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,
- 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 to be stable, as it should be
// 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.
- inline Move pick_best(ExtMove* begin, ExtMove* end)
+ // 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;
/// 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,
- Move* cm, Move* fm, 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);
- endBadCaptures = moves + MAX_MOVES - 1;
- countermoves = cm;
- followupmoves = fm;
- ss = s;
-
- if (pos.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);
- endMoves += (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 s) : pos(p), history(h) {
+MovePicker::MovePicker(const Position& p, Move ttm, Depth d, Square s)
+ : pos(p) {
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_NO_CHECKS;
else
{
- stage = RECAPTURE;
+ stage = QSEARCH_RECAPTURES;
recaptureSquare = s;
- ttm = MOVE_NONE;
+ return;
}
- ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
- endMoves += (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) {
+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);
+ // 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;
- if (ttMove && (!pos.capture(ttMove) || pos.see(ttMove) <= captureThreshold))
- ttMove = MOVE_NONE;
-
- endMoves += (ttMove != MOVE_NONE);
+ stage += (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/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.
+ // has been picked up, saving some SEE calls in case we get a cutoff.
for (auto& m : *this)
- if (type_of(m) == ENPASSANT)
- m.value = PieceValue[MG][PAWN] - Value(PAWN);
-
- else if (type_of(m) == PROMOTION)
- m.value = PieceValue[MG][pos.piece_on(to_sq(m))] - Value(PAWN)
- + PieceValue[MG][promotion_type(m)] - PieceValue[MG][PAWN];
- else
- m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
- - Value(type_of(pos.moved_piece(m)));
+ 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>() {
+
+ const FromToStats& fromTo = pos.this_thread()->fromTo;
+
+ const CounterMoveStats* cmh = (ss-1)->counterMoves;
+ const CounterMoveStats* fmh = (ss-2)->counterMoves;
+ const CounterMoveStats* fmh2 = (ss-4)->counterMoves;
+
+ Color c = pos.side_to_move();
+
for (auto& m : *this)
- m.value = history[pos.moved_piece(m)][to_sq(m)];
+ m.value = (cmh ? (*cmh)[pos.moved_piece(m)][to_sq(m)] : VALUE_ZERO)
+ + (fmh ? (*fmh)[pos.moved_piece(m)][to_sq(m)] : VALUE_ZERO)
+ + (fmh2 ? (*fmh2)[pos.moved_piece(m)][to_sq(m)] : VALUE_ZERO)
+ + fromTo.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 value.
- Value see;
+ // Try captures ordered by MVV/LVA, then non-captures ordered by stats heuristics
+ const FromToStats& fromTo = pos.this_thread()->fromTo;
+ Color c = pos.side_to_move();
for (auto& m : *this)
- if ((see = pos.see_sign(m)) < VALUE_ZERO)
- m.value = see - HistoryStats::Max; // At the bottom
-
- else if (pos.capture(m))
+ if (pos.capture(m))
m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
- - Value(type_of(pos.moved_piece(m))) + HistoryStats::Max;
+ - Value(type_of(pos.moved_piece(m))) + FromToStats::Max;
else
- m.value = history[pos.moved_piece(m)][to_sq(m)];
-}
-
-
-/// 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() {
-
- cur = moves;
-
- switch (++stage) {
-
- case CAPTURES_S1: case CAPTURES_S3: case CAPTURES_S4: case CAPTURES_S5: case CAPTURES_S6:
- endMoves = generate<CAPTURES>(pos, moves);
- score<CAPTURES>();
- break;
-
- case KILLERS_S1:
- cur = killers;
- endMoves = cur + 2;
-
- killers[0] = ss->killers[0];
- killers[1] = ss->killers[1];
- killers[2].move = killers[3].move = MOVE_NONE;
- killers[4].move = killers[5].move = MOVE_NONE;
-
- // In SMP case countermoves[] and followupmoves[] could have duplicated entries
- // in rare cases (less than 1 out of a million). This is harmless.
-
- // Be sure countermoves and followupmoves are different from killers
- for (int i = 0; i < 2; ++i)
- if ( countermoves[i] != killers[0]
- && countermoves[i] != killers[1])
- *endMoves++ = countermoves[i];
-
- for (int i = 0; i < 2; ++i)
- if ( followupmoves[i] != killers[0]
- && followupmoves[i] != killers[1]
- && followupmoves[i] != killers[2]
- && followupmoves[i] != killers[3])
- *endMoves++ = followupmoves[i];
- break;
-
- case QUIETS_1_S1:
- 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:
- 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
- cur = moves + MAX_MOVES - 1;
- endMoves = endBadCaptures;
- break;
-
- case EVASIONS_S2:
- endMoves = generate<EVASIONS>(pos, moves);
- if (endMoves - moves > 1)
- score<EVASIONS>();
- break;
-
- case QUIET_CHECKS_S3:
- endMoves = generate<QUIET_CHECKS>(pos, moves);
- break;
-
- case EVASION: case QSEARCH_0: case QSEARCH_1: case PROBCUT: case RECAPTURE:
- stage = STOP;
- /* Fall through */
-
- case STOP:
- endMoves = cur + 1; // Avoid another generate_next_stage() call
- break;
-
- default:
- assert(false);
- }
+ m.value = fromTo.get(c, m);
}
/// 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)
- generate_next_stage();
+ 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:
+ case GOOD_CAPTURES:
+ while (cur < endMoves)
+ {
move = pick_best(cur++, endMoves);
if (move != ttMove)
{
- if (pos.see_sign(move) >= VALUE_ZERO)
+ if (pos.see_ge(move, VALUE_ZERO))
return move;
- // Losing capture, move it to the tail of the array
- *endBadCaptures-- = move;
+ // Losing capture, move it to the beginning of the array
+ *endBadCaptures++ = move;
}
- break;
+ }
- case KILLERS_S1:
- move = *cur++;
- if ( move != MOVE_NONE
- && move != ttMove
- && pos.pseudo_legal(move)
- && !pos.capture(move))
- return move;
- break;
+ ++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 QUIETS_1_S1: case QUIETS_2_S1:
+ case QUIET:
+ while (cur < endMoves)
+ {
move = *cur++;
if ( move != ttMove
- && move != killers[0]
- && move != killers[1]
- && move != killers[2]
- && move != killers[3]
- && move != killers[4]
- && move != killers[5])
+ && move != ss->killers[0]
+ && move != ss->killers[1]
+ && move != countermove)
return move;
- break;
+ }
+ ++stage;
+ cur = moves; // Point to beginning of bad captures
+
+ case BAD_CAPTURES:
+ if (cur < endBadCaptures)
+ return *cur++;
+ break;
- case BAD_CAPTURES_S1:
- return *cur--;
+ case EVASIONS_INIT:
+ cur = moves;
+ endMoves = generate<EVASIONS>(pos, cur);
+ score<EVASIONS>();
+ ++stage;
- case EVASIONS_S2: case CAPTURES_S3: case CAPTURES_S4:
+ 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++, endMoves);
- 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:
+ case PROBCUT_CAPTURES:
+ while (cur < endMoves)
+ {
move = pick_best(cur++, endMoves);
- if (to_sq(move) == recaptureSquare)
+ if ( move != ttMove
+ && pos.see_ge(move, threshold))
return move;
- break;
+ }
+ break;
- case QUIET_CHECKS_S3:
- move = *cur++;
+ case QCAPTURES_1_INIT: case QCAPTURES_2_INIT:
+ cur = moves;
+ endMoves = generate<CAPTURES>(pos, cur);
+ score<CAPTURES>();
+ ++stage;
+
+ 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;
+}
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