Simplify Zobrist key for captures.

No functional change bench: 934447
official-stockfish · Dec 20, 2024 · 8f094c5 · 8f094c5
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commit 8f094c5
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Showing 2 changed files with 3 additions and 6 deletions.
diff --git a/src/position.cpp b/src/position.cpp
@@ -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);
@@ -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);
 }

diff --git a/src/position.h b/src/position.h
@@ -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