Remove two useless assignments (#2093)

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 30f280728e274055d49771ceb2a413d5b91aa9dd..15e88ca4f2746939bd3c3e25b04ed15ff11b3824 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -86,8 +86,8 @@ namespace {
 
   // Add a small random component to draw evaluations to avoid 3fold-blindness
   Value value_draw(Depth depth, Thread* thisThread) {
-    return depth < 4 ? VALUE_DRAW
-                     : VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1);
+    return depth < 4 * ONE_PLY ? VALUE_DRAW
+                               : VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1);
   }
 
   // Skill structure is used to implement strength limit
@@ -468,8 +468,10 @@ void Thread::search() {
 
           // Use part of the gained time from a previous stable move for the current move
           for (Thread* th : Threads)
+          {
               totBestMoveChanges += th->bestMoveChanges;
-
+              th->bestMoveChanges = 0;
+          }
           double bestMoveInstability = 1 + totBestMoveChanges / Threads.size();
 
           // Stop the search if we have only one legal move, or if available time elapsed
@@ -605,15 +607,6 @@ namespace {
             : ttHit    ? tte->move() : MOVE_NONE;
     ttPv = (ttHit && tte->is_pv()) || (PvNode && depth > 4 * ONE_PLY);
 
-    // if position has been searched at higher depths and we are shuffling, return value_draw
-    if (pos.rule50_count() > 36
-        && ss->ply > 36
-        && depth < 3 * ONE_PLY
-        && ttHit
-        && tte->depth() > depth
-        && pos.count<PAWN>() > 0)
-        return VALUE_DRAW;
-
     // At non-PV nodes we check for an early TT cutoff
     if (  !PvNode
         && ttHit
@@ -630,9 +623,8 @@ namespace {
                 if (!pos.capture_or_promotion(ttMove))
                     update_quiet_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth));
 
-                // Extra penalty for a quiet TT or main killer move in previous ply when it gets refuted
-                if (    ((ss-1)->moveCount == 1 || (ss-1)->currentMove == (ss-1)->killers[0])
-                     && !pos.captured_piece())
+                // Extra penalty for early quiet moves of the previous ply
+                if ((ss-1)->moveCount <= 2 && !pos.captured_piece())
                         update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
             }
             // Penalty for a quiet ttMove that fails low
@@ -783,7 +775,7 @@ namespace {
 
             // Do verification search at high depths, with null move pruning disabled
             // for us, until ply exceeds nmpMinPly.
-            thisThread->nmpMinPly = ss->ply + 3 * (depth-R) / 4;
+            thisThread->nmpMinPly = ss->ply + 3 * (depth-R) / (4 * ONE_PLY);
             thisThread->nmpColor = us;
 
             Value v = search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
@@ -910,8 +902,9 @@ moves_loop: // When in check, search starts from here
           &&  pos.legal(move))
       {
           Value singularBeta = ttValue - 2 * depth / ONE_PLY;
+          Depth halfDepth = depth / (2 * ONE_PLY) * ONE_PLY; // ONE_PLY invariant
           ss->excludedMove = move;
-          value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, depth / 2, cutNode);
+          value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, halfDepth, cutNode);
           ss->excludedMove = MOVE_NONE;
 
           if (value < singularBeta)
@@ -931,14 +924,16 @@ moves_loop: // When in check, search starts from here
                && (pos.blockers_for_king(~us) & from_sq(move) || pos.see_ge(move)))
           extension = ONE_PLY;
 
-      // Shuffle extension
-      else if(pos.rule50_count() > 14 && ss->ply > 14 && depth < 3 * ONE_PLY && PvNode)
-          extension = ONE_PLY;
-
       // Castling extension
       else if (type_of(move) == CASTLING)
           extension = ONE_PLY;
 
+      // Passed pawn extension
+      else if (   move == ss->killers[0]
+               && pos.advanced_pawn_push(move)
+               && pos.pawn_passed(us, to_sq(move)))
+          extension = ONE_PLY;
+
       // Calculate new depth for this move
       newDepth = depth - ONE_PLY + extension;
 
@@ -959,7 +954,8 @@ moves_loop: // When in check, search starts from here
                   continue;
 
               // Reduced depth of the next LMR search
-              int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;
+              int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO);
+              lmrDepth /= ONE_PLY;
 
               // Countermoves based pruning (~20 Elo)
               if (   lmrDepth < 3 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1)
@@ -1230,8 +1226,7 @@ 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];
+    bestMove = MOVE_NONE;
     inCheck = pos.checkers();
     moveCount = 0;