Simplified shuffle extension version (#2121)

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 7fffae263008e0175cc553844b0adc7137536fd0..44347f79f8b85ec1aee88b579c65c6f9d9b48908 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -67,10 +67,10 @@ namespace {
   }
 
   // Reductions lookup table, initialized at startup
-  int Reductions[64]; // [depth or moveNumber]
+  int Reductions[MAX_MOVES]; // [depth or moveNumber]
 
   template <bool PvNode> Depth reduction(bool i, Depth d, int mn) {
-    int r = Reductions[std::min(d / ONE_PLY, 63)] * Reductions[std::min(mn, 63)] / 1024;
+    int r = Reductions[d / ONE_PLY] * Reductions[mn] / 1024;
     return ((r + 512) / 1024 + (!i && r > 1024) - PvNode) * ONE_PLY;
   }
 
@@ -147,7 +147,7 @@ namespace {
 
 void Search::init() {
 
-  for (int i = 1; i < 64; ++i)
+  for (int i = 1; i < MAX_MOVES; ++i)
       Reductions[i] = int(1024 * std::log(i) / std::sqrt(1.95));
 }
 
@@ -584,8 +584,7 @@ namespace {
     assert(0 <= ss->ply && ss->ply < MAX_PLY);
 
     (ss+1)->ply = ss->ply + 1;
-    ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
-    ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
+    (ss+1)->excludedMove = bestMove = MOVE_NONE;
     (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
     Square prevSq = to_sq((ss-1)->currentMove);
 
@@ -607,15 +606,6 @@ 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
@@ -632,9 +622,8 @@ 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
@@ -934,14 +923,17 @@ 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;
 
+      // Shuffle extension
+      else if (   PvNode
+               && pos.rule50_count() > 18
+               && depth < 3 * ONE_PLY
+               && ss->ply < 3 * thisThread->rootDepth / ONE_PLY) // To avoid too deep searches
+          extension = ONE_PLY;
+
       // Passed pawn extension
       else if (   move == ss->killers[0]
                && pos.advanced_pawn_push(move)
@@ -1240,8 +1232,7 @@ 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;