Decrease reduction in case we had singular extension. #2146

Passed STC http://tests.stockfishchess.org/tests/view/5cda71790ebc5925cf057a84
LLR: 2.95 (-2.94,2.94) [0.50,4.50]
Total: 73454 W: 16482 L: 15954 D: 41018

Passed LTC http://tests.stockfishchess.org/tests/view/5cdab17b0ebc5925cf05822f
LLR: 2.95 (-2.94,2.94) [0.00,3.50]
Total: 56696 W: 9877 L: 9538 D: 37281

Original idea by @locutus2

bench 3378510

diff --git a/src/search.cpp b/src/search.cpp
index 5d6babb45f716200c82dd30b2265d9857a0e81b3..f021f8ff5eb183517a9391bd6cff6faee74d571c 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -855,6 +855,7 @@ moves_loop: // When in check, search starts from here
     value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
     moveCountPruning = false;
     ttCapture = ttMove && pos.capture_or_promotion(ttMove);
     value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
     moveCountPruning = false;
     ttCapture = ttMove && pos.capture_or_promotion(ttMove);

+    int singularExtensionLMRmultiplier = 0;

 
     // Step 12. Loop through all pseudo-legal moves until no moves remain
     // or a beta cutoff occurs.
 
     // Step 12. Loop through all pseudo-legal moves until no moves remain
     // or a beta cutoff occurs.


@@ -911,7 +912,12 @@ moves_loop: // When in check, search starts from here
           ss->excludedMove = MOVE_NONE;
 
           if (value < singularBeta)
           ss->excludedMove = MOVE_NONE;
 
           if (value < singularBeta)

+              {

               extension = ONE_PLY;
               extension = ONE_PLY;

+              singularExtensionLMRmultiplier++;
+              if (value < singularBeta - std::min(3 * depth / ONE_PLY, 39))
+                 singularExtensionLMRmultiplier++;
+              }

 
           // Multi-cut pruning
           // Our ttMove is assumed to fail high, and now we failed high also on a reduced
 
           // Multi-cut pruning
           // Our ttMove is assumed to fail high, and now we failed high also on a reduced


@@ -1021,6 +1027,8 @@ moves_loop: // When in check, search starts from here
           // Decrease reduction if opponent's move count is high (~10 Elo)
           if ((ss-1)->moveCount > 15)
               r -= ONE_PLY;
           // Decrease reduction if opponent's move count is high (~10 Elo)
           if ((ss-1)->moveCount > 15)
               r -= ONE_PLY;

+          // Decrease reduction if move has been singularly extended
+          r -= singularExtensionLMRmultiplier * ONE_PLY;

 
           if (!captureOrPromotion)
           {
 
           if (!captureOrPromotion)
           {