/*
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) 2008-2014 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
namespace {
- enum Sequencer {
+ 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,
STOP
};
- // Our insertion sort, guaranteed to be stable, as is needed
- void insertion_sort(MoveStack* begin, MoveStack* end)
+ // Our insertion sort, which is guaranteed (and also needed) to be stable
+ void insertion_sort(ExtMove* begin, ExtMove* end)
{
- MoveStack tmp, *p, *q;
+ ExtMove tmp, *p, *q;
for (p = begin + 1; p < end; ++p)
{
}
}
- // 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& ms) { return ms.score > 0; }
+ // Unary predicate used by std::partition to split positive values from remaining
+ // ones so as to sort the two sets separately, with the second sort delayed.
+ inline bool has_positive_value(const ExtMove& ms) { return ms.value > 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.
- inline MoveStack* pick_best(MoveStack* begin, MoveStack* end)
+ // 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, Value beta) : pos(p), history(h), depth(d) {
+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) {
assert(d > DEPTH_ZERO);
- captureThreshold = 0;
cur = end = moves;
endBadCaptures = moves + MAX_MOVES - 1;
countermoves = cm;
+ followupmoves = fm;
ss = s;
- if (p.checkers())
- phase = EVASION;
+ if (pos.checkers())
+ stage = EVASION;
else
- {
- phase = MAIN_SEARCH;
-
- // Consider sligtly negative captures as good if at low depth and far from beta
- if (ss->staticEval < beta - PawnValueMg && d < 3 * ONE_PLY)
- captureThreshold = -PawnValueMg;
-
- // Consider negative captures as good if still enough to reach beta
- else if (ss->staticEval > beta)
- captureThreshold = beta - ss->staticEval;
- }
+ stage = MAIN_SEARCH;
- ttMove = (ttm && pos.is_pseudo_legal(ttm) ? ttm : MOVE_NONE);
+ ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
end += (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), cur(moves), end(moves) {
assert(d <= DEPTH_ZERO);
- if (p.checkers())
- phase = EVASION;
+ if (pos.checkers())
+ stage = EVASION;
else if (d > DEPTH_QS_NO_CHECKS)
- phase = QSEARCH_0;
+ stage = QSEARCH_0;
else if (d > DEPTH_QS_RECAPTURES)
{
- phase = QSEARCH_1;
+ stage = QSEARCH_1;
- // Skip TT move if is not a capture or a promotion, this avoids 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))
+ if (ttm && !pos.capture_or_promotion(ttm))
ttm = MOVE_NONE;
}
else
{
- phase = RECAPTURE;
- recaptureSquare = sq;
+ stage = RECAPTURE;
+ recaptureSquare = s;
ttm = MOVE_NONE;
}
- ttMove = (ttm && pos.is_pseudo_legal(ttm) ? ttm : MOVE_NONE);
+ ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
end += (ttMove != MOVE_NONE);
}
assert(!pos.checkers());
- phase = PROBCUT;
+ 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);
}
-/// 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).
+ // 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.
Move m;
- for (MoveStack* it = moves; it != end; ++it)
+ 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));
+ it->value = PieceValue[MG][pos.piece_on(to_sq(m))]
+ - Value(type_of(pos.moved_piece(m)));
- if (type_of(m) == PROMOTION)
- it->score += PieceValue[MG][promotion_type(m)] - PieceValue[MG][PAWN];
+ if (type_of(m) == ENPASSANT)
+ it->value += PieceValue[MG][PAWN];
- else if (type_of(m) == ENPASSANT)
- it->score += PieceValue[MG][PAWN];
+ else if (type_of(m) == PROMOTION)
+ it->value += PieceValue[MG][promotion_type(m)] - PieceValue[MG][PAWN];
}
}
Move m;
- for (MoveStack* it = moves; it != end; ++it)
+ for (ExtMove* it = moves; it != end; ++it)
{
m = it->move;
- it->score = history[pos.piece_moved(m)][to_sq(m)];
+ it->value = history[pos.moved_piece(m)][to_sq(m)];
}
}
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.
+ // moves with a negative SEE. This last group is ordered by the SEE value.
Move m;
- int seeScore;
+ Value see;
- for (MoveStack* it = moves; it != end; ++it)
+ 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
+ if ((see = pos.see_sign(m)) < VALUE_ZERO)
+ it->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))
+ it->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)];
+ it->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 (++phase) {
+ switch (++stage) {
case CAPTURES_S1: case CAPTURES_S3: case CAPTURES_S4: case CAPTURES_S5: case CAPTURES_S6:
end = generate<CAPTURES>(pos, moves);
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;
+
+ // 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->move && countermoves[i] != (cur+1)->move)
+ for (int i = 0; i < 2; ++i)
+ if ( countermoves[i] != (cur+0)->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;
-
+ // 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)
+ (end++)->move = followupmoves[i];
return;
case QUIETS_1_S1:
endQuiets = end = generate<QUIETS>(pos, moves);
score<QUIETS>();
- end = std::partition(cur, end, has_positive_score);
+ end = std::partition(cur, end, has_positive_value);
insertion_sort(cur, end);
return;
return;
case EVASION: case QSEARCH_0: case QSEARCH_1: case PROBCUT: case RECAPTURE:
- phase = STOP;
+ stage = STOP;
+ /* Fall through */
+
case STOP:
end = cur + 1; // Avoid another next_phase() call
return;
/// 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();
+ generate_next_stage();
- switch (phase) {
+ 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;
if (move != ttMove)
{
- assert(captureThreshold <= 0); // Otherwise we cannot use see_sign()
-
- if (pos.see_sign(move) >= captureThreshold)
+ 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;
projects / stockfish / blobdiff