Linear Protector bonus by distance

FauziAkram · zamar · commit 6b4959e3e000 · 2017-05-07T21:11:51.000-07:00
Replacing the old Protector table with a simple linear formula which takes into account a different slope for each different piece type. The idea of this simplification of Protector is originated by Alain (Rocky) STC: LLR: 2.95 (-2.94,2.94) [-3.00,1.00] Total: 70382 W: 12859 L: 12823 D: 44700 LTC: LLR: 2.95 (-2.94,2.94) [-3.00,1.00] Total: 61554 W: 8098 L: 8031 D: 45425 Bench: 6107863 Closes #1099
diff --git a/src/evaluate.cpp b/src/evaluate.cpp
@@ -174,14 +174,8 @@ namespace {
     S(-20,-12), S( 1, -8), S( 2, 10), S(  9, 10)
   };
 
-  // Protector[PieceType-2][distance] contains a protecting bonus for our king,
-  // indexed by piece type and distance between the piece and the king.
-  const Score Protector[][8] = {
-    { S(0, 0), S( 7, 9), S( 7, 1), S( 1, 5), S(-10,-4), S( -1,-4), S( -7,-3), S(-16,-10) }, // Knight
-    { S(0, 0), S(11, 8), S(-7,-1), S(-1,-2), S( -1,-7), S(-11,-3), S( -9,-1), S(-16, -1) }, // Bishop
-    { S(0, 0), S(10, 0), S(-2, 2), S(-5, 4), S( -6, 2), S(-14,-3), S( -2,-9), S(-12, -7) }, // Rook
-    { S(0, 0), S( 3,-5), S( 2,-5), S(-4, 0), S( -9,-6), S( -4, 7), S(-13,-7), S(-10, -7) }  // Queen
-  };
+  // KingProtector[PieceType-2] * "distance to own king" determines a bonus for each piece.
+  const Score KingProtector[] = {S(-3, -5), S(-4, -3), S(-3, 0), S(-1, 1) };
 
   // Assorted bonuses and penalties used by evaluation
   const Score MinorBehindPawn     = S( 16,  0);
@@ -299,8 +293,7 @@ namespace {
 
         mobility[Us] += MobilityBonus[Pt-2][mob];
 
-        // Bonus for this piece as a king protector
-        score += Protector[Pt-2][distance(s, pos.square<KING>(Us))];
+        score += KingProtector[Pt-2] * distance(s, pos.square<KING>(Us));
 
         if (Pt == BISHOP || Pt == KNIGHT)
         {
diff --git a/src/types.h b/src/types.h
@@ -184,10 +184,10 @@ enum Value : int {
   VALUE_MATED_IN_MAX_PLY = -VALUE_MATE + 2 * MAX_PLY,
 
   PawnValueMg   = 188,   PawnValueEg   = 248,
-  KnightValueMg = 753,   KnightValueEg = 832,
-  BishopValueMg = 814,   BishopValueEg = 890,
-  RookValueMg   = 1285,  RookValueEg   = 1371,
-  QueenValueMg  = 2513,  QueenValueEg  = 2648,
+  KnightValueMg = 764,   KnightValueEg = 848,
+  BishopValueMg = 826,   BishopValueEg = 891,
+  RookValueMg   = 1282,  RookValueEg   = 1373,
+  QueenValueMg  = 2526,  QueenValueEg  = 2646,
 
   MidgameLimit  = 15258, EndgameLimit  = 3915
 };
