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Micro-optimize castleRights update

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When updating castleRights in do_move() perform only one
64bit xor with zobCastle[] instead of two.

The trick here is to define zobCastle[] keys of composite
castling rights as a xor combination of the keys of the
single castling rights, instead of 16 independent keys.

Idea from Critter although implementation is different.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2012-02-18 21:30:33 +01:00
parent 6088ac2108
commit 821e1c7233
1 changed files with 15 additions and 8 deletions
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23
src/position.cpp
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@ -843,9 +843,9 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveI
if ( st->castleRights != CASTLES_NONE
&& (castleRightsMask[from] & castleRightsMask[to]) != ALL_CASTLES)
{
k ^= zobCastle[st->castleRights];
st->castleRights &= castleRightsMask[from] & castleRightsMask[to];
k ^= zobCastle[st->castleRights];
int cr = castleRightsMask[from] & castleRightsMask[to];
k ^= zobCastle[st->castleRights & (cr ^ ALL_CASTLES)];
st->castleRights &= cr;
}
// Prefetch TT access as soon as we know key is updated
@ -1151,9 +1151,9 @@ void Position::do_castle_move(Move m) {
}
// Update castling rights
st->key ^= zobCastle[st->castleRights];
st->castleRights &= castleRightsMask[kfrom];
st->key ^= zobCastle[st->castleRights];
int cr = castleRightsMask[kfrom];
st->key ^= zobCastle[st->castleRights & (cr ^ ALL_CASTLES)];
st->castleRights &= cr;
// Update checkers BB
st->checkersBB = attackers_to(king_square(~us)) & pieces(us);
@ -1545,8 +1545,15 @@ void Position::init() {
for (Square s = SQ_A1; s <= SQ_H8; s++)
zobEp[s] = rk.rand<Key>();
for (int i = 0; i < 16; i++)
zobCastle[i] = rk.rand<Key>();
for (int cr = CASTLES_NONE; cr <= ALL_CASTLES; cr++)
{
Bitboard b = cr;
while (b)
{
Key k = zobCastle[1 << pop_1st_bit(&b)];
zobCastle[cr] ^= k ? k : rk.rand<Key>();
}
}
zobSideToMove = rk.rand<Key>();
zobExclusion = rk.rand<Key>();