/*
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
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
STOP
};
- // Our insertion sort, guaranteed to be stable, as is needed
+ // Our insertion sort, which is guaranteed (and also needed) to be stable
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 and moves to the front the best move in the range [begin, end),
- // it is faster than sorting all the moves in advance when moves are few, as
- // normally are the possible captures.
+ // 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)
{
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 HistoryStats& h,
- Move* cm, Search::Stack* s) : pos(p), history(h), depth(d) {
+ Move* cm, Move* fm, Search::Stack* s) : pos(p), history(h), depth(d) {
assert(d > DEPTH_ZERO);
- cur = end = moves;
endBadCaptures = moves + MAX_MOVES - 1;
countermoves = cm;
+ followupmoves = fm;
ss = s;
- if (p.checkers())
+ if (pos.checkers())
stage = EVASION;
else
stage = MAIN_SEARCH;
- ttMove = (ttm && pos.is_pseudo_legal(ttm) ? ttm : MOVE_NONE);
- end += (ttMove != MOVE_NONE);
+ ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
+ endMoves += (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) {
+ Square s) : pos(p), history(h) {
assert(d <= DEPTH_ZERO);
- if (p.checkers())
+ if (pos.checkers())
stage = EVASION;
else if (d > DEPTH_QS_NO_CHECKS)
stage = QSEARCH_0;
else if (d > DEPTH_QS_RECAPTURES)
- {
stage = QSEARCH_1;
- // 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
{
stage = RECAPTURE;
- recaptureSquare = sq;
+ recaptureSquare = s;
ttm = MOVE_NONE;
}
- ttMove = (ttm && pos.is_pseudo_legal(ttm) ? ttm : MOVE_NONE);
- end += (ttMove != MOVE_NONE);
+ ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
+ endMoves += (ttMove != MOVE_NONE);
}
MovePicker::MovePicker(const Position& p, Move ttm, const HistoryStats& h, PieceType pt)
- : pos(p), history(h), cur(moves), end(moves) {
+ : pos(p), history(h) {
assert(!pos.checkers());
stage = PROBCUT;
- // In ProbCut we generate only captures better than parent's captured piece
+ // In ProbCut we generate only captures that are better than the parent's
+ // captured piece.
captureThreshold = PieceValue[MG][pt];
- ttMove = (ttm && pos.is_pseudo_legal(ttm) ? ttm : MOVE_NONE);
+ ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
- if (ttMove && (!pos.is_capture(ttMove) || pos.see(ttMove) <= captureThreshold))
+ if (ttMove && (!pos.capture(ttMove) || pos.see(ttMove) <= captureThreshold))
ttMove = MOVE_NONE;
- end += (ttMove != MOVE_NONE);
+ endMoves += (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() assign 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.
// 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 (ExtMove* it = moves; it != end; ++it)
- {
- m = it->move;
- it->score = PieceValue[MG][pos.piece_on(to_sq(m))]
- - type_of(pos.piece_moved(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];
- }
+ // 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 in pick_move_from_list(). This way we save some SEE
+ // calls in case we get a cutoff.
+ for (auto& m : *this)
+ m.value = PieceValue[MG][pos.piece_on(to_sq(m))]
+ - Value(type_of(pos.moved_piece(m)))
+ + (type_of(m) == ENPASSANT ? PieceValue[MG][PAWN] :
+ type_of(m) == PROMOTION ? PieceValue[MG][promotion_type(m)] - PieceValue[MG][PAWN]
+ : VALUE_ZERO);
}
template<>
void MovePicker::score<QUIETS>() {
-
- Move m;
-
- for (ExtMove* it = moves; it != end; ++it)
- {
- m = it->move;
- it->score = history[pos.piece_moved(m)][to_sq(m)];
- }
+ for (auto& m : *this)
+ m.value = history[pos.moved_piece(m)][to_sq(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;
+ // moves with a negative SEE. This last group is ordered by the SEE value.
+ Value see;
- 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
+ for (auto& m : *this)
+ if ((see = pos.see_sign(m)) < VALUE_ZERO)
+ m.value = see - HistoryStats::Max; // At the bottom
- else if (pos.is_capture(m))
- it->score = PieceValue[MG][pos.piece_on(to_sq(m))]
- - type_of(pos.piece_moved(m)) + HistoryStats::Max;
+ 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
- it->score = history[pos.piece_moved(m)][to_sq(m)];
- }
+ m.value = 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.
+/// 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() {
+void MovePicker::generate_next_stage() {
cur = moves;
switch (++stage) {
case CAPTURES_S1: case CAPTURES_S3: case CAPTURES_S4: case CAPTURES_S5: case CAPTURES_S6:
- end = generate<CAPTURES>(pos, moves);
+ endMoves = generate<CAPTURES>(pos, moves);
score<CAPTURES>();
return;
case KILLERS_S1:
cur = killers;
- end = cur + 2;
+ endMoves = cur + 2;
killers[0].move = ss->killers[0];
killers[1].move = ss->killers[1];
killers[2].move = killers[3].move = MOVE_NONE;
+ killers[4].move = killers[5].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;
+ // Please note that following code is racy and could yield to rare (less
+ // than 1 out of a million) duplicated entries in SMP case. This is harmless.
+ // Be sure countermoves are different from killers
+ for (int i = 0; i < 2; ++i)
+ if ( countermoves[i] != (cur+0)->move
+ && countermoves[i] != (cur+1)->move)
+ (endMoves++)->move = countermoves[i];
+
+ // Be sure followupmoves are different from killers and countermoves
+ for (int i = 0; i < 2; ++i)
+ if ( followupmoves[i] != (cur+0)->move
+ && followupmoves[i] != (cur+1)->move
+ && followupmoves[i] != (cur+2)->move
+ && followupmoves[i] != (cur+3)->move)
+ (endMoves++)->move = followupmoves[i];
return;
case QUIETS_1_S1:
- endQuiets = end = generate<QUIETS>(pos, moves);
+ endQuiets = endMoves = generate<QUIETS>(pos, moves);
score<QUIETS>();
- end = std::partition(cur, end, has_positive_score);
- insertion_sort(cur, end);
+ endMoves = std::partition(cur, endMoves, [](const ExtMove& m) { return m.value > VALUE_ZERO; });
+ insertion_sort(cur, endMoves);
return;
case QUIETS_2_S1:
- cur = end;
- end = endQuiets;
+ cur = endMoves;
+ endMoves = endQuiets;
if (depth >= 3 * ONE_PLY)
- insertion_sort(cur, end);
+ insertion_sort(cur, endMoves);
return;
case BAD_CAPTURES_S1:
// Just pick them in reverse order to get MVV/LVA ordering
cur = moves + MAX_MOVES - 1;
- end = endBadCaptures;
+ endMoves = endBadCaptures;
return;
case EVASIONS_S2:
- end = generate<EVASIONS>(pos, moves);
- if (end > moves + 1)
+ endMoves = generate<EVASIONS>(pos, moves);
+ if (endMoves > moves + 1)
score<EVASIONS>();
return;
case QUIET_CHECKS_S3:
- end = generate<QUIET_CHECKS>(pos, moves);
+ endMoves = generate<QUIET_CHECKS>(pos, moves);
return;
case EVASION: case QSEARCH_0: case QSEARCH_1: case PROBCUT: case RECAPTURE:
stage = STOP;
+ /* Fall through */
+
case STOP:
- end = cur + 1; // Avoid another next_phase() call
+ endMoves = cur + 1; // Avoid another next_phase() call
return;
default:
/// next_move() is the most important method of the MovePicker class. It returns
-/// a new pseudo legal move every time 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.
+/// 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>() {
while (true)
{
- while (cur == end)
- generate_next();
+ while (cur == endMoves)
+ generate_next_stage();
switch (stage) {
case MAIN_SEARCH: case EVASION: case QSEARCH_0: case QSEARCH_1: case PROBCUT:
- cur++;
+ ++cur;
return ttMove;
case CAPTURES_S1:
- move = pick_best(cur++, end)->move;
+ move = pick_best(cur++, endMoves)->move;
if (move != ttMove)
{
- if (pos.see_sign(move) >= 0)
+ if (pos.see_sign(move) >= VALUE_ZERO)
return move;
// Losing capture, move it to the tail of the array
case KILLERS_S1:
move = (cur++)->move;
if ( move != MOVE_NONE
- && pos.is_pseudo_legal(move)
&& move != ttMove
- && !pos.is_capture(move))
+ && pos.pseudo_legal(move)
+ && !pos.capture(move))
return move;
break;
&& move != killers[0].move
&& move != killers[1].move
&& move != killers[2].move
- && move != killers[3].move)
+ && move != killers[3].move
+ && move != killers[4].move
+ && move != killers[5].move)
return move;
break;
return (cur--)->move;
case EVASIONS_S2: case CAPTURES_S3: case CAPTURES_S4:
- move = pick_best(cur++, end)->move;
+ move = pick_best(cur++, endMoves)->move;
if (move != ttMove)
return move;
break;
case CAPTURES_S5:
- move = pick_best(cur++, end)->move;
+ move = pick_best(cur++, endMoves)->move;
if (move != ttMove && pos.see(move) > captureThreshold)
return move;
break;
case CAPTURES_S6:
- move = pick_best(cur++, end)->move;
+ move = pick_best(cur++, endMoves)->move;
if (to_sq(move) == recaptureSquare)
return move;
break;
projects / stockfish / blobdiff