Simplify reductions on singular extension

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 6cf999380b6001e9069dcd154a812cc6e4827d3d..c70fbf60cd6c1efa9b9599d31c898cfd116960d7 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -334,7 +334,7 @@ void Thread::search() {
 
   std::memset(ss-7, 0, 10 * sizeof(Stack));
   for (int i = 7; i > 0; i--)
-      (ss-i)->continuationHistory = &this->continuationHistory[0][NO_PIECE][0]; // Use as a sentinel
+      (ss-i)->continuationHistory = &this->continuationHistory[0][0][NO_PIECE][0]; // Use as a sentinel
 
   ss->pv = pv;
 
@@ -412,7 +412,7 @@ void Thread::search() {
           if (rootDepth >= 4)
           {
               Value previousScore = rootMoves[pvIdx].previousScore;
-              delta = Value(23);
+              delta = Value(21 + abs(previousScore) / 128);
               alpha = std::max(previousScore - delta,-VALUE_INFINITE);
               beta  = std::min(previousScore + delta, VALUE_INFINITE);
 
@@ -595,16 +595,16 @@ namespace {
     Depth extension, newDepth;
     Value bestValue, value, ttValue, eval, maxValue;
     bool ttHit, ttPv, inCheck, givesCheck, improving, doLMR, priorCapture;
-    bool captureOrPromotion, doFullDepthSearch, moveCountPruning, ttCapture;
+    bool captureOrPromotion, doFullDepthSearch, moveCountPruning, ttCapture, singularLMR;
     Piece movedPiece;
-    int moveCount, captureCount, quietCount, singularLMR;
+    int moveCount, captureCount, quietCount;
 
     // Step 1. Initialize node
     Thread* thisThread = pos.this_thread();
     inCheck = pos.checkers();
     priorCapture = pos.captured_piece();
     Color us = pos.side_to_move();
-    moveCount = captureCount = quietCount = singularLMR = ss->moveCount = 0;
+    moveCount = captureCount = quietCount = ss->moveCount = 0;
     bestValue = -VALUE_INFINITE;
     maxValue = VALUE_INFINITE;
 
@@ -816,7 +816,7 @@ namespace {
         Depth R = (835 + 70 * depth) / 256 + std::min(int(eval - beta) / 185, 3);
 
         ss->currentMove = MOVE_NULL;
-        ss->continuationHistory = &thisThread->continuationHistory[0][NO_PIECE][0];
+        ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0];
 
         pos.do_null_move(st);
 
@@ -864,12 +864,17 @@ namespace {
                && probCutCount < 2 + 2 * cutNode)
             if (move != excludedMove && pos.legal(move))
             {
+                assert(pos.capture_or_promotion(move));
+                assert(depth >= 5);
+
+                captureOrPromotion = true;
                 probCutCount++;
 
                 ss->currentMove = move;
-                ss->continuationHistory = &thisThread->continuationHistory[priorCapture][pos.moved_piece(move)][to_sq(move)];
-
-                assert(depth >= 5);
+                ss->continuationHistory = &thisThread->continuationHistory[inCheck]
+                                                                          [captureOrPromotion]
+                                                                          [pos.moved_piece(move)]
+                                                                          [to_sq(move)];
 
                 pos.do_move(move, st);
 
@@ -900,8 +905,8 @@ namespace {
 moves_loop: // When in check, search starts from here
 
     const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
-                                          nullptr, (ss-4)->continuationHistory,
-                                          nullptr, (ss-6)->continuationHistory };
+                                          nullptr                   , (ss-4)->continuationHistory,
+                                          nullptr                   , (ss-6)->continuationHistory };
 
     Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
 
@@ -911,8 +916,8 @@ moves_loop: // When in check, search starts from here
                                       countermove,
                                       ss->killers);
 
-    value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
-    moveCountPruning = false;
+    value = bestValue;
+    singularLMR = moveCountPruning = false;
     ttCapture = ttMove && pos.capture_or_promotion(ttMove);
 
     // Mark this node as being searched
@@ -975,10 +980,7 @@ moves_loop: // When in check, search starts from here
           if (value < singularBeta)
           {
               extension = 1;
-              singularLMR++;
-
-              if (value < singularBeta - std::min(4 * depth, 36))
-                  singularLMR++;
+              singularLMR = true;
           }
 
           // Multi-cut pruning
@@ -1068,7 +1070,10 @@ moves_loop: // When in check, search starts from here
 
       // Update the current move (this must be done after singular extension search)
       ss->currentMove = move;
-      ss->continuationHistory = &thisThread->continuationHistory[priorCapture][movedPiece][to_sq(move)];
+      ss->continuationHistory = &thisThread->continuationHistory[inCheck]
+                                                                [captureOrPromotion]
+                                                                [movedPiece]
+                                                                [to_sq(move)];
 
       // Step 15. Make the move
       pos.do_move(move, st, givesCheck);
@@ -1098,7 +1103,8 @@ moves_loop: // When in check, search starts from here
               r--;
 
           // Decrease reduction if ttMove has been singularly extended
-          r -= singularLMR;
+          if (singularLMR)
+              r -= 2;
 
           if (!captureOrPromotion)
           {
@@ -1323,7 +1329,7 @@ moves_loop: // When in check, search starts from here
     Move ttMove, move, bestMove;
     Depth ttDepth;
     Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
-    bool ttHit, pvHit, inCheck, givesCheck, evasionPrunable, priorCapture;
+    bool ttHit, pvHit, inCheck, givesCheck, captureOrPromotion, evasionPrunable;
     int moveCount;
 
     if (PvNode)
@@ -1337,7 +1343,6 @@ moves_loop: // When in check, search starts from here
     (ss+1)->ply = ss->ply + 1;
     bestMove = MOVE_NONE;
     inCheck = pos.checkers();
-    priorCapture = pos.captured_piece();
     moveCount = 0;
 
     // Check for an immediate draw or maximum ply reached
@@ -1408,8 +1413,8 @@ moves_loop: // When in check, search starts from here
     }
 
     const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
-                                          nullptr, (ss-4)->continuationHistory,
-                                          nullptr, (ss-6)->continuationHistory };
+                                          nullptr                   , (ss-4)->continuationHistory,
+                                          nullptr                   , (ss-6)->continuationHistory };
 
     // Initialize a MovePicker object for the current position, and prepare
     // to search the moves. Because the depth is <= 0 here, only captures,
@@ -1426,6 +1431,7 @@ moves_loop: // When in check, search starts from here
       assert(is_ok(move));
 
       givesCheck = pos.gives_check(move);
+      captureOrPromotion = pos.capture_or_promotion(move);
 
       moveCount++;
 
@@ -1475,7 +1481,10 @@ moves_loop: // When in check, search starts from here
       }
 
       ss->currentMove = move;
-      ss->continuationHistory = &thisThread->continuationHistory[priorCapture][pos.moved_piece(move)][to_sq(move)];
+      ss->continuationHistory = &thisThread->continuationHistory[inCheck]
+                                                                [captureOrPromotion]
+                                                                [pos.moved_piece(move)]
+                                                                [to_sq(move)];
 
       // Make and search the move
       pos.do_move(move, st, givesCheck);