Fix incorrect pruning in qsearch

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index eaa79fb92bffe836472c6382d63daac2f10aa7ab..743449fa39c5b7e13cd81dc68cd44f90d53fdf41 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -417,7 +417,7 @@ void Thread::search() {
           // Start with a small aspiration window and, in the case of a fail
           // high/low, re-search with a bigger window until we don't fail
           // high/low anymore.
-          int failedHighCnt = 0;
+          failedHighCnt = 0;
           while (true)
           {
               Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - searchAgainCounter);
@@ -565,6 +565,7 @@ namespace {
 
     constexpr bool PvNode = NT == PV;
     const bool rootNode = PvNode && ss->ply == 0;
+    const Depth maxNextDepth = rootNode ? depth : depth + 1;
 
     // Check if we have an upcoming move which draws by repetition, or
     // if the opponent had an alternative move earlier to this position.
@@ -1177,6 +1178,9 @@ moves_loop: // When in check, search starts from here
               if (ttCapture)
                   r++;
 
+              // Increase reduction at root if failing high
+              r += rootNode ? thisThread->failedHighCnt * thisThread->failedHighCnt * moveCount / 512 : 0;
+
               // Increase reduction for cut nodes (~10 Elo)
               if (cutNode)
                   r += 2;
@@ -1256,7 +1260,8 @@ moves_loop: // When in check, search starts from here
           (ss+1)->pv = pv;
           (ss+1)->pv[0] = MOVE_NONE;
 
-          value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
+          value = -search<PV>(pos, ss+1, -beta, -alpha,
+                              std::min(maxNextDepth, newDepth), false);
       }
 
       // Step 18. Undo move
@@ -1560,7 +1565,7 @@ moves_loop: // When in check, search starts from here
 
       // CounterMove based pruning
       if (  !captureOrPromotion
-          && moveCount
+          && bestValue > VALUE_TB_LOSS_IN_MAX_PLY
           && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold
           && (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold)
           continue;
@@ -1595,7 +1600,11 @@ moves_loop: // When in check, search starts from here
     // All legal moves have been searched. A special case: if we're in check
     // and no legal moves were found, it is checkmate.
     if (ss->inCheck && bestValue == -VALUE_INFINITE)
+    {
+        assert(!MoveList<LEGAL>(pos).size());
+
         return mated_in(ss->ply); // Plies to mate from the root
+    }
 
     tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit,
               bestValue >= beta ? BOUND_LOWER :