Add mild extension in low depths

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 98bf24a828e7174e48d4687785b7579b81e3406f..ab34a8451cceda529f7996faf4df0500d6715f0c 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -172,6 +172,9 @@ namespace {
   const bool PruneDefendingMoves = false;
   const bool PruneBlockingMoves  = false;
 
+  // Only move margin
+  const Value OnlyMoveMargin = Value(100);
+
   // Margins for futility pruning in the quiescence search, and at frontier
   // and near frontier nodes.
   const Value FutilityMarginQS = Value(0x80);
@@ -1132,12 +1135,34 @@ namespace {
       moveIsCheck = pos.move_is_check(move, ci);
       captureOrPromotion = pos.move_is_capture_or_promotion(move);
 
-      movesSearched[moveCount++] = ss[ply].currentMove = move;
+      movesSearched[moveCount++] = move;
 
       // Decide the new search depth
       ext = extension(pos, move, true, captureOrPromotion, moveIsCheck, singleReply, mateThreat, &dangerous);
+
+      // Only move extension
+      if (   moveCount == 1
+          && ext < OnePly
+          && depth >= 4 * OnePly
+          && tte
+          && (tte->type() & VALUE_TYPE_LOWER)
+          && tte->move() != MOVE_NONE
+          && tte->depth() >= depth - 3 * OnePly)
+      {
+          Value ttValue = value_from_tt(tte->value(), ply);
+          if (abs(ttValue) < VALUE_KNOWN_WIN)
+          {
+              Value excValue = search(pos, ss, ttValue - OnlyMoveMargin, Max(Min(depth / 2,  depth - 4 * OnePly), OnePly), ply, false, threadID, tte->move());
+              if (excValue < ttValue - OnlyMoveMargin)
+                  ext = (depth >= 8 * OnePly)? OnePly : ext + OnePly / 2;
+          }
+      }
+
       newDepth = depth - OnePly + ext;
 
+      // Update current move
+      ss[ply].currentMove = move;
+
       // Make and search the move
       pos.do_move(move, st, ci, moveIsCheck);
 
@@ -1412,12 +1437,35 @@ namespace {
       moveIsCheck = pos.move_is_check(move, ci);
       captureOrPromotion = pos.move_is_capture_or_promotion(move);
 
-      movesSearched[moveCount++] = ss[ply].currentMove = move;
+      movesSearched[moveCount++] = move;
 
       // Decide the new search depth
       ext = extension(pos, move, false, captureOrPromotion, moveIsCheck, singleReply, mateThreat, &dangerous);
+
+      // Only move extension
+      if (   forbiddenMove == MOVE_NONE
+          && moveCount == 1
+          && ext < OnePly
+          && depth >= 4 * OnePly
+          && tte
+          && (tte->type() & VALUE_TYPE_LOWER)
+          && tte->move() != MOVE_NONE
+          && tte->depth() >= depth - 3 * OnePly)
+      {
+          Value ttValue = value_from_tt(tte->value(), ply);
+          if (abs(ttValue) < VALUE_KNOWN_WIN)
+          {
+              Value excValue = search(pos, ss, ttValue - OnlyMoveMargin, Max(Min(depth / 2,  depth - 4 * OnePly), OnePly), ply, false, threadID, tte->move());
+              if (excValue < ttValue - OnlyMoveMargin)
+                  ext = (depth >= 8 * OnePly)? OnePly : ext + OnePly / 2;
+          }
+      }
+
       newDepth = depth - OnePly + ext;
 
+      // Update current move
+      ss[ply].currentMove = move;
+
       // Futility pruning
       if (    useFutilityPruning
           && !dangerous