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Code Issues Releases Wiki Activity

Simplify En Passant

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simplifies the handling of en passant during search, needs a little more care in initialization.

Passed STC:
LLR: 2.95 (-2.94,2.94) {-1.25,0.25}
Total: 72608 W: 6569 L: 6559 D: 59480
Ptnml(0-2): 233, 5117, 25629, 5057, 268
https://tests.stockfishchess.org/tests/view/600f1363735dd7f0f0352ce7

Passed LTC:
LLR: 2.92 (-2.94,2.94) {-0.75,0.25}
Total: 24328 W: 913 L: 864 D: 22551
Ptnml(0-2): 10, 731, 10633, 780, 10
https://tests.stockfishchess.org/tests/view/600f2e93735dd7f0f0352cf6

closes https://github.com/official-stockfish/Stockfish/pull/3330

No functional change.
This commit is contained in:
bmc4 2021-01-31 10:12:32 -03:00 • committed by Joost VandeVondele
parent 6617ad6e03
commit 9f8058bd26
1 changed files with 26 additions and 29 deletions
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55
src/position.cpp
View file

@ -249,6 +249,8 @@ Position& Position::set(const string& fenStr, bool isChess960, StateInfo* si, Th
set_castling_right(c, rsq);
}
set_state(st);
// 4. En passant square.
// Ignore if square is invalid or not on side to move relative rank 6.
bool enpassant = false;
@ -262,12 +264,24 @@ Position& Position::set(const string& fenStr, bool isChess960, StateInfo* si, Th
// a) side to move have a pawn threatening epSquare
// b) there is an enemy pawn in front of epSquare
// c) there is no piece on epSquare or behind epSquare
// d) enemy pawn didn't block a check of its own color by moving forward
enpassant = pawn_attacks_bb(~sideToMove, st->epSquare) & pieces(sideToMove, PAWN)
&& (pieces(~sideToMove, PAWN) & (st->epSquare + pawn_push(~sideToMove)))
&& !(pieces() & (st->epSquare | (st->epSquare + pawn_push(sideToMove))));
&& !(pieces() & (st->epSquare | (st->epSquare + pawn_push(sideToMove))))
&& (file_of(square<KING>(sideToMove)) == file_of(st->epSquare)
|| !(blockers_for_king(sideToMove) & (st->epSquare + pawn_push(~sideToMove))));
}
if (!enpassant)
// It's necessary for st->previous to be intialized in this way because legality check relies on its existence
if (enpassant) {
st->previous = new StateInfo();
remove_piece(st->epSquare - pawn_push(sideToMove));
st->previous->checkersBB = attackers_to(square<KING>(~sideToMove)) & pieces(sideToMove);
st->previous->blockersForKing[WHITE] = slider_blockers(pieces(BLACK), square<KING>(WHITE), st->previous->pinners[BLACK]);
st->previous->blockersForKing[BLACK] = slider_blockers(pieces(WHITE), square<KING>(BLACK), st->previous->pinners[WHITE]);
put_piece(make_piece(~sideToMove, PAWN), st->epSquare - pawn_push(sideToMove));
}
else
st->epSquare = SQ_NONE;
// 5-6. Halfmove clock and fullmove number
@ -279,7 +293,6 @@ Position& Position::set(const string& fenStr, bool isChess960, StateInfo* si, Th
chess960 = isChess960;
thisThread = th;
set_state(st);
st->accumulator.state[WHITE] = Eval::NNUE::INIT;
st->accumulator.state[BLACK] = Eval::NNUE::INIT;
@ -502,23 +515,11 @@ bool Position::legal(Move m) const {
assert(color_of(moved_piece(m)) == us);
assert(piece_on(square<KING>(us)) == make_piece(us, KING));
// En passant captures are a tricky special case. Because they are rather
// uncommon, we do it simply by testing whether the king is attacked after
// the move is made.
// st->previous->blockersForKing consider capsq as empty.
// If pinned, it has to move along the king ray.
if (type_of(m) == EN_PASSANT)
{
Square ksq = square<KING>(us);
Square capsq = to - pawn_push(us);
Bitboard occupied = (pieces() ^ from ^ capsq) | to;
assert(to == ep_square());
assert(moved_piece(m) == make_piece(us, PAWN));
assert(piece_on(capsq) == make_piece(~us, PAWN));
assert(piece_on(to) == NO_PIECE);
return !(attacks_bb< ROOK>(ksq, occupied) & pieces(~us, QUEEN, ROOK))
&& !(attacks_bb<BISHOP>(ksq, occupied) & pieces(~us, QUEEN, BISHOP));
}
return !(st->previous->blockersForKing[sideToMove] & from) ||
aligned(from, to, square<KING>(us));
// Castling moves generation does not check if the castling path is clear of
// enemy attacks, it is delayed at a later time: now!
@ -651,18 +652,14 @@ bool Position::gives_check(Move m) const {
case PROMOTION:
return attacks_bb(promotion_type(m), to, pieces() ^ from) & square<KING>(~sideToMove);
// En passant capture with check? We have already handled the case
// of direct checks and ordinary discovered check, so the only case we
// need to handle is the unusual case of a discovered check through
// the captured pawn.
// The double-pushed pawn blocked a check? En Passant will remove the blocker.
// The only discovery check that wasn't handle is through capsq and fromsq
// So the King must be in the same rank as fromsq to consider this possibility.
// st->previous->blockersForKing consider capsq as empty.
case EN_PASSANT:
{
Square capsq = make_square(file_of(to), rank_of(from));
Bitboard b = (pieces() ^ from ^ capsq) | to;
return st->previous->checkersBB || (rank_of(square<KING>(~sideToMove)) == rank_of(from)
&& st->previous->blockersForKing[~sideToMove] & from);
return (attacks_bb< ROOK>(square<KING>(~sideToMove), b) & pieces(sideToMove, QUEEN, ROOK))
| (attacks_bb<BISHOP>(square<KING>(~sideToMove), b) & pieces(sideToMove, QUEEN, BISHOP));
}
default: //CASTLING
{
// Castling is encoded as 'king captures the rook'