Use fail high count for LMR

candirufish · vondele · commit a32d2086bc22 · 2022-05-03T17:58:01.000+02:00
Increase reduction if next ply has a lot of fail high else reset count to 0 Passed STC: https://tests.stockfishchess.org/tests/view/626ea8299116b52aa83b71f6 LLR: 2.94 (-2.94,2.94) <0.00,2.50> Total: 144288 W: 38377 L: 37902 D: 68009 Ptnml(0-2): 565, 16298, 38054, 16551, 676 Passed LTC: https://tests.stockfishchess.org/tests/view/626fa0fb79f761bab2e382f0 LLR: 2.98 (-2.94,2.94) <0.50,3.00> Total: 74872 W: 20050 L: 19686 D: 35136 Ptnml(0-2): 51, 7541, 21893, 7895, 56 closes #4006 bench: 7084802
diff --git a/src/search.cpp b/src/search.cpp
@@ -603,6 +603,7 @@ namespace {
     (ss+1)->ttPv         = false;
     (ss+1)->excludedMove = bestMove = MOVE_NONE;
     (ss+2)->killers[0]   = (ss+2)->killers[1] = MOVE_NONE;
+    (ss+2)->cutoffCnt    = 0;
     ss->doubleExtensions = (ss-1)->doubleExtensions;
     ss->depth            = depth;
     Square prevSq        = to_sq((ss-1)->currentMove);
@@ -1175,6 +1176,10 @@ namespace {
           if (PvNode)
               r -= 1 + 15 / ( 3 + depth );
 
+          // Increase reduction if next ply has a lot of fail high else reset count to 0
+          if ((ss+1)->cutoffCnt > 3 && !PvNode)
+              r++;
+
           ss->statScore =  thisThread->mainHistory[us][from_to(move)]
                          + (*contHist[0])[movedPiece][to_sq(move)]
                          + (*contHist[1])[movedPiece][to_sq(move)]
@@ -1298,11 +1303,15 @@ namespace {
                   alpha = value;
               else
               {
+                  ss->cutoffCnt++;
                   assert(value >= beta); // Fail high
                   break;
               }
           }
       }
+      else
+         ss->cutoffCnt = 0;
+
 
       // If the move is worse than some previously searched move, remember it to update its stats later
       if (move != bestMove)
diff --git a/src/search.h b/src/search.h
@@ -54,6 +54,7 @@ struct Stack {
   bool ttPv;
   bool ttHit;
   int doubleExtensions;
+  int cutoffCnt;
 };
 
 
