Remove noLMRExtension flag

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 1aaf53d84d1b018374a7bc612d57e34e968c5d35..9a2bd41565911c1bd1179df7d074a20b72ed0846 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -588,9 +588,9 @@ namespace {
     Value bestValue, value, ttValue, eval, maxValue, probCutBeta;
     bool givesCheck, improving, didLMR, priorCapture;
     bool captureOrPromotion, doFullDepthSearch, moveCountPruning,
-         ttCapture, singularQuietLMR, noLMRExtension;
+         ttCapture, singularQuietLMR;
     Piece movedPiece;
-    int moveCount, captureCount, quietCount, bestMoveCount;
+    int moveCount, captureCount, quietCount, bestMoveCount, improvement;
 
     // Step 1. Initialize node
     ss->inCheck        = pos.checkers();
@@ -766,6 +766,7 @@ namespace {
         // Skip early pruning when in check
         ss->staticEval = eval = VALUE_NONE;
         improving = false;
+        improvement = 0;
         goto moves_loop;
     }
     else if (ss->ttHit)
@@ -804,13 +805,15 @@ namespace {
         thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus;
     }
 
-    // Set up improving flag that is used in various pruning heuristics
-    // We define position as improving if static evaluation of position is better
-    // Than the previous static evaluation at our turn
-    // In case of us being in check at our previous move we look at move prior to it
-    improving =  (ss-2)->staticEval == VALUE_NONE
-               ? ss->staticEval > (ss-4)->staticEval || (ss-4)->staticEval == VALUE_NONE
-               : ss->staticEval > (ss-2)->staticEval;
+    // Set up the improvement variable, which is the difference between the current
+    // static evaluation and the previous static evaluation at our turn (if we were
+    // in check at our previous move we look at the move prior to it). The improvement
+    // margin and the improving flag are used in various pruning heuristics.
+    improvement =   (ss-2)->staticEval != VALUE_NONE ? ss->staticEval - (ss-2)->staticEval
+                  : (ss-4)->staticEval != VALUE_NONE ? ss->staticEval - (ss-4)->staticEval
+                  :                                    200;
+
+    improving = improvement > 0;
 
     // Step 7. Futility pruning: child node (~50 Elo).
     // The depth condition is important for mate finding.
@@ -826,7 +829,7 @@ namespace {
         && (ss-1)->statScore < 23767
         &&  eval >= beta
         &&  eval >= ss->staticEval
-        &&  ss->staticEval >= beta - 20 * depth - 22 * improving + 168 * ss->ttPv + 177
+        &&  ss->staticEval >= beta - 20 * depth - improvement / 15 + 168 * ss->ttPv + 177
         && !excludedMove
         &&  pos.non_pawn_material(us)
         && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
@@ -981,7 +984,7 @@ moves_loop: // When in check, search starts here
                                       ss->ply);
 
     value = bestValue;
-    singularQuietLMR = moveCountPruning = noLMRExtension = false;
+    singularQuietLMR = moveCountPruning = false;
 
     // Indicate PvNodes that will probably fail low if the node was searched
     // at a depth equal or greater than the current depth, and the result of this search was a fail low.
@@ -1105,10 +1108,7 @@ moves_loop: // When in check, search starts here
               if (   !PvNode
                   && value < singularBeta - 75
                   && ss->doubleExtensions <= 6)
-              {
                   extension = 2;
-                  noLMRExtension = true;
-              }
           }
 
           // Multi-cut pruning
@@ -1216,13 +1216,12 @@ moves_loop: // When in check, search starts here
 
           // In general we want to cap the LMR depth search at newDepth. But if reductions
           // are really negative and movecount is low, we allow this move to be searched
-          // deeper than the first move (this may lead to hidden double extensions if
-          // newDepth got its own extension before).
-          int deeper =   r >= -1               ? 0
-                       : noLMRExtension        ? 0
-                       : moveCount <= 5        ? 1
-                       : (depth > 6 && PvNode) ? 1
-                       :                         0;
+          // deeper than the first move (this may lead to hidden double extensions).
+          int deeper =   r >= -1                   ? 0
+                       : moveCount <= 3 && r <= -3 ? 2
+                       : moveCount <= 5            ? 1
+                       : PvNode && depth > 6       ? 1
+                       :                             0;
 
           Depth d = std::clamp(newDepth - r, 1, newDepth + deeper);