Simplify outpost evaluation

STC

LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 114149 W: 21986 L: 22032 D: 70131

LTC

LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 52232 W: 8468 L: 8396 D: 35368

Bench: 6716940

No functional change

Resolves #363

Author: lucasart

src/evaluate.cpp

@@ -124,24 +124,8 @@ namespace {
       S( 94, 99), S( 96,100), S(99,111), S(99,112) }
   };
 
-  // Outpost[Bishop/Knight][Square] contains bonuses for knights and bishops
-  // outposts, indexed by piece type and square (from white's point of view).
-  const Value Outpost[][SQUARE_NB] = {
-  {// A     B     C     D     E     F     G     H
-    V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // Knights
-    V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
-    V(0), V(0), V(3), V(9), V(9), V(3), V(0), V(0),
-    V(0), V(4),V(18),V(25),V(25),V(18), V(4), V(0),
-    V(4), V(9),V(29),V(38),V(38),V(29), V(9), V(4),
-    V(2), V(9),V(19),V(15),V(15),V(19), V(9), V(2) },
-  {
-    V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0), // Bishops
-    V(0), V(0), V(0), V(0), V(0), V(0), V(0), V(0),
-    V(2), V(4), V(3), V(8), V(8), V(3), V(4), V(2),
-    V(1), V(9), V(9),V(13),V(13), V(9), V(9), V(1),
-    V(2), V(8),V(21),V(24),V(24),V(21), V(8), V(2),
-    V(0), V(4), V(6), V(6), V(6), V(6), V(4), V(0) }
-  };
+  // Outpost[knight/bishop][supported by pawn]
+  const Score Outpost[2][2] = {{S(28,7), S(42,11)}, {S(12,3), S(18,5)}};
 
   // Threat[defended/weak][minor/major attacking][attacked PieceType] contains
   // bonuses according to which piece type attacks which one.
@@ -235,33 +219,6 @@ namespace {
   }
 
 
-  // evaluate_outpost() evaluates bishop and knight outpost squares
-
-  template<PieceType Pt, Color Us>
-  Score evaluate_outpost(const Position& pos, const EvalInfo& ei, Square s) {
-
-    const Color Them = (Us == WHITE ? BLACK : WHITE);
-
-    assert (Pt == BISHOP || Pt == KNIGHT);
-
-    // Initial bonus based on square
-    Value bonus = Outpost[Pt == BISHOP][relative_square(Us, s)];
-
-    // Increase bonus if supported by pawn, especially if the opponent has
-    // no minor piece which can trade with the outpost piece.
-    if (bonus && (ei.attackedBy[Us][PAWN] & s))
-    {
-        if (   !pos.pieces(Them, KNIGHT)
-            && !(squares_of_color(s) & pos.pieces(Them, BISHOP)))
-            bonus += bonus + bonus / 2;
-        else
-            bonus += bonus / 2;
-    }
-
-    return make_score(bonus * 2, bonus / 2);
-  }
-
-
   // evaluate_pieces() assigns bonuses and penalties to the pieces of a given color
 
   template<PieceType Pt, Color Us, bool Trace>
@@ -310,8 +267,9 @@ namespace {
         if (Pt == BISHOP || Pt == KNIGHT)
         {
             // Bonus for outpost square
-            if (!(pos.pieces(Them, PAWN) & pawn_attack_span(Us, s)))
-                score += evaluate_outpost<Pt, Us>(pos, ei, s);
+            if (   relative_rank(Us, s) >= RANK_4
+                && !(pos.pieces(Them, PAWN) & pawn_attack_span(Us, s)))
+                score += Outpost[Pt == BISHOP][!!(ei.attackedBy[Us][PAWN] & s)];
 
             // Bonus when behind a pawn
             if (    relative_rank(Us, s) < RANK_5