X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fendgame.cpp;h=a868c0e82cb31405befb810a5a7bd19a995e9249;hp=a4526ff612939307f5ce9f25c6878713af247010;hb=3ec94abcdb5f4ad81cc8829aece2d7fa64bb21db;hpb=1a8e3f0b2e9e2a5b8a01b645ce1fc5b12e0aec55

diff --git a/src/endgame.cpp b/src/endgame.cpp
index a4526ff6..a868c0e8 100644
--- a/src/endgame.cpp
+++ b/src/endgame.cpp
@@ -1,7 +1,7 @@
 /*
   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
   Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
-  Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
+  Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, Tord Romstad
 
   Stockfish is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -17,6 +17,7 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include <algorithm>
 #include <cassert>
 
 #include "bitcount.h"
@@ -59,47 +60,33 @@ namespace {
   // the two kings in basic endgames.
   const int DistanceBonus[8] = { 0, 0, 100, 80, 60, 40, 20, 10 };
 
-  // Penalty for big distance between king and knight for the defending king
-  // and knight in KR vs KN endgames.
-  const int KRKNKingKnightDistancePenalty[8] = { 0, 0, 4, 10, 20, 32, 48, 70 };
+  // Get the material key of a 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 to do the work for us. Note that the
+  // fen string could correspond to an illegal position.
+  Key key(const string& code, Color c) {
 
-  // Build corresponding key code for the opposite color: "KBPKN" -> "KNKBP"
-  const string swap_colors(const string& keyCode) {
+    assert(code.length() > 0 && code.length() < 8);
+    assert(code[0] == 'K');
 
-    size_t idx = keyCode.find('K', 1);
-    return keyCode.substr(idx) + keyCode.substr(0, idx);
-  }
-
-  // Get the material key of a position out of the given endgame key code
-  // like "KBPKN". The trick here is to first build up a FEN string and then
-  // let a Position object to do the work for us. Note that the FEN string
-  // could correspond to an illegal position.
-  Key mat_key(const string& keyCode) {
-
-    assert(keyCode.length() > 0 && keyCode.length() < 8);
-    assert(keyCode[0] == 'K');
+    string sides[] = { code.substr(code.find('K', 1)),      // Weaker
+                       code.substr(0, code.find('K', 1)) }; // Stronger
 
-    string fen;
-    size_t i = 0;
+    transform(sides[c].begin(), sides[c].end(), sides[c].begin(), tolower);
 
-    // First add white and then black pieces
-    do fen += keyCode[i];                while (keyCode[++i] != 'K');
-    do fen += char(tolower(keyCode[i])); while (++i < keyCode.length());
+    string fen =  sides[0] + char('0' + int(8 - code.length()))
+                + sides[1] + "/8/8/8/8/8/8/8 w - - 0 10";
 
-    // Add file padding and remaining empty ranks
-    fen += string(1, '0' + int(8 - keyCode.length())) + "/8/8/8/8/8/8/8 w - - 0 10";
-
-    // Build a Position out of the fen string and get its material key
-    return Position(fen, false, 0).get_material_key();
+    return Position(fen, false, 0).material_key();
   }
 
-} // namespace
+  template<typename M>
+  void delete_endgame(const typename M::value_type& p) { delete p.second; }
 
+} // namespace
 
-/// Endgames member definitions
 
-template<> const Endgames::M1& Endgames::map<Endgames::M1>() const { return m1; }
-template<> const Endgames::M2& Endgames::map<Endgames::M2>() const { return m2; }
+/// Endgames members definitions
 
 Endgames::Endgames() {
 
@@ -122,21 +109,17 @@ Endgames::Endgames() {
 
 Endgames::~Endgames() {
 
-  for (M1::const_iterator it = m1.begin(); it != m1.end(); ++it)
-      delete it->second;
-
-  for (M2::const_iterator it = m2.begin(); it != m2.end(); ++it)
-      delete it->second;
+  for_each(m1.begin(), m1.end(), delete_endgame<M1>);
+  for_each(m2.begin(), m2.end(), delete_endgame<M2>);
 }
 
 template<EndgameType E>
-void Endgames::add(const string& keyCode) {
+void Endgames::add(const string& code) {
 
   typedef typename eg_family<E>::type T;
-  typedef typename Map<T>::type M;
 
-  const_cast<M&>(map<M>()).insert(std::make_pair(mat_key(keyCode), new Endgame<E>(WHITE)));
-  const_cast<M&>(map<M>()).insert(std::make_pair(mat_key(swap_colors(keyCode)), new Endgame<E>(BLACK)));
+  map((T*)0)[key(code, WHITE)] = new Endgame<E>(WHITE);
+  map((T*)0)[key(code, BLACK)] = new Endgame<E>(BLACK);
 }
 
 
@@ -145,7 +128,7 @@ void Endgames::add(const string& keyCode) {
 /// attacking side a bonus for driving the defending king towards the edge
 /// of the board, and for keeping the distance between the two kings small.
 template<>
-Value Endgame<KXK>::apply(const Position& pos) const {
+Value Endgame<KXK>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO);
   assert(pos.piece_count(weakerSide, PAWN) == VALUE_ZERO);
@@ -171,7 +154,7 @@ Value Endgame<KXK>::apply(const Position& pos) const {
 /// Mate with KBN vs K. This is similar to KX vs K, but we have to drive the
 /// defending king towards a corner square of the right color.
 template<>
-Value Endgame<KBNK>::apply(const Position& pos) const {
+Value Endgame<KBNK>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO);
   assert(pos.piece_count(weakerSide, PAWN) == VALUE_ZERO);
@@ -203,7 +186,7 @@ Value Endgame<KBNK>::apply(const Position& pos) const {
 
 /// KP vs K. This endgame is evaluated with the help of a bitbase.
 template<>
-Value Endgame<KPK>::apply(const Position& pos) const {
+Value Endgame<KPK>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(strongerSide) == VALUE_ZERO);
   assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO);
@@ -222,10 +205,10 @@ Value Endgame<KPK>::apply(const Position& pos) const {
   }
   else
   {
-      wksq = flip(pos.king_square(BLACK));
-      bksq = flip(pos.king_square(WHITE));
-      wpsq = flip(pos.piece_list(BLACK, PAWN)[0]);
-      stm = flip(pos.side_to_move());
+      wksq = ~pos.king_square(BLACK);
+      bksq = ~pos.king_square(WHITE);
+      wpsq = ~pos.piece_list(BLACK, PAWN)[0];
+      stm  = ~pos.side_to_move();
   }
 
   if (file_of(wpsq) >= FILE_E)
@@ -251,7 +234,7 @@ Value Endgame<KPK>::apply(const Position& pos) const {
 /// far advanced with support of the king, while the attacking king is far
 /// away.
 template<>
-Value Endgame<KRKP>::apply(const Position& pos) const {
+Value Endgame<KRKP>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(strongerSide) == RookValueMidgame);
   assert(pos.piece_count(strongerSide, PAWN) == 0);
@@ -268,10 +251,10 @@ Value Endgame<KRKP>::apply(const Position& pos) const {
 
   if (strongerSide == BLACK)
   {
-      wksq = flip(wksq);
-      wrsq = flip(wrsq);
-      bksq = flip(bksq);
-      bpsq = flip(bpsq);
+      wksq = ~wksq;
+      wrsq = ~wrsq;
+      bksq = ~bksq;
+      bpsq = ~bpsq;
   }
 
   Square queeningSq = make_square(file_of(bpsq), RANK_1);
@@ -308,7 +291,7 @@ Value Endgame<KRKP>::apply(const Position& pos) const {
 /// KR vs KB. This is very simple, and always returns drawish scores.  The
 /// score is slightly bigger when the defending king is close to the edge.
 template<>
-Value Endgame<KRKB>::apply(const Position& pos) const {
+Value Endgame<KRKB>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(strongerSide) == RookValueMidgame);
   assert(pos.piece_count(strongerSide, PAWN) == 0);
@@ -324,7 +307,7 @@ Value Endgame<KRKB>::apply(const Position& pos) const {
 /// KR vs KN.  The attacking side has slightly better winning chances than
 /// in KR vs KB, particularly if the king and the knight are far apart.
 template<>
-Value Endgame<KRKN>::apply(const Position& pos) const {
+Value Endgame<KRKN>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(strongerSide) == RookValueMidgame);
   assert(pos.piece_count(strongerSide, PAWN) == 0);
@@ -332,14 +315,11 @@ Value Endgame<KRKN>::apply(const Position& pos) const {
   assert(pos.piece_count(weakerSide, PAWN) == 0);
   assert(pos.piece_count(weakerSide, KNIGHT) == 1);
 
-  Square defendingKSq = pos.king_square(weakerSide);
-  Square nSq = pos.piece_list(weakerSide, KNIGHT)[0];
-
-  int d = square_distance(defendingKSq, nSq);
-  Value result =   Value(10)
-                 + MateTable[defendingKSq]
-                 + KRKNKingKnightDistancePenalty[d];
+  const int penalty[8] = { 0, 10, 14, 20, 30, 42, 58, 80 };
 
+  Square bksq = pos.king_square(weakerSide);
+  Square bnsq = pos.piece_list(weakerSide, KNIGHT)[0];
+  Value result = Value(MateTable[bksq] + penalty[square_distance(bksq, bnsq)]);
   return strongerSide == pos.side_to_move() ? result : -result;
 }
 
@@ -350,7 +330,7 @@ Value Endgame<KRKN>::apply(const Position& pos) const {
 /// for the defending side in the search, this is usually sufficient to be
 /// able to win KQ vs KR.
 template<>
-Value Endgame<KQKR>::apply(const Position& pos) const {
+Value Endgame<KQKR>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(strongerSide) == QueenValueMidgame);
   assert(pos.piece_count(strongerSide, PAWN) == 0);
@@ -369,13 +349,13 @@ Value Endgame<KQKR>::apply(const Position& pos) const {
 }
 
 template<>
-Value Endgame<KBBKN>::apply(const Position& pos) const {
+Value Endgame<KBBKN>::operator()(const Position& pos) const {
 
   assert(pos.piece_count(strongerSide, BISHOP) == 2);
   assert(pos.non_pawn_material(strongerSide) == 2*BishopValueMidgame);
   assert(pos.piece_count(weakerSide, KNIGHT) == 1);
   assert(pos.non_pawn_material(weakerSide) == KnightValueMidgame);
-  assert(pos.pieces(PAWN) == EmptyBoardBB);
+  assert(!pos.pieces(PAWN));
 
   Value result = BishopValueEndgame;
   Square wksq = pos.king_square(strongerSide);
@@ -389,7 +369,7 @@ Value Endgame<KBBKN>::apply(const Position& pos) const {
   result += Value(square_distance(bksq, nsq) * 32);
 
   // Bonus for restricting the knight's mobility
-  result += Value((8 - count_1s<CNT32_MAX15>(pos.attacks_from<KNIGHT>(nsq))) * 8);
+  result += Value((8 - popcount<Max15>(pos.attacks_from<KNIGHT>(nsq))) * 8);
 
   return strongerSide == pos.side_to_move() ? result : -result;
 }
@@ -398,22 +378,21 @@ Value Endgame<KBBKN>::apply(const Position& pos) const {
 /// K and two minors vs K and one or two minors or K and two knights against
 /// king alone are always draw.
 template<>
-Value Endgame<KmmKm>::apply(const Position&) const {
+Value Endgame<KmmKm>::operator()(const Position&) const {
   return VALUE_DRAW;
 }
 
 template<>
-Value Endgame<KNNK>::apply(const Position&) const {
+Value Endgame<KNNK>::operator()(const Position&) const {
   return VALUE_DRAW;
 }
 
-/// KBPKScalingFunction scales endgames where the stronger side has king,
-/// bishop and one or more pawns. It checks for draws with rook pawns and a
-/// bishop of the wrong color. If such a draw is detected, SCALE_FACTOR_ZERO is
-/// returned. If not, the return value is SCALE_FACTOR_NONE, i.e. no scaling
+/// K, bishop and one or more pawns vs K. It checks for draws with rook pawns and
+/// a bishop of the wrong color. If such a draw is detected, SCALE_FACTOR_DRAW
+/// is returned. If not, the return value is SCALE_FACTOR_NONE, i.e. no scaling
 /// will be used.
 template<>
-ScaleFactor Endgame<KBPsK>::apply(const Position& pos) const {
+ScaleFactor Endgame<KBPsK>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(strongerSide) == BishopValueMidgame);
   assert(pos.piece_count(strongerSide, BISHOP) == 1);
@@ -427,7 +406,7 @@ ScaleFactor Endgame<KBPsK>::apply(const Position& pos) const {
 
   // All pawns are on a single rook file ?
   if (   (pawnFile == FILE_A || pawnFile == FILE_H)
-      && (pawns & ~file_bb(pawnFile)) == EmptyBoardBB)
+      && !(pawns & ~file_bb(pawnFile)))
   {
       Square bishopSq = pos.piece_list(strongerSide, BISHOP)[0];
       Square queeningSq = relative_square(strongerSide, make_square(pawnFile, RANK_8));
@@ -437,17 +416,17 @@ ScaleFactor Endgame<KBPsK>::apply(const Position& pos) const {
           && abs(file_of(kingSq) - pawnFile) <= 1)
       {
           // The bishop has the wrong color, and the defending king is on the
-          // file of the pawn(s) or the neighboring file. Find the rank of the
+          // file of the pawn(s) or the adjacent file. Find the rank of the
           // frontmost pawn.
           Rank rank;
           if (strongerSide == WHITE)
           {
-              for (rank = RANK_7; (rank_bb(rank) & pawns) == EmptyBoardBB; rank--) {}
+              for (rank = RANK_7; !(rank_bb(rank) & pawns); rank--) {}
               assert(rank >= RANK_2 && rank <= RANK_7);
           }
           else
           {
-              for (rank = RANK_2; (rank_bb(rank) & pawns) == EmptyBoardBB; rank++) {}
+              for (rank = RANK_2; !(rank_bb(rank) & pawns); rank++) {}
               rank = Rank(rank ^ 7);  // HACK to get the relative rank
               assert(rank >= RANK_2 && rank <= RANK_7);
           }
@@ -455,19 +434,17 @@ ScaleFactor Endgame<KBPsK>::apply(const Position& pos) const {
           // is placed somewhere in front of the pawn, it's a draw.
           if (   square_distance(kingSq, queeningSq) <= 1
               || relative_rank(strongerSide, kingSq) >= rank)
-              return SCALE_FACTOR_ZERO;
+              return SCALE_FACTOR_DRAW;
       }
   }
   return SCALE_FACTOR_NONE;
 }
 
 
-/// KQKRPScalingFunction scales endgames where the stronger side has only
-/// king and queen, while the weaker side has at least a rook and a pawn.
-/// It tests for fortress draws with a rook on the third rank defended by
-/// a pawn.
+/// K and queen vs K, rook and one or more pawns. It tests for fortress draws with
+/// a rook on the third rank defended by a pawn.
 template<>
-ScaleFactor Endgame<KQKRPs>::apply(const Position& pos) const {
+ScaleFactor Endgame<KQKRPs>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(strongerSide) == QueenValueMidgame);
   assert(pos.piece_count(strongerSide, QUEEN) == 1);
@@ -484,21 +461,20 @@ ScaleFactor Endgame<KQKRPs>::apply(const Position& pos) const {
   {
       Square rsq = pos.piece_list(weakerSide, ROOK)[0];
       if (pos.attacks_from<PAWN>(rsq, strongerSide) & pos.pieces(PAWN, weakerSide))
-          return SCALE_FACTOR_ZERO;
+          return SCALE_FACTOR_DRAW;
   }
   return SCALE_FACTOR_NONE;
 }
 
 
-/// KRPKRScalingFunction scales KRP vs KR endgames. This function knows a
-/// handful of the most important classes of drawn positions, but is far
-/// from perfect. It would probably be a good idea to add more knowledge
-/// in the future.
+/// K, rook and one pawn vs K and a rook. This function knows a handful of the
+/// most important classes of drawn positions, but is far from perfect. It would
+/// probably be a good idea to add more knowledge in the future.
 ///
 /// It would also be nice to rewrite the actual code for this function,
 /// which is mostly copied from Glaurung 1.x, and not very pretty.
 template<>
-ScaleFactor Endgame<KRPKR>::apply(const Position& pos) const {
+ScaleFactor Endgame<KRPKR>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(strongerSide) == RookValueMidgame);
   assert(pos.piece_count(strongerSide, PAWN) == 1);
@@ -515,11 +491,11 @@ ScaleFactor Endgame<KRPKR>::apply(const Position& pos) const {
   // pawn is on the left half of the board.
   if (strongerSide == BLACK)
   {
-      wksq = flip(wksq);
-      wrsq = flip(wrsq);
-      wpsq = flip(wpsq);
-      bksq = flip(bksq);
-      brsq = flip(brsq);
+      wksq = ~wksq;
+      wrsq = ~wrsq;
+      wpsq = ~wpsq;
+      bksq = ~bksq;
+      brsq = ~brsq;
   }
   if (file_of(wpsq) > FILE_D)
   {
@@ -541,7 +517,7 @@ ScaleFactor Endgame<KRPKR>::apply(const Position& pos) const {
       && square_distance(bksq, queeningSq) <= 1
       && wksq <= SQ_H5
       && (rank_of(brsq) == RANK_6 || (r <= RANK_3 && rank_of(wrsq) != RANK_6)))
-      return SCALE_FACTOR_ZERO;
+      return SCALE_FACTOR_DRAW;
 
   // The defending side saves a draw by checking from behind in case the pawn
   // has advanced to the 6th rank with the king behind.
@@ -549,13 +525,13 @@ ScaleFactor Endgame<KRPKR>::apply(const Position& pos) const {
       && square_distance(bksq, queeningSq) <= 1
       && rank_of(wksq) + tempo <= RANK_6
       && (rank_of(brsq) == RANK_1 || (!tempo && abs(file_of(brsq) - f) >= 3)))
-      return SCALE_FACTOR_ZERO;
+      return SCALE_FACTOR_DRAW;
 
   if (   r >= RANK_6
       && bksq == queeningSq
       && rank_of(brsq) == RANK_1
       && (!tempo || square_distance(wksq, wpsq) >= 2))
-      return SCALE_FACTOR_ZERO;
+      return SCALE_FACTOR_DRAW;
 
   // White pawn on a7 and rook on a8 is a draw if black's king is on g7 or h7
   // and the black rook is behind the pawn.
@@ -564,7 +540,7 @@ ScaleFactor Endgame<KRPKR>::apply(const Position& pos) const {
       && (bksq == SQ_H7 || bksq == SQ_G7)
       && file_of(brsq) == FILE_A
       && (rank_of(brsq) <= RANK_3 || file_of(wksq) >= FILE_D || rank_of(wksq) <= RANK_5))
-      return SCALE_FACTOR_ZERO;
+      return SCALE_FACTOR_DRAW;
 
   // If the defending king blocks the pawn and the attacking king is too far
   // away, it's a draw.
@@ -572,7 +548,7 @@ ScaleFactor Endgame<KRPKR>::apply(const Position& pos) const {
       && bksq == wpsq + DELTA_N
       && square_distance(wksq, wpsq) - tempo >= 2
       && square_distance(wksq, brsq) - tempo >= 2)
-      return SCALE_FACTOR_ZERO;
+      return SCALE_FACTOR_DRAW;
 
   // Pawn on the 7th rank supported by the rook from behind usually wins if the
   // attacking king is closer to the queening square than the defending king,
@@ -612,11 +588,11 @@ ScaleFactor Endgame<KRPKR>::apply(const Position& pos) const {
 }
 
 
-/// KRPPKRPScalingFunction scales KRPP vs KRP endgames. There is only a
-/// single pattern: If the stronger side has no pawns and the defending king
+/// K, rook and two pawns vs K, rook and one pawn. There is only a single
+/// pattern: If the stronger side has no passed pawns and the defending king
 /// is actively placed, the position is drawish.
 template<>
-ScaleFactor Endgame<KRPPKRP>::apply(const Position& pos) const {
+ScaleFactor Endgame<KRPPKRP>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(strongerSide) == RookValueMidgame);
   assert(pos.piece_count(strongerSide, PAWN) == 2);
@@ -632,7 +608,7 @@ ScaleFactor Endgame<KRPPKRP>::apply(const Position& pos) const {
       || pos.pawn_is_passed(strongerSide, wpsq2))
       return SCALE_FACTOR_NONE;
 
-  Rank r = Max(relative_rank(strongerSide, wpsq1), relative_rank(strongerSide, wpsq2));
+  Rank r = std::max(relative_rank(strongerSide, wpsq1), relative_rank(strongerSide, wpsq2));
 
   if (   file_distance(bksq, wpsq1) <= 1
       && file_distance(bksq, wpsq2) <= 1
@@ -651,11 +627,10 @@ ScaleFactor Endgame<KRPPKRP>::apply(const Position& pos) const {
 }
 
 
-/// KPsKScalingFunction scales endgames with king and two or more pawns
-/// against king. There is just a single rule here: If all pawns are on
-/// the same rook file and are blocked by the defending king, it's a draw.
+/// K and two or more pawns vs K. There is just a single rule here: If all pawns
+/// are on the same rook file and are blocked by the defending king, it's a draw.
 template<>
-ScaleFactor Endgame<KPsK>::apply(const Position& pos) const {
+ScaleFactor Endgame<KPsK>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(strongerSide) == VALUE_ZERO);
   assert(pos.piece_count(strongerSide, PAWN) >= 2);
@@ -666,34 +641,33 @@ ScaleFactor Endgame<KPsK>::apply(const Position& pos) const {
   Bitboard pawns = pos.pieces(PAWN, strongerSide);
 
   // Are all pawns on the 'a' file?
-  if ((pawns & ~FileABB) == EmptyBoardBB)
+  if (!(pawns & ~FileABB))
   {
       // Does the defending king block the pawns?
       if (   square_distance(ksq, relative_square(strongerSide, SQ_A8)) <= 1
           || (   file_of(ksq) == FILE_A
-              && (in_front_bb(strongerSide, ksq) & pawns) == EmptyBoardBB))
-          return SCALE_FACTOR_ZERO;
+              && !in_front_bb(strongerSide, ksq) & pawns))
+          return SCALE_FACTOR_DRAW;
   }
   // Are all pawns on the 'h' file?
-  else if ((pawns & ~FileHBB) == EmptyBoardBB)
+  else if (!(pawns & ~FileHBB))
   {
     // Does the defending king block the pawns?
     if (   square_distance(ksq, relative_square(strongerSide, SQ_H8)) <= 1
         || (   file_of(ksq) == FILE_H
-            && (in_front_bb(strongerSide, ksq) & pawns) == EmptyBoardBB))
-        return SCALE_FACTOR_ZERO;
+            && !in_front_bb(strongerSide, ksq) & pawns))
+        return SCALE_FACTOR_DRAW;
   }
   return SCALE_FACTOR_NONE;
 }
 
 
-/// KBPKBScalingFunction scales KBP vs KB endgames. There are two rules:
-/// If the defending king is somewhere along the path of the pawn, and the
-/// square of the king is not of the same color as the stronger side's bishop,
-/// it's a draw. If the two bishops have opposite color, it's almost always
-/// a draw.
+/// K, bishop and a pawn vs K and a bishop. There are two rules: If the defending
+/// king is somewhere along the path of the pawn, and the square of the king is
+/// not of the same color as the stronger side's bishop, it's a draw. If the two
+/// bishops have opposite color, it's almost always a draw.
 template<>
-ScaleFactor Endgame<KBPKB>::apply(const Position& pos) const {
+ScaleFactor Endgame<KBPKB>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(strongerSide) == BishopValueMidgame);
   assert(pos.piece_count(strongerSide, BISHOP) == 1);
@@ -712,7 +686,7 @@ ScaleFactor Endgame<KBPKB>::apply(const Position& pos) const {
       && relative_rank(strongerSide, pawnSq) < relative_rank(strongerSide, weakerKingSq)
       && (   opposite_colors(weakerKingSq, strongerBishopSq)
           || relative_rank(strongerSide, weakerKingSq) <= RANK_6))
-      return SCALE_FACTOR_ZERO;
+      return SCALE_FACTOR_DRAW;
 
   // Case 2: Opposite colored bishops
   if (opposite_colors(strongerBishopSq, weakerBishopSq))
@@ -728,27 +702,27 @@ ScaleFactor Endgame<KBPKB>::apply(const Position& pos) const {
       // reasonably well.
 
       if (relative_rank(strongerSide, pawnSq) <= RANK_5)
-          return SCALE_FACTOR_ZERO;
+          return SCALE_FACTOR_DRAW;
       else
       {
           Bitboard path = squares_in_front_of(strongerSide, pawnSq);
 
           if (path & pos.pieces(KING, weakerSide))
-              return SCALE_FACTOR_ZERO;
+              return SCALE_FACTOR_DRAW;
 
           if (  (pos.attacks_from<BISHOP>(weakerBishopSq) & path)
               && square_distance(weakerBishopSq, pawnSq) >= 3)
-              return SCALE_FACTOR_ZERO;
+              return SCALE_FACTOR_DRAW;
       }
   }
   return SCALE_FACTOR_NONE;
 }
 
 
-/// KBPPKBScalingFunction scales KBPP vs KB endgames. It detects a few basic
-/// draws with opposite-colored bishops.
+/// K, bishop and two pawns vs K and bishop. It detects a few basic draws with
+/// opposite-colored bishops.
 template<>
-ScaleFactor Endgame<KBPPKB>::apply(const Position& pos) const {
+ScaleFactor Endgame<KBPPKB>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(strongerSide) == BishopValueMidgame);
   assert(pos.piece_count(strongerSide, BISHOP) == 1);
@@ -789,12 +763,12 @@ ScaleFactor Endgame<KBPPKB>::apply(const Position& pos) const {
     if (   file_of(ksq) == file_of(blockSq1)
         && relative_rank(strongerSide, ksq) >= relative_rank(strongerSide, blockSq1)
         && opposite_colors(ksq, wbsq))
-        return SCALE_FACTOR_ZERO;
+        return SCALE_FACTOR_DRAW;
     else
         return SCALE_FACTOR_NONE;
 
   case 1:
-    // Pawns on neighboring files. Draw if defender firmly controls the square
+    // Pawns on adjacent files. Draw if defender firmly controls the square
     // in front of the frontmost pawn's path, and the square diagonally behind
     // this square on the file of the other pawn.
     if (   ksq == blockSq1
@@ -802,13 +776,13 @@ ScaleFactor Endgame<KBPPKB>::apply(const Position& pos) const {
         && (   bbsq == blockSq2
             || (pos.attacks_from<BISHOP>(blockSq2) & pos.pieces(BISHOP, weakerSide))
             || abs(r1 - r2) >= 2))
-        return SCALE_FACTOR_ZERO;
+        return SCALE_FACTOR_DRAW;
 
     else if (   ksq == blockSq2
              && opposite_colors(ksq, wbsq)
              && (   bbsq == blockSq1
                  || (pos.attacks_from<BISHOP>(blockSq1) & pos.pieces(BISHOP, weakerSide))))
-        return SCALE_FACTOR_ZERO;
+        return SCALE_FACTOR_DRAW;
     else
         return SCALE_FACTOR_NONE;
 
@@ -819,12 +793,11 @@ ScaleFactor Endgame<KBPPKB>::apply(const Position& pos) const {
 }
 
 
-/// KBPKNScalingFunction scales KBP vs KN endgames. There is a single rule:
-/// If the defending king is somewhere along the path of the pawn, and the
-/// square of the king is not of the same color as the stronger side's bishop,
-/// it's a draw.
+/// K, bisop and a pawn vs K and knight. There is a single rule: If the defending
+/// king is somewhere along the path of the pawn, and the square of the king is
+/// not of the same color as the stronger side's bishop, it's a draw.
 template<>
-ScaleFactor Endgame<KBPKN>::apply(const Position& pos) const {
+ScaleFactor Endgame<KBPKN>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(strongerSide) == BishopValueMidgame);
   assert(pos.piece_count(strongerSide, BISHOP) == 1);
@@ -841,17 +814,17 @@ ScaleFactor Endgame<KBPKN>::apply(const Position& pos) const {
       && relative_rank(strongerSide, pawnSq) < relative_rank(strongerSide, weakerKingSq)
       && (   opposite_colors(weakerKingSq, strongerBishopSq)
           || relative_rank(strongerSide, weakerKingSq) <= RANK_6))
-      return SCALE_FACTOR_ZERO;
+      return SCALE_FACTOR_DRAW;
 
   return SCALE_FACTOR_NONE;
 }
 
 
-/// KNPKScalingFunction scales KNP vs K endgames. 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.
+/// K, knight and a pawn 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.
 template<>
-ScaleFactor Endgame<KNPK>::apply(const Position& pos) const {
+ScaleFactor Endgame<KNPK>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(strongerSide) == KnightValueMidgame);
   assert(pos.piece_count(strongerSide, KNIGHT) == 1);
@@ -864,46 +837,40 @@ ScaleFactor Endgame<KNPK>::apply(const Position& pos) const {
 
   if (   pawnSq == relative_square(strongerSide, SQ_A7)
       && square_distance(weakerKingSq, relative_square(strongerSide, SQ_A8)) <= 1)
-      return SCALE_FACTOR_ZERO;
+      return SCALE_FACTOR_DRAW;
 
   if (   pawnSq == relative_square(strongerSide, SQ_H7)
       && square_distance(weakerKingSq, relative_square(strongerSide, SQ_H8)) <= 1)
-      return SCALE_FACTOR_ZERO;
+      return SCALE_FACTOR_DRAW;
 
   return SCALE_FACTOR_NONE;
 }
 
 
-/// KPKPScalingFunction scales KP vs KP endgames. This is done by removing
-/// the weakest side's pawn and probing the KP vs K bitbase: If the weakest
-/// side has a draw without the pawn, she probably has at least a draw with
-/// the pawn as well. The exception is when the stronger side's pawn is far
-/// advanced and not on a rook file; in this case it is often possible to win
-/// (e.g. 8/4k3/3p4/3P4/6K1/8/8/8 w - - 0 1).
+/// K and a pawn vs K and a pawn. This is done by removing the weakest side's
+/// pawn and probing the KP vs K bitbase: If the weakest side has a draw without
+/// the pawn, she probably has at least a draw with the pawn as well. The exception
+/// is when the stronger side's pawn is far advanced and not on a rook file; in
+/// this case it is often possible to win (e.g. 8/4k3/3p4/3P4/6K1/8/8/8 w - - 0 1).
 template<>
-ScaleFactor Endgame<KPKP>::apply(const Position& pos) const {
+ScaleFactor Endgame<KPKP>::operator()(const Position& pos) const {
 
   assert(pos.non_pawn_material(strongerSide) == VALUE_ZERO);
   assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO);
   assert(pos.piece_count(WHITE, PAWN) == 1);
   assert(pos.piece_count(BLACK, PAWN) == 1);
 
-  Square wksq, bksq, wpsq;
-  Color stm;
+  Square wksq = pos.king_square(strongerSide);
+  Square bksq = pos.king_square(weakerSide);
+  Square wpsq = pos.piece_list(strongerSide, PAWN)[0];
+  Color stm = pos.side_to_move();
 
-  if (strongerSide == WHITE)
-  {
-      wksq = pos.king_square(WHITE);
-      bksq = pos.king_square(BLACK);
-      wpsq = pos.piece_list(WHITE, PAWN)[0];
-      stm = pos.side_to_move();
-  }
-  else
+  if (strongerSide == BLACK)
   {
-      wksq = flip(pos.king_square(BLACK));
-      bksq = flip(pos.king_square(WHITE));
-      wpsq = flip(pos.piece_list(BLACK, PAWN)[0]);
-      stm = flip(pos.side_to_move());
+      wksq = ~wksq;
+      bksq = ~bksq;
+      wpsq = ~wpsq;
+      stm  = ~stm;
   }
 
   if (file_of(wpsq) >= FILE_E)
@@ -919,7 +886,7 @@ ScaleFactor Endgame<KPKP>::apply(const Position& pos) const {
       && file_of(wpsq) != FILE_A)
       return SCALE_FACTOR_NONE;
 
-  // Probe the KPK bitbase with the weakest side's pawn removed. If it's a
-  // draw, it's probably at least a draw even with the pawn.
-  return probe_kpk_bitbase(wksq, wpsq, bksq, stm) ? SCALE_FACTOR_NONE : SCALE_FACTOR_ZERO;
+  // Probe the KPK bitbase with the weakest side's pawn removed. If it's a draw,
+  // it's probably at least a draw even with the pawn.
+  return probe_kpk_bitbase(wksq, wpsq, bksq, stm) ? SCALE_FACTOR_NONE : SCALE_FACTOR_DRAW;
 }