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Stockfish/src/search.cpp
Marco Costalba 1c42d15340 Rewrite how uci info is sent to GUI 
It is now much more modular than before and also we
always send the seldepth when we send the depth, this
avoids to make seldepth disappearing from GUI at the
start of a new iteration.

Print also fails high/low pv lines at high enough
search depths.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
2011-06-22 17:32:22 +01:00

2226 lines
75 KiB
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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 { Root, PV, NonPV, SplitPointPV, SplitPointNonPV };
// 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);
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_first(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
int bestMoveChanges;
};
/// 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 <bool PvNode> inline Depth reduction(Depth d, int mn) {
return (Depth) Reductions[PvNode][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 NT>
Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
template <NodeType NT>
Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
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 score_to_uci(Value v, Value alpha, Value beta);
std::string speed_to_uci(int64_t nodes);
std::string pv_to_uci(Move pv[], int pvNum);
std::string depth_to_uci(Depth depth);
void poll(const Position& pos);
void wait_for_stop_or_ponderhit();
// 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<NodeType> 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) {}
RootMove& current() { assert(false); return Rml[0]; } // Dummy, needed to compile
};
// In case of a SpNode we use split point's shared MovePicker object as moves source
template<> struct MovePickerExt<SplitPointNonPV> : public MovePickerExt<NonPV> {
MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
: MovePickerExt<NonPV>(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
Move get_next_move() { return mp->get_next_move(); }
MovePicker* mp;
};
template<> struct MovePickerExt<SplitPointPV> : public MovePickerExt<SplitPointNonPV> {
MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
: MovePickerExt<SplitPointNonPV>(p, ttm, d, h, ss, b) {}
};
// In case of a Root node we use RootMoveList as moves source
template<> struct MovePickerExt<Root> : public MovePicker {
MovePickerExt(const Position&, Move, Depth, const History&, SearchStack*, Value);
RootMove& current() { return Rml[cur]; }
Move get_next_move() { return ++cur < (int)Rml.size() ? Rml[cur].pv[0] : MOVE_NONE; }
int cur;
};
// 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;
}
// 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 <bool PvNode>
FORCE_INLINE 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);
}
} // 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[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
Reductions[0][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 output steram in normal or chess960 mode
cout << set960(pos.is_chess960());
// 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;
// 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);
// 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, 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())
{
cout << "info" << depth_to_uci(DEPTH_ZERO)
<< score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW, alpha, beta) << 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;
// 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<Root>(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;
// Send full PV info to GUI if we are going to leave the loop or
// if we have a fail high/low and we are deep in the search.
if ((value > alpha && value < beta) || current_search_time() > 2000)
for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
cout << "info"
<< depth_to_uci(depth * ONE_PLY)
<< score_to_uci(Rml[i].pv_score, alpha, beta)
<< speed_to_uci(pos.nodes_searched())
<< pv_to_uci(Rml[i].pv, i + 1) << endl;
// 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);
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 NT>
Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV);
const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV);
const bool RootNode = (NT == Root);
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;
int moveCount = 0, playedMoveCount = 0;
Thread& thread = Threads[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 && thread.maxPly < ss->ply)
thread.maxPly = ss->ply;
if (SpNode)
{
sp = ss->sp;
tte = NULL;
ttMove = excludedMove = MOVE_NONE;
threatMove = sp->threatMove;
goto split_point_start;
}
// 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] = MOVE_NONE;
if (pos.thread() == 0 && ++NodesSincePoll > NodesBetweenPolls)
{
NodesSincePoll = 0;
poll(pos);
}
// Step 2. Check for aborted search and immediate draw
if (( StopRequest
|| pos.is_draw<false>()
|| ss->ply > PLY_MAX) && !RootNode)
return VALUE_DRAW;
// Step 3. Mate distance pruning
if (!RootNode)
{
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 (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 = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
: - 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. ProbCut (is omitted in PV nodes)
// 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 ( !PvNode
&& depth >= RazorDepth + ONE_PLY
&& !inCheck
&& !ss->skipNullMove
&& excludedMove == MOVE_NONE
&& abs(beta) < VALUE_MATE_IN_PLY_MAX)
{
Value rbeta = beta + 200;
Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
assert(rdepth >= ONE_PLY);
MovePicker mp(pos, ttMove, H, Position::see_value(pos.captured_piece_type()));
CheckInfo ci(pos);
while ((move = mp.get_next_move()) != MOVE_NONE)
if (pos.pl_move_is_legal(move, ci.pinned))
{
pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
pos.undo_move(move);
if (value >= rbeta)
return value;
}
}
// Step 10. 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 ? PV : NonPV>(pos, ss, alpha, beta, d);
ss->skipNullMove = false;
tte = TT.probe(posKey);
ttMove = tte ? tte->move() : MOVE_NONE;
}
split_point_start: // At split points actual search starts from here
// Initialize a MovePicker object for the current position
MovePickerExt<NT> mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
CheckInfo ci(pos);
ss->bestMove = MOVE_NONE;
futilityBase = ss->eval + ss->evalMargin;
singularExtensionNode = !RootNode
&& !SpNode
&& depth >= SingularExtensionDepth[PvNode]
&& ttMove != MOVE_NONE
&& !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 11. Loop through moves
// Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
while ( bestValue < beta
&& (move = mp.get_next_move()) != MOVE_NONE
&& !thread.cutoff_occurred())
{
assert(move_is_ok(move));
if (move == excludedMove)
continue;
// At PV and SpNode nodes we want the moves to be legal
if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, ci.pinned))
continue;
if (SpNode)
{
moveCount = ++sp->moveCount;
lock_release(&(sp->lock));
}
else
moveCount++;
if (RootNode)
{
// 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;
}
// For long searches send to GUI current move
if (current_search_time() > 2000)
cout << "info" << depth_to_uci(depth)
<< " 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 <= (RootNode ? depth <= ONE_PLY ? MAX_MOVES : MultiPV : 1));
givesCheck = pos.move_gives_check(move, ci);
captureOrPromotion = pos.move_is_capture(move) || move_is_promotion(move);
// Step 12. 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 == ttMove
&& pos.pl_move_is_legal(move, ci.pinned)
&& 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)
newDepth = depth - ONE_PLY + ext;
// Step 13. 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<PvNode>(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;
}
}
// Check for legality only before to do the move
if (!pos.pl_move_is_legal(move, ci.pinned))
{
moveCount--;
continue;
}
ss->currentMove = move;
// Step 14. 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)
value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
: - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
else
{
// Step 15. 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 = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
: - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
doFullDepthSearch = (value > alpha);
}
ss->reduction = DEPTH_ZERO; // Restore original reduction
}
// Step 16. Full depth search
if (doFullDepthSearch)
{
alpha = SpNode ? sp->alpha : alpha;
value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
: - 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 && (RootNode || value < beta))
value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
: - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
}
}
// Step 17. Undo move
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
// Step 18. Check for new best move
if (SpNode)
{
lock_grab(&(sp->lock));
bestValue = sp->bestValue;
alpha = sp->alpha;
}
if (value > bestValue && !(SpNode && thread.cutoff_occurred()))
{
bestValue = value;
if (SpNode)
sp->bestValue = value;
if (!RootNode && 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;
ss->bestMove = move;
if (SpNode)
sp->ss->bestMove = move;
}
}
if (RootNode)
{
// 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.current().nodes += pos.nodes_searched() - nodes;
// PV move or new best move ?
if (isPvMove || value > alpha)
{
// Update PV
ss->bestMove = move;
mp.current().pv_score = value;
mp.current().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++;
// It is critical that sorting is done with a stable algorithm
// because all the values but the first are usually set to
// -VALUE_INFINITE and we want to keep the same order for all
// the moves but the new PV that goes to head.
Rml.sort_first(moveCount);
// Update alpha. In multi-pv we don't use aspiration window, so set
// alpha equal to minimum score among the PV lines searched so far.
if (MultiPV > 1)
alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score;
else if (value > alpha)
alpha = value;
}
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.
mp.current().pv_score = -VALUE_INFINITE;
} // RootNode
// Step 19. Check for split
if ( !RootNode
&& !SpNode
&& depth >= Threads.min_split_depth()
&& bestValue < beta
&& Threads.available_slave_exists(pos.thread())
&& !StopRequest
&& !thread.cutoff_occurred())
Threads.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
threatMove, moveCount, &mp, PvNode);
}
// 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.
// If one move was excluded return fail low score.
if (!SpNode && !moveCount)
return excludedMove ? oldAlpha : inCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
// Step 21. Update tables
// If the search is not aborted, update the transposition table,
// history counters, and killer moves.
if (!SpNode && !StopRequest && !thread.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(move)
&& !move_is_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[pos.thread()] = 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 NT>
Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
const bool PvNode = (NT == PV);
assert(NT == PV || NT == NonPV);
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 (pos.is_draw<true>() || ss->ply > PLY_MAX)
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);
// 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, move_to((ss-1)->currentMove));
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 = !PvNode
&& 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(move)
&& !move_is_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;
}
// Check for legality only before to do the move
if (!pos.pl_move_is_legal(move, ci.pinned))
continue;
// Update current move
ss->currentMove = move;
// Make and search the move
pos.do_move(move, st, ci, givesCheck);
value = -qsearch<NT>(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;
}
// 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_is_capture(m) && !move_is_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;
}
// score_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 score_to_uci(Value v, Value alpha, Value beta) {
std::stringstream s;
if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
s << " score cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
else
s << " score mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
s << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
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();
}
// pv_to_uci() returns a string with information on the current PV line
// formatted according to UCI specification.
std::string pv_to_uci(Move pv[], int pvNum) {
std::stringstream s;
s << " multipv " << pvNum << " pv ";
for ( ; *pv != MOVE_NONE; pv++)
s << *pv << " ";
return s.str();
}
// depth_to_uci() returns a string with information on the current depth and
// seldepth formatted according to UCI specification.
std::string depth_to_uci(Depth depth) {
std::stringstream s;
// Retrieve max searched depth among threads
int selDepth = 0;
for (int i = 0; i < Threads.size(); i++)
if (Threads[i].maxPly > selDepth)
selDepth = Threads[i].maxPly;
s << " depth " << depth / ONE_PLY << " seldepth " << selDepth;
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_pl(pv[0]));
pos.do_move(pv[0], *st++);
while ( (tte = TT.probe(pos.get_key())) != NULL
&& tte->move() != MOVE_NONE
&& pos.move_is_pl(tte->move())
&& pos.pl_move_is_legal(tte->move(), pos.pinned_pieces(pos.side_to_move()))
&& ply < PLY_MAX
&& (!pos.is_draw<false>() || 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_pl(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);
}
// Specializations for MovePickerExt in case of Root node
MovePickerExt<Root>::MovePickerExt(const Position& p, Move ttm, Depth d,
const History& h, SearchStack* ss, Value b)
: MovePicker(p, ttm, d, h, ss, b), cur(-1) {
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 (RootMoveList::iterator rm = Rml.begin(); rm != Rml.end(); ++rm)
if (rm->pv[0] == move)
{
rm->non_pv_score = score--;
break;
}
Rml.sort();
}
} // 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<SplitPointPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
else
search<SplitPointNonPV>(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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