/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, 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
#include <cassert>
-#include "movegen.h"
#include "movepick.h"
-#include "search.h"
-#include "types.h"
+#include "thread.h"
namespace {
- enum MovegenPhase {
- PH_TT_MOVES, // Transposition table move and mate killer
- PH_GOOD_CAPTURES, // Queen promotions and captures with SEE values >= 0
- PH_KILLERS, // Killer moves from the current ply
- PH_NONCAPTURES, // Non-captures and underpromotions
- PH_BAD_CAPTURES, // Queen promotions and captures with SEE values < 0
- PH_EVASIONS, // Check evasions
- PH_QCAPTURES, // Captures in quiescence search
- PH_QCHECKS, // Non-capture checks in quiescence search
- PH_STOP
+ enum Stages {
+ 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
};
- CACHE_LINE_ALIGNMENT
- const uint8_t MainSearchTable[] = { PH_TT_MOVES, PH_GOOD_CAPTURES, PH_KILLERS, PH_NONCAPTURES, PH_BAD_CAPTURES, PH_STOP };
- const uint8_t EvasionTable[] = { PH_TT_MOVES, PH_EVASIONS, PH_STOP };
- const uint8_t QsearchWithChecksTable[] = { PH_TT_MOVES, PH_QCAPTURES, PH_QCHECKS, PH_STOP };
- const uint8_t QsearchWithoutChecksTable[] = { PH_TT_MOVES, PH_QCAPTURES, PH_STOP };
-}
+ // Our insertion sort, which is guaranteed to be stable, as it should be
+ void insertion_sort(ExtMove* begin, ExtMove* end)
+ {
+ ExtMove tmp, *p, *q;
+
+ for (p = begin + 1; p < end; ++p)
+ {
+ tmp = *p;
+ for (q = p; 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)
+ {
+ std::swap(*begin, *std::max_element(begin, end));
+ return *begin;
+ }
+
+} // namespace
-/// 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
+/// 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 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,
- SearchStack* ss, Value beta) : pos(p), H(h) {
- int searchTT = ttm;
- ttMoves[0].move = ttm;
- badCaptureThreshold = 0;
- badCaptures = moves + MOVES_MAX;
+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), ss(s), countermove(cm), depth(d) {
assert(d > DEPTH_ZERO);
- pinned = p.pinned_pieces(pos.side_to_move());
+ stage = pos.checkers() ? EVASION : MAIN_SEARCH;
+ ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
+ endMoves += (ttMove != MOVE_NONE);
+}
- if (p.is_check())
- {
- ttMoves[1].move = killers[0].move = killers[1].move = MOVE_NONE;
- phasePtr = EvasionTable;
- }
- else
- {
- ttMoves[1].move = (ss->mateKiller == ttm) ? MOVE_NONE : ss->mateKiller;
- searchTT |= ttMoves[1].move;
- killers[0].move = ss->killers[0];
- killers[1].move = ss->killers[1];
+MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const HistoryStats& h,
+ const CounterMovesHistoryStats& cmh, Square s)
+ : pos(p), history(h), counterMovesHistory(cmh) {
+
+ assert(d <= DEPTH_ZERO);
+
+ if (pos.checkers())
+ stage = EVASION;
- // Consider sligtly negative captures as good if at low
- // depth and far from beta.
- if (ss && ss->eval < beta - PawnValueMidgame && d < 3 * ONE_PLY)
- badCaptureThreshold = -PawnValueMidgame;
+ else if (d > DEPTH_QS_NO_CHECKS)
+ stage = QSEARCH_WITH_CHECKS;
- phasePtr = MainSearchTable;
+ else if (d > DEPTH_QS_RECAPTURES)
+ stage = QSEARCH_WITHOUT_CHECKS;
+
+ else
+ {
+ stage = RECAPTURE;
+ recaptureSquare = s;
+ ttm = MOVE_NONE;
}
- phasePtr += int(!searchTT) - 1;
- go_next_phase();
+ ttMove = ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE;
+ endMoves += (ttMove != MOVE_NONE);
}
-MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const History& h)
- : pos(p), H(h) {
- int searchTT = ttm;
- ttMoves[0].move = ttm;
- ttMoves[1].move = MOVE_NONE;
+MovePicker::MovePicker(const Position& p, Move ttm, const HistoryStats& h,
+ const CounterMovesHistoryStats& cmh, Value th)
+ : pos(p), history(h), counterMovesHistory(cmh), threshold(th) {
- assert(d <= DEPTH_ZERO);
+ assert(!pos.checkers());
- pinned = p.pinned_pieces(pos.side_to_move());
+ stage = PROBCUT;
- if (p.is_check())
- phasePtr = EvasionTable;
- else if (d >= DEPTH_QS_CHECKS)
- phasePtr = QsearchWithChecksTable;
- else
- {
- phasePtr = QsearchWithoutChecksTable;
+ // 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;
- // 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 != MOVE_NONE && !pos.move_is_capture_or_promotion(ttm))
- searchTT = ttMoves[0].move = MOVE_NONE;
- }
+ endMoves += (ttMove != MOVE_NONE);
+}
- phasePtr += int(!searchTT) - 1;
- go_next_phase();
+
+/// 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, preferring
+ // captures near our home rank. Suprisingly, 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 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, 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>() {
-/// MovePicker::go_next_phase() generates, scores and sorts the next bunch
-/// of moves when there are no more moves to try for the current phase.
+ Square prevSq = to_sq((ss-1)->currentMove);
+ const HistoryStats& cmh = counterMovesHistory[pos.piece_on(prevSq)][prevSq];
-void MovePicker::go_next_phase() {
+ for (auto& m : *this)
+ m.value = history[pos.moved_piece(m)][to_sq(m)]
+ + cmh[pos.moved_piece(m)][to_sq(m)] * 3;
+}
- curMove = moves;
- phase = *(++phasePtr);
- switch (phase) {
+template<>
+void MovePicker::score<EVASIONS>() {
+ // Try winning and equal captures 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;
- case PH_TT_MOVES:
- curMove = ttMoves;
- lastMove = curMove + 2;
- return;
+ for (auto& m : *this)
+ if ((see = pos.see_sign(m)) < VALUE_ZERO)
+ m.value = see - HistoryStats::Max; // At the bottom
- case PH_GOOD_CAPTURES:
- lastMove = generate<MV_CAPTURE>(pos, moves);
- score_captures();
- return;
+ else if (pos.capture(m))
+ m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
+ - Value(type_of(pos.moved_piece(m))) + HistoryStats::Max;
+ else
+ m.value = history[pos.moved_piece(m)][to_sq(m)];
+}
- case PH_KILLERS:
- curMove = killers;
- lastMove = curMove + 2;
- return;
- case PH_NONCAPTURES:
- lastMove = generate<MV_NON_CAPTURE>(pos, moves);
- score_noncaptures();
- sort_moves(moves, lastMove, &lastGoodNonCapture);
- return;
+/// generate_next_stage() generates, scores and sorts the next bunch of moves,
+/// when there are no more moves to try for the current stage.
- case PH_BAD_CAPTURES:
- // Bad captures SEE value is already calculated so just pick
- // them in order to get SEE move ordering.
- curMove = badCaptures;
- lastMove = moves + MOVES_MAX;
- return;
+void MovePicker::generate_next_stage() {
- case PH_EVASIONS:
- assert(pos.is_check());
- lastMove = generate<MV_EVASION>(pos, moves);
- score_evasions();
- return;
+ assert(stage != STOP);
- case PH_QCAPTURES:
- lastMove = generate<MV_CAPTURE>(pos, moves);
- score_captures();
- return;
+ cur = moves;
- case PH_QCHECKS:
- lastMove = generate<MV_NON_CAPTURE_CHECK>(pos, moves);
- return;
+ switch (++stage) {
- case PH_STOP:
- lastMove = curMove + 1; // Avoid another go_next_phase() call
- return;
+ case GOOD_CAPTURES: case QCAPTURES_1: case QCAPTURES_2:
+ case PROBCUT_CAPTURES: case RECAPTURES:
+ endMoves = generate<CAPTURES>(pos, moves);
+ score<CAPTURES>();
+ break;
- default:
- assert(false);
- return;
- }
-}
+ case KILLERS:
+ killers[0] = ss->killers[0];
+ killers[1] = ss->killers[1];
+ killers[2] = countermove;
+ cur = killers;
+ endMoves = cur + 2 + (countermove != killers[0] && countermove != killers[1]);
+ break;
+ 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;
-/// 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 get_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;
-
- // Use MVV/LVA ordering
- for (MoveStack* cur = moves; cur != lastMove; cur++)
- {
- m = cur->move;
- if (move_is_promotion(m))
- cur->score = QueenValueMidgame;
- else
- cur->score = pos.midgame_value_of_piece_on(move_to(m))
- - pos.type_of_piece_on(move_from(m));
- }
-}
+ case BAD_QUIETS:
+ cur = endMoves;
+ endMoves = endQuiets;
+ if (depth >= 3 * ONE_PLY)
+ insertion_sort(cur, endMoves);
+ break;
-void MovePicker::score_noncaptures() {
- // Score by history and max gain for the move.
- Move m;
- Piece piece;
- Square from, to;
+ case BAD_CAPTURES:
+ // Just pick them in reverse order to get correct ordering
+ cur = moves + MAX_MOVES - 1;
+ endMoves = endBadCaptures;
+ break;
- for (MoveStack* cur = moves; cur != lastMove; cur++)
- {
- m = cur->move;
- from = move_from(m);
- to = move_to(m);
- piece = pos.piece_on(from);
- cur->score = H.value(piece, to) + H.gain(piece, to);
- }
-}
+ case ALL_EVASIONS:
+ endMoves = generate<EVASIONS>(pos, moves);
+ if (endMoves - moves > 1)
+ score<EVASIONS>();
+ break;
-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, and at the end bad-captures and non-captures with a
- // negative SEE. This last group is ordered by the SEE score.
- Move m;
- int seeScore;
+ case CHECKS:
+ endMoves = generate<QUIET_CHECKS>(pos, moves);
+ break;
- // Skip if we don't have at least two moves to order
- if (lastMove < moves + 2)
- return;
+ case EVASION: case QSEARCH_WITH_CHECKS: case QSEARCH_WITHOUT_CHECKS:
+ case PROBCUT: case RECAPTURE: case STOP:
+ stage = STOP;
+ break;
- 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.move_is_capture(m))
- cur->score = pos.midgame_value_of_piece_on(move_to(m))
- - pos.type_of_piece_on(move_from(m)) + History::MaxValue;
- else
- cur->score = H.value(pos.piece_on(move_from(m)), move_to(m));
+ default:
+ assert(false);
}
}
-/// 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. 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::get_next_move() {
+/// 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.
+template<>
+Move MovePicker::next_move<false>() {
Move move;
while (true)
{
- while (curMove == lastMove)
- go_next_phase();
+ while (cur == endMoves && stage != STOP)
+ generate_next_stage();
- switch (phase) {
+ switch (stage) {
- case PH_TT_MOVES:
- move = (curMove++)->move;
- if ( move != MOVE_NONE
- && pos.move_is_legal(move, pinned))
- return move;
- break;
+ case MAIN_SEARCH: case EVASION: case QSEARCH_WITH_CHECKS:
+ case QSEARCH_WITHOUT_CHECKS: case PROBCUT:
+ ++cur;
+ return ttMove;
- case PH_GOOD_CAPTURES:
- move = pick_best(curMove++, lastMove).move;
- if ( move != ttMoves[0].move
- && move != ttMoves[1].move
- && pos.pl_move_is_legal(move, pinned))
+ case GOOD_CAPTURES:
+ move = pick_best(cur++, endMoves);
+ if (move != ttMove)
{
- // Check for a non negative SEE now
- int seeValue = pos.see_sign(move);
- if (seeValue >= badCaptureThreshold)
+ if (pos.see_sign(move) >= VALUE_ZERO)
return move;
- // Losing capture, move it to the tail of the array, note
- // that move has now been already checked for legality.
- (--badCaptures)->move = move;
- badCaptures->score = seeValue;
+ // Losing capture, move it to the tail of the array
+ *endBadCaptures-- = move;
}
break;
- case PH_KILLERS:
- move = (curMove++)->move;
- if ( move != MOVE_NONE
- && pos.move_is_legal(move, pinned)
- && move != ttMoves[0].move
- && move != ttMoves[1].move
- && !pos.move_is_capture(move))
+ case KILLERS:
+ move = *cur++;
+ if ( move != MOVE_NONE
+ && move != ttMove
+ && pos.pseudo_legal(move)
+ && !pos.capture(move))
+ return move;
+ break;
+
+ case GOOD_QUIETS: case BAD_QUIETS:
+ move = *cur++;
+ if ( move != ttMove
+ && move != killers[0]
+ && move != killers[1]
+ && move != killers[2])
return move;
break;
- case PH_NONCAPTURES:
- // Sort negative scored moves only when we get there
- if (curMove == lastGoodNonCapture)
- insertion_sort<MoveStack>(lastGoodNonCapture, lastMove);
-
- move = (curMove++)->move;
- if ( move != ttMoves[0].move
- && move != ttMoves[1].move
- && move != killers[0].move
- && move != killers[1].move
- && pos.pl_move_is_legal(move, pinned))
+ case BAD_CAPTURES:
+ return *cur--;
+
+ case ALL_EVASIONS: case QCAPTURES_1: case QCAPTURES_2:
+ move = pick_best(cur++, endMoves);
+ if (move != ttMove)
return move;
break;
- case PH_BAD_CAPTURES:
- move = pick_best(curMove++, lastMove).move;
- return move;
+ case PROBCUT_CAPTURES:
+ move = pick_best(cur++, endMoves);
+ if (move != ttMove && pos.see(move) > threshold)
+ return move;
+ break;
- case PH_EVASIONS:
- case PH_QCAPTURES:
- move = pick_best(curMove++, lastMove).move;
- if ( move != ttMoves[0].move
- && pos.pl_move_is_legal(move, pinned))
+ case RECAPTURES:
+ move = pick_best(cur++, endMoves);
+ if (to_sq(move) == recaptureSquare)
return move;
break;
- case PH_QCHECKS:
- move = (curMove++)->move;
- if ( move != ttMoves[0].move
- && pos.pl_move_is_legal(move, pinned))
+ case CHECKS:
+ move = *cur++;
+ if (move != ttMove)
return move;
break;
- case PH_STOP:
+ case STOP:
return MOVE_NONE;
default:
assert(false);
- break;
}
}
}
+
+
+/// 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>(); }