/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2015-2018 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
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
-#include <algorithm>
#include <cassert>
-#include "movegen.h"
#include "movepick.h"
namespace {
- enum Sequencer {
- MAIN_SEARCH, TT_MOVE_S1, GOOD_CAPTURES_S1, KILLERS_S1, NONCAPTURES_1_S1,
- NONCAPTURES_2_S1, BAD_CAPTURES_S1, STOP_S1,
- EVASIONS, TT_MOVE_S2, EVASIONS_S2, STOP_S2,
- CAPTURES_AND_CHECKS, TT_MOVE_S3, CAPTURES_S3, CHECKS_S3, STOP_S3,
- CAPTURES, TT_MOVE_S4, CAPTURES_S4, STOP_S4,
- PROBCUT, TT_MOVE_S5, CAPTURES_S5, STOP_S5,
- RECAPTURES, RECAPTURES_S6, STOP_S6
+ enum Stages {
+ MAIN_SEARCH, CAPTURES_INIT, GOOD_CAPTURES, KILLERS, COUNTERMOVE, QUIET_INIT, QUIET, BAD_CAPTURES,
+ EVASION, EVASIONS_INIT, ALL_EVASIONS,
+ PROBCUT, PROBCUT_CAPTURES_INIT, PROBCUT_CAPTURES,
+ QSEARCH, QCAPTURES_INIT, QCAPTURES, QCHECKS, QSEARCH_RECAPTURES, QRECAPTURES
};
- // 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 MoveStack& move) { return move.score > 0; }
+ // partial_insertion_sort() sorts moves in descending order up to and including
+ // a given limit. The order of moves smaller than the limit is left unspecified.
+ void partial_insertion_sort(ExtMove* begin, ExtMove* end, int limit) {
+
+ for (ExtMove *sortedEnd = begin, *p = begin + 1; p < end; ++p)
+ if (p->value >= limit)
+ {
+ ExtMove tmp = *p, *q;
+ *p = *++sortedEnd;
+ for (q = sortedEnd; q != begin && *(q - 1) < tmp; --q)
+ *q = *(q - 1);
+ *q = tmp;
+ }
+ }
+
+ // 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) {
- // Picks and moves to the front the best move in the range [firstMove, lastMove),
- // it is faster than sorting all the moves in advance when moves are few, as
- // normally are the possible captures.
- inline MoveStack* pick_best(MoveStack* firstMove, MoveStack* lastMove)
- {
- std::swap(*firstMove, *std::max_element(firstMove, lastMove));
- return firstMove;
+ std::swap(*begin, *std::max_element(begin, end));
+ 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 History& h,
- Search::Stack* ss, Value beta) : pos(p), H(h), depth(d) {
+/// MovePicker constructor for the main search
+MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
+ const CapturePieceToHistory* cph, const PieceToHistory** ch, Move cm, Move* killers_p)
+ : pos(p), mainHistory(mh), captureHistory(cph), contHistory(ch), countermove(cm),
+ killers{killers_p[0], killers_p[1]}, depth(d){
assert(d > DEPTH_ZERO);
- captureThreshold = 0;
- curMove = lastMove = 0;
- badCaptures = moves + MAX_MOVES;
-
- if (p.in_check())
- phase = EVASIONS;
-
- else
- {
- killers[0].move = ss->killers[0];
- killers[1].move = ss->killers[1];
-
- // Consider sligtly negative captures as good if at low depth and far from beta
- if (ss && ss->eval < beta - PawnValueMidgame && d < 3 * ONE_PLY)
- captureThreshold = -PawnValueMidgame;
-
- // Consider negative captures as good if still enough to reach beta
- else if (ss && ss->eval > beta)
- captureThreshold = beta - ss->eval;
-
- phase = MAIN_SEARCH;
- }
-
- ttMove = (ttm && pos.is_pseudo_legal(ttm) ? ttm : MOVE_NONE);
- phase += (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 History& h,
- Square sq) : pos(p), H(h), curMove(0), lastMove(0) {
+/// MovePicker constructor for quiescence search
+MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh, const CapturePieceToHistory* cph, Square s)
+ : pos(p), mainHistory(mh), captureHistory(cph), depth(d) {
assert(d <= DEPTH_ZERO);
- if (p.in_check())
- phase = EVASIONS;
-
- else if (d >= DEPTH_QS_CHECKS)
- phase = CAPTURES_AND_CHECKS;
+ if (pos.checkers())
+ stage = EVASION;
- else if (d >= DEPTH_QS_RECAPTURES)
- {
- phase = CAPTURES;
+ else if (d > DEPTH_QS_RECAPTURES)
+ stage = QSEARCH;
- // 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.is_capture_or_promotion(ttm))
- ttm = MOVE_NONE;
- }
else
{
- phase = RECAPTURES - 1;
- recaptureSquare = sq;
- ttm = MOVE_NONE;
+ stage = QSEARCH_RECAPTURES;
+ recaptureSquare = s;
+ return;
}
- ttMove = (ttm && pos.is_pseudo_legal(ttm) ? ttm : MOVE_NONE);
- phase += (ttMove == MOVE_NONE);
-}
-
-MovePicker::MovePicker(const Position& p, Move ttm, const History& h, PieceType parentCapture)
- : pos(p), H(h), curMove(0), lastMove(0) {
-
- assert (!pos.in_check());
-
- // In ProbCut we consider only captures better than parent's move
- captureThreshold = PieceValueMidgame[Piece(parentCapture)];
- phase = PROBCUT;
-
- if ( ttm != MOVE_NONE
- && (!pos.is_capture(ttm) || pos.see(ttm) <= captureThreshold))
- ttm = MOVE_NONE;
-
- ttMove = (ttm && pos.is_pseudo_legal(ttm) ? ttm : MOVE_NONE);
- phase += (ttMove == MOVE_NONE);
+ ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
+ stage += (ttMove == MOVE_NONE);
}
+/// MovePicker constructor for ProbCut: we generate captures with SEE higher
+/// than or equal to the given threshold.
+MovePicker::MovePicker(const Position& p, Move ttm, Value th, const CapturePieceToHistory* cph)
+ : pos(p), captureHistory(cph), threshold(th) {
-/// MovePicker::score_captures(), MovePicker::score_noncaptures() and
-/// MovePicker::score_evasions() assign a numerical move ordering score
-/// to each move in a move list. The moves with highest scores will be
-/// picked first by next_move().
-
-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
- // badCaptures[] array, but instead of doing it now we delay till when
- // the move has been picked up in pick_move_from_list(), this way we save
- // some SEE calls in case we get a cutoff (idea from Pablo Vazquez).
- Move m;
-
- for (MoveStack* cur = moves; cur != lastMove; cur++)
- {
- m = cur->move;
- cur->score = PieceValueMidgame[pos.piece_on(to_sq(m))]
- - type_of(pos.piece_moved(m));
-
- if (is_promotion(m))
- cur->score += PieceValueMidgame[Piece(promotion_piece_type(m))];
- }
-}
+ assert(!pos.checkers());
-void MovePicker::score_noncaptures() {
+ stage = PROBCUT;
+ ttMove = ttm
+ && pos.pseudo_legal(ttm)
+ && pos.capture(ttm)
+ && pos.see_ge(ttm, threshold) ? ttm : MOVE_NONE;
- Move m;
- Square from;
-
- for (MoveStack* cur = moves; cur != lastMove; cur++)
- {
- m = cur->move;
- from = from_sq(m);
- cur->score = H.value(pos.piece_on(from), to_sq(m));
- }
+ stage += (ttMove == MOVE_NONE);
}
-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;
-
- if (lastMove < moves + 2)
- return;
-
- for (MoveStack* cur = moves; cur != lastMove; cur++)
- {
- m = cur->move;
- if ((seeScore = pos.see_sign(m)) < 0)
- cur->score = seeScore - History::MaxValue; // Be sure we are at the bottom
- else if (pos.is_capture(m))
- cur->score = PieceValueMidgame[pos.piece_on(to_sq(m))]
- - type_of(pos.piece_moved(m)) + History::MaxValue;
- else
- cur->score = H.value(pos.piece_moved(m), to_sq(m));
- }
-}
-
-
-/// MovePicker::next_phase() generates, scores and sorts the next bunch of moves,
-/// when there are no more moves to try for the current phase.
-
-void MovePicker::next_phase() {
-
- curMove = moves;
-
- switch (++phase) {
-
- case TT_MOVE_S1: case TT_MOVE_S2: case TT_MOVE_S3: case TT_MOVE_S4: case TT_MOVE_S5:
- lastMove = curMove + 1;
- return;
-
- case GOOD_CAPTURES_S1:
- case CAPTURES_S3: case CAPTURES_S4: case CAPTURES_S5:
- case RECAPTURES_S6:
- lastMove = generate<MV_CAPTURE>(pos, moves);
- score_captures();
- return;
-
- case KILLERS_S1:
- curMove = killers;
- lastMove = curMove + 2;
- return;
-
- case NONCAPTURES_1_S1:
- lastNonCapture = lastMove = generate<MV_NON_CAPTURE>(pos, moves);
- score_noncaptures();
- lastMove = std::partition(curMove, lastMove, has_positive_score);
- sort<MoveStack>(curMove, lastMove);
- return;
-
- case NONCAPTURES_2_S1:
- curMove = lastMove;
- lastMove = lastNonCapture;
- if (depth >= 3 * ONE_PLY)
- sort<MoveStack>(curMove, lastMove);
- return;
-
- case BAD_CAPTURES_S1:
- // Bad captures SEE value is already calculated so just pick them in order
- // to get SEE move ordering.
- curMove = badCaptures;
- lastMove = moves + MAX_MOVES;
- return;
-
- case EVASIONS_S2:
- assert(pos.in_check());
- lastMove = generate<MV_EVASION>(pos, moves);
- score_evasions();
- return;
-
- case CHECKS_S3:
- lastMove = generate<MV_NON_CAPTURE_CHECK>(pos, moves);
- return;
-
- case STOP_S1: case STOP_S2: case STOP_S3: case STOP_S4: case STOP_S5: case STOP_S6:
- lastMove = curMove + 1; // Avoid another next_phase() call
- return;
-
- default:
- assert(false);
- }
+/// score() assigns a numerical value to each move in a list, used for sorting.
+/// Captures are ordered by Most Valuable Victim (MVV), preferring captures
+/// with a good history. Quiets are ordered using the histories.
+template<GenType Type>
+void MovePicker::score() {
+
+ static_assert(Type == CAPTURES || Type == QUIETS || Type == EVASIONS, "Wrong type");
+
+ for (auto& m : *this)
+ if (Type == CAPTURES)
+ m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
+ + Value((*captureHistory)[pos.moved_piece(m)][to_sq(m)][type_of(pos.piece_on(to_sq(m)))]);
+
+ else if (Type == QUIETS)
+ m.value = (*mainHistory)[pos.side_to_move()][from_to(m)]
+ + (*contHistory[0])[pos.moved_piece(m)][to_sq(m)]
+ + (*contHistory[1])[pos.moved_piece(m)][to_sq(m)]
+ + (*contHistory[3])[pos.moved_piece(m)][to_sq(m)];
+
+ else // Type == EVASIONS
+ {
+ if (pos.capture(m))
+ m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
+ - Value(type_of(pos.moved_piece(m)));
+ else
+ m.value = (*mainHistory)[pos.side_to_move()][from_to(m)] - (1 << 28);
+ }
}
+/// 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 value from a list of generated moves
+/// taking care not to return the ttMove if it has already been searched.
-/// MovePicker::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 to return the tt move if has already been
-/// searched previously. Note that this function is not thread safe so should be
-/// lock protected by caller when accessed through a shared MovePicker object.
-
-Move MovePicker::next_move() {
+Move MovePicker::next_move(bool skipQuiets) {
Move move;
- while (true)
- {
- while (curMove == lastMove)
- next_phase();
+ switch (stage) {
- switch (phase) {
+ case MAIN_SEARCH: case EVASION: case QSEARCH: case PROBCUT:
+ ++stage;
+ return ttMove;
- case TT_MOVE_S1: case TT_MOVE_S2: case TT_MOVE_S3: case TT_MOVE_S4: case TT_MOVE_S5:
- curMove++;
- return ttMove;
- break;
+ case CAPTURES_INIT:
+ case PROBCUT_CAPTURES_INIT:
+ case QCAPTURES_INIT:
+ case QSEARCH_RECAPTURES:
+ endBadCaptures = cur = moves;
+ endMoves = generate<CAPTURES>(pos, cur);
+ score<CAPTURES>();
+ ++stage;
- case GOOD_CAPTURES_S1:
- move = pick_best(curMove++, lastMove)->move;
+ // Rebranch at the top of the switch via a recursive call
+ return next_move(skipQuiets);
+
+ case GOOD_CAPTURES:
+ while (cur < endMoves)
+ {
+ move = pick_best(cur++, endMoves);
if (move != ttMove)
{
- assert(captureThreshold <= 0); // Otherwise we cannot use see_sign()
-
- int seeScore = pos.see_sign(move);
- if (seeScore >= captureThreshold)
+ if (pos.see_ge(move, Value(-55 * (cur-1)->value / 1024)))
return move;
- // Losing capture, move it to the tail of the array
- (--badCaptures)->move = move;
- badCaptures->score = seeScore;
+ // Losing capture, move it to the beginning of the array
+ *endBadCaptures++ = move;
}
- break;
+ }
- case KILLERS_S1:
- move = (curMove++)->move;
- if ( move != MOVE_NONE
- && pos.is_pseudo_legal(move)
- && move != ttMove
- && !pos.is_capture(move))
+ ++stage;
+ move = killers[0]; // First killer move
+ if ( move != MOVE_NONE
+ && move != ttMove
+ && pos.pseudo_legal(move)
+ && !pos.capture(move))
+ return move;
+ /* fallthrough */
+
+ case KILLERS:
+ ++stage;
+ move = killers[1]; // Second killer move
+ if ( move != MOVE_NONE
+ && move != ttMove
+ && pos.pseudo_legal(move)
+ && !pos.capture(move))
+ return move;
+ /* fallthrough */
+
+ case COUNTERMOVE:
+ ++stage;
+ move = countermove;
+ if ( move != MOVE_NONE
+ && move != ttMove
+ && move != killers[0]
+ && move != killers[1]
+ && pos.pseudo_legal(move)
+ && !pos.capture(move))
+ return move;
+ /* fallthrough */
+
+ case QUIET_INIT:
+ cur = endBadCaptures;
+ endMoves = generate<QUIETS>(pos, cur);
+ score<QUIETS>();
+ partial_insertion_sort(cur, endMoves, -4000 * depth / ONE_PLY);
+ ++stage;
+ /* fallthrough */
+
+ case QUIET:
+ if (!skipQuiets)
+ while (cur < endMoves)
+ {
+ move = *cur++;
+
+ if ( move != ttMove
+ && move != killers[0]
+ && move != killers[1]
+ && move != countermove)
+ return move;
+ }
+ ++stage;
+ cur = moves; // Point to beginning of bad captures
+ /* fallthrough */
+
+ case BAD_CAPTURES:
+ if (cur < endBadCaptures)
+ return *cur++;
+ break;
+
+ case EVASIONS_INIT:
+ cur = moves;
+ endMoves = generate<EVASIONS>(pos, cur);
+ score<EVASIONS>();
+ ++stage;
+ /* fallthrough */
+
+ case ALL_EVASIONS:
+ while (cur < endMoves)
+ {
+ move = pick_best(cur++, endMoves);
+ if (move != ttMove)
return move;
- break;
+ }
+ break;
- case NONCAPTURES_1_S1:
- case NONCAPTURES_2_S1:
- move = (curMove++)->move;
+ case PROBCUT_CAPTURES:
+ while (cur < endMoves)
+ {
+ move = pick_best(cur++, endMoves);
if ( move != ttMove
- && move != killers[0].move
- && move != killers[1].move)
+ && pos.see_ge(move, threshold))
return move;
- break;
-
- case BAD_CAPTURES_S1:
- move = pick_best(curMove++, lastMove)->move;
- return move;
+ }
+ break;
- case EVASIONS_S2:
- case CAPTURES_S3:
- case CAPTURES_S4:
- move = pick_best(curMove++, lastMove)->move;
+ case QCAPTURES:
+ while (cur < endMoves)
+ {
+ move = pick_best(cur++, endMoves);
if (move != ttMove)
return move;
+ }
+ if (depth <= DEPTH_QS_NO_CHECKS)
break;
-
- case CAPTURES_S5:
- move = pick_best(curMove++, lastMove)->move;
- if ( move != ttMove
- && pos.see(move) > captureThreshold)
- return move;
- break;
-
- case RECAPTURES_S6:
- move = (curMove++)->move;
- if (to_sq(move) == recaptureSquare)
- return move;
- break;
-
- case CHECKS_S3:
- move = (curMove++)->move;
+ cur = moves;
+ endMoves = generate<QUIET_CHECKS>(pos, cur);
+ ++stage;
+ /* fallthrough */
+
+ case QCHECKS:
+ while (cur < endMoves)
+ {
+ move = cur++->move;
if (move != ttMove)
return move;
- break;
-
- case STOP_S1: case STOP_S2: case STOP_S3: case STOP_S4: case STOP_S5: case STOP_S6:
- return MOVE_NONE;
+ }
+ break;
- default:
- assert(false);
+ case QRECAPTURES:
+ while (cur < endMoves)
+ {
+ move = *cur++;
+ if (to_sq(move) == recaptureSquare)
+ return move;
}
+ break;
+
+ default:
+ assert(false);
}
+
+ return MOVE_NONE;
}
projects / stockfish / blobdiff