Asymmetry bonus for the attacking side

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 0554f490227b51e4b60ddacb1cee315bf03c174c..bbca9964f4337d9506c23d0d49353af9f0e2e9d3 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -686,6 +686,27 @@ namespace {
     return make_score(bonus * weight * weight, 0);
   }
 
+
+  // evaluate_initiative() computes the initiative correction value for the position, i.e. 
+  // second order bonus/malus based on the known attacking/defending status of the players. 
+  Score evaluate_initiative(const Position& pos, const EvalInfo& ei, const Score positional_score) {
+
+    int pawns           =  pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
+    int king_separation =  distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
+    int asymmetry       =  ei.pi->pawn_asymmetry();
+
+    // Compute the initiative bonus for the attacking side
+    int attacker_bonus =   8 * (pawns + asymmetry + king_separation) - 120;
+
+    // Now apply the bonus: note that we find the attacking side by extracting the sign 
+    // of the endgame value of "positional_score", and that we carefully cap the bonus so
+    // that the endgame score with the correction will never be divided by more than two.
+    int eg = eg_value(positional_score);
+    int value = ((eg > 0) - (eg < 0)) * std::max( attacker_bonus , -abs( eg / 2 ) );
+
+    return make_score( 0 , value ) ; 
+  }
+
 } // namespace
 
 
@@ -767,6 +788,9 @@ Value Eval::evaluate(const Position& pos) {
   // Evaluate space for both sides, only during opening
   if (pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 12222)
       score += (evaluate_space<WHITE>(pos, ei) - evaluate_space<BLACK>(pos, ei)) * Weights[Space];
+  
+  // Evaluate initiative
+  score += evaluate_initiative(pos, ei, score);
 
   // Scale winning side if position is more drawish than it appears
   Color strongSide = eg_value(score) > VALUE_DRAW ? WHITE : BLACK;
@@ -798,11 +822,6 @@ Value Eval::evaluate(const Position& pos) {
           sf = ei.pi->pawn_span(strongSide) ? ScaleFactor(51) : ScaleFactor(37);
   }
 
-  // Scale endgame by number of pawns
-  int p = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
-  int v_eg = 1 + abs(int(eg_value(score)));
-  sf = ScaleFactor(std::max(sf / 2, sf - 8 * SCALE_FACTOR_NORMAL * (12 - p) / v_eg));
-
   // Interpolate between a middlegame and a (scaled by 'sf') endgame score
   Value v =  mg_value(score) * int(me->game_phase())
            + eg_value(score) * int(PHASE_MIDGAME - me->game_phase()) * sf / SCALE_FACTOR_NORMAL;