Adjust stand pat in qsearch on pv nodes

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 10a36cbf26131b6ac449a92885b18579c6d27aaa..27c2c84e9dd580d8bbc26622a09cabb2767ef5da 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1468,14 +1468,19 @@ Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
             ss->staticEval = bestValue =
               (ss - 1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss - 1)->staticEval;
 
-        // Stand pat. Return immediately if static value is at least beta
+        // Stand pat. Return immediately if bestValue is at least beta at non-Pv nodes.
+        // At PvNodes set bestValue between alpha and beta instead
         if (bestValue >= beta)
         {
-            if (!ss->ttHit)
-                tte->save(posKey, value_to_tt(bestValue, ss->ply), false, BOUND_LOWER, DEPTH_NONE,
-                          MOVE_NONE, ss->staticEval);
+            if (!PvNode || abs(bestValue) >= VALUE_TB_WIN_IN_MAX_PLY)
+            {
+                if (!ss->ttHit)
+                    tte->save(posKey, value_to_tt(bestValue, ss->ply), false, BOUND_LOWER,
+                              DEPTH_NONE, MOVE_NONE, ss->staticEval);
 
-            return bestValue;
+                return bestValue;
+            }
+            bestValue = std::min((alpha + beta) / 2, beta - 1);
         }
 
         if (bestValue > alpha)