X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=b7e04fad2b22484ec2237e9d1f3ecdd81aece60a;hp=fe9b446e42d61b15b98212b3d05fa237e0701543;hb=d2acdac1012cfbd8563fbe70157b2adbb05b2002;hpb=eb6d7f537d214c4dc8bde7d4fdc2aaead47dd3c3

diff --git a/src/search.cpp b/src/search.cpp
index fe9b446e..b7e04fad 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -577,7 +577,7 @@ namespace {
     Move ttMove, move, excludedMove, bestMove;
     Depth extension, newDepth;
     Value bestValue, value, ttValue, eval, maxValue, pureStaticEval;
-    bool ttHit, inCheck, givesCheck, improving;
+    bool ttHit, pvHit, inCheck, givesCheck, improving;
     bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture, pvExact;
     Piece movedPiece;
     int moveCount, captureCount, quietCount;
@@ -643,6 +643,7 @@ namespace {
     ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
     ttMove =  rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0]
             : ttHit    ? tte->move() : MOVE_NONE;
+    pvHit = ttHit ? tte->pv_hit() : false;
 
     // At non-PV nodes we check for an early TT cutoff
     if (  !PvNode
@@ -676,6 +677,11 @@ namespace {
         return ttValue;
     }
 
+    if (   depth > 6 * ONE_PLY
+        && !excludedMove
+        && PvNode)
+        pvHit = true;
+
     // Step 5. Tablebases probe
     if (!rootNode && TB::Cardinality)
     {
@@ -709,7 +715,7 @@ namespace {
                 if (    b == BOUND_EXACT
                     || (b == BOUND_LOWER ? value >= beta : value <= alpha))
                 {
-                    tte->save(posKey, value_to_tt(value, ss->ply), b,
+                    tte->save(posKey, value_to_tt(value, ss->ply), pvHit, b,
                               std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
                               MOVE_NONE, VALUE_NONE);
 
@@ -760,7 +766,7 @@ namespace {
         else
             ss->staticEval = eval = pureStaticEval = -(ss-1)->staticEval + 2 * Eval::Tempo;
 
-        tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, pureStaticEval);
+        tte->save(posKey, VALUE_NONE, pvHit, BOUND_NONE, DEPTH_NONE, MOVE_NONE, pureStaticEval);
     }
 
     // Step 7. Razoring (~2 Elo)
@@ -875,6 +881,7 @@ namespace {
         tte = TT.probe(posKey, ttHit);
         ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
         ttMove = ttHit ? tte->move() : MOVE_NONE;
+        pvHit = ttHit ? tte->pv_hit() : false;
     }
 
 moves_loop: // When in check, search starts from here
@@ -943,13 +950,21 @@ moves_loop: // When in check, search starts from here
           &&  tte->depth() >= depth - 3 * ONE_PLY
           &&  pos.legal(move))
       {
-          Value reducedBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
+          Value singularBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
           ss->excludedMove = move;
-          value = search<NonPV>(pos, ss, reducedBeta - 1, reducedBeta, depth / 2, cutNode);
+          value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, depth / 2, cutNode);
           ss->excludedMove = MOVE_NONE;
 
-          if (value < reducedBeta)
+          if (value < singularBeta)
               extension = ONE_PLY;
+
+          // Multi-cut pruning
+          // Our ttMove is assumed to fail high, and now we failed high also on a reduced
+          // search without the ttMove. So we assume this expected Cut-node is not singular,
+          // that is multiple moves fail high, and we can prune the whole subtree by returning
+          // the hard beta bound.
+          else if (cutNode && singularBeta > beta)
+              return beta;
       }
       else if (    givesCheck // Check extension (~2 Elo)
                &&  pos.see_ge(move))
@@ -1027,6 +1042,10 @@ moves_loop: // When in check, search starts from here
       {
           Depth r = reduction<PvNode>(improving, depth, moveCount);
 
+          // Decrease reduction if position is or has been on the PV
+          if (pvHit && !PvNode)
+              r -= ONE_PLY;
+
           // Decrease reduction if opponent's move count is high (~10 Elo)
           if ((ss-1)->moveCount > 15)
               r -= ONE_PLY;
@@ -1209,7 +1228,7 @@ moves_loop: // When in check, search starts from here
         bestValue = std::min(bestValue, maxValue);
 
     if (!excludedMove)
-        tte->save(posKey, value_to_tt(bestValue, ss->ply),
+        tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit,
                   bestValue >= beta ? BOUND_LOWER :
                   PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
                   depth, bestMove, pureStaticEval);
@@ -1239,7 +1258,7 @@ moves_loop: // When in check, search starts from here
     Move ttMove, move, bestMove;
     Depth ttDepth;
     Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
-    bool ttHit, inCheck, givesCheck, evasionPrunable;
+    bool ttHit, pvHit, inCheck, givesCheck, evasionPrunable;
     int moveCount;
 
     if (PvNode)
@@ -1273,6 +1292,7 @@ moves_loop: // When in check, search starts from here
     tte = TT.probe(posKey, ttHit);
     ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
     ttMove = ttHit ? tte->move() : MOVE_NONE;
+    pvHit = ttHit ? tte->pv_hit() : false;
 
     if (  !PvNode
         && ttHit
@@ -1310,7 +1330,7 @@ moves_loop: // When in check, search starts from here
         if (bestValue >= beta)
         {
             if (!ttHit)
-                tte->save(posKey, value_to_tt(bestValue, ss->ply), BOUND_LOWER,
+                tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit, BOUND_LOWER,
                           DEPTH_NONE, MOVE_NONE, ss->staticEval);
 
             return bestValue;
@@ -1421,7 +1441,7 @@ moves_loop: // When in check, search starts from here
     if (inCheck && bestValue == -VALUE_INFINITE)
         return mated_in(ss->ply); // Plies to mate from the root
 
-    tte->save(posKey, value_to_tt(bestValue, ss->ply),
+    tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit,
               bestValue >= beta ? BOUND_LOWER :
               PvNode && bestValue > oldAlpha  ? BOUND_EXACT : BOUND_UPPER,
               ttDepth, bestMove, ss->staticEval);