Fix cycle detection in presence of repetitions

[stockfish] / src / position.cpp

diff --git a/src/position.cpp b/src/position.cpp
index 84892d094a60fd3d770b1af0ba2546724ef7b8a9..a86d77ad7707bcfc6337f293cfa7180af31c6635 100644 (file)
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -18,6 +18,7 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include <algorithm>
 #include <cassert>
 #include <cstddef> // For offsetof()
 #include <cstring> // For std::memset, std::memcmp
@@ -340,13 +341,8 @@ void Position::set_castling_right(Color c, Square rfrom) {
   Square kto = relative_square(c, cs == KING_SIDE ? SQ_G1 : SQ_C1);
   Square rto = relative_square(c, cs == KING_SIDE ? SQ_F1 : SQ_D1);
 
-  for (Square s = std::min(rfrom, rto); s <= std::max(rfrom, rto); ++s)
-      if (s != kfrom && s != rfrom)
-          castlingPath[cr] |= s;
-
-  for (Square s = std::min(kfrom, kto); s <= std::max(kfrom, kto); ++s)
-      if (s != kfrom && s != rfrom)
-          castlingPath[cr] |= s;
+  castlingPath[cr] =   (between_bb(rfrom, rto) | between_bb(kfrom, kto) | rto | kto)
+                    & ~(square_bb(kfrom) | rfrom);
 }
 
 
@@ -864,7 +860,6 @@ void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
 
       // Update pawn hash key and prefetch access to pawnsTable
       st->pawnKey ^= Zobrist::psq[pc][from] ^ Zobrist::psq[pc][to];
-      prefetch2(thisThread->pawnsTable[st->pawnKey]);
 
       // Reset rule 50 draw counter
       st->rule50 = 0;
@@ -1211,6 +1206,11 @@ bool Position::has_game_cycle(int ply) const {
               if (ply > i)
                   return true;
 
+              // For nodes before or at the root, check that the move is a repetition one
+              // rather than a move to the current position
+              if (color_of(piece_on(empty(s1) ? s2 : s1)) != side_to_move())
+                  continue;
+
               // For repetitions before or at the root, require one more
               StateInfo* next_stp = stp;
               for (int k = i + 2; k <= end; k += 2)