Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
-
Stockfish is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
namespace {
enum Stages {
- MAIN_SEARCH, CAPTURES_S1, KILLERS_S1, QUIETS_1_S1, QUIETS_2_S1, BAD_CAPTURES_S1,
- EVASION, EVASIONS_S2,
- QSEARCH_0, CAPTURES_S3, QUIET_CHECKS_S3,
- QSEARCH_1, CAPTURES_S4,
- PROBCUT, CAPTURES_S5,
- RECAPTURE, CAPTURES_S6,
+ MAIN_SEARCH, GOOD_CAPTURES, KILLERS, GOOD_QUIETS, BAD_QUIETS, BAD_CAPTURES,
+ EVASION, ALL_EVASIONS,
+ QSEARCH_WITH_CHECKS, QCAPTURES_1, CHECKS,
+ QSEARCH_WITHOUT_CHECKS, QCAPTURES_2,
+ PROBCUT, PROBCUT_CAPTURES,
+ RECAPTURE, RECAPTURES,
STOP
};
// pick_best() finds the best move in the range (begin, end) and moves it to
// the front. It's faster than sorting all the moves in advance when there
- // are few moves e.g. the possible captures.
+ // are few moves, e.g., the possible captures.
Move pick_best(ExtMove* begin, ExtMove* end)
{
std::swap(*begin, *std::max_element(begin, end));
/// Constructors of the MovePicker class. As arguments we pass information
/// to help it to return the (presumably) good moves first, to decide which
/// moves to return (in the quiescence search, for instance, we only want to
-/// search captures, promotions and some checks) and how important good move
+/// search captures, promotions, and some checks) and how important good move
/// ordering is at the current node.
-MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const HistoryStats& h, const CounterMovesHistoryStats& cmh,
- Move cm, Search::Stack* s) : pos(p), history(h), counterMovesHistory(cmh), depth(d) {
+MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const HistoryStats& h,
+ const CounterMoveStats& cmh, Move cm, Search::Stack* s)
+ : pos(p), history(h), counterMoveHistory(&cmh), ss(s), countermove(cm), depth(d) {
assert(d > DEPTH_ZERO);
- endBadCaptures = moves + MAX_MOVES - 1;
- countermove = cm;
- ss = s;
-
- if (pos.checkers())
- stage = EVASION;
-
- else
- stage = MAIN_SEARCH;
-
- ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
+ stage = pos.checkers() ? EVASION : MAIN_SEARCH;
+ ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
endMoves += (ttMove != MOVE_NONE);
}
-MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const HistoryStats& h, const CounterMovesHistoryStats& cmh,
- Square s) : pos(p), history(h), counterMovesHistory(cmh) {
+MovePicker::MovePicker(const Position& p, Move ttm, Depth d,
+ const HistoryStats& h, Square s)
+ : pos(p), history(h), counterMoveHistory(nullptr) {
assert(d <= DEPTH_ZERO);
stage = EVASION;
else if (d > DEPTH_QS_NO_CHECKS)
- stage = QSEARCH_0;
+ stage = QSEARCH_WITH_CHECKS;
else if (d > DEPTH_QS_RECAPTURES)
- stage = QSEARCH_1;
+ stage = QSEARCH_WITHOUT_CHECKS;
else
{
ttm = MOVE_NONE;
}
- ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
+ ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
endMoves += (ttMove != MOVE_NONE);
}
-MovePicker::MovePicker(const Position& p, Move ttm, const HistoryStats& h, const CounterMovesHistoryStats& cmh, PieceType pt)
- : pos(p), history(h), counterMovesHistory(cmh) {
+MovePicker::MovePicker(const Position& p, Move ttm, const HistoryStats& h, Value th)
+ : pos(p), history(h), counterMoveHistory(nullptr), threshold(th) {
assert(!pos.checkers());
stage = PROBCUT;
- // In ProbCut we generate only captures that are better than the parent's
- // captured piece.
- captureThreshold = PieceValue[MG][pt];
- ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
-
- if (ttMove && (!pos.capture(ttMove) || pos.see(ttMove) <= captureThreshold))
- ttMove = MOVE_NONE;
+ // In ProbCut we generate captures with SEE higher than the given threshold
+ ttMove = ttm
+ && pos.pseudo_legal(ttm)
+ && pos.capture(ttm)
+ && pos.see(ttm) > threshold ? ttm : MOVE_NONE;
endMoves += (ttMove != MOVE_NONE);
}
-/// score() assign a numerical value to each move in a move list. The moves with
+/// score() assigns a numerical value to each move in a move list. The moves with
/// highest values will be picked first.
template<>
void MovePicker::score<CAPTURES>() {
- // Winning and equal captures in the main search are ordered by MVV.
- // Suprisingly, this appears to perform slightly better than SEE based
- // move ordering. The reason is probably that in a position with a winning
- // capture, capturing a valuable (but sufficiently defended) piece
- // first usually doesn't hurt. The opponent will have to recapture, and
- // the hanging piece will still be hanging (except in the unusual cases
- // where it is possible to recapture with the hanging piece). Exchanging
- // big pieces before capturing a hanging piece probably helps to reduce
- // the subtree size.
- // In main search we want to push captures with negative SEE values to the
+ // Winning and equal captures in the main search are ordered by MVV, preferring
+ // captures near our home rank. Surprisingly, this appears to perform slightly
+ // better than SEE-based move ordering: exchanging big pieces before capturing
+ // a hanging piece probably helps to reduce the subtree size.
+ // In the main search we want to push captures with negative SEE values to the
// badCaptures[] array, but instead of doing it now we delay until the move
- // has been picked up in pick_move_from_list(). This way we save some SEE
- // calls in case we get a cutoff.
+ // has been picked up, saving some SEE calls in case we get a cutoff.
for (auto& m : *this)
m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
- - 200 * relative_rank(pos.side_to_move(), to_sq(m));
+ - Value(200 * relative_rank(pos.side_to_move(), to_sq(m)));
}
template<>
void MovePicker::score<QUIETS>() {
- Square prevSq = to_sq((ss-1)->currentMove);
- const HistoryStats& cmh = counterMovesHistory[pos.piece_on(prevSq)][prevSq];
-
for (auto& m : *this)
m.value = history[pos.moved_piece(m)][to_sq(m)]
- + cmh[pos.moved_piece(m)][to_sq(m)] * 3;
+ + (*counterMoveHistory)[pos.moved_piece(m)][to_sq(m)];
}
template<>
void MovePicker::score<EVASIONS>() {
- // Try good captures ordered by MVV/LVA, then non-captures if destination square
- // is not under attack, ordered by history value, then bad-captures and quiet
- // moves with a negative SEE. This last group is ordered by the SEE value.
+ // Try winning and equal captures ordered by MVV/LVA, then non-captures ordered
+ // by history value, then bad captures and quiet moves with a negative SEE ordered
+ // by SEE value.
Value see;
for (auto& m : *this)
}
-/// generate_next_stage() generates, scores and sorts the next bunch of moves,
+/// generate_next_stage() generates, scores, and sorts the next bunch of moves
/// when there are no more moves to try for the current stage.
void MovePicker::generate_next_stage() {
+ assert(stage != STOP);
+
cur = moves;
switch (++stage) {
- case CAPTURES_S1: case CAPTURES_S3: case CAPTURES_S4: case CAPTURES_S5: case CAPTURES_S6:
+ case GOOD_CAPTURES: case QCAPTURES_1: case QCAPTURES_2:
+ case PROBCUT_CAPTURES: case RECAPTURES:
endMoves = generate<CAPTURES>(pos, moves);
score<CAPTURES>();
break;
- case KILLERS_S1:
- cur = killers;
- endMoves = cur + 2;
-
+ case KILLERS:
killers[0] = ss->killers[0];
killers[1] = ss->killers[1];
- killers[2].move = MOVE_NONE;
-
- // Be sure countermoves are different from killers
- if ( countermove != killers[0]
- && countermove != killers[1])
- *endMoves++ = countermove;
+ killers[2] = countermove;
+ cur = killers;
+ endMoves = cur + 2 + (countermove != killers[0] && countermove != killers[1]);
break;
- case QUIETS_1_S1:
+ case GOOD_QUIETS:
endQuiets = endMoves = generate<QUIETS>(pos, moves);
score<QUIETS>();
endMoves = std::partition(cur, endMoves, [](const ExtMove& m) { return m.value > VALUE_ZERO; });
insertion_sort(cur, endMoves);
break;
- case QUIETS_2_S1:
+ case BAD_QUIETS:
cur = endMoves;
endMoves = endQuiets;
if (depth >= 3 * ONE_PLY)
insertion_sort(cur, endMoves);
break;
- case BAD_CAPTURES_S1:
- // Just pick them in reverse order to get MVV/LVA ordering
+ case BAD_CAPTURES:
+ // Just pick them in reverse order to get correct ordering
cur = moves + MAX_MOVES - 1;
endMoves = endBadCaptures;
break;
- case EVASIONS_S2:
+ case ALL_EVASIONS:
endMoves = generate<EVASIONS>(pos, moves);
if (endMoves - moves > 1)
score<EVASIONS>();
break;
- case QUIET_CHECKS_S3:
+ case CHECKS:
endMoves = generate<QUIET_CHECKS>(pos, moves);
break;
- case EVASION: case QSEARCH_0: case QSEARCH_1: case PROBCUT: case RECAPTURE:
+ case EVASION: case QSEARCH_WITH_CHECKS: case QSEARCH_WITHOUT_CHECKS:
+ case PROBCUT: case RECAPTURE: case STOP:
stage = STOP;
- /* Fall through */
-
- case STOP:
- endMoves = cur + 1; // Avoid another generate_next_stage() call
break;
default:
/// a new pseudo legal move every time it is called, until there are no more moves
/// left. It picks the move with the biggest value from a list of generated moves
/// taking care not to return the ttMove if it has already been searched.
-template<>
-Move MovePicker::next_move<false>() {
+
+Move MovePicker::next_move() {
Move move;
while (true)
{
- while (cur == endMoves)
+ while (cur == endMoves && stage != STOP)
generate_next_stage();
switch (stage) {
- case MAIN_SEARCH: case EVASION: case QSEARCH_0: case QSEARCH_1: case PROBCUT:
+ case MAIN_SEARCH: case EVASION: case QSEARCH_WITH_CHECKS:
+ case QSEARCH_WITHOUT_CHECKS: case PROBCUT:
++cur;
return ttMove;
- case CAPTURES_S1:
+ case GOOD_CAPTURES:
move = pick_best(cur++, endMoves);
if (move != ttMove)
{
}
break;
- case KILLERS_S1:
+ case KILLERS:
move = *cur++;
if ( move != MOVE_NONE
&& move != ttMove
return move;
break;
- case QUIETS_1_S1: case QUIETS_2_S1:
+ case GOOD_QUIETS: case BAD_QUIETS:
move = *cur++;
if ( move != ttMove
&& move != killers[0]
return move;
break;
- case BAD_CAPTURES_S1:
+ case BAD_CAPTURES:
return *cur--;
- case EVASIONS_S2: case CAPTURES_S3: case CAPTURES_S4:
+ case ALL_EVASIONS: case QCAPTURES_1: case QCAPTURES_2:
move = pick_best(cur++, endMoves);
if (move != ttMove)
return move;
break;
- case CAPTURES_S5:
+ case PROBCUT_CAPTURES:
move = pick_best(cur++, endMoves);
- if (move != ttMove && pos.see(move) > captureThreshold)
+ if (move != ttMove && pos.see(move) > threshold)
return move;
break;
- case CAPTURES_S6:
+ case RECAPTURES:
move = pick_best(cur++, endMoves);
if (to_sq(move) == recaptureSquare)
return move;
break;
- case QUIET_CHECKS_S3:
+ case CHECKS:
move = *cur++;
if (move != ttMove)
return move;
}
}
}
-
-
-/// Version of next_move() to use at split point nodes where the move is grabbed
-/// from the split point's shared MovePicker object. This function is not thread
-/// safe so must be lock protected by the caller.
-template<>
-Move MovePicker::next_move<true>() { return ss->splitPoint->movePicker->next_move<false>(); }