/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2015-2017 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,
- STOP
+ MAIN_SEARCH, CAPTURES_INIT, GOOD_CAPTURES, KILLERS, COUNTERMOVE, QUIET_INIT, QUIET, BAD_CAPTURES,
+ EVASION, EVASIONS_INIT, ALL_EVASIONS,
+ PROBCUT, PROBCUT_INIT, PROBCUT_CAPTURES,
+ QSEARCH_WITH_CHECKS, QCAPTURES_1_INIT, QCAPTURES_1, QCHECKS,
+ QSEARCH_NO_CHECKS, QCAPTURES_2_INIT, QCAPTURES_2,
+ QSEARCH_RECAPTURES, QRECAPTURES
};
- // Our insertion sort, which is guaranteed (and also needed) to be stable
+ // Our insertion sort, which is guaranteed to be stable, as it should be
void insertion_sort(ExtMove* begin, ExtMove* end)
{
ExtMove tmp, *p, *q;
}
}
- // Unary predicate used by std::partition to split positive scores from remaining
- // ones so to sort separately the two sets, and with the second sort delayed.
- inline bool has_positive_score(const ExtMove& ms) { return ms.score > 0; }
-
- // Picks 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. possible captures.
- inline ExtMove* pick_best(ExtMove* begin, ExtMove* end)
+ // 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.
+ Move pick_best(ExtMove* begin, ExtMove* end)
{
std::swap(*begin, *std::max_element(begin, end));
- return begin;
+ return *begin;
}
-}
+
+} // namespace
/// Constructors of the MovePicker class. As arguments we pass information
-/// to help it to return the presumably good moves first, to decide which
+/// 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 about how important good
-/// move ordering is at the current node.
+/// 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,
- Move* cm, Search::Stack* s) : pos(p), history(h), depth(d) {
+MovePicker::MovePicker(const Position& p, Move ttm, Depth d, Search::Stack* s)
+ : pos(p), ss(s), depth(d) {
assert(d > DEPTH_ZERO);
- cur = end = moves;
- endBadCaptures = moves + MAX_MOVES - 1;
- countermoves = cm;
- ss = s;
-
- if (p.checkers())
- stage = EVASION;
-
- else
- stage = MAIN_SEARCH;
+ Square prevSq = to_sq((ss-1)->currentMove);
+ countermove = pos.this_thread()->counterMoves[pos.piece_on(prevSq)][prevSq];
- ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
- end += (ttMove != MOVE_NONE);
+ stage = pos.checkers() ? EVASION : MAIN_SEARCH;
+ ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
+ stage += (ttMove == MOVE_NONE);
}
-MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const HistoryStats& h,
- Square sq) : pos(p), history(h), cur(moves), end(moves) {
+MovePicker::MovePicker(const Position& p, Move ttm, Depth d, Square s)
+ : pos(p) {
assert(d <= DEPTH_ZERO);
- if (p.checkers())
+ if (pos.checkers())
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_NO_CHECKS;
- // Skip TT move if is not a capture or a promotion. This avoids qsearch
- // tree explosion due to a possible perpetual check or similar rare cases
- // when TT table is full.
- if (ttm && !pos.capture_or_promotion(ttm))
- ttm = MOVE_NONE;
- }
else
{
- stage = RECAPTURE;
- recaptureSquare = sq;
- ttm = MOVE_NONE;
+ stage = QSEARCH_RECAPTURES;
+ recaptureSquare = s;
+ return;
}
- ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
- end += (ttMove != MOVE_NONE);
+ ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
+ stage += (ttMove == MOVE_NONE);
}
-MovePicker::MovePicker(const Position& p, Move ttm, const HistoryStats& h, PieceType pt)
- : pos(p), history(h), cur(moves), end(moves) {
+MovePicker::MovePicker(const Position& p, Move ttm, Value th)
+ : pos(p), 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 or equal to the given threshold
+ ttMove = ttm
+ && pos.pseudo_legal(ttm)
+ && pos.capture(ttm)
+ && pos.see_ge(ttm, threshold)? ttm : MOVE_NONE;
- end += (ttMove != MOVE_NONE);
+ stage += (ttMove == MOVE_NONE);
}
-/// score() assign a numerical move ordering score to each move in a move list.
-/// The moves with highest scores will be picked first.
+/// 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/LVA.
- // 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 more 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.
- Move m;
-
- for (ExtMove* it = moves; it != end; ++it)
- {
- m = it->move;
- it->score = PieceValue[MG][pos.piece_on(to_sq(m))]
- - type_of(pos.moved_piece(m));
-
- if (type_of(m) == PROMOTION)
- it->score += PieceValue[MG][promotion_type(m)] - PieceValue[MG][PAWN];
-
- else if (type_of(m) == ENPASSANT)
- it->score += PieceValue[MG][PAWN];
- }
+ // 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))]
+ - Value(200 * relative_rank(pos.side_to_move(), to_sq(m)));
}
template<>
void MovePicker::score<QUIETS>() {
- Move m;
+ const HistoryStats& history = pos.this_thread()->history;
- for (ExtMove* it = moves; it != end; ++it)
- {
- m = it->move;
- it->score = history[pos.moved_piece(m)][to_sq(m)];
- }
+ const CounterMoveStats& cmh = *(ss-1)->counterMoves;
+ const CounterMoveStats& fmh = *(ss-2)->counterMoves;
+ const CounterMoveStats& fm2 = *(ss-4)->counterMoves;
+
+ Color c = pos.side_to_move();
+
+ for (auto& m : *this)
+ m.value = cmh[pos.moved_piece(m)][to_sq(m)]
+ + fmh[pos.moved_piece(m)][to_sq(m)]
+ + fm2[pos.moved_piece(m)][to_sq(m)]
+ + history.get(c, 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 score.
- Move m;
- int seeScore;
-
- for (ExtMove* it = moves; it != end; ++it)
- {
- m = it->move;
- if ((seeScore = pos.see_sign(m)) < 0)
- it->score = seeScore - HistoryStats::Max; // At the bottom
-
- else if (pos.capture(m))
- it->score = PieceValue[MG][pos.piece_on(to_sq(m))]
- - type_of(pos.moved_piece(m)) + HistoryStats::Max;
+ // Try captures ordered by MVV/LVA, then non-captures ordered by stats heuristics
+ const HistoryStats& history = pos.this_thread()->history;
+ Color c = pos.side_to_move();
+
+ for (auto& m : *this)
+ if (pos.capture(m))
+ m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
+ - Value(type_of(pos.moved_piece(m))) + HistoryStats::Max;
else
- it->score = history[pos.moved_piece(m)][to_sq(m)];
- }
-}
-
-
-/// generate_next() generates, scores and sorts the next bunch of moves, when
-/// there are no more moves to try for the current phase.
-
-void MovePicker::generate_next() {
-
- cur = moves;
-
- switch (++stage) {
-
- case CAPTURES_S1: case CAPTURES_S3: case CAPTURES_S4: case CAPTURES_S5: case CAPTURES_S6:
- end = generate<CAPTURES>(pos, moves);
- score<CAPTURES>();
- return;
-
- case KILLERS_S1:
- cur = killers;
- end = cur + 2;
-
- killers[0].move = ss->killers[0];
- killers[1].move = ss->killers[1];
- killers[2].move = killers[3].move = MOVE_NONE;
-
- // Be sure countermoves are different from killers
- for (int i = 0; i < 2; ++i)
- if (countermoves[i] != cur->move && countermoves[i] != (cur+1)->move)
- (end++)->move = countermoves[i];
-
- if (countermoves[1] && countermoves[1] == countermoves[0]) // Due to SMP races
- killers[3].move = MOVE_NONE;
-
- return;
-
- case QUIETS_1_S1:
- endQuiets = end = generate<QUIETS>(pos, moves);
- score<QUIETS>();
- end = std::partition(cur, end, has_positive_score);
- insertion_sort(cur, end);
- return;
-
- case QUIETS_2_S1:
- cur = end;
- end = endQuiets;
- if (depth >= 3 * ONE_PLY)
- insertion_sort(cur, end);
- return;
-
- case BAD_CAPTURES_S1:
- // Just pick them in reverse order to get MVV/LVA ordering
- cur = moves + MAX_MOVES - 1;
- end = endBadCaptures;
- return;
-
- case EVASIONS_S2:
- end = generate<EVASIONS>(pos, moves);
- if (end > moves + 1)
- score<EVASIONS>();
- return;
-
- case QUIET_CHECKS_S3:
- end = generate<QUIET_CHECKS>(pos, moves);
- return;
-
- case EVASION: case QSEARCH_0: case QSEARCH_1: case PROBCUT: case RECAPTURE:
- stage = STOP;
- case STOP:
- end = cur + 1; // Avoid another next_phase() call
- return;
-
- default:
- assert(false);
- }
+ m.value = history.get(c, m);
}
/// next_move() is the most important method of the MovePicker class. It returns
/// a new pseudo legal move every time it is called, until there are no more moves
-/// left. It picks the move with the biggest score from a list of generated moves
-/// taking care not returning the ttMove if has already been searched previously.
-template<>
-Move MovePicker::next_move<false>() {
+/// 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.
+
+Move MovePicker::next_move() {
Move move;
- while (true)
- {
- while (cur == end)
- generate_next();
+ switch (stage) {
- switch (stage) {
+ case MAIN_SEARCH: case EVASION: case QSEARCH_WITH_CHECKS:
+ case QSEARCH_NO_CHECKS: case PROBCUT:
+ ++stage;
+ return ttMove;
- case MAIN_SEARCH: case EVASION: case QSEARCH_0: case QSEARCH_1: case PROBCUT:
- ++cur;
- return ttMove;
+ case CAPTURES_INIT:
+ endBadCaptures = cur = moves;
+ endMoves = generate<CAPTURES>(pos, cur);
+ score<CAPTURES>();
+ ++stage;
- case CAPTURES_S1:
- move = pick_best(cur++, end)->move;
+ case GOOD_CAPTURES:
+ while (cur < endMoves)
+ {
+ move = pick_best(cur++, endMoves);
if (move != ttMove)
{
- if (pos.see_sign(move) >= 0)
+ if (pos.see_ge(move, VALUE_ZERO))
return move;
- // Losing capture, move it to the tail of the array
- (endBadCaptures--)->move = move;
+ // Losing capture, move it to the beginning of the array
+ *endBadCaptures++ = move;
}
- break;
-
- case KILLERS_S1:
- move = (cur++)->move;
- if ( move != MOVE_NONE
- && pos.pseudo_legal(move)
- && move != ttMove
- && !pos.capture(move))
- return move;
- break;
+ }
- case QUIETS_1_S1: case QUIETS_2_S1:
- move = (cur++)->move;
+ ++stage;
+ move = ss->killers[0]; // First killer move
+ if ( move != MOVE_NONE
+ && move != ttMove
+ && pos.pseudo_legal(move)
+ && !pos.capture(move))
+ return move;
+
+ case KILLERS:
+ ++stage;
+ move = ss->killers[1]; // Second killer move
+ if ( move != MOVE_NONE
+ && move != ttMove
+ && pos.pseudo_legal(move)
+ && !pos.capture(move))
+ return move;
+
+ case COUNTERMOVE:
+ ++stage;
+ move = countermove;
+ if ( move != MOVE_NONE
+ && move != ttMove
+ && move != ss->killers[0]
+ && move != ss->killers[1]
+ && pos.pseudo_legal(move)
+ && !pos.capture(move))
+ return move;
+
+ case QUIET_INIT:
+ cur = endBadCaptures;
+ endMoves = generate<QUIETS>(pos, cur);
+ score<QUIETS>();
+ if (depth < 3 * ONE_PLY)
+ {
+ ExtMove* goodQuiet = std::partition(cur, endMoves, [](const ExtMove& m)
+ { return m.value > VALUE_ZERO; });
+ insertion_sort(cur, goodQuiet);
+ } else
+ insertion_sort(cur, endMoves);
+ ++stage;
+
+ case QUIET:
+ while (cur < endMoves)
+ {
+ move = *cur++;
if ( move != ttMove
- && move != killers[0].move
- && move != killers[1].move
- && move != killers[2].move
- && move != killers[3].move)
+ && move != ss->killers[0]
+ && move != ss->killers[1]
+ && move != countermove)
return move;
- break;
-
- case BAD_CAPTURES_S1:
- return (cur--)->move;
-
- case EVASIONS_S2: case CAPTURES_S3: case CAPTURES_S4:
- move = pick_best(cur++, end)->move;
+ }
+ ++stage;
+ cur = moves; // Point to beginning of bad captures
+
+ case BAD_CAPTURES:
+ if (cur < endBadCaptures)
+ return *cur++;
+ break;
+
+ case EVASIONS_INIT:
+ cur = moves;
+ endMoves = generate<EVASIONS>(pos, cur);
+ score<EVASIONS>();
+ ++stage;
+
+ case ALL_EVASIONS:
+ while (cur < endMoves)
+ {
+ move = pick_best(cur++, endMoves);
if (move != ttMove)
return move;
- break;
+ }
+ break;
- case CAPTURES_S5:
- move = pick_best(cur++, end)->move;
- if (move != ttMove && pos.see(move) > captureThreshold)
- return move;
- break;
+ case PROBCUT_INIT:
+ cur = moves;
+ endMoves = generate<CAPTURES>(pos, cur);
+ score<CAPTURES>();
+ ++stage;
- case CAPTURES_S6:
- move = pick_best(cur++, end)->move;
- if (to_sq(move) == recaptureSquare)
+ case PROBCUT_CAPTURES:
+ while (cur < endMoves)
+ {
+ move = pick_best(cur++, endMoves);
+ if ( move != ttMove
+ && pos.see_ge(move, threshold))
return move;
- break;
+ }
+ break;
+
+ case QCAPTURES_1_INIT: case QCAPTURES_2_INIT:
+ cur = moves;
+ endMoves = generate<CAPTURES>(pos, cur);
+ score<CAPTURES>();
+ ++stage;
- case QUIET_CHECKS_S3:
- move = (cur++)->move;
+ case QCAPTURES_1: case QCAPTURES_2:
+ while (cur < endMoves)
+ {
+ move = pick_best(cur++, endMoves);
if (move != ttMove)
return move;
+ }
+ if (stage == QCAPTURES_2)
break;
+ cur = moves;
+ endMoves = generate<QUIET_CHECKS>(pos, cur);
+ ++stage;
+
+ case QCHECKS:
+ while (cur < endMoves)
+ {
+ move = cur++->move;
+ if (move != ttMove)
+ return move;
+ }
+ break;
- case STOP:
- return MOVE_NONE;
+ case QSEARCH_RECAPTURES:
+ cur = moves;
+ endMoves = generate<CAPTURES>(pos, cur);
+ score<CAPTURES>();
+ ++stage;
- default:
- assert(false);
+ case QRECAPTURES:
+ while (cur < endMoves)
+ {
+ move = pick_best(cur++, endMoves);
+ if (to_sq(move) == recaptureSquare)
+ return move;
}
- }
-}
+ break;
+ default:
+ assert(false);
+ }
-/// 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>(); }
+ return MOVE_NONE;
+}
projects / stockfish / blobdiff