Simplify reduction condition for cutNodes

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 07f18a34fe3e1e2e163fce496b6b2bf3a2f8b689..96b1d0f1a0c77e35319236254060952d2a2e595c 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -373,7 +373,9 @@ void Thread::search() {
           int failedHighCnt = 0;
           while (true)
           {
-              Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - searchAgainCounter);
+              // Adjust the effective depth searched, but ensuring at least one effective increment for every
+              // four searchAgain steps (see issue #2717).
+              Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - 3 * (searchAgainCounter + 1) / 4);
               bestValue = Stockfish::search<Root>(rootPos, ss, alpha, beta, adjustedDepth, false);
 
               // Bring the best move to the front. It is critical that sorting
@@ -472,7 +474,7 @@ void Thread::search() {
           double reduction = (1.56 + mainThread->previousTimeReduction) / (2.20 * timeReduction);
           double bestMoveInstability = 1 + 1.7 * totBestMoveChanges / Threads.size();
           int complexity = mainThread->complexityAverage.value();
-          double complexPosition = std::clamp(1.0 + (complexity - 277) / 1819.1, 0.5, 1.5);
+          double complexPosition = std::min(1.0 + (complexity - 277) / 1819.1, 1.5);
 
           double totalTime = Time.optimum() * fallingEval * reduction * bestMoveInstability * complexPosition;
 
@@ -1154,7 +1156,7 @@ moves_loop: // When in check, search starts here
               r--;
 
           // Increase reduction for cut nodes (~3 Elo)
-          if (cutNode && move != ss->killers[0])
+          if (cutNode)
               r += 2;
 
           // Increase reduction if ttMove is a capture (~3 Elo)