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Remove two xors by setting the hash keys for unreachable squares to zero

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performance before:
3.6714 +- 0.20%  Gcycles
3.6620 +- 0.12%  Gcycles
3.6704 +- 0.26%  Gcycles
3.6602 +- 0.27%  Gcycles
3.6799 +- 0.37%  Gcycles

after:
3.6540 +- 0.30%  Gcycles
3.6388 +- 0.25%  Gcycles
3.6557 +- 0.17%  Gcycles
3.6449 +- 0.15%  Gcycles
3.6460 +- 0.26%  Gcycles

(every line is a different `profile-build` and shows the number of
cycles needed for `./stockfish bench`, measured with `perf stat -r 10`)

closes https://github.com/official-stockfish/Stockfish/pull/5754

No functional change
This commit is contained in:
Carlos Esparza
2025-01-07 01:47:37 +01:00
committed by Disservin
parent d66e603070
commit e089f723d8
1 changed files with 9 additions and 6 deletions
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src/position.cpp
+9 -6
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@@ -119,6 +119,9 @@ void Position::init() {
for (Piece pc : Pieces)
for (Square s = SQ_A1; s <= SQ_H8; ++s)
Zobrist::psq[pc][s] = rng.rand<Key>();
// pawns on these squares will promote
std::fill_n(Zobrist::psq[W_PAWN] + SQ_A8, 8, 0);
std::fill_n(Zobrist::psq[B_PAWN], 8, 0);
for (File f = FILE_A; f <= FILE_H; ++f)
Zobrist::enpassant[f] = rng.rand<Key>();
@@ -376,7 +379,7 @@ void Position::set_state() const {
for (Piece pc : Pieces)
for (int cnt = 0; cnt < pieceCount[pc]; ++cnt)
st->materialKey ^= Zobrist::psq[pc][cnt];
st->materialKey ^= Zobrist::psq[pc][8 + cnt];
}
@@ -776,7 +779,7 @@ void Position::do_move(Move m,
remove_piece(capsq);
k ^= Zobrist::psq[captured][capsq];
st->materialKey ^= Zobrist::psq[captured][pieceCount[captured]];
st->materialKey ^= Zobrist::psq[captured][8 + pieceCount[captured]];
// Reset rule 50 counter
st->rule50 = 0;
@@ -840,10 +843,10 @@ void Position::do_move(Move m,
dp.dirty_num++;
// Update hash keys
k ^= Zobrist::psq[pc][to] ^ Zobrist::psq[promotion][to];
st->pawnKey ^= Zobrist::psq[pc][to];
st->materialKey ^=
Zobrist::psq[promotion][pieceCount[promotion] - 1] ^ Zobrist::psq[pc][pieceCount[pc]];
// Zobrist::psq[pc][to] is zero, so we don't need to clear it
k ^= Zobrist::psq[promotion][to];
st->materialKey ^= Zobrist::psq[promotion][8 + pieceCount[promotion] - 1]
^ Zobrist::psq[pc][8 + pieceCount[pc]];
if (promotionType <= BISHOP)
st->minorPieceKey ^= Zobrist::psq[promotion][to];