Determine opposite colors mathematically

protonspring · snicolet · commit f3c83ed46cdc · 2020-01-23T17:59:03.000+01:00
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 #2498 No functional change
diff --git a/src/bitboard.h b/src/bitboard.h
@@ -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;
 }
 
 

Original file line number	Diff line number	Diff line change
`@@ -129,8 +129,8 @@ constexpr bool more_than_one(Bitboard b) {`
`129`	`129`	`return b & (b - 1);`
`130`	`130`	`}`
`131`	`131`
`132`		`-inline bool opposite_colors(Square s1, Square s2) {`
`133`		`- return bool(DarkSquares & s1) != bool(DarkSquares & s2);`
	`132`	`+constexpr bool opposite_colors(Square s1, Square s2) {`
	`133`	`+ return (s1 + rank_of(s1) + s2 + rank_of(s2)) & 1;`
`134`	`134`	`}`
`135`	`135`
`136`	`136`