Use legal positions for endgame initialization

[stockfish] / src / endgame.cpp

diff --git a/src/endgame.cpp b/src/endgame.cpp
index dbb98310239903e4215b72bcb25fac25635e0759..572c160d42ba60c018a64bfbe13ed4c4403f42a1 100644 (file)
--- a/src/endgame.cpp
+++ b/src/endgame.cpp
@@ -82,8 +82,7 @@ namespace {
 
   // Get the material key of Position out of the given endgame key code
   // like "KBPKN". The trick here is to first forge an ad-hoc FEN string
-  // and then let a Position object do the work for us. Note that the
-  // FEN string could correspond to an illegal position.
+  // and then let a Position object do the work for us.
   Key key(const string& code, Color c) {
 
     assert(code.length() > 0 && code.length() < 8);
@@ -94,8 +93,8 @@ namespace {
 
     std::transform(sides[c].begin(), sides[c].end(), sides[c].begin(), tolower);
 
-    string fen =  sides[0] + char('0' + int(8 - code.length()))
-                + sides[1] + "/8/8/8/8/8/8/8 w - - 0 10";
+    string fen =  sides[0] + char(8 - sides[0].length() + '0') + "/8/8/8/8/8/8/"
+                + sides[1] + char(8 - sides[1].length() + '0') + " w - - 0 10";
 
     return Position(fen, false, NULL).material_key();
   }
@@ -118,7 +117,6 @@ Endgames::Endgames() {
   add<KRKN>("KRKN");
   add<KQKP>("KQKP");
   add<KQKR>("KQKR");
-  add<KBBKN>("KBBKN");
 
   add<KNPK>("KNPK");
   add<KNPKB>("KNPKB");
@@ -348,32 +346,8 @@ Value Endgame<KQKR>::operator()(const Position& pos) const {
 }
 
 
-/// KBB vs KN. This is almost always a win. We try to push the enemy king to a corner
-/// and away from his knight. For a reference of this difficult endgame see:
-/// en.wikipedia.org/wiki/Chess_endgame#Effect_of_tablebases_on_endgame_theory
-
-template<>
-Value Endgame<KBBKN>::operator()(const Position& pos) const {
-
-  assert(verify_material(pos, strongSide, 2 * BishopValueMg, 0));
-  assert(verify_material(pos, weakSide, KnightValueMg, 0));
-
-  Square winnerKSq = pos.king_square(strongSide);
-  Square loserKSq = pos.king_square(weakSide);
-  Square knightSq = pos.list<KNIGHT>(weakSide)[0];
-
-  Value result =  VALUE_KNOWN_WIN
-                + PushToCorners[loserKSq]
-                + PushClose[square_distance(winnerKSq, loserKSq)]
-                + PushAway[square_distance(loserKSq, knightSq)];
-
-  return strongSide == pos.side_to_move() ? result : -result;
-}
-
-
 /// Some cases of trivial draws
 template<> Value Endgame<KNNK>::operator()(const Position&) const { return VALUE_DRAW; }
-template<> Value Endgame<KmmKm>::operator()(const Position&) const { return VALUE_DRAW; }
 
 
 /// KB and one or more pawns vs K. It checks for draws with rook pawns and
@@ -817,7 +791,7 @@ ScaleFactor Endgame<KBPKN>::operator()(const Position& pos) const {
 
 
 /// KNP vs K. There is a single rule: if the pawn is a rook pawn on the 7th rank
-/// and the defending king prevents the pawn from advancing the position is drawn.
+/// and the defending king prevents the pawn from advancing, the position is drawn.
 template<>
 ScaleFactor Endgame<KNPK>::operator()(const Position& pos) const {