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Determine opposite colors mathematically

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This is a non-functional speed-up: master has to access SquareBB twice while this patch
determines opposite_colors just using the values of the squares. It doesn't seem to change
the overall speed of bench, but calling opposite_colors(...) 10 Million times:

master: 39.4 seconds
patch: 11.4 seconds.

The only data point I have (other than my own tests), is a quite old failed STC test:
LLR: -2.93 (-2.94,2.94) [-1.50,4.50]
Total: 24308 W: 5331 L: 5330 D: 13647
Ptnml(0-2): 315, 2577, 6326, 2623, 289
http://tests.stockfishchess.org/tests/view/5e010256c13ac2425c4a9a67

Closes https://github.com/official-stockfish/Stockfish/pull/2498

No functional change
This commit is contained in:
protonspring 2019-12-23 10:58:30 -07:00 • committed by Stéphane Nicolet
parent 75dfdeac11
commit f3c83ed46c
1 changed files with 2 additions and 2 deletions
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4
src/bitboard.h
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@ -129,8 +129,8 @@ constexpr bool more_than_one(Bitboard b) {
return b & (b - 1);
}
inline bool opposite_colors(Square s1, Square s2) {
return bool(DarkSquares & s1) != bool(DarkSquares & s2);
constexpr bool opposite_colors(Square s1, Square s2) {
return (s1 + rank_of(s1) + s2 + rank_of(s2)) & 1;
}