Shuffle detection #2064

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 7043e49dbe2bd8cac54fee35c5365baad1685cd0..cfa737dbd6773bf72cd460a19eb71f9b143232e1 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -18,7 +18,6 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#include <algorithm>
 #include <cassert>
 #include <cmath>
 #include <cstring>   // For std::memset
@@ -116,13 +115,6 @@ namespace {
   void update_quiet_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietCount, int bonus);
   void update_capture_stats(const Position& pos, Move move, Move* captures, int captureCount, int bonus);
 
-  inline bool gives_check(const Position& pos, Move move) {
-    Color us = pos.side_to_move();
-    return  type_of(move) == NORMAL && !(pos.blockers_for_king(~us) & pos.pieces(us))
-          ? pos.check_squares(type_of(pos.moved_piece(move))) & to_sq(move)
-          : pos.gives_check(move);
-  }
-
   // perft() is our utility to verify move generation. All the leaf nodes up
   // to the given depth are generated and counted, and the sum is returned.
   template<bool Root>
@@ -468,7 +460,7 @@ void Thread::search() {
           && !mainThread->stopOnPonderhit)
       {
           double fallingEval = (306 + 9 * (mainThread->previousScore - bestValue)) / 581.0;
-          fallingEval        = std::max(0.5, std::min(1.5, fallingEval));
+          fallingEval = clamp(fallingEval, 0.5, 1.5);
 
           // If the bestMove is stable over several iterations, reduce time accordingly
           timeReduction = lastBestMoveDepth + 10 * ONE_PLY < completedDepth ? 1.95 : 1.0;
@@ -610,6 +602,15 @@ 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
@@ -887,7 +888,7 @@ moves_loop: // When in check, search starts from here
       extension = DEPTH_ZERO;
       captureOrPromotion = pos.capture_or_promotion(move);
       movedPiece = pos.moved_piece(move);
-      givesCheck = gives_check(pos, move);
+      givesCheck = pos.gives_check(move);
 
       // Step 13. Extensions (~70 Elo)
 
@@ -928,6 +929,10 @@ 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;
@@ -1313,7 +1318,7 @@ moves_loop: // When in check, search starts from here
     {
       assert(is_ok(move));
 
-      givesCheck = gives_check(pos, move);
+      givesCheck = pos.gives_check(move);
 
       moveCount++;