Do more reductions for late quiet moves in case of consecutive fail highs.

Vizvezdenec · vondele · commit 560c77639748 · 2020-10-18T13:54:28.000+02:00
Idea of this patch can be described as following - in case we have consecutive fail highs and we reach late enough moves at root node probability of remaining quiet moves being able to produce even bigger value than moves that produced previous cutoff (so ones that should be high in move ordering but now they fail to produce beta cutoff because we actually reached high move count) should be quiet small so we can reduce them more. passed STC LLR: 2.94 (-2.94,2.94) {-0.25,1.25} Total: 53392 W: 5681 L: 5474 D: 42237 Ptnml(0-2): 214, 4104, 17894, 4229, 255 https://tests.stockfishchess.org/tests/view/5f88501adcdad978fe8c527e passed LTC LLR: 2.94 (-2.94,2.94) {0.25,1.25} Total: 59136 W: 2773 L: 2564 D: 53799 Ptnml(0-2): 30, 2117, 25078, 2300, 43 https://tests.stockfishchess.org/tests/view/5f884dbfdcdad978fe8c527a closes #3184 Bench: 4066972
diff --git 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);
@@ -1177,6 +1177,9 @@ namespace {
               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;
diff --git a/src/thread.h b/src/thread.h
@@ -73,6 +73,7 @@ class Thread {
   CapturePieceToHistory captureHistory;
   ContinuationHistory continuationHistory[2][2];
   Score contempt;
+  int failedHighCnt;
 };
 
 
