/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- Copyright (C) 2008-2009 Marco Costalba
+ Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2015-2020 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/>.
*/
-
-////
-//// Includes
-////
-
-#include <algorithm>
#include <cassert>
-#include "history.h"
-#include "evaluate.h"
-#include "movegen.h"
#include "movepick.h"
-#include "search.h"
-#include "value.h"
-
-
-////
-//// Local definitions
-////
namespace {
- /// Variables
+ enum Stages {
+ MAIN_TT, CAPTURE_INIT, GOOD_CAPTURE, REFUTATION, QUIET_INIT, QUIET, BAD_CAPTURE,
+ EVASION_TT, EVASION_INIT, EVASION,
+ PROBCUT_TT, PROBCUT_INIT, PROBCUT,
+ QSEARCH_TT, QCAPTURE_INIT, QCAPTURE, QCHECK_INIT, QCHECK
+ };
+
+ // 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;
+ }
+ }
- CACHE_LINE_ALIGNMENT
- const MovegenPhaseT MainSearchPhaseTable[] = { PH_STOP, PH_NULL_MOVE, PH_TT_MOVES, PH_GOOD_CAPTURES, PH_KILLERS, PH_NONCAPTURES, PH_BAD_CAPTURES, PH_STOP};
- const MovegenPhaseT MainSearchNoNullPhaseTable[] = { PH_STOP, PH_TT_MOVES, PH_GOOD_CAPTURES, PH_KILLERS, PH_NONCAPTURES, PH_BAD_CAPTURES, PH_STOP};
- const MovegenPhaseT LowSearchPhaseTable[] = { PH_STOP, PH_TT_MOVES, PH_GOOD_CAPTURES, PH_NULL_MOVE, PH_KILLERS, PH_NONCAPTURES, PH_BAD_CAPTURES, PH_STOP};
- const MovegenPhaseT EvasionsPhaseTable[] = { PH_STOP, PH_EVASIONS, PH_STOP};
- const MovegenPhaseT QsearchWithChecksPhaseTable[] = { PH_STOP, PH_TT_MOVES, PH_QCAPTURES, PH_QCHECKS, PH_STOP};
- const MovegenPhaseT QsearchWithoutChecksPhaseTable[] = { PH_STOP, PH_TT_MOVES, PH_QCAPTURES, PH_STOP};
-}
+} // namespace
-////
-//// Functions
-////
+/// 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
+/// ordering is at the current node.
+/// 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)
+ : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch),
+ refutations{{killers[0], 0}, {killers[1], 0}, {cm, 0}}, depth(d) {
-/// Constructor for the MovePicker class. Apart from the position for which
-/// it is asked to pick legal moves, MovePicker also wants some 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 about how important good
-/// move ordering is at the current node.
+ assert(d > 0);
-MovePicker::MovePicker(const Position& p, Move ttm, Depth d,
- const History& h, SearchStack* ss, bool useNullMove) : pos(p), H(h) {
- ttMoves[0] = ttm;
- if (ss)
- {
- ttMoves[1] = (ss->mateKiller == ttm)? MOVE_NONE : ss->mateKiller;
- killers[0] = ss->killers[0];
- killers[1] = ss->killers[1];
- } else
- ttMoves[1] = killers[0] = killers[1] = MOVE_NONE;
-
- movesPicked = numOfMoves = numOfBadCaptures = 0;
- finished = false;
-
- if (p.is_check())
- phasePtr = EvasionsPhaseTable;
- else if (d >= Depth(3 * OnePly))
- phasePtr = useNullMove ? MainSearchPhaseTable : MainSearchNoNullPhaseTable;
- else if (d > Depth(0))
- phasePtr = useNullMove ? LowSearchPhaseTable : MainSearchNoNullPhaseTable;
- else if (d == Depth(0))
- phasePtr = QsearchWithChecksPhaseTable;
- else
- phasePtr = QsearchWithoutChecksPhaseTable;
-
- Color us = pos.side_to_move();
-
- dc = p.discovered_check_candidates(us);
- pinned = p.pinned_pieces(us);
+ stage = pos.checkers() ? EVASION_TT : MAIN_TT;
+ ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
+ stage += (ttMove == MOVE_NONE);
}
+/// MovePicker constructor for quiescence search
+MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const ButterflyHistory* mh,
+ const CapturePieceToHistory* cph, const PieceToHistory** ch, Square rs)
+ : pos(p), mainHistory(mh), captureHistory(cph), continuationHistory(ch), recaptureSquare(rs), depth(d) {
-/// MovePicker::get_next_move() is the most important method of the MovePicker
-/// class. It returns a new legal move every time it is called, until there
-/// are no more moves left of the types we are interested in.
+ assert(d <= 0);
-Move MovePicker::get_next_move() {
+ stage = pos.checkers() ? EVASION_TT : QSEARCH_TT;
+ ttMove = ttm
+ && (depth > DEPTH_QS_RECAPTURES || to_sq(ttm) == recaptureSquare)
+ && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
+ stage += (ttMove == MOVE_NONE);
+}
- Move move;
+/// MovePicker constructor for ProbCut: we generate captures with SEE greater
+/// 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) {
- while (true)
- {
- // If we already have a list of generated moves, pick the best move from
- // the list, and return it.
- move = pick_move_from_list();
- if (move != MOVE_NONE)
- {
- assert(move_is_ok(move));
- return move;
- }
-
- // Next phase
- phasePtr++;
- switch (*phasePtr) {
-
- case PH_NULL_MOVE:
- return MOVE_NULL;
-
- case PH_TT_MOVES:
- movesPicked = 0; // This is used as index to ttMoves[]
- break;
-
- case PH_GOOD_CAPTURES:
- numOfMoves = generate_captures(pos, moves);
- score_captures();
- std::sort(moves, moves + numOfMoves);
- movesPicked = 0;
- break;
-
- case PH_KILLERS:
- movesPicked = 0; // This is used as index to killers[]
- break;
-
- case PH_NONCAPTURES:
- numOfMoves = generate_noncaptures(pos, moves);
- score_noncaptures();
- std::sort(moves, moves + numOfMoves);
- movesPicked = 0;
- break;
-
- case PH_BAD_CAPTURES:
- // Bad captures SEE value is already calculated so just sort them
- // to get SEE move ordering.
- std::sort(badCaptures, badCaptures + numOfBadCaptures);
- movesPicked = 0;
- break;
-
- case PH_EVASIONS:
- assert(pos.is_check());
- numOfMoves = generate_evasions(pos, moves, pinned);
- score_evasions();
- std::sort(moves, moves + numOfMoves);
- movesPicked = 0;
- break;
-
- case PH_QCAPTURES:
- numOfMoves = generate_captures(pos, moves);
- score_captures();
- std::sort(moves, moves + numOfMoves);
- movesPicked = 0;
- break;
-
- case PH_QCHECKS:
- // Perhaps we should order moves move here? FIXME
- numOfMoves = generate_non_capture_checks(pos, moves, dc);
- movesPicked = 0;
- break;
-
- case PH_STOP:
- return MOVE_NONE;
-
- default:
- assert(false);
- return MOVE_NONE;
- }
- }
+ assert(!pos.checkers());
+
+ stage = PROBCUT_TT;
+ ttMove = ttm
+ && pos.capture(ttm)
+ && pos.pseudo_legal(ttm)
+ && pos.see_ge(ttm, threshold) ? ttm : MOVE_NONE;
+ stage += (ttMove == MOVE_NONE);
}
+/// MovePicker::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 moves are ordered using the histories.
+template<GenType Type>
+void MovePicker::score() {
-/// A variant of get_next_move() which takes a lock as a parameter, used to
-/// prevent multiple threads from picking the same move at a split point.
+ static_assert(Type == CAPTURES || Type == QUIETS || Type == EVASIONS, "Wrong type");
-Move MovePicker::get_next_move(Lock &lock) {
+ for (auto& m : *this)
+ if (Type == CAPTURES)
+ m.value = int(PieceValue[MG][pos.piece_on(to_sq(m))]) * 6
+ + (*captureHistory)[pos.moved_piece(m)][to_sq(m)][type_of(pos.piece_on(to_sq(m)))];
- lock_grab(&lock);
- if (finished)
- {
- lock_release(&lock);
- return MOVE_NONE;
- }
- Move m = get_next_move();
- if (m == MOVE_NONE)
- finished = true;
+ else if (Type == QUIETS)
+ m.value = (*mainHistory)[pos.side_to_move()][from_to(m)]
+ + 2 * (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]
+ + 2 * (*continuationHistory[1])[pos.moved_piece(m)][to_sq(m)]
+ + 2 * (*continuationHistory[3])[pos.moved_piece(m)][to_sq(m)]
+ + (*continuationHistory[5])[pos.moved_piece(m)][to_sq(m)];
- lock_release(&lock);
- return 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)]
+ + (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]
+ - (1 << 28);
+ }
}
+/// MovePicker::select() returns the next move satisfying a predicate function.
+/// It never returns the TT move.
+template<MovePicker::PickType T, typename Pred>
+Move MovePicker::select(Pred filter) {
-/// MovePicker::score_captures(), MovePicker::score_noncaptures(),
-/// MovePicker::score_evasions() and MovePicker::score_qcaptures() assign a
-/// numerical move ordering score to each move in a move list. The moves
-/// with highest scores will be picked first by pick_move_from_list().
-
-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;
-
- // Use MVV/LVA ordering
- for (int i = 0; i < numOfMoves; i++)
+ while (cur < endMoves)
{
- m = moves[i].move;
- if (move_is_promotion(m))
- moves[i].score = QueenValueMidgame;
- else
- moves[i].score = int(pos.midgame_value_of_piece_on(move_to(m)))
- -int(pos.type_of_piece_on(move_from(m)));
+ if (T == Best)
+ std::swap(*cur, *std::max_element(cur, endMoves));
+
+ if (*cur != ttMove && filter())
+ return *cur++;
+
+ cur++;
}
+ return MOVE_NONE;
}
-void MovePicker::score_noncaptures() {
- // First score by history, when no history is available then use
- // piece/square tables values. This seems to be better then a
- // random choice when we don't have an history for any move.
- Piece piece;
- Square from, to;
- int hs;
-
- for (int i = 0; i < numOfMoves; i++)
- {
- from = move_from(moves[i].move);
- to = move_to(moves[i].move);
- piece = pos.piece_on(from);
- hs = H.move_ordering_score(piece, to);
+/// 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, picking the move with the highest score from a list of generated moves.
+Move MovePicker::next_move(bool skipQuiets) {
+
+top:
+ switch (stage) {
+
+ case MAIN_TT:
+ case EVASION_TT:
+ case QSEARCH_TT:
+ case PROBCUT_TT:
+ ++stage;
+ return ttMove;
+
+ case CAPTURE_INIT:
+ case PROBCUT_INIT:
+ case QCAPTURE_INIT:
+ cur = endBadCaptures = moves;
+ endMoves = generate<CAPTURES>(pos, cur);
+
+ score<CAPTURES>();
+ ++stage;
+ goto top;
+
+ case GOOD_CAPTURE:
+ if (select<Best>([&](){
+ return pos.see_ge(*cur, Value(-55 * cur->value / 1024)) ?
+ // Move losing capture to endBadCaptures to be tried later
+ true : (*endBadCaptures++ = *cur, false); }))
+ return *(cur - 1);
+
+ // Prepare the pointers to loop over the refutations array
+ cur = std::begin(refutations);
+ endMoves = std::end(refutations);
+
+ // If the countermove is the same as a killer, skip it
+ if ( refutations[0].move == refutations[2].move
+ || refutations[1].move == refutations[2].move)
+ --endMoves;
+
+ ++stage;
+ /* fallthrough */
+
+ case REFUTATION:
+ if (select<Next>([&](){ return *cur != MOVE_NONE
+ && !pos.capture(*cur)
+ && pos.pseudo_legal(*cur); }))
+ return *(cur - 1);
+ ++stage;
+ /* fallthrough */
+
+ case QUIET_INIT:
+ if (!skipQuiets)
+ {
+ cur = endBadCaptures;
+ endMoves = generate<QUIETS>(pos, cur);
- // Ensure history is always preferred to pst
- if (hs > 0)
- hs += 1000;
+ score<QUIETS>();
+ partial_insertion_sort(cur, endMoves, -3000 * depth);
+ }
- // pst based scoring
- moves[i].score = hs + pos.pst_delta<Position::MidGame>(piece, from, to);
- }
-}
+ ++stage;
+ /* fallthrough */
-void MovePicker::score_evasions() {
+ case QUIET:
+ if ( !skipQuiets
+ && select<Next>([&](){return *cur != refutations[0].move
+ && *cur != refutations[1].move
+ && *cur != refutations[2].move;}))
+ return *(cur - 1);
- for (int i = 0; i < numOfMoves; i++)
- {
- Move m = moves[i].move;
- if (m == ttMoves[0])
- moves[i].score = 2*HistoryMax;
- else if (!pos.square_is_empty(move_to(m)))
- {
- int seeScore = pos.see(m);
- moves[i].score = (seeScore >= 0)? seeScore + HistoryMax : seeScore;
- } else
- moves[i].score = H.move_ordering_score(pos.piece_on(move_from(m)), move_to(m));
- }
-}
+ // Prepare the pointers to loop over the bad captures
+ cur = moves;
+ endMoves = endBadCaptures;
+ ++stage;
+ /* fallthrough */
-/// MovePicker::pick_move_from_list() picks the move with the biggest score
-/// from a list of generated moves (moves[] or badCaptures[], depending on
-/// the current move generation phase). It takes care not to return the
-/// transposition table move if that has already been serched previously.
+ case BAD_CAPTURE:
+ return select<Next>([](){ return true; });
-Move MovePicker::pick_move_from_list() {
+ case EVASION_INIT:
+ cur = moves;
+ endMoves = generate<EVASIONS>(pos, cur);
- assert(movesPicked >= 0);
- assert(!pos.is_check() || *phasePtr == PH_EVASIONS || *phasePtr == PH_STOP);
- assert( pos.is_check() || *phasePtr != PH_EVASIONS);
+ score<EVASIONS>();
+ ++stage;
+ /* fallthrough */
- switch (*phasePtr) {
+ case EVASION:
+ return select<Best>([](){ return true; });
- case PH_TT_MOVES:
- while (movesPicked < 2) {
- Move move = ttMoves[movesPicked++];
- if ( move != MOVE_NONE
- && move_is_legal(pos, move, pinned))
- return move;
- }
- break;
+ case PROBCUT:
+ return select<Best>([&](){ return pos.see_ge(*cur, threshold); });
- case PH_GOOD_CAPTURES:
- while (movesPicked < numOfMoves)
- {
- Move move = moves[movesPicked++].move;
- if ( move != ttMoves[0]
- && move != ttMoves[1]
- && pos.pl_move_is_legal(move, pinned))
- {
- // Check for a non negative SEE now
- int seeValue = pos.see_sign(move);
- if (seeValue >= 0)
- return move;
-
- // Losing capture, move it to the badCaptures[] array, note
- // that move has now been already checked for legality.
- assert(numOfBadCaptures < 63);
- badCaptures[numOfBadCaptures].move = move;
- badCaptures[numOfBadCaptures++].score = seeValue;
- }
- }
- break;
-
- case PH_KILLERS:
- while (movesPicked < 2) {
- Move move = killers[movesPicked++];
- if ( move != MOVE_NONE
- && move != ttMoves[0]
- && move != ttMoves[1]
- && move_is_legal(pos, move, pinned)
- && !pos.move_is_capture(move))
- return move;
- }
- break;
+ case QCAPTURE:
+ if (select<Best>([&](){ return depth > DEPTH_QS_RECAPTURES
+ || to_sq(*cur) == recaptureSquare; }))
+ return *(cur - 1);
- case PH_NONCAPTURES:
- while (movesPicked < numOfMoves)
- {
- Move move = moves[movesPicked++].move;
- if ( move != ttMoves[0]
- && move != ttMoves[1]
- && move != killers[0]
- && move != killers[1]
- && pos.pl_move_is_legal(move, pinned))
- return move;
- }
- break;
+ // If we did not find any move and we do not try checks, we have finished
+ if (depth != DEPTH_QS_CHECKS)
+ return MOVE_NONE;
- case PH_EVASIONS:
- if (movesPicked < numOfMoves)
- return moves[movesPicked++].move;
- break;
+ ++stage;
+ /* fallthrough */
- case PH_BAD_CAPTURES:
- if (movesPicked < numOfBadCaptures)
- return badCaptures[movesPicked++].move;
- break;
+ case QCHECK_INIT:
+ cur = moves;
+ endMoves = generate<QUIET_CHECKS>(pos, cur);
- case PH_QCAPTURES:
- case PH_QCHECKS:
- while (movesPicked < numOfMoves)
- {
- Move move = moves[movesPicked++].move;
- // Maybe postpone the legality check until after futility pruning?
- if ( move != ttMoves[0]
- && pos.pl_move_is_legal(move, pinned))
- return move;
- }
- break;
+ ++stage;
+ /* fallthrough */
- default:
- break;
+ case QCHECK:
+ return select<Next>([](){ return true; });
}
- return MOVE_NONE;
+
+ assert(false);
+ return MOVE_NONE; // Silence warning
}
projects / stockfish / blobdiff