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droidfish/DroidFish/jni/stockfish/search.cpp
Peter Osterlund ed834bdfbd DroidFish: Updated Stockfish engine to version 2.1.1.
2011-11-19 10:11:26 +00:00

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/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, 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
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Stockfish is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <cassert>
#include <cmath>
#include <cstring>
#include <fstream>
#include <iostream>
#include <sstream>
#include <vector>
#include "book.h"
#include "evaluate.h"
#include "history.h"
#include "misc.h"
#include "move.h"
#include "movegen.h"
#include "movepick.h"
#include "search.h"
#include "timeman.h"
#include "thread.h"
#include "tt.h"
#include "ucioption.h"
using std::cout;
using std::endl;
namespace {
// Set to true to force running with one thread. Used for debugging
const bool FakeSplit = false;
// Different node types, used as template parameter
enum NodeType { NonPV, PV };
// RootMove struct is used for moves at the root of the tree. For each root
// move, we store two scores, a node count, and a PV (really a refutation
// in the case of moves which fail low). Value pv_score is normally set at
// -VALUE_INFINITE for all non-pv moves, while non_pv_score is computed
// according to the order in which moves are returned by MovePicker.
struct RootMove {
RootMove();
RootMove(const RootMove& rm) { *this = rm; }
RootMove& operator=(const RootMove& rm);
// RootMove::operator<() is the comparison function used when
// sorting the moves. A move m1 is considered to be better
// than a move m2 if it has an higher pv_score, or if it has
// equal pv_score but m1 has the higher non_pv_score. In this way
// we are guaranteed that PV moves are always sorted as first.
bool operator<(const RootMove& m) const {
return pv_score != m.pv_score ? pv_score < m.pv_score
: non_pv_score < m.non_pv_score;
}
void extract_pv_from_tt(Position& pos);
void insert_pv_in_tt(Position& pos);
std::string pv_info_to_uci(Position& pos, int depth, int selDepth,
Value alpha, Value beta, int pvIdx);
int64_t nodes;
Value pv_score;
Value non_pv_score;
Move pv[PLY_MAX_PLUS_2];
};
// RootMoveList struct is just a vector of RootMove objects,
// with an handful of methods above the standard ones.
struct RootMoveList : public std::vector<RootMove> {
typedef std::vector<RootMove> Base;
void init(Position& pos, Move searchMoves[]);
void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
int bestMoveChanges;
};
// MovePickerExt template class extends MovePicker and allows to choose at compile
// time the proper moves source according to the type of node. In the default case
// we simply create and use a standard MovePicker object.
template<bool SpNode, bool Root> struct MovePickerExt : public MovePicker {
MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
: MovePicker(p, ttm, d, h, ss, b) {}
RootMoveList::iterator rm; // Dummy, needed to compile
};
// In case of a SpNode we use split point's shared MovePicker object as moves source
template<> struct MovePickerExt<true, false> : public MovePicker {
MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
: MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
Move get_next_move() { return mp->get_next_move(); }
RootMoveList::iterator rm; // Dummy, needed to compile
MovePicker* mp;
};
// In case of a Root node we use RootMoveList as moves source
template<> struct MovePickerExt<false, true> : public MovePicker {
MovePickerExt(const Position&, Move, Depth, const History&, SearchStack*, Value);
Move get_next_move();
RootMoveList::iterator rm;
bool firstCall;
};
/// Constants
// Lookup table to check if a Piece is a slider and its access function
const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
inline bool piece_is_slider(Piece p) { return Slidings[p]; }
// Step 6. Razoring
// Maximum depth for razoring
const Depth RazorDepth = 4 * ONE_PLY;
// Dynamic razoring margin based on depth
inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
// Maximum depth for use of dynamic threat detection when null move fails low
const Depth ThreatDepth = 5 * ONE_PLY;
// Step 9. Internal iterative deepening
// Minimum depth for use of internal iterative deepening
const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
// At Non-PV nodes we do an internal iterative deepening search
// when the static evaluation is bigger then beta - IIDMargin.
const Value IIDMargin = Value(0x100);
// Step 11. Decide the new search depth
// Extensions. Array index 0 is used for non-PV nodes, index 1 for PV nodes
const Depth CheckExtension[] = { ONE_PLY / 2, ONE_PLY / 1 };
const Depth PawnEndgameExtension[] = { ONE_PLY / 1, ONE_PLY / 1 };
const Depth PawnPushTo7thExtension[] = { ONE_PLY / 2, ONE_PLY / 2 };
const Depth PassedPawnExtension[] = { DEPTH_ZERO, ONE_PLY / 2 };
// Minimum depth for use of singular extension
const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
// Step 12. Futility pruning
// Futility margin for quiescence search
const Value FutilityMarginQS = Value(0x80);
// Futility lookup tables (initialized at startup) and their access functions
Value FutilityMargins[16][64]; // [depth][moveNumber]
int FutilityMoveCounts[32]; // [depth]
inline Value futility_margin(Depth d, int mn) {
return d < 7 * ONE_PLY ? FutilityMargins[Max(d, 1)][Min(mn, 63)]
: 2 * VALUE_INFINITE;
}
inline int futility_move_count(Depth d) {
return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
}
// Step 14. Reduced search
// Reduction lookup tables (initialized at startup) and their access function
int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
template <NodeType PV> inline Depth reduction(Depth d, int mn) {
return (Depth) Reductions[PV][Min(d / ONE_PLY, 63)][Min(mn, 63)];
}
// Easy move margin. An easy move candidate must be at least this much
// better than the second best move.
const Value EasyMoveMargin = Value(0x200);
/// Namespace variables
// Root move list
RootMoveList Rml;
// MultiPV mode
int MultiPV, UCIMultiPV;
// Time management variables
bool StopOnPonderhit, FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
TimeManager TimeMgr;
SearchLimits Limits;
// Log file
std::ofstream LogFile;
// Skill level adjustment
int SkillLevel;
bool SkillLevelEnabled;
// Node counters, used only by thread[0] but try to keep in different cache
// lines (64 bytes each) from the heavy multi-thread read accessed variables.
bool SendSearchedNodes;
int NodesSincePoll;
int NodesBetweenPolls = 30000;
// History table
History H;
/// Local functions
Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
template <NodeType PvNode, bool SpNode, bool Root>
Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
template <NodeType PvNode>
Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
template <NodeType PvNode>
inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO)
: search<PvNode, false, false>(pos, ss, alpha, beta, depth);
}
template <NodeType PvNode>
Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool* dangerous);
bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
bool connected_moves(const Position& pos, Move m1, Move m2);
Value value_to_tt(Value v, int ply);
Value value_from_tt(Value v, int ply);
bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
bool connected_threat(const Position& pos, Move m, Move threat);
Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
void update_gains(const Position& pos, Move move, Value before, Value after);
void do_skill_level(Move* best, Move* ponder);
int current_search_time(int set = 0);
std::string value_to_uci(Value v);
std::string speed_to_uci(int64_t nodes);
void poll(const Position& pos);
void wait_for_stop_or_ponderhit();
// Overload operator<<() to make it easier to print moves in a coordinate
// notation compatible with UCI protocol.
std::ostream& operator<<(std::ostream& os, Move m) {
bool chess960 = (os.iword(0) != 0); // See set960()
return os << move_to_uci(m, chess960);
}
// When formatting a move for std::cout we must know if we are in Chess960
// or not. To keep using the handy operator<<() on the move the trick is to
// embed this flag in the stream itself. Function-like named enum set960 is
// used as a custom manipulator and the stream internal general-purpose array,
// accessed through ios_base::iword(), is used to pass the flag to the move's
// operator<<() that will read it to properly format castling moves.
enum set960 {};
std::ostream& operator<< (std::ostream& os, const set960& f) {
os.iword(0) = int(f);
return os;
}
} // namespace
/// init_search() is called during startup to initialize various lookup tables
void init_search() {
int d; // depth (ONE_PLY == 2)
int hd; // half depth (ONE_PLY == 1)
int mc; // moveCount
// Init reductions array
for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
{
double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
Reductions[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
Reductions[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
}
// 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);
// Init futility move count array
for (d = 0; d < 32; d++)
FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
}
/// 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.
int64_t perft(Position& pos, Depth depth) {
MoveStack mlist[MAX_MOVES];
StateInfo st;
Move m;
int64_t sum = 0;
// Generate all legal moves
MoveStack* last = generate<MV_LEGAL>(pos, mlist);
// If we are at the last ply we don't need to do and undo
// the moves, just to count them.
if (depth <= ONE_PLY)
return int(last - mlist);
// Loop through all legal moves
CheckInfo ci(pos);
for (MoveStack* cur = mlist; cur != last; cur++)
{
m = cur->move;
pos.do_move(m, st, ci, pos.move_gives_check(m, ci));
sum += perft(pos, depth - ONE_PLY);
pos.undo_move(m);
}
return sum;
}
/// think() is the external interface to Stockfish's search, and is called when
/// the program receives the UCI 'go' command. It initializes various global
/// variables, and calls id_loop(). It returns false when a "quit" command is
/// received during the search.
bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
static Book book;
// Initialize global search-related variables
StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
NodesSincePoll = 0;
current_search_time(get_system_time());
Limits = limits;
TimeMgr.init(Limits, pos.startpos_ply_counter());
// Set best NodesBetweenPolls interval to avoid lagging under time pressure
if (Limits.maxNodes)
NodesBetweenPolls = Min(Limits.maxNodes, 30000);
else if (Limits.time && Limits.time < 1000)
NodesBetweenPolls = 1000;
else if (Limits.time && Limits.time < 5000)
NodesBetweenPolls = 5000;
else
NodesBetweenPolls = 30000;
NodesBetweenPolls /= 16;
// Look for a book move
if (Options["OwnBook"].value<bool>())
{
if (Options["Book File"].value<std::string>() != book.name())
book.open(Options["Book File"].value<std::string>());
Move bookMove = book.get_move(pos, Options["Best Book Move"].value<bool>());
if (bookMove != MOVE_NONE)
{
if (Limits.ponder)
wait_for_stop_or_ponderhit();
cout << "bestmove " << bookMove << endl;
return !QuitRequest;
}
}
// Read UCI options
UCIMultiPV = Options["MultiPV"].value<int>();
SkillLevel = Options["Skill Level"].value<int>();
read_evaluation_uci_options(pos.side_to_move());
Threads.read_uci_options();
// If needed allocate pawn and material hash tables and adjust TT size
Threads.init_hash_tables();
TT.set_size(Options["Hash"].value<int>());
if (Options["Clear Hash"].value<bool>())
{
Options["Clear Hash"].set_value("false");
TT.clear();
}
// Do we have to play with skill handicap? In this case enable MultiPV that
// we will use behind the scenes to retrieve a set of possible moves.
SkillLevelEnabled = (SkillLevel < 20);
MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
// Wake up needed threads and reset maxPly counter
for (int i = 0; i < Threads.size(); i++)
{
Threads[i].wake_up();
Threads[i].maxPly = 0;
}
// Write to log file and keep it open to be accessed during the search
if (Options["Use Search Log"].value<bool>())
{
std::string name = Options["Search Log Filename"].value<std::string>();
LogFile.open(name.c_str(), std::ios::out | std::ios::app);
if (LogFile.is_open())
LogFile << "\nSearching: " << pos.to_fen()
<< "\ninfinite: " << Limits.infinite
<< " ponder: " << Limits.ponder
<< " time: " << Limits.time
<< " increment: " << Limits.increment
<< " moves to go: " << Limits.movesToGo
<< endl;
}
// We're ready to start thinking. Call the iterative deepening loop function
Move ponderMove = MOVE_NONE;
Move bestMove = id_loop(pos, searchMoves, &ponderMove);
cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
// Write final search statistics and close log file
if (LogFile.is_open())
{
int t = current_search_time();
LogFile << "Nodes: " << pos.nodes_searched()
<< "\nNodes/second: " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
<< "\nBest move: " << move_to_san(pos, bestMove);
StateInfo st;
pos.do_move(bestMove, st);
LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
pos.undo_move(bestMove); // Return from think() with unchanged position
LogFile.close();
}
// This makes all the threads to go to sleep
Threads.set_size(1);
// If we are pondering or in infinite search, we shouldn't print the
// best move before we are told to do so.
if (!StopRequest && (Limits.ponder || Limits.infinite))
wait_for_stop_or_ponderhit();
// Could be MOVE_NONE when searching on a stalemate position
cout << "bestmove " << bestMove;
// UCI protol is not clear on allowing sending an empty ponder move, instead
// it is clear that ponder move is optional. So skip it if empty.
if (ponderMove != MOVE_NONE)
cout << " ponder " << ponderMove;
cout << endl;
return !QuitRequest;
}
namespace {
// 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.
Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
SearchStack ss[PLY_MAX_PLUS_2];
Value bestValues[PLY_MAX_PLUS_2];
int bestMoveChanges[PLY_MAX_PLUS_2];
int depth, selDepth, aspirationDelta;
Value value, alpha, beta;
Move bestMove, easyMove, skillBest, skillPonder;
// Initialize stuff before a new search
memset(ss, 0, 4 * sizeof(SearchStack));
TT.new_search();
H.clear();
*ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
depth = aspirationDelta = 0;
alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
// Moves to search are verified and copied
Rml.init(pos, searchMoves);
// Handle special case of searching on a mate/stalemate position
if (Rml.size() == 0)
{
cout << "info depth 0 score "
<< value_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW)
<< endl;
return MOVE_NONE;
}
// Iterative deepening loop until requested to stop or target depth reached
while (!StopRequest && ++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth))
{
Rml.bestMoveChanges = 0;
cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
// Calculate dynamic aspiration window based on previous iterations
if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
{
int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
}
// Start with a small aspiration window and, in case of fail high/low,
// research with bigger window until not failing high/low anymore.
do {
// Search starting from ss+1 to allow calling update_gains()
value = search<PV, false, true>(pos, ss+1, alpha, beta, depth * ONE_PLY);
// Write PV back to transposition table in case the relevant entries
// have been overwritten during the search.
for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
Rml[i].insert_pv_in_tt(pos);
// Value cannot be trusted. Break out immediately!
if (StopRequest)
break;
assert(value >= alpha);
// In case of failing high/low increase aspiration window and research,
// otherwise exit the fail high/low loop.
if (value >= beta)
{
beta = Min(beta + aspirationDelta, VALUE_INFINITE);
aspirationDelta += aspirationDelta / 2;
}
else if (value <= alpha)
{
AspirationFailLow = true;
StopOnPonderhit = false;
alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
aspirationDelta += aspirationDelta / 2;
}
else
break;
} while (abs(value) < VALUE_KNOWN_WIN);
// Collect info about search result
bestMove = Rml[0].pv[0];
*ponderMove = Rml[0].pv[1];
bestValues[depth] = value;
bestMoveChanges[depth] = Rml.bestMoveChanges;
// Do we need to pick now the best and the ponder moves ?
if (SkillLevelEnabled && depth == 1 + SkillLevel)
do_skill_level(&skillBest, &skillPonder);
// Retrieve max searched depth among threads
selDepth = 0;
for (int i = 0; i < Threads.size(); i++)
if (Threads[i].maxPly > selDepth)
selDepth = Threads[i].maxPly;
// Send PV line to GUI and to log file
for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
cout << Rml[i].pv_info_to_uci(pos, depth, selDepth, alpha, beta, i) << endl;
if (LogFile.is_open())
LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
// Init easyMove after first iteration or drop if differs from the best move
if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
easyMove = bestMove;
else if (bestMove != easyMove)
easyMove = MOVE_NONE;
// Check for some early stop condition
if (!StopRequest && Limits.useTimeManagement())
{
// Stop search early when the last two iterations returned a mate score
if ( depth >= 5
&& abs(bestValues[depth]) >= VALUE_MATE_IN_PLY_MAX
&& abs(bestValues[depth - 1]) >= VALUE_MATE_IN_PLY_MAX)
StopRequest = true;
// Stop search early if one move seems to be much better than the
// others or if there is only a single legal move. Also in the latter
// case we search up to some depth anyway to get a proper score.
if ( depth >= 7
&& easyMove == bestMove
&& ( Rml.size() == 1
||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
&& current_search_time() > TimeMgr.available_time() / 16)
||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
&& current_search_time() > TimeMgr.available_time() / 32)))
StopRequest = true;
// Take in account some extra time if the best move has changed
if (depth > 4 && depth < 50)
TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth - 1]);
// 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 (current_search_time() > (TimeMgr.available_time() * 62) / 100)
StopRequest = true;
// If we are allowed to ponder do not stop the search now but keep pondering
if (StopRequest && Limits.ponder)
{
StopRequest = false;
StopOnPonderhit = true;
}
}
}
// When using skills overwrite best and ponder moves with the sub-optimal ones
if (SkillLevelEnabled)
{
if (skillBest == MOVE_NONE) // Still unassigned ?
do_skill_level(&skillBest, &skillPonder);
bestMove = skillBest;
*ponderMove = skillPonder;
}
return bestMove;
}
// 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.
template <NodeType PvNode, bool SpNode, bool Root>
Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
assert(beta > alpha && beta <= VALUE_INFINITE);
assert(PvNode || alpha == beta - 1);
assert(pos.thread() >= 0 && pos.thread() < Threads.size());
Move movesSearched[MAX_MOVES];
int64_t nodes;
StateInfo st;
const TTEntry *tte;
Key posKey;
Move ttMove, move, excludedMove, threatMove;
Depth ext, newDepth;
ValueType vt;
Value bestValue, value, oldAlpha;
Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
bool isPvMove, inCheck, singularExtensionNode, givesCheck, captureOrPromotion, dangerous, isBadCap;
int moveCount = 0, playedMoveCount = 0;
int threadID = pos.thread();
SplitPoint* sp = NULL;
refinedValue = bestValue = value = -VALUE_INFINITE;
oldAlpha = alpha;
inCheck = pos.in_check();
ss->ply = (ss-1)->ply + 1;
// Used to send selDepth info to GUI
if (PvNode && Threads[threadID].maxPly < ss->ply)
Threads[threadID].maxPly = ss->ply;
if (SpNode)
{
sp = ss->sp;
tte = NULL;
ttMove = excludedMove = MOVE_NONE;
threatMove = sp->threatMove;
goto split_point_start;
}
else if (Root)
bestValue = alpha;
// Step 1. Initialize node and poll. Polling can abort search
ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
(ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
(ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
{
NodesSincePoll = 0;
poll(pos);
}
// Step 2. Check for aborted search and immediate draw
if (( StopRequest
|| Threads[threadID].cutoff_occurred()
|| pos.is_draw()
|| ss->ply > PLY_MAX) && !Root)
return VALUE_DRAW;
// Step 3. Mate distance pruning
alpha = Max(value_mated_in(ss->ply), alpha);
beta = Min(value_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.
excludedMove = ss->excludedMove;
posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
tte = TT.probe(posKey);
ttMove = tte ? tte->move() : MOVE_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.
if ( !Root
&& tte
&& (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
: ok_to_use_TT(tte, depth, beta, ss->ply)))
{
TT.refresh(tte);
ss->bestMove = ttMove; // Can be MOVE_NONE
return value_from_tt(tte->value(), ss->ply);
}
// Step 5. Evaluate the position statically and update parent's gain statistics
if (inCheck)
ss->eval = ss->evalMargin = VALUE_NONE;
else if (tte)
{
assert(tte->static_value() != VALUE_NONE);
ss->eval = tte->static_value();
ss->evalMargin = tte->static_value_margin();
refinedValue = refine_eval(tte, ss->eval, ss->ply);
}
else
{
refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
}
// Save gain for the parent non-capture move
update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
// Step 6. Razoring (is omitted in PV nodes)
if ( !PvNode
&& depth < RazorDepth
&& !inCheck
&& refinedValue + razor_margin(depth) < beta
&& ttMove == MOVE_NONE
&& abs(beta) < VALUE_MATE_IN_PLY_MAX
&& !pos.has_pawn_on_7th(pos.side_to_move()))
{
Value rbeta = beta - razor_margin(depth);
Value v = qsearch<NonPV>(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.
return v;
}
// Step 7. Static null move pruning (is omitted in PV nodes)
// 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 < RazorDepth
&& !inCheck
&& refinedValue - futility_margin(depth, 0) >= beta
&& abs(beta) < VALUE_MATE_IN_PLY_MAX
&& pos.non_pawn_material(pos.side_to_move()))
return refinedValue - futility_margin(depth, 0);
// Step 8. Null move search with verification search (is omitted in PV nodes)
if ( !PvNode
&& !ss->skipNullMove
&& depth > ONE_PLY
&& !inCheck
&& refinedValue >= beta
&& abs(beta) < VALUE_MATE_IN_PLY_MAX
&& pos.non_pawn_material(pos.side_to_move()))
{
ss->currentMove = MOVE_NULL;
// Null move dynamic reduction based on depth
int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
// Null move dynamic reduction based on value
if (refinedValue - PawnValueMidgame > beta)
R++;
pos.do_null_move(st);
(ss+1)->skipNullMove = true;
nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
(ss+1)->skipNullMove = false;
pos.undo_null_move();
if (nullValue >= beta)
{
// Do not return unproven mate scores
if (nullValue >= VALUE_MATE_IN_PLY_MAX)
nullValue = beta;
if (depth < 6 * ONE_PLY)
return nullValue;
// Do verification search at high depths
ss->skipNullMove = true;
Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
ss->skipNullMove = 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)->bestMove;
if ( depth < ThreatDepth
&& (ss-1)->reduction
&& threatMove != MOVE_NONE
&& connected_moves(pos, (ss-1)->currentMove, threatMove))
return beta - 1;
}
}
// Step 9. Internal iterative deepening
if ( depth >= IIDDepth[PvNode]
&& ttMove == MOVE_NONE
&& (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
{
Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
ss->skipNullMove = true;
search<PvNode>(pos, ss, alpha, beta, d);
ss->skipNullMove = false;
ttMove = ss->bestMove;
tte = TT.probe(posKey);
}
split_point_start: // At split points actual search starts from here
// Initialize a MovePicker object for the current position
MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
CheckInfo ci(pos);
ss->bestMove = MOVE_NONE;
futilityBase = ss->eval + ss->evalMargin;
singularExtensionNode = !Root
&& !SpNode
&& depth >= SingularExtensionDepth[PvNode]
&& tte
&& tte->move()
&& !excludedMove // Do not allow recursive singular extension search
&& (tte->type() & VALUE_TYPE_LOWER)
&& tte->depth() >= depth - 3 * ONE_PLY;
if (SpNode)
{
lock_grab(&(sp->lock));
bestValue = sp->bestValue;
}
// Step 10. Loop through moves
// Loop through all legal moves until no moves remain or a beta cutoff occurs
while ( bestValue < beta
&& (move = mp.get_next_move()) != MOVE_NONE
&& !Threads[threadID].cutoff_occurred())
{
assert(move_is_ok(move));
if (SpNode)
{
moveCount = ++sp->moveCount;
lock_release(&(sp->lock));
}
else if (move == excludedMove)
continue;
else
moveCount++;
if (Root)
{
// This is used by time management
FirstRootMove = (moveCount == 1);
// Save the current node count before the move is searched
nodes = pos.nodes_searched();
// If it's time to send nodes info, do it here where we have the
// correct accumulated node counts searched by each thread.
if (SendSearchedNodes)
{
SendSearchedNodes = false;
cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
}
if (current_search_time() > 2000)
cout << "info currmove " << move
<< " currmovenumber " << moveCount << endl;
}
// At Root and at first iteration do a PV search on all the moves to score root moves
isPvMove = (PvNode && moveCount <= (Root ? depth <= ONE_PLY ? 1000 : MultiPV : 1));
givesCheck = pos.move_gives_check(move, ci);
captureOrPromotion = pos.move_is_capture_or_promotion(move);
// Step 11. Decide the new search depth
ext = extension<PvNode>(pos, move, captureOrPromotion, givesCheck, &dangerous);
// 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.
if ( singularExtensionNode
&& move == tte->move()
&& ext < ONE_PLY)
{
Value ttValue = value_from_tt(tte->value(), ss->ply);
if (abs(ttValue) < VALUE_KNOWN_WIN)
{
Value rBeta = ttValue - int(depth);
ss->excludedMove = move;
ss->skipNullMove = true;
Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
ss->skipNullMove = false;
ss->excludedMove = MOVE_NONE;
ss->bestMove = MOVE_NONE;
if (v < rBeta)
ext = ONE_PLY;
}
}
// Update current move (this must be done after singular extension search)
ss->currentMove = move;
newDepth = depth - ONE_PLY + ext;
// Step 12. Futility pruning (is omitted in PV nodes)
if ( !PvNode
&& !captureOrPromotion
&& !inCheck
&& !dangerous
&& move != ttMove
&& !move_is_castle(move))
{
// Move count based pruning
if ( moveCount >= futility_move_count(depth)
&& (!threatMove || !connected_threat(pos, move, threatMove))
&& bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
{
if (SpNode)
lock_grab(&(sp->lock));
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<NonPV>(depth, moveCount);
futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
+ H.gain(pos.piece_on(move_from(move)), move_to(move));
if (futilityValueScaled < beta)
{
if (SpNode)
{
lock_grab(&(sp->lock));
if (futilityValueScaled > sp->bestValue)
sp->bestValue = bestValue = futilityValueScaled;
}
else if (futilityValueScaled > bestValue)
bestValue = futilityValueScaled;
continue;
}
// Prune moves with negative SEE at low depths
if ( predictedDepth < 2 * ONE_PLY
&& bestValue > VALUE_MATED_IN_PLY_MAX
&& pos.see_sign(move) < 0)
{
if (SpNode)
lock_grab(&(sp->lock));
continue;
}
}
// Bad capture detection. Will be used by prob-cut search
isBadCap = depth >= 3 * ONE_PLY
&& depth < 8 * ONE_PLY
&& captureOrPromotion
&& move != ttMove
&& !dangerous
&& !move_is_promotion(move)
&& abs(alpha) < VALUE_MATE_IN_PLY_MAX
&& pos.see_sign(move) < 0;
// Step 13. Make the move
pos.do_move(move, st, ci, givesCheck);
if (!SpNode && !captureOrPromotion)
movesSearched[playedMoveCount++] = move;
// Step extra. pv search (only in PV nodes)
// The first move in list is the expected PV
if (isPvMove)
{
// Aspiration window is disabled in multi-pv case
if (Root && MultiPV > 1)
alpha = -VALUE_INFINITE;
value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
}
else
{
// Step 14. Reduced depth search
// If the move fails high will be re-searched at full depth.
bool doFullDepthSearch = true;
alpha = SpNode ? sp->alpha : alpha;
if ( depth >= 3 * ONE_PLY
&& !captureOrPromotion
&& !dangerous
&& !move_is_castle(move)
&& ss->killers[0] != move
&& ss->killers[1] != move)
{
ss->reduction = reduction<PvNode>(depth, moveCount);
if (ss->reduction)
{
Depth d = newDepth - ss->reduction;
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
doFullDepthSearch = (value > alpha);
}
ss->reduction = DEPTH_ZERO; // Restore original reduction
}
// Probcut search for bad captures. If a reduced search returns a value
// very below beta then we can (almost) safely prune the bad capture.
if (isBadCap)
{
ss->reduction = 3 * ONE_PLY;
Value rAlpha = alpha - 300;
Depth d = newDepth - ss->reduction;
value = -search<NonPV>(pos, ss+1, -(rAlpha+1), -rAlpha, d);
doFullDepthSearch = (value > rAlpha);
ss->reduction = DEPTH_ZERO; // Restore original reduction
}
// Step 15. Full depth search
if (doFullDepthSearch)
{
alpha = SpNode ? sp->alpha : alpha;
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
// Step extra. pv search (only in PV nodes)
// Search only for possible new PV nodes, if instead value >= beta then
// parent node fails low with value <= alpha and tries another move.
if (PvNode && value > alpha && (Root || value < beta))
value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
}
}
// Step 16. Undo move
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
// Step 17. Check for new best move
if (SpNode)
{
lock_grab(&(sp->lock));
bestValue = sp->bestValue;
alpha = sp->alpha;
}
if (value > bestValue && !(SpNode && Threads[threadID].cutoff_occurred()))
{
bestValue = value;
if (SpNode)
sp->bestValue = value;
if (!Root && value > alpha)
{
if (PvNode && value < beta) // We want always alpha < beta
{
alpha = value;
if (SpNode)
sp->alpha = value;
}
else if (SpNode)
sp->is_betaCutoff = true;
if (value == value_mate_in(ss->ply + 1))
ss->mateKiller = move;
ss->bestMove = move;
if (SpNode)
sp->ss->bestMove = move;
}
}
if (Root)
{
// Finished searching the move. If StopRequest 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 break out of the loop without updating the best
// move and/or PV.
if (StopRequest)
break;
// Remember searched nodes counts for this move
mp.rm->nodes += pos.nodes_searched() - nodes;
// PV move or new best move ?
if (isPvMove || value > alpha)
{
// Update PV
ss->bestMove = move;
mp.rm->pv_score = value;
mp.rm->extract_pv_from_tt(pos);
// 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 (!isPvMove && MultiPV == 1)
Rml.bestMoveChanges++;
Rml.sort_multipv(moveCount);
// Update alpha. In multi-pv we don't use aspiration window, so
// set alpha equal to minimum score among the PV lines.
if (MultiPV > 1)
alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
else if (value > alpha)
alpha = value;
}
else
mp.rm->pv_score = -VALUE_INFINITE;
} // Root
// Step 18. Check for split
if ( !Root
&& !SpNode
&& depth >= Threads.min_split_depth()
&& bestValue < beta
&& Threads.available_slave_exists(threadID)
&& !StopRequest
&& !Threads[threadID].cutoff_occurred())
Threads.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
threatMove, moveCount, &mp, PvNode);
}
// Step 19. Check for mate and stalemate
// All legal moves have been searched and if there are
// no legal moves, it must be mate or stalemate.
// If one move was excluded return fail low score.
if (!SpNode && !moveCount)
return excludedMove ? oldAlpha : inCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
// Step 20. Update tables
// If the search is not aborted, update the transposition table,
// history counters, and killer moves.
if (!SpNode && !StopRequest && !Threads[threadID].cutoff_occurred())
{
move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
: bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
// Update killers and history only for non capture moves that fails high
if ( bestValue >= beta
&& !pos.move_is_capture_or_promotion(move))
{
if (move != ss->killers[0])
{
ss->killers[1] = ss->killers[0];
ss->killers[0] = move;
}
update_history(pos, move, depth, movesSearched, playedMoveCount);
}
}
if (SpNode)
{
// Here we have the lock still grabbed
sp->is_slave[threadID] = false;
sp->nodes += pos.nodes_searched();
lock_release(&(sp->lock));
}
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
return bestValue;
}
// qsearch() is the quiescence search function, which is called by the main
// search function when the remaining depth is zero (or, to be more precise,
// less than ONE_PLY).
template <NodeType PvNode>
Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
assert(PvNode || alpha == beta - 1);
assert(depth <= 0);
assert(pos.thread() >= 0 && pos.thread() < Threads.size());
StateInfo st;
Move ttMove, move;
Value bestValue, value, evalMargin, futilityValue, futilityBase;
bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
const TTEntry* tte;
Depth ttDepth;
Value oldAlpha = alpha;
ss->bestMove = ss->currentMove = MOVE_NONE;
ss->ply = (ss-1)->ply + 1;
// Check for an instant draw or maximum ply reached
if (ss->ply > PLY_MAX || pos.is_draw())
return VALUE_DRAW;
// 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.
inCheck = pos.in_check();
ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
// Transposition table lookup. At PV nodes, we don't use the TT for
// pruning, but only for move ordering.
tte = TT.probe(pos.get_key());
ttMove = (tte ? tte->move() : MOVE_NONE);
if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ss->ply))
{
ss->bestMove = ttMove; // Can be MOVE_NONE
return value_from_tt(tte->value(), ss->ply);
}
// Evaluate the position statically
if (inCheck)
{
bestValue = futilityBase = -VALUE_INFINITE;
ss->eval = evalMargin = VALUE_NONE;
enoughMaterial = false;
}
else
{
if (tte)
{
assert(tte->static_value() != VALUE_NONE);
evalMargin = tte->static_value_margin();
ss->eval = bestValue = tte->static_value();
}
else
ss->eval = bestValue = evaluate(pos, evalMargin);
update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
// Stand pat. Return immediately if static value is at least beta
if (bestValue >= beta)
{
if (!tte)
TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
return bestValue;
}
if (PvNode && bestValue > alpha)
alpha = bestValue;
// Futility pruning parameters, not needed when in check
futilityBase = ss->eval + evalMargin + FutilityMarginQS;
enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
}
// 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, H);
CheckInfo ci(pos);
// Loop through the moves until no moves remain or a beta cutoff occurs
while ( alpha < beta
&& (move = mp.get_next_move()) != MOVE_NONE)
{
assert(move_is_ok(move));
givesCheck = pos.move_gives_check(move, ci);
// Futility pruning
if ( !PvNode
&& !inCheck
&& !givesCheck
&& move != ttMove
&& enoughMaterial
&& !move_is_promotion(move)
&& !pos.move_is_passed_pawn_push(move))
{
futilityValue = futilityBase
+ pos.endgame_value_of_piece_on(move_to(move))
+ (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
if (futilityValue < alpha)
{
if (futilityValue > bestValue)
bestValue = futilityValue;
continue;
}
// Prune moves with negative or equal SEE
if ( futilityBase < beta
&& depth < DEPTH_ZERO
&& pos.see(move) <= 0)
continue;
}
// Detect non-capture evasions that are candidate to be pruned
evasionPrunable = inCheck
&& bestValue > VALUE_MATED_IN_PLY_MAX
&& !pos.move_is_capture(move)
&& !pos.can_castle(pos.side_to_move());
// Don't search moves with negative SEE values
if ( !PvNode
&& (!inCheck || evasionPrunable)
&& move != ttMove
&& !move_is_promotion(move)
&& pos.see_sign(move) < 0)
continue;
// Don't search useless checks
if ( !PvNode
&& !inCheck
&& givesCheck
&& move != ttMove
&& !pos.move_is_capture_or_promotion(move)
&& ss->eval + PawnValueMidgame / 4 < beta
&& !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
{
if (ss->eval + PawnValueMidgame / 4 > bestValue)
bestValue = ss->eval + PawnValueMidgame / 4;
continue;
}
// Update current move
ss->currentMove = move;
// Make and search the move
pos.do_move(move, st, ci, givesCheck);
value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
// New best move?
if (value > bestValue)
{
bestValue = value;
if (value > alpha)
{
alpha = value;
ss->bestMove = move;
}
}
}
// 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)
return value_mated_in(ss->ply);
// Update transposition table
ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
return bestValue;
}
// check_is_dangerous() tests if a checking move can be pruned in qsearch().
// bestValue is updated only when returning false because in that case move
// will be pruned.
bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
{
Bitboard b, occ, oldAtt, newAtt, kingAtt;
Square from, to, ksq, victimSq;
Piece pc;
Color them;
Value futilityValue, bv = *bestValue;
from = move_from(move);
to = move_to(move);
them = opposite_color(pos.side_to_move());
ksq = pos.king_square(them);
kingAtt = pos.attacks_from<KING>(ksq);
pc = pos.piece_on(from);
occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
oldAtt = pos.attacks_from(pc, from, occ);
newAtt = pos.attacks_from(pc, to, occ);
// Rule 1. Checks which give opponent's king at most one escape square are dangerous
b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
if (!(b && (b & (b - 1))))
return true;
// Rule 2. Queen contact check is very dangerous
if ( type_of_piece(pc) == QUEEN
&& bit_is_set(kingAtt, to))
return true;
// Rule 3. Creating new double threats with checks
b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
while (b)
{
victimSq = pop_1st_bit(&b);
futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
// Note that here we generate illegal "double move"!
if ( futilityValue >= beta
&& pos.see_sign(make_move(from, victimSq)) >= 0)
return true;
if (futilityValue > bv)
bv = futilityValue;
}
// Update bestValue only if check is not dangerous (because we will prune the move)
*bestValue = bv;
return false;
}
// connected_moves() tests whether two moves are 'connected' in the sense
// that the first move somehow made the second move possible (for instance
// if the moving piece is the same in both moves). The first move is assumed
// to be the move that was made to reach the current position, while the
// second move is assumed to be a move from the current position.
bool connected_moves(const Position& pos, Move m1, Move m2) {
Square f1, t1, f2, t2;
Piece p;
assert(m1 && move_is_ok(m1));
assert(m2 && move_is_ok(m2));
// Case 1: The moving piece is the same in both moves
f2 = move_from(m2);
t1 = move_to(m1);
if (f2 == t1)
return true;
// Case 2: The destination square for m2 was vacated by m1
t2 = move_to(m2);
f1 = move_from(m1);
if (t2 == f1)
return true;
// Case 3: Moving through the vacated square
if ( piece_is_slider(pos.piece_on(f2))
&& bit_is_set(squares_between(f2, t2), f1))
return true;
// Case 4: The destination square for m2 is defended by the moving piece in m1
p = pos.piece_on(t1);
if (bit_is_set(pos.attacks_from(p, t1), t2))
return true;
// Case 5: Discovered check, checking piece is the piece moved in m1
if ( piece_is_slider(p)
&& bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
&& !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
{
// discovered_check_candidates() works also if the Position's side to
// move is the opposite of the checking piece.
Color them = opposite_color(pos.side_to_move());
Bitboard dcCandidates = pos.discovered_check_candidates(them);
if (bit_is_set(dcCandidates, f2))
return true;
}
return false;
}
// value_to_tt() adjusts a mate score from "plies to mate from the root" to
// "plies to mate from the current ply". Non-mate scores are unchanged.
// The function is called before storing a value to the transposition table.
Value value_to_tt(Value v, int ply) {
if (v >= VALUE_MATE_IN_PLY_MAX)
return v + ply;
if (v <= VALUE_MATED_IN_PLY_MAX)
return v - ply;
return v;
}
// value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
// the transposition table to a mate score corrected for the current ply.
Value value_from_tt(Value v, int ply) {
if (v >= VALUE_MATE_IN_PLY_MAX)
return v - ply;
if (v <= VALUE_MATED_IN_PLY_MAX)
return v + ply;
return v;
}
// extension() decides whether a move should be searched with normal depth,
// or with extended depth. Certain classes of moves (checking moves, in
// particular) are searched with bigger depth than ordinary moves and in
// any case are marked as 'dangerous'. Note that also if a move is not
// extended, as example because the corresponding UCI option is set to zero,
// the move is marked as 'dangerous' so, at least, we avoid to prune it.
template <NodeType PvNode>
Depth extension(const Position& pos, Move m, bool captureOrPromotion,
bool moveIsCheck, bool* dangerous) {
assert(m != MOVE_NONE);
Depth result = DEPTH_ZERO;
*dangerous = moveIsCheck;
if (moveIsCheck && pos.see_sign(m) >= 0)
result += CheckExtension[PvNode];
if (pos.type_of_piece_on(move_from(m)) == PAWN)
{
Color c = pos.side_to_move();
if (relative_rank(c, move_to(m)) == RANK_7)
{
result += PawnPushTo7thExtension[PvNode];
*dangerous = true;
}
if (pos.pawn_is_passed(c, move_to(m)))
{
result += PassedPawnExtension[PvNode];
*dangerous = true;
}
}
if ( captureOrPromotion
&& pos.type_of_piece_on(move_to(m)) != PAWN
&& ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
- pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
&& !move_is_special(m))
{
result += PawnEndgameExtension[PvNode];
*dangerous = true;
}
return Min(result, ONE_PLY);
}
// connected_threat() tests whether it is safe to forward prune a move or if
// is somehow connected to the threat move returned by null search.
bool connected_threat(const Position& pos, Move m, Move threat) {
assert(move_is_ok(m));
assert(threat && move_is_ok(threat));
assert(!pos.move_gives_check(m));
assert(!pos.move_is_capture_or_promotion(m));
assert(!pos.move_is_passed_pawn_push(m));
Square mfrom, mto, tfrom, tto;
mfrom = move_from(m);
mto = move_to(m);
tfrom = move_from(threat);
tto = move_to(threat);
// Case 1: Don't prune moves which move the threatened piece
if (mfrom == tto)
return true;
// Case 2: If the threatened piece has value less than or equal to the
// value of the threatening piece, don't prune moves which defend it.
if ( pos.move_is_capture(threat)
&& ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
|| pos.type_of_piece_on(tfrom) == KING)
&& pos.move_attacks_square(m, tto))
return true;
// Case 3: If the moving piece in the threatened move is a slider, don't
// prune safe moves which block its ray.
if ( piece_is_slider(pos.piece_on(tfrom))
&& bit_is_set(squares_between(tfrom, tto), mto)
&& pos.see_sign(m) >= 0)
return true;
return false;
}
// ok_to_use_TT() returns true if a transposition table score
// can be used at a given point in search.
bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
Value v = value_from_tt(tte->value(), ply);
return ( tte->depth() >= depth
|| v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
|| v < Min(VALUE_MATED_IN_PLY_MAX, beta))
&& ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
|| ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
}
// refine_eval() returns the transposition table score if
// possible otherwise falls back on static position evaluation.
Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
assert(tte);
Value v = value_from_tt(tte->value(), ply);
if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
|| ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
return v;
return defaultEval;
}
// update_history() registers a good move that produced a beta-cutoff
// in history and marks as failures all the other moves of that ply.
void update_history(const Position& pos, Move move, Depth depth,
Move movesSearched[], int moveCount) {
Move m;
Value bonus = Value(int(depth) * int(depth));
H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
for (int i = 0; i < moveCount - 1; i++)
{
m = movesSearched[i];
assert(m != move);
H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
}
}
// update_gains() updates the gains table of a non-capture move given
// the static position evaluation before and after the move.
void update_gains(const Position& pos, Move m, Value before, Value after) {
if ( m != MOVE_NULL
&& before != VALUE_NONE
&& after != VALUE_NONE
&& pos.captured_piece_type() == PIECE_TYPE_NONE
&& !move_is_special(m))
H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
}
// current_search_time() returns the number of milliseconds which have passed
// since the beginning of the current search.
int current_search_time(int set) {
static int searchStartTime;
if (set)
searchStartTime = set;
return get_system_time() - searchStartTime;
}
// value_to_uci() converts a value to a string suitable for use with the UCI
// protocol specifications:
//
// cp <x> The score from the engine's point of view in centipawns.
// mate <y> Mate in y moves, not plies. If the engine is getting mated
// use negative values for y.
std::string value_to_uci(Value v) {
std::stringstream s;
if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
else
s << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
return s.str();
}
// speed_to_uci() returns a string with time stats of current search suitable
// to be sent to UCI gui.
std::string speed_to_uci(int64_t nodes) {
std::stringstream s;
int t = current_search_time();
s << " nodes " << nodes
<< " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
<< " time " << t;
return s.str();
}
// poll() performs two different functions: It polls for user input, and it
// looks at the time consumed so far and decides if it's time to abort the
// search.
void poll(const Position& pos) {
static int lastInfoTime;
int t = current_search_time();
// Poll for input
if (input_available())
{
// We are line oriented, don't read single chars
std::string command;
if (!std::getline(std::cin, command) || command == "quit")
{
// Quit the program as soon as possible
Limits.ponder = false;
QuitRequest = StopRequest = true;
return;
}
else if (command == "stop")
{
// Stop calculating as soon as possible, but still send the "bestmove"
// and possibly the "ponder" token when finishing the search.
Limits.ponder = false;
StopRequest = true;
}
else if (command == "ponderhit")
{
// The opponent has played the expected move. GUI sends "ponderhit" if
// we were told to ponder on the same move the opponent has played. We
// should continue searching but switching from pondering to normal search.
Limits.ponder = false;
if (StopOnPonderhit)
StopRequest = true;
}
}
// Print search information
if (t < 1000)
lastInfoTime = 0;
else if (lastInfoTime > t)
// HACK: Must be a new search where we searched less than
// NodesBetweenPolls nodes during the first second of search.
lastInfoTime = 0;
else if (t - lastInfoTime >= 1000)
{
lastInfoTime = t;
dbg_print_mean();
dbg_print_hit_rate();
// Send info on searched nodes as soon as we return to root
SendSearchedNodes = true;
}
// Should we stop the search?
if (Limits.ponder)
return;
bool stillAtFirstMove = FirstRootMove
&& !AspirationFailLow
&& t > TimeMgr.available_time();
bool noMoreTime = t > TimeMgr.maximum_time()
|| stillAtFirstMove;
if ( (Limits.useTimeManagement() && noMoreTime)
|| (Limits.maxTime && t >= Limits.maxTime)
|| (Limits.maxNodes && pos.nodes_searched() >= Limits.maxNodes)) // FIXME
StopRequest = true;
}
// wait_for_stop_or_ponderhit() is called when the maximum depth is reached
// while the program is pondering. The point is to work around a wrinkle in
// the UCI protocol: When pondering, the engine is not allowed to give a
// "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
// We simply wait here until one of these commands is sent, and return,
// after which the bestmove and pondermove will be printed.
void wait_for_stop_or_ponderhit() {
std::string command;
// Wait for a command from stdin
while ( std::getline(std::cin, command)
&& command != "ponderhit" && command != "stop" && command != "quit") {};
if (command != "ponderhit" && command != "stop")
QuitRequest = true; // Must be "quit" or getline() returned false
}
// When playing with strength handicap choose best move among the MultiPV set
// using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
void do_skill_level(Move* best, Move* ponder) {
assert(MultiPV > 1);
static RKISS rk;
// Rml list is already sorted by pv_score in descending order
int s;
int max_s = -VALUE_INFINITE;
int size = Min(MultiPV, (int)Rml.size());
int max = Rml[0].pv_score;
int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
int wk = 120 - 2 * SkillLevel;
// PRNG sequence should be non deterministic
for (int i = abs(get_system_time() % 50); i > 0; i--)
rk.rand<unsigned>();
// Choose best move. For each move's score we add two terms both dependent
// on wk, one deterministic and bigger for weaker moves, and one random,
// then we choose the move with the resulting highest score.
for (int i = 0; i < size; i++)
{
s = Rml[i].pv_score;
// Don't allow crazy blunders even at very low skills
if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
break;
// This is our magical formula
s += ((max - s) * wk + var * (rk.rand<unsigned>() % wk)) / 128;
if (s > max_s)
{
max_s = s;
*best = Rml[i].pv[0];
*ponder = Rml[i].pv[1];
}
}
}
/// RootMove and RootMoveList method's definitions
RootMove::RootMove() {
nodes = 0;
pv_score = non_pv_score = -VALUE_INFINITE;
pv[0] = MOVE_NONE;
}
RootMove& RootMove::operator=(const RootMove& rm) {
const Move* src = rm.pv;
Move* dst = pv;
// Avoid a costly full rm.pv[] copy
do *dst++ = *src; while (*src++ != MOVE_NONE);
nodes = rm.nodes;
pv_score = rm.pv_score;
non_pv_score = rm.non_pv_score;
return *this;
}
void RootMoveList::init(Position& pos, Move searchMoves[]) {
MoveStack mlist[MAX_MOVES];
Move* sm;
clear();
bestMoveChanges = 0;
// Generate all legal moves and add them to RootMoveList
MoveStack* last = generate<MV_LEGAL>(pos, mlist);
for (MoveStack* cur = mlist; cur != last; cur++)
{
// If we have a searchMoves[] list then verify cur->move
// is in the list before to add it.
for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
if (searchMoves[0] && *sm != cur->move)
continue;
RootMove rm;
rm.pv[0] = cur->move;
rm.pv[1] = MOVE_NONE;
rm.pv_score = -VALUE_INFINITE;
push_back(rm);
}
}
// extract_pv_from_tt() builds a PV by adding moves from the transposition table.
// We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
// allow to always have a ponder move even when we fail high at root and also a
// long PV to print that is important for position analysis.
void RootMove::extract_pv_from_tt(Position& pos) {
StateInfo state[PLY_MAX_PLUS_2], *st = state;
TTEntry* tte;
int ply = 1;
assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
pos.do_move(pv[0], *st++);
while ( (tte = TT.probe(pos.get_key())) != NULL
&& tte->move() != MOVE_NONE
&& pos.move_is_legal(tte->move())
&& ply < PLY_MAX
&& (!pos.is_draw() || ply < 2))
{
pv[ply] = tte->move();
pos.do_move(pv[ply++], *st++);
}
pv[ply] = MOVE_NONE;
do pos.undo_move(pv[--ply]); while (ply);
}
// 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[PLY_MAX_PLUS_2], *st = state;
TTEntry* tte;
Key k;
Value v, m = VALUE_NONE;
int ply = 0;
assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
do {
k = pos.get_key();
tte = TT.probe(k);
// Don't overwrite existing correct entries
if (!tte || tte->move() != pv[ply])
{
v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
}
pos.do_move(pv[ply], *st++);
} while (pv[++ply] != MOVE_NONE);
do pos.undo_move(pv[--ply]); while (ply);
}
// pv_info_to_uci() returns a string with information on the current PV line
// formatted according to UCI specification.
std::string RootMove::pv_info_to_uci(Position& pos, int depth, int selDepth, Value alpha,
Value beta, int pvIdx) {
std::stringstream s;
s << "info depth " << depth
<< " seldepth " << selDepth
<< " multipv " << pvIdx + 1
<< " score " << value_to_uci(pv_score)
<< (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
<< speed_to_uci(pos.nodes_searched())
<< " pv ";
for (Move* m = pv; *m != MOVE_NONE; m++)
s << *m << " ";
return s.str();
}
// Specializations for MovePickerExt in case of Root node
MovePickerExt<false, true>::MovePickerExt(const Position& p, Move ttm, Depth d,
const History& h, SearchStack* ss, Value b)
: MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
Move move;
Value score = VALUE_ZERO;
// Score root moves using standard ordering used in main search, the moves
// are scored according to the order in which they are returned by MovePicker.
// This is the second order score that is used to compare the moves when
// the first orders pv_score of both moves are equal.
while ((move = MovePicker::get_next_move()) != MOVE_NONE)
for (rm = Rml.begin(); rm != Rml.end(); ++rm)
if (rm->pv[0] == move)
{
rm->non_pv_score = score--;
break;
}
Rml.sort();
rm = Rml.begin();
}
Move MovePickerExt<false, true>::get_next_move() {
if (!firstCall)
++rm;
else
firstCall = false;
return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
}
} // namespace
// ThreadsManager::idle_loop() is where the threads are parked when they have no work
// to do. The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
// object for which the current thread is the master.
void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
assert(threadID >= 0 && threadID < MAX_THREADS);
int i;
bool allFinished;
while (true)
{
// Slave threads can exit as soon as AllThreadsShouldExit raises,
// master should exit as last one.
if (allThreadsShouldExit)
{
assert(!sp);
threads[threadID].state = Thread::TERMINATED;
return;
}
// If we are not thinking, wait for a condition to be signaled
// instead of wasting CPU time polling for work.
while ( threadID >= activeThreads
|| threads[threadID].state == Thread::INITIALIZING
|| (useSleepingThreads && threads[threadID].state == Thread::AVAILABLE))
{
assert(!sp || useSleepingThreads);
assert(threadID != 0 || useSleepingThreads);
if (threads[threadID].state == Thread::INITIALIZING)
threads[threadID].state = Thread::AVAILABLE;
// Grab the lock to avoid races with Thread::wake_up()
lock_grab(&threads[threadID].sleepLock);
// If we are master and all slaves have finished do not go to sleep
for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
allFinished = (i == activeThreads);
if (allFinished || allThreadsShouldExit)
{
lock_release(&threads[threadID].sleepLock);
break;
}
// Do sleep here after retesting sleep conditions
if (threadID >= activeThreads || threads[threadID].state == Thread::AVAILABLE)
cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
lock_release(&threads[threadID].sleepLock);
}
// If this thread has been assigned work, launch a search
if (threads[threadID].state == Thread::WORKISWAITING)
{
assert(!allThreadsShouldExit);
threads[threadID].state = Thread::SEARCHING;
// Copy split point position and search stack and call search()
// with SplitPoint template parameter set to true.
SearchStack ss[PLY_MAX_PLUS_2];
SplitPoint* tsp = threads[threadID].splitPoint;
Position pos(*tsp->pos, threadID);
memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
(ss+1)->sp = tsp;
if (tsp->pvNode)
search<PV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
else
search<NonPV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
assert(threads[threadID].state == Thread::SEARCHING);
threads[threadID].state = Thread::AVAILABLE;
// 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 ( useSleepingThreads
&& threadID != tsp->master
&& threads[tsp->master].state == Thread::AVAILABLE)
threads[tsp->master].wake_up();
}
// 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.
for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
allFinished = (i == activeThreads);
if (allFinished)
{
// Because sp->slaves[] is reset under lock protection,
// be sure sp->lock has been released before to return.
lock_grab(&(sp->lock));
lock_release(&(sp->lock));
// In helpful master concept a master can help only a sub-tree, and
// because here is all finished is not possible master is booked.
assert(threads[threadID].state == Thread::AVAILABLE);
threads[threadID].state = Thread::SEARCHING;
return;
}
}
}
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