LMR Capture Tweak

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 744bb7886c5a2f06749faf41e23e68445f25e32c..7c9c1b6936bfc9220f0b7be372e969a529ee2fd8 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -547,6 +547,7 @@ namespace {
     // Step 1. Initialize node
     Thread* thisThread = pos.this_thread();
     inCheck = pos.checkers();
+    Color us = pos.side_to_move();
     moveCount = captureCount = quietCount = ss->moveCount = 0;
     bestValue = -VALUE_INFINITE;
     maxValue = VALUE_INFINITE;
@@ -577,6 +578,17 @@ namespace {
         beta = std::min(mate_in(ss->ply+1), beta);
         if (alpha >= beta)
             return alpha;
+
+        // Check if there exists a move which draws by repetition, or an alternative
+        // earlier move to this position.
+        if (   pos.rule50_count() >= 3
+            && alpha < VALUE_DRAW
+            && pos.has_game_cycle(ss->ply))
+        {
+            alpha = VALUE_DRAW;
+            if (alpha >= beta)
+                return alpha;
+        }
     }
 
     assert(0 <= ss->ply && ss->ply < MAX_PLY);
@@ -628,7 +640,7 @@ namespace {
             else if (!pos.capture_or_promotion(ttMove))
             {
                 int penalty = -stat_bonus(depth);
-                thisThread->mainHistory[pos.side_to_move()][from_to(ttMove)] << penalty;
+                thisThread->mainHistory[us][from_to(ttMove)] << penalty;
                 update_continuation_histories(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty);
             }
         }
@@ -682,12 +694,12 @@ namespace {
         }
     }
 
-    // Step 6. Evaluate the position statically
+    // Step 6. Static evaluation of the position
     if (inCheck)
     {
         ss->staticEval = eval = VALUE_NONE;
         improving = false;
-        goto moves_loop;
+        goto moves_loop;  // Skip early pruning when in check
     }
     else if (ttHit)
     {
@@ -710,13 +722,7 @@ namespace {
                   ss->staticEval, TT.generation());
     }
 
-    improving =   ss->staticEval >= (ss-2)->staticEval
-               ||(ss-2)->staticEval == VALUE_NONE;
-
-    if (ss->excludedMove || !pos.non_pawn_material(pos.side_to_move()))
-        goto moves_loop;
-
-    // Step 7. Razoring (skipped when in check, ~2 Elo)
+    // Step 7. Razoring (~2 Elo)
     if (  !PvNode
         && depth < 3 * ONE_PLY
         && eval <= alpha - RazorMargin[depth / ONE_PLY])
@@ -727,7 +733,10 @@ namespace {
             return v;
     }
 
-    // Step 8. Futility pruning: child node (skipped when in check, ~30 Elo)
+    improving =   ss->staticEval >= (ss-2)->staticEval
+               || (ss-2)->staticEval == VALUE_NONE;
+
+    // Step 8. Futility pruning: child node (~30 Elo)
     if (   !rootNode
         &&  depth < 7 * ONE_PLY
         &&  eval - futility_margin(depth, improving) >= beta
@@ -737,10 +746,12 @@ namespace {
     // Step 9. Null move search with verification search (~40 Elo)
     if (   !PvNode
         && (ss-1)->currentMove != MOVE_NULL
-        && (ss-1)->statScore < 30000
+        && (ss-1)->statScore < 22500
         &&  eval >= beta
         &&  ss->staticEval >= beta - 36 * depth / ONE_PLY + 225
-        && (ss->ply >= thisThread->nmp_ply || ss->ply % 2 != thisThread->nmp_odd))
+        && !excludedMove
+        &&  pos.non_pawn_material(us)
+        && (ss->ply > thisThread->nmp_min_ply || us != thisThread->nmp_color))
     {
         assert(eval - beta >= 0);
 
@@ -762,24 +773,26 @@ namespace {
             if (nullValue >= VALUE_MATE_IN_MAX_PLY)
                 nullValue = beta;
 
-            if (abs(beta) < VALUE_KNOWN_WIN && (depth < 12 * ONE_PLY || thisThread->nmp_ply))
+            if (thisThread->nmp_min_ply || (abs(beta) < VALUE_KNOWN_WIN && depth < 12 * ONE_PLY))
                 return nullValue;
 
-            // Do verification search at high depths. Disable null move pruning
-            // for side to move for the first part of the remaining search tree.
-            thisThread->nmp_ply = ss->ply + 3 * (depth-R) / 4;
-            thisThread->nmp_odd = ss->ply % 2;
+            assert(!thisThread->nmp_min_ply); // Recursive verification is not allowed
+
+            // Do verification search at high depths, with null move pruning disabled
+            // for us, until ply exceeds nmp_min_ply.
+            thisThread->nmp_min_ply = ss->ply + 3 * (depth-R) / 4 - 1;
+            thisThread->nmp_color = us;
 
             Value v = search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
 
-            thisThread->nmp_odd = thisThread->nmp_ply = 0;
+            thisThread->nmp_min_ply = 0;
 
             if (v >= beta)
                 return nullValue;
         }
     }
 
-    // Step 10. ProbCut (skipped when in check, ~10 Elo)
+    // Step 10. ProbCut (~10 Elo)
     // If we have a good enough capture and a reduced search returns a value
     // much above beta, we can (almost) safely prune the previous move.
     if (   !PvNode
@@ -817,7 +830,7 @@ namespace {
             }
     }
 
-    // Step 11. Internal iterative deepening (skipped when in check, ~2 Elo)
+    // Step 11. Internal iterative deepening (~2 Elo)
     if (    depth >= 8 * ONE_PLY
         && !ttMove)
     {
@@ -913,7 +926,7 @@ moves_loop: // When in check, search starts from here
 
       // Step 14. Pruning at shallow depth (~170 Elo)
       if (  !rootNode
-          && pos.non_pawn_material(pos.side_to_move())
+          && pos.non_pawn_material(us)
           && bestValue > VALUE_MATED_IN_MAX_PLY)
       {
           if (   !captureOrPromotion
@@ -982,7 +995,14 @@ moves_loop: // When in check, search starts from here
           Depth r = reduction<PvNode>(improving, depth, moveCount);
 
           if (captureOrPromotion) // (~5 Elo)
+          {
+              //Increase reduction by comparing opponent's stat score
+              if (   (ss-1)->statScore >= 0 
+                  && thisThread->captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 0)
+                  r += ONE_PLY;
+                            
               r -= r ? ONE_PLY : DEPTH_ZERO;
+          }
           else
           {
               // Decrease reduction if opponent's move count is high (~5 Elo)
@@ -1008,7 +1028,7 @@ moves_loop: // When in check, search starts from here
                        && !pos.see_ge(make_move(to_sq(move), from_sq(move))))
                   r -= 2 * ONE_PLY;
 
-              ss->statScore =  thisThread->mainHistory[~pos.side_to_move()][from_to(move)]
+              ss->statScore =  thisThread->mainHistory[us][from_to(move)]
                              + (*contHist[0])[movedPiece][to_sq(move)]
                              + (*contHist[1])[movedPiece][to_sq(move)]
                              + (*contHist[3])[movedPiece][to_sq(move)]
@@ -1107,7 +1127,7 @@ moves_loop: // When in check, search starts from here
               else
               {
                   assert(value >= beta); // Fail high
-                  ss->statScore = std::max(ss->statScore, 0);
+                  ss->statScore = 0;
                   break;
               }
           }
@@ -1154,7 +1174,7 @@ moves_loop: // When in check, search starts from here
             update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
     }
     // Bonus for prior countermove that caused the fail low
-    else if (    depth >= 3 * ONE_PLY
+    else if (   (depth >= 3 * ONE_PLY || PvNode)
              && !pos.captured_piece()
              && is_ok((ss-1)->currentMove))
         update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));