Allow FICS-style atomic castling (fix official-stockfish#560)

ddugovic · ddugovic · commit dd8e73035d30 · 2019-09-03T21:46:30.000-05:00
STC LLR: 2.96 (-2.94,2.94) [-10.00,5.00] Total: 19229 W: 6266 L: 6337 D: 6626 http://35.161.250.236:6543/tests/view/5d6e41f86e23db3768ec07da
diff --git a/src/position.cpp b/src/position.cpp
@@ -1040,8 +1040,11 @@ bool Position::legal(Move m) const {
           if (is_atomic())
           {
               // Atomic king cannot castle through check or discovered check
+              // Allow FICS-style atomic castling whereby the castling rook
+              // is moved before the king is moved and thereby blocks a check
+              Bitboard occupied = (s == to) ? pieces() : (pieces() ^ from);
               if (   !(attacks_bb(KING, square<KING>(~us), 0) & s)
-                  &&  (attackers_to(s, pieces() ^ from) & pieces(~us)))
+                  &&  (attackers_to(s, occupied) & pieces(~us)))
                   return false;
           }
           else

Original file line number	Diff line number	Diff line change
`@@ -1040,8 +1040,11 @@ bool Position::legal(Move m) const {`
`1040`	`1040`	`if (is_atomic())`
`1041`	`1041`	`{`
`1042`	`1042`	`// Atomic king cannot castle through check or discovered check`
	`1043`	`+ // Allow FICS-style atomic castling whereby the castling rook`
	`1044`	`+ // is moved before the king is moved and thereby blocks a check`
	`1045`	`+ Bitboard occupied = (s == to) ? pieces() : (pieces() ^ from);`
`1043`	`1046`	`if ( !(attacks_bb(KING, square<KING>(~us), 0) & s)`
`1044`		`- && (attackers_to(s, pieces() ^ from) & pieces(~us)))`
	`1047`	`+ && (attackers_to(s, occupied) & pieces(~us)))`
`1045`	`1048`	`return false;`
`1046`	`1049`	`}`
`1047`	`1050`	`else`