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search.cpp
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search.cpp
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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 Marco Costalba
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/>.
*/
////
//// Includes
////
#include <cassert>
#include <fstream>
#include <iostream>
#include <sstream>
#include "book.h"
#include "evaluate.h"
#include "history.h"
#include "misc.h"
#include "movepick.h"
#include "san.h"
#include "search.h"
#include "thread.h"
#include "tt.h"
#include "ucioption.h"
////
//// Local definitions
////
namespace {
/// Types
// The BetaCounterType class is used to order moves at ply one.
// Apart for the first one that has its score, following moves
// normally have score -VALUE_INFINITE, so are ordered according
// to the number of beta cutoffs occurred under their subtree during
// the last iteration.
struct BetaCounterType {
BetaCounterType();
void clear();
void add(Color us, Depth d, int threadID);
void read(Color us, int64_t& our, int64_t& their);
int64_t hits[THREAD_MAX][2];
};
// The RootMove class is used for moves at the root at the tree. For each
// root move, we store a score, a node count, and a PV (really a refutation
// in the case of moves which fail low).
struct RootMove {
RootMove();
bool operator<(const RootMove&); // used to sort
Move move;
Value score;
int64_t nodes, cumulativeNodes;
Move pv[PLY_MAX_PLUS_2];
int64_t ourBeta, theirBeta;
};
// The RootMoveList class is essentially an array of RootMove objects, with
// a handful of methods for accessing the data in the individual moves.
class RootMoveList {
public:
RootMoveList(Position &pos, Move searchMoves[]);
inline Move get_move(int moveNum) const;
inline Value get_move_score(int moveNum) const;
inline void set_move_score(int moveNum, Value score);
inline void set_move_nodes(int moveNum, int64_t nodes);
inline void set_beta_counters(int moveNum, int64_t our, int64_t their);
void set_move_pv(int moveNum, const Move pv[]);
inline Move get_move_pv(int moveNum, int i) const;
inline int64_t get_move_cumulative_nodes(int moveNum) const;
inline int move_count() const;
Move scan_for_easy_move() const;
inline void sort();
void sort_multipv(int n);
private:
static const int MaxRootMoves = 500;
RootMove moves[MaxRootMoves];
int count;
};
/// Constants and variables
// Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV
// nodes:
int LMRPVMoves = 15;
int LMRNonPVMoves = 4;
// Depth limit for use of dynamic threat detection:
Depth ThreatDepth = 5*OnePly;
// Depth limit for selective search:
Depth SelectiveDepth = 7*OnePly;
// Use internal iterative deepening?
const bool UseIIDAtPVNodes = true;
const bool UseIIDAtNonPVNodes = false;
// Use null move driven internal iterative deepening?
bool UseNullDrivenIID = false;
// Internal iterative deepening margin. At Non-PV moves, when
// UseIIDAtNonPVNodes is true, we do an internal iterative deepening search
// when the static evaluation is at most IIDMargin below beta.
const Value IIDMargin = Value(0x100);
// Easy move margin. An easy move candidate must be at least this much
// better than the second best move.
const Value EasyMoveMargin = Value(0x200);
// Problem margin. If the score of the first move at iteration N+1 has
// dropped by more than this since iteration N, the boolean variable
// "Problem" is set to true, which will make the program spend some extra
// time looking for a better move.
const Value ProblemMargin = Value(0x28);
// No problem margin. If the boolean "Problem" is true, and a new move
// is found at the root which is less than NoProblemMargin worse than the
// best move from the previous iteration, Problem is set back to false.
const Value NoProblemMargin = Value(0x14);
// Null move margin. A null move search will not be done if the approximate
// evaluation of the position is more than NullMoveMargin below beta.
const Value NullMoveMargin = Value(0x300);
// Pruning criterions. See the code and comments in ok_to_prune() to
// understand their precise meaning.
const bool PruneEscapeMoves = false;
const bool PruneDefendingMoves = false;
const bool PruneBlockingMoves = false;
// Use futility pruning?
bool UseQSearchFutilityPruning = true;
bool UseFutilityPruning = true;
// Margins for futility pruning in the quiescence search, and at frontier
// and near frontier nodes
Value FutilityMarginQS = Value(0x80);
Value FutilityMargins[6] = { Value(0x100), Value(0x200), Value(0x250),
Value(0x2A0), Value(0x340), Value(0x3A0) };
// Razoring
const bool RazorAtDepthOne = false;
Depth RazorDepth = 4*OnePly;
Value RazorMargin = Value(0x300);
// Last seconds noise filtering (LSN)
bool UseLSNFiltering = false;
bool looseOnTime = false;
int LSNTime = 4 * 1000; // In milliseconds
Value LSNValue = Value(0x200);
// Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
Depth CheckExtension[2] = {OnePly, OnePly};
Depth SingleReplyExtension[2] = {OnePly / 2, OnePly / 2};
Depth PawnPushTo7thExtension[2] = {OnePly / 2, OnePly / 2};
Depth PassedPawnExtension[2] = {Depth(0), Depth(0)};
Depth PawnEndgameExtension[2] = {OnePly, OnePly};
Depth MateThreatExtension[2] = {Depth(0), Depth(0)};
// Search depth at iteration 1
const Depth InitialDepth = OnePly /*+ OnePly/2*/;
// Node counters
int NodesSincePoll;
int NodesBetweenPolls = 30000;
// Iteration counters
int Iteration;
bool LastIterations;
BetaCounterType BetaCounter;
// Scores and number of times the best move changed for each iteration:
Value ValueByIteration[PLY_MAX_PLUS_2];
int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
// MultiPV mode
int MultiPV = 1;
// Time managment variables
int SearchStartTime;
int MaxNodes, MaxDepth;
int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime;
Move BestRootMove, PonderMove, EasyMove;
int RootMoveNumber;
bool InfiniteSearch;
bool PonderSearch;
bool StopOnPonderhit;
bool AbortSearch;
bool Quit;
bool FailHigh;
bool Problem;
bool PonderingEnabled;
int ExactMaxTime;
// Show current line?
bool ShowCurrentLine = false;
// Log file
bool UseLogFile = false;
std::ofstream LogFile;
// MP related variables
Depth MinimumSplitDepth = 4*OnePly;
int MaxThreadsPerSplitPoint = 4;
Thread Threads[THREAD_MAX];
Lock MPLock;
bool AllThreadsShouldExit = false;
const int MaxActiveSplitPoints = 8;
SplitPoint SplitPointStack[THREAD_MAX][MaxActiveSplitPoints];
bool Idle = true;
#if !defined(_MSC_VER)
pthread_cond_t WaitCond;
pthread_mutex_t WaitLock;
#else
HANDLE SitIdleEvent[THREAD_MAX];
#endif
/// Functions
Value id_loop(const Position &pos, Move searchMoves[]);
Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml);
Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
Depth depth, int ply, int threadID);
Value search(Position &pos, SearchStack ss[], Value beta,
Depth depth, int ply, bool allowNullmove, int threadID);
Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
Depth depth, int ply, int threadID);
void sp_search(SplitPoint *sp, int threadID);
void sp_search_pv(SplitPoint *sp, int threadID);
void init_search_stack(SearchStack& ss);
void init_search_stack(SearchStack ss[]);
void init_node(const Position &pos, SearchStack ss[], int ply, int threadID);
void update_pv(SearchStack ss[], int ply);
void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply);
bool connected_moves(const Position &pos, Move m1, Move m2);
bool value_is_mate(Value value);
bool move_is_killer(Move m, const SearchStack& ss);
Depth extension(const Position &pos, Move m, bool pvNode, bool capture, bool check, bool singleReply, bool mateThreat, bool* dangerous);
bool ok_to_do_nullmove(const Position &pos);
bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d);
bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
bool ok_to_history(const Position &pos, Move m);
void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
void update_killers(Move m, SearchStack& ss);
bool fail_high_ply_1();
int current_search_time();
int nps();
void poll();
void ponderhit();
void print_current_line(SearchStack ss[], int ply, int threadID);
void wait_for_stop_or_ponderhit();
void idle_loop(int threadID, SplitPoint *waitSp);
void init_split_point_stack();
void destroy_split_point_stack();
bool thread_should_stop(int threadID);
bool thread_is_available(int slave, int master);
bool idle_thread_exists(int master);
bool split(const Position &pos, SearchStack *ss, int ply,
Value *alpha, Value *beta, Value *bestValue, Depth depth,
int *moves, MovePicker *mp, Bitboard dcCandidates, int master,
bool pvNode);
void wake_sleeping_threads();
#if !defined(_MSC_VER)
void *init_thread(void *threadID);
#else
DWORD WINAPI init_thread(LPVOID threadID);
#endif
}
////
//// Global variables
////
// The main transposition table
TranspositionTable TT = TranspositionTable(TTDefaultSize);
// Number of active threads:
int ActiveThreads = 1;
// Locks. In principle, there is no need for IOLock to be a global variable,
// but it could turn out to be useful for debugging.
Lock IOLock;
History H; // Should be made local?
// The empty search stack
SearchStack EmptySearchStack;
////
//// Functions
////
/// think() is the external interface to Stockfish's search, and is called when
/// the program receives the UCI 'go' command. It initializes various
/// search-related global variables, and calls root_search()
void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
int time[], int increment[], int movesToGo, int maxDepth,
int maxNodes, int maxTime, Move searchMoves[]) {
// Look for a book move
if (!infinite && !ponder && get_option_value_bool("OwnBook"))
{
Move bookMove;
if (get_option_value_string("Book File") != OpeningBook.file_name())
{
OpeningBook.close();
OpeningBook.open("book.bin");
}
bookMove = OpeningBook.get_move(pos);
if (bookMove != MOVE_NONE)
{
std::cout << "bestmove " << bookMove << std::endl;
return;
}
}
// Initialize global search variables
Idle = false;
SearchStartTime = get_system_time();
BestRootMove = MOVE_NONE;
PonderMove = MOVE_NONE;
EasyMove = MOVE_NONE;
for (int i = 0; i < THREAD_MAX; i++)
{
Threads[i].nodes = 0ULL;
Threads[i].failHighPly1 = false;
}
NodesSincePoll = 0;
InfiniteSearch = infinite;
PonderSearch = ponder;
StopOnPonderhit = false;
AbortSearch = false;
Quit = false;
FailHigh = false;
Problem = false;
ExactMaxTime = maxTime;
// Read UCI option values
TT.set_size(get_option_value_int("Hash"));
if (button_was_pressed("Clear Hash"))
TT.clear();
PonderingEnabled = get_option_value_bool("Ponder");
MultiPV = get_option_value_int("MultiPV");
CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
SingleReplyExtension[1] = Depth(get_option_value_int("Single Reply Extension (PV nodes)"));
SingleReplyExtension[0] = Depth(get_option_value_int("Single Reply Extension (non-PV nodes)"));
PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
SelectiveDepth = get_option_value_int("Selective Plies") * OnePly;
Chess960 = get_option_value_bool("UCI_Chess960");
ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
UseLogFile = get_option_value_bool("Use Search Log");
if (UseLogFile)
LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
UseNullDrivenIID = get_option_value_bool("Null driven IID");
UseQSearchFutilityPruning = get_option_value_bool("Futility Pruning (Quiescence Search)");
UseFutilityPruning = get_option_value_bool("Futility Pruning (Main Search)");
FutilityMarginQS = value_from_centipawns(get_option_value_int("Futility Margin (Quiescence Search)"));
int fmScale = get_option_value_int("Futility Margin Scale Factor (Main Search)");
for (int i = 0; i < 6; i++)
FutilityMargins[i] = (FutilityMargins[i] * fmScale) / 100;
RazorDepth = (get_option_value_int("Maximum Razoring Depth") + 1) * OnePly;
RazorMargin = value_from_centipawns(get_option_value_int("Razoring Margin"));
UseLSNFiltering = get_option_value_bool("LSN filtering");
LSNTime = get_option_value_int("LSN Time Margin (sec)") * 1000;
LSNValue = value_from_centipawns(get_option_value_int("LSN Value Margin"));
MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
read_weights(pos.side_to_move());
int newActiveThreads = get_option_value_int("Threads");
if (newActiveThreads != ActiveThreads)
{
ActiveThreads = newActiveThreads;
init_eval(ActiveThreads);
}
// Wake up sleeping threads:
wake_sleeping_threads();
for (int i = 1; i < ActiveThreads; i++)
assert(thread_is_available(i, 0));
// Set thinking time:
int myTime = time[side_to_move];
int myIncrement = increment[side_to_move];
if (!movesToGo) // Sudden death time control
{
if (myIncrement)
{
MaxSearchTime = myTime / 30 + myIncrement;
AbsoluteMaxSearchTime = Max(myTime / 4, myIncrement - 100);
} else { // Blitz game without increment
MaxSearchTime = myTime / 30;
AbsoluteMaxSearchTime = myTime / 8;
}
}
else // (x moves) / (y minutes)
{
if (movesToGo == 1)
{
MaxSearchTime = myTime / 2;
AbsoluteMaxSearchTime = Min(myTime / 2, myTime - 500);
} else {
MaxSearchTime = myTime / Min(movesToGo, 20);
AbsoluteMaxSearchTime = Min((4 * myTime) / movesToGo, myTime / 3);
}
}
if (PonderingEnabled)
{
MaxSearchTime += MaxSearchTime / 4;
MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
}
// Fixed depth or fixed number of nodes?
MaxDepth = maxDepth;
if (MaxDepth)
InfiniteSearch = true; // HACK
MaxNodes = maxNodes;
if (MaxNodes)
{
NodesBetweenPolls = Min(MaxNodes, 30000);
InfiniteSearch = true; // HACK
}
else
NodesBetweenPolls = 30000;
// Write information to search log file:
if (UseLogFile)
LogFile << "Searching: " << pos.to_fen() << std::endl
<< "infinite: " << infinite
<< " ponder: " << ponder
<< " time: " << myTime
<< " increment: " << myIncrement
<< " moves to go: " << movesToGo << std::endl;
// We're ready to start thinking. Call the iterative deepening loop
// function:
if (!looseOnTime)
{
Value v = id_loop(pos, searchMoves);
looseOnTime = ( UseLSNFiltering
&& myTime < LSNTime
&& myIncrement == 0
&& v < -LSNValue);
}
else
{
looseOnTime = false; // reset for next match
while (SearchStartTime + myTime + 1000 > get_system_time())
; // wait here
id_loop(pos, searchMoves); // to fail gracefully
}
if (UseLogFile)
LogFile.close();
if (Quit)
{
OpeningBook.close();
stop_threads();
quit_eval();
exit(0);
}
Idle = true;
}
/// init_threads() is called during startup. It launches all helper threads,
/// and initializes the split point stack and the global locks and condition
/// objects.
void init_threads() {
volatile int i;
#if !defined(_MSC_VER)
pthread_t pthread[1];
#endif
for (i = 0; i < THREAD_MAX; i++)
Threads[i].activeSplitPoints = 0;
// Initialize global locks:
lock_init(&MPLock, NULL);
lock_init(&IOLock, NULL);
init_split_point_stack();
#if !defined(_MSC_VER)
pthread_mutex_init(&WaitLock, NULL);
pthread_cond_init(&WaitCond, NULL);
#else
for (i = 0; i < THREAD_MAX; i++)
SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
#endif
// All threads except the main thread should be initialized to idle state
for (i = 1; i < THREAD_MAX; i++)
{
Threads[i].stop = false;
Threads[i].workIsWaiting = false;
Threads[i].idle = true;
Threads[i].running = false;
}
// Launch the helper threads
for(i = 1; i < THREAD_MAX; i++)
{
#if !defined(_MSC_VER)
pthread_create(pthread, NULL, init_thread, (void*)(&i));
#else
DWORD iID[1];
CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
#endif
// Wait until the thread has finished launching:
while (!Threads[i].running);
}
// Init also the empty search stack
init_search_stack(EmptySearchStack);
}
/// stop_threads() is called when the program exits. It makes all the
/// helper threads exit cleanly.
void stop_threads() {
ActiveThreads = THREAD_MAX; // HACK
Idle = false; // HACK
wake_sleeping_threads();
AllThreadsShouldExit = true;
for (int i = 1; i < THREAD_MAX; i++)
{
Threads[i].stop = true;
while(Threads[i].running);
}
destroy_split_point_stack();
}
/// nodes_searched() returns the total number of nodes searched so far in
/// the current search.
int64_t nodes_searched() {
int64_t result = 0ULL;
for (int i = 0; i < ActiveThreads; i++)
result += Threads[i].nodes;
return result;
}
namespace {
// id_loop() is the main iterative deepening loop. It calls root_search
// repeatedly with increasing depth until the allocated thinking time has
// been consumed, the user stops the search, or the maximum search depth is
// reached.
Value id_loop(const Position &pos, Move searchMoves[]) {
Position p(pos);
SearchStack ss[PLY_MAX_PLUS_2];
// searchMoves are verified, copied, scored and sorted
RootMoveList rml(p, searchMoves);
// Initialize
TT.new_search();
H.clear();
init_search_stack(ss);
ValueByIteration[0] = Value(0);
ValueByIteration[1] = rml.get_move_score(0);
Iteration = 1;
LastIterations = false;
EasyMove = rml.scan_for_easy_move();
// Iterative deepening loop
while (!AbortSearch && Iteration < PLY_MAX)
{
// Initialize iteration
rml.sort();
Iteration++;
BestMoveChangesByIteration[Iteration] = 0;
if (Iteration <= 5)
ExtraSearchTime = 0;
std::cout << "info depth " << Iteration << std::endl;
// Search to the current depth
ValueByIteration[Iteration] = root_search(p, ss, rml);
// Erase the easy move if it differs from the new best move
if (ss[0].pv[0] != EasyMove)
EasyMove = MOVE_NONE;
Problem = false;
if (!InfiniteSearch)
{
// Time to stop?
bool stopSearch = false;
// Stop search early if there is only a single legal move:
if (Iteration >= 6 && rml.move_count() == 1)
stopSearch = true;
// Stop search early when the last two iterations returned a mate score
if ( Iteration >= 6
&& abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
&& abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
stopSearch = true;
// Stop search early if one move seems to be much better than the rest
int64_t nodes = nodes_searched();
if ( Iteration >= 8
&& EasyMove == ss[0].pv[0]
&& ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
&& current_search_time() > MaxSearchTime / 16)
||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
&& current_search_time() > MaxSearchTime / 32)))
stopSearch = true;
// Add some extra time if the best move has changed during the last two iterations
if (Iteration > 5 && Iteration <= 50)
ExtraSearchTime = BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2)
+ BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
// Try to guess if the current iteration is the last one or the last two
LastIterations = (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*58) / 128);
// Stop search if most of MaxSearchTime is consumed at the end of the
// iteration. We probably don't have enough time to search the first
// move at the next iteration anyway.
if (current_search_time() > ((MaxSearchTime + ExtraSearchTime)*80) / 128)
stopSearch = true;
if (stopSearch)
{
if (!PonderSearch)
break;
else
StopOnPonderhit = true;
}
}
// Write PV to transposition table, in case the relevant entries have
// been overwritten during the search:
TT.insert_pv(p, ss[0].pv);
if (MaxDepth && Iteration >= MaxDepth)
break;
}
rml.sort();
// If we are pondering, we shouldn't print the best move before we
// are told to do so
if (PonderSearch)
wait_for_stop_or_ponderhit();
else
// Print final search statistics
std::cout << "info nodes " << nodes_searched()
<< " nps " << nps()
<< " time " << current_search_time()
<< " hashfull " << TT.full() << std::endl;
// Print the best move and the ponder move to the standard output
std::cout << "bestmove " << ss[0].pv[0];
if (ss[0].pv[1] != MOVE_NONE)
std::cout << " ponder " << ss[0].pv[1];
std::cout << std::endl;
if (UseLogFile)
{
if (dbg_show_mean)
dbg_print_mean(LogFile);
if (dbg_show_hit_rate)
dbg_print_hit_rate(LogFile);
UndoInfo u;
LogFile << "Nodes: " << nodes_searched() << std::endl
<< "Nodes/second: " << nps() << std::endl
<< "Best move: " << move_to_san(p, ss[0].pv[0]) << std::endl;
p.do_move(ss[0].pv[0], u);
LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1])
<< std::endl << std::endl;
}
return rml.get_move_score(0);
}
// root_search() is the function which searches the root node. It is
// similar to search_pv except that it uses a different move ordering
// scheme (perhaps we should try to use this at internal PV nodes, too?)
// and prints some information to the standard output.
Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml) {
Value alpha = -VALUE_INFINITE;
Value beta = VALUE_INFINITE, value;
Bitboard dcCandidates = pos.discovered_check_candidates(pos.side_to_move());
// Loop through all the moves in the root move list
for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
{
int64_t nodes;
Move move;
UndoInfo u;
Depth ext, newDepth;
RootMoveNumber = i + 1;
FailHigh = false;
// Remember the node count before the move is searched. The node counts
// are used to sort the root moves at the next iteration.
nodes = nodes_searched();
// Reset beta cut-off counters
BetaCounter.clear();
// Pick the next root move, and print the move and the move number to
// the standard output.
move = ss[0].currentMove = rml.get_move(i);
if (current_search_time() >= 1000)
std::cout << "info currmove " << move
<< " currmovenumber " << i + 1 << std::endl;
// Decide search depth for this move
bool dangerous;
ext = extension(pos, move, true, pos.move_is_capture(move), pos.move_is_check(move), false, false, &dangerous);
newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
// Make the move, and search it
pos.do_move(move, u, dcCandidates);
if (i < MultiPV)
{
value = -search_pv(pos, ss, -beta, VALUE_INFINITE, newDepth, 1, 0);
// If the value has dropped a lot compared to the last iteration,
// set the boolean variable Problem to true. This variable is used
// for time managment: When Problem is true, we try to complete the
// current iteration before playing a move.
Problem = (Iteration >= 2 && value <= ValueByIteration[Iteration-1] - ProblemMargin);
if (Problem && StopOnPonderhit)
StopOnPonderhit = false;
}
else
{
value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
if (value > alpha)
{
// Fail high! Set the boolean variable FailHigh to true, and
// re-search the move with a big window. The variable FailHigh is
// used for time managment: We try to avoid aborting the search
// prematurely during a fail high research.
FailHigh = true;
value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
}
}
pos.undo_move(move, u);
// Finished searching the move. If AbortSearch 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 (AbortSearch)
break;
// Remember the node count for this move. The node counts are used to
// sort the root moves at the next iteration.
rml.set_move_nodes(i, nodes_searched() - nodes);
// Remember the beta-cutoff statistics
int64_t our, their;
BetaCounter.read(pos.side_to_move(), our, their);
rml.set_beta_counters(i, our, their);
assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
if (value <= alpha && i >= MultiPV)
rml.set_move_score(i, -VALUE_INFINITE);
else
{
// New best move!
// Update PV
rml.set_move_score(i, value);
update_pv(ss, 0);
rml.set_move_pv(i, ss[0].pv);
if (MultiPV == 1)
{
// We record how often the best move has been changed in each
// iteration. This information is used for time managment: When
// the best move changes frequently, we allocate some more time.
if (i > 0)
BestMoveChangesByIteration[Iteration]++;
// Print search information to the standard output:
std::cout << "info depth " << Iteration
<< " score " << value_to_string(value)
<< " time " << current_search_time()
<< " nodes " << nodes_searched()
<< " nps " << nps()
<< " pv ";
for (int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
std::cout << ss[0].pv[j] << " ";
std::cout << std::endl;
if (UseLogFile)
LogFile << pretty_pv(pos, current_search_time(), Iteration, nodes_searched(), value, ss[0].pv)
<< std::endl;
alpha = value;
// Reset the global variable Problem to false if the value isn't too
// far below the final value from the last iteration.
if (value > ValueByIteration[Iteration - 1] - NoProblemMargin)
Problem = false;
}
else // MultiPV > 1
{
rml.sort_multipv(i);
for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
{
int k;
std::cout << "info multipv " << j + 1
<< " score " << value_to_string(rml.get_move_score(j))
<< " depth " << ((j <= i)? Iteration : Iteration - 1)
<< " time " << current_search_time()
<< " nodes " << nodes_searched()
<< " nps " << nps()
<< " pv ";
for (k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
std::cout << rml.get_move_pv(j, k) << " ";
std::cout << std::endl;
}
alpha = rml.get_move_score(Min(i, MultiPV-1));
}
}
}
return alpha;
}
// search_pv() is the main search function for PV nodes.
Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
Depth depth, int ply, int threadID) {
assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
assert(beta > alpha && beta <= VALUE_INFINITE);
assert(ply >= 0 && ply < PLY_MAX);
assert(threadID >= 0 && threadID < ActiveThreads);
if (depth < OnePly)
return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
// Initialize, and make an early exit in case of an aborted search,
// an instant draw, maximum ply reached, etc.
init_node(pos, ss, ply, threadID);
// After init_node() that calls poll()
if (AbortSearch || thread_should_stop(threadID))
return Value(0);
if (pos.is_draw())
return VALUE_DRAW;
EvalInfo ei;
if (ply >= PLY_MAX - 1)
return evaluate(pos, ei, threadID);
// Mate distance pruning
Value oldAlpha = alpha;
alpha = Max(value_mated_in(ply), alpha);
beta = Min(value_mate_in(ply+1), beta);
if (alpha >= beta)
return alpha;
// Transposition table lookup. At PV nodes, we don't use the TT for
// pruning, but only for move ordering.
const TTEntry* tte = TT.retrieve(pos);
Move ttMove = (tte ? tte->move() : MOVE_NONE);
// Go with internal iterative deepening if we don't have a TT move
if (UseIIDAtPVNodes && ttMove == MOVE_NONE && depth >= 5*OnePly)
{
search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
ttMove = ss[ply].pv[ply];
}
// Initialize a MovePicker object for the current position, and prepare
// to search all moves
MovePicker mp = MovePicker(pos, true, ttMove, ss[ply], depth);
Move move, movesSearched[256];
int moveCount = 0;
Value value, bestValue = -VALUE_INFINITE;
Bitboard dcCandidates = mp.discovered_check_candidates();
bool isCheck = pos.is_check();
bool mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
// Loop through all legal moves until no moves remain or a beta cutoff
// occurs.
while ( alpha < beta
&& (move = mp.get_next_move()) != MOVE_NONE
&& !thread_should_stop(threadID))
{
assert(move_is_ok(move));
bool singleReply = (isCheck && mp.number_of_moves() == 1);
bool moveIsCheck = pos.move_is_check(move, dcCandidates);
bool moveIsCapture = pos.move_is_capture(move);