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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) 2008-2009 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 <cstring>
#include <fstream>
#include <iostream>
#include <sstream>
#include "bitcount.h"
#include "book.h"
#include "evaluate.h"
#include "history.h"
#include "misc.h"
#include "movegen.h"
#include "movepick.h"
#include "lock.h"
#include "san.h"
#include "search.h"
#include "thread.h"
#include "tt.h"
#include "ucioption.h"
////
//// Local definitions
////
namespace {
/// Types
// IterationInfoType stores search results for each iteration
//
// Because we use relatively small (dynamic) aspiration window,
// there happens many fail highs and fail lows in root. And
// because we don't do researches in those cases, "value" stored
// here is not necessarily exact. Instead in case of fail high/low
// we guess what the right value might be and store our guess
// as a "speculated value" and then move on. Speculated values are
// used just to calculate aspiration window width, so also if are
// not exact is not big a problem.
struct IterationInfoType {
IterationInfoType(Value v = Value(0), Value sv = Value(0))
: value(v), speculatedValue(sv) {}
Value value, speculatedValue;
};
// 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. The counters are per thread variables to avoid
// concurrent accessing under SMP case.
struct BetaCounterType {
BetaCounterType();
void clear();
void add(Color us, Depth d, int threadID);
void read(Color us, int64_t& our, int64_t& their);
};
// 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
// Search depth at iteration 1
const Depth InitialDepth = OnePly /*+ OnePly/2*/;
// Depth limit for selective search
const Depth SelectiveDepth = 7 * OnePly;
// Use internal iterative deepening?
const bool UseIIDAtPVNodes = true;
const bool UseIIDAtNonPVNodes = 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;
// Margins for futility pruning in the quiescence search, and at frontier
// and near frontier nodes.
const Value FutilityMarginQS = Value(0x80);
// Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
const Value FutilityMargins[12] = { Value(0x100), Value(0x120), Value(0x200), Value(0x220), Value(0x250), Value(0x270),
// 4 ply 4.5 ply 5 ply 5.5 ply 6 ply 6.5 ply
Value(0x2A0), Value(0x2C0), Value(0x340), Value(0x360), Value(0x3A0), Value(0x3C0) };
// Razoring
const Depth RazorDepth = 4*OnePly;
// Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
const Value RazorMargins[6] = { Value(0x180), Value(0x300), Value(0x300), Value(0x3C0), Value(0x3C0), Value(0x3C0) };
// Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
const Value RazorApprMargins[6] = { Value(0x520), Value(0x300), Value(0x300), Value(0x300), Value(0x300), Value(0x300) };
/// Variables initialized by UCI options
// Adjustable playing strength
int Slowdown = 0;
const int SlowdownArray[32] = {
19, 41, 70, 110, 160, 230, 320, 430, 570, 756, 1000, 1300, 1690, 2197,
2834, 3600, 4573, 5809, 7700, 9863, 12633, 16181, 20726, 26584, 34005,
43557, 55792, 71463, 91536, 117247, 150180, 192363
};
int Strength;
const int MaxStrength = 25;
// Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV nodes
int LMRPVMoves, LMRNonPVMoves; // heavy SMP read access for the latter
// Depth limit for use of dynamic threat detection
Depth ThreatDepth; // heavy SMP read access
// Last seconds noise filtering (LSN)
const bool UseLSNFiltering = true;
const int LSNTime = 4000; // In milliseconds
const Value LSNValue = value_from_centipawns(200);
bool loseOnTime = false;
// Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
// There is heavy SMP read access on these arrays
Depth CheckExtension[2], SingleReplyExtension[2], PawnPushTo7thExtension[2];
Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
// Iteration counters
int Iteration;
BetaCounterType BetaCounter; // has per-thread internal data
// Scores and number of times the best move changed for each iteration
IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
// MultiPV mode
int MultiPV;
// Time managment variables
int SearchStartTime;
int MaxNodes, MaxDepth;
int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
int RootMoveNumber;
bool InfiniteSearch;
bool PonderSearch;
bool StopOnPonderhit;
bool AbortSearch; // heavy SMP read access
bool Quit;
bool FailHigh;
bool FailLow;
bool Problem;
// Show current line?
bool ShowCurrentLine;
// Log file
bool UseLogFile;
std::ofstream LogFile;
// MP related variables
int ActiveThreads = 1;
Depth MinimumSplitDepth;
int MaxThreadsPerSplitPoint;
Thread Threads[THREAD_MAX];
Lock MPLock;
Lock IOLock;
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
// Node counters, used only by thread[0] but try to keep in different
// cache lines (64 bytes each) from the heavy SMP read accessed variables.
int NodesSincePoll;
int NodesBetweenPolls = 30000;
// History table
History H;
/// Functions
Value id_loop(const Position& pos, Move searchMoves[]);
Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta);
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_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);
void slowdown(const Position& pos);
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
}
////
//// 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(). It returns false
/// when a quit command is received during the search.
bool 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.open("book.bin");
bookMove = OpeningBook.get_move(pos);
if (bookMove != MOVE_NONE)
{
std::cout << "bestmove " << bookMove << std::endl;
return true;
}
}
// Initialize global search variables
Idle = false;
SearchStartTime = get_system_time();
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;
FailLow = 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();
loseOnTime = false; // reset at the beginning of a new game
}
bool 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;
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);
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());
// Set the number of active threads. If UCI_LimitStrength is enabled, never
// use more than one thread.
int newActiveThreads =
get_option_value_bool("UCI_LimitStrength")? 1 : 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 playing strength
if (get_option_value_bool("UCI_LimitStrength"))
{
Strength = (get_option_value_int("UCI_Elo") - 2100) / 25;
Slowdown =
(Strength == MaxStrength)? 0 : SlowdownArray[Max(0, 31-Strength)];
}
else
{
Strength = MaxStrength;
Slowdown = 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 if (Slowdown) {
if (Slowdown > 50000) NodesBetweenPolls = 30;
else if (Slowdown > 10000) NodesBetweenPolls = 100;
else if (Slowdown > 1000) NodesBetweenPolls = 500;
else if (Slowdown > 100) NodesBetweenPolls = 3000;
else NodesBetweenPolls = 15000;
}
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
//
// FIXME we really need to cleanup all this LSN ugliness
if (!loseOnTime)
{
Value v = id_loop(pos, searchMoves);
loseOnTime = ( UseLSNFiltering
&& myTime < LSNTime
&& myIncrement == 0
&& v < -LSNValue);
}
else
{
loseOnTime = 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();
Idle = true;
return !Quit;
}
/// 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);
}
}
/// 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;
}
// SearchStack::init() initializes a search stack. Used at the beginning of a
// new search from the root.
void SearchStack::init(int ply) {
pv[ply] = pv[ply + 1] = MOVE_NONE;
currentMove = threatMove = MOVE_NONE;
reduction = Depth(0);
}
void SearchStack::initKillers() {
mateKiller = MOVE_NONE;
for (int i = 0; i < KILLER_MAX; i++)
killers[i] = MOVE_NONE;
}
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();
for (int i = 0; i < 3; i++)
{
ss[i].init(i);
ss[i].initKillers();
}
IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
Iteration = 1;
Move EasyMove = rml.scan_for_easy_move();
// Iterative deepening loop
while (Iteration < PLY_MAX)
{
// Initialize iteration
rml.sort();
Iteration++;
BestMoveChangesByIteration[Iteration] = 0;
if (Iteration <= 5)
ExtraSearchTime = 0;
std::cout << "info depth " << Iteration << std::endl;
// Calculate dynamic search window based on previous iterations
Value alpha, beta;
if (MultiPV == 1 && Iteration >= 6 && abs(IterationInfo[Iteration - 1].value) < VALUE_KNOWN_WIN)
{
int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
int delta = Max(2 * abs(prevDelta1) + abs(prevDelta2), ProblemMargin);
alpha = Max(IterationInfo[Iteration - 1].value - delta, -VALUE_INFINITE);
beta = Min(IterationInfo[Iteration - 1].value + delta, VALUE_INFINITE);
}
else
{
alpha = - VALUE_INFINITE;
beta = VALUE_INFINITE;
}
// Search to the current depth
Value value = root_search(p, ss, rml, alpha, beta);
// Write PV to transposition table, in case the relevant entries have
// been overwritten during the search.
TT.insert_pv(p, ss[0].pv);
if (AbortSearch)
break; // Value cannot be trusted. Break out immediately!
//Save info about search result
Value speculatedValue;
bool fHigh = false;
bool fLow = false;
Value delta = value - IterationInfo[Iteration - 1].value;
if (value >= beta)
{
assert(delta > 0);
fHigh = true;
speculatedValue = value + delta;
BestMoveChangesByIteration[Iteration] += 2; // Allocate more time
}
else if (value <= alpha)
{
assert(value == alpha);
assert(delta < 0);
fLow = true;
speculatedValue = value + delta;
BestMoveChangesByIteration[Iteration] += 3; // Allocate more time
} else
speculatedValue = value;
speculatedValue = Min(Max(speculatedValue, -VALUE_INFINITE), VALUE_INFINITE);
IterationInfo[Iteration] = IterationInfoType(value, speculatedValue);
// 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(IterationInfo[Iteration].value) >= abs(VALUE_MATE) - 100
&& abs(IterationInfo[Iteration-1].value) >= 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
&& !fLow
&& !fHigh
&& 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);
// 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)
{
//FIXME: Implement fail-low emergency measures
if (!PonderSearch)
break;
else
StopOnPonderhit = true;
}
}
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
if (ss[0].pv[0] == MOVE_NONE)
{
ss[0].pv[0] = rml.get_move(0);
ss[0].pv[1] = MOVE_NONE;
}
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);
StateInfo st;
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], st);
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 beta) {
Value oldAlpha = alpha;
Value 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++)
{
if (alpha >= beta)
{
// We failed high, invalidate and skip next moves, leave node-counters
// and beta-counters as they are and quickly return, we will try to do
// a research at the next iteration with a bigger aspiration window.
rml.set_move_score(i, -VALUE_INFINITE);
continue;
}
int64_t nodes;
Move move;
StateInfo st;
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 moveIsCapture = pos.move_is_capture(move);
bool dangerous;
ext = extension(pos, move, true, moveIsCapture, pos.move_is_check(move), false, false, &dangerous);
newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
// Make the move, and search it
pos.do_move(move, st, dcCandidates);
if (i < MultiPV)
{
// Aspiration window is disabled in multi-pv case
if (MultiPV > 1)
alpha = -VALUE_INFINITE;
value = -search_pv(pos, ss, -beta, -alpha, 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 <= IterationInfo[Iteration-1].value - ProblemMargin);
if (Problem && StopOnPonderhit)
StopOnPonderhit = false;
}
else
{
if ( newDepth >= 3*OnePly
&& i >= MultiPV + LMRPVMoves
&& !dangerous
&& !moveIsCapture
&& !move_is_promotion(move)
&& !move_is_castle(move))
{
ss[0].reduction = OnePly;
value = -search(pos, ss, -alpha, newDepth-OnePly, 1, true, 0);
} else
value = alpha + 1; // Just to trigger next condition
if (value > alpha)
{
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);
// 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
{
// PV move or new best move!
// Update PV
rml.set_move_score(i, value);
update_pv(ss, 0);
TT.extract_pv(pos, ss[0].pv);
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)
<< ((value >= beta)?
" lowerbound" : ((value <= alpha)? " upperbound" : ""))
<< " 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;