Scale down complexity for almost unwinnable endgames

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 05fa45bc9e08f8e127ad36793b98ff292aa6ed6d..73e2144cc2d248faaf1fad03e08e43f6f3cb5870 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -140,6 +140,7 @@ namespace {
   constexpr Score PawnlessFlank      = S( 17, 95);
   constexpr Score RestrictedPiece    = S(  7,  7);
   constexpr Score RookOnPawn         = S( 10, 32);
+  constexpr Score RookOnQueenFile    = S( 11,  4);
   constexpr Score SliderOnQueen      = S( 59, 18);
   constexpr Score ThreatByKing       = S( 24, 89);
   constexpr Score ThreatByPawnPush   = S( 48, 39);
@@ -346,6 +347,10 @@ namespace {
             if (relative_rank(Us, s) >= RANK_5)
                 score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);
 
+            // Bonus for rook on same file as their queen
+            if (file_bb(s) & pos.pieces(Them, QUEEN))
+                score += RookOnQueenFile;
+
             // Bonus for rook on an open or semi-open file
             if (pos.is_on_semiopen_file(Us, s))
                 score += RookOnFile[bool(pos.is_on_semiopen_file(Them, s))];
@@ -720,12 +725,17 @@ namespace {
     bool pawnsOnBothFlanks =   (pos.pieces(PAWN) & QueenSide)
                             && (pos.pieces(PAWN) & KingSide);
 
+    bool almostUnwinnable =   !pe->passed_count()
+                           &&  outflanking < 0
+                           && !pawnsOnBothFlanks;
+
     // Compute the initiative bonus for the attacking side
     int complexity =   9 * pe->passed_count()
                     + 11 * pos.count<PAWN>()
                     +  9 * outflanking
                     + 18 * pawnsOnBothFlanks
                     + 49 * !pos.non_pawn_material()
+                    - 36 * almostUnwinnable
                     -103 ;
 
     // Now apply the bonus: note that we find the attacking side by extracting