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stockfish/src/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
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Stockfish is free software: you can redistribute it and/or modify
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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,
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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.
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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>
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#include <fstream>
#include <iostream>
#include <sstream>
#include "book.h"
#include "evaluate.h"
#include "history.h"
#include "misc.h"
#include "movegen.h"
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#include "movepick.h"
#include "lock.h"
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#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);
};
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// 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 {
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RootMove();
bool operator<(const RootMove&); // used to sort
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Move move;
Value score;
int64_t nodes, cumulativeNodes;
Move pv[PLY_MAX_PLUS_2];
int64_t ourBeta, theirBeta;
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};
// 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);
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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;
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Move scan_for_easy_move() const;
inline void sort();
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void sort_multipv(int n);
private:
static const int MaxRootMoves = 500;
RootMove moves[MaxRootMoves];
int count;
};
/// Constants
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// Search depth at iteration 1
const Depth InitialDepth = OnePly /*+ OnePly/2*/;
// Depth limit for selective search
const Depth SelectiveDepth = 7 * OnePly;
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// 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.
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const Value IIDMargin = Value(0x100);
// Easy move margin. An easy move candidate must be at least this much
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// 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
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// 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
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// 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
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// 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
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// understand their precise meaning.
const bool PruneEscapeMoves = false;
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const bool PruneDefendingMoves = false;
const bool PruneBlockingMoves = false;
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// Margins for futility pruning in the quiescence search, and at frontier
// and near frontier nodes.
const Value FutilityMarginQS = Value(0x80);
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// 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;
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// 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) };
// The main transposition table
TranspositionTable TT;
/// Variables initialized by UCI options
// 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
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// Last seconds noise filtering (LSN)
bool UseLSNFiltering;
bool looseOnTime = false;
int LSNTime; // In milliseconds
Value LSNValue;
// 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];
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// Iteration counters
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int Iteration;
BetaCounterType BetaCounter; // has per-thread internal data
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// Scores and number of times the best move changed for each iteration
IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
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int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
// MultiPV mode
int MultiPV;
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// Time managment variables
int SearchStartTime;
int MaxNodes, MaxDepth;
int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime;
Move EasyMove;
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int RootMoveNumber;
bool InfiniteSearch;
bool PonderSearch;
bool StopOnPonderhit;
bool AbortSearch; // heavy SMP read access
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bool Quit;
bool FailHigh;
bool FailLow;
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bool Problem;
bool PonderingEnabled;
int ExactMaxTime;
// Show current line?
bool ShowCurrentLine;
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// Log file
bool UseLogFile;
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std::ofstream LogFile;
// MP related variables
int ActiveThreads = 1;
Depth MinimumSplitDepth;
int MaxThreadsPerSplitPoint;
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Thread Threads[THREAD_MAX];
Lock MPLock;
Lock IOLock;
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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;
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/// 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(SearchStack ss[], int ply, int threadID);
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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, const History& H);
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, History& H, Move movesSearched[], int moveCount);
void update_killers(Move m, SearchStack& ss);
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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);
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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);
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void wake_sleeping_threads();
#if !defined(_MSC_VER)
void *init_thread(void *threadID);
#else
DWORD WINAPI init_thread(LPVOID threadID);
#endif
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}
////
//// 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.
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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[]) {
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// 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;
}
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}
// Initialize global search variables
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Idle = false;
SearchStartTime = get_system_time();
EasyMove = MOVE_NONE;
for (int i = 0; i < THREAD_MAX; i++)
{
Threads[i].nodes = 0ULL;
Threads[i].failHighPly1 = false;
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}
NodesSincePoll = 0;
InfiniteSearch = infinite;
PonderSearch = ponder;
StopOnPonderhit = false;
AbortSearch = false;
Quit = false;
FailHigh = false;
FailLow = false;
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Problem = false;
ExactMaxTime = maxTime;
// Read UCI option values
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TT.set_size(get_option_value_int("Hash"));
if (button_was_pressed("Clear Hash"))
TT.clear();
PonderingEnabled = get_option_value_bool("Ponder");
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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)"));
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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;
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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);
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"));
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MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
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read_weights(pos.side_to_move());
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int newActiveThreads = get_option_value_int("Threads");
if (newActiveThreads != ActiveThreads)
{
ActiveThreads = newActiveThreads;
init_eval(ActiveThreads);
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}
// Wake up sleeping threads
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wake_sleeping_threads();
for (int i = 1; i < ActiveThreads; i++)
assert(thread_is_available(i, 0));
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// 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;
}
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}
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);
}
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}
if (PonderingEnabled)
{
MaxSearchTime += MaxSearchTime / 4;
MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
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}
// Fixed depth or fixed number of nodes?
MaxDepth = maxDepth;
if (MaxDepth)
InfiniteSearch = true; // HACK
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MaxNodes = maxNodes;
if (MaxNodes)
{
NodesBetweenPolls = Min(MaxNodes, 30000);
InfiniteSearch = true; // HACK
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}
else
NodesBetweenPolls = 30000;
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// 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
}
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if (UseLogFile)
LogFile.close();
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Idle = true;
return !Quit;
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}
/// 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() {
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volatile int i;
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#if !defined(_MSC_VER)
pthread_t pthread[1];
#endif
for (i = 0; i < THREAD_MAX; i++)
Threads[i].activeSplitPoints = 0;
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// Initialize global locks
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lock_init(&MPLock, NULL);
lock_init(&IOLock, NULL);
init_split_point_stack();
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#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);
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#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;
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}
// Launch the helper threads
for(i = 1; i < THREAD_MAX; i++)
{
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#if !defined(_MSC_VER)
pthread_create(pthread, NULL, init_thread, (void*)(&i));
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#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);
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}
}
/// stop_threads() is called when the program exits. It makes all the
/// helper threads exit cleanly.
void stop_threads() {
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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);
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}
destroy_split_point_stack();
}
/// nodes_searched() returns the total number of nodes searched so far in
/// the current search.
int64_t nodes_searched() {
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int64_t result = 0ULL;
for (int i = 0; i < ActiveThreads; i++)
result += Threads[i].nodes;
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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;
}
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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[]) {
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Position p(pos);
SearchStack ss[PLY_MAX_PLUS_2];
// searchMoves are verified, copied, scored and sorted
RootMoveList rml(p, searchMoves);
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// Initialize
TT.new_search();
for (int i = 0; i < THREAD_MAX; i++)
Threads[i].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));
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Iteration = 1;
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;
}
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}
if (MaxDepth && Iteration >= MaxDepth)
break;
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}
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();
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else
// Print final search statistics
std::cout << "info nodes " << nodes_searched()
<< " nps " << nps()
<< " time " << current_search_time()
<< " hashfull " << TT.full() << std::endl;
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// 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;
}
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std::cout << "bestmove " << ss[0].pv[0];
if (ss[0].pv[1] != MOVE_NONE)
std::cout << " ponder " << ss[0].pv[1];
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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;
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}
return rml.get_move_score(0);
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}
// 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());
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// 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 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, 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
{
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);
}
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}
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);
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;
if (value > alpha)
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 > IterationInfo[Iteration - 1].value - 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));
}
} // New best move case
assert(alpha >= oldAlpha);
FailLow = (alpha == oldAlpha);
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}
return alpha;
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}
// search_pv() is the main search function for PV nodes.
Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
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Depth depth, int ply, int threadID) {
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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);
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// Initialize, and make an early exit in case of an aborted search,
// an instant draw, maximum ply reached, etc.
init_node(ss, ply, threadID);
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// After init_node() that calls poll()
if (AbortSearch || thread_should_stop(threadID))
return Value(0);
if (pos.is_draw())
return VALUE_DRAW;
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EvalInfo ei;
if (ply >= PLY_MAX - 1)
return evaluate(pos, ei, threadID);
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// Mate distance pruning
Value oldAlpha = alpha;
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alpha = Max(value_mated_in(ply), alpha);
beta = Min(value_mate_in(ply+1), beta);
if (alpha >= beta)
return alpha;
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// 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.get_key());
Move ttMove = (tte ? tte->move() : MOVE_NONE);
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// 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];
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}
// Initialize a MovePicker object for the current position, and prepare
// to search all moves
MovePicker mp = MovePicker(pos, ttMove, depth, Threads[threadID].H, &ss[ply]);
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Move move, movesSearched[256];
int moveCount = 0;
Value value, bestValue = -VALUE_INFINITE;
Bitboard dcCandidates = mp.discovered_check_candidates();
Color us = pos.side_to_move();
bool isCheck = pos.is_check();
bool mateThreat = pos.has_mate_threat(opposite_color(us));
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// 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);
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bool moveIsCapture = pos.move_is_capture(move);
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movesSearched[moveCount++] = ss[ply].currentMove = move;
// Decide the new search depth
bool dangerous;
Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
Depth newDepth = depth - OnePly + ext;
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// Make and search the move
StateInfo st;
pos.do_move(move, st, dcCandidates);
if (moveCount == 1) // The first move in list is the PV
value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
else
{
// Try to reduce non-pv search depth by one ply if move seems not problematic,
// if the move fails high will be re-searched at full depth.
if ( depth >= 2*OnePly
&& moveCount >= LMRPVMoves
&& !dangerous
&& !moveIsCapture
&& !move_is_promotion(move)
&& !move_is_castle(move)
&& !move_is_killer(move, ss[ply]))
{
ss[ply].reduction = OnePly;
value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true, threadID);
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}
else
value = alpha + 1; // Just to trigger next condition
if (value > alpha) // Go with full depth non-pv search
{
ss[ply].reduction = Depth(0);
value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
if (value > alpha && value < beta)
{
// When the search fails high at ply 1 while searching the first
// move at the root, set the flag failHighPly1. This is used for
// time managment: We don't want to stop the search early in
// such cases, because resolving the fail high at ply 1 could
// result in a big drop in score at the root.
if (ply == 1 && RootMoveNumber == 1)
Threads[threadID].failHighPly1 = true;
// A fail high occurred. Re-search at full window (pv search)
value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
Threads[threadID].failHighPly1 = false;
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}
}
}
pos.undo_move(move);
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assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
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// New best move?
if (value > bestValue)
{
bestValue = value;
if (value > alpha)
{
alpha = value;
update_pv(ss, ply);
if (value == value_mate_in(ply + 1))
ss[ply].mateKiller = move;
}
// If we are at ply 1, and we are searching the first root move at
// ply 0, set the 'Problem' variable if the score has dropped a lot
// (from the computer's point of view) since the previous iteration.
if ( ply == 1
&& Iteration >= 2
&& -value <= IterationInfo[Iteration-1].value - ProblemMargin)
Problem = true;
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}
// Split?
if ( ActiveThreads > 1
&& bestValue < beta
&& depth >= MinimumSplitDepth
&& Iteration <= 99
&& idle_thread_exists(threadID)
&& !AbortSearch
&& !thread_should_stop(threadID)
&& split(pos, ss, ply, &alpha, &beta, &bestValue, depth,
&moveCount, &mp, dcCandidates, threadID, true))
break;
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}
// All legal moves have been searched. A special case: If there were
// no legal moves, it must be mate or stalemate.
if (moveCount == 0)
return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
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// If the search is not aborted, update the transposition table,
// history counters, and killer moves.
if (AbortSearch || thread_should_stop(threadID))
return bestValue;
if (bestValue <= oldAlpha)
TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
else if (bestValue >= beta)
{
BetaCounter.add(pos.side_to_move(), depth, threadID);
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Move m = ss[ply].pv[ply];
if (ok_to_history(pos, m)) // Only non capture moves are considered
{
update_history(pos, m, depth, Threads[threadID].H, movesSearched, moveCount);
update_killers(m, ss[ply]);
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}
TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
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}
else
TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
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return bestValue;
}
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// search() is the search function for zero-width nodes.
Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
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int ply, bool allowNullmove, int threadID) {
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assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
assert(ply >= 0 && ply < PLY_MAX);
assert(threadID >= 0 && threadID < ActiveThreads);
if (depth < OnePly)
return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
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// Initialize, and make an early exit in case of an aborted search,
// an instant draw, maximum ply reached, etc.
init_node(ss, ply, threadID);
// After init_node() that calls poll()
if (AbortSearch || thread_should_stop(threadID))
return Value(0);
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if (pos.is_draw())
return VALUE_DRAW;
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EvalInfo ei;
if (ply >= PLY_MAX - 1)
return evaluate(pos, ei, threadID);
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// Mate distance pruning
if (value_mated_in(ply) >= beta)
return beta;
if (value_mate_in(ply + 1) < beta)
return beta - 1;
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// Transposition table lookup
const TTEntry* tte = TT.retrieve(pos.get_key());
Move ttMove = (tte ? tte->move() : MOVE_NONE);
if (tte && ok_to_use_TT(tte, depth, beta, ply))
{
ss[ply].currentMove = ttMove; // can be MOVE_NONE
return value_from_tt(tte->value(), ply);
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}
Value approximateEval = quick_evaluate(pos);
bool mateThreat = false;
bool isCheck = pos.is_check();
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// Null move search
if ( allowNullmove
&& depth > OnePly
&& !isCheck
&& !value_is_mate(beta)
&& ok_to_do_nullmove(pos)
&& approximateEval >= beta - NullMoveMargin)
{
ss[ply].currentMove = MOVE_NULL;
StateInfo st;
pos.do_null_move(st);
int R = (depth >= 5 * OnePly ? 4 : 3); // Null move dynamic reduction
Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
pos.undo_null_move();
if (value_is_mate(nullValue))
{
/* Do not return unproven mates */
}
else if (nullValue >= beta)
{
if (depth < 6 * OnePly)
return beta;
// Do zugzwang verification search
Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
if (v >= beta)
return beta;
} 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).
if (nullValue == value_mated_in(ply + 2))
mateThreat = true;
ss[ply].threatMove = ss[ply + 1].currentMove;
if ( depth < ThreatDepth
&& ss[ply - 1].reduction
&& connected_moves(pos, ss[ply - 1].currentMove, ss[ply].threatMove))
return beta - 1;
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}
}
// Null move search not allowed, try razoring
else if ( !value_is_mate(beta)
&& depth < RazorDepth
&& approximateEval < beta - RazorApprMargins[int(depth) - 2]
&& ss[ply - 1].currentMove != MOVE_NULL
&& ttMove == MOVE_NONE
&& !pos.has_pawn_on_7th(pos.side_to_move()))
{
Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
if (v < beta - RazorMargins[int(depth) - 2])
return v;
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}
// Go with internal iterative deepening if we don't have a TT move
if (UseIIDAtNonPVNodes && ttMove == MOVE_NONE && depth >= 8*OnePly &&
evaluate(pos, ei, threadID) >= beta - IIDMargin)
{
search(pos, ss, beta, Min(depth/2, depth-2*OnePly), ply, false, threadID);
ttMove = ss[ply].pv[ply];
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}
// Initialize a MovePicker object for the current position, and prepare
// to search all moves.
MovePicker mp = MovePicker(pos, ttMove, depth, Threads[threadID].H, &ss[ply]);
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Move move, movesSearched[256];
int moveCount = 0;
Value value, bestValue = -VALUE_INFINITE;
Bitboard dcCandidates = mp.discovered_check_candidates();
Value futilityValue = VALUE_NONE;
bool useFutilityPruning = depth < SelectiveDepth
&& !isCheck;
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// Loop through all legal moves until no moves remain or a beta cutoff
// occurs.
while ( bestValue < beta
&& (move = mp.get_next_move()) != MOVE_NONE
&& !thread_should_stop(threadID))
{
assert(move_is_ok(move));
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bool singleReply = (isCheck && mp.number_of_moves() == 1);
bool moveIsCheck = pos.move_is_check(move, dcCandidates);
bool moveIsCapture = pos.move_is_capture(move);
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movesSearched[moveCount++] = ss[ply].currentMove = move;
// Decide the new search depth
bool dangerous;
Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, singleReply, mateThreat, &dangerous);
Depth newDepth = depth - OnePly + ext;
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// Futility pruning
if ( useFutilityPruning
&& !dangerous
&& !moveIsCapture
&& !move_is_promotion(move))
{
// History pruning. See ok_to_prune() definition
if ( moveCount >= 2 + int(depth)
&& ok_to_prune(pos, move, ss[ply].threatMove, depth, Threads[threadID].H))
continue;
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// Value based pruning
if (approximateEval < beta)
{
if (futilityValue == VALUE_NONE)
futilityValue = evaluate(pos, ei, threadID)
+ FutilityMargins[int(depth) - 2];
if (futilityValue < beta)
{
if (futilityValue > bestValue)
bestValue = futilityValue;
continue;
}
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}
}
// Make and search the move
StateInfo st;
pos.do_move(move, st, dcCandidates);
// Try to reduce non-pv search depth by one ply if move seems not problematic,
// if the move fails high will be re-searched at full depth.
if ( depth >= 2*OnePly
&& moveCount >= LMRNonPVMoves
&& !dangerous
&& !moveIsCapture
&& !move_is_promotion(move)
&& !move_is_castle(move)
&& !move_is_killer(move, ss[ply]))
{
ss[ply].reduction = OnePly;
value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true, threadID);
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}
else
value = beta; // Just to trigger next condition
if (value >= beta) // Go with full depth non-pv search
{
ss[ply].reduction = Depth(0);
value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
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}
pos.undo_move(move);
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assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
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// New best move?
if (value > bestValue)
{
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bestValue = value;
if (value >= beta)
update_pv(ss, ply);
if (value == value_mate_in(ply + 1))
ss[ply].mateKiller = move;
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}
// Split?
if ( ActiveThreads > 1
&& bestValue < beta
&& depth >= MinimumSplitDepth
&& Iteration <= 99
&& idle_thread_exists(threadID)
&& !AbortSearch
&& !thread_should_stop(threadID)
&& split(pos, ss, ply, &beta, &beta, &bestValue, depth, &moveCount,
&mp, dcCandidates, threadID, false))
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break;
}
// All legal moves have been searched. A special case: If there were
// no legal moves, it must be mate or stalemate.
if (moveCount == 0)
return (pos.is_check() ? value_mated_in(ply) : VALUE_DRAW);
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// If the search is not aborted, update the transposition table,
// history counters, and killer moves.
if (AbortSearch || thread_should_stop(threadID))
return bestValue;
if (bestValue < beta)
TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
else
{
BetaCounter.add(pos.side_to_move(), depth, threadID);
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Move m = ss[ply].pv[ply];
if (ok_to_history(pos, m)) // Only non capture moves are considered
{
update_history(pos, m, depth, Threads[threadID].H, movesSearched, moveCount);
update_killers(m, ss[ply]);
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}
TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
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}
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
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return bestValue;
}
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// 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 OnePly).
Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
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Depth depth, int ply, int threadID) {
assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
assert(depth <= 0);
assert(ply >= 0 && ply < PLY_MAX);
assert(threadID >= 0 && threadID < ActiveThreads);
// Initialize, and make an early exit in case of an aborted search,
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// an instant draw, maximum ply reached, etc.
init_node(ss, ply, threadID);
// After init_node() that calls poll()
if (AbortSearch || thread_should_stop(threadID))
return Value(0);
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if (pos.is_draw())
return VALUE_DRAW;
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// Transposition table lookup, only when not in PV
TTEntry* tte = NULL;
bool pvNode = (beta - alpha != 1);
if (!pvNode)
{
tte = TT.retrieve(pos.get_key());
if (tte && ok_to_use_TT(tte, depth, beta, ply))
{
assert(tte->type() != VALUE_TYPE_EVAL);
return value_from_tt(tte->value(), ply);
}
}
Move ttMove = (tte ? tte->move() : MOVE_NONE);
// Evaluate the position statically
EvalInfo ei;
Value staticValue;
bool isCheck = pos.is_check();
ei.futilityMargin = Value(0); // Manually initialize futilityMargin
if (isCheck)
staticValue = -VALUE_INFINITE;
else if (tte && tte->type() == VALUE_TYPE_EVAL)
{
// Use the cached evaluation score if possible
assert(tte->value() == evaluate(pos, ei, threadID));
assert(ei.futilityMargin == Value(0));
staticValue = tte->value();
}
else
staticValue = evaluate(pos, ei, threadID);
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if (ply == PLY_MAX - 1)
return evaluate(pos, ei, threadID);
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// Initialize "stand pat score", and return it immediately if it is
// at least beta.
Value bestValue = staticValue;
if (bestValue >= beta)
{
// Store the score to avoid a future costly evaluation() call
if (!isCheck && !tte && ei.futilityMargin == 0)
TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EVAL, Depth(-127*OnePly), MOVE_NONE);
return bestValue;
}
if (bestValue > alpha)
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alpha = bestValue;
// 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 == 0) will be generated.
MovePicker mp = MovePicker(pos, ttMove, depth, Threads[threadID].H);
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Move move;
int moveCount = 0;
Bitboard dcCandidates = mp.discovered_check_candidates();
Color us = pos.side_to_move();
bool enoughMaterial = pos.non_pawn_material(us) > RookValueMidgame;
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// Loop through the moves until no moves remain or a beta cutoff
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// occurs.
while ( alpha < beta
&& (move = mp.get_next_move()) != MOVE_NONE)
{
assert(move_is_ok(move));
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moveCount++;
ss[ply].currentMove = move;
// Futility pruning
if ( enoughMaterial
&& !isCheck
&& !pvNode
&& !move_is_promotion(move)
&& !pos.move_is_check(move, dcCandidates)
&& !pos.move_is_passed_pawn_push(move))
{
Value futilityValue = staticValue
+ Max(pos.midgame_value_of_piece_on(move_to(move)),
pos.endgame_value_of_piece_on(move_to(move)))
+ (move_is_ep(move) ? PawnValueEndgame : Value(0))
+ FutilityMarginQS
+ ei.futilityMargin;
if (futilityValue < alpha)
{
if (futilityValue > bestValue)
bestValue = futilityValue;
continue;
}
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}
// Don't search captures and checks with negative SEE values
if ( !isCheck
&& !move_is_promotion(move)
&& (pos.midgame_value_of_piece_on(move_from(move)) >
pos.midgame_value_of_piece_on(move_to(move)))
&& pos.see(move) < 0)
continue;
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// Make and search the move.
StateInfo st;
pos.do_move(move, st, dcCandidates);
Value value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
pos.undo_move(move);
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assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
// New best move?
if (value > bestValue)
{
bestValue = value;
if (value > alpha)
{
alpha = value;
update_pv(ss, ply);
}
}
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}
// All legal moves have been searched. A special case: If we're in check
// and no legal moves were found, it is checkmate.
if (pos.is_check() && moveCount == 0) // Mate!
return value_mated_in(ply);
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assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
// Update transposition table
Move m = ss[ply].pv[ply];
if (!pvNode)
{
Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
if (bestValue < beta)
TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE);
else
TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, m);
}
// Update killers only for good check moves
if (alpha >= beta && ok_to_history(pos, m)) // Only non capture moves are considered
update_killers(m, ss[ply]);
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return bestValue;
}
// sp_search() is used to search from a split point. This function is called
// by each thread working at the split point. It is similar to the normal
// search() function, but 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 in sp_search(). 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.
void sp_search(SplitPoint* sp, int threadID) {
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assert(threadID >= 0 && threadID < ActiveThreads);
assert(ActiveThreads > 1);
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Position pos = Position(sp->pos);
SearchStack* ss = sp->sstack[threadID];
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Value value;
Move move;
bool isCheck = pos.is_check();
bool useFutilityPruning = sp->depth < SelectiveDepth
&& !isCheck;
while ( sp->bestValue < sp->beta
&& !thread_should_stop(threadID)
&& (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
{
assert(move_is_ok(move));
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bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
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bool moveIsCapture = pos.move_is_capture(move);
lock_grab(&(sp->lock));
int moveCount = ++sp->moves;
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lock_release(&(sp->lock));
ss[sp->ply].currentMove = move;
// Decide the new search depth.
bool dangerous;
Depth ext = extension(pos, move, false, moveIsCapture, moveIsCheck, false, false, &dangerous);
Depth newDepth = sp->depth - OnePly + ext;
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// Prune?
if ( useFutilityPruning
&& !dangerous
&& !moveIsCapture
&& !move_is_promotion(move)
&& moveCount >= 2 + int(sp->depth)
&& ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth, Threads[threadID].H))
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continue;
// Make and search the move.
StateInfo st;
pos.do_move(move, st, sp->dcCandidates);
// Try to reduce non-pv search depth by one ply if move seems not problematic,
// if the move fails high will be re-searched at full depth.
if ( !dangerous
&& moveCount >= LMRNonPVMoves
&& !moveIsCapture
&& !move_is_promotion(move)
&& !move_is_castle(move)
&& !move_is_killer(move, ss[sp->ply]))
{
ss[sp->ply].reduction = OnePly;
value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1, true, threadID);
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}
else
value = sp->beta; // Just to trigger next condition
if (value >= sp->beta) // Go with full depth non-pv search
{
ss[sp->ply].reduction = Depth(0);
value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true, threadID);
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}
pos.undo_move(move);
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assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
if (thread_should_stop(threadID))
break;
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// New best move?
lock_grab(&(sp->lock));
if (value > sp->bestValue && !thread_should_stop(threadID))
{
sp->bestValue = value;
if (sp->bestValue >= sp->beta)
{
sp_update_pv(sp->parentSstack, ss, sp->ply);
for (int i = 0; i < ActiveThreads; i++)
if (i != threadID && (i == sp->master || sp->slaves[i]))
Threads[i].stop = true;
sp->finished = true;
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}
}
lock_release(&(sp->lock));
}
lock_grab(&(sp->lock));
// If this is the master thread and we have been asked to stop because of
// a beta cutoff higher up in the tree, stop all slave threads.
if (sp->master == threadID && thread_should_stop(threadID))
for (int i = 0; i < ActiveThreads; i++)
if (sp->slaves[i])
Threads[i].stop = true;
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sp->cpus--;
sp->slaves[threadID] = 0;
lock_release(&(sp->lock));
}
// sp_search_pv() is used to search from a PV split point. This function
// is called by each thread working at the split point. It is similar to
// the normal search_pv() function, but simpler. Because we have already
// probed the hash table and searched the first move before splitting, we
// don't have to repeat all this work in sp_search_pv(). We also don't
// need to store anything to the hash table here: This is taken care of
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// after we return from the split point.
void sp_search_pv(SplitPoint* sp, int threadID) {
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assert(threadID >= 0 && threadID < ActiveThreads);
assert(ActiveThreads > 1);
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Position pos = Position(sp->pos);
SearchStack* ss = sp->sstack[threadID];
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Value value;
Move move;
while ( sp->alpha < sp->beta
&& !thread_should_stop(threadID)
&& (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE)
{
bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
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bool moveIsCapture = pos.move_is_capture(move);
assert(move_is_ok(move));
lock_grab(&(sp->lock));
int moveCount = ++sp->moves;
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lock_release(&(sp->lock));
ss[sp->ply].currentMove = move;
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// Decide the new search depth.
bool dangerous;
Depth ext = extension(pos, move, true, moveIsCapture, moveIsCheck, false, false, &dangerous);
Depth newDepth = sp->depth - OnePly + ext;
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// Make and search the move.
StateInfo st;
pos.do_move(move, st, sp->dcCandidates);
// Try to reduce non-pv search depth by one ply if move seems not problematic,
// if the move fails high will be re-searched at full depth.
if ( !dangerous
&& moveCount >= LMRPVMoves
&& !moveIsCapture
&& !move_is_promotion(move)
&& !move_is_castle(move)
&& !move_is_killer(move, ss[sp->ply]))
{
ss[sp->ply].reduction = OnePly;
value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1, true, threadID);
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}
else
value = sp->alpha + 1; // Just to trigger next condition
if (value > sp->alpha) // Go with full depth non-pv search
{
ss[sp->ply].reduction = Depth(0);
value = -search(pos, ss, -sp->alpha, newDepth, sp->ply+1, true, threadID);
if (value > sp->alpha && value < sp->beta)
{
// When the search fails high at ply 1 while searching the first
// move at the root, set the flag failHighPly1. This is used for
// time managment: We don't want to stop the search early in
// such cases, because resolving the fail high at ply 1 could
// result in a big drop in score at the root.
if (sp->ply == 1 && RootMoveNumber == 1)
Threads[threadID].failHighPly1 = true;
value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth, sp->ply+1, threadID);
Threads[threadID].failHighPly1 = false;
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}
}
pos.undo_move(move);
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assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
if (thread_should_stop(threadID))
break;
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// New best move?
lock_grab(&(sp->lock));
if (value > sp->bestValue && !thread_should_stop(threadID))
{
sp->bestValue = value;
if (value > sp->alpha)
{
sp->alpha = value;
sp_update_pv(sp->parentSstack, ss, sp->ply);
if (value == value_mate_in(sp->ply + 1))
ss[sp->ply].mateKiller = move;
if (value >= sp->beta)
{
for (int i = 0; i < ActiveThreads; i++)
if (i != threadID && (i == sp->master || sp->slaves[i]))
Threads[i].stop = true;
sp->finished = true;
}
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}
// If we are at ply 1, and we are searching the first root move at
// ply 0, set the 'Problem' variable if the score has dropped a lot
// (from the computer's point of view) since the previous iteration.
if ( sp->ply == 1
&& Iteration >= 2
&& -value <= IterationInfo[Iteration-1].value - ProblemMargin)
Problem = true;
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}
lock_release(&(sp->lock));
}
lock_grab(&(sp->lock));
// If this is the master thread and we have been asked to stop because of
// a beta cutoff higher up in the tree, stop all slave threads.
if (sp->master == threadID && thread_should_stop(threadID))
for (int i = 0; i < ActiveThreads; i++)
if (sp->slaves[i])
Threads[i].stop = true;
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sp->cpus--;
sp->slaves[threadID] = 0;
lock_release(&(sp->lock));
}
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/// The BetaCounterType class
BetaCounterType::BetaCounterType() { clear(); }
void BetaCounterType::clear() {
for (int i = 0; i < THREAD_MAX; i++)
Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
}
void BetaCounterType::add(Color us, Depth d, int threadID) {
// Weighted count based on depth
Threads[threadID].betaCutOffs[us] += unsigned(d);
}
void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
our = their = 0UL;
for (int i = 0; i < THREAD_MAX; i++)
{
our += Threads[i].betaCutOffs[us];
their += Threads[i].betaCutOffs[opposite_color(us)];
}
}
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/// The RootMove class
// Constructor
RootMove::RootMove() {
nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL;
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}
// 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 a higher score, or if the moves
// have equal score but m1 has the higher node count.
bool RootMove::operator<(const RootMove& m) {
if (score != m.score)
return (score < m.score);
return theirBeta <= m.theirBeta;
}
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/// The RootMoveList class
// Constructor
RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
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MoveStack mlist[MaxRootMoves];
bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
// Generate all legal moves
int lm_count = generate_legal_moves(pos, mlist);
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// Add each move to the moves[] array
for (int i = 0; i < lm_count; i++)
{
bool includeMove = includeAllMoves;
for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
includeMove = (searchMoves[k] == mlist[i].move);
if (!includeMove)
continue;
// Find a quick score for the move
StateInfo st;
SearchStack ss[PLY_MAX_PLUS_2];
moves[count].move = mlist[i].move;
pos.do_move(moves[count].move, st);
moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
pos.undo_move(moves[count].move);
moves[count].pv[0] = moves[count].move;
moves[count].pv[1] = MOVE_NONE; // FIXME
count++;
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}
sort();
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}
// Simple accessor methods for the RootMoveList class
inline Move RootMoveList::get_move(int moveNum) const {
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return moves[moveNum].move;
}
inline Value RootMoveList::get_move_score(int moveNum) const {
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return moves[moveNum].score;
}
inline void RootMoveList::set_move_score(int moveNum, Value score) {
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moves[moveNum].score = score;
}
inline void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
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moves[moveNum].nodes = nodes;
moves[moveNum].cumulativeNodes += nodes;
}
inline void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
moves[moveNum].ourBeta = our;
moves[moveNum].theirBeta = their;
}
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void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
int j;
for(j = 0; pv[j] != MOVE_NONE; j++)
moves[moveNum].pv[j] = pv[j];
moves[moveNum].pv[j] = MOVE_NONE;
}
inline Move RootMoveList::get_move_pv(int moveNum, int i) const {
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return moves[moveNum].pv[i];
}
inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) const {
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return moves[moveNum].cumulativeNodes;
}
inline int RootMoveList::move_count() const {
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return count;
}
// RootMoveList::scan_for_easy_move() is called at the end of the first
// iteration, and is used to detect an "easy move", i.e. a move which appears
// to be much bester than all the rest. If an easy move is found, the move
// is returned, otherwise the function returns MOVE_NONE. It is very
// important that this function is called at the right moment: The code
// assumes that the first iteration has been completed and the moves have
// been sorted. This is done in RootMoveList c'tor.
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Move RootMoveList::scan_for_easy_move() const {
assert(count);
if (count == 1)
return get_move(0);
// moves are sorted so just consider the best and the second one
if (get_move_score(0) > get_move_score(1) + EasyMoveMargin)
return get_move(0);
return MOVE_NONE;
}
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// RootMoveList::sort() sorts the root move list at the beginning of a new
// iteration.
inline void RootMoveList::sort() {
sort_multipv(count - 1); // all items
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}
// RootMoveList::sort_multipv() sorts the first few moves in the root move
// list by their scores and depths. It is used to order the different PVs
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// correctly in MultiPV mode.
void RootMoveList::sort_multipv(int n) {
for (int i = 1; i <= n; i++)
{
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RootMove rm = moves[i];
int j;
for (j = i; j > 0 && moves[j-1] < rm; j--)
moves[j] = moves[j-1];
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moves[j] = rm;
}
}
// init_node() is called at the beginning of all the search functions
// (search(), search_pv(), qsearch(), and so on) and initializes the search
// stack object corresponding to the current node. Once every
// NodesBetweenPolls nodes, init_node() also calls poll(), which polls
// for user input and checks whether it is time to stop the search.
void init_node(SearchStack ss[], int ply, int threadID) {
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assert(ply >= 0 && ply < PLY_MAX);
assert(threadID >= 0 && threadID < ActiveThreads);
Threads[threadID].nodes++;
if (threadID == 0)
{
NodesSincePoll++;
if (NodesSincePoll >= NodesBetweenPolls)
{
poll();
NodesSincePoll = 0;
}
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}
ss[ply].init(ply);
ss[ply+2].initKillers();
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if (Threads[threadID].printCurrentLine)
print_current_line(ss, ply, threadID);
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}
// update_pv() is called whenever a search returns a value > alpha. It
// updates the PV in the SearchStack object corresponding to the current
// node.
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void update_pv(SearchStack ss[], int ply) {
assert(ply >= 0 && ply < PLY_MAX);
ss[ply].pv[ply] = ss[ply].currentMove;
int p;
for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
ss[ply].pv[p] = ss[ply+1].pv[p];
ss[ply].pv[p] = MOVE_NONE;
}
// sp_update_pv() is a variant of update_pv for use at split points. The
// difference between the two functions is that sp_update_pv also updates
// the PV at the parent node.
void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
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assert(ply >= 0 && ply < PLY_MAX);
ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
int p;
for(p = ply + 1; ss[ply+1].pv[p] != MOVE_NONE; p++)
ss[ply].pv[p] = pss[ply].pv[p] = ss[ply+1].pv[p];
ss[ply].pv[p] = pss[ply].pv[p] = MOVE_NONE;
}
// 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) {
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Square f1, t1, f2, t2;
assert(move_is_ok(m1));
assert(move_is_ok(m2));
if (m2 == MOVE_NONE)
return false;
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// Case 1: The moving piece is the same in both moves
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f2 = move_from(m2);
t1 = move_to(m1);
if (f2 == t1)
return true;
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// Case 2: The destination square for m2 was vacated by m1
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t2 = move_to(m2);
f1 = move_from(m1);
if (t2 == f1)
return true;
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// Case 3: Moving through the vacated square
if ( piece_is_slider(pos.piece_on(f2))
&& bit_is_set(squares_between(f2, t2), f1))
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return true;
// Case 4: The destination square for m2 is attacked by the moving piece in m1
if (pos.piece_attacks_square(pos.piece_on(t1), t1, t2))
return true;
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// Case 5: Discovered check, checking piece is the piece moved in m1
if ( piece_is_slider(pos.piece_on(t1))
&& bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
&& !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())), t2))
{
Bitboard occ = pos.occupied_squares();
Color us = pos.side_to_move();
Square ksq = pos.king_square(us);
clear_bit(&occ, f2);
if (pos.type_of_piece_on(t1) == BISHOP)
{
if (bit_is_set(bishop_attacks_bb(ksq, occ), t1))
return true;
}
else if (pos.type_of_piece_on(t1) == ROOK)
{
if (bit_is_set(rook_attacks_bb(ksq, occ), t1))
return true;
}
else
{
assert(pos.type_of_piece_on(t1) == QUEEN);
if (bit_is_set(queen_attacks_bb(ksq, occ), t1))
return true;
}
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}
return false;
}
// value_is_mate() checks if the given value is a mate one
// eventually compensated for the ply.
bool value_is_mate(Value value) {
assert(abs(value) <= VALUE_INFINITE);
return value <= value_mated_in(PLY_MAX)
|| value >= value_mate_in(PLY_MAX);
}
// move_is_killer() checks if the given move is among the
// killer moves of that ply.
bool move_is_killer(Move m, const SearchStack& ss) {
const Move* k = ss.killers;
for (int i = 0; i < KILLER_MAX; i++, k++)
if (*k == m)
return true;
return false;
}
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// 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.
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Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check,
bool singleReply, bool mateThreat, bool* dangerous) {
assert(m != MOVE_NONE);
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Depth result = Depth(0);
*dangerous = check || singleReply || mateThreat;
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if (check)
result += CheckExtension[pvNode];
if (singleReply)
result += SingleReplyExtension[pvNode];
if (mateThreat)
result += MateThreatExtension[pvNode];
if (pos.type_of_piece_on(move_from(m)) == PAWN)
{
if (pos.move_is_pawn_push_to_7th(m))
{
result += PawnPushTo7thExtension[pvNode];
*dangerous = true;
}
if (pos.move_is_passed_pawn_push(m))
{
result += PassedPawnExtension[pvNode];
*dangerous = true;
}
}
if ( capture
&& 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(0))
&& !move_is_promotion(m)
&& !move_is_ep(m))
{
result += PawnEndgameExtension[pvNode];
*dangerous = true;
}
if ( pvNode
&& capture
&& pos.type_of_piece_on(move_to(m)) != PAWN
&& pos.see(m) >= 0)
{
result += OnePly/2;
*dangerous = true;
}
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return Min(result, OnePly);
}
// ok_to_do_nullmove() looks at the current position and decides whether
// doing a 'null move' should be allowed. In order to avoid zugzwang
// problems, null moves are not allowed when the side to move has very
// little material left. Currently, the test is a bit too simple: Null
// moves are avoided only when the side to move has only pawns left. It's
// probably a good idea to avoid null moves in at least some more
// complicated endgames, e.g. KQ vs KR. FIXME
bool ok_to_do_nullmove(const Position& pos) {
return pos.non_pawn_material(pos.side_to_move()) != Value(0);
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}
// ok_to_prune() tests whether it is safe to forward prune a move. Only
// non-tactical moves late in the move list close to the leaves are
// candidates for pruning.
bool ok_to_prune(const Position& pos, Move m, Move threat, Depth d, const History& H) {
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assert(move_is_ok(m));
assert(threat == MOVE_NONE || move_is_ok(threat));
assert(!move_is_promotion(m));
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assert(!pos.move_is_check(m));
assert(!pos.move_is_capture(m));
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assert(!pos.move_is_passed_pawn_push(m));
assert(d >= OnePly);
Square mfrom, mto, tfrom, tto;
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mfrom = move_from(m);
mto = move_to(m);
tfrom = move_from(threat);
tto = move_to(threat);
// Case 1: Castling moves are never pruned
if (move_is_castle(m))
return false;
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// Case 2: Don't prune moves which move the threatened piece
if (!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
return false;
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// Case 3: If the threatened piece has value less than or equal to the
// value of the threatening piece, don't prune move which defend it.
if ( !PruneDefendingMoves
&& threat != MOVE_NONE
&& 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 false;
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// Case 4: Don't prune moves with good history
if (!H.ok_to_prune(pos.piece_on(mfrom), mto, d))
return false;
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// Case 5: If the moving piece in the threatened move is a slider, don't
// prune safe moves which block its ray.
if ( !PruneBlockingMoves
&& threat != MOVE_NONE
&& piece_is_slider(pos.piece_on(tfrom))
&& bit_is_set(squares_between(tfrom, tto), mto)
&& pos.see(m) >= 0)
return false;
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return true;
}
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// 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(100), beta)
|| v < Min(value_mated_in(100), beta))
&& ( (is_lower_bound(tte->type()) && v >= beta)
|| (is_upper_bound(tte->type()) && v < beta));
}
// ok_to_history() returns true if a move m can be stored
// in history. Should be a non capturing move nor a promotion.
bool ok_to_history(const Position& pos, Move m) {
return !pos.move_is_capture(m) && !move_is_promotion(m);
}
// 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 m, Depth depth, History& H,
Move movesSearched[], int moveCount) {
H.success(pos.piece_on(move_from(m)), move_to(m), depth);
for (int i = 0; i < moveCount - 1; i++)
{
assert(m != movesSearched[i]);
if (ok_to_history(pos, movesSearched[i]))
H.failure(pos.piece_on(move_from(movesSearched[i])), move_to(movesSearched[i]));
}
}
// update_killers() add a good move that produced a beta-cutoff
// among the killer moves of that ply.
void update_killers(Move m, SearchStack& ss) {
if (m == ss.killers[0])
return;
for (int i = KILLER_MAX - 1; i > 0; i--)
ss.killers[i] = ss.killers[i - 1];
ss.killers[0] = m;
}
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// fail_high_ply_1() checks if some thread is currently resolving a fail
// high at ply 1 at the node below the first root node. This information
// is used for time managment.
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bool fail_high_ply_1() {
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for(int i = 0; i < ActiveThreads; i++)
if (Threads[i].failHighPly1)
return true;
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return false;
}
// current_search_time() returns the number of milliseconds which have passed
// since the beginning of the current search.
int current_search_time() {
return get_system_time() - SearchStartTime;
}
// nps() computes the current nodes/second count.
int nps() {
int t = current_search_time();
return (t > 0)? int((nodes_searched() * 1000) / t) : 0;
}
// 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() {
static int lastInfoTime;
int t = current_search_time();
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// Poll for input
if (Bioskey())
{
// We are line oriented, don't read single chars
std::string command;
if (!std::getline(std::cin, command))
command = "quit";
if (command == "quit")
{
AbortSearch = true;
PonderSearch = false;
Quit = true;
return;
}
else if (command == "stop")
{
AbortSearch = true;
PonderSearch = false;
}
else if (command == "ponderhit")
ponderhit();
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}
// 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;
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else if (t - lastInfoTime >= 1000)
{
lastInfoTime = t;
lock_grab(&IOLock);
if (dbg_show_mean)
dbg_print_mean();
if (dbg_show_hit_rate)
dbg_print_hit_rate();
std::cout << "info nodes " << nodes_searched() << " nps " << nps()
<< " time " << t << " hashfull " << TT.full() << std::endl;
lock_release(&IOLock);
if (ShowCurrentLine)
Threads[0].printCurrentLine = true;
}
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// Should we stop the search?
if (PonderSearch)
return;
bool overTime = t > AbsoluteMaxSearchTime
|| (RootMoveNumber == 1 && t > MaxSearchTime + ExtraSearchTime && !FailLow) //FIXME: We are not checking any problem flags, BUG?
|| ( !FailHigh && !FailLow && !fail_high_ply_1() && !Problem
&& t > 6*(MaxSearchTime + ExtraSearchTime));
if ( (Iteration >= 3 && (!InfiniteSearch && overTime))
|| (ExactMaxTime && t >= ExactMaxTime)
|| (Iteration >= 3 && MaxNodes && nodes_searched() >= MaxNodes))
AbortSearch = true;
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}
// ponderhit() is called when the program is pondering (i.e. thinking while
// it's the opponent's turn to move) in order to let the engine know that
// it correctly predicted the opponent's move.
void ponderhit() {
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int t = current_search_time();
PonderSearch = false;
if (Iteration >= 3 &&
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(!InfiniteSearch && (StopOnPonderhit ||
t > AbsoluteMaxSearchTime ||
(RootMoveNumber == 1 &&
t > MaxSearchTime + ExtraSearchTime && !FailLow) ||
(!FailHigh && !FailLow && !fail_high_ply_1() && !Problem &&
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t > 6*(MaxSearchTime + ExtraSearchTime)))))
AbortSearch = true;
}
// print_current_line() prints the current line of search for a given
// thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
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void print_current_line(SearchStack ss[], int ply, int threadID) {
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assert(ply >= 0 && ply < PLY_MAX);
assert(threadID >= 0 && threadID < ActiveThreads);
if (!Threads[threadID].idle)
{
lock_grab(&IOLock);
std::cout << "info currline " << (threadID + 1);
for (int p = 0; p < ply; p++)
std::cout << " " << ss[p].currentMove;
std::cout << std::endl;
lock_release(&IOLock);
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}
Threads[threadID].printCurrentLine = false;
if (threadID + 1 < ActiveThreads)
Threads[threadID + 1].printCurrentLine = true;
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}
// 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 (in id_loop()).
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void wait_for_stop_or_ponderhit() {
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std::string command;
while (true)
{
if (!std::getline(std::cin, command))
command = "quit";
if (command == "quit")
{
Quit = true;
break;
}
else if (command == "ponderhit" || command == "stop")
break;
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}
}
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// idle_loop() is where the threads are parked when they have no work to do.
// The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
// object for which the current thread is the master.
void idle_loop(int threadID, SplitPoint* waitSp) {
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assert(threadID >= 0 && threadID < THREAD_MAX);
Threads[threadID].running = true;
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while(true) {
if(AllThreadsShouldExit && threadID != 0)
break;
// If we are not thinking, wait for a condition to be signaled instead
// of wasting CPU time polling for work:
while(threadID != 0 && (Idle || threadID >= ActiveThreads)) {
#if !defined(_MSC_VER)
pthread_mutex_lock(&WaitLock);
if(Idle || threadID >= ActiveThreads)
pthread_cond_wait(&WaitCond, &WaitLock);
pthread_mutex_unlock(&WaitLock);
#else
WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
#endif
}
// If this thread has been assigned work, launch a search
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if(Threads[threadID].workIsWaiting) {
Threads[threadID].workIsWaiting = false;
if(Threads[threadID].splitPoint->pvNode)
sp_search_pv(Threads[threadID].splitPoint, threadID);
else
sp_search(Threads[threadID].splitPoint, threadID);
Threads[threadID].idle = true;
}
// If this thread is the master of a split point and all threads have
// finished their work at this split point, return from the idle loop.
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if(waitSp != NULL && waitSp->cpus == 0)
return;
}
Threads[threadID].running = false;
}
// init_split_point_stack() is called during program initialization, and
// initializes all split point objects.
void init_split_point_stack() {
for(int i = 0; i < THREAD_MAX; i++)
for(int j = 0; j < MaxActiveSplitPoints; j++) {
SplitPointStack[i][j].parent = NULL;
lock_init(&(SplitPointStack[i][j].lock), NULL);
}
}
// destroy_split_point_stack() is called when the program exits, and
// destroys all locks in the precomputed split point objects.
void destroy_split_point_stack() {
for(int i = 0; i < THREAD_MAX; i++)
for(int j = 0; j < MaxActiveSplitPoints; j++)
lock_destroy(&(SplitPointStack[i][j].lock));
}
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// thread_should_stop() checks whether the thread with a given threadID has
// been asked to stop, directly or indirectly. This can happen if a beta
// cutoff has occured in thre thread's currently active split point, or in
// some ancestor of the current split point.
bool thread_should_stop(int threadID) {
assert(threadID >= 0 && threadID < ActiveThreads);
SplitPoint* sp;
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if(Threads[threadID].stop)
return true;
if(ActiveThreads <= 2)
return false;
for(sp = Threads[threadID].splitPoint; sp != NULL; sp = sp->parent)
if(sp->finished) {
Threads[threadID].stop = true;
return true;
}
return false;
}
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// thread_is_available() checks whether the thread with threadID "slave" is
// available to help the thread with threadID "master" at a split point. An
// obvious requirement is that "slave" must be idle. With more than two
// threads, this is not by itself sufficient: If "slave" is the master of
// some active split point, it is only available as a slave to the other
// threads which are busy searching the split point at the top of "slave"'s
// split point stack (the "helpful master concept" in YBWC terminology).
bool thread_is_available(int slave, int master) {
assert(slave >= 0 && slave < ActiveThreads);
assert(master >= 0 && master < ActiveThreads);
assert(ActiveThreads > 1);
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if(!Threads[slave].idle || slave == master)
return false;
if(Threads[slave].activeSplitPoints == 0)
// No active split points means that the thread is available as a slave
// for any other thread.
return true;
if(ActiveThreads == 2)
return true;
// Apply the "helpful master" concept if possible.
if(SplitPointStack[slave][Threads[slave].activeSplitPoints-1].slaves[master])
return true;
return false;
}
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// idle_thread_exists() tries to find an idle thread which is available as
// a slave for the thread with threadID "master".
bool idle_thread_exists(int master) {
assert(master >= 0 && master < ActiveThreads);
assert(ActiveThreads > 1);
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for(int i = 0; i < ActiveThreads; i++)
if(thread_is_available(i, master))
return true;
return false;
}
// split() does the actual work of distributing the work at a node between
// several threads at PV nodes. If it does not succeed in splitting the
// node (because no idle threads are available, or because we have no unused
// split point objects), the function immediately returns false. If
// splitting is possible, a SplitPoint object is initialized with all the
// data that must be copied to the helper threads (the current position and
// search stack, alpha, beta, the search depth, etc.), and we tell our
// helper threads that they have been assigned work. This will cause them
// to instantly leave their idle loops and call sp_search_pv(). When all
// threads have returned from sp_search_pv (or, equivalently, when
// splitPoint->cpus becomes 0), split() returns true.
bool split(const Position& p, SearchStack* sstck, int ply,
Value* alpha, Value* beta, Value* bestValue, Depth depth, int* moves,
MovePicker* mp, Bitboard dcCandidates, int master, bool pvNode) {
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assert(p.is_ok());
assert(sstck != NULL);
assert(ply >= 0 && ply < PLY_MAX);
assert(*bestValue >= -VALUE_INFINITE && *bestValue <= *alpha);
assert(!pvNode || *alpha < *beta);
assert(*beta <= VALUE_INFINITE);
assert(depth > Depth(0));
assert(master >= 0 && master < ActiveThreads);
assert(ActiveThreads > 1);
SplitPoint* splitPoint;
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int i;
lock_grab(&MPLock);
// If no other thread is available to help us, or if we have too many
// active split points, don't split.
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if(!idle_thread_exists(master) ||
Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
lock_release(&MPLock);
return false;
}
// Pick the next available split point object from the split point stack
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splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
Threads[master].activeSplitPoints++;
// Initialize the split point object
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splitPoint->parent = Threads[master].splitPoint;
splitPoint->finished = false;
splitPoint->ply = ply;
splitPoint->depth = depth;
splitPoint->alpha = pvNode? *alpha : (*beta - 1);
splitPoint->beta = *beta;
splitPoint->pvNode = pvNode;
splitPoint->dcCandidates = dcCandidates;
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splitPoint->bestValue = *bestValue;
splitPoint->master = master;
splitPoint->mp = mp;
splitPoint->moves = *moves;
splitPoint->cpus = 1;
splitPoint->pos.copy(p);
splitPoint->parentSstack = sstck;
for(i = 0; i < ActiveThreads; i++)
splitPoint->slaves[i] = 0;
// Copy the current position and the search stack to the master thread
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memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
Threads[master].splitPoint = splitPoint;
// Make copies of the current position and search stack for each thread
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for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
i++)
if(thread_is_available(i, master)) {
memcpy(splitPoint->sstack[i], sstck, (ply+1)*sizeof(SearchStack));
Threads[i].splitPoint = splitPoint;
splitPoint->slaves[i] = 1;
splitPoint->cpus++;
}
// Tell the threads that they have work to do. This will make them leave
// their idle loop.
for(i = 0; i < ActiveThreads; i++)
if(i == master || splitPoint->slaves[i]) {
Threads[i].workIsWaiting = true;
Threads[i].idle = false;
Threads[i].stop = false;
}
lock_release(&MPLock);
// Everything is set up. The master thread enters the idle loop, from
// which it will instantly launch a search, because its workIsWaiting
// slot is 'true'. We send the split point as a second parameter to the
// idle loop, which means that the main thread will return from the idle
// loop when all threads have finished their work at this split point
// (i.e. when // splitPoint->cpus == 0).
idle_loop(master, splitPoint);
// We have returned from the idle loop, which means that all threads are
// finished. Update alpha, beta and bestvalue, and return.
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lock_grab(&MPLock);
if(pvNode) *alpha = splitPoint->alpha;
*beta = splitPoint->beta;
*bestValue = splitPoint->bestValue;
Threads[master].stop = false;
Threads[master].idle = false;
Threads[master].activeSplitPoints--;
Threads[master].splitPoint = splitPoint->parent;
lock_release(&MPLock);
return true;
}
// wake_sleeping_threads() wakes up all sleeping threads when it is time
// to start a new search from the root.
void wake_sleeping_threads() {
if(ActiveThreads > 1) {
for(int i = 1; i < ActiveThreads; i++) {
Threads[i].idle = true;
Threads[i].workIsWaiting = false;
}
#if !defined(_MSC_VER)
pthread_mutex_lock(&WaitLock);
pthread_cond_broadcast(&WaitCond);
pthread_mutex_unlock(&WaitLock);
#else
for(int i = 1; i < THREAD_MAX; i++)
SetEvent(SitIdleEvent[i]);
#endif
}
}
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// init_thread() is the function which is called when a new thread is
// launched. It simply calls the idle_loop() function with the supplied
// threadID. There are two versions of this function; one for POSIX threads
// and one for Windows threads.
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#if !defined(_MSC_VER)
void *init_thread(void *threadID) {
idle_loop(*(int *)threadID, NULL);
return NULL;
}
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#else
DWORD WINAPI init_thread(LPVOID threadID) {
idle_loop(*(int *)threadID, NULL);
return NULL;
}
#endif
}