Simplify prior countermove bonus

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 616d11336eee92595882ce885f2175d114782e81..e51e2f4dae122310673d40cfced2c5afaea79129 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -616,7 +616,7 @@ namespace {
     // At non-PV nodes we check for an early TT cutoff
     if (  !PvNode
         && !excludedMove
-        && tte->depth() > depth - (tte->bound() == BOUND_EXACT)
+        && tte->depth() > depth
         && ttValue != VALUE_NONE // Possible in case of TT access race or if !ttHit
         && (tte->bound() & (ttValue >= beta ? BOUND_LOWER : BOUND_UPPER)))
     {
@@ -745,8 +745,8 @@ namespace {
     }
 
     // Set up the improving flag, which is true if current static evaluation is
-    // bigger than the previous static evaluation at our turn (if we were in 
-    // check at our previous move we look at static evaluaion at move prior to it
+    // bigger than the previous static evaluation at our turn (if we were in
+    // check at our previous move we look at static evaluation at move prior to it
     // and if we were in check at move prior to it flag is set to true) and is
     // false otherwise. The improving flag is used in various pruning heuristics.
     improving =   (ss-2)->staticEval != VALUE_NONE ? ss->staticEval > (ss-2)->staticEval
@@ -1037,7 +1037,7 @@ moves_loop: // When in check, search starts here
               lmrDepth = std::max(lmrDepth, 0);
 
               // Prune moves with negative SEE (~4 Elo)
-              if (!pos.see_ge(move, Value(-27 * lmrDepth * lmrDepth - 16 * lmrDepth)))
+              if (!pos.see_ge(move, Value(-31 * lmrDepth * lmrDepth)))
                   continue;
           }
       }
@@ -1099,15 +1099,11 @@ moves_loop: // When in check, search starts here
 
               // If we are on a cutNode, reduce it based on depth (negative extension) (~1 Elo)
               else if (cutNode)
-                  extension = depth > 8 && depth < 17 ? -3 : -1;
+                  extension = depth < 17 ? -3 : -1;
 
               // If the eval of ttMove is less than value, we reduce it (negative extension) (~1 Elo)
               else if (ttValue <= value)
                   extension = -1;
-
-              // If the eval of ttMove is less than alpha, we reduce it (negative extension) (~1 Elo)
-              else if (ttValue <= alpha)
-                  extension = -1;
           }
 
           // Check extensions (~1 Elo)
@@ -1375,8 +1371,9 @@ moves_loop: // When in check, search starts here
     // Bonus for prior countermove that caused the fail low
     else if (!priorCapture && prevSq != SQ_NONE)
     {
-        int bonus = (depth > 5) + (PvNode || cutNode) + (bestValue < alpha - 113 * depth) + ((ss-1)->moveCount > 12);
+        int bonus = (depth > 5) + (PvNode || cutNode) + (bestValue < alpha - 800) + ((ss-1)->moveCount > 12);
         update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * bonus);
+        thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << stat_bonus(depth) * bonus / 2;
     }
 
     if (PvNode)
@@ -1413,6 +1410,18 @@ moves_loop: // When in check, search starts here
     assert(PvNode || (alpha == beta - 1));
     assert(depth <= 0);
 
+    // Check if we have an upcoming move that draws by repetition, or
+    // if the opponent had an alternative move earlier to this position.
+    if (   depth < 0
+        && pos.rule50_count() >= 3
+        && alpha < VALUE_DRAW
+        && pos.has_game_cycle(ss->ply))
+    {
+        alpha = value_draw(pos.this_thread());
+        if (alpha >= beta)
+            return alpha;
+    }
+
     Move pv[MAX_PLY+1];
     StateInfo st;
     ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize);
@@ -1499,7 +1508,7 @@ moves_loop: // When in check, search starts here
         if (bestValue > alpha)
             alpha = bestValue;
 
-        futilityBase = bestValue + 200;
+        futilityBase = std::min(ss->staticEval, bestValue) + 200;
     }
 
     const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,