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stockfish/src/search.cpp

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/*
Glaurung, a UCI chess playing engine.
Copyright (C) 2004-2008 Tord Romstad
Glaurung is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Glaurung is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
////
//// Includes
////
#include <cassert>
#include <cstdio>
#include <fstream>
#include <iostream>
#include <sstream>
#include "book.h"
#include "evaluate.h"
#include "history.h"
#include "misc.h"
#include "movepick.h"
#include "san.h"
#include "search.h"
#include "thread.h"
#include "tt.h"
#include "ucioption.h"
////
//// Local definitions
////
namespace {
/// Types
// The 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).
class RootMove {
public:
RootMove();
Move move;
Value score;
int64_t nodes, cumulativeNodes;
Move pv[PLY_MAX_PLUS_2];
};
// 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[]);
Move get_move(int moveNum) const;
Value get_move_score(int moveNum) const;
void set_move_score(int moveNum, Value score);
void set_move_nodes(int moveNum, int64_t nodes);
void set_move_pv(int moveNum, const Move pv[]);
Move get_move_pv(int moveNum, int i) const;
int64_t get_move_cumulative_nodes(int moveNum);
int move_count() const;
Move scan_for_easy_move() const;
void sort();
void sort_multipv(int n);
private:
static int compare_root_moves(const RootMove &rm1, const RootMove &rm2);
static const int MaxRootMoves = 500;
RootMove moves[MaxRootMoves];
int count;
};
/// Constants and variables
// Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV
// nodes:
int LMRPVMoves = 15;
int LMRNonPVMoves = 4;
// Depth limit for use of dynamic threat detection:
Depth ThreatDepth = 5*OnePly;
// Depth limit for selective search:
Depth SelectiveDepth = 7*OnePly;
// Use internal iterative deepening?
const bool UseIIDAtPVNodes = true;
const bool UseIIDAtNonPVNodes = false;
// Internal iterative deepening margin. At Non-PV moves, when
// UseIIDAtNonPVNodes is true, we do an internal iterative deepening search
// when the static evaluation is at most IIDMargin below beta.
const Value IIDMargin = Value(0x100);
// Use easy moves?
const bool UseEasyMove = true;
// Easy move margin. An easy move candidate must be at least this much
// better than the second best move.
const Value EasyMoveMargin = Value(0x200);
// Problem margin. If the score of the first move at iteration N+1 has
// dropped by more than this since iteration N, the boolean variable
// "Problem" is set to true, which will make the program spend some extra
// time looking for a better move.
const Value ProblemMargin = Value(0x28);
// No problem margin. If the boolean "Problem" is true, and a new move
// is found at the root which is less than NoProblemMargin worse than the
// best move from the previous iteration, Problem is set back to false.
const Value NoProblemMargin = Value(0x14);
// Null move margin. A null move search will not be done if the approximate
// evaluation of the position is more than NullMoveMargin below beta.
const Value NullMoveMargin = Value(0x300);
// Pruning criterions. See the code and comments in ok_to_prune() to
// understand their precise meaning.
const bool PruneEscapeMoves = false;
const bool PruneDefendingMoves = false;
const bool PruneBlockingMoves = false;
// Use futility pruning?
bool UseQSearchFutilityPruning = true;
bool UseFutilityPruning = true;
// Margins for futility pruning in the quiescence search, at frontier
// nodes, and at pre-frontier nodes:
Value FutilityMargin0 = Value(0x80);
Value FutilityMargin1 = Value(0x100);
Value FutilityMargin2 = Value(0x300);
// Razoring
Depth RazorDepth = 4*OnePly;
Value RazorMargin = Value(0x300);
// Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
Depth CheckExtension[2] = {OnePly, OnePly};
Depth SingleReplyExtension[2] = {OnePly / 2, OnePly / 2};
Depth PawnPushTo7thExtension[2] = {OnePly / 2, OnePly / 2};
Depth PassedPawnExtension[2] = {Depth(0), Depth(0)};
Depth PawnEndgameExtension[2] = {OnePly, OnePly};
Depth MateThreatExtension[2] = {Depth(0), Depth(0)};
// Search depth at iteration 1:
const Depth InitialDepth = OnePly /*+ OnePly/2*/;
// Node counters
int NodesSincePoll;
int NodesBetweenPolls = 30000;
// Iteration counter:
int Iteration;
// Scores and number of times the best move changed for each iteration:
Value ValueByIteration[PLY_MAX_PLUS_2];
int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
// MultiPV mode:
int MultiPV = 1;
// Time managment variables
int SearchStartTime;
int MaxNodes, MaxDepth;
int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime;
Move BestRootMove, PonderMove, EasyMove;
int RootMoveNumber;
bool InfiniteSearch;
bool PonderSearch;
bool StopOnPonderhit;
bool AbortSearch;
bool Quit;
bool FailHigh;
bool Problem;
bool PonderingEnabled;
int ExactMaxTime;
// Show current line?
bool ShowCurrentLine = false;
// Log file
bool UseLogFile = false;
std::ofstream LogFile;
// MP related variables
Depth MinimumSplitDepth = 4*OnePly;
int MaxThreadsPerSplitPoint = 4;
Thread Threads[THREAD_MAX];
Lock MPLock;
bool AllThreadsShouldExit = false;
const int MaxActiveSplitPoints = 8;
SplitPoint SplitPointStack[THREAD_MAX][MaxActiveSplitPoints];
bool Idle = true;
#if !defined(_MSC_VER)
pthread_cond_t WaitCond;
pthread_mutex_t WaitLock;
#else
HANDLE SitIdleEvent[THREAD_MAX];
#endif
/// Functions
void id_loop(const Position &pos, Move searchMoves[]);
Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml);
Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
Depth depth, int ply, int threadID);
Value search(Position &pos, SearchStack ss[], Value beta,
Depth depth, int ply, bool allowNullmove, int threadID);
Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
Depth depth, int ply, int threadID);
void sp_search(SplitPoint *sp, int threadID);
void sp_search_pv(SplitPoint *sp, int threadID);
void init_search_stack(SearchStack ss[]);
void init_node(const Position &pos, SearchStack ss[], int ply, int threadID);
void update_pv(SearchStack ss[], int ply);
void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply);
bool connected_moves(const Position &pos, Move m1, Move m2);
Depth extension(const Position &pos, Move m, bool pvNode, bool check,
bool singleReply, bool mateThreat);
bool ok_to_do_nullmove(const Position &pos);
bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d);
bool fail_high_ply_1();
int current_search_time();
int nps();
void poll();
void ponderhit();
void print_current_line(SearchStack ss[], int ply, int threadID);
void wait_for_stop_or_ponderhit();
void idle_loop(int threadID, SplitPoint *waitSp);
void init_split_point_stack();
void destroy_split_point_stack();
bool thread_should_stop(int threadID);
bool thread_is_available(int slave, int master);
bool idle_thread_exists(int master);
bool split(const Position &pos, SearchStack *ss, int ply,
Value *alpha, Value *beta, Value *bestValue, Depth depth,
int *moves, MovePicker *mp, Bitboard dcCandidates, int master,
bool pvNode);
void wake_sleeping_threads();
#if !defined(_MSC_VER)
void *init_thread(void *threadID);
#else
DWORD WINAPI init_thread(LPVOID threadID);
#endif
}
////
//// Global variables
////
// The main transposition table
TranspositionTable TT = TranspositionTable(TTDefaultSize);
// Number of active threads:
int ActiveThreads = 1;
// Locks. In principle, there is no need for IOLock to be a global variable,
// but it could turn out to be useful for debugging.
Lock IOLock;
History H; // Should be made local?
////
//// Functions
////
/// think() is the external interface to Glaurung's search, and is called when
/// the program receives the UCI 'go' command. It initializes various
/// search-related global variables, and calls root_search()
void think(const Position &pos, bool infinite, bool ponder, int time,
int increment, int movesToGo, int maxDepth, int maxNodes,
int maxTime, Move searchMoves[]) {
// Look for a book move:
if(!infinite && !ponder && get_option_value_bool("OwnBook")) {
Move bookMove;
if(get_option_value_string("Book File") != OpeningBook.file_name()) {
OpeningBook.close();
OpeningBook.open("book.bin");
}
bookMove = OpeningBook.get_move(pos);
if(bookMove != MOVE_NONE) {
std::cout << "bestmove " << bookMove << std::endl;
return;
}
}
// Initialize global search variables:
Idle = false;
SearchStartTime = get_system_time();
BestRootMove = MOVE_NONE;
PonderMove = MOVE_NONE;
EasyMove = MOVE_NONE;
for(int i = 0; i < THREAD_MAX; i++) {
Threads[i].nodes = 0ULL;
Threads[i].failHighPly1 = false;
}
NodesSincePoll = 0;
InfiniteSearch = infinite;
PonderSearch = ponder;
StopOnPonderhit = false;
AbortSearch = false;
Quit = false;
FailHigh = false;
Problem = false;
ExactMaxTime = maxTime;
// Read UCI option values:
TT.set_size(get_option_value_int("Hash"));
if(button_was_pressed("Clear Hash"))
TT.clear();
PonderingEnabled = get_option_value_int("Ponder");
MultiPV = get_option_value_int("MultiPV");
CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
CheckExtension[0] =
Depth(get_option_value_int("Check Extension (non-PV nodes)"));
SingleReplyExtension[1] = Depth(get_option_value_int("Single Reply Extension (PV nodes)"));
SingleReplyExtension[0] =
Depth(get_option_value_int("Single Reply Extension (non-PV nodes)"));
PawnPushTo7thExtension[1] =
Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
PawnPushTo7thExtension[0] =
Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
PassedPawnExtension[1] =
Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
PassedPawnExtension[0] =
Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
PawnEndgameExtension[1] =
Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
PawnEndgameExtension[0] =
Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
MateThreatExtension[1] =
Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
MateThreatExtension[0] =
Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
LMRPVMoves = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
ThreatDepth = get_option_value_int("Threat Depth") * OnePly;
SelectiveDepth = get_option_value_int("Selective Plies") * OnePly;
Chess960 = get_option_value_bool("UCI_Chess960");
ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
UseLogFile = get_option_value_bool("Use Search Log");
if(UseLogFile)
LogFile.open(get_option_value_string("Search Log Filename").c_str(),
std::ios::out | std::ios::app);
UseQSearchFutilityPruning =
get_option_value_bool("Futility Pruning (Quiescence Search)");
UseFutilityPruning =
get_option_value_bool("Futility Pruning (Main Search)");
FutilityMargin0 =
value_from_centipawns(get_option_value_int("Futility Margin 0"));
FutilityMargin1 =
value_from_centipawns(get_option_value_int("Futility Margin 1"));
FutilityMargin2 =
value_from_centipawns(get_option_value_int("Futility Margin 2"));
RazorDepth = (get_option_value_int("Maximum Razoring Depth") + 1) * OnePly;
RazorMargin = value_from_centipawns(get_option_value_int("Razoring Margin"));
MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
MaxThreadsPerSplitPoint =
get_option_value_int("Maximum Number of Threads per Split Point");
read_weights(pos.side_to_move());
int newActiveThreads = get_option_value_int("Threads");
if(newActiveThreads != ActiveThreads) {
ActiveThreads = newActiveThreads;
init_eval(ActiveThreads);
}
// Write information to search log file:
if(UseLogFile) {
LogFile << "Searching: " << pos.to_fen() << '\n';
LogFile << "infinite: " << infinite << " ponder: " << ponder
<< " time: " << time << " increment: " << increment
<< " moves to go: " << movesToGo << '\n';
}
// Wake up sleeping threads:
wake_sleeping_threads();
for(int i = 1; i < ActiveThreads; i++)
assert(thread_is_available(i, 0));
// Set thinking time:
if(!movesToGo) { // Sudden death time control
if(increment) {
MaxSearchTime = time / 30 + increment;
AbsoluteMaxSearchTime = Max(time / 4, increment - 100);
}
else { // Blitz game without increment
MaxSearchTime = time / 40;
AbsoluteMaxSearchTime = time / 8;
}
}
else { // (x moves) / (y minutes)
if(movesToGo == 1) {
MaxSearchTime = time / 2;
AbsoluteMaxSearchTime = Min(time / 2, time - 500);
}
else {
MaxSearchTime = time / Min(movesToGo, 20);
AbsoluteMaxSearchTime = Min((4 * time) / movesToGo, time / 3);
}
}
if(PonderingEnabled) {
MaxSearchTime += MaxSearchTime / 4;
MaxSearchTime = Min(MaxSearchTime, AbsoluteMaxSearchTime);
}
// Fixed depth or fixed number of nodes?
MaxDepth = maxDepth;
if(MaxDepth)
InfiniteSearch = true; // HACK
MaxNodes = maxNodes;
if(MaxNodes) {
NodesBetweenPolls = Min(MaxNodes, 30000);
InfiniteSearch = true; // HACK
}
else
NodesBetweenPolls = 30000;
// We're ready to start thinking. Call the iterative deepening loop
// function:
id_loop(pos, searchMoves);
if(UseLogFile)
LogFile.close();
if(Quit) {
OpeningBook.close();
stop_threads();
quit_eval();
exit(0);
}
Idle = true;
}
/// init_threads() is called during startup. It launches all helper threads,
/// and initializes the split point stack and the global locks and condition
/// objects.
void init_threads() {
volatile int i;
#if !defined(_MSC_VER)
pthread_t pthread[1];
#endif
for(i = 0; i < THREAD_MAX; i++)
Threads[i].activeSplitPoints = 0;
// Initialize global locks:
lock_init(&MPLock, NULL);
lock_init(&IOLock, NULL);
init_split_point_stack();
#if !defined(_MSC_VER)
pthread_mutex_init(&WaitLock, NULL);
pthread_cond_init(&WaitCond, NULL);
#else
for(i = 0; i < THREAD_MAX; i++)
SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
#endif
// All threads except the main thread should be initialized to idle state:
for(i = 1; i < THREAD_MAX; i++) {
Threads[i].stop = false;
Threads[i].workIsWaiting = false;
Threads[i].idle = true;
Threads[i].running = false;
}
// Launch the helper threads:
for(i = 1; i < THREAD_MAX; i++) {
#if !defined(_MSC_VER)
pthread_create(pthread, NULL, init_thread, (void*)(&i));
#else
{
DWORD iID[1];
CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
}
#endif
// Wait until the thread has finished launching:
while(!Threads[i].running);
}
}
/// stop_threads() is called when the program exits. It makes all the
/// helper threads exit cleanly.
void stop_threads() {
ActiveThreads = THREAD_MAX; // HACK
Idle = false; // HACK
wake_sleeping_threads();
AllThreadsShouldExit = true;
for(int i = 1; i < THREAD_MAX; i++) {
Threads[i].stop = true;
while(Threads[i].running);
}
destroy_split_point_stack();
}
/// nodes_searched() returns the total number of nodes searched so far in
/// the current search.
int64_t nodes_searched() {
int64_t result = 0ULL;
for(int i = 0; i < ActiveThreads; i++)
result += Threads[i].nodes;
return result;
}
namespace {
// id_loop() is the main iterative deepening loop. It calls root_search
// repeatedly with increasing depth until the allocated thinking time has
// been consumed, the user stops the search, or the maximum search depth is
// reached.
void id_loop(const Position &pos, Move searchMoves[]) {
Position p(pos);
RootMoveList rml(p, searchMoves);
SearchStack ss[PLY_MAX_PLUS_2];
// Initialize
TT.new_search();
H.clear();
init_search_stack(ss);
ValueByIteration[0] = Value(0);
ValueByIteration[1] = rml.get_move_score(0);
Iteration = 1;
EasyMove = rml.scan_for_easy_move();
// Iterative deepening loop
while(!AbortSearch && Iteration < PLY_MAX) {
// Initialize iteration
rml.sort();
Iteration++;
BestMoveChangesByIteration[Iteration] = 0;
if(Iteration <= 5)
ExtraSearchTime = 0;
std::cout << "info depth " << Iteration << std::endl;
// Search to the current depth
ValueByIteration[Iteration] = root_search(p, ss, rml);
// Erase the easy move if it differs from the new best move
if(ss[0].pv[0] != EasyMove)
EasyMove = MOVE_NONE;
Problem = false;
if(!InfiniteSearch) {
// Time to stop?
bool stopSearch = false;
// Stop search early if there is only a single legal move:
if(Iteration >= 6 && rml.move_count() == 1)
stopSearch = true;
// Stop search early when the last two iterations returned a mate
// score:
if(Iteration >= 6
&& abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
&& abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
stopSearch = true;
// Stop search early if one move seems to be much better than the
// rest:
int64_t nodes = nodes_searched();
if(Iteration >= 8 && EasyMove == ss[0].pv[0] &&
((rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100 &&
current_search_time() > MaxSearchTime / 16) ||
(rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100 &&
current_search_time() > MaxSearchTime / 32)))
stopSearch = true;
// Add some extra time if the best move has changed during the last
// two iterations:
if(Iteration > 5 && Iteration <= 50)
ExtraSearchTime =
BestMoveChangesByIteration[Iteration] * (MaxSearchTime / 2) +
BestMoveChangesByIteration[Iteration-1] * (MaxSearchTime / 3);
// Stop search if most of MaxSearchTime is consumed at the end of the
// iteration. We probably don't have enough time to search the first
// move at the next iteration anyway.
if(current_search_time() > ((MaxSearchTime + ExtraSearchTime)*80) / 128)
stopSearch = true;
if(stopSearch) {
if(!PonderSearch)
break;
else
StopOnPonderhit = true;
}
}
// Write PV to transposition table, in case the relevant entries have
// been overwritten during the search:
TT.insert_pv(p, ss[0].pv);
if(MaxDepth && Iteration >= MaxDepth)
break;
}
rml.sort();
// If we are pondering, we shouldn't print the best move before we
// are told to do so
if(PonderSearch)
wait_for_stop_or_ponderhit();
else
// Print final search statistics
std::cout << "info nodes " << nodes_searched() << " nps " << nps()
<< " time " << current_search_time()
<< " hashfull " << TT.full() << std::endl;
// Print the best move and the ponder move to the standard output:
std::cout << "bestmove " << ss[0].pv[0];
if(ss[0].pv[1] != MOVE_NONE)
std::cout << " ponder " << ss[0].pv[1];
std::cout << std::endl;
if(UseLogFile) {
UndoInfo u;
LogFile << "Nodes: " << nodes_searched() << '\n';
LogFile << "Nodes/second: " << nps() << '\n';
LogFile << "Best move: " << move_to_san(p, ss[0].pv[0]) << '\n';
p.do_move(ss[0].pv[0], u);
LogFile << "Ponder move: " << move_to_san(p, ss[0].pv[1]) << '\n';
LogFile << std::endl;
}
}
// root_search() is the function which searches the root node. It is
// similar to search_pv except that it uses a different move ordering
// scheme (perhaps we should try to use this at internal PV nodes, too?)
// and prints some information to the standard output.
Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml) {
Value alpha = -VALUE_INFINITE, beta = VALUE_INFINITE, value;
Bitboard dcCandidates = pos.discovered_check_candidates(pos.side_to_move());
// Loop through all the moves in the root move list:
for(int i = 0; i < rml.move_count() && !AbortSearch; i++) {
int64_t nodes;
Move move;
UndoInfo u;
Depth ext, newDepth;
RootMoveNumber = i + 1;
FailHigh = false;
// Remember the node count before the move is searched. The node counts
// are used to sort the root moves at the next iteration.
nodes = nodes_searched();
// 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:
ext = extension(pos, move, true, pos.move_is_check(move), false, false);
newDepth = (Iteration-2)*OnePly + ext + InitialDepth;
// Make the move, and search it.
pos.do_move(move, u, dcCandidates);
if(i < MultiPV) {
value = -search_pv(pos, ss, -beta, VALUE_INFINITE, newDepth, 1, 0);
// If the value has dropped a lot compared to the last iteration,
// set the boolean variable Problem to true. This variable is used
// for time managment: When Problem is true, we try to complete the
// current iteration before playing a move.
Problem = (Iteration >= 2 &&
value <= ValueByIteration[Iteration-1] - ProblemMargin);
if(Problem && StopOnPonderhit)
StopOnPonderhit = false;
}
else {
value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
if(value > alpha) {
// Fail high! Set the boolean variable FailHigh to true, and
// re-search the move with a big window. The variable FailHigh is
// used for time managment: We try to avoid aborting the search
// prematurely during a fail high research.
FailHigh = true;
value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
}
}
pos.undo_move(move, u);
// Finished searching the move. If AbortSearch is true, the search
// was aborted because the user interrupted the search or because we
// ran out of time. In this case, the return value of the search cannot
// be trusted, and we break out of the loop without updating the best
// move and/or PV:
if(AbortSearch)
break;
// Remember the node count for this move. The node counts are used to
// sort the root moves at the next iteration.
rml.set_move_nodes(i, nodes_searched() - nodes);
assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
if(value <= alpha && i >= MultiPV)
rml.set_move_score(i, -VALUE_INFINITE);
else {
// New best move!
// Update PV:
rml.set_move_score(i, value);
update_pv(ss, 0);
rml.set_move_pv(i, ss[0].pv);
if(MultiPV == 1) {
// We record how often the best move has been changed in each
// iteration. This information is used for time managment: When
// the best move changes frequently, we allocate some more time.
if(i > 0)
BestMoveChangesByIteration[Iteration]++;
// Print search information to the standard output:
std::cout << "info depth " << Iteration
<< " score " << value_to_string(value)
<< " time " << current_search_time()
<< " nodes " << nodes_searched()
<< " nps " << nps()
<< " pv ";
for(int j = 0; ss[0].pv[j] != MOVE_NONE && j < PLY_MAX; j++)
std::cout << ss[0].pv[j] << " ";
std::cout << std::endl;
if(UseLogFile)
LogFile << pretty_pv(pos, current_search_time(), Iteration,
nodes_searched(), value, ss[0].pv)
<< std::endl;
alpha = value;
// Reset the global variable Problem to false if the value isn't too
// far below the final value from the last iteration.
if(value > ValueByIteration[Iteration - 1] - NoProblemMargin)
Problem = false;
}
else { // MultiPV > 1
rml.sort_multipv(i);
for(int j = 0; j < Min(MultiPV, rml.move_count()); j++) {
int k;
std::cout << "info multipv " << j + 1
<< " score " << value_to_string(rml.get_move_score(j))
<< " depth " << ((j <= i)? Iteration : Iteration - 1)
<< " time " << current_search_time()
<< " nodes " << nodes_searched()
<< " nps " << nps()
<< " pv ";
for(k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
std::cout << rml.get_move_pv(j, k) << " ";
std::cout << std::endl;
}
alpha = rml.get_move_score(Min(i, MultiPV-1));
}
}
}
return alpha;
}
// search_pv() is the main search function for PV nodes.
Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
Depth depth, int ply, int threadID) {
assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
assert(beta > alpha && beta <= VALUE_INFINITE);
assert(ply >= 0 && ply < PLY_MAX);
assert(threadID >= 0 && threadID < ActiveThreads);
EvalInfo ei;
// Initialize, and make an early exit in case of an aborted search,
// an instant draw, maximum ply reached, etc.
Value oldAlpha = alpha;
if(AbortSearch || thread_should_stop(threadID))
return Value(0);
if(depth < OnePly)
return qsearch(pos, ss, alpha, beta, Depth(0), ply, threadID);
init_node(pos, ss, ply, threadID);
if(pos.is_draw())
return VALUE_DRAW;
if(ply >= PLY_MAX - 1)
return evaluate(pos, ei, threadID);
// Mate distance pruning
alpha = Max(value_mated_in(ply), alpha);
beta = Min(value_mate_in(ply+1), beta);
if(alpha >= beta)
return alpha;
// Transposition table lookup. At PV nodes, we don't use the TT for
// pruning, but only for move ordering.
Value ttValue;
Depth ttDepth;
Move ttMove = MOVE_NONE;
ValueType ttValueType;
TT.retrieve(pos, &ttValue, &ttDepth, &ttMove, &ttValueType);
// Internal iterative deepening.
if(UseIIDAtPVNodes && ttMove == MOVE_NONE && depth >= 5*OnePly) {
search_pv(pos, ss, alpha, beta, depth-2*OnePly, ply, threadID);
ttMove = ss[ply].pv[ply];
}
// Initialize a MovePicker object for the current position, and prepare
// to search all moves:
MovePicker mp = MovePicker(pos, true, ttMove, ss[ply].mateKiller,
ss[ply].killer1, ss[ply].killer2, depth);
Move move, movesSearched[256];
int moveCount = 0;
Value value, bestValue = -VALUE_INFINITE;
Bitboard dcCandidates = mp.discovered_check_candidates();
bool mateThreat =
MateThreatExtension[1] > Depth(0)
&& pos.has_mate_threat(opposite_color(pos.side_to_move()));
// Loop through all legal moves until no moves remain or a beta cutoff
// occurs.
while(alpha < beta && !thread_should_stop(threadID)
&& (move = mp.get_next_move()) != MOVE_NONE) {
UndoInfo u;
Depth ext, newDepth;
bool singleReply = (pos.is_check() && mp.number_of_moves() == 1);
bool moveIsCheck = pos.move_is_check(move, dcCandidates);
bool moveIsCapture = pos.move_is_capture(move);
bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move);
assert(move_is_ok(move));
movesSearched[moveCount++] = ss[ply].currentMove = move;
ss[ply].currentMoveCaptureValue = move_is_ep(move)?
PawnValueMidgame : pos.midgame_value_of_piece_on(move_to(move));
// Decide the new search depth.
ext = extension(pos, move, true, moveIsCheck, singleReply, mateThreat);
newDepth = depth - OnePly + ext;
// Make and search the move.
pos.do_move(move, u, dcCandidates);
if(moveCount == 1)
value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1, threadID);
else {
if(depth >= 2*OnePly && ext == Depth(0) && moveCount >= LMRPVMoves
&& !moveIsCapture && !move_promotion(move)
&& !moveIsPassedPawnPush && !move_is_castle(move)
&& move != ss[ply].killer1 && move != ss[ply].killer2) {
ss[ply].reduction = OnePly;
value = -search(pos, ss, -alpha, newDepth-OnePly, ply+1, true,
threadID);
}
else value = alpha + 1;
if(value > alpha) {
ss[ply].reduction = Depth(0);
value = -search(pos, ss, -alpha, newDepth, ply+1, true, threadID);
if(value > alpha && value < beta) {
if(ply == 1 && RootMoveNumber == 1)
// 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.
Threads[threadID].failHighPly1 = true;
value = -search_pv(pos, ss, -beta, -alpha, newDepth, ply+1,
threadID);
Threads[threadID].failHighPly1 = false;
}
}
}
pos.undo_move(move, u);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
// 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(Iteration >= 2 &&
-value <= ValueByIteration[Iteration-1] - ProblemMargin)
Problem = true;
}
// 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;
}
// All legal moves have been searched. A special case: If there were
// no legal moves, it must be mate or stalemate:
if(moveCount == 0) {
if(pos.is_check())
return value_mated_in(ply);
else
return VALUE_DRAW;
}
// If the search is not aborted, update the transposition table,
// history counters, and killer moves. This code is somewhat messy,
// and definitely needs to be cleaned up. FIXME
if(!AbortSearch && !thread_should_stop(threadID)) {
if(bestValue <= oldAlpha)
TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE,
VALUE_TYPE_UPPER);
else if(bestValue >= beta) {
Move m = ss[ply].pv[ply];
if(pos.square_is_empty(move_to(m)) && !move_promotion(m) &&
!move_is_ep(m)) {
for(int i = 0; i < moveCount - 1; i++)
if(pos.square_is_empty(move_to(movesSearched[i]))
&& !move_promotion(movesSearched[i])
&& !move_is_ep(movesSearched[i]))
H.failure(pos.piece_on(move_from(movesSearched[i])),
movesSearched[i]);
H.success(pos.piece_on(move_from(m)), m, depth);
if(m != ss[ply].killer1) {
ss[ply].killer2 = ss[ply].killer1;
ss[ply].killer1 = m;
}
}
TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
}
else
TT.store(pos, value_to_tt(bestValue, ply), depth, ss[ply].pv[ply],
VALUE_TYPE_EXACT);
}
return bestValue;
}
// search() is the search function for zero-width nodes.
Value search(Position &pos, SearchStack ss[], Value beta, Depth depth,
int ply, bool allowNullmove, int threadID) {
assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
assert(ply >= 0 && ply < PLY_MAX);
assert(threadID >= 0 && threadID < ActiveThreads);
EvalInfo ei;
// Initialize, and make an early exit in case of an aborted search,
// an instant draw, maximum ply reached, etc.
if(AbortSearch || thread_should_stop(threadID))
return Value(0);
if(depth < OnePly)
return qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
init_node(pos, ss, ply, threadID);
if(pos.is_draw())
return VALUE_DRAW;
if(ply >= PLY_MAX - 1)
return evaluate(pos, ei, threadID);
// Mate distance pruning
if(value_mated_in(ply) >= beta)
return beta;
if(value_mate_in(ply+1) < beta)
return beta-1;
// Transposition table lookup
bool ttFound;
Value ttValue;
Depth ttDepth;
Move ttMove = MOVE_NONE;
ValueType ttValueType;
ttFound = TT.retrieve(pos, &ttValue, &ttDepth, &ttMove, &ttValueType);
if(ttFound) {
ttValue = value_from_tt(ttValue, ply);
if(ttDepth >= depth
|| ttValue >= Max(value_mate_in(100), beta)
|| ttValue < Min(value_mated_in(100), beta)) {
if((is_lower_bound(ttValueType) && ttValue >= beta) ||
(is_upper_bound(ttValueType) && ttValue < beta)) {
ss[ply].currentMove = ttMove;
return ttValue;
}
}
}
Value approximateEval = quick_evaluate(pos);
bool mateThreat = false;
// Null move search
if(!pos.is_check() && allowNullmove && ok_to_do_nullmove(pos)
&& approximateEval >= beta - NullMoveMargin) {
UndoInfo u;
Value nullValue;
ss[ply].currentMove = MOVE_NULL;
pos.do_null_move(u);
nullValue = -search(pos, ss, -(beta-1), depth-4*OnePly, ply+1, false,
threadID);
pos.undo_null_move(u);
if(nullValue >= beta) {
if(depth >= 6 * OnePly) { // Do zugzwang verification search
Value v = search(pos, ss, beta, depth-5*OnePly, ply, false, threadID);
if(v >= beta)
return beta;
}
else
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;
}
}
// Razoring:
else if(depth < RazorDepth && approximateEval < beta - RazorMargin &&
evaluate(pos, ei, threadID) < beta - RazorMargin) {
Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
if(v < beta)
return v;
}
// Internal iterative deepening
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];
}
// Initialize a MovePicker object for the current position, and prepare
// to search all moves:
MovePicker mp = MovePicker(pos, false, ttMove, ss[ply].mateKiller,
ss[ply].killer1, ss[ply].killer2, depth);
Move move, movesSearched[256];
int moveCount = 0;
Value value, bestValue = -VALUE_INFINITE, futilityValue = VALUE_NONE;
Bitboard dcCandidates = mp.discovered_check_candidates();
bool isCheck = pos.is_check();
bool useFutilityPruning =
UseFutilityPruning && depth < SelectiveDepth && !isCheck;
// Loop through all legal moves until no moves remain or a beta cutoff
// occurs.
while(bestValue < beta && !thread_should_stop(threadID)
&& (move = mp.get_next_move()) != MOVE_NONE) {
UndoInfo u;
Depth ext, newDepth;
bool singleReply = (isCheck && mp.number_of_moves() == 1);
bool moveIsCheck = pos.move_is_check(move, dcCandidates);
bool moveIsCapture = pos.move_is_capture(move);
bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move);
assert(move_is_ok(move));
movesSearched[moveCount++] = ss[ply].currentMove = move;
// Decide the new search depth.
ext = extension(pos, move, false, moveIsCheck, singleReply, mateThreat);
newDepth = depth - OnePly + ext;
// Futility pruning
if(useFutilityPruning && ext == Depth(0) && !moveIsCapture &&
!moveIsPassedPawnPush && !move_promotion(move)) {
if(moveCount >= 2 + int(depth)
&& ok_to_prune(pos, move, ss[ply].threatMove, depth))
continue;
if(depth < 3 * OnePly && approximateEval < beta) {
if(futilityValue == VALUE_NONE)
futilityValue = evaluate(pos, ei, threadID)
+ ((depth < 2 * OnePly)? FutilityMargin1 : FutilityMargin2);
if(futilityValue < beta) {
if(futilityValue > bestValue)
bestValue = futilityValue;
continue;
}
}
}
// Make and search the move.
pos.do_move(move, u, dcCandidates);
if(depth >= 2*OnePly && ext == Depth(0) && moveCount >= LMRNonPVMoves
&& !moveIsCapture && !move_promotion(move) && !moveIsPassedPawnPush
&& !move_is_castle(move)
&& move != ss[ply].killer1 && move != ss[ply].killer2) {
ss[ply].reduction = OnePly;
value = -search(pos, ss, -(beta-1), newDepth-OnePly, ply+1, true,
threadID);
}
else
value = beta;
if(value >= beta) {
ss[ply].reduction = Depth(0);
value = -search(pos, ss, -(beta-1), newDepth, ply+1, true, threadID);
}
pos.undo_move(move, u);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
// New best move?
if(value > bestValue) {
bestValue = value;
if(value >= beta)
update_pv(ss, ply);
if(value == value_mate_in(ply + 1))
ss[ply].mateKiller = move;
}
// 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))
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) {
if(pos.is_check())
return value_mated_in(ply);
else
return VALUE_DRAW;
}
// If the search is not aborted, update the transposition table,
// history counters, and killer moves. This code is somewhat messy,
// and definitely needs to be cleaned up. FIXME
if(!AbortSearch && !thread_should_stop(threadID)) {
if(bestValue < beta)
TT.store(pos, value_to_tt(bestValue, ply), depth, MOVE_NONE,
VALUE_TYPE_UPPER);
else {
Move m = ss[ply].pv[ply];
if(pos.square_is_empty(move_to(m)) && !move_promotion(m) &&
!move_is_ep(m)) {
for(int i = 0; i < moveCount - 1; i++)
if(pos.square_is_empty(move_to(movesSearched[i]))
&& !move_promotion(movesSearched[i])
&& !move_is_ep(movesSearched[i]))
H.failure(pos.piece_on(move_from(movesSearched[i])),
movesSearched[i]);
H.success(pos.piece_on(move_from(m)), m, depth);
if(m != ss[ply].killer1) {
ss[ply].killer2 = ss[ply].killer1;
ss[ply].killer1 = m;
}
}
TT.store(pos, value_to_tt(bestValue, ply), depth, m, VALUE_TYPE_LOWER);
}
}
return bestValue;
}
// qsearch() is the quiescence search function, which is called by the main
// search function when the remaining depth is zero (or, to be more precise,
// less than OnePly).
Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
Depth depth, int ply, int threadID) {
Value staticValue, bestValue, value;
EvalInfo ei;
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,
// an instant draw, maximum ply reached, etc.
if(AbortSearch || thread_should_stop(threadID))
return Value(0);
init_node(pos, ss, ply, threadID);
if(pos.is_draw())
return VALUE_DRAW;
// Evaluate the position statically:
staticValue = evaluate(pos, ei, threadID);
if(ply == PLY_MAX - 1) return staticValue;
// Initialize "stand pat score", and return it immediately if it is
// at least beta.
if(pos.is_check())
bestValue = -VALUE_INFINITE;
else {
bestValue = staticValue;
if(bestValue >= beta)
return bestValue;
if(bestValue > alpha)
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, false, MOVE_NONE, MOVE_NONE, MOVE_NONE,
MOVE_NONE, depth);
Move move;
int moveCount = 0;
Bitboard dcCandidates = mp.discovered_check_candidates();
bool isCheck = pos.is_check();
// Loop through the moves until no moves remain or a beta cutoff
// occurs.
while(alpha < beta && ((move = mp.get_next_move()) != MOVE_NONE)) {
UndoInfo u;
bool moveIsCheck = pos.move_is_check(move, dcCandidates);
bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move);
assert(move_is_ok(move));
moveCount++;
ss[ply].currentMove = move;
// Futility pruning
if(UseQSearchFutilityPruning && !isCheck && !moveIsCheck &&
!move_promotion(move) && !moveIsPassedPawnPush &&
beta - alpha == 1 &&
pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame) {
Value futilityValue =
staticValue
+ Max(pos.midgame_value_of_piece_on(move_to(move)),
pos.endgame_value_of_piece_on(move_to(move)))
+ FutilityMargin0
+ ei.futilityMargin;
if(futilityValue < alpha) {
if(futilityValue > bestValue)
bestValue = futilityValue;
continue;
}
}
// Don't search captures and checks with negative SEE values.
if(!isCheck && !move_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;
// Make and search the move.
pos.do_move(move, u, dcCandidates);
value = -qsearch(pos, ss, -beta, -alpha, depth-OnePly, ply+1, threadID);
pos.undo_move(move, u);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
// New best move?
if(value > bestValue) {
bestValue = value;
if(value > alpha) {
alpha = value;
update_pv(ss, ply);
}
}
}
// 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);
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
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) {
assert(threadID >= 0 && threadID < ActiveThreads);
assert(ActiveThreads > 1);
Position pos = Position(sp->pos);
SearchStack *ss = sp->sstack[threadID];
Value value;
Move move;
int moveCount = sp->moves;
bool isCheck = pos.is_check();
bool useFutilityPruning =
UseFutilityPruning && sp->depth < SelectiveDepth && !isCheck;
while(sp->bestValue < sp->beta && !thread_should_stop(threadID)
&& (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE) {
UndoInfo u;
Depth ext, newDepth;
bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
bool moveIsCapture = pos.move_is_capture(move);
bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move);
assert(move_is_ok(move));
lock_grab(&(sp->lock));
sp->moves++;
moveCount = sp->moves;
lock_release(&(sp->lock));
ss[sp->ply].currentMove = move;
// Decide the new search depth.
ext = extension(pos, move, false, moveIsCheck, false, false);
newDepth = sp->depth - OnePly + ext;
// Prune?
if(useFutilityPruning && ext == Depth(0) && !moveIsCapture
&& !moveIsPassedPawnPush && !move_promotion(move)
&& moveCount >= 2 + int(sp->depth)
&& ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
continue;
// Make and search the move.
pos.do_move(move, u, sp->dcCandidates);
if(ext == Depth(0) && moveCount >= LMRNonPVMoves
&& !moveIsCapture && !move_promotion(move) && !moveIsPassedPawnPush
&& !move_is_castle(move)
&& move != ss[sp->ply].killer1 && move != ss[sp->ply].killer2) {
ss[sp->ply].reduction = OnePly;
value = -search(pos, ss, -(sp->beta-1), newDepth - OnePly, sp->ply+1,
true, threadID);
}
else
value = sp->beta;
if(value >= sp->beta) {
ss[sp->ply].reduction = Depth(0);
value = -search(pos, ss, -(sp->beta - 1), newDepth, sp->ply+1, true,
threadID);
}
pos.undo_move(move, u);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
if(thread_should_stop(threadID))
break;
// 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;
}
}
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;
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
// after we return from the split point.
void sp_search_pv(SplitPoint *sp, int threadID) {
assert(threadID >= 0 && threadID < ActiveThreads);
assert(ActiveThreads > 1);
Position pos = Position(sp->pos);
SearchStack *ss = sp->sstack[threadID];
Value value;
Move move;
int moveCount = sp->moves;
while(sp->alpha < sp->beta && !thread_should_stop(threadID)
&& (move = sp->mp->get_next_move(sp->lock)) != MOVE_NONE) {
UndoInfo u;
Depth ext, newDepth;
bool moveIsCheck = pos.move_is_check(move, sp->dcCandidates);
bool moveIsCapture = pos.move_is_capture(move);
bool moveIsPassedPawnPush = pos.move_is_passed_pawn_push(move);
assert(move_is_ok(move));
ss[sp->ply].currentMoveCaptureValue = move_is_ep(move)?
PawnValueMidgame : pos.midgame_value_of_piece_on(move_to(move));
lock_grab(&(sp->lock));
sp->moves++;
moveCount = sp->moves;
lock_release(&(sp->lock));
ss[sp->ply].currentMove = move;
// Decide the new search depth.
ext = extension(pos, move, true, moveIsCheck, false, false);
newDepth = sp->depth - OnePly + ext;
// Make and search the move.
pos.do_move(move, u, sp->dcCandidates);
if(ext == Depth(0) && moveCount >= LMRPVMoves && !moveIsCapture
&& !move_promotion(move) && !moveIsPassedPawnPush
&& !move_is_castle(move)
&& move != ss[sp->ply].killer1 && move != ss[sp->ply].killer2) {
ss[sp->ply].reduction = OnePly;
value = -search(pos, ss, -sp->alpha, newDepth - OnePly, sp->ply+1,
true, threadID);
}
else
value = sp->alpha + 1;
if(value > sp->alpha) {
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) {
if(sp->ply == 1 && RootMoveNumber == 1)
// 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.
Threads[threadID].failHighPly1 = true;
value = -search_pv(pos, ss, -sp->beta, -sp->alpha, newDepth,
sp->ply+1, threadID);
Threads[threadID].failHighPly1 = false;
}
}
pos.undo_move(move, u);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
if(thread_should_stop(threadID))
break;
// 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;
}
}
// 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(Iteration >= 2 &&
-value <= ValueByIteration[Iteration-1] - ProblemMargin)
Problem = true;
}
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;
sp->cpus--;
sp->slaves[threadID] = 0;
lock_release(&(sp->lock));
}
/// The RootMove class
// Constructor
RootMove::RootMove() {
nodes = cumulativeNodes = 0ULL;
}
/// The RootMoveList class
// Constructor
RootMoveList::RootMoveList(Position &pos, Move searchMoves[]) {
MoveStack mlist[MaxRootMoves];
bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
int i, j = 0, k;
// Generate all legal moves
count = generate_legal_moves(pos, mlist);
// Add each move to the moves[] array
for(i = 0; i < count; i++) {
UndoInfo u;
SearchStack ss[PLY_MAX_PLUS_2];
bool includeMove;
if(includeAllMoves)
includeMove = true;
else {
includeMove = false;
for(k = 0; searchMoves[k] != MOVE_NONE; k++)
if(searchMoves[k] == mlist[i].move) {
includeMove = true;
break;
}
}
if(includeMove) {
moves[j].move = mlist[i].move;
moves[j].nodes = 0ULL;
pos.do_move(moves[j].move, u);
moves[j].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE,
Depth(0), 1, 0);
pos.undo_move(moves[j].move, u);
moves[j].pv[0] = moves[i].move;
moves[j].pv[1] = MOVE_NONE; // FIXME
j++;
}
}
count = j;
this->sort();
}
// Simple accessor methods for the RootMoveList class
Move RootMoveList::get_move(int moveNum) const {
return moves[moveNum].move;
}
Value RootMoveList::get_move_score(int moveNum) const {
return moves[moveNum].score;
}
void RootMoveList::set_move_score(int moveNum, Value score) {
moves[moveNum].score = score;
}
void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
moves[moveNum].nodes = nodes;
moves[moveNum].cumulativeNodes += nodes;
}
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;
}
Move RootMoveList::get_move_pv(int moveNum, int i) const {
return moves[moveNum].pv[i];
}
int64_t RootMoveList::get_move_cumulative_nodes(int moveNum) {
return moves[moveNum].cumulativeNodes;
}
int RootMoveList::move_count() const {
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.
Move RootMoveList::scan_for_easy_move() const {
Value bestMoveValue = this->get_move_score(0);
for(int i = 1; i < this->move_count(); i++)
if(this->get_move_score(i) >= bestMoveValue - EasyMoveMargin)
return MOVE_NONE;
return this->get_move(0);
}
// RootMoveList::sort() sorts the root move list at the beginning of a new
// iteration.
void RootMoveList::sort() {
for(int i = 1; i < count; i++) {
RootMove rm = moves[i];
int j;
for(j = i; j > 0 && compare_root_moves(moves[j-1], rm); j--)
moves[j] = moves[j-1];
moves[j] = rm;
}
}
// 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
// correctly in MultiPV mode.
void RootMoveList::sort_multipv(int n) {
for(int i = 1; i <= n; i++) {
RootMove rm = moves[i];
int j;
for(j = i; j > 0 && moves[j-1].score < rm.score; j--)
moves[j] = moves[j-1];
moves[j] = rm;
}
}
// RootMoveList::compare_root_moves() is the comparison function used by
// RootMoveList::sort 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.
int RootMoveList::compare_root_moves(const RootMove &rm1,
const RootMove &rm2) {
if(rm1.score < rm2.score) return 1;
else if(rm1.score > rm2.score) return 0;
else if(rm1.nodes < rm2.nodes) return 1;
else if(rm1.nodes > rm2.nodes) return 0;
else return 1;
}
// init_search_stack() initializes a search stack at the beginning of a
// new search from the root.
void init_search_stack(SearchStack ss[]) {
for(int i = 0; i < 3; i++) {
ss[i].pv[i] = MOVE_NONE;
ss[i].pv[i+1] = MOVE_NONE;
ss[i].currentMove = MOVE_NONE;
ss[i].mateKiller = MOVE_NONE;
ss[i].killer1 = MOVE_NONE;
ss[i].killer2 = MOVE_NONE;
ss[i].threatMove = MOVE_NONE;
ss[i].reduction = Depth(0);
}
}
// 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(const Position &pos, SearchStack ss[], int ply, int threadID) {
assert(ply >= 0 && ply < PLY_MAX);
assert(threadID >= 0 && threadID < ActiveThreads);
Threads[threadID].nodes++;
if(threadID == 0) {
NodesSincePoll++;
if(NodesSincePoll >= NodesBetweenPolls) {
poll();
NodesSincePoll = 0;
}
}
ss[ply].pv[ply] = ss[ply].pv[ply+1] = ss[ply].currentMove = MOVE_NONE;
ss[ply+2].mateKiller = MOVE_NONE;
ss[ply+2].killer1 = ss[ply+2].killer2 = MOVE_NONE;
ss[ply].threatMove = MOVE_NONE;
ss[ply].reduction = Depth(0);
ss[ply].currentMoveCaptureValue = Value(0);
if(Threads[threadID].printCurrentLine)
print_current_line(ss, ply, threadID);
}
// update_pv() is called whenever a search returns a value > alpha. It
// updates the PV in the SearchStack object corresponding to the current
// node.
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) {
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) {
Square f1, t1, f2, t2;
assert(move_is_ok(m1));
assert(move_is_ok(m2));
if(m2 == MOVE_NONE)
return false;
// Case 1: The moving piece is the same in both moves.
f2 = move_from(m2);
t1 = move_to(m1);
if(f2 == t1)
return true;
// Case 2: The destination square for m2 was vacated by m1.
t2 = move_to(m2);
f1 = move_from(m1);
if(t2 == f1)
return true;
// Case 3: Moving through the vacated square:
if(piece_is_slider(pos.piece_on(f2)) &&
bit_is_set(squares_between(f2, t2), f1))
return true;
// Case 4: The destination square for m2 is attacked by the moving piece
// in m1:
if(pos.piece_attacks_square(t1, t2))
return true;
// 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;
}
}
return false;
}
// 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.
Depth extension(const Position &pos, Move m, bool pvNode,
bool check, bool singleReply, bool mateThreat) {
Depth result = Depth(0);
if(check)
result += CheckExtension[pvNode];
if(singleReply)
result += SingleReplyExtension[pvNode];
if(pos.move_is_pawn_push_to_7th(m))
result += PawnPushTo7thExtension[pvNode];
if(pos.move_is_passed_pawn_push(m))
result += PassedPawnExtension[pvNode];
if(mateThreat)
result += MateThreatExtension[pvNode];
if(pos.midgame_value_of_piece_on(move_to(m)) >= RookValueMidgame
&& (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
- pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
&& !move_promotion(m))
result += PawnEndgameExtension[pvNode];
if(pvNode && pos.move_is_capture(m)
&& pos.type_of_piece_on(move_to(m)) != PAWN && pos.see(m) >= 0)
result += OnePly/2;
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) {
if(pos.non_pawn_material(pos.side_to_move()) == Value(0))
return false;
return true;
}
// 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) {
Square mfrom, mto, tfrom, tto;
assert(move_is_ok(m));
assert(threat == MOVE_NONE || move_is_ok(threat));
assert(!move_promotion(m));
assert(!pos.move_is_check(m));
assert(!pos.move_is_capture(m));
assert(!pos.move_is_passed_pawn_push(m));
assert(d >= OnePly);
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;
// Case 2: Don't prune moves which move the threatened piece
if(!PruneEscapeMoves && threat != MOVE_NONE && mfrom == tto)
return false;
// 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
&& (piece_value_midgame(pos.piece_on(tfrom))
>= piece_value_midgame(pos.piece_on(tto)))
&& pos.move_attacks_square(m, tto))
return false;
// Case 4: Don't prune moves with good history.
if(!H.ok_to_prune(pos.piece_on(move_from(m)), m, d))
return false;
// 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;
return true;
}
// 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.
bool fail_high_ply_1() {
for(int i = 0; i < ActiveThreads; i++)
if(Threads[i].failHighPly1)
return true;
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() {
int t, data;
static int lastInfoTime;
t = current_search_time();
// Poll for input
data = Bioskey();
if(data) {
char input[256];
if(fgets(input, 255, stdin) == NULL)
strcpy(input, "quit\n");
if(strncmp(input, "quit", 4) == 0) {
AbortSearch = true;
PonderSearch = false;
Quit = true;
}
else if(strncmp(input, "stop", 4) == 0) {
AbortSearch = true;
PonderSearch = false;
}
else if(strncmp(input, "ponderhit", 9) == 0)
ponderhit();
}
// Print search information
if(t < 1000)
lastInfoTime = 0;
else if(lastInfoTime > t)
// HACK: Must be a new search where we searched less than
// NodesBetweenPolls nodes during the first second of search.
lastInfoTime = 0;
else if(t - lastInfoTime >= 1000) {
lastInfoTime = t;
lock_grab(&IOLock);
std::cout << "info nodes " << nodes_searched() << " nps " << nps()
<< " time " << t << " hashfull " << TT.full() << std::endl;
lock_release(&IOLock);
if(ShowCurrentLine)
Threads[0].printCurrentLine = true;
}
// Should we stop the search?
if(!PonderSearch && Iteration >= 2 &&
(!InfiniteSearch && (t > AbsoluteMaxSearchTime ||
(RootMoveNumber == 1 &&
t > MaxSearchTime + ExtraSearchTime) ||
(!FailHigh && !fail_high_ply_1() && !Problem &&
t > 6*(MaxSearchTime + ExtraSearchTime)))))
AbortSearch = true;
if(!PonderSearch && ExactMaxTime && t >= ExactMaxTime)
AbortSearch = true;
if(!PonderSearch && Iteration >= 3 && MaxNodes
&& nodes_searched() >= MaxNodes)
AbortSearch = true;
}
// 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() {
int t = current_search_time();
PonderSearch = false;
if(Iteration >= 2 &&
(!InfiniteSearch && (StopOnPonderhit ||
t > AbsoluteMaxSearchTime ||
(RootMoveNumber == 1 &&
t > MaxSearchTime + ExtraSearchTime) ||
(!FailHigh && !fail_high_ply_1() && !Problem &&
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'.
void print_current_line(SearchStack ss[], int ply, int threadID) {
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);
}
Threads[threadID].printCurrentLine = false;
if(threadID + 1 < ActiveThreads)
Threads[threadID + 1].printCurrentLine = true;
}
// wait_for_stop_or_ponderhit() is called when the maximum depth is reached
// while the program is pondering. The point is to work around a wrinkle in
// the UCI protocol: When pondering, the engine is not allowed to give a
// "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
// We simply wait here until one of these commands is sent, and return,
// after which the bestmove and pondermove will be printed (in id_loop()).
void wait_for_stop_or_ponderhit() {
std::string command;
while(true) {
if(!std::getline(std::cin, command))
command = "quit";
if(command == "quit") {
OpeningBook.close();
stop_threads();
quit_eval();
exit(0);
}
else if(command == "ponderhit" || command == "stop")
break;
}
}
// 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) {
assert(threadID >= 0 && threadID < THREAD_MAX);
Threads[threadID].running = true;
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:
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:
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));
}
// 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;
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;
}
// 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);
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;
}
// 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);
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) {
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;
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:
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:
splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
Threads[master].activeSplitPoints++;
// Initialize the split point object:
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;
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:
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:
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:
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
}
}
// 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.
#if !defined(_MSC_VER)
void *init_thread(void *threadID) {
idle_loop(*(int *)threadID, NULL);
return NULL;
}
#else
DWORD WINAPI init_thread(LPVOID threadID) {
idle_loop(*(int *)threadID, NULL);
return NULL;
}
#endif
}
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