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Remove old zobrist trick for castling rights

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Removes an 8 year old micro optimization aimed at 32-bit architectures
because back then doing an xor of a Key could not be done in one instruction.
See original commit here 821e1c7

STC https://tests.stockfishchess.org/tests/view/5ef5833dde213bf647527d0c
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 162648 W: 31053 L: 31097 D: 100498
Ptnml(0-2): 2841, 18966, 37715, 19000, 2802

LTC https://tests.stockfishchess.org/tests/view/5ef7b1bbf993893290cc1489
LLR: 2.93 (-2.94,2.94) {-1.50,0.50}
Total: 62360 W: 7617 L: 7586 D: 47157
Ptnml(0-2): 423, 5662, 18994, 5663, 438

closes https://github.com/official-stockfish/Stockfish/pull/2775

bench: 4591425
This commit is contained in:
mstembera 2020-06-25 22:08:17 -07:00 • committed by Joost VandeVondele
parent de24fcebc8
commit 547c4a216a
1 changed files with 4 additions and 12 deletions
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16
src/position.cpp
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@ -119,15 +119,7 @@ void Position::init() {
Zobrist::enpassant[f] = rng.rand<Key>();
for (int cr = NO_CASTLING; cr <= ANY_CASTLING; ++cr)
{
Zobrist::castling[cr] = 0;
Bitboard b = cr;
while (b)
{
Key k = Zobrist::castling[1ULL << pop_lsb(&b)];
Zobrist::castling[cr] ^= k ? k : rng.rand<Key>();
}
}
Zobrist::castling[cr] = rng.rand<Key>();
Zobrist::side = rng.rand<Key>();
Zobrist::noPawns = rng.rand<Key>();
@ -780,9 +772,9 @@ void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
// Update castling rights if needed
if (st->castlingRights && (castlingRightsMask[from] | castlingRightsMask[to]))
{
int cr = castlingRightsMask[from] | castlingRightsMask[to];
k ^= Zobrist::castling[st->castlingRights & cr];
st->castlingRights &= ~cr;
k ^= Zobrist::castling[st->castlingRights];
st->castlingRights &= ~(castlingRightsMask[from] | castlingRightsMask[to]);
k ^= Zobrist::castling[st->castlingRights];
}
// Move the piece. The tricky Chess960 castling is handled earlier