Scale factor in opposite-color bishop endings

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 7eafacf8233a4a74eb11c748e232cada3854ee18..cbcebd045f684d392975bbe7373648d6e152b09c 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -398,9 +398,9 @@ namespace {
 
     // Enemy rooks checks
     rookChecks = b1 & safe & attackedBy[Them][ROOK];
-
     if (rookChecks)
-        kingDanger += RookSafeCheck;
+        kingDanger += more_than_one(rookChecks) ? RookSafeCheck * 3/2
+                                                : RookSafeCheck;
     else
         unsafeChecks |= b1 & attackedBy[Them][ROOK];
 
@@ -411,9 +411,9 @@ namespace {
                  & safe
                  & ~attackedBy[Us][QUEEN]
                  & ~rookChecks;
-
     if (queenChecks)
-        kingDanger += QueenSafeCheck;
+        kingDanger += more_than_one(queenChecks) ? QueenSafeCheck * 3/2
+                                                 : QueenSafeCheck;
 
     // Enemy bishops checks: we count them only if they are from squares from
     // which we can't give a queen check, because queen checks are more valuable.
@@ -421,17 +421,17 @@ namespace {
                   & attackedBy[Them][BISHOP]
                   & safe
                   & ~queenChecks;
-
     if (bishopChecks)
-        kingDanger += BishopSafeCheck;
+        kingDanger += more_than_one(bishopChecks) ? BishopSafeCheck * 3/2
+                                                  : BishopSafeCheck;
     else
         unsafeChecks |= b2 & attackedBy[Them][BISHOP];
 
     // Enemy knights checks
     knightChecks = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];
-
     if (knightChecks & safe)
-        kingDanger += KnightSafeCheck;
+        kingDanger += more_than_one(knightChecks & safe) ? KnightSafeCheck * 3/2
+                                                         : KnightSafeCheck;
     else
         unsafeChecks |= knightChecks;
 
@@ -761,11 +761,16 @@ namespace {
     // If scale is not already specific, scale down the endgame via general heuristics
     if (sf == SCALE_FACTOR_NORMAL)
     {
-        if (   pos.opposite_bishops()
-            && pos.non_pawn_material() == 2 * BishopValueMg)
-            sf = 22;
+        if (pos.opposite_bishops())
+        {
+            if (   pos.non_pawn_material(WHITE) == BishopValueMg
+                && pos.non_pawn_material(BLACK) == BishopValueMg)
+                sf = 22;
+            else
+                sf = 22 + 3 * pos.count<ALL_PIECES>(strongSide);
+        }
         else
-            sf = std::min(sf, 36 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide));
+            sf = std::min(sf, 36 + 7 * pos.count<PAWN>(strongSide));
 
         sf = std::max(0, sf - (pos.rule50_count() - 12) / 4);
     }