Call cycle detection before qsearch()

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 93651cc047b466724bb959f1102a463f8c2257f3..2185a3214fc59dd651c3e6639669cbcead83d7df 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -519,13 +519,25 @@ namespace {
   template <NodeType NT>
   Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
 
-    // Use quiescence search when needed
-    if (depth < ONE_PLY)
-        return qsearch<NT>(pos, ss, alpha, beta);
-
     constexpr bool PvNode = NT == PV;
     const bool rootNode = PvNode && ss->ply == 0;
 
+    // Check if we have an upcoming move which draws by repetition, or 
+    // if the opponent had an alternative move earlier to this position.
+    if (   pos.rule50_count() >= 3
+        && alpha < VALUE_DRAW
+        && !rootNode
+        && pos.has_game_cycle(ss->ply))
+    {
+        alpha = VALUE_DRAW;
+        if (alpha >= beta)
+            return alpha;
+    }
+
+    // Dive into quiescence search when the depth reaches zero
+    if (depth < ONE_PLY)
+        return qsearch<NT>(pos, ss, alpha, beta);
+
     assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
     assert(PvNode || (alpha == beta - 1));
     assert(DEPTH_ZERO < depth && depth < DEPTH_MAX);
@@ -578,17 +590,6 @@ namespace {
         beta = std::min(mate_in(ss->ply+1), beta);
         if (alpha >= beta)
             return alpha;
-
-        // Check if there exists a move which draws by repetition, or an alternative
-        // earlier move to this position.
-        if (   pos.rule50_count() >= 3
-            && alpha < VALUE_DRAW
-            && pos.has_game_cycle(ss->ply))
-        {
-            alpha = VALUE_DRAW;
-            if (alpha >= beta)
-                return alpha;
-        }
     }
 
     assert(0 <= ss->ply && ss->ply < MAX_PLY);