X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fendgame.cpp;h=311443ec939f82ac7b2af69c836524ba8e8768a4;hp=913be63f1702c21eb4d76277c2cc4a6daaeb3954;hb=15e21911110f9d459c4fef2bb17903d97345d0b9;hpb=94b9c65e09b5d396bebb29b62d9979139b5fbdfa

diff --git a/src/endgame.cpp b/src/endgame.cpp
index 913be63f..311443ec 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) 2008-2014 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
@@ -17,27 +17,21 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-
-////
-//// Includes
-////
-
+#include <algorithm>
 #include <cassert>
 
-#include "bitbase.h"
+#include "bitboard.h"
 #include "bitcount.h"
 #include "endgame.h"
+#include "movegen.h"
 
-
-////
-//// Local definitions
-////
+using std::string;
 
 namespace {
 
-  // Table used to drive the defending king towards the edge of the board
+  // Table used to drive the king towards the edge of the board
   // in KX vs K and KQ vs KR endgames.
-  const uint8_t MateTable[64] = {
+  const int PushToEdges[SQUARE_NB] = {
     100, 90, 80, 70, 70, 80, 90, 100,
      90, 70, 60, 50, 50, 60, 70,  90,
      80, 60, 40, 30, 30, 40, 60,  80,
@@ -48,9 +42,9 @@ namespace {
     100, 90, 80, 70, 70, 80, 90, 100,
   };
 
-  // Table used to drive the defending king towards a corner square of the
+  // Table used to drive the king towards a corner square of the
   // right color in KBN vs K endgames.
-  const uint8_t KBNKMateTable[64] = {
+  const int PushToCorners[SQUARE_NB] = {
     200, 190, 180, 170, 160, 150, 140, 130,
     190, 180, 170, 160, 150, 140, 130, 140,
     180, 170, 155, 140, 140, 125, 140, 150,
@@ -61,156 +55,174 @@ namespace {
     130, 140, 150, 160, 170, 180, 190, 200
   };
 
-  // The attacking side is given a descending bonus based on distance between
-  // the two kings in basic endgames.
-  const int DistanceBonus[8] = { 0, 0, 100, 80, 60, 40, 20, 10 };
+  // Tables used to drive a piece towards or away from another piece
+  const int PushClose[8] = { 0, 0, 100, 80, 60, 40, 20, 10 };
+  const int PushAway [8] = { 0, 5, 20, 40, 60, 80, 90, 100 };
 
-  // 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 };
+#ifndef NDEBUG
+  bool verify_material(const Position& pos, Color c, Value npm, int num_pawns) {
+    return pos.non_pawn_material(c) == npm && pos.count<PAWN>(c) == num_pawns;
+  }
+#endif
 
-  // Bitbase for KP vs K
-  uint8_t KPKBitbase[24576];
+  // Map the square as if strongSide is white and strongSide's only pawn
+  // is on the left half of the board.
+  Square normalize(const Position& pos, Color strongSide, Square sq) {
 
-  // Various inline functions for accessing the above arrays
-  inline Value mate_table(Square s) {
-    return Value(MateTable[s]);
-  }
+    assert(pos.count<PAWN>(strongSide) == 1);
 
-  inline Value kbnk_mate_table(Square s) {
-    return Value(KBNKMateTable[s]);
-  }
+    if (file_of(pos.list<PAWN>(strongSide)[0]) >= FILE_E)
+        sq = Square(sq ^ 7); // Mirror SQ_H1 -> SQ_A1
+
+    if (strongSide == BLACK)
+        sq = ~sq;
 
-  inline Value distance_bonus(int d) {
-    return Value(DistanceBonus[d]);
+    return sq;
   }
 
-  inline Value krkn_king_knight_distance_penalty(int d) {
-    return Value(KRKNKingKnightDistancePenalty[d]);
+  // 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.
+  Key key(const string& code, Color c) {
+
+    assert(code.length() > 0 && code.length() < 8);
+    assert(code[0] == 'K');
+
+    string sides[] = { code.substr(code.find('K', 1)),      // Weak
+                       code.substr(0, code.find('K', 1)) }; // Strong
+
+    std::transform(sides[c].begin(), sides[c].end(), sides[c].begin(), tolower);
+
+    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();
   }
 
-  // Function for probing the KP vs K bitbase
-  int probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm);
+  template<typename M>
+  void delete_endgame(const typename M::value_type& p) { delete p.second; }
+
+} // namespace
+
 
+/// Endgames members definitions
+
+Endgames::Endgames() {
+
+  add<KPK>("KPK");
+  add<KNNK>("KNNK");
+  add<KBNK>("KBNK");
+  add<KRKP>("KRKP");
+  add<KRKB>("KRKB");
+  add<KRKN>("KRKN");
+  add<KQKP>("KQKP");
+  add<KQKR>("KQKR");
+
+  add<KNPK>("KNPK");
+  add<KNPKB>("KNPKB");
+  add<KRPKR>("KRPKR");
+  add<KRPKB>("KRPKB");
+  add<KBPKB>("KBPKB");
+  add<KBPKN>("KBPKN");
+  add<KBPPKB>("KBPPKB");
+  add<KRPPKRP>("KRPPKRP");
 }
 
+Endgames::~Endgames() {
 
-////
-//// Functions
-////
+  for_each(m1.begin(), m1.end(), delete_endgame<M1>);
+  for_each(m2.begin(), m2.end(), delete_endgame<M2>);
+}
 
-/// init_bitbases() is called during program initialization, and simply loads
-/// bitbases from disk into memory.  At the moment, there is only the bitbase
-/// for KP vs K, but we may decide to add other bitbases later.
+template<EndgameType E>
+void Endgames::add(const string& code) {
 
-void init_bitbases() {
-  generate_kpk_bitbase(KPKBitbase);
+  map((Endgame<E>*)0)[key(code, WHITE)] = new Endgame<E>(WHITE);
+  map((Endgame<E>*)0)[key(code, BLACK)] = new Endgame<E>(BLACK);
 }
 
 
 /// Mate with KX vs K. This function is used to evaluate positions with
-/// King and plenty of material vs a lone king. It simply gives the
+/// king and plenty of material vs a lone king. It simply gives the
 /// 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 EvaluationFunction<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);
+  assert(verify_material(pos, weakSide, VALUE_ZERO, 0));
+  assert(!pos.checkers()); // Eval is never called when in check
 
-  Square winnerKSq = pos.king_square(strongerSide);
-  Square loserKSq = pos.king_square(weakerSide);
+  // Stalemate detection with lone king
+  if (pos.side_to_move() == weakSide && !MoveList<LEGAL>(pos).size())
+      return VALUE_DRAW;
+
+  Square winnerKSq = pos.king_square(strongSide);
+  Square loserKSq = pos.king_square(weakSide);
 
-  Value result =   pos.non_pawn_material(strongerSide)
-                 + pos.piece_count(strongerSide, PAWN) * PawnValueEndgame
-                 + mate_table(loserKSq)
-                 + distance_bonus(square_distance(winnerKSq, loserKSq));
+  Value result =  pos.non_pawn_material(strongSide)
+                + pos.count<PAWN>(strongSide) * PawnValueEg
+                + PushToEdges[loserKSq]
+                + PushClose[square_distance(winnerKSq, loserKSq)];
 
-  if (   pos.piece_count(strongerSide, QUEEN)
-      || pos.piece_count(strongerSide, ROOK)
-      || pos.piece_count(strongerSide, BISHOP) > 1)
-      // TODO: check for two equal-colored bishops!
+  if (   pos.count<QUEEN>(strongSide)
+      || pos.count<ROOK>(strongSide)
+      ||(pos.count<BISHOP>(strongSide) && pos.count<KNIGHT>(strongSide))
+      || pos.bishop_pair(strongSide))
       result += VALUE_KNOWN_WIN;
 
-  return strongerSide == pos.side_to_move() ? result : -result;
+  return strongSide == pos.side_to_move() ? result : -result;
 }
 
 
 /// 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 EvaluationFunction<KBNK>::apply(const Position& pos) const {
-
-  assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO);
-  assert(pos.piece_count(weakerSide, PAWN) == VALUE_ZERO);
-  assert(pos.non_pawn_material(strongerSide) == KnightValueMidgame + BishopValueMidgame);
-  assert(pos.piece_count(strongerSide, BISHOP) == 1);
-  assert(pos.piece_count(strongerSide, KNIGHT) == 1);
-  assert(pos.piece_count(strongerSide, PAWN) == 0);
-
-  Square winnerKSq = pos.king_square(strongerSide);
-  Square loserKSq = pos.king_square(weakerSide);
-  Square bishopSquare = pos.piece_list(strongerSide, BISHOP, 0);
-
-  // kbnk_mate_table() tries to drive toward corners A1 or H8,
-  // if we have a bishop that cannot reach the above squares we
-  // mirror the kings so to drive enemy toward corners A8 or H1.
-  if (!same_color_squares(bishopSquare, SQ_A1))
+Value Endgame<KBNK>::operator()(const Position& pos) const {
+
+  assert(verify_material(pos, strongSide, KnightValueMg + BishopValueMg, 0));
+  assert(verify_material(pos, weakSide, VALUE_ZERO, 0));
+
+  Square winnerKSq = pos.king_square(strongSide);
+  Square loserKSq = pos.king_square(weakSide);
+  Square bishopSq = pos.list<BISHOP>(strongSide)[0];
+
+  // kbnk_mate_table() tries to drive toward corners A1 or H8. If we have a
+  // bishop that cannot reach the above squares, we flip the kings in order
+  // to drive the enemy toward corners A8 or H1.
+  if (opposite_colors(bishopSq, SQ_A1))
   {
-      winnerKSq = flop_square(winnerKSq);
-      loserKSq = flop_square(loserKSq);
+      winnerKSq = ~winnerKSq;
+      loserKSq  = ~loserKSq;
   }
 
   Value result =  VALUE_KNOWN_WIN
-                + distance_bonus(square_distance(winnerKSq, loserKSq))
-                + kbnk_mate_table(loserKSq);
+                + PushClose[square_distance(winnerKSq, loserKSq)]
+                + PushToCorners[loserKSq];
 
-  return strongerSide == pos.side_to_move() ? result : -result;
+  return strongSide == pos.side_to_move() ? result : -result;
 }
 
 
 /// KP vs K. This endgame is evaluated with the help of a bitbase.
 template<>
-Value EvaluationFunction<KPK>::apply(const Position& pos) const {
-
-  assert(pos.non_pawn_material(strongerSide) == VALUE_ZERO);
-  assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO);
-  assert(pos.piece_count(strongerSide, PAWN) == 1);
-  assert(pos.piece_count(weakerSide, PAWN) == 0);
+Value Endgame<KPK>::operator()(const Position& pos) const {
 
-  Square wksq, bksq, wpsq;
-  Color stm;
+  assert(verify_material(pos, strongSide, VALUE_ZERO, 1));
+  assert(verify_material(pos, weakSide, VALUE_ZERO, 0));
 
-  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
-  {
-      wksq = flip_square(pos.king_square(BLACK));
-      bksq = flip_square(pos.king_square(WHITE));
-      wpsq = flip_square(pos.piece_list(BLACK, PAWN, 0));
-      stm = opposite_color(pos.side_to_move());
-  }
+  // Assume strongSide is white and the pawn is on files A-D
+  Square wksq = normalize(pos, strongSide, pos.king_square(strongSide));
+  Square bksq = normalize(pos, strongSide, pos.king_square(weakSide));
+  Square psq  = normalize(pos, strongSide, pos.list<PAWN>(strongSide)[0]);
 
-  if (square_file(wpsq) >= FILE_E)
-  {
-      wksq = flop_square(wksq);
-      bksq = flop_square(bksq);
-      wpsq = flop_square(wpsq);
-  }
+  Color us = strongSide == pos.side_to_move() ? WHITE : BLACK;
 
-  if (!probe_kpk(wksq, wpsq, bksq, stm))
+  if (!Bitbases::probe_kpk(wksq, psq, bksq, us))
       return VALUE_DRAW;
 
-  Value result =  VALUE_KNOWN_WIN
-                + PawnValueEndgame
-                + Value(square_rank(wpsq));
+  Value result = VALUE_KNOWN_WIN + PawnValueEg + Value(rank_of(psq));
 
-  return strongerSide == pos.side_to_move() ? result : -result;
+  return strongSide == pos.side_to_move() ? result : -result;
 }
 
 
@@ -219,320 +231,271 @@ Value EvaluationFunction<KPK>::apply(const Position& pos) const {
 /// far advanced with support of the king, while the attacking king is far
 /// away.
 template<>
-Value EvaluationFunction<KRKP>::apply(const Position& pos) const {
-
-  assert(pos.non_pawn_material(strongerSide) == RookValueMidgame);
-  assert(pos.piece_count(strongerSide, PAWN) == 0);
-  assert(pos.non_pawn_material(weakerSide) == 0);
-  assert(pos.piece_count(weakerSide, PAWN) == 1);
-
-  Square wksq, wrsq, bksq, bpsq;
-  int tempo = (pos.side_to_move() == strongerSide);
+Value Endgame<KRKP>::operator()(const Position& pos) const {
 
-  wksq = pos.king_square(strongerSide);
-  wrsq = pos.piece_list(strongerSide, ROOK, 0);
-  bksq = pos.king_square(weakerSide);
-  bpsq = pos.piece_list(weakerSide, PAWN, 0);
+  assert(verify_material(pos, strongSide, RookValueMg, 0));
+  assert(verify_material(pos, weakSide, VALUE_ZERO, 1));
 
-  if (strongerSide == BLACK)
-  {
-      wksq = flip_square(wksq);
-      wrsq = flip_square(wrsq);
-      bksq = flip_square(bksq);
-      bpsq = flip_square(bpsq);
-  }
+  Square wksq = relative_square(strongSide, pos.king_square(strongSide));
+  Square bksq = relative_square(strongSide, pos.king_square(weakSide));
+  Square rsq  = relative_square(strongSide, pos.list<ROOK>(strongSide)[0]);
+  Square psq  = relative_square(strongSide, pos.list<PAWN>(weakSide)[0]);
 
-  Square queeningSq = make_square(square_file(bpsq), RANK_1);
+  Square queeningSq = make_square(file_of(psq), RANK_1);
   Value result;
 
   // If the stronger side's king is in front of the pawn, it's a win
-  if (wksq < bpsq && square_file(wksq) == square_file(bpsq))
-      result = RookValueEndgame - Value(square_distance(wksq, bpsq));
+  if (wksq < psq && file_of(wksq) == file_of(psq))
+      result = RookValueEg - square_distance(wksq, psq);
 
   // If the weaker side's king is too far from the pawn and the rook,
-  // it's a win
-  else if (   square_distance(bksq, bpsq) - (tempo ^ 1) >= 3
-           && square_distance(bksq, wrsq) >= 3)
-      result = RookValueEndgame - Value(square_distance(wksq, bpsq));
+  // it's a win.
+  else if (   square_distance(bksq, psq) >= 3 + (pos.side_to_move() == weakSide)
+           && square_distance(bksq, rsq) >= 3)
+      result = RookValueEg - square_distance(wksq, psq);
 
   // If the pawn is far advanced and supported by the defending king,
   // the position is drawish
-  else if (   square_rank(bksq) <= RANK_3
-           && square_distance(bksq, bpsq) == 1
-           && square_rank(wksq) >= RANK_4
-           && square_distance(wksq, bpsq) - tempo > 2)
-      result = Value(80 - square_distance(wksq, bpsq) * 8);
+  else if (   rank_of(bksq) <= RANK_3
+           && square_distance(bksq, psq) == 1
+           && rank_of(wksq) >= RANK_4
+           && square_distance(wksq, psq) > 2 + (pos.side_to_move() == strongSide))
+      result = Value(80) - 8 * square_distance(wksq, psq);
 
   else
-      result =  Value(200)
-              - Value(square_distance(wksq, bpsq + DELTA_S) * 8)
-              + Value(square_distance(bksq, bpsq + DELTA_S) * 8)
-              + Value(square_distance(bpsq, queeningSq) * 8);
+      result =  Value(200) - 8 * (  square_distance(wksq, psq + DELTA_S)
+                                  - square_distance(bksq, psq + DELTA_S)
+                                  - square_distance(psq, queeningSq));
 
-  return strongerSide == pos.side_to_move() ? result : -result;
+  return strongSide == pos.side_to_move() ? result : -result;
 }
 
 
 /// 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 EvaluationFunction<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);
-  assert(pos.non_pawn_material(weakerSide) == BishopValueMidgame);
-  assert(pos.piece_count(weakerSide, PAWN) == 0);
-  assert(pos.piece_count(weakerSide, BISHOP) == 1);
+  assert(verify_material(pos, strongSide, RookValueMg, 0));
+  assert(verify_material(pos, weakSide, BishopValueMg, 0));
 
-  Value result = mate_table(pos.king_square(weakerSide));
-  return strongerSide == pos.side_to_move() ? result : -result;
+  Value result = Value(PushToEdges[pos.king_square(weakSide)]);
+  return strongSide == pos.side_to_move() ? result : -result;
 }
 
 
-/// KR vs KN.  The attacking side has slightly better winning chances than
+/// 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 EvaluationFunction<KRKN>::apply(const Position& pos) const {
-
-  assert(pos.non_pawn_material(strongerSide) == RookValueMidgame);
-  assert(pos.piece_count(strongerSide, PAWN) == 0);
-  assert(pos.non_pawn_material(weakerSide) == KnightValueMidgame);
-  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);
+Value Endgame<KRKN>::operator()(const Position& pos) const {
 
-  int d = square_distance(defendingKSq, nSq);
-  Value result =   Value(10)
-                 + mate_table(defendingKSq)
-                 + krkn_king_knight_distance_penalty(d);
+  assert(verify_material(pos, strongSide, RookValueMg, 0));
+  assert(verify_material(pos, weakSide, KnightValueMg, 0));
 
-  return strongerSide == pos.side_to_move() ? result : -result;
+  Square bksq = pos.king_square(weakSide);
+  Square bnsq = pos.list<KNIGHT>(weakSide)[0];
+  Value result = Value(PushToEdges[bksq] + PushAway[square_distance(bksq, bnsq)]);
+  return strongSide == pos.side_to_move() ? result : -result;
 }
 
 
-/// KQ vs KR.  This is almost identical to KX vs K:  We give the attacking
-/// king a bonus for having the kings close together, and for forcing the
-/// defending king towards the edge.  If we also take care to avoid null move
-/// for the defending side in the search, this is usually sufficient to be
-/// able to win KQ vs KR.
+/// KQ vs KP. In general, this is a win for the stronger side, but there are a
+/// few important exceptions. A pawn on 7th rank and on the A,C,F or H files
+/// with a king positioned next to it can be a draw, so in that case, we only
+/// use the distance between the kings.
 template<>
-Value EvaluationFunction<KQKR>::apply(const Position& pos) const {
+Value Endgame<KQKP>::operator()(const Position& pos) const {
 
-  assert(pos.non_pawn_material(strongerSide) == QueenValueMidgame);
-  assert(pos.piece_count(strongerSide, PAWN) == 0);
-  assert(pos.non_pawn_material(weakerSide) == RookValueMidgame);
-  assert(pos.piece_count(weakerSide, PAWN) == 0);
+  assert(verify_material(pos, strongSide, QueenValueMg, 0));
+  assert(verify_material(pos, weakSide, VALUE_ZERO, 1));
 
-  Square winnerKSq = pos.king_square(strongerSide);
-  Square loserKSq = pos.king_square(weakerSide);
+  Square winnerKSq = pos.king_square(strongSide);
+  Square loserKSq = pos.king_square(weakSide);
+  Square pawnSq = pos.list<PAWN>(weakSide)[0];
 
-  Value result =  QueenValueEndgame
-                - RookValueEndgame
-                + mate_table(loserKSq)
-                + distance_bonus(square_distance(winnerKSq, loserKSq));
+  Value result = Value(PushClose[square_distance(winnerKSq, loserKSq)]);
 
-  return strongerSide == pos.side_to_move() ? result : -result;
-}
+  if (   relative_rank(weakSide, pawnSq) != RANK_7
+      || square_distance(loserKSq, pawnSq) != 1
+      || !((FileABB | FileCBB | FileFBB | FileHBB) & pawnSq))
+      result += QueenValueEg - PawnValueEg;
 
-template<>
-Value EvaluationFunction<KBBKN>::apply(const Position& pos) const {
+  return strongSide == pos.side_to_move() ? result : -result;
+}
 
-  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);
 
-  Value result = BishopValueEndgame;
-  Square wksq = pos.king_square(strongerSide);
-  Square bksq = pos.king_square(weakerSide);
-  Square nsq = pos.piece_list(weakerSide, KNIGHT, 0);
+/// KQ vs KR.  This is almost identical to KX vs K:  We give the attacking
+/// king a bonus for having the kings close together, and for forcing the
+/// defending king towards the edge. If we also take care to avoid null move for
+/// the defending side in the search, this is usually sufficient to win KQ vs KR.
+template<>
+Value Endgame<KQKR>::operator()(const Position& pos) const {
 
-  // Bonus for attacking king close to defending king
-  result += distance_bonus(square_distance(wksq, bksq));
+  assert(verify_material(pos, strongSide, QueenValueMg, 0));
+  assert(verify_material(pos, weakSide, RookValueMg, 0));
 
-  // Bonus for driving the defending king and knight apart
-  result += Value(square_distance(bksq, nsq) * 32);
+  Square winnerKSq = pos.king_square(strongSide);
+  Square loserKSq = pos.king_square(weakSide);
 
-  // Bonus for restricting the knight's mobility
-  result += Value((8 - count_1s_max_15(pos.attacks_from<KNIGHT>(nsq))) * 8);
+  Value result =  QueenValueEg
+                - RookValueEg
+                + PushToEdges[loserKSq]
+                + PushClose[square_distance(winnerKSq, loserKSq)];
 
-  return strongerSide == pos.side_to_move() ? result : -result;
+  return strongSide == pos.side_to_move() ? result : -result;
 }
 
 
-/// K and two minors vs K and one or two minors or K and two knights against
-/// king alone are always draw.
-template<>
-Value EvaluationFunction<KmmKm>::apply(const Position&) const {
-  return VALUE_ZERO;
-}
+/// Some cases of trivial draws
+template<> Value Endgame<KNNK>::operator()(const Position&) const { return VALUE_DRAW; }
 
-template<>
-Value EvaluationFunction<KNNK>::apply(const Position&) const {
-  return VALUE_ZERO;
-}
 
-/// 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
+/// KB 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 ScalingFunction<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);
-  assert(pos.piece_count(strongerSide, PAWN) >= 1);
+  assert(pos.non_pawn_material(strongSide) == BishopValueMg);
+  assert(pos.count<PAWN>(strongSide) >= 1);
 
-  // No assertions about the material of weakerSide, because we want draws to
+  // No assertions about the material of weakSide, because we want draws to
   // be detected even when the weaker side has some pawns.
 
-  Bitboard pawns = pos.pieces(PAWN, strongerSide);
-  File pawnFile = square_file(pos.piece_list(strongerSide, PAWN, 0));
+  Bitboard pawns = pos.pieces(strongSide, PAWN);
+  File pawnFile = file_of(pos.list<PAWN>(strongSide)[0]);
 
   // All pawns are on a single rook file ?
-  if (   (pawnFile == FILE_A || pawnFile == FILE_H)
-      && (pawns & ~file_bb(pawnFile)) == EmptyBoardBB)
+  if (    (pawnFile == FILE_A || pawnFile == FILE_H)
+      && !(pawns & ~file_bb(pawnFile)))
   {
-      Square bishopSq = pos.piece_list(strongerSide, BISHOP, 0);
-      Square queeningSq = relative_square(strongerSide, make_square(pawnFile, RANK_8));
-      Square kingSq = pos.king_square(weakerSide);
+      Square bishopSq = pos.list<BISHOP>(strongSide)[0];
+      Square queeningSq = relative_square(strongSide, make_square(pawnFile, RANK_8));
+      Square kingSq = pos.king_square(weakSide);
+
+      if (   opposite_colors(queeningSq, bishopSq)
+          && square_distance(queeningSq, kingSq) <= 1)
+          return SCALE_FACTOR_DRAW;
+  }
 
-      if (  !same_color_squares(queeningSq, bishopSq)
-          && file_distance(square_file(kingSq), pawnFile) <= 1)
+  // If all the pawns are on the same B or G file, then it's potentially a draw
+  if (    (pawnFile == FILE_B || pawnFile == FILE_G)
+      && !(pos.pieces(PAWN) & ~file_bb(pawnFile))
+      && pos.non_pawn_material(weakSide) == 0
+      && pos.count<PAWN>(weakSide) >= 1)
+  {
+      // Get weakSide pawn that is closest to the home rank
+      Square weakPawnSq = backmost_sq(weakSide, pos.pieces(weakSide, PAWN));
+
+      Square strongKingSq = pos.king_square(strongSide);
+      Square weakKingSq = pos.king_square(weakSide);
+      Square bishopSq = pos.list<BISHOP>(strongSide)[0];
+
+      // There's potential for a draw if our pawn is blocked on the 7th rank,
+      // the bishop cannot attack it or they only have one pawn left
+      if (   relative_rank(strongSide, weakPawnSq) == RANK_7
+          && (pos.pieces(strongSide, PAWN) & (weakPawnSq + pawn_push(weakSide)))
+          && (opposite_colors(bishopSq, weakPawnSq) || pos.count<PAWN>(strongSide) == 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
-          // frontmost pawn.
-          Rank rank;
-          if (strongerSide == WHITE)
-          {
-              for (rank = RANK_7; (rank_bb(rank) & pawns) == EmptyBoardBB; rank--) {}
-              assert(rank >= RANK_2 && rank <= RANK_7);
-          }
-          else
-          {
-              for (rank = RANK_2; (rank_bb(rank) & pawns) == EmptyBoardBB; rank++) {}
-              rank = Rank(rank ^ 7);  // HACK to get the relative rank
-              assert(rank >= RANK_2 && rank <= RANK_7);
-          }
-          // If the defending king has distance 1 to the promotion square or
-          // 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;
+          int strongKingDist = square_distance(weakPawnSq, strongKingSq);
+          int weakKingDist = square_distance(weakPawnSq, weakKingSq);
+
+          // It's a draw if the weak king is on its back two ranks, within 2
+          // squares of the blocking pawn and the strong king is not
+          // closer. (I think this rule only fails in practically
+          // unreachable positions such as 5k1K/6p1/6P1/8/8/3B4/8/8 w
+          // and positions where qsearch will immediately correct the
+          // problem such as 8/4k1p1/6P1/1K6/3B4/8/8/8 w)
+          if (   relative_rank(strongSide, weakKingSq) >= RANK_7
+              && weakKingDist <= 2
+              && weakKingDist <= strongKingDist)
+              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.
+/// KQ vs KR and one or more pawns. It tests for fortress draws with a rook on
+/// the third rank defended by a pawn.
 template<>
-ScaleFactor ScalingFunction<KQKRPs>::apply(const Position& pos) const {
-
-  assert(pos.non_pawn_material(strongerSide) == QueenValueMidgame);
-  assert(pos.piece_count(strongerSide, QUEEN) == 1);
-  assert(pos.piece_count(strongerSide, PAWN) == 0);
-  assert(pos.piece_count(weakerSide, ROOK) == 1);
-  assert(pos.piece_count(weakerSide, PAWN) >= 1);
-
-  Square kingSq = pos.king_square(weakerSide);
-  if (   relative_rank(weakerSide, kingSq) <= RANK_2
-      && relative_rank(weakerSide, pos.king_square(strongerSide)) >= RANK_4
-      && (pos.pieces(ROOK, weakerSide) & relative_rank_bb(weakerSide, RANK_3))
-      && (pos.pieces(PAWN, weakerSide) & relative_rank_bb(weakerSide, RANK_2))
-      && (pos.attacks_from<KING>(kingSq) & pos.pieces(PAWN, weakerSide)))
-  {
-      Square rsq = pos.piece_list(weakerSide, ROOK, 0);
-      if (pos.attacks_from<PAWN>(rsq, strongerSide) & pos.pieces(PAWN, weakerSide))
-          return SCALE_FACTOR_ZERO;
-  }
+ScaleFactor Endgame<KQKRPs>::operator()(const Position& pos) const {
+
+  assert(verify_material(pos, strongSide, QueenValueMg, 0));
+  assert(pos.count<ROOK>(weakSide) == 1);
+  assert(pos.count<PAWN>(weakSide) >= 1);
+
+  Square kingSq = pos.king_square(weakSide);
+  Square rsq = pos.list<ROOK>(weakSide)[0];
+
+  if (    relative_rank(weakSide, kingSq) <= RANK_2
+      &&  relative_rank(weakSide, pos.king_square(strongSide)) >= RANK_4
+      &&  relative_rank(weakSide, rsq) == RANK_3
+      && (  pos.pieces(weakSide, PAWN)
+          & pos.attacks_from<KING>(kingSq)
+          & pos.attacks_from<PAWN>(rsq, strongSide)))
+          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.
+/// KRP vs KR. 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.
+/// which is mostly copied from Glaurung 1.x, and isn't very pretty.
 template<>
-ScaleFactor ScalingFunction<KRPKR>::apply(const Position& pos) const {
-
-  assert(pos.non_pawn_material(strongerSide) == RookValueMidgame);
-  assert(pos.piece_count(strongerSide, PAWN) == 1);
-  assert(pos.non_pawn_material(weakerSide) == RookValueMidgame);
-  assert(pos.piece_count(weakerSide, PAWN) == 0);
-
-  Square wksq = pos.king_square(strongerSide);
-  Square wrsq = pos.piece_list(strongerSide, ROOK, 0);
-  Square wpsq = pos.piece_list(strongerSide, PAWN, 0);
-  Square bksq = pos.king_square(weakerSide);
-  Square brsq = pos.piece_list(weakerSide, ROOK, 0);
-
-  // Orient the board in such a way that the stronger side is white, and the
-  // pawn is on the left half of the board.
-  if (strongerSide == BLACK)
-  {
-      wksq = flip_square(wksq);
-      wrsq = flip_square(wrsq);
-      wpsq = flip_square(wpsq);
-      bksq = flip_square(bksq);
-      brsq = flip_square(brsq);
-  }
-  if (square_file(wpsq) > FILE_D)
-  {
-      wksq = flop_square(wksq);
-      wrsq = flop_square(wrsq);
-      wpsq = flop_square(wpsq);
-      bksq = flop_square(bksq);
-      brsq = flop_square(brsq);
-  }
+ScaleFactor Endgame<KRPKR>::operator()(const Position& pos) const {
 
-  File f = square_file(wpsq);
-  Rank r = square_rank(wpsq);
+  assert(verify_material(pos, strongSide, RookValueMg, 1));
+  assert(verify_material(pos, weakSide,   RookValueMg, 0));
+
+  // Assume strongSide is white and the pawn is on files A-D
+  Square wksq = normalize(pos, strongSide, pos.king_square(strongSide));
+  Square bksq = normalize(pos, strongSide, pos.king_square(weakSide));
+  Square wrsq = normalize(pos, strongSide, pos.list<ROOK>(strongSide)[0]);
+  Square wpsq = normalize(pos, strongSide, pos.list<PAWN>(strongSide)[0]);
+  Square brsq = normalize(pos, strongSide, pos.list<ROOK>(weakSide)[0]);
+
+  File f = file_of(wpsq);
+  Rank r = rank_of(wpsq);
   Square queeningSq = make_square(f, RANK_8);
-  int tempo = (pos.side_to_move() == strongerSide);
+  int tempo = (pos.side_to_move() == strongSide);
 
   // If the pawn is not too far advanced and the defending king defends the
   // queening square, use the third-rank defence.
   if (   r <= RANK_5
       && square_distance(bksq, queeningSq) <= 1
       && wksq <= SQ_H5
-      && (square_rank(brsq) == RANK_6 || (r <= RANK_3 && square_rank(wrsq) != RANK_6)))
-      return SCALE_FACTOR_ZERO;
+      && (rank_of(brsq) == RANK_6 || (r <= RANK_3 && rank_of(wrsq) != RANK_6)))
+      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.
   if (   r == RANK_6
       && square_distance(bksq, queeningSq) <= 1
-      && square_rank(wksq) + tempo <= RANK_6
-      && (square_rank(brsq) == RANK_1 || (!tempo && abs(square_file(brsq) - f) >= 3)))
-      return SCALE_FACTOR_ZERO;
+      && rank_of(wksq) + tempo <= RANK_6
+      && (rank_of(brsq) == RANK_1 || (!tempo && abs(file_of(brsq) - f) >= 3)))
+      return SCALE_FACTOR_DRAW;
 
   if (   r >= RANK_6
       && bksq == queeningSq
-      && square_rank(brsq) == RANK_1
+      && 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.
   if (   wpsq == SQ_A7
       && wrsq == SQ_A8
       && (bksq == SQ_H7 || bksq == SQ_G7)
-      && square_file(brsq) == FILE_A
-      && (square_rank(brsq) <= RANK_3 || square_file(wksq) >= FILE_D || square_rank(wksq) <= RANK_5))
-      return SCALE_FACTOR_ZERO;
+      && file_of(brsq) == FILE_A
+      && (rank_of(brsq) <= RANK_3 || file_of(wksq) >= FILE_D || rank_of(wksq) <= RANK_5))
+      return SCALE_FACTOR_DRAW;
 
   // If the defending king blocks the pawn and the attacking king is too far
   // away, it's a draw.
@@ -540,14 +503,14 @@ ScaleFactor ScalingFunction<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,
   // and the defending king cannot gain tempi by threatening the attacking rook.
   if (   r == RANK_7
       && f != FILE_A
-      && square_file(wrsq) == f
+      && file_of(wrsq) == f
       && wrsq != queeningSq
       && (square_distance(wksq, queeningSq) < square_distance(bksq, queeningSq) - 2 + tempo)
       && (square_distance(wksq, queeningSq) < square_distance(bksq, wrsq) + tempo))
@@ -555,7 +518,7 @@ ScaleFactor ScalingFunction<KRPKR>::apply(const Position& pos) const {
 
   // Similar to the above, but with the pawn further back
   if (   f != FILE_A
-      && square_file(wrsq) == f
+      && file_of(wrsq) == f
       && wrsq < wpsq
       && (square_distance(wksq, queeningSq) < square_distance(bksq, queeningSq) - 2 + tempo)
       && (square_distance(wksq, wpsq + DELTA_N) < square_distance(bksq, wpsq + DELTA_N) - 2 + tempo)
@@ -566,45 +529,84 @@ ScaleFactor ScalingFunction<KRPKR>::apply(const Position& pos) const {
                          - 8 * square_distance(wpsq, queeningSq)
                          - 2 * square_distance(wksq, queeningSq));
 
-  // If the pawn is not far advanced, and the defending king is somewhere in
+  // If the pawn is not far advanced and the defending king is somewhere in
   // the pawn's path, it's probably a draw.
   if (r <= RANK_4 && bksq > wpsq)
   {
-      if (square_file(bksq) == square_file(wpsq))
+      if (file_of(bksq) == file_of(wpsq))
           return ScaleFactor(10);
-      if (   abs(square_file(bksq) - square_file(wpsq)) == 1
+      if (   abs(file_of(bksq) - file_of(wpsq)) == 1
           && square_distance(wksq, bksq) > 2)
           return ScaleFactor(24 - 2 * square_distance(wksq, bksq));
   }
   return SCALE_FACTOR_NONE;
 }
 
+template<>
+ScaleFactor Endgame<KRPKB>::operator()(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
-/// is actively placed, the position is drawish.
+  assert(verify_material(pos, strongSide, RookValueMg, 1));
+  assert(verify_material(pos, weakSide, BishopValueMg, 0));
+
+  // Test for a rook pawn
+  if (pos.pieces(PAWN) & (FileABB | FileHBB))
+  {
+      Square ksq = pos.king_square(weakSide);
+      Square bsq = pos.list<BISHOP>(weakSide)[0];
+      Square psq = pos.list<PAWN>(strongSide)[0];
+      Rank rk = relative_rank(strongSide, psq);
+      Square push = pawn_push(strongSide);
+
+      // If the pawn is on the 5th rank and the pawn (currently) is on
+      // the same color square as the bishop then there is a chance of
+      // a fortress. Depending on the king position give a moderate
+      // reduction or a stronger one if the defending king is near the
+      // corner but not trapped there.
+      if (rk == RANK_5 && !opposite_colors(bsq, psq))
+      {
+          int d = square_distance(psq + 3 * push, ksq);
+
+          if (d <= 2 && !(d == 0 && ksq == pos.king_square(strongSide) + 2 * push))
+              return ScaleFactor(24);
+          else
+              return ScaleFactor(48);
+      }
+
+      // When the pawn has moved to the 6th rank we can be fairly sure
+      // it's drawn if the bishop attacks the square in front of the
+      // pawn from a reasonable distance and the defending king is near
+      // the corner
+      if (   rk == RANK_6
+          && square_distance(psq + 2 * push, ksq) <= 1
+          && (PseudoAttacks[BISHOP][bsq] & (psq + push))
+          && file_distance(bsq, psq) >= 2)
+          return ScaleFactor(8);
+  }
+
+  return SCALE_FACTOR_NONE;
+}
+
+/// KRPP vs KRP. There is just a single rule: if the stronger side has no passed
+/// pawns and the defending king is actively placed, the position is drawish.
 template<>
-ScaleFactor ScalingFunction<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);
-  assert(pos.non_pawn_material(weakerSide) == RookValueMidgame);
-  assert(pos.piece_count(weakerSide, PAWN) == 1);
+  assert(verify_material(pos, strongSide, RookValueMg, 2));
+  assert(verify_material(pos, weakSide,   RookValueMg, 1));
 
-  Square wpsq1 = pos.piece_list(strongerSide, PAWN, 0);
-  Square wpsq2 = pos.piece_list(strongerSide, PAWN, 1);
-  Square bksq = pos.king_square(weakerSide);
+  Square wpsq1 = pos.list<PAWN>(strongSide)[0];
+  Square wpsq2 = pos.list<PAWN>(strongSide)[1];
+  Square bksq = pos.king_square(weakSide);
 
   // Does the stronger side have a passed pawn?
-  if (   pos.pawn_is_passed(strongerSide, wpsq1)
-      || pos.pawn_is_passed(strongerSide, wpsq2))
+  if (pos.pawn_passed(strongSide, wpsq1) || pos.pawn_passed(strongSide, wpsq2))
       return SCALE_FACTOR_NONE;
 
-  Rank r = Max(relative_rank(strongerSide, wpsq1), relative_rank(strongerSide, wpsq2));
+  Rank r = std::max(relative_rank(strongSide, wpsq1), relative_rank(strongSide, wpsq2));
 
   if (   file_distance(bksq, wpsq1) <= 1
       && file_distance(bksq, wpsq2) <= 1
-      && relative_rank(strongerSide, bksq) > r)
+      && relative_rank(strongSide, bksq) > r)
   {
       switch (r) {
       case RANK_2: return ScaleFactor(10);
@@ -619,71 +621,54 @@ ScaleFactor ScalingFunction<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 ScalingFunction<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);
-  assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO);
-  assert(pos.piece_count(weakerSide, PAWN) == 0);
+  assert(pos.non_pawn_material(strongSide) == VALUE_ZERO);
+  assert(pos.count<PAWN>(strongSide) >= 2);
+  assert(verify_material(pos, weakSide, VALUE_ZERO, 0));
 
-  Square ksq = pos.king_square(weakerSide);
-  Bitboard pawns = pos.pieces(PAWN, strongerSide);
+  Square ksq = pos.king_square(weakSide);
+  Bitboard pawns = pos.pieces(strongSide, PAWN);
+  Square psq = pos.list<PAWN>(strongSide)[0];
+
+  // If all pawns are ahead of the king, on a single rook file and
+  // the king is within one file of the pawns, it's a draw.
+  if (   !(pawns & ~in_front_bb(weakSide, rank_of(ksq)))
+      && !((pawns & ~FileABB) && (pawns & ~FileHBB))
+      && file_distance(ksq, psq) <= 1)
+      return SCALE_FACTOR_DRAW;
 
-  // Are all pawns on the 'a' file?
-  if ((pawns & ~FileABB) == EmptyBoardBB)
-  {
-      // Does the defending king block the pawns?
-      if (   square_distance(ksq, relative_square(strongerSide, SQ_A8)) <= 1
-          || (   square_file(ksq) == FILE_A
-              && (in_front_bb(strongerSide, ksq) & pawns) == EmptyBoardBB))
-          return SCALE_FACTOR_ZERO;
-  }
-  // Are all pawns on the 'h' file?
-  else if ((pawns & ~FileHBB) == EmptyBoardBB)
-  {
-    // Does the defending king block the pawns?
-    if (   square_distance(ksq, relative_square(strongerSide, SQ_H8)) <= 1
-        || (   square_file(ksq) == FILE_H
-            && (in_front_bb(strongerSide, ksq) & pawns) == EmptyBoardBB))
-        return SCALE_FACTOR_ZERO;
-  }
   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.
+/// KBP vs KB. 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 ScalingFunction<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);
-  assert(pos.piece_count(strongerSide, PAWN) == 1);
-  assert(pos.non_pawn_material(weakerSide) == BishopValueMidgame);
-  assert(pos.piece_count(weakerSide, BISHOP) == 1);
-  assert(pos.piece_count(weakerSide, PAWN) == 0);
+  assert(verify_material(pos, strongSide, BishopValueMg, 1));
+  assert(verify_material(pos, weakSide,   BishopValueMg, 0));
 
-  Square pawnSq = pos.piece_list(strongerSide, PAWN, 0);
-  Square strongerBishopSq = pos.piece_list(strongerSide, BISHOP, 0);
-  Square weakerBishopSq = pos.piece_list(weakerSide, BISHOP, 0);
-  Square weakerKingSq = pos.king_square(weakerSide);
+  Square pawnSq = pos.list<PAWN>(strongSide)[0];
+  Square strongBishopSq = pos.list<BISHOP>(strongSide)[0];
+  Square weakBishopSq = pos.list<BISHOP>(weakSide)[0];
+  Square weakKingSq = pos.king_square(weakSide);
 
   // Case 1: Defending king blocks the pawn, and cannot be driven away
-  if (   square_file(weakerKingSq) == square_file(pawnSq)
-      && relative_rank(strongerSide, pawnSq) < relative_rank(strongerSide, weakerKingSq)
-      && (  !same_color_squares(weakerKingSq, strongerBishopSq)
-          || relative_rank(strongerSide, weakerKingSq) <= RANK_6))
-      return SCALE_FACTOR_ZERO;
+  if (   file_of(weakKingSq) == file_of(pawnSq)
+      && relative_rank(strongSide, pawnSq) < relative_rank(strongSide, weakKingSq)
+      && (   opposite_colors(weakKingSq, strongBishopSq)
+          || relative_rank(strongSide, weakKingSq) <= RANK_6))
+      return SCALE_FACTOR_DRAW;
 
   // Case 2: Opposite colored bishops
-  if (!same_color_squares(strongerBishopSq, weakerBishopSq))
+  if (opposite_colors(strongBishopSq, weakBishopSq))
   {
       // We assume that the position is drawn in the following three situations:
       //
@@ -695,88 +680,83 @@ ScaleFactor ScalingFunction<KBPKB>::apply(const Position& pos) const {
       // These rules are probably not perfect, but in practice they work
       // reasonably well.
 
-      if (relative_rank(strongerSide, pawnSq) <= RANK_5)
-          return SCALE_FACTOR_ZERO;
+      if (relative_rank(strongSide, pawnSq) <= RANK_5)
+          return SCALE_FACTOR_DRAW;
       else
       {
-          Bitboard ray = ray_bb(pawnSq, (strongerSide == WHITE)? SIGNED_DIR_N : SIGNED_DIR_S);
-          if (ray & pos.pieces(KING, weakerSide))
-              return SCALE_FACTOR_ZERO;
+          Bitboard path = forward_bb(strongSide, pawnSq);
 
-          if (  (pos.attacks_from<BISHOP>(weakerBishopSq) & ray)
-              && square_distance(weakerBishopSq, pawnSq) >= 3)
-              return SCALE_FACTOR_ZERO;
+          if (path & pos.pieces(weakSide, KING))
+              return SCALE_FACTOR_DRAW;
+
+          if (  (pos.attacks_from<BISHOP>(weakBishopSq) & path)
+              && square_distance(weakBishopSq, pawnSq) >= 3)
+              return SCALE_FACTOR_DRAW;
       }
   }
   return SCALE_FACTOR_NONE;
 }
 
 
-/// KBPPKBScalingFunction scales KBPP vs KB endgames. It detects a few basic
-/// draws with opposite-colored bishops.
+/// KBPP vs KB. It detects a few basic draws with opposite-colored bishops
 template<>
-ScaleFactor ScalingFunction<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);
-  assert(pos.piece_count(strongerSide, PAWN) == 2);
-  assert(pos.non_pawn_material(weakerSide) == BishopValueMidgame);
-  assert(pos.piece_count(weakerSide, BISHOP) == 1);
-  assert(pos.piece_count(weakerSide, PAWN) == 0);
+  assert(verify_material(pos, strongSide, BishopValueMg, 2));
+  assert(verify_material(pos, weakSide,   BishopValueMg, 0));
 
-  Square wbsq = pos.piece_list(strongerSide, BISHOP, 0);
-  Square bbsq = pos.piece_list(weakerSide, BISHOP, 0);
+  Square wbsq = pos.list<BISHOP>(strongSide)[0];
+  Square bbsq = pos.list<BISHOP>(weakSide)[0];
 
-  if (same_color_squares(wbsq, bbsq))
-      // Not opposite-colored bishops, no scaling
+  if (!opposite_colors(wbsq, bbsq))
       return SCALE_FACTOR_NONE;
 
-  Square ksq = pos.king_square(weakerSide);
-  Square psq1 = pos.piece_list(strongerSide, PAWN, 0);
-  Square psq2 = pos.piece_list(strongerSide, PAWN, 1);
-  Rank r1 = square_rank(psq1);
-  Rank r2 = square_rank(psq2);
+  Square ksq = pos.king_square(weakSide);
+  Square psq1 = pos.list<PAWN>(strongSide)[0];
+  Square psq2 = pos.list<PAWN>(strongSide)[1];
+  Rank r1 = rank_of(psq1);
+  Rank r2 = rank_of(psq2);
   Square blockSq1, blockSq2;
 
-  if (relative_rank(strongerSide, psq1) > relative_rank(strongerSide, psq2))
+  if (relative_rank(strongSide, psq1) > relative_rank(strongSide, psq2))
   {
-      blockSq1 = psq1 + pawn_push(strongerSide);
-      blockSq2 = make_square(square_file(psq2), square_rank(psq1));
+      blockSq1 = psq1 + pawn_push(strongSide);
+      blockSq2 = make_square(file_of(psq2), rank_of(psq1));
   }
   else
   {
-      blockSq1 = psq2 + pawn_push(strongerSide);
-      blockSq2 = make_square(square_file(psq1), square_rank(psq2));
+      blockSq1 = psq2 + pawn_push(strongSide);
+      blockSq2 = make_square(file_of(psq1), rank_of(psq2));
   }
 
   switch (file_distance(psq1, psq2))
   {
   case 0:
-    // Both pawns are on the same file. Easy draw if defender firmly controls
-    // some square in the frontmost pawn's path.
-    if (   square_file(ksq) == square_file(blockSq1)
-        && relative_rank(strongerSide, ksq) >= relative_rank(strongerSide, blockSq1)
-        && !same_color_squares(ksq, wbsq))
-        return SCALE_FACTOR_ZERO;
+    // Both pawns are on the same file. It's an easy draw if the defender firmly
+    // controls some square in the frontmost pawn's path.
+    if (   file_of(ksq) == file_of(blockSq1)
+        && relative_rank(strongSide, ksq) >= relative_rank(strongSide, blockSq1)
+        && opposite_colors(ksq, wbsq))
+        return SCALE_FACTOR_DRAW;
     else
         return SCALE_FACTOR_NONE;
 
   case 1:
-    // Pawns on neighboring 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.
+    // Pawns on adjacent files. It's a draw if the 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
-        && !same_color_squares(ksq, wbsq)
+        && opposite_colors(ksq, wbsq)
         && (   bbsq == blockSq2
-            || (pos.attacks_from<BISHOP>(blockSq2) & pos.pieces(BISHOP, weakerSide))
-            || rank_distance(r1, r2) >= 2))
-        return SCALE_FACTOR_ZERO;
+            || (pos.attacks_from<BISHOP>(blockSq2) & pos.pieces(weakSide, BISHOP))
+            || abs(r1 - r2) >= 2))
+        return SCALE_FACTOR_DRAW;
 
     else if (   ksq == blockSq2
-             && !same_color_squares(ksq, wbsq)
+             && opposite_colors(ksq, wbsq)
              && (   bbsq == blockSq1
-                 || (pos.attacks_from<BISHOP>(blockSq1) & pos.pieces(BISHOP, weakerSide))))
-        return SCALE_FACTOR_ZERO;
+                 || (pos.attacks_from<BISHOP>(blockSq1) & pos.pieces(weakSide, BISHOP))))
+        return SCALE_FACTOR_DRAW;
     else
         return SCALE_FACTOR_NONE;
 
@@ -787,123 +767,90 @@ ScaleFactor ScalingFunction<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.
+/// KBP vs KN. 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 ScalingFunction<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);
-  assert(pos.piece_count(strongerSide, PAWN) == 1);
-  assert(pos.non_pawn_material(weakerSide) == KnightValueMidgame);
-  assert(pos.piece_count(weakerSide, KNIGHT) == 1);
-  assert(pos.piece_count(weakerSide, PAWN) == 0);
+  assert(verify_material(pos, strongSide, BishopValueMg, 1));
+  assert(verify_material(pos, weakSide, KnightValueMg, 0));
 
-  Square pawnSq = pos.piece_list(strongerSide, PAWN, 0);
-  Square strongerBishopSq = pos.piece_list(strongerSide, BISHOP, 0);
-  Square weakerKingSq = pos.king_square(weakerSide);
+  Square pawnSq = pos.list<PAWN>(strongSide)[0];
+  Square strongBishopSq = pos.list<BISHOP>(strongSide)[0];
+  Square weakKingSq = pos.king_square(weakSide);
 
-  if (   square_file(weakerKingSq) == square_file(pawnSq)
-      && relative_rank(strongerSide, pawnSq) < relative_rank(strongerSide, weakerKingSq)
-      && (  !same_color_squares(weakerKingSq, strongerBishopSq)
-          || relative_rank(strongerSide, weakerKingSq) <= RANK_6))
-      return SCALE_FACTOR_ZERO;
+  if (   file_of(weakKingSq) == file_of(pawnSq)
+      && relative_rank(strongSide, pawnSq) < relative_rank(strongSide, weakKingSq)
+      && (   opposite_colors(weakKingSq, strongBishopSq)
+          || relative_rank(strongSide, weakKingSq) <= RANK_6))
+      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.
+/// 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.
 template<>
-ScaleFactor ScalingFunction<KNPK>::apply(const Position& pos) const {
-
-  assert(pos.non_pawn_material(strongerSide) == KnightValueMidgame);
-  assert(pos.piece_count(strongerSide, KNIGHT) == 1);
-  assert(pos.piece_count(strongerSide, PAWN) == 1);
-  assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO);
-  assert(pos.piece_count(weakerSide, PAWN) == 0);
+ScaleFactor Endgame<KNPK>::operator()(const Position& pos) const {
 
-  Square pawnSq = pos.piece_list(strongerSide, PAWN, 0);
-  Square weakerKingSq = pos.king_square(weakerSide);
+  assert(verify_material(pos, strongSide, KnightValueMg, 1));
+  assert(verify_material(pos, weakSide, VALUE_ZERO, 0));
 
-  if (   pawnSq == relative_square(strongerSide, SQ_A7)
-      && square_distance(weakerKingSq, relative_square(strongerSide, SQ_A8)) <= 1)
-      return SCALE_FACTOR_ZERO;
+  // Assume strongSide is white and the pawn is on files A-D
+  Square pawnSq     = normalize(pos, strongSide, pos.list<PAWN>(strongSide)[0]);
+  Square weakKingSq = normalize(pos, strongSide, pos.king_square(weakSide));
 
-  if (   pawnSq == relative_square(strongerSide, SQ_H7)
-      && square_distance(weakerKingSq, relative_square(strongerSide, SQ_H8)) <= 1)
-      return SCALE_FACTOR_ZERO;
+  if (pawnSq == SQ_A7 && square_distance(SQ_A8, weakKingSq) <= 1)
+      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).
+/// KNP vs KB. If knight can block bishop from taking pawn, it's a win.
+/// Otherwise the position is drawn.
 template<>
-ScaleFactor ScalingFunction<KPKP>::apply(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;
-
-  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
-  {
-      wksq = flip_square(pos.king_square(BLACK));
-      bksq = flip_square(pos.king_square(WHITE));
-      wpsq = flip_square(pos.piece_list(BLACK, PAWN, 0));
-      stm = opposite_color(pos.side_to_move());
-  }
+ScaleFactor Endgame<KNPKB>::operator()(const Position& pos) const {
 
-  if (square_file(wpsq) >= FILE_E)
-  {
-      wksq = flop_square(wksq);
-      bksq = flop_square(bksq);
-      wpsq = flop_square(wpsq);
-  }
+  Square pawnSq = pos.list<PAWN>(strongSide)[0];
+  Square bishopSq = pos.list<BISHOP>(weakSide)[0];
+  Square weakKingSq = pos.king_square(weakSide);
 
-  // If the pawn has advanced to the fifth rank or further, and is not a
-  // rook pawn, it's too dangerous to assume that it's at least a draw.
-  if (   square_rank(wpsq) >= RANK_5
-      && square_file(wpsq) != FILE_A)
-      return SCALE_FACTOR_NONE;
+  // King needs to get close to promoting pawn to prevent knight from blocking.
+  // Rules for this are very tricky, so just approximate.
+  if (forward_bb(strongSide, pawnSq) & pos.attacks_from<BISHOP>(bishopSq))
+      return ScaleFactor(square_distance(weakKingSq, pawnSq));
 
-  // 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(wksq, wpsq, bksq, stm) ? SCALE_FACTOR_NONE : SCALE_FACTOR_ZERO;
+  return SCALE_FACTOR_NONE;
 }
 
 
-namespace {
+/// KP vs KP. 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, it 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>::operator()(const Position& pos) const {
 
-  // Probe the KP vs K bitbase
+  assert(verify_material(pos, strongSide, VALUE_ZERO, 1));
+  assert(verify_material(pos, weakSide,   VALUE_ZERO, 1));
 
-  int probe_kpk(Square wksq, Square wpsq, Square bksq, Color stm) {
+  // Assume strongSide is white and the pawn is on files A-D
+  Square wksq = normalize(pos, strongSide, pos.king_square(strongSide));
+  Square bksq = normalize(pos, strongSide, pos.king_square(weakSide));
+  Square psq  = normalize(pos, strongSide, pos.list<PAWN>(strongSide)[0]);
 
-    int wp = square_file(wpsq) + 4 * (square_rank(wpsq) - 1);
-    int index = int(stm) + 2 * bksq + 128 * wksq + 8192 * wp;
+  Color us = strongSide == pos.side_to_move() ? WHITE : BLACK;
 
-    assert(index >= 0 && index < 24576 * 8);
+  // If the pawn has advanced to the fifth rank or further, and is not a
+  // rook pawn, it's too dangerous to assume that it's at least a draw.
+  if (rank_of(psq) >= RANK_5 && file_of(psq) != FILE_A)
+      return SCALE_FACTOR_NONE;
 
-    return KPKBitbase[index / 8] & (1 << (index & 7));
-  }
+  // 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 Bitbases::probe_kpk(wksq, psq, bksq, us) ? SCALE_FACTOR_NONE : SCALE_FACTOR_DRAW;
 }