Simplify IID depth formula

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index d419cd30ede15e192142b040de9caf14d8b8005c..57a5517614e67c5f9f37febb857b9d2a0b3840d5 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -134,7 +134,6 @@ namespace {
   Value DrawValue[COLOR_NB];
   HistoryStats History;
   CounterMovesHistoryStats CounterMovesHistory;
-  GainsStats Gains;
   MovesStats Countermoves;
 
   template <NodeType NT, bool SpNode>
@@ -188,7 +187,6 @@ void Search::reset () {
   TT.clear();
   History.clear();
   CounterMovesHistory.clear();
-  Gains.clear();
   Countermoves.clear();
 }
 
@@ -555,7 +553,7 @@ namespace {
         goto moves_loop;
     }
 
-    moveCount = quietCount = 0;
+    moveCount = quietCount =  ss->moveCount = 0;
     bestValue = -VALUE_INFINITE;
     ss->ply = (ss-1)->ply + 1;
 
@@ -643,7 +641,7 @@ namespace {
         }
     }
 
-    // Step 5. Evaluate the position statically and update parent's gain statistics
+    // Step 5. Evaluate the position statically
     if (inCheck)
     {
         ss->staticEval = eval = VALUE_NONE;
@@ -672,23 +670,11 @@ namespace {
     if (ss->skipEarlyPruning)
         goto moves_loop;
 
-    if (   !pos.captured_piece_type()
-        &&  ss->staticEval != VALUE_NONE
-        && (ss-1)->staticEval != VALUE_NONE
-        && (move = (ss-1)->currentMove) != MOVE_NULL
-        &&  move != MOVE_NONE
-        &&  type_of(move) == NORMAL)
-    {
-        Square to = to_sq(move);
-        Gains.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
-    }
-
     // Step 6. Razoring (skipped when in check)
     if (   !PvNode
         &&  depth < 4 * ONE_PLY
         &&  eval + razor_margin(depth) <= alpha
-        &&  ttMove == MOVE_NONE
-        && !pos.pawn_on_7th(pos.side_to_move()))
+        &&  ttMove == MOVE_NONE)
     {
         if (   depth <= ONE_PLY
             && eval + razor_margin(3 * ONE_PLY) <= alpha)
@@ -763,7 +749,7 @@ namespace {
         assert((ss-1)->currentMove != MOVE_NONE);
         assert((ss-1)->currentMove != MOVE_NULL);
 
-        MovePicker mp(pos, ttMove, History, CounterMovesHistory, pos.captured_piece_type());
+        MovePicker mp(pos, ttMove, History, CounterMovesHistory, PieceValue[MG][pos.captured_piece_type()]);
         CheckInfo ci(pos);
 
         while ((move = mp.next_move<false>()) != MOVE_NONE)
@@ -783,9 +769,9 @@ namespace {
         && !ttMove
         && (PvNode || ss->staticEval + 256 >= beta))
     {
-        Depth d = 2 * (depth - 2 * ONE_PLY) - (PvNode ? DEPTH_ZERO : depth / 2);
+        Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
         ss->skipEarlyPruning = true;
-        search<PvNode ? PV : NonPV, false>(pos, ss, alpha, beta, d / 2, true);
+        search<PvNode ? PV : NonPV, false>(pos, ss, alpha, beta, d, true);
         ss->skipEarlyPruning = false;
 
         tte = TT.probe(posKey, ttHit);
@@ -835,11 +821,11 @@ moves_loop: // When in check and at SpNode search starts from here
           if (!pos.legal(move, ci.pinned))
               continue;
 
-          moveCount = ++splitPoint->moveCount;
+          ss->moveCount = moveCount = ++splitPoint->moveCount;
           splitPoint->spinlock.release();
       }
       else
-          ++moveCount;
+          ss->moveCount = ++moveCount;
 
       if (RootNode)
       {
@@ -915,8 +901,7 @@ moves_loop: // When in check and at SpNode search starts from here
           // Futility pruning: parent node
           if (predictedDepth < 7 * ONE_PLY)
           {
-              futilityValue =  ss->staticEval + futility_margin(predictedDepth)
-                             + 128 + Gains[pos.moved_piece(move)][to_sq(move)];
+              futilityValue = ss->staticEval + futility_margin(predictedDepth) + 256;
 
               if (futilityValue <= alpha)
               {
@@ -948,7 +933,7 @@ moves_loop: // When in check and at SpNode search starts from here
       // Check for legality just before making the move
       if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
       {
-          moveCount--;
+          ss->moveCount = --moveCount;
           continue;
       }
 
@@ -973,7 +958,9 @@ moves_loop: // When in check and at SpNode search starts from here
                                         [pos.piece_on(to_sq(move))][to_sq(move)] <= VALUE_ZERO))
               ss->reduction += ONE_PLY;
 
-          if (move == countermove)
+          if (   History[pos.piece_on(to_sq(move))][to_sq(move)] > VALUE_ZERO
+              && CounterMovesHistory[pos.piece_on(prevMoveSq)][prevMoveSq]
+                                    [pos.piece_on(to_sq(move))][to_sq(move)] > VALUE_ZERO)
               ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
 
           // Decrease reduction for moves that escape a capture
@@ -989,13 +976,6 @@ moves_loop: // When in check and at SpNode search starts from here
 
           value = -search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, d, true);
 
-          // Re-search at intermediate depth if reduction is very high
-          if (value > alpha && ss->reduction >= 4 * ONE_PLY)
-          {
-              Depth d2 = std::max(newDepth - 2 * ONE_PLY, ONE_PLY);
-              value = -search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, d2, true);
-          }
-
           doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
           ss->reduction = DEPTH_ZERO;
       }
@@ -1445,8 +1425,8 @@ moves_loop: // When in check and at SpNode search starts from here
             cmh.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
     }
 
-    // Extra penalty for TT move in previous ply when it gets refuted
-    if (is_ok((ss-2)->currentMove) && (ss-1)->currentMove == (ss-1)->ttMove)
+    // Extra penalty for PV move in previous ply when it gets refuted
+    if (is_ok((ss-2)->currentMove) && (ss-1)->moveCount == 1 && !pos.captured_piece_type())
     {
         Square prevPrevSq = to_sq((ss-2)->currentMove);
         HistoryStats& ttMoveCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq];