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 };
62 // Get the material key of a Position out of the given endgame key code
63 // like "KBPKN". The trick here is to first forge an ad-hoc fen string
64 // and then let a Position object to do the work for us. Note that the
65 // fen string could correspond to an illegal position.
66 Key key(const string& code, Color c) {
68 assert(code.length() > 0 && code.length() < 8);
69 assert(code[0] == 'K');
71 string sides[] = { code.substr(code.find('K', 1)), // Weaker
72 code.substr(0, code.find('K', 1)) }; // Stronger
74 std::transform(sides[c].begin(), sides[c].end(), sides[c].begin(), tolower);
76 string fen = sides[0] + char('0' + int(8 - code.length()))
77 + sides[1] + "/8/8/8/8/8/8/8 w - - 0 10";
79 return Position(fen, false, NULL).material_key();
83 void delete_endgame(const typename M::value_type& p) { delete p.second; }
88 /// Endgames members definitions
90 Endgames::Endgames() {
108 add<KBPPKB>("KBPPKB");
109 add<KRPPKRP>("KRPPKRP");
112 Endgames::~Endgames() {
114 for_each(m1.begin(), m1.end(), delete_endgame<M1>);
115 for_each(m2.begin(), m2.end(), delete_endgame<M2>);
118 template<EndgameType E>
119 void Endgames::add(const string& code) {
121 map((Endgame<E>*)0)[key(code, WHITE)] = new Endgame<E>(WHITE);
122 map((Endgame<E>*)0)[key(code, BLACK)] = new Endgame<E>(BLACK);
126 /// Mate with KX vs K. This function is used to evaluate positions with
127 /// King and plenty of material vs a lone king. It simply gives the
128 /// attacking side a bonus for driving the defending king towards the edge
129 /// of the board, and for keeping the distance between the two kings small.
131 Value Endgame<KXK>::operator()(const Position& pos) const {
133 assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO);
134 assert(!pos.count<PAWN>(weakerSide));
135 assert(!pos.checkers()); // Eval is never called when in check
137 // Stalemate detection with lone king
138 if (pos.side_to_move() == weakerSide && !MoveList<LEGAL>(pos).size())
141 Square winnerKSq = pos.king_square(strongerSide);
142 Square loserKSq = pos.king_square(weakerSide);
144 Value result = pos.non_pawn_material(strongerSide)
145 + pos.count<PAWN>(strongerSide) * PawnValueEg
146 + PushToEdges[loserKSq]
147 + PushClose[square_distance(winnerKSq, loserKSq)];
149 if ( pos.count<QUEEN>(strongerSide)
150 || pos.count<ROOK>(strongerSide)
151 || pos.bishop_pair(strongerSide))
152 result += VALUE_KNOWN_WIN;
154 return strongerSide == pos.side_to_move() ? result : -result;
158 /// Mate with KBN vs K. This is similar to KX vs K, but we have to drive the
159 /// defending king towards a corner square of the right color.
161 Value Endgame<KBNK>::operator()(const Position& pos) const {
163 assert(pos.non_pawn_material(strongerSide) == KnightValueMg + BishopValueMg);
164 assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO);
165 assert(pos.count<BISHOP>(strongerSide) == 1);
166 assert(pos.count<KNIGHT>(strongerSide) == 1);
167 assert(pos.count< PAWN>(strongerSide) == 0);
168 assert(pos.count< PAWN>(weakerSide ) == 0);
170 Square winnerKSq = pos.king_square(strongerSide);
171 Square loserKSq = pos.king_square(weakerSide);
172 Square bishopSq = pos.list<BISHOP>(strongerSide)[0];
174 // kbnk_mate_table() tries to drive toward corners A1 or H8,
175 // if we have a bishop that cannot reach the above squares we
176 // mirror the kings so to drive enemy toward corners A8 or H1.
177 if (opposite_colors(bishopSq, SQ_A1))
179 winnerKSq = mirror(winnerKSq);
180 loserKSq = mirror(loserKSq);
183 Value result = VALUE_KNOWN_WIN
184 + PushClose[square_distance(winnerKSq, loserKSq)]
185 + PushToCorners[loserKSq];
187 return strongerSide == pos.side_to_move() ? result : -result;
191 /// KP vs K. This endgame is evaluated with the help of a bitbase.
193 Value Endgame<KPK>::operator()(const Position& pos) const {
195 assert(pos.non_pawn_material(strongerSide) == VALUE_ZERO);
196 assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO);
197 assert(pos.count<PAWN>(strongerSide) == 1);
198 assert(pos.count<PAWN>(weakerSide ) == 0);
200 Square wksq = pos.king_square(strongerSide);
201 Square bksq = pos.king_square(weakerSide);
202 Square psq = pos.list<PAWN>(strongerSide)[0];
203 Color us = pos.side_to_move();
205 if (strongerSide == BLACK)
213 if (file_of(psq) >= FILE_E)
220 if (!Bitbases::probe_kpk(wksq, psq, bksq, us))
223 Value result = VALUE_KNOWN_WIN + PawnValueEg + Value(rank_of(psq));
225 return strongerSide == pos.side_to_move() ? result : -result;
229 /// KR vs KP. This is a somewhat tricky endgame to evaluate precisely without
230 /// a bitbase. The function below returns drawish scores when the pawn is
231 /// far advanced with support of the king, while the attacking king is far
234 Value Endgame<KRKP>::operator()(const Position& pos) const {
236 assert(pos.non_pawn_material(strongerSide) == RookValueMg);
237 assert(pos.non_pawn_material(weakerSide) == 0);
238 assert(pos.count<PAWN>(strongerSide) == 0);
239 assert(pos.count<PAWN>(weakerSide ) == 1);
241 Square wksq = pos.king_square(strongerSide);
242 Square bksq = pos.king_square(weakerSide);
243 Square rsq = pos.list<ROOK>(strongerSide)[0];
244 Square psq = pos.list<PAWN>(weakerSide)[0];
246 if (strongerSide == BLACK)
254 Square queeningSq = file_of(psq) | RANK_1;
257 // If the stronger side's king is in front of the pawn, it's a win
258 if (wksq < psq && file_of(wksq) == file_of(psq))
259 result = RookValueEg - Value(square_distance(wksq, psq));
261 // If the weaker side's king is too far from the pawn and the rook,
263 else if ( square_distance(bksq, psq) >= 3 + (pos.side_to_move() == weakerSide)
264 && square_distance(bksq, rsq) >= 3)
265 result = RookValueEg - Value(square_distance(wksq, psq));
267 // If the pawn is far advanced and supported by the defending king,
268 // the position is drawish
269 else if ( rank_of(bksq) <= RANK_3
270 && square_distance(bksq, psq) == 1
271 && rank_of(wksq) >= RANK_4
272 && square_distance(wksq, psq) > 2 + (pos.side_to_move() == strongerSide))
273 result = Value(80 - square_distance(wksq, psq) * 8);
277 - Value(square_distance(wksq, psq + DELTA_S) * 8)
278 + Value(square_distance(bksq, psq + DELTA_S) * 8)
279 + Value(square_distance(psq, queeningSq) * 8);
281 return strongerSide == pos.side_to_move() ? result : -result;
285 /// KR vs KB. This is very simple, and always returns drawish scores. The
286 /// score is slightly bigger when the defending king is close to the edge.
288 Value Endgame<KRKB>::operator()(const Position& pos) const {
290 assert(pos.non_pawn_material(strongerSide) == RookValueMg);
291 assert(pos.non_pawn_material(weakerSide ) == BishopValueMg);
292 assert(pos.count<BISHOP>(weakerSide ) == 1);
293 assert(pos.count< PAWN>(weakerSide ) == 0);
294 assert(pos.count< PAWN>(strongerSide) == 0);
296 Value result = Value(PushToEdges[pos.king_square(weakerSide)]);
297 return strongerSide == pos.side_to_move() ? result : -result;
301 /// KR vs KN. The attacking side has slightly better winning chances than
302 /// in KR vs KB, particularly if the king and the knight are far apart.
304 Value Endgame<KRKN>::operator()(const Position& pos) const {
306 assert(pos.non_pawn_material(strongerSide) == RookValueMg);
307 assert(pos.non_pawn_material(weakerSide ) == KnightValueMg);
308 assert(pos.count<KNIGHT>(weakerSide ) == 1);
309 assert(pos.count< PAWN>(weakerSide ) == 0);
310 assert(pos.count< PAWN>(strongerSide) == 0);
312 Square bksq = pos.king_square(weakerSide);
313 Square bnsq = pos.list<KNIGHT>(weakerSide)[0];
314 Value result = Value(PushToEdges[bksq] + PushAway[square_distance(bksq, bnsq)]);
315 return strongerSide == pos.side_to_move() ? result : -result;
319 /// KQ vs KP. In general, a win for the stronger side, however, there are a few
320 /// important exceptions. Pawn on 7th rank, A,C,F or H file, with king next can
321 /// be a draw, so we scale down to distance between kings only.
323 Value Endgame<KQKP>::operator()(const Position& pos) const {
325 assert(pos.non_pawn_material(strongerSide) == QueenValueMg);
326 assert(pos.non_pawn_material(weakerSide ) == VALUE_ZERO);
327 assert(pos.count<PAWN>(strongerSide) == 0);
328 assert(pos.count<PAWN>(weakerSide ) == 1);
330 Square winnerKSq = pos.king_square(strongerSide);
331 Square loserKSq = pos.king_square(weakerSide);
332 Square pawnSq = pos.list<PAWN>(weakerSide)[0];
334 Value result = Value(PushClose[square_distance(winnerKSq, loserKSq)]);
336 if ( relative_rank(weakerSide, pawnSq) != RANK_7
337 || square_distance(loserKSq, pawnSq) != 1
338 || !((FileABB | FileCBB | FileFBB | FileHBB) & pawnSq))
339 result += QueenValueEg - PawnValueEg;
341 return strongerSide == pos.side_to_move() ? result : -result;
345 /// KQ vs KR. This is almost identical to KX vs K: We give the attacking
346 /// king a bonus for having the kings close together, and for forcing the
347 /// defending king towards the edge. If we also take care to avoid null move
348 /// for the defending side in the search, this is usually sufficient to be
349 /// able to win KQ vs KR.
351 Value Endgame<KQKR>::operator()(const Position& pos) const {
353 assert(pos.non_pawn_material(strongerSide) == QueenValueMg);
354 assert(pos.non_pawn_material(weakerSide ) == RookValueMg);
355 assert(pos.count<PAWN>(strongerSide) == 0);
356 assert(pos.count<PAWN>(weakerSide ) == 0);
358 Square winnerKSq = pos.king_square(strongerSide);
359 Square loserKSq = pos.king_square(weakerSide);
361 Value result = QueenValueEg
363 + PushToEdges[loserKSq]
364 + PushClose[square_distance(winnerKSq, loserKSq)];
366 return strongerSide == pos.side_to_move() ? result : -result;
370 /// KBB vs KN. This is almost always a win. We try to push enemy king to a corner
371 /// and away from his knight. For a reference of this difficult endgame see:
372 /// en.wikipedia.org/wiki/Chess_endgame#Effect_of_tablebases_on_endgame_theory
375 Value Endgame<KBBKN>::operator()(const Position& pos) const {
377 assert(pos.non_pawn_material(strongerSide) == 2 * BishopValueMg);
378 assert(pos.non_pawn_material(weakerSide ) == KnightValueMg);
379 assert(pos.count<BISHOP>(strongerSide) == 2);
380 assert(pos.count<KNIGHT>(weakerSide ) == 1);
381 assert(!pos.pieces(PAWN));
383 Square winnerKSq = pos.king_square(strongerSide);
384 Square loserKSq = pos.king_square(weakerSide);
385 Square knightSq = pos.list<KNIGHT>(weakerSide)[0];
387 Value result = VALUE_KNOWN_WIN
388 + PushToCorners[loserKSq]
389 + PushClose[square_distance(winnerKSq, loserKSq)]
390 + PushAway[square_distance(loserKSq, knightSq)];
392 return strongerSide == pos.side_to_move() ? result : -result;
396 /// Some cases of trivial draws
397 template<> Value Endgame<KNNK>::operator()(const Position&) const { return VALUE_DRAW; }
398 template<> Value Endgame<KmmKm>::operator()(const Position&) const { return VALUE_DRAW; }
401 /// K, bishop and one or more pawns vs K. It checks for draws with rook pawns and
402 /// a bishop of the wrong color. If such a draw is detected, SCALE_FACTOR_DRAW
403 /// is returned. If not, the return value is SCALE_FACTOR_NONE, i.e. no scaling
406 ScaleFactor Endgame<KBPsK>::operator()(const Position& pos) const {
408 assert(pos.non_pawn_material(strongerSide) == BishopValueMg);
409 assert(pos.count<BISHOP>(strongerSide) == 1);
410 assert(pos.count< PAWN>(strongerSide) >= 1);
412 // No assertions about the material of weakerSide, because we want draws to
413 // be detected even when the weaker side has some pawns.
415 Bitboard pawns = pos.pieces(strongerSide, PAWN);
416 File pawnFile = file_of(pos.list<PAWN>(strongerSide)[0]);
418 // All pawns are on a single rook file ?
419 if ( (pawnFile == FILE_A || pawnFile == FILE_H)
420 && !(pawns & ~file_bb(pawnFile)))
422 Square bishopSq = pos.list<BISHOP>(strongerSide)[0];
423 Square queeningSq = relative_square(strongerSide, pawnFile | RANK_8);
424 Square kingSq = pos.king_square(weakerSide);
426 if ( opposite_colors(queeningSq, bishopSq)
427 && abs(file_of(kingSq) - pawnFile) <= 1)
429 // The bishop has the wrong color, and the defending king is on the
430 // file of the pawn(s) or the adjacent file. Find the rank of the
432 Square pawnSq = frontmost_sq(strongerSide, pawns);
434 // If the defending king has distance 1 to the promotion square or
435 // is placed somewhere in front of the pawn, it's a draw.
436 if ( square_distance(kingSq, queeningSq) <= 1
437 || relative_rank(weakerSide, kingSq) <= relative_rank(weakerSide, pawnSq))
438 return SCALE_FACTOR_DRAW;
442 // All pawns on same B or G file? Then potential draw
443 if ( (pawnFile == FILE_B || pawnFile == FILE_G)
444 && !(pos.pieces(PAWN) & ~file_bb(pawnFile))
445 && pos.non_pawn_material(weakerSide) == 0
446 && pos.count<PAWN>(weakerSide) >= 1)
448 // Get weakerSide pawn that is closest to home rank
449 Square weakerPawnSq = backmost_sq(weakerSide, pos.pieces(weakerSide, PAWN));
451 Square strongerKingSq = pos.king_square(strongerSide);
452 Square weakerKingSq = pos.king_square(weakerSide);
453 Square bishopSq = pos.list<BISHOP>(strongerSide)[0];
455 // Potential for a draw if our pawn is blocked on the 7th rank
456 // the bishop cannot attack it or they only have one pawn left
457 if ( relative_rank(strongerSide, weakerPawnSq) == RANK_7
458 && (pos.pieces(strongerSide, PAWN) & (weakerPawnSq + pawn_push(weakerSide)))
459 && (opposite_colors(bishopSq, weakerPawnSq) || pos.count<PAWN>(strongerSide) == 1))
461 int strongerKingDist = square_distance(weakerPawnSq, strongerKingSq);
462 int weakerKingDist = square_distance(weakerPawnSq, weakerKingSq);
464 // Draw if the weak king is on it's back two ranks, within 2
465 // squares of the blocking pawn and the strong king is not
466 // closer. (I think this rule only fails in practically
467 // unreachable positions such as 5k1K/6p1/6P1/8/8/3B4/8/8 w
468 // and positions where qsearch will immediately correct the
469 // problem such as 8/4k1p1/6P1/1K6/3B4/8/8/8 w)
470 if ( relative_rank(strongerSide, weakerKingSq) >= RANK_7
471 && weakerKingDist <= 2
472 && weakerKingDist <= strongerKingDist)
473 return SCALE_FACTOR_DRAW;
477 return SCALE_FACTOR_NONE;
481 /// K and queen vs K, rook and one or more pawns. It tests for fortress draws with
482 /// a rook on the third rank defended by a pawn.
484 ScaleFactor Endgame<KQKRPs>::operator()(const Position& pos) const {
486 assert(pos.non_pawn_material(strongerSide) == QueenValueMg);
487 assert(pos.count<QUEEN>(strongerSide) == 1);
488 assert(pos.count< PAWN>(strongerSide) == 0);
489 assert(pos.count< ROOK>(weakerSide ) == 1);
490 assert(pos.count< PAWN>(weakerSide ) >= 1);
492 Square kingSq = pos.king_square(weakerSide);
493 Square rsq = pos.list<ROOK>(weakerSide)[0];
495 if ( relative_rank(weakerSide, kingSq) <= RANK_2
496 && relative_rank(weakerSide, pos.king_square(strongerSide)) >= RANK_4
497 && (pos.pieces(weakerSide, ROOK) & rank_bb(relative_rank(weakerSide, RANK_3)))
498 && (pos.pieces(weakerSide, PAWN) & rank_bb(relative_rank(weakerSide, RANK_2)))
499 && (pos.attacks_from<KING>(kingSq) & pos.pieces(weakerSide, PAWN))
500 && (pos.attacks_from<PAWN>(rsq, strongerSide) & pos.pieces(weakerSide, PAWN)))
501 return SCALE_FACTOR_DRAW;
503 return SCALE_FACTOR_NONE;
507 /// K, rook and one pawn vs K and a rook. This function knows a handful of the
508 /// most important classes of drawn positions, but is far from perfect. It would
509 /// probably be a good idea to add more knowledge in the future.
511 /// It would also be nice to rewrite the actual code for this function,
512 /// which is mostly copied from Glaurung 1.x, and not very pretty.
514 ScaleFactor Endgame<KRPKR>::operator()(const Position& pos) const {
516 assert(pos.non_pawn_material(strongerSide) == RookValueMg);
517 assert(pos.non_pawn_material(weakerSide) == RookValueMg);
518 assert(pos.count<PAWN>(strongerSide) == 1);
519 assert(pos.count<PAWN>(weakerSide ) == 0);
521 Square wksq = pos.king_square(strongerSide);
522 Square bksq = pos.king_square(weakerSide);
523 Square wrsq = pos.list<ROOK>(strongerSide)[0];
524 Square wpsq = pos.list<PAWN>(strongerSide)[0];
525 Square brsq = pos.list<ROOK>(weakerSide)[0];
527 // Orient the board in such a way that the stronger side is white, and the
528 // pawn is on the left half of the board.
529 if (strongerSide == BLACK)
538 if (file_of(wpsq) > FILE_D)
547 File f = file_of(wpsq);
548 Rank r = rank_of(wpsq);
549 Square queeningSq = f | RANK_8;
550 int tempo = (pos.side_to_move() == strongerSide);
552 // If the pawn is not too far advanced and the defending king defends the
553 // queening square, use the third-rank defence.
555 && square_distance(bksq, queeningSq) <= 1
557 && (rank_of(brsq) == RANK_6 || (r <= RANK_3 && rank_of(wrsq) != RANK_6)))
558 return SCALE_FACTOR_DRAW;
560 // The defending side saves a draw by checking from behind in case the pawn
561 // has advanced to the 6th rank with the king behind.
563 && square_distance(bksq, queeningSq) <= 1
564 && rank_of(wksq) + tempo <= RANK_6
565 && (rank_of(brsq) == RANK_1 || (!tempo && abs(file_of(brsq) - f) >= 3)))
566 return SCALE_FACTOR_DRAW;
569 && bksq == queeningSq
570 && rank_of(brsq) == RANK_1
571 && (!tempo || square_distance(wksq, wpsq) >= 2))
572 return SCALE_FACTOR_DRAW;
574 // White pawn on a7 and rook on a8 is a draw if black's king is on g7 or h7
575 // and the black rook is behind the pawn.
578 && (bksq == SQ_H7 || bksq == SQ_G7)
579 && file_of(brsq) == FILE_A
580 && (rank_of(brsq) <= RANK_3 || file_of(wksq) >= FILE_D || rank_of(wksq) <= RANK_5))
581 return SCALE_FACTOR_DRAW;
583 // If the defending king blocks the pawn and the attacking king is too far
584 // away, it's a draw.
586 && bksq == wpsq + DELTA_N
587 && square_distance(wksq, wpsq) - tempo >= 2
588 && square_distance(wksq, brsq) - tempo >= 2)
589 return SCALE_FACTOR_DRAW;
591 // Pawn on the 7th rank supported by the rook from behind usually wins if the
592 // attacking king is closer to the queening square than the defending king,
593 // and the defending king cannot gain tempi by threatening the attacking rook.
596 && file_of(wrsq) == f
597 && wrsq != queeningSq
598 && (square_distance(wksq, queeningSq) < square_distance(bksq, queeningSq) - 2 + tempo)
599 && (square_distance(wksq, queeningSq) < square_distance(bksq, wrsq) + tempo))
600 return ScaleFactor(SCALE_FACTOR_MAX - 2 * square_distance(wksq, queeningSq));
602 // Similar to the above, but with the pawn further back
604 && file_of(wrsq) == f
606 && (square_distance(wksq, queeningSq) < square_distance(bksq, queeningSq) - 2 + tempo)
607 && (square_distance(wksq, wpsq + DELTA_N) < square_distance(bksq, wpsq + DELTA_N) - 2 + tempo)
608 && ( square_distance(bksq, wrsq) + tempo >= 3
609 || ( square_distance(wksq, queeningSq) < square_distance(bksq, wrsq) + tempo
610 && (square_distance(wksq, wpsq + DELTA_N) < square_distance(bksq, wrsq) + tempo))))
611 return ScaleFactor( SCALE_FACTOR_MAX
612 - 8 * square_distance(wpsq, queeningSq)
613 - 2 * square_distance(wksq, queeningSq));
615 // If the pawn is not far advanced, and the defending king is somewhere in
616 // the pawn's path, it's probably a draw.
617 if (r <= RANK_4 && bksq > wpsq)
619 if (file_of(bksq) == file_of(wpsq))
620 return ScaleFactor(10);
621 if ( abs(file_of(bksq) - file_of(wpsq)) == 1
622 && square_distance(wksq, bksq) > 2)
623 return ScaleFactor(24 - 2 * square_distance(wksq, bksq));
625 return SCALE_FACTOR_NONE;
629 ScaleFactor Endgame<KRPKB>::operator()(const Position& pos) const {
631 assert(pos.non_pawn_material(strongerSide) == RookValueMg);
632 assert(pos.non_pawn_material(weakerSide) == BishopValueMg);
633 assert(pos.count<PAWN>(strongerSide) == 1);
634 assert(pos.count<PAWN>(weakerSide) == 0);
636 // Test for a rook pawn
637 if (pos.pieces(PAWN) & (FileABB | FileHBB))
639 Square ksq = pos.king_square(weakerSide);
640 Square bsq = pos.list<BISHOP>(weakerSide)[0];
641 Square psq = pos.list<PAWN>(strongerSide)[0];
642 Rank rk = relative_rank(strongerSide, psq);
643 Square push = pawn_push(strongerSide);
645 // If the pawn is on the 5th rank and the pawn (currently) is on
646 // the same color square as the bishop then there is a chance of
647 // a fortress. Depending on the king position give a moderate
648 // reduction or a stronger one if the defending king is near the
649 // corner but not trapped there.
650 if (rk == RANK_5 && !opposite_colors(bsq, psq))
652 int d = square_distance(psq + 3 * push, ksq);
654 if (d <= 2 && !(d == 0 && ksq == pos.king_square(strongerSide) + 2 * push))
655 return ScaleFactor(24);
657 return ScaleFactor(48);
660 // When the pawn has moved to the 6th rank we can be fairly sure
661 // it's drawn if the bishop attacks the square in front of the
662 // pawn from a reasonable distance and the defending king is near
665 && square_distance(psq + 2 * push, ksq) <= 1
666 && (PseudoAttacks[BISHOP][bsq] & (psq + push))
667 && file_distance(bsq, psq) >= 2)
668 return ScaleFactor(8);
671 return SCALE_FACTOR_NONE;
674 /// K, rook and two pawns vs K, rook and one pawn. There is only a single
675 /// pattern: If the stronger side has no passed pawns and the defending king
676 /// is actively placed, the position is drawish.
678 ScaleFactor Endgame<KRPPKRP>::operator()(const Position& pos) const {
680 assert(pos.non_pawn_material(strongerSide) == RookValueMg);
681 assert(pos.non_pawn_material(weakerSide) == RookValueMg);
682 assert(pos.count<PAWN>(strongerSide) == 2);
683 assert(pos.count<PAWN>(weakerSide ) == 1);
685 Square wpsq1 = pos.list<PAWN>(strongerSide)[0];
686 Square wpsq2 = pos.list<PAWN>(strongerSide)[1];
687 Square bksq = pos.king_square(weakerSide);
689 // Does the stronger side have a passed pawn?
690 if (pos.pawn_passed(strongerSide, wpsq1) || pos.pawn_passed(strongerSide, wpsq2))
691 return SCALE_FACTOR_NONE;
693 Rank r = std::max(relative_rank(strongerSide, wpsq1), relative_rank(strongerSide, wpsq2));
695 if ( file_distance(bksq, wpsq1) <= 1
696 && file_distance(bksq, wpsq2) <= 1
697 && relative_rank(strongerSide, bksq) > r)
700 case RANK_2: return ScaleFactor(10);
701 case RANK_3: return ScaleFactor(10);
702 case RANK_4: return ScaleFactor(15);
703 case RANK_5: return ScaleFactor(20);
704 case RANK_6: return ScaleFactor(40);
705 default: assert(false);
708 return SCALE_FACTOR_NONE;
712 /// K and two or more pawns vs K. There is just a single rule here: If all pawns
713 /// are on the same rook file and are blocked by the defending king, it's a draw.
715 ScaleFactor Endgame<KPsK>::operator()(const Position& pos) const {
717 assert(pos.non_pawn_material(strongerSide) == VALUE_ZERO);
718 assert(pos.non_pawn_material(weakerSide) == VALUE_ZERO);
719 assert(pos.count<PAWN>(strongerSide) >= 2);
720 assert(pos.count<PAWN>(weakerSide ) == 0);
722 Square ksq = pos.king_square(weakerSide);
723 Bitboard pawns = pos.pieces(strongerSide, PAWN);
725 // Are all pawns on the 'a' file?
726 if (!(pawns & ~FileABB))
728 // Does the defending king block the pawns?
729 if ( square_distance(ksq, relative_square(strongerSide, SQ_A8)) <= 1
730 || ( file_of(ksq) == FILE_A
731 && !(in_front_bb(strongerSide, rank_of(ksq)) & pawns)))
732 return SCALE_FACTOR_DRAW;
734 // Are all pawns on the 'h' file?
735 else if (!(pawns & ~FileHBB))
737 // Does the defending king block the pawns?
738 if ( square_distance(ksq, relative_square(strongerSide, SQ_H8)) <= 1
739 || ( file_of(ksq) == FILE_H
740 && !(in_front_bb(strongerSide, rank_of(ksq)) & pawns)))
741 return SCALE_FACTOR_DRAW;
743 return SCALE_FACTOR_NONE;
747 /// K, bishop and a pawn vs K and a bishop. There are two rules: If the defending
748 /// king is somewhere along the path of the pawn, and the square of the king is
749 /// not of the same color as the stronger side's bishop, it's a draw. If the two
750 /// bishops have opposite color, it's almost always a draw.
752 ScaleFactor Endgame<KBPKB>::operator()(const Position& pos) const {
754 assert(pos.non_pawn_material(strongerSide) == BishopValueMg);
755 assert(pos.non_pawn_material(weakerSide ) == BishopValueMg);
756 assert(pos.count<BISHOP>(strongerSide) == 1);
757 assert(pos.count<BISHOP>(weakerSide ) == 1);
758 assert(pos.count< PAWN>(strongerSide) == 1);
759 assert(pos.count< PAWN>(weakerSide ) == 0);
761 Square pawnSq = pos.list<PAWN>(strongerSide)[0];
762 Square strongerBishopSq = pos.list<BISHOP>(strongerSide)[0];
763 Square weakerBishopSq = pos.list<BISHOP>(weakerSide)[0];
764 Square weakerKingSq = pos.king_square(weakerSide);
766 // Case 1: Defending king blocks the pawn, and cannot be driven away
767 if ( file_of(weakerKingSq) == file_of(pawnSq)
768 && relative_rank(strongerSide, pawnSq) < relative_rank(strongerSide, weakerKingSq)
769 && ( opposite_colors(weakerKingSq, strongerBishopSq)
770 || relative_rank(strongerSide, weakerKingSq) <= RANK_6))
771 return SCALE_FACTOR_DRAW;
773 // Case 2: Opposite colored bishops
774 if (opposite_colors(strongerBishopSq, weakerBishopSq))
776 // We assume that the position is drawn in the following three situations:
778 // a. The pawn is on rank 5 or further back.
779 // b. The defending king is somewhere in the pawn's path.
780 // c. The defending bishop attacks some square along the pawn's path,
781 // and is at least three squares away from the pawn.
783 // These rules are probably not perfect, but in practice they work
786 if (relative_rank(strongerSide, pawnSq) <= RANK_5)
787 return SCALE_FACTOR_DRAW;
790 Bitboard path = forward_bb(strongerSide, pawnSq);
792 if (path & pos.pieces(weakerSide, KING))
793 return SCALE_FACTOR_DRAW;
795 if ( (pos.attacks_from<BISHOP>(weakerBishopSq) & path)
796 && square_distance(weakerBishopSq, pawnSq) >= 3)
797 return SCALE_FACTOR_DRAW;
800 return SCALE_FACTOR_NONE;
804 /// K, bishop and two pawns vs K and bishop. It detects a few basic draws with
805 /// opposite-colored bishops.
807 ScaleFactor Endgame<KBPPKB>::operator()(const Position& pos) const {
809 assert(pos.non_pawn_material(strongerSide) == BishopValueMg);
810 assert(pos.non_pawn_material(weakerSide ) == BishopValueMg);
811 assert(pos.count<BISHOP>(strongerSide) == 1);
812 assert(pos.count<BISHOP>(weakerSide ) == 1);
813 assert(pos.count< PAWN>(strongerSide) == 2);
814 assert(pos.count< PAWN>(weakerSide ) == 0);
816 Square wbsq = pos.list<BISHOP>(strongerSide)[0];
817 Square bbsq = pos.list<BISHOP>(weakerSide)[0];
819 if (!opposite_colors(wbsq, bbsq))
820 return SCALE_FACTOR_NONE;
822 Square ksq = pos.king_square(weakerSide);
823 Square psq1 = pos.list<PAWN>(strongerSide)[0];
824 Square psq2 = pos.list<PAWN>(strongerSide)[1];
825 Rank r1 = rank_of(psq1);
826 Rank r2 = rank_of(psq2);
827 Square blockSq1, blockSq2;
829 if (relative_rank(strongerSide, psq1) > relative_rank(strongerSide, psq2))
831 blockSq1 = psq1 + pawn_push(strongerSide);
832 blockSq2 = file_of(psq2) | rank_of(psq1);
836 blockSq1 = psq2 + pawn_push(strongerSide);
837 blockSq2 = file_of(psq1) | rank_of(psq2);
840 switch (file_distance(psq1, psq2))
843 // Both pawns are on the same file. Easy draw if defender firmly controls
844 // some square in the frontmost pawn's path.
845 if ( file_of(ksq) == file_of(blockSq1)
846 && relative_rank(strongerSide, ksq) >= relative_rank(strongerSide, blockSq1)
847 && opposite_colors(ksq, wbsq))
848 return SCALE_FACTOR_DRAW;
850 return SCALE_FACTOR_NONE;
853 // Pawns on adjacent files. Draw if defender firmly controls the square
854 // in front of the frontmost pawn's path, and the square diagonally behind
855 // this square on the file of the other pawn.
857 && opposite_colors(ksq, wbsq)
858 && ( bbsq == blockSq2
859 || (pos.attacks_from<BISHOP>(blockSq2) & pos.pieces(weakerSide, BISHOP))
860 || abs(r1 - r2) >= 2))
861 return SCALE_FACTOR_DRAW;
863 else if ( ksq == blockSq2
864 && opposite_colors(ksq, wbsq)
865 && ( bbsq == blockSq1
866 || (pos.attacks_from<BISHOP>(blockSq1) & pos.pieces(weakerSide, BISHOP))))
867 return SCALE_FACTOR_DRAW;
869 return SCALE_FACTOR_NONE;
872 // The pawns are not on the same file or adjacent files. No scaling.
873 return SCALE_FACTOR_NONE;
878 /// K, bisop and a pawn vs K and knight. There is a single rule: If the defending
879 /// king is somewhere along the path of the pawn, and the square of the king is
880 /// not of the same color as the stronger side's bishop, it's a draw.
882 ScaleFactor Endgame<KBPKN>::operator()(const Position& pos) const {
884 assert(pos.non_pawn_material(strongerSide) == BishopValueMg);
885 assert(pos.non_pawn_material(weakerSide ) == KnightValueMg);
886 assert(pos.count<BISHOP>(strongerSide) == 1);
887 assert(pos.count<KNIGHT>(weakerSide ) == 1);
888 assert(pos.count< PAWN>(strongerSide) == 1);
889 assert(pos.count< PAWN>(weakerSide ) == 0);
891 Square pawnSq = pos.list<PAWN>(strongerSide)[0];
892 Square strongerBishopSq = pos.list<BISHOP>(strongerSide)[0];
893 Square weakerKingSq = pos.king_square(weakerSide);
895 if ( file_of(weakerKingSq) == file_of(pawnSq)
896 && relative_rank(strongerSide, pawnSq) < relative_rank(strongerSide, weakerKingSq)
897 && ( opposite_colors(weakerKingSq, strongerBishopSq)
898 || relative_rank(strongerSide, weakerKingSq) <= RANK_6))
899 return SCALE_FACTOR_DRAW;
901 return SCALE_FACTOR_NONE;
905 /// K, knight and a pawn vs K. There is a single rule: If the pawn is a rook pawn
906 /// on the 7th rank and the defending king prevents the pawn from advancing, the
907 /// position is drawn.
909 ScaleFactor Endgame<KNPK>::operator()(const Position& pos) const {
911 assert(pos.non_pawn_material(strongerSide) == KnightValueMg);
912 assert(pos.non_pawn_material(weakerSide ) == VALUE_ZERO);
913 assert(pos.count<KNIGHT>(strongerSide) == 1);
914 assert(pos.count< PAWN>(strongerSide) == 1);
915 assert(pos.count< PAWN>(weakerSide ) == 0);
917 Square pawnSq = pos.list<PAWN>(strongerSide)[0];
918 Square weakerKingSq = pos.king_square(weakerSide);
920 if ( pawnSq == relative_square(strongerSide, SQ_A7)
921 && square_distance(weakerKingSq, relative_square(strongerSide, SQ_A8)) <= 1)
922 return SCALE_FACTOR_DRAW;
924 if ( pawnSq == relative_square(strongerSide, SQ_H7)
925 && square_distance(weakerKingSq, relative_square(strongerSide, SQ_H8)) <= 1)
926 return SCALE_FACTOR_DRAW;
928 return SCALE_FACTOR_NONE;
932 /// K, knight and a pawn vs K and bishop. If knight can block bishop from taking
933 /// pawn, it's a win. Otherwise, drawn.
935 ScaleFactor Endgame<KNPKB>::operator()(const Position& pos) const {
937 Square pawnSq = pos.list<PAWN>(strongerSide)[0];
938 Square bishopSq = pos.list<BISHOP>(weakerSide)[0];
939 Square weakerKingSq = pos.king_square(weakerSide);
941 // King needs to get close to promoting pawn to prevent knight from blocking.
942 // Rules for this are very tricky, so just approximate.
943 if (forward_bb(strongerSide, pawnSq) & pos.attacks_from<BISHOP>(bishopSq))
944 return ScaleFactor(square_distance(weakerKingSq, pawnSq));
946 return SCALE_FACTOR_NONE;
950 /// K and a pawn vs K and a pawn. This is done by removing the weakest side's
951 /// pawn and probing the KP vs K bitbase: If the weakest side has a draw without
952 /// the pawn, she probably has at least a draw with the pawn as well. The exception
953 /// is when the stronger side's pawn is far advanced and not on a rook file; in
954 /// this case it is often possible to win (e.g. 8/4k3/3p4/3P4/6K1/8/8/8 w - - 0 1).
956 ScaleFactor Endgame<KPKP>::operator()(const Position& pos) const {
958 assert(pos.non_pawn_material(strongerSide) == VALUE_ZERO);
959 assert(pos.non_pawn_material(weakerSide ) == VALUE_ZERO);
960 assert(pos.count<PAWN>(WHITE) == 1);
961 assert(pos.count<PAWN>(BLACK) == 1);
963 Square wksq = pos.king_square(strongerSide);
964 Square bksq = pos.king_square(weakerSide);
965 Square psq = pos.list<PAWN>(strongerSide)[0];
966 Color us = pos.side_to_move();
968 if (strongerSide == BLACK)
976 if (file_of(psq) >= FILE_E)
983 // If the pawn has advanced to the fifth rank or further, and is not a
984 // rook pawn, it's too dangerous to assume that it's at least a draw.
985 if (rank_of(psq) >= RANK_5 && file_of(psq) != FILE_A)
986 return SCALE_FACTOR_NONE;
988 // Probe the KPK bitbase with the weakest side's pawn removed. If it's a draw,
989 // it's probably at least a draw even with the pawn.
990 return Bitbases::probe_kpk(wksq, psq, bksq, us) ? SCALE_FACTOR_NONE : SCALE_FACTOR_DRAW;