Remove doEvenDeeperSearch

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index b947fc5f3e85ccfcea7aa62054a006b595e62617..ae83ab3475831d91b07668c94599c89404b4ef3e 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -372,8 +372,8 @@ void Thread::search() {
             beta      = std::min(avg + delta, VALUE_INFINITE);
 
             // Adjust optimism based on root move's averageScore (~4 Elo)
-            optimism[us]  = 103 * (avg + 33) / (std::abs(avg + 34) + 119);
-            optimism[~us] = -116 * (avg + 40) / (std::abs(avg + 12) + 123);
+            optimism[us]  = 110 * avg / (std::abs(avg) + 121);
+            optimism[~us] = -optimism[us];
 
             // 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
@@ -1045,7 +1045,7 @@ moves_loop:  // When in check, search starts here
                 && tte->depth() >= depth - 3)
             {
                 Value singularBeta  = ttValue - (64 + 57 * (ss->ttPv && !PvNode)) * depth / 64;
-                Depth singularDepth = (depth - 1) / 2;
+                Depth singularDepth = newDepth / 2;
 
                 ss->excludedMove = move;
                 value =
@@ -1100,6 +1100,12 @@ moves_loop:  // When in check, search starts here
             else if (PvNode && move == ttMove && move == ss->killers[0]
                      && (*contHist[0])[movedPiece][to_sq(move)] >= 4194)
                 extension = 1;
+
+            // Recapture extensions (~1 Elo)
+            else if (PvNode && move == ttMove && to_sq(move) == prevSq
+                     && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))]
+                          > 4000)
+                extension = 1;
         }
 
         // Add extension to new depth
@@ -1172,7 +1178,9 @@ moves_loop:  // When in check, search starts here
             // In general we want to cap the LMR depth search at newDepth, but when
             // reduction is negative, we allow this move a limited search extension
             // beyond the first move depth. This may lead to hidden double extensions.
-            Depth d = std::clamp(newDepth - r, 1, newDepth + 1);
+            // To prevent problems when the max value is less than the min value,
+            // std::clamp has been replaced by a more robust implementation.
+            Depth d = std::max(1, std::min(newDepth - r, newDepth + 1));
 
             value = -search<NonPV>(pos, ss + 1, -(alpha + 1), -alpha, d, true);
 
@@ -1182,12 +1190,9 @@ moves_loop:  // When in check, search starts here
                 // Adjust full-depth search based on LMR results - if the result
                 // was good enough search deeper, if it was bad enough search shallower.
                 const bool doDeeperSearch     = value > (bestValue + 51 + 10 * (newDepth - d));
-                const bool doEvenDeeperSearch = value > alpha + 700 && ss->doubleExtensions <= 6;
                 const bool doShallowerSearch  = value < bestValue + newDepth;
 
-                ss->doubleExtensions = ss->doubleExtensions + doEvenDeeperSearch;
-
-                newDepth += doDeeperSearch - doShallowerSearch + doEvenDeeperSearch;
+                newDepth += doDeeperSearch - doShallowerSearch;
 
                 if (newDepth > d)
                     value = -search<NonPV>(pos, ss + 1, -(alpha + 1), -alpha, newDepth, !cutNode);