Revert "Allowing singular extension in mate positions"

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index e75d085b08051f7082d3d76fb8ec670bf01125fb..9165468ae0590e82740f53c7296f7aef9f7ce643 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -71,12 +71,16 @@ namespace {
     return Value((175 - 50 * improving) * d / ONE_PLY);
   }
 
-  // Futility and reductions lookup tables, initialized at startup
-  int FutilityMoveCounts[2][16]; // [improving][depth]
-  int Reductions[2][64][64];  // [improving][depth][moveNumber]
+  // Reductions lookup table, initialized at startup
+  int Reductions[64]; // [depth or moveNumber]
 
   template <bool PvNode> Depth reduction(bool i, Depth d, int mn) {
-    return (Reductions[i][std::min(d / ONE_PLY, 63)][std::min(mn, 63)] - PvNode) * ONE_PLY;
+    int r = Reductions[std::min(d / ONE_PLY, 63)] * Reductions[std::min(mn, 63)] / 1024;
+    return ((r + 512) / 1024 + (!i && r > 1024) - PvNode) * ONE_PLY;
+  }
+
+  constexpr int futility_move_count(bool improving, int depth) {
+    return (5 + depth * depth) * (1 + improving) / 2;
   }
 
   // History and stats update bonus, based on depth
@@ -156,24 +160,8 @@ namespace {
 
 void Search::init() {
 
-  for (int imp = 0; imp <= 1; ++imp)
-      for (int d = 1; d < 64; ++d)
-          for (int mc = 1; mc < 64; ++mc)
-          {
-              double r = log(d) * log(mc) / 1.95;
-
-              Reductions[imp][d][mc] = std::round(r);
-
-              // Increase reduction for non-PV nodes when eval is not improving
-              if (!imp && r > 1.0)
-                Reductions[imp][d][mc]++;
-          }
-
-  for (int d = 0; d < 16; ++d)
-  {
-      FutilityMoveCounts[0][d] = int(2.4 + 0.74 * pow(d, 1.78));
-      FutilityMoveCounts[1][d] = int(5.0 + 1.00 * pow(d, 2.00));
-  }
+  for (int i = 1; i < 64; ++i)
+      Reductions[i] = int(1024 * std::log(i) / std::sqrt(1.95));
 }
 
 
@@ -845,7 +833,7 @@ namespace {
                 // Perform a preliminary qsearch to verify that the move holds
                 value = -qsearch<NonPV>(pos, ss+1, -raisedBeta, -raisedBeta+1);
 
-                // If the qsearch held perform the regular search
+                // If the qsearch held, perform the regular search
                 if (value >= raisedBeta)
                     value = -search<NonPV>(pos, ss+1, -raisedBeta, -raisedBeta+1, depth - 4 * ONE_PLY, !cutNode);
 
@@ -926,12 +914,13 @@ moves_loop: // When in check, search starts from here
           &&  move == ttMove
           && !rootNode
           && !excludedMove // Avoid recursive singular search
-          &&  ttValue != VALUE_NONE
+      /*  &&  ttValue != VALUE_NONE Already implicit in the next condition */
+          &&  abs(ttValue) < VALUE_KNOWN_WIN
           && (tte->bound() & BOUND_LOWER)
           &&  tte->depth() >= depth - 3 * ONE_PLY
           &&  pos.legal(move))
       {
-          Value singularBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
+          Value singularBeta = ttValue - 2 * depth / ONE_PLY;
           ss->excludedMove = move;
           value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, depth / 2, cutNode);
           ss->excludedMove = MOVE_NONE;
@@ -966,8 +955,7 @@ moves_loop: // When in check, search starts from here
           && bestValue > VALUE_MATED_IN_MAX_PLY)
       {
           // Skip quiet moves if movecount exceeds our FutilityMoveCount threshold
-          moveCountPruning = depth < 16 * ONE_PLY
-                          && moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY];
+          moveCountPruning = moveCount >= futility_move_count(improving,depth / ONE_PLY);
 
           if (   !captureOrPromotion
               && !givesCheck