/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- Copyright (C) 2008 Marco Costalba
+ Copyright (C) 2008-2009 Marco Costalba
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 "history.h"
-#include "evaluate.h"
#include "movegen.h"
#include "movepick.h"
#include "search.h"
namespace {
- /// Variables
-
- MovePicker::MovegenPhase PhaseTable[32];
- int MainSearchPhaseIndex;
- int EvasionsPhaseIndex;
- int QsearchWithChecksPhaseIndex;
- int QsearchWithoutChecksPhaseIndex;
-
+ 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
+ };
+
+ CACHE_LINE_ALIGNMENT
+ const uint8_t MainSearchPhaseTable[] = { PH_TT_MOVES, PH_GOOD_CAPTURES, PH_KILLERS, PH_NONCAPTURES, PH_BAD_CAPTURES, PH_STOP};
+ const uint8_t EvasionsPhaseTable[] = { PH_TT_MOVES, PH_EVASIONS, PH_STOP};
+ const uint8_t QsearchWithChecksPhaseTable[] = { PH_TT_MOVES, PH_QCAPTURES, PH_QCHECKS, PH_STOP};
+ const uint8_t QsearchWithoutChecksPhaseTable[] = { PH_TT_MOVES, PH_QCAPTURES, PH_STOP};
}
////
-/// Constructor for the MovePicker class. Apart from the position for which
+/// 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.
-MovePicker::MovePicker(const Position& p, bool pv, Move ttm,
- const SearchStack& ss, Depth d) : pos(p) {
- pvNode = pv;
- ttMove = ttm;
- mateKiller = (ss.mateKiller == ttm)? MOVE_NONE : ss.mateKiller;
- killer1 = ss.killers[0];
- killer2 = ss.killers[1];
- depth = d;
- movesPicked = 0;
- numOfMoves = 0;
- numOfBadCaptures = 0;
+MovePicker::MovePicker(const Position& p, Move ttm, Depth d,
+ const History& h, SearchStack* ss) : pos(p), H(h) {
+ int searchTT = ttm;
+ ttMoves[0].move = ttm;
+ lastBadCapture = badCaptures;
+
+ pinned = p.pinned_pieces(pos.side_to_move());
+
+ if (ss && !p.is_check())
+ {
+ 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];
+ } else
+ ttMoves[1].move = killers[0].move = killers[1].move = MOVE_NONE;
if (p.is_check())
- phaseIndex = EvasionsPhaseIndex;
- else if (depth > Depth(0))
- phaseIndex = MainSearchPhaseIndex;
- else if (depth == Depth(0))
- phaseIndex = QsearchWithChecksPhaseIndex;
+ phasePtr = EvasionsPhaseTable;
+ else if (d > Depth(0))
+ phasePtr = MainSearchPhaseTable;
+ else if (d == Depth(0))
+ phasePtr = QsearchWithChecksPhaseTable;
else
- phaseIndex = QsearchWithoutChecksPhaseIndex;
-
- Color us = pos.side_to_move();
+ {
+ phasePtr = QsearchWithoutChecksPhaseTable;
- dc = p.discovered_check_candidates(us);
- pinned = p.pinned_pieces(us);
+ // 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;
+ }
- finished = false;
+ phasePtr += !searchTT - 1;
+ go_next_phase();
}
-/// 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.
+/// 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.
-Move MovePicker::get_next_move() {
+void MovePicker::go_next_phase() {
- Move move;
+ curMove = moves;
+ phase = *(++phasePtr);
+ switch (phase) {
- 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
- phaseIndex++;
- switch (PhaseTable[phaseIndex]) {
-
- case PH_TT_MOVE:
- if (ttMove != MOVE_NONE)
- {
- assert(move_is_ok(ttMove));
- if (move_is_legal(pos, ttMove, pinned))
- return ttMove;
- }
- break;
-
- case PH_MATE_KILLER:
- if (mateKiller != MOVE_NONE)
- {
- assert(move_is_ok(mateKiller));
- if (move_is_legal(pos, mateKiller, pinned))
- return mateKiller;
- }
- break;
-
- case PH_GOOD_CAPTURES:
- numOfMoves = generate_captures(pos, moves);
- score_captures();
- movesPicked = 0;
- break;
-
- case PH_BAD_CAPTURES:
- movesPicked = 0;
- break;
-
- case PH_NONCAPTURES:
- numOfMoves = generate_noncaptures(pos, moves);
- score_noncaptures();
- movesPicked = 0;
- break;
-
- case PH_EVASIONS:
- assert(pos.is_check());
- numOfMoves = generate_evasions(pos, moves, pinned);
- score_evasions();
- movesPicked = 0;
- break;
-
- case PH_QCAPTURES:
- numOfMoves = generate_captures(pos, moves);
- score_qcaptures();
- movesPicked = 0;
- break;
-
- case PH_QCHECKS:
- numOfMoves = generate_checks(pos, moves, dc);
- movesPicked = 0;
- break;
-
- case PH_STOP:
- return MOVE_NONE;
-
- default:
- assert(false);
- return MOVE_NONE;
- }
- }
-}
+ case PH_TT_MOVES:
+ curMove = ttMoves;
+ lastMove = curMove + 2;
+ return;
+ case PH_GOOD_CAPTURES:
+ lastMove = generate_captures(pos, moves);
+ score_captures();
+ return;
-/// 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.
+ case PH_KILLERS:
+ curMove = killers;
+ lastMove = curMove + 2;
+ return;
-Move MovePicker::get_next_move(Lock &lock) {
+ case PH_NONCAPTURES:
+ lastMove = generate_noncaptures(pos, moves);
+ score_noncaptures();
+ sort_moves(moves, lastMove);
+ return;
- lock_grab(&lock);
- if (finished)
- {
- lock_release(&lock);
- return MOVE_NONE;
- }
- Move m = get_next_move();
- if (m == MOVE_NONE)
- finished = true;
+ case PH_BAD_CAPTURES:
+ // Bad captures SEE value is already calculated so just sort them
+ // to get SEE move ordering.
+ curMove = badCaptures;
+ lastMove = lastBadCapture;
+ return;
+
+ case PH_EVASIONS:
+ assert(pos.is_check());
+ lastMove = generate_evasions(pos, moves);
+ score_evasions_or_checks();
+ return;
+
+ case PH_QCAPTURES:
+ lastMove = generate_captures(pos, moves);
+ score_captures();
+ return;
- lock_release(&lock);
- return m;
+ case PH_QCHECKS:
+ lastMove = generate_non_capture_checks(pos, moves);
+ score_evasions_or_checks();
+ return;
+
+ case PH_STOP:
+ lastMove = curMove + 1; // Avoids another go_next_phase() call
+ return;
+
+ default:
+ assert(false);
+ return;
+ }
}
-/// 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().
+/// 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
+ // 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
+ // 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.
- // While scoring captures it moves all captures with negative SEE values
- // to the badCaptures[] array.
+ // 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;
- int seeValue;
- for (int i = 0; i < numOfMoves; i++)
+ // Use MVV/LVA ordering
+ for (MoveStack* cur = moves; cur != lastMove; cur++)
{
- m = moves[i].move;
- seeValue = pos.see(m);
- if (seeValue >= 0)
- {
- if (move_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)));
- }
+ m = cur->move;
+ if (move_is_promotion(m))
+ cur->score = QueenValueMidgame;
else
- {
- // Losing capture, move it to the badCaptures[] array
- assert(numOfBadCaptures < 63);
- moves[i].score = seeValue;
- badCaptures[numOfBadCaptures++] = moves[i];
- moves[i--] = moves[--numOfMoves];
- }
+ cur->score = pos.midgame_value_of_piece_on(move_to(m))
+ - pos.type_of_piece_on(move_from(m));
}
}
// piece/square tables values. This seems to be better then a
// random choice when we don't have an history for any move.
Move m;
- int hs;
+ Piece piece;
+ Square from, to;
- for (int i = 0; i < numOfMoves; i++)
+ for (MoveStack* cur = moves; cur != lastMove; cur++)
{
- m = moves[i].move;
-
- if (m == killer1)
- hs = HistoryMax + 2;
- else if (m == killer2)
- hs = HistoryMax + 1;
- else
- hs = H.move_ordering_score(pos.piece_on(move_from(m)), m);
-
- // Ensure history is always preferred to pst
- if (hs > 0)
- hs += 1000;
-
- // pst based scoring
- moves[i].score = hs + pos.mg_pst_delta(m);
+ m = cur->move;
+ from = move_from(m);
+ to = move_to(m);
+ piece = pos.piece_on(from);
+ cur->score = H.move_ordering_score(piece, to);
}
}
-void MovePicker::score_evasions() {
-
- for (int i = 0; i < numOfMoves; i++)
- {
- Move m = moves[i].move;
- if (m == ttMove)
- 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)), m);
- }
-}
+void MovePicker::score_evasions_or_checks() {
+ // 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;
-void MovePicker::score_qcaptures() {
+ // Skip if we don't have at least two moves to order
+ if (lastMove < moves + 2)
+ return;
- // Use MVV/LVA ordering
- for (int i = 0; i < numOfMoves; i++)
+ for (MoveStack* cur = moves; cur != lastMove; cur++)
{
- Move m = moves[i].move;
- if (move_promotion(m))
- moves[i].score = QueenValueMidgame;
+ m = cur->move;
+ if ((seeScore = pos.see_sign(m)) < 0)
+ cur->score = seeScore;
+ 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)) + HistoryMax;
else
- moves[i].score = int(pos.midgame_value_of_piece_on(move_to(m)))
- -int(pos.type_of_piece_on(move_from(m)));
+ cur->score = H.move_ordering_score(pos.piece_on(move_from(m)), move_to(m));
}
}
+/// 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.
-/// find_best_index() loops across the moves and returns index of
-/// the highest scored one.
-
-int MovePicker::find_best_index() const {
-
- assert(movesPicked < numOfMoves);
-
- int bestIndex = movesPicked;
- int bestScore = moves[movesPicked].score;
-
- for (int i = movesPicked + 1; i < numOfMoves; i++)
- if (moves[i].score > bestScore)
- {
- bestIndex = i;
- bestScore = moves[i].score;
- }
- return bestIndex;
-}
-
-
-/// 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.
-
-Move MovePicker::pick_move_from_list() {
+Move MovePicker::get_next_move() {
- int bestIndex;
Move move;
- switch (PhaseTable[phaseIndex]) {
-
- case PH_GOOD_CAPTURES:
- assert(!pos.is_check());
- assert(movesPicked >= 0);
-
- while (movesPicked < numOfMoves)
- {
- bestIndex = find_best_index();
- move = moves[bestIndex].move;
- moves[bestIndex] = moves[movesPicked++];
- if ( move != ttMove
- && move != mateKiller
- && pos.pl_move_is_legal(move, pinned))
- return move;
- }
- break;
-
- case PH_NONCAPTURES:
- assert(!pos.is_check());
- assert(movesPicked >= 0);
-
- while (movesPicked < numOfMoves)
- {
- // If this is a PV node or we have only picked a few moves, scan
- // the entire move list for the best move. If many moves have already
- // been searched and it is not a PV node, we are probably failing low
- // anyway, so we just pick the first move from the list.
- bestIndex = (pvNode || movesPicked < 12) ? find_best_index() : movesPicked;
- move = moves[bestIndex].move;
- moves[bestIndex] = moves[movesPicked++];
- if ( move != ttMove
- && move != mateKiller
- && pos.pl_move_is_legal(move, pinned))
- return move;
- }
- break;
-
- case PH_EVASIONS:
- assert(pos.is_check());
- assert(movesPicked >= 0);
-
- while (movesPicked < numOfMoves)
- {
- bestIndex = find_best_index();
- move = moves[bestIndex].move;
- moves[bestIndex] = moves[movesPicked++];
- return move;
- }
- break;
-
- case PH_BAD_CAPTURES:
- assert(!pos.is_check());
- assert(movesPicked >= 0);
- // It's probably a good idea to use SEE move ordering here, instead
- // of just picking the first move. FIXME
- while (movesPicked < numOfBadCaptures)
- {
- move = badCaptures[movesPicked++].move;
- if ( move != ttMove
- && move != mateKiller
- && pos.pl_move_is_legal(move, pinned))
- return move;
- }
- break;
-
- case PH_QCAPTURES:
- assert(!pos.is_check());
- assert(movesPicked >= 0);
- while (movesPicked < numOfMoves)
+ while (true)
+ {
+ while (curMove != lastMove)
{
- bestIndex = (movesPicked < 4 ? find_best_index() : movesPicked);
- move = moves[bestIndex].move;
- moves[bestIndex] = moves[movesPicked++];
- // Maybe postpone the legality check until after futility pruning?
- if ( move != ttMove
- && pos.pl_move_is_legal(move, pinned))
+ switch (phase) {
+
+ case PH_TT_MOVES:
+ move = (curMove++)->move;
+ if ( move != MOVE_NONE
+ && move_is_legal(pos, move, pinned))
+ return move;
+ break;
+
+ 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))
+ {
+ // 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(int(lastBadCapture - badCaptures) < 63);
+ lastBadCapture->move = move;
+ lastBadCapture->score = seeValue;
+ lastBadCapture++;
+ }
+ break;
+
+ case PH_KILLERS:
+ move = (curMove++)->move;
+ if ( move != MOVE_NONE
+ && move != ttMoves[0].move
+ && move != ttMoves[1].move
+ && move_is_legal(pos, move, pinned)
+ && !pos.move_is_capture(move))
+ return move;
+ break;
+
+ case PH_NONCAPTURES:
+ 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))
+ return move;
+ break;
+
+ case PH_BAD_CAPTURES:
+ move = pick_best(curMove++, lastMove).move;
return move;
- }
- break;
- case PH_QCHECKS:
- assert(!pos.is_check());
- assert(movesPicked >= 0);
- // Perhaps we should do something better than just picking the first
- // move here? FIXME
- while (movesPicked < numOfMoves)
- {
- move = moves[movesPicked++].move;
- if ( move != ttMove
- && pos.pl_move_is_legal(move, pinned))
- return move;
+ case PH_EVASIONS:
+ case PH_QCAPTURES:
+ move = pick_best(curMove++, lastMove).move;
+ if ( move != ttMoves[0].move
+ && pos.pl_move_is_legal(move, pinned))
+ return move;
+ break;
+
+ case PH_QCHECKS:
+ move = (curMove++)->move;
+ if ( move != ttMoves[0].move
+ && pos.pl_move_is_legal(move, pinned))
+ return move;
+ break;
+
+ case PH_STOP:
+ return MOVE_NONE;
+
+ default:
+ assert(false);
+ break;
+ }
}
- break;
-
- default:
- break;
+ go_next_phase();
}
- return MOVE_NONE;
}
-
-/// MovePicker::init_phase_table() initializes the PhaseTable[],
-/// MainSearchPhaseIndex, EvasionPhaseIndex, QsearchWithChecksPhaseIndex
-/// and QsearchWithoutChecksPhaseIndex. It is only called once during
-/// program startup, and never again while the program is running.
-
-void MovePicker::init_phase_table() {
-
- int i = 0;
-
- // Main search
- MainSearchPhaseIndex = i - 1;
- PhaseTable[i++] = PH_TT_MOVE;
- PhaseTable[i++] = PH_MATE_KILLER;
- PhaseTable[i++] = PH_GOOD_CAPTURES;
- // PH_KILLER_1 and PH_KILLER_2 are not yet used.
- // PhaseTable[i++] = PH_KILLER_1;
- // PhaseTable[i++] = PH_KILLER_2;
- PhaseTable[i++] = PH_NONCAPTURES;
- PhaseTable[i++] = PH_BAD_CAPTURES;
- PhaseTable[i++] = PH_STOP;
-
- // Check evasions
- EvasionsPhaseIndex = i - 1;
- PhaseTable[i++] = PH_EVASIONS;
- PhaseTable[i++] = PH_STOP;
-
- // Quiescence search with checks
- QsearchWithChecksPhaseIndex = i - 1;
- PhaseTable[i++] = PH_TT_MOVE;
- PhaseTable[i++] = PH_QCAPTURES;
- PhaseTable[i++] = PH_QCHECKS;
- PhaseTable[i++] = PH_STOP;
-
- // Quiescence search without checks
- QsearchWithoutChecksPhaseIndex = i - 1;
- PhaseTable[i++] = PH_TT_MOVE;
- PhaseTable[i++] = PH_QCAPTURES;
- PhaseTable[i++] = PH_STOP;
-}
projects / stockfish / blobdiff