Use equations for PushAway and PushClose

[stockfish] / src / endgame.cpp

diff --git a/src/endgame.cpp b/src/endgame.cpp
index 6745ee2664c612689646c283f78833355d509dcf..73a4463362a6e2fb4e63cc1c676cab66aa779ab0 100644 (file)
--- a/src/endgame.cpp
+++ b/src/endgame.cpp
@@ -54,9 +54,9 @@ namespace {
      4160, 4480, 4800, 5120, 5440, 5760, 6080, 6400
   };
 
-  // Tables used to drive a piece towards or away from another piece
-  constexpr int PushClose[8] = { 0, 0, 100, 80, 60, 40, 20, 10 };
-  constexpr int PushAway [8] = { 0, 5, 20, 40, 60, 80, 90, 100 };
+  // Drive a piece close to or away from another piece
+  inline int push_close(Square s1, Square s2) { return 140 - 20 * distance(s1, s2); }
+  inline int push_away(Square s1, Square s2) { return 120 - push_close(s1, s2); }
 
   // Pawn Rank based scaling factors used in KRPPKRP endgame
   constexpr int KRPPKRPScaleFactors[RANK_NB] = { 0, 9, 10, 14, 21, 44, 0, 0 };
@@ -74,9 +74,9 @@ namespace {
     assert(pos.count<PAWN>(strongSide) == 1);
 
     if (file_of(pos.square<PAWN>(strongSide)) >= FILE_E)
-        sq = Square(int(sq) ^ 7); // Mirror SQ_H1 -> SQ_A1
+        sq = flip_file(sq);
 
-    return strongSide == WHITE ? sq : ~sq;
+    return strongSide == WHITE ? sq : flip_rank(sq);
   }
 
 } // namespace
@@ -130,7 +130,7 @@ Value Endgame<KXK>::operator()(const Position& pos) const {
   Value result =  pos.non_pawn_material(strongSide)
                 + pos.count<PAWN>(strongSide) * PawnValueEg
                 + PushToEdges[loserKSq]
-                + PushClose[distance(winnerKSq, loserKSq)];
+                + push_close(winnerKSq, loserKSq);
 
   if (   pos.count<QUEEN>(strongSide)
       || pos.count<ROOK>(strongSide)
@@ -159,7 +159,7 @@ Value Endgame<KBNK>::operator()(const Position& pos) const {
   // to drive to opposite corners (A8/H1).
 
   Value result =  VALUE_KNOWN_WIN
-                + PushClose[distance(winnerKSq, loserKSq)]
+                + push_close(winnerKSq, loserKSq)
                 + PushToCorners[opposite_colors(bishopSq, SQ_A1) ? ~loserKSq : loserKSq];
 
   assert(abs(result) < VALUE_TB_WIN_IN_MAX_PLY);
@@ -258,7 +258,7 @@ Value Endgame<KRKN>::operator()(const Position& pos) const {
 
   Square bksq = pos.square<KING>(weakSide);
   Square bnsq = pos.square<KNIGHT>(weakSide);
-  Value result = Value(PushToEdges[bksq] + PushAway[distance(bksq, bnsq)]);
+  Value result = Value(PushToEdges[bksq] + push_away(bksq, bnsq));
   return strongSide == pos.side_to_move() ? result : -result;
 }
 
@@ -277,11 +277,11 @@ Value Endgame<KQKP>::operator()(const Position& pos) const {
   Square loserKSq = pos.square<KING>(weakSide);
   Square pawnSq = pos.square<PAWN>(weakSide);
 
-  Value result = Value(PushClose[distance(winnerKSq, loserKSq)]);
+  Value result = Value(push_close(winnerKSq, loserKSq));
 
   if (   relative_rank(weakSide, pawnSq) != RANK_7
       || distance(loserKSq, pawnSq) != 1
-      || !((FileABB | FileCBB | FileFBB | FileHBB) & pawnSq))
+      || ((FileBBB | FileDBB | FileEBB | FileGBB) & pawnSq))
       result += QueenValueEg - PawnValueEg;
 
   return strongSide == pos.side_to_move() ? result : -result;
@@ -304,22 +304,23 @@ Value Endgame<KQKR>::operator()(const Position& pos) const {
   Value result =  QueenValueEg
                 - RookValueEg
                 + PushToEdges[loserKSq]
-                + PushClose[distance(winnerKSq, loserKSq)];
+                + push_close(winnerKSq, loserKSq);
 
   return strongSide == pos.side_to_move() ? result : -result;
 }
 
 
-/// KNN vs KP. Simply push the opposing king to the corner
+/// KNN vs KP. Very drawish, but there are some mate opportunities if we can
+//  press the weakSide King to a corner before the pawn advances too much.
 template<>
 Value Endgame<KNNKP>::operator()(const Position& pos) const {
 
   assert(verify_material(pos, strongSide, 2 * KnightValueMg, 0));
   assert(verify_material(pos, weakSide, VALUE_ZERO, 1));
 
-  Value result =  2 * KnightValueEg
-                - PawnValueEg
-                + PushToEdges[pos.square<KING>(weakSide)];
+  Value result =      PawnValueEg
+               +  2 * PushToEdges[pos.square<KING>(weakSide)]
+               - 10 * relative_rank(weakSide, pos.square<PAWN>(weakSide));
 
   return strongSide == pos.side_to_move() ? result : -result;
 }