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Simplify away the special case for en passant in the legality check

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Since as of 94175524b1 the en passant square is
only set if there is a legal en passant capture, the special handling is
redundant

Passed Non-Regression STC:
https://tests.stockfishchess.org/tests/view/696ffb6512ee1f6231b96fe8
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 79072 W: 20380 L: 20210 D: 38482.

closes https://github.com/official-stockfish/Stockfish/pull/6560

No functional change
This commit is contained in:
rn5f107s2
2026-04-15 20:35:32 +02:00
committed by Joost VandeVondele
parent 45711fceb4
commit b1fb50ae69
1 changed files with 0 additions and 18 deletions
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src/position.cpp
-18
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@@ -673,24 +673,6 @@ 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.
if (m.type_of() == 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));
}
// Castling moves generation does not check if the castling path is clear of
// enemy attacks, it is delayed at a later time: now!
if (m.type_of() == CASTLING)