2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
32 // Table used to drive the king towards the edge of the board
33 // in KX vs K and KQ vs KR endgames.
34 const int PushToEdges[SQUARE_NB] = {
35 100, 90, 80, 70, 70, 80, 90, 100,
36 90, 70, 60, 50, 50, 60, 70, 90,
37 80, 60, 40, 30, 30, 40, 60, 80,
38 70, 50, 30, 20, 20, 30, 50, 70,
39 70, 50, 30, 20, 20, 30, 50, 70,
40 80, 60, 40, 30, 30, 40, 60, 80,
41 90, 70, 60, 50, 50, 60, 70, 90,
42 100, 90, 80, 70, 70, 80, 90, 100,
45 // Table used to drive the king towards a corner square of the
46 // right color in KBN vs K endgames.
47 const int PushToCorners[SQUARE_NB] = {
48 200, 190, 180, 170, 160, 150, 140, 130,
49 190, 180, 170, 160, 150, 140, 130, 140,
50 180, 170, 155, 140, 140, 125, 140, 150,
51 170, 160, 140, 120, 110, 140, 150, 160,
52 160, 150, 140, 110, 120, 140, 160, 170,
53 150, 140, 125, 140, 140, 155, 170, 180,
54 140, 130, 140, 150, 160, 170, 180, 190,
55 130, 140, 150, 160, 170, 180, 190, 200
58 // Tables used to drive a piece towards or away from another piece
59 const int PushClose[8] = { 0, 0, 100, 80, 60, 40, 20, 10 };
60 const int PushAway [8] = { 0, 5, 20, 40, 60, 80, 90, 100 };
63 bool verify_material(const Position& pos, Color c, Value npm, int num_pawns) {
64 return pos.non_pawn_material(c) == npm && pos.count<PAWN>(c) == num_pawns;
68 // Get the material key of a Position out of the given endgame key code
69 // like "KBPKN". The trick here is to first forge an ad-hoc fen string
70 // and then let a Position object to do the work for us. Note that the
71 // fen string could correspond to an illegal position.
72 Key key(const string& code, Color c) {
74 assert(code.length() > 0 && code.length() < 8);
75 assert(code[0] == 'K');
77 string sides[] = { code.substr(code.find('K', 1)), // Weak
78 code.substr(0, code.find('K', 1)) }; // Strong
80 std::transform(sides[c].begin(), sides[c].end(), sides[c].begin(), tolower);
82 string fen = sides[0] + char('0' + int(8 - code.length()))
83 + sides[1] + "/8/8/8/8/8/8/8 w - - 0 10";
85 return Position(fen, false, NULL).material_key();
89 void delete_endgame(const typename M::value_type& p) { delete p.second; }
94 /// Endgames members definitions
96 Endgames::Endgames() {
114 add<KBPPKB>("KBPPKB");
115 add<KRPPKRP>("KRPPKRP");
118 Endgames::~Endgames() {
120 for_each(m1.begin(), m1.end(), delete_endgame<M1>);
121 for_each(m2.begin(), m2.end(), delete_endgame<M2>);
124 template<EndgameType E>
125 void Endgames::add(const string& code) {
127 map((Endgame<E>*)0)[key(code, WHITE)] = new Endgame<E>(WHITE);
128 map((Endgame<E>*)0)[key(code, BLACK)] = new Endgame<E>(BLACK);
132 /// Mate with KX vs K. This function is used to evaluate positions with
133 /// King and plenty of material vs a lone king. It simply gives the
134 /// attacking side a bonus for driving the defending king towards the edge
135 /// of the board, and for keeping the distance between the two kings small.
137 Value Endgame<KXK>::operator()(const Position& pos) const {
139 assert(verify_material(pos, weakSide, VALUE_ZERO, 0));
140 assert(!pos.checkers()); // Eval is never called when in check
142 // Stalemate detection with lone king
143 if (pos.side_to_move() == weakSide && !MoveList<LEGAL>(pos).size())
146 Square winnerKSq = pos.king_square(strongSide);
147 Square loserKSq = pos.king_square(weakSide);
149 Value result = pos.non_pawn_material(strongSide)
150 + pos.count<PAWN>(strongSide) * PawnValueEg
151 + PushToEdges[loserKSq]
152 + PushClose[square_distance(winnerKSq, loserKSq)];
154 if ( pos.count<QUEEN>(strongSide)
155 || pos.count<ROOK>(strongSide)
156 || pos.bishop_pair(strongSide))
157 result += VALUE_KNOWN_WIN;
159 return strongSide == pos.side_to_move() ? result : -result;
163 /// Mate with KBN vs K. This is similar to KX vs K, but we have to drive the
164 /// defending king towards a corner square of the right color.
166 Value Endgame<KBNK>::operator()(const Position& pos) const {
168 assert(verify_material(pos, strongSide, KnightValueMg + BishopValueMg, 0));
169 assert(verify_material(pos, weakSide, VALUE_ZERO, 0));
171 Square winnerKSq = pos.king_square(strongSide);
172 Square loserKSq = pos.king_square(weakSide);
173 Square bishopSq = pos.list<BISHOP>(strongSide)[0];
175 // kbnk_mate_table() tries to drive toward corners A1 or H8,
176 // if we have a bishop that cannot reach the above squares we
177 // flip the kings so to drive enemy toward corners A8 or H1.
178 if (opposite_colors(bishopSq, SQ_A1))
180 winnerKSq = ~winnerKSq;
181 loserKSq = ~loserKSq;
184 Value result = VALUE_KNOWN_WIN
185 + PushClose[square_distance(winnerKSq, loserKSq)]
186 + PushToCorners[loserKSq];
188 return strongSide == pos.side_to_move() ? result : -result;
191 // Returns a square that will allow us to orient the board so that
192 // strongSide is white and strongSide's only pawn is on the left
194 Square get_flip_sq(const Position& pos, Color strongSide) {
196 assert(pos.count<PAWN>(strongSide) == 1);
198 Square psq = pos.list<PAWN>(strongSide)[0];
200 return (FILE_H * (file_of(psq) >= FILE_E)) | (RANK_8 * int(strongSide));
203 Square operator^(Square s, Square flip_sq) {
204 assert(flip_sq == SQ_A1 || flip_sq == SQ_H1 || flip_sq == SQ_A8 || flip_sq == SQ_H8);
205 return Square(int(s) ^ int(flip_sq));
208 /// KP vs K. This endgame is evaluated with the help of a bitbase.
210 Value Endgame<KPK>::operator()(const Position& pos) const {
212 assert(verify_material(pos, strongSide, VALUE_ZERO, 1));
213 assert(verify_material(pos, weakSide, VALUE_ZERO, 0));
215 // Assume strongSide is white and the pawn is on files A-D
216 Square flip_sq = get_flip_sq(pos, strongSide);
218 Square wksq = pos.king_square(strongSide) ^ flip_sq;
219 Square bksq = pos.king_square(weakSide) ^ flip_sq;
220 Square psq = pos.list<PAWN>(strongSide)[0] ^ flip_sq;
222 Color us = strongSide == pos.side_to_move() ? WHITE : BLACK;
224 if (!Bitbases::probe_kpk(wksq, psq, bksq, us))
227 Value result = VALUE_KNOWN_WIN + PawnValueEg + Value(rank_of(psq));
229 return strongSide == pos.side_to_move() ? result : -result;
233 /// KR vs KP. This is a somewhat tricky endgame to evaluate precisely without
234 /// a bitbase. The function below returns drawish scores when the pawn is
235 /// far advanced with support of the king, while the attacking king is far
238 Value Endgame<KRKP>::operator()(const Position& pos) const {
240 assert(verify_material(pos, strongSide, RookValueMg, 0));
241 assert(verify_material(pos, weakSide, VALUE_ZERO, 1));
243 Square wksq = relative_square(strongSide, pos.king_square(strongSide));
244 Square bksq = relative_square(strongSide, pos.king_square(weakSide));
245 Square rsq = relative_square(strongSide, pos.list<ROOK>(strongSide)[0]);
246 Square psq = relative_square(strongSide, pos.list<PAWN>(weakSide)[0]);
248 Square queeningSq = file_of(psq) | RANK_1;
251 // If the stronger side's king is in front of the pawn, it's a win
252 if (wksq < psq && file_of(wksq) == file_of(psq))
253 result = RookValueEg - Value(square_distance(wksq, psq));
255 // If the weaker side's king is too far from the pawn and the rook,
257 else if ( square_distance(bksq, psq) >= 3 + (pos.side_to_move() == weakSide)
258 && square_distance(bksq, rsq) >= 3)
259 result = RookValueEg - Value(square_distance(wksq, psq));
261 // If the pawn is far advanced and supported by the defending king,
262 // the position is drawish
263 else if ( rank_of(bksq) <= RANK_3
264 && square_distance(bksq, psq) == 1
265 && rank_of(wksq) >= RANK_4
266 && square_distance(wksq, psq) > 2 + (pos.side_to_move() == strongSide))
267 result = Value(80 - square_distance(wksq, psq) * 8);
271 - Value(square_distance(wksq, psq + DELTA_S) * 8)
272 + Value(square_distance(bksq, psq + DELTA_S) * 8)
273 + Value(square_distance(psq, queeningSq) * 8);
275 return strongSide == pos.side_to_move() ? result : -result;
279 /// KR vs KB. This is very simple, and always returns drawish scores. The
280 /// score is slightly bigger when the defending king is close to the edge.
282 Value Endgame<KRKB>::operator()(const Position& pos) const {
284 assert(verify_material(pos, strongSide, RookValueMg, 0));
285 assert(verify_material(pos, weakSide, BishopValueMg, 0));
287 Value result = Value(PushToEdges[pos.king_square(weakSide)]);
288 return strongSide == pos.side_to_move() ? result : -result;
292 /// KR vs KN. The attacking side has slightly better winning chances than
293 /// in KR vs KB, particularly if the king and the knight are far apart.
295 Value Endgame<KRKN>::operator()(const Position& pos) const {
297 assert(verify_material(pos, strongSide, RookValueMg, 0));
298 assert(verify_material(pos, weakSide, KnightValueMg, 0));
300 Square bksq = pos.king_square(weakSide);
301 Square bnsq = pos.list<KNIGHT>(weakSide)[0];
302 Value result = Value(PushToEdges[bksq] + PushAway[square_distance(bksq, bnsq)]);
303 return strongSide == pos.side_to_move() ? result : -result;
307 /// KQ vs KP. In general, a win for the stronger side, however, there are a few
308 /// important exceptions. Pawn on 7th rank, A,C,F or H file, with king next can
309 /// be a draw, so we scale down to distance between kings only.
311 Value Endgame<KQKP>::operator()(const Position& pos) const {
313 assert(verify_material(pos, strongSide, QueenValueMg, 0));
314 assert(verify_material(pos, weakSide, VALUE_ZERO, 1));
316 Square winnerKSq = pos.king_square(strongSide);
317 Square loserKSq = pos.king_square(weakSide);
318 Square pawnSq = pos.list<PAWN>(weakSide)[0];
320 Value result = Value(PushClose[square_distance(winnerKSq, loserKSq)]);
322 if ( relative_rank(weakSide, pawnSq) != RANK_7
323 || square_distance(loserKSq, pawnSq) != 1
324 || !((FileABB | FileCBB | FileFBB | FileHBB) & pawnSq))
325 result += QueenValueEg - PawnValueEg;
327 return strongSide == pos.side_to_move() ? result : -result;
331 /// KQ vs KR. This is almost identical to KX vs K: We give the attacking
332 /// king a bonus for having the kings close together, and for forcing the
333 /// defending king towards the edge. If we also take care to avoid null move
334 /// for the defending side in the search, this is usually sufficient to be
335 /// able to win KQ vs KR.
337 Value Endgame<KQKR>::operator()(const Position& pos) const {
339 assert(verify_material(pos, strongSide, QueenValueMg, 0));
340 assert(verify_material(pos, weakSide, RookValueMg, 0));
342 Square winnerKSq = pos.king_square(strongSide);
343 Square loserKSq = pos.king_square(weakSide);
345 Value result = QueenValueEg
347 + PushToEdges[loserKSq]
348 + PushClose[square_distance(winnerKSq, loserKSq)];
350 return strongSide == pos.side_to_move() ? result : -result;
354 /// KBB vs KN. This is almost always a win. We try to push enemy king to a corner
355 /// and away from his knight. For a reference of this difficult endgame see:
356 /// en.wikipedia.org/wiki/Chess_endgame#Effect_of_tablebases_on_endgame_theory
359 Value Endgame<KBBKN>::operator()(const Position& pos) const {
361 assert(verify_material(pos, strongSide, 2 * BishopValueMg, 0));
362 assert(verify_material(pos, weakSide, KnightValueMg, 0));
364 Square winnerKSq = pos.king_square(strongSide);
365 Square loserKSq = pos.king_square(weakSide);
366 Square knightSq = pos.list<KNIGHT>(weakSide)[0];
368 Value result = VALUE_KNOWN_WIN
369 + PushToCorners[loserKSq]
370 + PushClose[square_distance(winnerKSq, loserKSq)]
371 + PushAway[square_distance(loserKSq, knightSq)];
373 return strongSide == pos.side_to_move() ? result : -result;
377 /// Some cases of trivial draws
378 template<> Value Endgame<KNNK>::operator()(const Position&) const { return VALUE_DRAW; }
379 template<> Value Endgame<KmmKm>::operator()(const Position&) const { return VALUE_DRAW; }
382 /// K, bishop and one or more pawns vs K. It checks for draws with rook pawns and
383 /// a bishop of the wrong color. If such a draw is detected, SCALE_FACTOR_DRAW
384 /// is returned. If not, the return value is SCALE_FACTOR_NONE, i.e. no scaling
387 ScaleFactor Endgame<KBPsK>::operator()(const Position& pos) const {
389 assert(pos.non_pawn_material(strongSide) == BishopValueMg);
390 assert(pos.count<PAWN>(strongSide) >= 1);
392 // No assertions about the material of weakSide, because we want draws to
393 // be detected even when the weaker side has some pawns.
395 Bitboard pawns = pos.pieces(strongSide, PAWN);
396 File pawnFile = file_of(pos.list<PAWN>(strongSide)[0]);
398 // All pawns are on a single rook file ?
399 if ( (pawnFile == FILE_A || pawnFile == FILE_H)
400 && !(pawns & ~file_bb(pawnFile)))
402 Square bishopSq = pos.list<BISHOP>(strongSide)[0];
403 Square queeningSq = relative_square(strongSide, pawnFile | RANK_8);
404 Square kingSq = pos.king_square(weakSide);
406 if ( opposite_colors(queeningSq, bishopSq)
407 && square_distance(queeningSq, kingSq) <= 1)
408 return SCALE_FACTOR_DRAW;
411 // All pawns on same B or G file? Then potential draw
412 if ( (pawnFile == FILE_B || pawnFile == FILE_G)
413 && !(pos.pieces(PAWN) & ~file_bb(pawnFile))
414 && pos.non_pawn_material(weakSide) == 0
415 && pos.count<PAWN>(weakSide) >= 1)
417 // Get weakSide pawn that is closest to home rank
418 Square weakPawnSq = backmost_sq(weakSide, pos.pieces(weakSide, PAWN));
420 Square strongKingSq = pos.king_square(strongSide);
421 Square weakKingSq = pos.king_square(weakSide);
422 Square bishopSq = pos.list<BISHOP>(strongSide)[0];
424 // Potential for a draw if our pawn is blocked on the 7th rank
425 // the bishop cannot attack it or they only have one pawn left
426 if ( relative_rank(strongSide, weakPawnSq) == RANK_7
427 && (pos.pieces(strongSide, PAWN) & (weakPawnSq + pawn_push(weakSide)))
428 && (opposite_colors(bishopSq, weakPawnSq) || pos.count<PAWN>(strongSide) == 1))
430 int strongKingDist = square_distance(weakPawnSq, strongKingSq);
431 int weakKingDist = square_distance(weakPawnSq, weakKingSq);
433 // Draw if the weak king is on it's back two ranks, within 2
434 // squares of the blocking pawn and the strong king is not
435 // closer. (I think this rule only fails in practically
436 // unreachable positions such as 5k1K/6p1/6P1/8/8/3B4/8/8 w
437 // and positions where qsearch will immediately correct the
438 // problem such as 8/4k1p1/6P1/1K6/3B4/8/8/8 w)
439 if ( relative_rank(strongSide, weakKingSq) >= RANK_7
441 && weakKingDist <= strongKingDist)
442 return SCALE_FACTOR_DRAW;
446 return SCALE_FACTOR_NONE;
450 /// K and queen vs K, rook and one or more pawns. It tests for fortress draws with
451 /// a rook on the third rank defended by a pawn.
453 ScaleFactor Endgame<KQKRPs>::operator()(const Position& pos) const {
455 assert(verify_material(pos, strongSide, QueenValueMg, 0));
456 assert(pos.count<ROOK>(weakSide) == 1);
457 assert(pos.count<PAWN>(weakSide) >= 1);
459 Square kingSq = pos.king_square(weakSide);
460 Square rsq = pos.list<ROOK>(weakSide)[0];
462 if ( relative_rank(weakSide, kingSq) <= RANK_2
463 && relative_rank(weakSide, pos.king_square(strongSide)) >= RANK_4
464 && relative_rank(weakSide, rsq) == RANK_3
465 && ( pos.pieces(weakSide, PAWN)
466 & pos.attacks_from<KING>(kingSq)
467 & pos.attacks_from<PAWN>(rsq, strongSide)))
468 return SCALE_FACTOR_DRAW;
470 return SCALE_FACTOR_NONE;
474 /// K, rook and one pawn vs K and a rook. This function knows a handful of the
475 /// most important classes of drawn positions, but is far from perfect. It would
476 /// probably be a good idea to add more knowledge in the future.
478 /// It would also be nice to rewrite the actual code for this function,
479 /// which is mostly copied from Glaurung 1.x, and not very pretty.
481 ScaleFactor Endgame<KRPKR>::operator()(const Position& pos) const {
483 assert(verify_material(pos, strongSide, RookValueMg, 1));
484 assert(verify_material(pos, weakSide, RookValueMg, 0));
486 // Assume strongSide is white and the pawn is on files A-D
487 Square flip_sq = get_flip_sq(pos, strongSide);
489 Square wksq = pos.king_square(strongSide) ^ flip_sq;
490 Square bksq = pos.king_square(weakSide) ^ flip_sq;
491 Square wrsq = pos.list<ROOK>(strongSide)[0] ^ flip_sq;
492 Square wpsq = pos.list<PAWN>(strongSide)[0] ^ flip_sq;
493 Square brsq = pos.list<ROOK>(weakSide)[0] ^ flip_sq;
495 File f = file_of(wpsq);
496 Rank r = rank_of(wpsq);
497 Square queeningSq = f | RANK_8;
498 int tempo = (pos.side_to_move() == strongSide);
500 // If the pawn is not too far advanced and the defending king defends the
501 // queening square, use the third-rank defence.
503 && square_distance(bksq, queeningSq) <= 1
505 && (rank_of(brsq) == RANK_6 || (r <= RANK_3 && rank_of(wrsq) != RANK_6)))
506 return SCALE_FACTOR_DRAW;
508 // The defending side saves a draw by checking from behind in case the pawn
509 // has advanced to the 6th rank with the king behind.
511 && square_distance(bksq, queeningSq) <= 1
512 && rank_of(wksq) + tempo <= RANK_6
513 && (rank_of(brsq) == RANK_1 || (!tempo && abs(file_of(brsq) - f) >= 3)))
514 return SCALE_FACTOR_DRAW;
517 && bksq == queeningSq
518 && rank_of(brsq) == RANK_1
519 && (!tempo || square_distance(wksq, wpsq) >= 2))
520 return SCALE_FACTOR_DRAW;
522 // White pawn on a7 and rook on a8 is a draw if black's king is on g7 or h7
523 // and the black rook is behind the pawn.
526 && (bksq == SQ_H7 || bksq == SQ_G7)
527 && file_of(brsq) == FILE_A
528 && (rank_of(brsq) <= RANK_3 || file_of(wksq) >= FILE_D || rank_of(wksq) <= RANK_5))
529 return SCALE_FACTOR_DRAW;
531 // If the defending king blocks the pawn and the attacking king is too far
532 // away, it's a draw.
534 && bksq == wpsq + DELTA_N
535 && square_distance(wksq, wpsq) - tempo >= 2
536 && square_distance(wksq, brsq) - tempo >= 2)
537 return SCALE_FACTOR_DRAW;
539 // Pawn on the 7th rank supported by the rook from behind usually wins if the
540 // attacking king is closer to the queening square than the defending king,
541 // and the defending king cannot gain tempi by threatening the attacking rook.
544 && file_of(wrsq) == f
545 && wrsq != queeningSq
546 && (square_distance(wksq, queeningSq) < square_distance(bksq, queeningSq) - 2 + tempo)
547 && (square_distance(wksq, queeningSq) < square_distance(bksq, wrsq) + tempo))
548 return ScaleFactor(SCALE_FACTOR_MAX - 2 * square_distance(wksq, queeningSq));
550 // Similar to the above, but with the pawn further back
552 && file_of(wrsq) == f
554 && (square_distance(wksq, queeningSq) < square_distance(bksq, queeningSq) - 2 + tempo)
555 && (square_distance(wksq, wpsq + DELTA_N) < square_distance(bksq, wpsq + DELTA_N) - 2 + tempo)
556 && ( square_distance(bksq, wrsq) + tempo >= 3
557 || ( square_distance(wksq, queeningSq) < square_distance(bksq, wrsq) + tempo
558 && (square_distance(wksq, wpsq + DELTA_N) < square_distance(bksq, wrsq) + tempo))))
559 return ScaleFactor( SCALE_FACTOR_MAX
560 - 8 * square_distance(wpsq, queeningSq)
561 - 2 * square_distance(wksq, queeningSq));
563 // If the pawn is not far advanced, and the defending king is somewhere in
564 // the pawn's path, it's probably a draw.
565 if (r <= RANK_4 && bksq > wpsq)
567 if (file_of(bksq) == file_of(wpsq))
568 return ScaleFactor(10);
569 if ( abs(file_of(bksq) - file_of(wpsq)) == 1
570 && square_distance(wksq, bksq) > 2)
571 return ScaleFactor(24 - 2 * square_distance(wksq, bksq));
573 return SCALE_FACTOR_NONE;
577 ScaleFactor Endgame<KRPKB>::operator()(const Position& pos) const {
579 assert(verify_material(pos, strongSide, RookValueMg, 1));
580 assert(verify_material(pos, weakSide, BishopValueMg, 0));
582 // Test for a rook pawn
583 if (pos.pieces(PAWN) & (FileABB | FileHBB))
585 Square ksq = pos.king_square(weakSide);
586 Square bsq = pos.list<BISHOP>(weakSide)[0];
587 Square psq = pos.list<PAWN>(strongSide)[0];
588 Rank rk = relative_rank(strongSide, psq);
589 Square push = pawn_push(strongSide);
591 // If the pawn is on the 5th rank and the pawn (currently) is on
592 // the same color square as the bishop then there is a chance of
593 // a fortress. Depending on the king position give a moderate
594 // reduction or a stronger one if the defending king is near the
595 // corner but not trapped there.
596 if (rk == RANK_5 && !opposite_colors(bsq, psq))
598 int d = square_distance(psq + 3 * push, ksq);
600 if (d <= 2 && !(d == 0 && ksq == pos.king_square(strongSide) + 2 * push))
601 return ScaleFactor(24);
603 return ScaleFactor(48);
606 // When the pawn has moved to the 6th rank we can be fairly sure
607 // it's drawn if the bishop attacks the square in front of the
608 // pawn from a reasonable distance and the defending king is near
611 && square_distance(psq + 2 * push, ksq) <= 1
612 && (PseudoAttacks[BISHOP][bsq] & (psq + push))
613 && file_distance(bsq, psq) >= 2)
614 return ScaleFactor(8);
617 return SCALE_FACTOR_NONE;
620 /// K, rook and two pawns vs K, rook and one pawn. There is only a single
621 /// pattern: If the stronger side has no passed pawns and the defending king
622 /// is actively placed, the position is drawish.
624 ScaleFactor Endgame<KRPPKRP>::operator()(const Position& pos) const {
626 assert(verify_material(pos, strongSide, RookValueMg, 2));
627 assert(verify_material(pos, weakSide, RookValueMg, 1));
629 Square wpsq1 = pos.list<PAWN>(strongSide)[0];
630 Square wpsq2 = pos.list<PAWN>(strongSide)[1];
631 Square bksq = pos.king_square(weakSide);
633 // Does the stronger side have a passed pawn?
634 if (pos.pawn_passed(strongSide, wpsq1) || pos.pawn_passed(strongSide, wpsq2))
635 return SCALE_FACTOR_NONE;
637 Rank r = std::max(relative_rank(strongSide, wpsq1), relative_rank(strongSide, wpsq2));
639 if ( file_distance(bksq, wpsq1) <= 1
640 && file_distance(bksq, wpsq2) <= 1
641 && relative_rank(strongSide, bksq) > r)
644 case RANK_2: return ScaleFactor(10);
645 case RANK_3: return ScaleFactor(10);
646 case RANK_4: return ScaleFactor(15);
647 case RANK_5: return ScaleFactor(20);
648 case RANK_6: return ScaleFactor(40);
649 default: assert(false);
652 return SCALE_FACTOR_NONE;
656 /// K and two or more pawns vs K. There is just a single rule here: If all pawns
657 /// are on the same rook file and are blocked by the defending king, it's a draw.
659 ScaleFactor Endgame<KPsK>::operator()(const Position& pos) const {
661 assert(pos.non_pawn_material(strongSide) == VALUE_ZERO);
662 assert(pos.count<PAWN>(strongSide) >= 2);
663 assert(verify_material(pos, weakSide, VALUE_ZERO, 0));
665 Square ksq = pos.king_square(weakSide);
666 Bitboard pawns = pos.pieces(strongSide, PAWN);
667 Square psq = pos.list<PAWN>(strongSide)[0];
669 // If all pawns are ahead of the king, all pawns are on a single
670 // rook file and the king is within one file of the pawns then draw.
671 if ( !(pawns & ~in_front_bb(weakSide, rank_of(ksq)))
672 && !((pawns & ~FileABB) && (pawns & ~FileHBB))
673 && file_distance(ksq, psq) <= 1)
674 return SCALE_FACTOR_DRAW;
676 return SCALE_FACTOR_NONE;
680 /// K, bishop and a pawn vs K and a bishop. There are two rules: If the defending
681 /// king is somewhere along the path of the pawn, and the square of the king is
682 /// not of the same color as the stronger side's bishop, it's a draw. If the two
683 /// bishops have opposite color, it's almost always a draw.
685 ScaleFactor Endgame<KBPKB>::operator()(const Position& pos) const {
687 assert(verify_material(pos, strongSide, BishopValueMg, 1));
688 assert(verify_material(pos, weakSide, BishopValueMg, 0));
690 Square pawnSq = pos.list<PAWN>(strongSide)[0];
691 Square strongBishopSq = pos.list<BISHOP>(strongSide)[0];
692 Square weakBishopSq = pos.list<BISHOP>(weakSide)[0];
693 Square weakKingSq = pos.king_square(weakSide);
695 // Case 1: Defending king blocks the pawn, and cannot be driven away
696 if ( file_of(weakKingSq) == file_of(pawnSq)
697 && relative_rank(strongSide, pawnSq) < relative_rank(strongSide, weakKingSq)
698 && ( opposite_colors(weakKingSq, strongBishopSq)
699 || relative_rank(strongSide, weakKingSq) <= RANK_6))
700 return SCALE_FACTOR_DRAW;
702 // Case 2: Opposite colored bishops
703 if (opposite_colors(strongBishopSq, weakBishopSq))
705 // We assume that the position is drawn in the following three situations:
707 // a. The pawn is on rank 5 or further back.
708 // b. The defending king is somewhere in the pawn's path.
709 // c. The defending bishop attacks some square along the pawn's path,
710 // and is at least three squares away from the pawn.
712 // These rules are probably not perfect, but in practice they work
715 if (relative_rank(strongSide, pawnSq) <= RANK_5)
716 return SCALE_FACTOR_DRAW;
719 Bitboard path = forward_bb(strongSide, pawnSq);
721 if (path & pos.pieces(weakSide, KING))
722 return SCALE_FACTOR_DRAW;
724 if ( (pos.attacks_from<BISHOP>(weakBishopSq) & path)
725 && square_distance(weakBishopSq, pawnSq) >= 3)
726 return SCALE_FACTOR_DRAW;
729 return SCALE_FACTOR_NONE;
733 /// K, bishop and two pawns vs K and bishop. It detects a few basic draws with
734 /// opposite-colored bishops.
736 ScaleFactor Endgame<KBPPKB>::operator()(const Position& pos) const {
738 assert(verify_material(pos, strongSide, BishopValueMg, 2));
739 assert(verify_material(pos, weakSide, BishopValueMg, 0));
741 Square wbsq = pos.list<BISHOP>(strongSide)[0];
742 Square bbsq = pos.list<BISHOP>(weakSide)[0];
744 if (!opposite_colors(wbsq, bbsq))
745 return SCALE_FACTOR_NONE;
747 Square ksq = pos.king_square(weakSide);
748 Square psq1 = pos.list<PAWN>(strongSide)[0];
749 Square psq2 = pos.list<PAWN>(strongSide)[1];
750 Rank r1 = rank_of(psq1);
751 Rank r2 = rank_of(psq2);
752 Square blockSq1, blockSq2;
754 if (relative_rank(strongSide, psq1) > relative_rank(strongSide, psq2))
756 blockSq1 = psq1 + pawn_push(strongSide);
757 blockSq2 = file_of(psq2) | rank_of(psq1);
761 blockSq1 = psq2 + pawn_push(strongSide);
762 blockSq2 = file_of(psq1) | rank_of(psq2);
765 switch (file_distance(psq1, psq2))
768 // Both pawns are on the same file. Easy draw if defender firmly controls
769 // some square in the frontmost pawn's path.
770 if ( file_of(ksq) == file_of(blockSq1)
771 && relative_rank(strongSide, ksq) >= relative_rank(strongSide, blockSq1)
772 && opposite_colors(ksq, wbsq))
773 return SCALE_FACTOR_DRAW;
775 return SCALE_FACTOR_NONE;
778 // Pawns on adjacent files. Draw if defender firmly controls the square
779 // in front of the frontmost pawn's path, and the square diagonally behind
780 // this square on the file of the other pawn.
782 && opposite_colors(ksq, wbsq)
783 && ( bbsq == blockSq2
784 || (pos.attacks_from<BISHOP>(blockSq2) & pos.pieces(weakSide, BISHOP))
785 || abs(r1 - r2) >= 2))
786 return SCALE_FACTOR_DRAW;
788 else if ( ksq == blockSq2
789 && opposite_colors(ksq, wbsq)
790 && ( bbsq == blockSq1
791 || (pos.attacks_from<BISHOP>(blockSq1) & pos.pieces(weakSide, BISHOP))))
792 return SCALE_FACTOR_DRAW;
794 return SCALE_FACTOR_NONE;
797 // The pawns are not on the same file or adjacent files. No scaling.
798 return SCALE_FACTOR_NONE;
803 /// K, bisop and a pawn vs K and knight. There is a single rule: If the defending
804 /// king is somewhere along the path of the pawn, and the square of the king is
805 /// not of the same color as the stronger side's bishop, it's a draw.
807 ScaleFactor Endgame<KBPKN>::operator()(const Position& pos) const {
809 assert(verify_material(pos, strongSide, BishopValueMg, 1));
810 assert(verify_material(pos, weakSide, KnightValueMg, 0));
812 Square pawnSq = pos.list<PAWN>(strongSide)[0];
813 Square strongBishopSq = pos.list<BISHOP>(strongSide)[0];
814 Square weakKingSq = pos.king_square(weakSide);
816 if ( file_of(weakKingSq) == file_of(pawnSq)
817 && relative_rank(strongSide, pawnSq) < relative_rank(strongSide, weakKingSq)
818 && ( opposite_colors(weakKingSq, strongBishopSq)
819 || relative_rank(strongSide, weakKingSq) <= RANK_6))
820 return SCALE_FACTOR_DRAW;
822 return SCALE_FACTOR_NONE;
826 /// K, knight and a pawn vs K. There is a single rule: If the pawn is a rook pawn
827 /// on the 7th rank and the defending king prevents the pawn from advancing, the
828 /// position is drawn.
830 ScaleFactor Endgame<KNPK>::operator()(const Position& pos) const {
832 assert(verify_material(pos, strongSide, KnightValueMg, 1));
833 assert(verify_material(pos, weakSide, VALUE_ZERO, 0));
835 // Assume strongSide is white and the pawn is on files A-D
836 Square flip_sq = get_flip_sq(pos, strongSide);
838 Square pawnSq = pos.list<PAWN>(strongSide)[0] ^ flip_sq;
839 Square weakKingSq = pos.king_square(weakSide) ^ flip_sq;
841 if (pawnSq == SQ_A7 && square_distance(SQ_A8, weakKingSq) <= 1)
842 return SCALE_FACTOR_DRAW;
844 return SCALE_FACTOR_NONE;
848 /// K, knight and a pawn vs K and bishop. If knight can block bishop from taking
849 /// pawn, it's a win. Otherwise, drawn.
851 ScaleFactor Endgame<KNPKB>::operator()(const Position& pos) const {
853 Square pawnSq = pos.list<PAWN>(strongSide)[0];
854 Square bishopSq = pos.list<BISHOP>(weakSide)[0];
855 Square weakKingSq = pos.king_square(weakSide);
857 // King needs to get close to promoting pawn to prevent knight from blocking.
858 // Rules for this are very tricky, so just approximate.
859 if (forward_bb(strongSide, pawnSq) & pos.attacks_from<BISHOP>(bishopSq))
860 return ScaleFactor(square_distance(weakKingSq, pawnSq));
862 return SCALE_FACTOR_NONE;
866 /// K and a pawn vs K and a pawn. This is done by removing the weakest side's
867 /// pawn and probing the KP vs K bitbase: If the weakest side has a draw without
868 /// the pawn, she probably has at least a draw with the pawn as well. The exception
869 /// is when the stronger side's pawn is far advanced and not on a rook file; in
870 /// this case it is often possible to win (e.g. 8/4k3/3p4/3P4/6K1/8/8/8 w - - 0 1).
872 ScaleFactor Endgame<KPKP>::operator()(const Position& pos) const {
874 assert(verify_material(pos, strongSide, VALUE_ZERO, 1));
875 assert(verify_material(pos, weakSide, VALUE_ZERO, 1));
877 // Assume strongSide is white and the pawn is on files A-D
878 Square flip_sq = get_flip_sq(pos, strongSide);
880 Square wksq = pos.king_square(strongSide) ^ flip_sq;
881 Square bksq = pos.king_square(weakSide) ^ flip_sq;
882 Square psq = pos.list<PAWN>(strongSide)[0] ^ flip_sq;
884 Color us = strongSide == pos.side_to_move() ? WHITE : BLACK;
886 // If the pawn has advanced to the fifth rank or further, and is not a
887 // rook pawn, it's too dangerous to assume that it's at least a draw.
888 if (rank_of(psq) >= RANK_5 && file_of(psq) != FILE_A)
889 return SCALE_FACTOR_NONE;
891 // Probe the KPK bitbase with the weakest side's pawn removed. If it's a draw,
892 // it's probably at least a draw even with the pawn.
893 return Bitbases::probe_kpk(wksq, psq, bksq, us) ? SCALE_FACTOR_NONE : SCALE_FACTOR_DRAW;