LMR: remove `deeper`

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 1ab71a5620a941978d9ed77e122fe7256e14e063..37277ec418bf4556a99c19c17aa62ed0ac40c669 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -867,8 +867,6 @@ namespace {
         assert(probCutBeta < VALUE_INFINITE);
 
         MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, depth - 3, &captureHistory);
-        bool ttPv = ss->ttPv;
-        ss->ttPv = false;
 
         while ((move = mp.next_move()) != MOVE_NONE)
             if (move != excludedMove && pos.legal(move))
@@ -894,16 +892,11 @@ namespace {
 
                 if (value >= probCutBeta)
                 {
-                    // if transposition table doesn't have equal or more deep info write probCut data into it
-                    if (!(   ss->ttHit
-                          && tte->depth() >= depth - 3
-                          && ttValue != VALUE_NONE))
-                        tte->save(posKey, value_to_tt(value, ss->ply), ttPv,
-                                  BOUND_LOWER, depth - 3, move, ss->staticEval);
+                    // Save ProbCut data into transposition table
+                    tte->save(posKey, value_to_tt(value, ss->ply), ss->ttPv, BOUND_LOWER, depth - 3, move, ss->staticEval);
                     return value;
                 }
             }
-         ss->ttPv = ttPv;
     }
 
     // Step 11. If the position is not in TT, decrease depth by 3.
@@ -1185,15 +1178,10 @@ moves_loop: // When in check, search starts here
           // Decrease/increase reduction for moves with a good/bad history (~30 Elo)
           r -= ss->statScore / 15914;
 
-          // 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).
-          int deeper =   r >= -1                   ? 0
-                       : moveCount <= 4            ? 2
-                       : PvNode || cutNode         ? 1
-                       :                             0;
-
-          Depth d = std::clamp(newDepth - r, 1, newDepth + deeper);
+          // 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);
 
           value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);