LMR simplification

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index aa27ec2b02eec827a5bb7b5b7092d2043044d041..8f7d263aa0367973286914920c6c231b49be1ebb 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -246,15 +246,30 @@ void MainThread::search() {
       && !Skill(Options["Skill Level"]).enabled()
       &&  rootMoves[0].pv[0] != MOVE_NONE)
   {
-      for (Thread* th : Threads)
+      std::map<Move, int> votes;
+      Value minScore = this->rootMoves[0].score;
+
+      // Find out minimum score and reset votes for moves which can be voted
+      for (Thread* th: Threads)
       {
-          Depth depthDiff = th->completedDepth - bestThread->completedDepth;
-          Value scoreDiff = th->rootMoves[0].score - bestThread->rootMoves[0].score;
+          minScore = std::min(minScore, th->rootMoves[0].score);
+          votes[th->rootMoves[0].pv[0]] = 0;
+      }
+
+      // Vote according to score and depth
+      for (Thread* th : Threads)
+          votes[th->rootMoves[0].pv[0]] +=  int(th->rootMoves[0].score - minScore)  
+                                          + int(th->completedDepth);
 
-          // Select the thread with the best score, always if it is a mate
-          if (    scoreDiff > 0
-              && (depthDiff >= 0 || th->rootMoves[0].score >= VALUE_MATE_IN_MAX_PLY))
+      // Select best thread
+      int bestVote = votes[this->rootMoves[0].pv[0]];
+      for (Thread* th : Threads)
+      {
+          if (votes[th->rootMoves[0].pv[0]] > bestVote)
+          {
+              bestVote = votes[th->rootMoves[0].pv[0]];
               bestThread = th;
+          }
       }
   }
 
@@ -290,7 +305,7 @@ void Thread::search() {
 
   std::memset(ss-4, 0, 7 * sizeof(Stack));
   for (int i = 4; i > 0; i--)
-     (ss-i)->continuationHistory = this->continuationHistory[NO_PIECE][0].get(); // Use as sentinel
+     (ss-i)->continuationHistory = &this->continuationHistory[NO_PIECE][0]; // Use as sentinel
 
   bestValue = delta = alpha = -VALUE_INFINITE;
   beta = VALUE_INFINITE;
@@ -587,7 +602,7 @@ namespace {
 
     (ss+1)->ply = ss->ply + 1;
     ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
-    ss->continuationHistory = thisThread->continuationHistory[NO_PIECE][0].get();
+    ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
     (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
     Square prevSq = to_sq((ss-1)->currentMove);
 
@@ -751,7 +766,7 @@ namespace {
         Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
 
         ss->currentMove = MOVE_NULL;
-        ss->continuationHistory = thisThread->continuationHistory[NO_PIECE][0].get();
+        ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
 
         pos.do_null_move(st);
 
@@ -802,7 +817,7 @@ namespace {
                 probCutCount++;
 
                 ss->currentMove = move;
-                ss->continuationHistory = thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)].get();
+                ss->continuationHistory = &thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)];
 
                 assert(depth >= 5 * ONE_PLY);
 
@@ -935,8 +950,7 @@ moves_loop: // When in check, search starts from here
               int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;
 
               // Countermoves based pruning (~20 Elo)
-              if (   lmrDepth < 4
-                  && (lmrDepth < 3 || ((ss - 1)->statScore > 0 && !PvNode))
+              if (   lmrDepth < 3 + ((ss-1)->statScore > 0)
                   && (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
                   && (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
                   continue;
@@ -971,7 +985,7 @@ moves_loop: // When in check, search starts from here
 
       // Update the current move (this must be done after singular extension search)
       ss->currentMove = move;
-      ss->continuationHistory = thisThread->continuationHistory[movedPiece][to_sq(move)].get();
+      ss->continuationHistory = &thisThread->continuationHistory[movedPiece][to_sq(move)];
 
       // Step 15. Make the move
       pos.do_move(move, st, givesCheck);
@@ -984,18 +998,12 @@ moves_loop: // When in check, search starts from here
       {
           Depth r = reduction<PvNode>(improving, depth, moveCount);
 
-          if (captureOrPromotion) // (~5 Elo)
-          {
-              // Decrease reduction by comparing opponent's stat score
-              if ((ss-1)->statScore < 0)
-                  r -= ONE_PLY;
-          }
-          else
-          {
-              // Decrease reduction if opponent's move count is high (~5 Elo)
-              if ((ss-1)->moveCount > 15)
-                  r -= ONE_PLY;
+          // Decrease reduction if opponent's move count is high (~10 Elo)
+          if ((ss-1)->moveCount > 15)
+              r -= ONE_PLY;
 
+          if (!captureOrPromotion)
+          {
               // Decrease reduction for exact PV nodes (~0 Elo)
               if (pvExact)
                   r -= ONE_PLY;
@@ -1214,7 +1222,7 @@ moves_loop: // When in check, search starts from here
     Thread* thisThread = pos.this_thread();
     (ss+1)->ply = ss->ply + 1;
     ss->currentMove = bestMove = MOVE_NONE;
-    ss->continuationHistory = thisThread->continuationHistory[NO_PIECE][0].get();
+    ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
     inCheck = pos.checkers();
     moveCount = 0;
 
@@ -1349,7 +1357,7 @@ moves_loop: // When in check, search starts from here
       }
 
       ss->currentMove = move;
-      ss->continuationHistory = thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)].get();
+      ss->continuationHistory = &thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)];
 
       // Make and search the move
       pos.do_move(move, st, givesCheck);