Simplified shuffle extension version (#2121)

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 645b1f9cb0b80b6395717733e6b9b978a2565af0..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);
 
@@ -623,9 +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
@@ -929,6 +927,13 @@ moves_loop: // When in check, search starts from here
       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)
@@ -1227,8 +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;