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Simplify Zobrist keys for captures #5731

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Simplify Zobrist keys for captures #5731

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7 changes: 2 additions & 5 deletions src/position.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1012,7 +1012,7 @@ void Position::do_castling(Color us, Square from, Square& to, Square& rfrom, Squ

// Used to do a "null move": it flips
// the side to move without executing any move on the board.
void Position::do_null_move(StateInfo& newSt, TranspositionTable& tt) {
void Position::do_null_move(StateInfo& newSt, const TranspositionTable& tt) {

assert(!checkers());
assert(&newSt != st);
Expand Down Expand Up @@ -1071,10 +1071,7 @@ Key Position::key_after(Move m) const {
Piece captured = piece_on(to);
Key k = st->key ^ Zobrist::side;

if (captured)
k ^= Zobrist::psq[captured][to];

k ^= Zobrist::psq[pc][to] ^ Zobrist::psq[pc][from];
k ^= Zobrist::psq[captured][to] ^ Zobrist::psq[pc][to] ^ Zobrist::psq[pc][from];

return (captured || type_of(pc) == PAWN) ? k : adjust_key50<true>(k);
}
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2 changes: 1 addition & 1 deletion src/position.h
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Expand Up @@ -143,7 +143,7 @@ class Position {
void do_move(Move m, StateInfo& newSt);
void do_move(Move m, StateInfo& newSt, bool givesCheck);
void undo_move(Move m);
void do_null_move(StateInfo& newSt, TranspositionTable& tt);
void do_null_move(StateInfo& newSt, const TranspositionTable& tt);
void undo_null_move();

// Static Exchange Evaluation
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