Refine SEE threshold for capture pruning.

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 7b7737ea9fd2a946303a66b0af53d8235a30a766..f0783363e79766fc682dabbf42fc4d0d0cda9469 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -72,6 +72,16 @@ namespace {
     return Value((175 - 50 * improving) * d / ONE_PLY);
   }
 
+  // Margin for pruning capturing moves: almost linear in depth
+  constexpr int CapturePruneMargin[] = { 0,
+                                         1 * PawnValueEg * 1055 / 1000,
+                                         2 * PawnValueEg * 1042 / 1000,
+                                         3 * PawnValueEg * 963  / 1000,
+                                         4 * PawnValueEg * 1038 / 1000,
+                                         5 * PawnValueEg * 950  / 1000,
+                                         6 * PawnValueEg * 930  / 1000
+                                       };
+
   // Futility and reductions lookup tables, initialized at startup
   int FutilityMoveCounts[2][16]; // [improving][depth]
   int Reductions[2][2][64][64];  // [pv][improving][depth][moveNumber]
@@ -160,7 +170,7 @@ void Search::init() {
               Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - 1, 0);
 
               // Increase reduction for non-PV nodes when eval is not improving
-              if (!imp && Reductions[NonPV][imp][d][mc] >= 2)
+              if (!imp && r > 1.0)
                 Reductions[NonPV][imp][d][mc]++;
           }
 
@@ -309,8 +319,8 @@ void Thread::search() {
   multiPV = std::min(multiPV, rootMoves.size());
 
   int ct = Options["Contempt"] * PawnValueEg / 100; // From centipawns
-  Eval::Contempt = (us == WHITE ?  make_score(ct, ct / 2)
-                                : -make_score(ct, ct / 2));
+  contempt = (us == WHITE ?  make_score(ct, ct / 2)
+                          : -make_score(ct, ct / 2));
 
   // Iterative deepening loop until requested to stop or the target depth is reached
   while (   (rootDepth += ONE_PLY) < DEPTH_MAX
@@ -353,8 +363,8 @@ void Thread::search() {
               // Adjust contempt based on root move's previousScore (dynamic contempt)
               ct += int(std::round(48 * atan(float(previousScore) / 128)));
 
-              Eval::Contempt = (us == WHITE ?  make_score(ct, ct / 2)
-                                            : -make_score(ct, ct / 2));
+              contempt = (us == WHITE ?  make_score(ct, ct / 2)
+                                      : -make_score(ct, ct / 2));
           }
 
           // Start with a small aspiration window and, in the case of a fail
@@ -919,7 +929,7 @@ moves_loop: // When in check, search starts from here
           }
           else if (    depth < 7 * ONE_PLY
                    && !extension
-                   && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY)))
+                   && !pos.see_ge(move, -Value(CapturePruneMargin[depth / ONE_PLY])))
                   continue;
       }