droidfish/DroidFish/jni/stockfish/movepick.cpp

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/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2014 Marco Costalba, Joona Kiiski, Tord Romstad
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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
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <cassert>
#include "movepick.h"
#include "thread.h"
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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
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};
// Our insertion sort, which is guaranteed (and also needed) to be stable
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;
}
}
// 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 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;
}
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}
/// Constructors of the MovePicker class. As arguments we pass information
/// to help it to return the (presumably) good moves first, to decide which
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/// moves to return (in the quiescence search, for instance, we only want to
/// search captures, promotions and some checks) and how important good move
/// ordering is at the current node.
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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) {
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assert(d > DEPTH_ZERO);
cur = end = moves;
endBadCaptures = moves + MAX_MOVES - 1;
countermoves = cm;
followupmoves = fm;
ss = s;
if (pos.checkers())
stage = EVASION;
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else
stage = MAIN_SEARCH;
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ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
end += (ttMove != MOVE_NONE);
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}
MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const HistoryStats& h,
Square s) : pos(p), history(h), cur(moves), end(moves) {
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assert(d <= DEPTH_ZERO);
if (pos.checkers())
stage = EVASION;
else if (d > DEPTH_QS_NO_CHECKS)
stage = QSEARCH_0;
else if (d > DEPTH_QS_RECAPTURES)
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{
stage = QSEARCH_1;
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// 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.capture_or_promotion(ttm))
ttm = MOVE_NONE;
}
else
{
stage = RECAPTURE;
recaptureSquare = s;
ttm = MOVE_NONE;
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}
ttMove = (ttm && pos.pseudo_legal(ttm) ? ttm : MOVE_NONE);
end += (ttMove != MOVE_NONE);
}
MovePicker::MovePicker(const Position& p, Move ttm, const HistoryStats& h, PieceType pt)
: pos(p), history(h), cur(moves), end(moves) {
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);
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if (ttMove && (!pos.capture(ttMove) || pos.see(ttMove) <= captureThreshold))
ttMove = MOVE_NONE;
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end += (ttMove != MOVE_NONE);
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}
/// 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>() {
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// 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
// 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.
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Move m;
for (ExtMove* it = moves; it != end; ++it)
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{
m = it->move;
it->value = PieceValue[MG][pos.piece_on(to_sq(m))]
- Value(type_of(pos.moved_piece(m)));
if (type_of(m) == ENPASSANT)
it->value += PieceValue[MG][PAWN];
else if (type_of(m) == PROMOTION)
it->value += PieceValue[MG][promotion_type(m)] - PieceValue[MG][PAWN];
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}
}
template<>
void MovePicker::score<QUIETS>() {
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Move m;
for (ExtMove* it = moves; it != end; ++it)
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{
m = it->move;
it->value = history[pos.moved_piece(m)][to_sq(m)];
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}
}
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.
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Move m;
Value see;
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for (ExtMove* it = moves; it != end; ++it)
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{
m = it->move;
if ((see = pos.see_sign(m)) < VALUE_ZERO)
it->value = see - HistoryStats::Max; // At the bottom
else if (pos.capture(m))
it->value = PieceValue[MG][pos.piece_on(to_sq(m))]
- Value(type_of(pos.moved_piece(m))) + HistoryStats::Max;
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else
it->value = history[pos.moved_piece(m)][to_sq(m)];
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}
}
/// 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:
end = generate<CAPTURES>(pos, moves);
score<CAPTURES>();
return;
case KILLERS_S1:
cur = killers;
end = 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;
// 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)
(end++)->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)
(end++)->move = followupmoves[i];
return;
case QUIETS_1_S1:
endQuiets = end = generate<QUIETS>(pos, moves);
score<QUIETS>();
end = std::partition(cur, end, has_positive_value);
insertion_sort(cur, end);
return;
case QUIETS_2_S1:
cur = end;
end = endQuiets;
if (depth >= 3 * ONE_PLY)
insertion_sort(cur, end);
return;
case BAD_CAPTURES_S1:
// Just pick them in reverse order to get MVV/LVA ordering
cur = moves + MAX_MOVES - 1;
end = endBadCaptures;
return;
case EVASIONS_S2:
end = generate<EVASIONS>(pos, moves);
if (end > moves + 1)
score<EVASIONS>();
return;
case QUIET_CHECKS_S3:
end = 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
return;
default:
assert(false);
}
}
/// 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>() {
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Move move;
while (true)
{
while (cur == end)
generate_next_stage();
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switch (stage) {
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case MAIN_SEARCH: case EVASION: case QSEARCH_0: case QSEARCH_1: case PROBCUT:
++cur;
return ttMove;
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case CAPTURES_S1:
move = pick_best(cur++, end)->move;
if (move != ttMove)
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{
if (pos.see_sign(move) >= VALUE_ZERO)
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return move;
// Losing capture, move it to the tail of the array
(endBadCaptures--)->move = move;
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}
break;
case KILLERS_S1:
move = (cur++)->move;
if ( move != MOVE_NONE
&& move != ttMove
&& pos.pseudo_legal(move)
&& !pos.capture(move))
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return move;
break;
case QUIETS_1_S1: case QUIETS_2_S1:
move = (cur++)->move;
if ( move != ttMove
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&& move != killers[0].move
&& move != killers[1].move
&& move != killers[2].move
&& move != killers[3].move
&& move != killers[4].move
&& move != killers[5].move)
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return move;
break;
case BAD_CAPTURES_S1:
return (cur--)->move;
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case EVASIONS_S2: case CAPTURES_S3: case CAPTURES_S4:
move = pick_best(cur++, end)->move;
if (move != ttMove)
return move;
break;
case CAPTURES_S5:
move = pick_best(cur++, end)->move;
if (move != ttMove && pos.see(move) > captureThreshold)
return move;
break;
case CAPTURES_S6:
move = pick_best(cur++, end)->move;
if (to_sq(move) == recaptureSquare)
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return move;
break;
case QUIET_CHECKS_S3:
move = (cur++)->move;
if (move != ttMove)
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return move;
break;
case STOP:
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return MOVE_NONE;
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>(); }