X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=src%2Fsearch.cpp;h=cae91018931b8a186084577498b6eb1a35b2b2dc;hb=0e32287af470dee230a30d9f513682c3ce798668;hp=a745d3bfdd0ed16933a9d53dcd8f7ab830637940;hpb=6d85f43e26cb8632337e67cea5ef88bab78121f3;p=stockfish

diff --git a/src/search.cpp b/src/search.cpp
index a745d3bf..cae91018 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -525,6 +525,10 @@ namespace {
     constexpr bool PvNode = nodeType != NonPV;
     constexpr bool rootNode = nodeType == Root;
 
+    // Dive into quiescence search when the depth reaches zero
+    if (depth <= 0)
+        return qsearch<PvNode ? PV : NonPV>(pos, ss, alpha, beta);
+
     // Check if we have an upcoming move that draws by repetition, or
     // if the opponent had an alternative move earlier to this position.
     if (   !rootNode
@@ -536,10 +540,6 @@ namespace {
             return alpha;
     }
 
-    // Dive into quiescence search when the depth reaches zero
-    if (depth <= 0)
-        return qsearch<PvNode ? PV : NonPV>(pos, ss, alpha, beta);
-
     assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
     assert(PvNode || (alpha == beta - 1));
     assert(0 < depth && depth < MAX_PLY);
@@ -928,7 +928,8 @@ moves_loop: // When in check, search starts here
     moveCountPruning = singularQuietLMR = false;
 
     // Indicate PvNodes that will probably fail low if the node was searched
-    // at a depth equal to or greater than the current depth, and the result of this search was a fail low.
+    // at a depth equal to or greater than the current depth, and the result
+    // of this search was a fail low.
     bool likelyFailLow =    PvNode
                          && ttMove
                          && (tte->bound() & BOUND_UPPER)
@@ -1039,10 +1040,10 @@ moves_loop: // When in check, search starts here
           // Singular extension search (~94 Elo). If all moves but one fail low on a
           // search of (alpha-s, beta-s), and just one fails high on (alpha, beta),
           // then that move is singular and should be extended. To verify this we do
-          // a reduced search on all the other moves but the ttMove and if the
-          // result is lower than ttValue minus a margin, then we will extend the ttMove.
-          // Depth margin and singularBeta margin are known for having non-linear scaling.
-          // Their values are optimized to time controls of 180+1.8 and longer
+          // a reduced search on all the other moves but the ttMove and if the result
+          // is lower than ttValue minus a margin, then we will extend the ttMove. Note
+          // that depth margin and singularBeta margin are known for having non-linear
+          // scaling. Their values are optimized to time controls of 180+1.8 and longer
           // so changing them requires tests at this type of time controls.
           if (   !rootNode
               &&  depth >= 4 - (thisThread->completedDepth > 22) + 2 * (PvNode && tte->is_pv())
@@ -1076,10 +1077,10 @@ moves_loop: // When in check, search starts here
               }
 
               // 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 multiple moves fail high, and we can prune the whole subtree by returning
-              // a softbound.
+              // 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 multiple moves fail high, and we can prune the
+              // whole subtree by returning a softbound.
               else if (singularBeta >= beta)
                   return singularBeta;
 
@@ -1126,8 +1127,7 @@ moves_loop: // When in check, search starts here
       // Step 16. Make the move
       pos.do_move(move, st, givesCheck);
 
-      // Decrease reduction if position is or has been on the PV
-      // and node is not likely to fail low. (~3 Elo)
+      // Decrease reduction if position is or has been on the PV and not likely to fail low. (~3 Elo)
       // Decrease further on cutNodes. (~1 Elo)
       if (   ss->ttPv
           && !likelyFailLow)
@@ -1162,6 +1162,7 @@ moves_loop: // When in check, search starts here
       if ((ss+1)->cutoffCnt > 3)
           r++;
 
+      // Decrease reduction for first generated move (ttMove)
       else if (move == ttMove)
           r--;
 
@@ -1406,8 +1407,7 @@ moves_loop: // When in check, search starts here
 
     // Check if we have an upcoming move that draws by repetition, or
     // if the opponent had an alternative move earlier to this position.
-    if (   depth < 0
-        && alpha < VALUE_DRAW
+    if (   alpha < VALUE_DRAW
         && pos.has_game_cycle(ss->ply))
     {
         alpha = value_draw(pos.this_thread());
@@ -1549,17 +1549,29 @@ moves_loop: // When in check, search starts here
 
                 futilityValue = futilityBase + PieceValue[pos.piece_on(to_sq(move))];
 
+                // If static eval + value of piece we are going to capture is much lower
+                // than alpha we can prune this move
                 if (futilityValue <= alpha)
                 {
                     bestValue = std::max(bestValue, futilityValue);
                     continue;
                 }
 
+                // If static eval is much lower than alpha and move is not winning material
+                // we can prune this move
                 if (futilityBase <= alpha && !pos.see_ge(move, VALUE_ZERO + 1))
                 {
                     bestValue = std::max(bestValue, futilityBase);
                     continue;
                 }
+
+                // If static exchange evaluation is much worse than what is needed to not
+                // fall below alpha we can prune this move
+                if (futilityBase > alpha && !pos.see_ge(move, (alpha - futilityBase) * 4))
+                {
+                    bestValue = alpha;
+                    continue;
+                }
             }
 
             // We prune after the second quiet check evasion move, where being 'in check' is