Slight simplification in scale factor computation

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 1d2c5f8e55304c1931790fa45c3649e9ddf0f55c..7fb0e26ae9ec90a5504eb5215de3514494a4fa24 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -89,7 +89,7 @@ namespace {
   constexpr Value SpaceThreshold = Value(12222);
 
   // KingAttackWeights[PieceType] contains king attack weights by piece type
-  constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
+  constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 77, 55, 44, 10 };
 
   // Penalties for enemy's safe checks
   constexpr int QueenSafeCheck  = 780;
@@ -281,7 +281,7 @@ namespace {
         else if (file_of(pos.square<KING>(Us)) == FILE_A)
             kingRing[Us] |= shift<EAST>(kingRing[Us]);
 
-        kingAttackersCount[Them] = popcount(attackedBy[Us][KING] & pe->pawn_attacks(Them));
+        kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
         kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
     }
     else
@@ -801,20 +801,13 @@ namespace {
     // If scale is not already specific, scale down the endgame via general heuristics
     if (sf == SCALE_FACTOR_NORMAL)
     {
-        if (pos.opposite_bishops())
-        {
+        if (   pos.opposite_bishops()
+            && pos.non_pawn_material(WHITE) == BishopValueMg
+            && pos.non_pawn_material(BLACK) == BishopValueMg)
             // Endgame with opposite-colored bishops and no other pieces is almost a draw
-            if (   pos.non_pawn_material(WHITE) == BishopValueMg
-                && pos.non_pawn_material(BLACK) == BishopValueMg)
-                sf = 31;
-
-            // Endgame with opposite-colored bishops, but also other pieces. Still
-            // a bit drawish, but not as drawish as with only the two bishops.
-            else
-                sf = 46;
-        }
+            sf = 31;
         else
-            sf = std::min(40 + 7 * pos.count<PAWN>(strongSide), sf);
+            sf = std::min(40 + (pos.opposite_bishops()? 2 : 7) * pos.count<PAWN>(strongSide), sf);
     }
 
     return ScaleFactor(sf);