]->maxPly = 0;
+ previousScore = bestThread->rootMoves[0].score;
- Threads.sleepWhileIdle = Options["Idle Threads Sleep"];
+ // Send new PV when needed
+ if (bestThread != this)
+ sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl;
- // Set best timer interval to avoid lagging under time pressure. Timer is
- // used to check for remaining available thinking time.
- Threads.timer->msec =
- Limits.use_time_management() ? std::min(100, std::max(TimeMgr.available_time() / 16, TimerResolution)) :
- Limits.nodes ? 2 * TimerResolution
- : 100;
+ sync_cout << "bestmove " << UCI::move(bestThread->rootMoves[0].pv[0], rootPos.is_chess960());
- Threads.timer->notify_one(); // Wake up the recurring timer
+ if (bestThread->rootMoves[0].pv.size() > 1 || bestThread->rootMoves[0].extract_ponder_from_tt(rootPos))
+ std::cout << " ponder " << UCI::move(bestThread->rootMoves[0].pv[1], rootPos.is_chess960());
- id_loop(RootPos); // Let's start searching !
+ std::cout << sync_endl;
+}
- Threads.timer->msec = 0; // Stop the timer
- Threads.sleepWhileIdle = true; // Send idle threads to sleep
- if (Options["Write Search Log"])
- {
- Time::point elapsed = Time::now() - SearchTime + 1;
+// Thread::search() is the main iterative deepening loop. It calls search()
+// repeatedly with increasing depth until the allocated thinking time has been
+// consumed, the user stops the search, or the maximum search depth is reached.
- Log log(Options["Search Log Filename"]);
- log << "Nodes: " << RootPos.nodes_searched()
- << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
- << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
+void Thread::search() {
- StateInfo st;
- RootPos.do_move(RootMoves[0].pv[0], st);
- log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
- RootPos.undo_move(RootMoves[0].pv[0]);
- }
+ Stack stack[MAX_PLY+7], *ss = stack+5; // To allow referencing (ss-5) and (ss+2)
+ Value bestValue, alpha, beta, delta;
+ Move easyMove = MOVE_NONE;
+ MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
-finalize:
+ std::memset(ss-5, 0, 8 * sizeof(Stack));
- // When search is stopped this info is not printed
- sync_cout << "info nodes " << RootPos.nodes_searched()
- << " time " << Time::now() - SearchTime + 1 << sync_endl;
+ bestValue = delta = alpha = -VALUE_INFINITE;
+ beta = VALUE_INFINITE;
+ completedDepth = DEPTH_ZERO;
- // When we reach max depth we arrive here even without Signals.stop is raised,
- // but if we are pondering or in infinite search, according to UCI protocol,
- // we shouldn't print the best move before the GUI sends a "stop" or "ponderhit"
- // command. We simply wait here until GUI sends one of those commands (that
- // raise Signals.stop).
- if (!Signals.stop && (Limits.ponder || Limits.infinite))
+ if (mainThread)
{
- Signals.stopOnPonderhit = true;
- RootPos.this_thread()->wait_for(Signals.stop);
+ easyMove = EasyMove.get(rootPos.key());
+ EasyMove.clear();
+ mainThread->easyMovePlayed = mainThread->failedLow = false;
+ mainThread->bestMoveChanges = 0;
+ TT.new_search();
}
- // Best move could be MOVE_NONE when searching on a stalemate position
- sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
- << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
- << sync_endl;
-}
+ size_t multiPV = Options["MultiPV"];
+ Skill skill(Options["Skill Level"]);
+ // When playing with strength handicap enable MultiPV search that we will
+ // use behind the scenes to retrieve a set of possible moves.
+ if (skill.enabled())
+ multiPV = std::max(multiPV, (size_t)4);
-namespace {
+ multiPV = std::min(multiPV, rootMoves.size());
- // id_loop() is the main iterative deepening loop. It calls search() repeatedly
- // with increasing depth until the allocated thinking time has been consumed,
- // user stops the search, or the maximum search depth is reached.
+ // Iterative deepening loop until requested to stop or the target depth is reached
+ while ( (rootDepth += ONE_PLY) < DEPTH_MAX
+ && !Signals.stop
+ && (!Limits.depth || Threads.main()->rootDepth / ONE_PLY <= Limits.depth))
+ {
+ // Set up the new depths for the helper threads skipping on average every
+ // 2nd ply (using a half-density matrix).
+ if (!mainThread)
+ {
+ const Row& row = HalfDensity[(idx - 1) % HalfDensitySize];
+ if (row[(rootDepth / ONE_PLY + rootPos.game_ply()) % row.size()])
+ continue;
+ }
- void id_loop(Position& pos) {
+ // Age out PV variability metric
+ if (mainThread)
+ mainThread->bestMoveChanges *= 0.505, mainThread->failedLow = false;
- Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
- int depth;
- Value bestValue, alpha, beta, delta;
+ // 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;
- std::memset(ss-2, 0, 5 * sizeof(Stack));
- (ss-1)->currentMove = MOVE_NULL; // Hack to skip update gains
+ // MultiPV loop. We perform a full root search for each PV line
+ for (PVIdx = 0; PVIdx < multiPV && !Signals.stop; ++PVIdx)
+ {
+ // Reset aspiration window starting size
+ if (rootDepth >= 5 * ONE_PLY)
+ {
+ delta = Value(18);
+ alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE);
+ beta = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE);
+ }
- depth = 0;
- BestMoveChanges = 0;
- bestValue = delta = alpha = -VALUE_INFINITE;
- beta = VALUE_INFINITE;
+ // 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 anymore.
+ while (true)
+ {
+ bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, 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
+ // first and eventually the new best one are set to -VALUE_INFINITE
+ // 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());
+
+ // If search has been stopped, break immediately. Sorting and
+ // writing PV back to TT is safe because RootMoves is still
+ // valid, although it refers to the previous iteration.
+ if (Signals.stop)
+ break;
+
+ // When failing high/low give some update (without cluttering
+ // the UI) before a re-search.
+ if ( mainThread
+ && multiPV == 1
+ && (bestValue <= alpha || bestValue >= beta)
+ && Time.elapsed() > 3000)
+ sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
+
+ // In case of failing low/high increase aspiration window and
+ // re-search, otherwise exit the loop.
+ if (bestValue <= alpha)
+ {
+ beta = (alpha + beta) / 2;
+ alpha = std::max(bestValue - delta, -VALUE_INFINITE);
+
+ if (mainThread)
+ {
+ mainThread->failedLow = true;
+ Signals.stopOnPonderhit = false;
+ }
+ }
+ else if (bestValue >= beta)
+ {
+ alpha = (alpha + beta) / 2;
+ beta = std::min(bestValue + delta, VALUE_INFINITE);
+ }
+ else
+ break;
- TT.new_search();
- History.clear();
- Gains.clear();
- Countermoves.clear();
+ delta += delta / 4 + 5;
- PVSize = Options["MultiPV"];
- Skill skill(Options["Skill Level"]);
+ assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
+ }
- // Do we have to play with skill handicap? In this case enable MultiPV search
- // that we will use behind the scenes to retrieve a set of possible moves.
- if (skill.enabled() && PVSize < 4)
- PVSize = 4;
+ // Sort the PV lines searched so far and update the GUI
+ std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1);
- PVSize = std::min(PVSize, RootMoves.size());
+ if (!mainThread)
+ continue;
- // Iterative deepening loop until requested to stop or target depth reached
- while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
- {
- // Age out PV variability metric
- BestMoveChanges *= 0.8;
+ if (Signals.stop)
+ sync_cout << "info nodes " << Threads.nodes_searched()
+ << " time " << Time.elapsed() << sync_endl;
- // Save last iteration's scores before first PV line is searched and all
- // the move scores but the (new) PV are set to -VALUE_INFINITE.
- for (size_t i = 0; i < RootMoves.size(); ++i)
- RootMoves[i].prevScore = RootMoves[i].score;
+ else if (PVIdx + 1 == multiPV || Time.elapsed() > 3000)
+ sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
+ }
- // MultiPV loop. We perform a full root search for each PV line
- for (PVIdx = 0; PVIdx < PVSize; ++PVIdx)
- {
- // Reset aspiration window starting size
- if (depth >= 5)
- {
- delta = Value(16);
- alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
- beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
- }
+ if (!Signals.stop)
+ completedDepth = rootDepth;
- // Start with a small aspiration window and, in case of fail high/low,
- // research with bigger window until not failing high/low anymore.
- while (true)
- {
- bestValue = search<Root>(pos, ss, alpha, beta, depth * ONE_PLY, false);
-
- // Bring to front the best move. It is critical that sorting is
- // done with a stable algorithm because all the values but the first
- // and eventually the new best one are set to -VALUE_INFINITE and
- // we want to keep the same order for all the moves but 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());
-
- // Write PV back to transposition table in case the relevant
- // entries have been overwritten during the search.
- for (size_t i = 0; i <= PVIdx; ++i)
- RootMoves[i].insert_pv_in_tt(pos);
-
- // If search has been stopped return immediately. Sorting and
- // writing PV back to TT is safe becuase RootMoves is still
- // valid, although refers to previous iteration.
- if (Signals.stop)
- return;
-
- // When failing high/low give some update (without cluttering
- // the UI) before to research.
- if ( (bestValue <= alpha || bestValue >= beta)
- && Time::now() - SearchTime > 3000)
- sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
-
- // In case of failing low/high increase aspiration window and
- // research, otherwise exit the loop.
- if (bestValue <= alpha)
- {
- alpha = std::max(bestValue - delta, -VALUE_INFINITE);
-
- Signals.failedLowAtRoot = true;
- Signals.stopOnPonderhit = false;
- }
- else if (bestValue >= beta)
- beta = std::min(bestValue + delta, VALUE_INFINITE);
-
- else
- break;
-
- delta += delta / 2;
-
- assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
- }
+ if (!mainThread)
+ continue;
- // Sort the PV lines searched so far and update the GUI
- std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
+ // 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 (PVIdx + 1 == PVSize || Time::now() - SearchTime > 3000)
- sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
- }
+ // Have we found a "mate in x"?
+ if ( Limits.mate
+ && bestValue >= VALUE_MATE_IN_MAX_PLY
+ && VALUE_MATE - bestValue <= 2 * Limits.mate)
+ Signals.stop = true;
- // Do we need to pick now the sub-optimal best move ?
- if (skill.enabled() && skill.time_to_pick(depth))
- skill.pick_move();
+ // Do we have time for the next iteration? Can we stop searching now?
+ if (Limits.use_time_management())
+ {
+ if (!Signals.stop && !Signals.stopOnPonderhit)
+ {
+ // Stop the search if only one legal move is available, or if all
+ // of the available time has been used, or if we matched an easyMove
+ // from the previous search and just did a fast verification.
+ 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 / 42;
+
+ if ( rootMoves.size() == 1
+ || Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 628
+ || (mainThread->easyMovePlayed = doEasyMove))
+ {
+ // If we are allowed to ponder do not stop the search now but
+ // keep pondering until the GUI sends "ponderhit" or "stop".
+ if (Limits.ponder)
+ Signals.stopOnPonderhit = true;
+ else
+ Signals.stop = true;
+ }
+ }
- if (Options["Write Search Log"])
- {
- RootMove& rm = RootMoves[0];
- if (skill.best != MOVE_NONE)
- rm = *std::find(RootMoves.begin(), RootMoves.end(), skill.best);
+ if (rootMoves[0].pv.size() >= 3)
+ EasyMove.update(rootPos, rootMoves[0].pv);
+ else
+ EasyMove.clear();
+ }
+ }
- Log log(Options["Search Log Filename"]);
- log << pretty_pv(pos, depth, rm.score, Time::now() - SearchTime, &rm.pv[0])
- << std::endl;
- }
+ if (!mainThread)
+ return;
- // Do we have found a "mate in x"?
- if ( Limits.mate
- && bestValue >= VALUE_MATE_IN_MAX_PLY
- && VALUE_MATE - bestValue <= 2 * Limits.mate)
- Signals.stop = true;
+ // 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();
- // Do we have time for the next iteration? Can we stop searching now?
- if (Limits.use_time_management() && !Signals.stopOnPonderhit)
- {
- bool stop = false; // Local variable, not the volatile Signals.stop
-
- // Take in account some extra time if the best move has changed
- if (depth > 4 && depth < 50 && PVSize == 1)
- TimeMgr.pv_instability(BestMoveChanges);
-
- // Stop search if most of available time is already consumed. We
- // probably don't have enough time to search the first move at the
- // next iteration anyway.
- if (Time::now() - SearchTime > (TimeMgr.available_time() * 62) / 100)
- stop = true;
-
- // Stop search early if one move seems to be much better than others
- if ( depth >= 12
- && !stop
- && PVSize == 1
- && bestValue > VALUE_MATED_IN_MAX_PLY
- && ( RootMoves.size() == 1
- || Time::now() - SearchTime > (TimeMgr.available_time() * 20) / 100))
- {
- Value rBeta = bestValue - 2 * PawnValueMg;
- ss->excludedMove = RootMoves[0].pv[0];
- ss->skipNullMove = true;
- Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, (depth - 3) * ONE_PLY, true);
- ss->skipNullMove = false;
- ss->excludedMove = MOVE_NONE;
-
- if (v < rBeta)
- stop = true;
- }
+ // 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)));
+}
- if (stop)
- {
- // If we are allowed to ponder do not stop the search now but
- // keep pondering until GUI sends "ponderhit" or "stop".
- if (Limits.ponder)
- Signals.stopOnPonderhit = true;
- else
- Signals.stop = true;
- }
- }
- }
- }
+namespace {
- // search<>() is the main search function for both PV and non-PV nodes and for
- // normal and SplitPoint nodes. When called just after a split point the search
- // is simpler because we have already probed the hash table, done a null move
- // search, and searched the first move before splitting, we don't have to repeat
- // all this work again. We also don't need to store anything to the hash table
- // here: This is taken care of after we return from the split point.
+ // 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) {
- const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
- const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
- const bool RootNode = (NT == Root || NT == SplitPointRoot);
+ const bool PvNode = NT == PV;
+ const bool rootNode = PvNode && (ss-1)->ply == 0;
- assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
+ assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
assert(PvNode || (alpha == beta - 1));
- assert(depth > DEPTH_ZERO);
+ assert(DEPTH_ZERO < depth && depth < DEPTH_MAX);
+ assert(!(PvNode && cutNode));
+ assert(depth / ONE_PLY * ONE_PLY == depth);
- Move quietsSearched[64];
+ Move pv[MAX_PLY+1], quietsSearched[64];
StateInfo st;
- const TTEntry *tte;
- SplitPoint* splitPoint;
+ TTEntry* tte;
Key posKey;
- Move ttMove, move, excludedMove, bestMove, threatMove;
- Depth ext, newDepth;
- Value bestValue, value, ttValue;
- Value eval, nullValue, futilityValue;
- bool inCheck, givesCheck, pvMove, singularExtensionNode, improving;
- bool captureOrPromotion, dangerous, doFullDepthSearch;
+ Move ttMove, move, excludedMove, bestMove;
+ Depth extension, newDepth, predictedDepth;
+ Value bestValue, value, ttValue, eval, nullValue;
+ bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
+ bool captureOrPromotion, doFullDepthSearch, moveCountPruning;
+ Piece moved_piece;
int moveCount, quietCount;
// Step 1. Initialize node
Thread* thisThread = pos.this_thread();
inCheck = pos.checkers();
+ moveCount = quietCount = ss->moveCount = 0;
+ bestValue = -VALUE_INFINITE;
+ ss->ply = (ss-1)->ply + 1;
- if (SpNode)
+ // Check for the available remaining time
+ if (thisThread->resetCalls.load(std::memory_order_relaxed))
{
- splitPoint = ss->splitPoint;
- bestMove = splitPoint->bestMove;
- threatMove = splitPoint->threatMove;
- bestValue = splitPoint->bestValue;
- tte = NULL;
- ttMove = excludedMove = MOVE_NONE;
- ttValue = VALUE_NONE;
-
- assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
-
- goto moves_loop;
+ thisThread->resetCalls = false;
+ thisThread->callsCnt = 0;
}
+ if (++thisThread->callsCnt > 4096)
+ {
+ for (Thread* th : Threads)
+ th->resetCalls = true;
- moveCount = quietCount = 0;
- bestValue = -VALUE_INFINITE;
- ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
- ss->ply = (ss-1)->ply + 1;
- ss->futilityMoveCount = 0;
- (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
- (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
+ check_time();
+ }
// Used to send selDepth info to GUI
if (PvNode && thisThread->maxPly < ss->ply)
thisThread->maxPly = ss->ply;
- if (!RootNode)
+ if (!rootNode)
{
// Step 2. Check for aborted search and immediate draw
- if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
- return DrawValue[pos.side_to_move()];
+ if (Signals.stop.load(std::memory_order_relaxed) || pos.is_draw() || ss->ply >= MAX_PLY)
+ return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos)
+ : DrawValue[pos.side_to_move()];
// 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
// a shorter mate was found upward in the tree then there is no need to search
- // further, we will never beat current alpha. Same logic but with reversed signs
- // applies also in the opposite condition of being mated instead of giving mate,
- // in this case return a fail-high score.
+ // because we will never beat the current alpha. Same logic but with reversed
+ // signs applies also in the opposite condition of being mated instead of giving
+ // mate. In this case return a fail-high score.
alpha = std::max(mated_in(ss->ply), alpha);
beta = std::min(mate_in(ss->ply+1), beta);
if (alpha >= beta)
return alpha;
}
- // 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.
+ assert(0 <= ss->ply && ss->ply < MAX_PLY);
+
+ ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
+ ss->counterMoves = nullptr;
+ (ss+1)->skipEarlyPruning = false;
+ (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
+
+ // Step 4. Transposition table lookup. We don't want the score of a partial
+ // search to overwrite a previous full search TT value, so we use a different
+ // position key in case of an excluded move.
excludedMove = ss->excludedMove;
- posKey = excludedMove ? pos.exclusion_key() : pos.key();
- tte = TT.probe(posKey);
- ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
- ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
-
- // At PV nodes we check for exact scores, while at non-PV nodes we check for
- // a fail high/low. Biggest advantage at probing at PV nodes is to have a
- // smooth experience in analysis mode. We don't probe at Root nodes otherwise
- // we should also update RootMoveList to avoid bogus output.
- if ( !RootNode
- && tte
+ posKey = pos.key() ^ Key(excludedMove);
+ tte = TT.probe(posKey, ttHit);
+ ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
+ ttMove = rootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
+ : ttHit ? tte->move() : MOVE_NONE;
+
+ // At non-PV nodes we check for an early TT cutoff
+ if ( !PvNode
+ && ttHit
&& tte->depth() >= depth
- && ttValue != VALUE_NONE // Only in case of TT access race
- && ( PvNode ? tte->bound() == BOUND_EXACT
- : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
- : (tte->bound() & BOUND_UPPER)))
+ && ttValue != VALUE_NONE // Possible in case of TT access race
+ && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
+ : (tte->bound() & BOUND_UPPER)))
{
- TT.refresh(tte);
ss->currentMove = ttMove; // Can be MOVE_NONE
- if ( ttValue >= beta
- && ttMove
- && !pos.capture_or_promotion(ttMove)
- && ttMove != ss->killers[0])
+ // If ttMove is quiet, update killers, history, counter move on TT hit
+ if (ttValue >= beta && ttMove)
{
- ss->killers[1] = ss->killers[0];
- ss->killers[0] = ttMove;
+ int d = depth / ONE_PLY;
+
+ if (!pos.capture_or_promotion(ttMove))
+ {
+ Value bonus = Value(d * d + 2 * d - 2);
+ update_stats(pos, ss, ttMove, nullptr, 0, bonus);
+ }
+
+ // Extra penalty for a quiet TT move in previous ply when it gets refuted
+ if ((ss-1)->moveCount == 1 && !pos.captured_piece())
+ {
+ Value penalty = Value(d * d + 4 * d + 1);
+ Square prevSq = to_sq((ss-1)->currentMove);
+ update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, -penalty);
+ }
}
return ttValue;
}
- // Step 5. Evaluate the position statically and update parent's gain statistics
+ // Step 4a. Tablebase probe
+ if (!rootNode && TB::Cardinality)
+ {
+ int piecesCnt = pos.count<ALL_PIECES>(WHITE) + pos.count<ALL_PIECES>(BLACK);
+
+ if ( piecesCnt <= TB::Cardinality
+ && (piecesCnt < TB::Cardinality || depth >= TB::ProbeDepth)
+ && pos.rule50_count() == 0
+ && !pos.can_castle(ANY_CASTLING))
+ {
+ int found, v = Tablebases::probe_wdl(pos, &found);
+
+ if (found)
+ {
+ TB::Hits++;
+
+ 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;
+
+ 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());
+
+ return value;
+ }
+ }
+ }
+
+ // Step 5. Evaluate the position statically
if (inCheck)
{
- ss->staticEval = ss->evalMargin = eval = VALUE_NONE;
+ ss->staticEval = eval = VALUE_NONE;
goto moves_loop;
}
- else if (tte)
+ else if (ttHit)
{
// Never assume anything on values stored in TT
- if ( (ss->staticEval = eval = tte->eval_value()) == VALUE_NONE
- ||(ss->evalMargin = tte->eval_margin()) == VALUE_NONE)
- eval = ss->staticEval = evaluate(pos, ss->evalMargin);
+ if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
+ eval = ss->staticEval = evaluate(pos);
// Can ttValue be used as a better position evaluation?
if (ttValue != VALUE_NONE)
}
else
{
- eval = ss->staticEval = evaluate(pos, ss->evalMargin);
- TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
- ss->staticEval, ss->evalMargin);
- }
+ eval = ss->staticEval =
+ (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
+ : -(ss-1)->staticEval + 2 * Eval::Tempo;
- // Update gain for the parent non-capture move given the static position
- // evaluation before and after the move.
- if ( !pos.captured_piece_type()
- && ss->staticEval != VALUE_NONE
- && (ss-1)->staticEval != VALUE_NONE
- && (move = (ss-1)->currentMove) != MOVE_NULL
- && type_of(move) == NORMAL)
- {
- Square to = to_sq(move);
- Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
+ tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
+ ss->staticEval, TT.generation());
}
+ if (ss->skipEarlyPruning)
+ goto moves_loop;
+
// Step 6. Razoring (skipped when in check)
if ( !PvNode
&& depth < 4 * ONE_PLY
- && eval + razor_margin(depth) < beta
&& ttMove == MOVE_NONE
- && abs(beta) < VALUE_MATE_IN_MAX_PLY
- && !pos.pawn_on_7th(pos.side_to_move()))
+ && eval + razor_margin[depth / ONE_PLY] <= alpha)
{
- Value rbeta = beta - razor_margin(depth);
- Value v = qsearch<NonPV, false>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
- if (v < rbeta)
- // Logically we should return (v + razor_margin(depth)), but
- // surprisingly this did slightly weaker in tests.
+ if ( depth <= ONE_PLY
+ && eval + razor_margin[3 * ONE_PLY] <= alpha)
+ return qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO);
+
+ Value ralpha = alpha - razor_margin[depth / ONE_PLY];
+ Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
+ if (v <= ralpha)
return v;
}
- // Step 7. Static null move pruning (skipped when in check)
- // We're betting that the opponent doesn't have a move that will reduce
- // the score by more than futility_margin(depth) if we do a null move.
- if ( !PvNode
- && !ss->skipNullMove
- && depth < 4 * ONE_PLY
- && eval - futility_margin(depth, (ss-1)->futilityMoveCount) >= beta
- && abs(beta) < VALUE_MATE_IN_MAX_PLY
- && abs(eval) < VALUE_KNOWN_WIN
+ // 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()))
- return eval - futility_margin(depth, (ss-1)->futilityMoveCount);
+ return eval - futility_margin(depth);
// Step 8. Null move search with verification search (is omitted in PV nodes)
if ( !PvNode
- && !ss->skipNullMove
- && depth >= 2 * ONE_PLY
&& eval >= beta
- && abs(beta) < VALUE_MATE_IN_MAX_PLY
+ && (ss->staticEval >= beta - 35 * (depth / ONE_PLY - 6) || depth >= 13 * ONE_PLY)
&& pos.non_pawn_material(pos.side_to_move()))
{
ss->currentMove = MOVE_NULL;
+ ss->counterMoves = nullptr;
- // Null move dynamic reduction based on depth
- Depth R = 3 * ONE_PLY + depth / 4;
+ assert(eval - beta >= 0);
- // Null move dynamic reduction based on value
- if (eval - PawnValueMg > beta)
- R += ONE_PLY;
+ // 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;
pos.do_null_move(st);
- (ss+1)->skipNullMove = true;
- nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
- : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R, !cutNode);
- (ss+1)->skipNullMove = false;
+ (ss+1)->skipEarlyPruning = true;
+ nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
+ : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
+ (ss+1)->skipEarlyPruning = false;
pos.undo_null_move();
if (nullValue >= beta)
if (nullValue >= VALUE_MATE_IN_MAX_PLY)
nullValue = beta;
- if (depth < 12 * ONE_PLY)
+ if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
return nullValue;
// Do verification search at high depths
- ss->skipNullMove = true;
- Value v = search<NonPV>(pos, ss, alpha, beta, depth-R, false);
- ss->skipNullMove = false;
+ ss->skipEarlyPruning = true;
+ Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
+ : search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
+ ss->skipEarlyPruning = false;
if (v >= beta)
return nullValue;
}
- else
- {
- // The null move failed low, which means that we may be faced with
- // some kind of threat. If the previous move was reduced, check if
- // the move that refuted the null move was somehow connected to the
- // move which was reduced. If a connection is found, return a fail
- // low score (which will cause the reduced move to fail high in the
- // parent node, which will trigger a re-search with full depth).
- threatMove = (ss+1)->currentMove;
-
- if ( depth < 5 * ONE_PLY
- && (ss-1)->reduction
- && threatMove != MOVE_NONE
- && allows(pos, (ss-1)->currentMove, threatMove))
- return alpha;
- }
}
// Step 9. ProbCut (skipped when in check)
- // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
- // and a reduced search returns a value much above beta, we can (almost) safely
- // prune the previous move.
+ // 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
- && !ss->skipNullMove
&& abs(beta) < VALUE_MATE_IN_MAX_PLY)
{
- Value rbeta = beta + 200;
- Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
+ Value rbeta = std::min(beta + 200, VALUE_INFINITE);
+ Depth rdepth = depth - 4 * ONE_PLY;
assert(rdepth >= ONE_PLY);
assert((ss-1)->currentMove != MOVE_NONE);
assert((ss-1)->currentMove != MOVE_NULL);
- MovePicker mp(pos, ttMove, History, pos.captured_piece_type());
- CheckInfo ci(pos);
+ MovePicker mp(pos, ttMove, rbeta - ss->staticEval);
- while ((move = mp.next_move<false>()) != MOVE_NONE)
- if (pos.legal(move, ci.pinned))
+ while ((move = mp.next_move()) != MOVE_NONE)
+ if (pos.legal(move))
{
ss->currentMove = move;
- pos.do_move(move, st, ci, pos.gives_check(move, ci));
+ ss->counterMoves = &CounterMoveHistory[pos.moved_piece(move)][to_sq(move)];
+ pos.do_move(move, st, pos.gives_check(move));
value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
pos.undo_move(move);
if (value >= rbeta)
}
// Step 10. Internal iterative deepening (skipped when in check)
- if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
- && ttMove == MOVE_NONE
- && (PvNode || ss->staticEval + Value(256) >= beta))
+ if ( depth >= 6 * ONE_PLY
+ && !ttMove
+ && (PvNode || ss->staticEval + 256 >= beta))
{
- Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
-
- ss->skipNullMove = true;
- search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
- ss->skipNullMove = false;
+ Depth d = (3 * depth / (4 * ONE_PLY) - 2) * ONE_PLY;
+ ss->skipEarlyPruning = true;
+ search<NT>(pos, ss, alpha, beta, d, cutNode);
+ ss->skipEarlyPruning = false;
- tte = TT.probe(posKey);
- ttMove = tte ? tte->move() : MOVE_NONE;
+ tte = TT.probe(posKey, ttHit);
+ ttMove = ttHit ? tte->move() : MOVE_NONE;
}
-moves_loop: // When in check and at SpNode search starts from here
+moves_loop: // When in check search starts from here
- Square prevMoveSq = to_sq((ss-1)->currentMove);
- Move countermoves[] = { Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].first,
- Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq].second };
+ const CounterMoveStats* cmh = (ss-1)->counterMoves;
+ const CounterMoveStats* fmh = (ss-2)->counterMoves;
+ const CounterMoveStats* fmh2 = (ss-4)->counterMoves;
- MovePicker mp(pos, ttMove, depth, History, countermoves, ss);
- CheckInfo ci(pos);
+ MovePicker mp(pos, ttMove, depth, ss);
value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
improving = ss->staticEval >= (ss-2)->staticEval
- || ss->staticEval == VALUE_NONE
+ /* || ss->staticEval == VALUE_NONE Already implicit in the previous condition */
||(ss-2)->staticEval == VALUE_NONE;
- singularExtensionNode = !RootNode
- && !SpNode
+ singularExtensionNode = !rootNode
&& depth >= 8 * ONE_PLY
&& ttMove != MOVE_NONE
+ /* && ttValue != VALUE_NONE Already implicit in the next condition */
+ && abs(ttValue) < VALUE_KNOWN_WIN
&& !excludedMove // Recursive singular search is not allowed
&& (tte->bound() & BOUND_LOWER)
&& tte->depth() >= depth - 3 * ONE_PLY;
// 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<SpNode>()) != MOVE_NONE)
+ while ((move = mp.next_move()) != MOVE_NONE)
{
assert(is_ok(move));
continue;
// 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
+ // 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(RootMoves.begin() + PVIdx, RootMoves.end(), move))
+ if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx,
+ thisThread->rootMoves.end(), move))
continue;
- if (SpNode)
- {
- // Shared counter cannot be decremented later if move turns out to be illegal
- if (!pos.legal(move, ci.pinned))
- continue;
-
- moveCount = ++splitPoint->moveCount;
- splitPoint->mutex.unlock();
- }
- else
- ++moveCount;
+ ss->moveCount = ++moveCount;
- if (RootNode)
- {
- Signals.firstRootMove = (moveCount == 1);
+ if (rootNode && thisThread == Threads.main() && Time.elapsed() > 3000)
+ sync_cout << "info depth " << depth / ONE_PLY
+ << " currmove " << UCI::move(move, pos.is_chess960())
+ << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl;
- if (thisThread == Threads.main() && Time::now() - SearchTime > 3000)
- sync_cout << "info depth " << depth / ONE_PLY
- << " currmove " << move_to_uci(move, pos.is_chess960())
- << " currmovenumber " << moveCount + PVIdx << sync_endl;
- }
+ if (PvNode)
+ (ss+1)->pv = nullptr;
- ext = DEPTH_ZERO;
+ extension = DEPTH_ZERO;
captureOrPromotion = pos.capture_or_promotion(move);
- givesCheck = pos.gives_check(move, ci);
- dangerous = givesCheck
- || pos.passed_pawn_push(move)
- || type_of(move) == CASTLE;
+ moved_piece = 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. Extend checks
- if (givesCheck && pos.see_sign(move) >= 0)
- ext = ONE_PLY;
+ if ( givesCheck
+ && !moveCountPruning
+ && pos.see_sign(move) >= VALUE_ZERO)
+ extension = ONE_PLY;
// 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, if result is lower than ttValue minus
- // a margin then we extend ttMove.
+ // on all the other moves but the ttMove and if the result is lower than
+ // ttValue minus a margin then we extend the ttMove.
if ( singularExtensionNode
&& move == ttMove
- && !ext
- && pos.legal(move, ci.pinned)
- && abs(ttValue) < VALUE_KNOWN_WIN)
+ && !extension
+ && pos.legal(move))
{
- assert(ttValue != VALUE_NONE);
-
- Value rBeta = ttValue - int(depth);
+ Value rBeta = ttValue - 2 * depth / ONE_PLY;
+ Depth d = (depth / (2 * ONE_PLY)) * ONE_PLY;
ss->excludedMove = move;
- ss->skipNullMove = true;
- value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
- ss->skipNullMove = false;
+ ss->skipEarlyPruning = true;
+ value = search<NonPV>(pos, ss, rBeta - 1, rBeta, d, cutNode);
+ ss->skipEarlyPruning = false;
ss->excludedMove = MOVE_NONE;
if (value < rBeta)
- ext = ONE_PLY;
+ extension = ONE_PLY;
}
- // Update current move (this must be done after singular extension search)
- newDepth = depth - ONE_PLY + ext;
+ // Update the current move (this must be done after singular extension search)
+ newDepth = depth - ONE_PLY + extension;
- // Step 13. Futility pruning (is omitted in PV nodes)
- if ( !PvNode
+ // Step 13. Pruning at shallow depth
+ if ( !rootNode
&& !captureOrPromotion
&& !inCheck
- && !dangerous
- /* && move != ttMove Already implicit in the next condition */
- && bestValue > VALUE_MATED_IN_MAX_PLY)
+ && !givesCheck
+ && bestValue > VALUE_MATED_IN_MAX_PLY
+ && !pos.advanced_pawn_push(move))
{
// Move count based pruning
- if ( depth < 16 * ONE_PLY
- && moveCount >= FutilityMoveCounts[improving][depth]
- && (!threatMove || !refutes(pos, move, threatMove)))
- {
- if (SpNode)
- splitPoint->mutex.lock();
-
+ if (moveCountPruning)
continue;
- }
- // Value based pruning
- // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
- // but fixing this made program slightly weaker.
- Depth predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
- futilityValue = ss->staticEval + ss->evalMargin + futility_margin(predictedDepth, moveCount)
- + Gains[pos.moved_piece(move)][to_sq(move)];
+ predictedDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO);
- if (futilityValue < beta)
- {
- bestValue = std::max(bestValue, futilityValue);
+ // Countermoves based pruning
+ if ( predictedDepth < 3 * ONE_PLY
+ && (!cmh || (*cmh )[moved_piece][to_sq(move)] < VALUE_ZERO)
+ && (!fmh || (*fmh )[moved_piece][to_sq(move)] < VALUE_ZERO)
+ && (!fmh2 || (*fmh2)[moved_piece][to_sq(move)] < VALUE_ZERO || (cmh && fmh)))
+ continue;
- if (SpNode)
- {
- splitPoint->mutex.lock();
- if (bestValue > splitPoint->bestValue)
- splitPoint->bestValue = bestValue;
- }
+ // Futility pruning: parent node
+ if ( predictedDepth < 7 * ONE_PLY
+ && ss->staticEval + 256 + 200 * predictedDepth / ONE_PLY <= alpha)
continue;
- }
- // Prune moves with negative SEE at low depths
- if ( predictedDepth < 4 * ONE_PLY
- && pos.see_sign(move) < 0)
+ // Prune moves with negative SEE at low depths and below a decreasing
+ // threshold at higher depths.
+ if (predictedDepth < 8 * ONE_PLY)
{
- if (SpNode)
- splitPoint->mutex.lock();
+ Value see_v = predictedDepth < 4 * ONE_PLY ? VALUE_ZERO
+ : -PawnValueMg * 2 * int(predictedDepth - 3 * ONE_PLY) / ONE_PLY;
- continue;
+ if (pos.see_sign(move) < see_v)
+ continue;
}
-
- // We have not pruned the move that will be searched, but remember how
- // far in the move list we are to be more aggressive in the child node.
- ss->futilityMoveCount = moveCount;
}
- else
- ss->futilityMoveCount = 0;
- // Check for legality only before to do the move
- if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
+ // Speculative prefetch as early as possible
+ prefetch(TT.first_entry(pos.key_after(move)));
+
+ // Check for legality just before making the move
+ if (!rootNode && !pos.legal(move))
{
- --moveCount;
+ ss->moveCount = --moveCount;
continue;
}
- pvMove = PvNode && moveCount == 1;
ss->currentMove = move;
- if (!SpNode && !captureOrPromotion && quietCount < 64)
- quietsSearched[quietCount++] = move;
+ ss->counterMoves = &CounterMoveHistory[moved_piece][to_sq(move)];
// Step 14. Make the move
- pos.do_move(move, st, ci, givesCheck);
+ pos.do_move(move, st, givesCheck);
- // Step 15. Reduced depth search (LMR). If the move fails high will be
+ // Step 15. Reduced depth search (LMR). If the move fails high it will be
// re-searched at full depth.
if ( depth >= 3 * ONE_PLY
- && !pvMove
- && !captureOrPromotion
- && move != ttMove
- && move != ss->killers[0]
- && move != ss->killers[1])
+ && moveCount > 1
+ && (!captureOrPromotion || moveCountPruning))
{
- ss->reduction = reduction<PvNode>(improving, depth, moveCount);
+ Depth r = reduction<PvNode>(improving, depth, moveCount);
- if (!PvNode && cutNode)
- ss->reduction += ONE_PLY;
-
- else if (History[pos.piece_on(to_sq(move))][to_sq(move)] < 0)
- ss->reduction += ONE_PLY / 2;
-
- if (move == countermoves[0] || move == countermoves[1])
- ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
+ if (captureOrPromotion)
+ r -= r ? ONE_PLY : DEPTH_ZERO;
+ else
+ {
+ // Increase reduction for cut nodes
+ if (cutNode)
+ r += 2 * ONE_PLY;
+
+ // Decrease reduction for moves that escape a capture. Filter out
+ // castling moves, because they are coded as "king captures rook" and
+ // hence break make_move(). Also use see() instead of see_sign(),
+ // because the destination square is empty.
+ else if ( type_of(move) == NORMAL
+ && type_of(pos.piece_on(to_sq(move))) != PAWN
+ && pos.see(make_move(to_sq(move), from_sq(move))) < VALUE_ZERO)
+ r -= 2 * ONE_PLY;
+
+ // Decrease/increase reduction for moves with a good/bad history
+ Value val = thisThread->history[moved_piece][to_sq(move)]
+ + (cmh ? (*cmh )[moved_piece][to_sq(move)] : VALUE_ZERO)
+ + (fmh ? (*fmh )[moved_piece][to_sq(move)] : VALUE_ZERO)
+ + (fmh2 ? (*fmh2)[moved_piece][to_sq(move)] : VALUE_ZERO)
+ + thisThread->fromTo.get(~pos.side_to_move(), move);
+ int rHist = (val - 8000) / 20000;
+ r = std::max(DEPTH_ZERO, (r / ONE_PLY - rHist) * ONE_PLY);
+ }
- Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
- if (SpNode)
- alpha = splitPoint->alpha;
+ Depth d = std::max(newDepth - r, ONE_PLY);
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
- doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
- ss->reduction = DEPTH_ZERO;
+ doFullDepthSearch = (value > alpha && d != newDepth);
}
else
- doFullDepthSearch = !pvMove;
+ doFullDepthSearch = !PvNode || moveCount > 1;
- // Step 16. Full depth search, when LMR is skipped or fails high
+ // Step 16. Full depth search when LMR is skipped or fails high
if (doFullDepthSearch)
+ value = newDepth < ONE_PLY ?
+ givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
+ : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
+ : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
+
+ // 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.
+ if (PvNode && (moveCount == 1 || (value > alpha && (rootNode || value < beta))))
{
- if (SpNode)
- alpha = splitPoint->alpha;
+ (ss+1)->pv = pv;
+ (ss+1)->pv[0] = MOVE_NONE;
- value = newDepth < ONE_PLY ?
- givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
- : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
- : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
+ value = newDepth < ONE_PLY ?
+ givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
+ : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
+ : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
}
- // Only for PV nodes 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 to fail low with value <= alpha and to try another move.
- if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
- value = newDepth < ONE_PLY ?
- givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
- : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
- : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
// Step 17. Undo move
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
- // Step 18. Check for new best move
- if (SpNode)
- {
- splitPoint->mutex.lock();
- bestValue = splitPoint->bestValue;
- alpha = splitPoint->alpha;
- }
+ // Step 18. 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.
+ if (Signals.stop.load(std::memory_order_relaxed))
+ return VALUE_ZERO;
- // Finished searching the move. If Signals.stop is true, the search
- // was aborted because the user interrupted the search or because we
- // ran out of time. In this case, the return value of the search cannot
- // be trusted, and we don't update the best move and/or PV.
- if (Signals.stop || thisThread->cutoff_occurred())
- return value; // To avoid returning VALUE_INFINITE
-
- if (RootNode)
+ if (rootNode)
{
- RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
+ RootMove& rm = *std::find(thisThread->rootMoves.begin(),
+ thisThread->rootMoves.end(), move);
// PV move or new best move ?
- if (pvMove || value > alpha)
+ if (moveCount == 1 || value > alpha)
{
rm.score = value;
- rm.extract_pv_from_tt(pos);
+ rm.pv.resize(1);
+
+ assert((ss+1)->pv);
+
+ for (Move* m = (ss+1)->pv; *m != MOVE_NONE; ++m)
+ rm.pv.push_back(*m);
// We record how often the best move has been changed in each
// iteration. This information is used for time management: When
// the best move changes frequently, we allocate some more time.
- if (!pvMove)
- ++BestMoveChanges;
+ if (moveCount > 1 && thisThread == Threads.main())
+ ++static_cast<MainThread*>(thisThread)->bestMoveChanges;
}
else
- // All other moves but the PV are set to the lowest value, this
- // is not a problem when sorting becuase sort is stable and move
- // position in the list is preserved, just the PV is pushed up.
+ // All other moves but the PV are set to the lowest value: this is
+ // not a problem when sorting because the sort is stable and the
+ // move position in the list is preserved - just the PV is pushed up.
rm.score = -VALUE_INFINITE;
}
if (value > bestValue)
{
- bestValue = SpNode ? splitPoint->bestValue = value : value;
+ bestValue = value;
if (value > alpha)
{
- bestMove = SpNode ? splitPoint->bestMove = move : move;
+ // If there is an easy move for this position, clear it if unstable
+ if ( PvNode
+ && thisThread == Threads.main()
+ && EasyMove.get(pos.key())
+ && (move != EasyMove.get(pos.key()) || moveCount > 1))
+ EasyMove.clear();
+
+ bestMove = move;
+
+ if (PvNode && !rootNode) // Update pv even in fail-high case
+ update_pv(ss->pv, move, (ss+1)->pv);
if (PvNode && value < beta) // Update alpha! Always alpha < beta
- alpha = SpNode ? splitPoint->alpha = value : value;
+ alpha = value;
else
{
assert(value >= beta); // Fail high
-
- if (SpNode)
- splitPoint->cutoff = true;
-
break;
}
}
}
- // Step 19. Check for splitting the search
- if ( !SpNode
- && depth >= Threads.minimumSplitDepth
- && Threads.available_slave(thisThread)
- && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
- {
- assert(bestValue < beta);
-
- thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
- depth, threatMove, moveCount, &mp, NT, cutNode);
- if (bestValue >= beta)
- break;
- }
+ if (!captureOrPromotion && move != bestMove && quietCount < 64)
+ quietsSearched[quietCount++] = move;
}
- if (SpNode)
- return bestValue;
+ // The following condition would detect a stop only after move loop has been
+ // completed. But in this case bestValue is valid because we have fully
+ // searched our subtree, and we can anyhow save the result in TT.
+ /*
+ if (Signals.stop)
+ return VALUE_DRAW;
+ */
// Step 20. Check for mate and stalemate
// All legal moves have been searched and if there are no legal moves, it
- // must be mate or stalemate. Note that we can have a false positive in
- // case of Signals.stop or thread.cutoff_occurred() are set, but this is
- // harmless because return value is discarded anyhow in the parent nodes.
- // If we are in a singular extension search then return a fail low score.
- // A split node has at least one move, the one tried before to be splitted.
+ // must be a mate or a stalemate. If we are in a singular extension search then
+ // return a fail low score.
if (!moveCount)
- return excludedMove ? alpha
- : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
-
- // If we have pruned all the moves without searching return a fail-low score
- if (bestValue == -VALUE_INFINITE)
- bestValue = alpha;
-
- TT.store(posKey, value_to_tt(bestValue, ss->ply),
- bestValue >= beta ? BOUND_LOWER :
- PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
- depth, bestMove, ss->staticEval, ss->evalMargin);
-
- // Quiet best move: update killers, history and countermoves
- if ( bestValue >= beta
- && !pos.capture_or_promotion(bestMove)
- && !inCheck)
+ bestValue = excludedMove ? alpha
+ : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
+ else if (bestMove)
{
- if (ss->killers[0] != bestMove)
+ int d = depth / ONE_PLY;
+
+ // Quiet best move: update killers, history and countermoves
+ if (!pos.capture_or_promotion(bestMove))
{
- ss->killers[1] = ss->killers[0];
- ss->killers[0] = bestMove;
+ Value bonus = Value(d * d + 2 * d - 2);
+ update_stats(pos, ss, bestMove, quietsSearched, quietCount, bonus);
}
- // Increase history value of the cut-off move and decrease all the other
- // played non-capture moves.
- Value bonus = Value(int(depth) * int(depth));
- History.update(pos.moved_piece(bestMove), to_sq(bestMove), bonus);
- for (int i = 0; i < quietCount - 1; ++i)
+ // Extra penalty for a quiet TT move in previous ply when it gets refuted
+ if ((ss-1)->moveCount == 1 && !pos.captured_piece())
{
- Move m = quietsSearched[i];
- History.update(pos.moved_piece(m), to_sq(m), -bonus);
+ Value penalty = Value(d * d + 4 * d + 1);
+ Square prevSq = to_sq((ss-1)->currentMove);
+ update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, -penalty);
}
-
- if (is_ok((ss-1)->currentMove))
- Countermoves.update(pos.piece_on(prevMoveSq), prevMoveSq, bestMove);
+ }
+ // Bonus for prior countermove that caused the fail low
+ else if ( depth >= 3 * ONE_PLY
+ && !pos.captured_piece()
+ && is_ok((ss-1)->currentMove))
+ {
+ int d = depth / ONE_PLY;
+ Value bonus = Value(d * d + 2 * d - 2);
+ Square prevSq = to_sq((ss-1)->currentMove);
+ update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, bonus);
}
+ tte->save(posKey, value_to_tt(bestValue, ss->ply),
+ bestValue >= beta ? BOUND_LOWER :
+ PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
+ depth, bestMove, ss->staticEval, TT.generation());
+
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
return bestValue;
template <NodeType NT, bool InCheck>
Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
- const bool PvNode = (NT == PV);
+ const bool PvNode = NT == PV;
- assert(NT == PV || NT == NonPV);
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);
+ Move pv[MAX_PLY+1];
StateInfo st;
- const TTEntry* tte;
+ TTEntry* tte;
Key posKey;
Move ttMove, move, bestMove;
Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
- bool givesCheck, evasionPrunable;
+ bool ttHit, givesCheck, evasionPrunable;
Depth ttDepth;
- // To flag BOUND_EXACT a node with eval above alpha and no available moves
if (PvNode)
- oldAlpha = alpha;
+ {
+ oldAlpha = alpha; // To flag BOUND_EXACT when eval above alpha and no available moves
+ (ss+1)->pv = pv;
+ ss->pv[0] = MOVE_NONE;
+ }
ss->currentMove = bestMove = MOVE_NONE;
ss->ply = (ss-1)->ply + 1;
- // Check for an instant draw or maximum ply reached
- if (pos.is_draw() || ss->ply > MAX_PLY)
- return DrawValue[pos.side_to_move()];
+ // Check for an instant draw or if the maximum ply has been reached
+ if (pos.is_draw() || ss->ply >= MAX_PLY)
+ return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos)
+ : DrawValue[pos.side_to_move()];
+
+ assert(0 <= ss->ply && ss->ply < MAX_PLY);
- // Decide whether or not to include checks, this fixes also the type of
+ // 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
// Transposition table lookup
posKey = pos.key();
- tte = TT.probe(posKey);
- ttMove = tte ? tte->move() : MOVE_NONE;
- ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
+ tte = TT.probe(posKey, ttHit);
+ ttMove = ttHit ? tte->move() : MOVE_NONE;
+ ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
- if ( tte
+ if ( !PvNode
+ && ttHit
&& tte->depth() >= ttDepth
&& ttValue != VALUE_NONE // Only in case of TT access race
- && ( PvNode ? tte->bound() == BOUND_EXACT
- : ttValue >= beta ? (tte->bound() & BOUND_LOWER)
- : (tte->bound() & BOUND_UPPER)))
+ && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
+ : (tte->bound() & BOUND_UPPER)))
{
ss->currentMove = ttMove; // Can be MOVE_NONE
return ttValue;
// Evaluate the position statically
if (InCheck)
{
- ss->staticEval = ss->evalMargin = VALUE_NONE;
+ ss->staticEval = VALUE_NONE;
bestValue = futilityBase = -VALUE_INFINITE;
}
else
{
- if (tte)
+ if (ttHit)
{
// Never assume anything on values stored in TT
- if ( (ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE
- ||(ss->evalMargin = tte->eval_margin()) == VALUE_NONE)
- ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
+ 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)
bestValue = ttValue;
}
else
- ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
+ ss->staticEval = bestValue =
+ (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
+ : -(ss-1)->staticEval + 2 * Eval::Tempo;
// Stand pat. Return immediately if static value is at least beta
if (bestValue >= beta)
{
- if (!tte)
- TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
- DEPTH_NONE, MOVE_NONE, ss->staticEval, ss->evalMargin);
+ if (!ttHit)
+ tte->save(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
+ DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
return bestValue;
}
if (PvNode && bestValue > alpha)
alpha = bestValue;
- futilityBase = bestValue + ss->evalMargin + Value(128);
+ futilityBase = bestValue + 128;
}
// 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.
- MovePicker mp(pos, ttMove, depth, History, to_sq((ss-1)->currentMove));
- CheckInfo ci(pos);
+ MovePicker mp(pos, ttMove, depth, to_sq((ss-1)->currentMove));
// Loop through the moves until no moves remain or a beta cutoff occurs
- while ((move = mp.next_move<false>()) != MOVE_NONE)
+ while ((move = mp.next_move()) != MOVE_NONE)
{
assert(is_ok(move));
- givesCheck = pos.gives_check(move, ci);
+ 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);
// Futility pruning
- if ( !PvNode
- && !InCheck
+ if ( !InCheck
&& !givesCheck
- && move != ttMove
- && type_of(move) != PROMOTION
&& futilityBase > -VALUE_KNOWN_WIN
- && !pos.passed_pawn_push(move))
+ && !pos.advanced_pawn_push(move))
{
- futilityValue = futilityBase
- + PieceValue[EG][pos.piece_on(to_sq(move))]
- + (type_of(move) == ENPASSANT ? PawnValueEg : VALUE_ZERO);
+ assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
+
+ futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
- if (futilityValue < beta)
+ if (futilityValue <= alpha)
{
bestValue = std::max(bestValue, futilityValue);
continue;
}
- // Prune moves with negative or equal SEE and also moves with positive
- // SEE where capturing piece loses a tempo and SEE < beta - futilityBase.
- if ( futilityBase < beta
- && pos.see(move, beta - futilityBase) <= 0)
+ if (futilityBase <= alpha && pos.see(move) <= VALUE_ZERO)
{
bestValue = std::max(bestValue, futilityBase);
continue;
}
}
- // Detect non-capture evasions that are candidate to be pruned
+ // Detect non-capture evasions that are candidates to be pruned
evasionPrunable = InCheck
&& bestValue > VALUE_MATED_IN_MAX_PLY
- && !pos.capture(move)
- && !pos.can_castle(pos.side_to_move());
+ && !pos.capture(move);
// Don't search moves with negative SEE values
- if ( !PvNode
- && (!InCheck || evasionPrunable)
- && move != ttMove
+ if ( (!InCheck || evasionPrunable)
&& type_of(move) != PROMOTION
- && pos.see_sign(move) < 0)
+ && pos.see_sign(move) < VALUE_ZERO)
continue;
- // Check for legality only before to do the move
- if (!pos.legal(move, ci.pinned))
+ // Speculative prefetch as early as possible
+ prefetch(TT.first_entry(pos.key_after(move)));
+
+ // Check for legality just before making the move
+ if (!pos.legal(move))
continue;
ss->currentMove = move;
// Make and search the move
- pos.do_move(move, st, ci, givesCheck);
+ 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);
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
- // Check for new best move
+ // Check for a new best move
if (value > bestValue)
{
bestValue = value;
if (value > alpha)
{
- if (PvNode && value < beta) // Update alpha here! Always alpha < beta
+ 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
{
- TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
- ttDepth, move, ss->staticEval, ss->evalMargin);
+ tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
+ ttDepth, move, ss->staticEval, TT.generation());
return value;
}
if (InCheck && bestValue == -VALUE_INFINITE)
return mated_in(ss->ply); // Plies to mate from the root
- TT.store(posKey, value_to_tt(bestValue, ss->ply),
- PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
- ttDepth, bestMove, ss->staticEval, ss->evalMargin);
+ tte->save(posKey, value_to_tt(bestValue, ss->ply),
+ PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
+ ttDepth, bestMove, ss->staticEval, TT.generation());
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.
- // The function is called before storing a value to the transposition table.
+ // The function is called before storing a value in the transposition table.
Value value_to_tt(Value v, int ply) {
// value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
- // from the transposition table (where refers to the plies to mate/be mated
+ // 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 value_from_tt(Value v, int ply) {
}
- // allows() tests whether the 'first' move at previous ply somehow makes the
- // 'second' move possible, for instance if the moving piece is the same in
- // both moves. Normally the second move is the threat (the best move returned
- // from a null search that fails low).
-
- bool allows(const Position& pos, Move first, Move second) {
+ // update_pv() adds current move and appends child pv[]
- assert(is_ok(first));
- assert(is_ok(second));
- assert(color_of(pos.piece_on(from_sq(second))) == ~pos.side_to_move());
- assert(type_of(first) == CASTLE || color_of(pos.piece_on(to_sq(first))) == ~pos.side_to_move());
+ void update_pv(Move* pv, Move move, Move* childPv) {
- Square m1from = from_sq(first);
- Square m2from = from_sq(second);
- Square m1to = to_sq(first);
- Square m2to = to_sq(second);
+ for (*pv++ = move; childPv && *childPv != MOVE_NONE; )
+ *pv++ = *childPv++;
+ *pv = MOVE_NONE;
+ }
- // The piece is the same or second's destination was vacated by the first move
- // We exclude the trivial case where a sliding piece does in two moves what
- // it could do in one move: eg. Ra1a2, Ra2a3.
- if ( m2to == m1from
- || (m1to == m2from && !squares_aligned(m1from, m2from, m2to)))
- return true;
- // Second one moves through the square vacated by first one
- if (between_bb(m2from, m2to) & m1from)
- return true;
+ // update_cm_stats() updates countermove and follow-up move history
- // Second's destination is defended by the first move's piece
- Bitboard m1att = pos.attacks_from(pos.piece_on(m1to), m1to, pos.pieces() ^ m2from);
- if (m1att & m2to)
- return true;
+ void update_cm_stats(Stack* ss, Piece pc, Square s, Value bonus) {
- // Second move gives a discovered check through the first's checking piece
- if (m1att & pos.king_square(pos.side_to_move()))
- {
- assert(between_bb(m1to, pos.king_square(pos.side_to_move())) & m2from);
- return true;
- }
-
- return false;
- }
+ CounterMoveStats* cmh = (ss-1)->counterMoves;
+ CounterMoveStats* fmh1 = (ss-2)->counterMoves;
+ CounterMoveStats* fmh2 = (ss-4)->counterMoves;
+ if (cmh)
+ cmh->update(pc, s, bonus);
- // refutes() tests whether a 'first' move is able to defend against a 'second'
- // opponent's move. In this case will not be pruned. Normally the second move
- // is the threat (the best move returned from a null search that fails low).
+ if (fmh1)
+ fmh1->update(pc, s, bonus);
- bool refutes(const Position& pos, Move first, Move second) {
+ if (fmh2)
+ fmh2->update(pc, s, bonus);
+ }
- assert(is_ok(first));
- assert(is_ok(second));
- Square m1from = from_sq(first);
- Square m2from = from_sq(second);
- Square m1to = to_sq(first);
- Square m2to = to_sq(second);
+ // update_stats() updates killers, history, countermove and countermove plus
+ // follow-up move history when a new quiet best move is found.
- // Don't prune moves of the threatened piece
- if (m1from == m2to)
- return true;
+ void update_stats(const Position& pos, Stack* ss, Move move,
+ Move* quiets, int quietsCnt, Value bonus) {
- // If the threatened piece has value less than or equal to the value of the
- // threat piece, don't prune moves which defend it.
- if ( pos.capture(second)
- && ( PieceValue[MG][pos.piece_on(m2from)] >= PieceValue[MG][pos.piece_on(m2to)]
- || type_of(pos.piece_on(m2from)) == KING))
+ if (ss->killers[0] != move)
{
- // Update occupancy as if the piece and the threat are moving
- Bitboard occ = pos.pieces() ^ m1from ^ m1to ^ m2from;
- Piece pc = pos.piece_on(m1from);
-
- // The moved piece attacks the square 'tto' ?
- if (pos.attacks_from(pc, m1to, occ) & m2to)
- return true;
+ ss->killers[1] = ss->killers[0];
+ ss->killers[0] = move;
+ }
- // Scan for possible X-ray attackers behind the moved piece
- Bitboard xray = (attacks_bb< ROOK>(m2to, occ) & pos.pieces(color_of(pc), QUEEN, ROOK))
- | (attacks_bb<BISHOP>(m2to, occ) & pos.pieces(color_of(pc), QUEEN, BISHOP));
+ Color c = pos.side_to_move();
+ Thread* thisThread = pos.this_thread();
+ thisThread->fromTo.update(c, move, bonus);
+ thisThread->history.update(pos.moved_piece(move), to_sq(move), bonus);
+ update_cm_stats(ss, pos.moved_piece(move), to_sq(move), bonus);
- // Verify attackers are triggered by our move and not already existing
- if (unlikely(xray) && (xray & ~pos.attacks_from<QUEEN>(m2to)))
- return true;
+ if ((ss-1)->counterMoves)
+ {
+ Square prevSq = to_sq((ss-1)->currentMove);
+ thisThread->counterMoves.update(pos.piece_on(prevSq), prevSq, move);
}
- // Don't prune safe moves which block the threat path
- if ((between_bb(m2from, m2to) & m1to) && pos.see_sign(first) >= 0)
- return true;
-
- return false;
+ // Decrease all the other played quiet moves
+ for (int i = 0; i < quietsCnt; ++i)
+ {
+ thisThread->fromTo.update(c, quiets[i], -bonus);
+ thisThread->history.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
+ update_cm_stats(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
+ }
}
- // When playing with strength handicap choose best move among the MultiPV set
+ // 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.
- Move Skill::pick_move() {
-
- static RKISS rk;
+ Move Skill::pick_best(size_t multiPV) {
- // PRNG sequence should be not deterministic
- for (int i = Time::now() % 50; i > 0; --i)
- rk.rand<unsigned>();
+ const RootMoves& rootMoves = Threads.main()->rootMoves;
+ static PRNG rng(now()); // PRNG sequence should be non-deterministic
// RootMoves are already sorted by score in descending order
- int variance = std::min(RootMoves[0].score - RootMoves[PVSize - 1].score, PawnValueMg);
+ Value topScore = rootMoves[0].score;
+ int delta = std::min(topScore - rootMoves[multiPV - 1].score, PawnValueMg);
int weakness = 120 - 2 * level;
- int max_s = -VALUE_INFINITE;
- best = MOVE_NONE;
+ int maxScore = -VALUE_INFINITE;
- // Choose best move. For each move score we add two terms both dependent on
- // weakness, one deterministic and bigger for weaker moves, and one random,
- // then we choose the move with the resulting highest score.
- for (size_t i = 0; i < PVSize; ++i)
+ // Choose best move. For each move score we add two terms, both dependent on
+ // weakness. One is deterministic and bigger for weaker levels, and one is
+ // random. Then we choose the move with the resulting highest score.
+ for (size_t i = 0; i < multiPV; ++i)
{
- int s = RootMoves[i].score;
-
- // Don't allow crazy blunders even at very low skills
- if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
- break;
-
// This is our magic formula
- s += ( weakness * int(RootMoves[0].score - s)
- + variance * (rk.rand<unsigned>() % weakness)) / 128;
+ int push = ( weakness * int(topScore - rootMoves[i].score)
+ + delta * (rng.rand<unsigned>() % weakness)) / 128;
- if (s > max_s)
+ if (rootMoves[i].score + push > maxScore)
{
- max_s = s;
- best = RootMoves[i].pv[0];
+ maxScore = rootMoves[i].score + push;
+ best = rootMoves[i].pv[0];
}
}
+
return best;
}
- // uci_pv() formats PV information according to UCI protocol. UCI requires
- // to send all the PV lines also if are still to be searched and so refer to
- // the previous search score.
+ // 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.
- string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
+ void check_time() {
- std::stringstream s;
- Time::point elapsed = Time::now() - SearchTime + 1;
- size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
- int selDepth = 0;
+ static TimePoint lastInfoTime = now();
- for (size_t i = 0; i < Threads.size(); ++i)
- if (Threads[i]->maxPly > selDepth)
- selDepth = Threads[i]->maxPly;
+ int elapsed = Time.elapsed();
+ TimePoint tick = Limits.startTime + elapsed;
- for (size_t i = 0; i < uciPVSize; ++i)
+ if (tick - lastInfoTime >= 1000)
{
- bool updated = (i <= PVIdx);
-
- if (depth == 1 && !updated)
- continue;
-
- int d = updated ? depth : depth - 1;
- Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
-
- if (s.rdbuf()->in_avail()) // Not at first line
- s << "\n";
-
- s << "info depth " << d
- << " seldepth " << selDepth
- << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
- << " nodes " << pos.nodes_searched()
- << " nps " << pos.nodes_searched() * 1000 / elapsed
- << " time " << elapsed
- << " multipv " << i + 1
- << " pv";
-
- for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; ++j)
- s << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
+ lastInfoTime = tick;
+ dbg_print();
}
- return s.str();
+ // An engine may not stop pondering until told so by the GUI
+ if (Limits.ponder)
+ return;
+
+ if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10)
+ || (Limits.movetime && elapsed >= Limits.movetime)
+ || (Limits.nodes && Threads.nodes_searched() >= Limits.nodes))
+ Signals.stop = true;
}
} // namespace
-/// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
-/// We consider also failing high nodes and not only BOUND_EXACT nodes so to
-/// allow to always have a ponder move even when we fail high at root, and a
-/// long PV to print that is important for position analysis.
-
-void RootMove::extract_pv_from_tt(Position& pos) {
-
- StateInfo state[MAX_PLY_PLUS_6], *st = state;
- const TTEntry* tte;
- int ply = 0;
- Move m = pv[0];
-
- pv.clear();
-
- do {
- pv.push_back(m);
-
- assert(MoveList<LEGAL>(pos).contains(pv[ply]));
-
- pos.do_move(pv[ply++], *st++);
- tte = TT.probe(pos.key());
-
- } while ( tte
- && pos.pseudo_legal(m = tte->move()) // Local copy, TT could change
- && pos.legal(m, pos.pinned_pieces())
- && ply < MAX_PLY
- && (!pos.is_draw() || ply < 2));
-
- pv.push_back(MOVE_NONE); // Must be zero-terminating
-
- while (ply) pos.undo_move(pv[--ply]);
-}
-
-
-/// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
-/// inserts the PV back into the TT. This makes sure the old PV moves are searched
-/// first, even if the old TT entries have been overwritten.
-
-void RootMove::insert_pv_in_tt(Position& pos) {
-
- StateInfo state[MAX_PLY_PLUS_6], *st = state;
- const TTEntry* tte;
- int ply = 0;
+/// 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.
- do {
- tte = TT.probe(pos.key());
+string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
- if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
- TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE, VALUE_NONE);
-
- assert(MoveList<LEGAL>(pos).contains(pv[ply]));
-
- pos.do_move(pv[ply++], *st++);
-
- } while (pv[ply] != MOVE_NONE);
-
- while (ply) pos.undo_move(pv[--ply]);
-}
+ std::stringstream ss;
+ int elapsed = Time.elapsed() + 1;
+ const RootMoves& rootMoves = pos.this_thread()->rootMoves;
+ size_t PVIdx = pos.this_thread()->PVIdx;
+ size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
+ uint64_t nodes_searched = Threads.nodes_searched();
-
-/// Thread::idle_loop() is where the thread is parked when it has no work to do
-
-void Thread::idle_loop() {
-
- // Pointer 'this_sp' is not null only if we are called from split(), and not
- // at the thread creation. So it means we are the split point's master.
- SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
-
- assert(!this_sp || (this_sp->masterThread == this && searching));
-
- while (true)
+ for (size_t i = 0; i < multiPV; ++i)
{
- // If we are not searching, wait for a condition to be signaled instead of
- // wasting CPU time polling for work.
- while ((!searching && Threads.sleepWhileIdle) || exit)
- {
- if (exit)
- {
- assert(!this_sp);
- return;
- }
-
- // Grab the lock to avoid races with Thread::notify_one()
- mutex.lock();
+ bool updated = (i <= PVIdx);
- // If we are master and all slaves have finished then exit idle_loop
- if (this_sp && !this_sp->slavesMask)
- {
- mutex.unlock();
- break;
- }
+ if (depth == ONE_PLY && !updated)
+ continue;
- // Do sleep after retesting sleep conditions under lock protection, in
- // particular we need to avoid a deadlock in case a master thread has,
- // in the meanwhile, allocated us and sent the notify_one() call before
- // we had the chance to grab the lock.
- if (!searching && !exit)
- sleepCondition.wait(mutex);
+ Depth d = updated ? depth : depth - ONE_PLY;
+ Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
- mutex.unlock();
- }
+ bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
+ v = tb ? TB::Score : v;
- // If this thread has been assigned work, launch a search
- if (searching)
- {
- assert(!exit);
+ if (ss.rdbuf()->in_avail()) // Not at first line
+ ss << "\n";
- Threads.mutex.lock();
+ ss << "info"
+ << " depth " << d / ONE_PLY
+ << " seldepth " << pos.this_thread()->maxPly
+ << " multipv " << i + 1
+ << " score " << UCI::value(v);
- assert(searching);
- assert(activeSplitPoint);
- SplitPoint* sp = activeSplitPoint;
+ if (!tb && i == PVIdx)
+ ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
- Threads.mutex.unlock();
+ ss << " nodes " << nodes_searched
+ << " nps " << nodes_searched * 1000 / elapsed;
- Stack stack[MAX_PLY_PLUS_6], *ss = stack+2; // To allow referencing (ss-2)
- Position pos(*sp->pos, this);
+ if (elapsed > 1000) // Earlier makes little sense
+ ss << " hashfull " << TT.hashfull();
- std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
- ss->splitPoint = sp;
+ ss << " tbhits " << TB::Hits
+ << " time " << elapsed
+ << " pv";
- sp->mutex.lock();
+ for (Move m : rootMoves[i].pv)
+ ss << " " << UCI::move(m, pos.is_chess960());
+ }
- assert(activePosition == NULL);
+ return ss.str();
+}
- activePosition = &pos;
- switch (sp->nodeType) {
- case Root:
- search<SplitPointRoot>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
- break;
- case PV:
- search<SplitPointPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
- break;
- case NonPV:
- search<SplitPointNonPV>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
- break;
- default:
- assert(false);
- }
+/// RootMove::extract_ponder_from_tt() is called in case we have no ponder move
+/// before exiting the search, for instance, in case we stop the search during a
+/// fail high at root. We try hard to have a ponder move to return to the GUI,
+/// otherwise in case of 'ponder on' we have nothing to think on.
- assert(searching);
+bool RootMove::extract_ponder_from_tt(Position& pos)
+{
+ StateInfo st;
+ bool ttHit;
- searching = false;
- activePosition = NULL;
- sp->slavesMask &= ~(1ULL << idx);
- sp->nodes += pos.nodes_searched();
+ assert(pv.size() == 1);
- // Wake up master thread so to allow it to return from the idle loop
- // in case we are the last slave of the split point.
- if ( Threads.sleepWhileIdle
- && this != sp->masterThread
- && !sp->slavesMask)
- {
- assert(!sp->masterThread->searching);
- sp->masterThread->notify_one();
- }
+ pos.do_move(pv[0], st, pos.gives_check(pv[0]));
+ TTEntry* tte = TT.probe(pos.key(), ttHit);
- // After releasing the lock we cannot access anymore any SplitPoint
- // related data in a safe way becuase it could have been released under
- // our feet by the sp master. Also accessing other Thread objects is
- // unsafe because if we are exiting there is a chance are already freed.
- sp->mutex.unlock();
- }
+ if (ttHit)
+ {
+ Move m = tte->move(); // Local copy to be SMP safe
+ if (MoveList<LEGAL>(pos).contains(m))
+ pv.push_back(m);
+ }
- // If this thread is the master of a split point and all slaves have finished
- // their work at this split point, return from the idle loop.
- if (this_sp && !this_sp->slavesMask)
- {
- this_sp->mutex.lock();
- bool finished = !this_sp->slavesMask; // Retest under lock protection
- this_sp->mutex.unlock();
- if (finished)
- return;
- }
- }
+ pos.undo_move(pv[0]);
+ return pv.size() > 1;
}
+void Tablebases::filter_root_moves(Position& pos, Search::RootMoves& rootMoves) {
-/// check_time() is called by the timer thread when the timer triggers. It is
-/// used to print debug info and, more important, to detect when we are out of
-/// available time and so stop the search.
-
-void check_time() {
-
- static Time::point lastInfoTime = Time::now();
- int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
+ Hits = 0;
+ RootInTB = false;
+ UseRule50 = Options["Syzygy50MoveRule"];
+ ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
+ Cardinality = Options["SyzygyProbeLimit"];
- if (Time::now() - lastInfoTime >= 1000)
- {
- lastInfoTime = Time::now();
- dbg_print();
- }
-
- if (Limits.ponder)
- return;
-
- if (Limits.nodes)
- {
- Threads.mutex.lock();
-
- nodes = RootPos.nodes_searched();
-
- // Loop across all split points and sum accumulated SplitPoint nodes plus
- // all the currently active positions nodes.
- for (size_t i = 0; i < Threads.size(); ++i)
- for (int j = 0; j < Threads[i]->splitPointsSize; ++j)
- {
- SplitPoint& sp = Threads[i]->splitPoints[j];
+ // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
+ if (Cardinality > MaxCardinality)
+ {
+ Cardinality = MaxCardinality;
+ ProbeDepth = DEPTH_ZERO;
+ }
- sp.mutex.lock();
+ if (Cardinality < popcount(pos.pieces()) || pos.can_castle(ANY_CASTLING))
+ return;
- nodes += sp.nodes;
- Bitboard sm = sp.slavesMask;
- while (sm)
- {
- Position* pos = Threads[pop_lsb(&sm)]->activePosition;
- if (pos)
- nodes += pos->nodes_searched();
- }
+ // 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);
- sp.mutex.unlock();
- }
+ if (RootInTB)
+ Cardinality = 0; // Do not probe tablebases during the search
- Threads.mutex.unlock();
- }
+ 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);
- Time::point elapsed = Time::now() - SearchTime;
- bool stillAtFirstMove = Signals.firstRootMove
- && !Signals.failedLowAtRoot
- && elapsed > TimeMgr.available_time();
+ // Only probe during search if winning
+ if (RootInTB && TB::Score <= VALUE_DRAW)
+ Cardinality = 0;
+ }
- bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerResolution
- || stillAtFirstMove;
+ if (RootInTB)
+ {
+ Hits = rootMoves.size();
- if ( (Limits.use_time_management() && noMoreTime)
- || (Limits.movetime && elapsed >= Limits.movetime)
- || (Limits.nodes && nodes >= Limits.nodes))
- Signals.stop = true;
+ if (!UseRule50)
+ TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1
+ : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1
+ : VALUE_DRAW;
+ }
}