X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fposition.cpp;h=40890acfd3b15e607211e137f889aa0ee3eef4b7;hp=f5081bd145d401acad94f986585e372695989fc2;hb=d490bb99734bd6e2f8a0a352d2f3f1ba264ece66;hpb=943ae89be11929b09be5c5d0447b2b62b5480ebd diff --git a/src/position.cpp b/src/position.cpp index f5081bd1..40890acf 100644 --- a/src/position.cpp +++ b/src/position.cpp @@ -2,7 +2,7 @@ Stockfish, a UCI chess playing engine derived from Glaurung 2.1 Copyright (C) 2004-2008 Tord Romstad (Glaurung author) Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad - Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad + Copyright (C) 2015-2017 Marco Costalba, Joona Kiiski, Gary Linscott, 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 @@ -32,6 +32,7 @@ #include "thread.h" #include "tt.h" #include "uci.h" +#include "syzygy/tbprobe.h" using std::string; @@ -44,14 +45,14 @@ namespace Zobrist { Key psq[PIECE_NB][SQUARE_NB]; Key enpassant[FILE_NB]; Key castling[CASTLING_RIGHT_NB]; - Key side; + Key side, noPawns; } namespace { const string PieceToChar(" PNBRQK pnbrqk"); -// min_attacker() is a helper function used by see() to locate the least +// min_attacker() is a helper function used by see_ge() to locate the least // valuable attacker for the side to move, remove the attacker we just found // from the bitboards and scan for new X-ray attacks behind it. @@ -98,11 +99,25 @@ std::ostream& operator<<(std::ostream& os, const Position& pos) { } os << "\nFen: " << pos.fen() << "\nKey: " << std::hex << std::uppercase - << std::setfill('0') << std::setw(16) << pos.key() << std::dec << "\nCheckers: "; + << std::setfill('0') << std::setw(16) << pos.key() + << std::setfill(' ') << std::dec << "\nCheckers: "; for (Bitboard b = pos.checkers(); b; ) os << UCI::square(pop_lsb(&b)) << " "; + if ( int(Tablebases::MaxCardinality) >= popcount(pos.pieces()) + && !pos.can_castle(ANY_CASTLING)) + { + StateInfo st; + Position p; + p.set(pos.fen(), pos.is_chess960(), &st, pos.this_thread()); + Tablebases::ProbeState s1, s2; + Tablebases::WDLScore wdl = Tablebases::probe_wdl(p, &s1); + int dtz = Tablebases::probe_dtz(p, &s2); + os << "\nTablebases WDL: " << std::setw(4) << wdl << " (" << s1 << ")" + << "\nTablebases DTZ: " << std::setw(4) << dtz << " (" << s2 << ")"; + } + return os; } @@ -133,6 +148,7 @@ void Position::init() { } Zobrist::side = rng.rand(); + Zobrist::noPawns = rng.rand(); } @@ -164,8 +180,9 @@ Position& Position::set(const string& fenStr, bool isChess960, StateInfo* si, Th 4) En passant target square (in algebraic notation). If there's no en passant target square, this is "-". If a pawn has just made a 2-square move, this - is the position "behind" the pawn. This is recorded regardless of whether - there is a pawn in position to make an en passant capture. + is the position "behind" the pawn. This is recorded only if there is a pawn + in position to make an en passant capture, and if there really is a pawn + that might have advanced two squares. 5) Halfmove clock. This is the number of halfmoves since the last pawn advance or capture. This is used to determine if a draw can be claimed under the @@ -242,7 +259,8 @@ Position& Position::set(const string& fenStr, bool isChess960, StateInfo* si, Th { st->epSquare = make_square(File(col - 'a'), Rank(row - '1')); - if (!(attackers_to(st->epSquare) & pieces(sideToMove, PAWN))) + if ( !(attackers_to(st->epSquare) & pieces(sideToMove, PAWN)) + || !(pieces(~sideToMove, PAWN) & (st->epSquare + pawn_push(~sideToMove)))) st->epSquare = SQ_NONE; } else @@ -317,7 +335,8 @@ void Position::set_check_info(StateInfo* si) const { void Position::set_state(StateInfo* si) const { - si->key = si->pawnKey = si->materialKey = 0; + si->key = si->materialKey = 0; + si->pawnKey = Zobrist::noPawns; si->nonPawnMaterial[WHITE] = si->nonPawnMaterial[BLACK] = VALUE_ZERO; si->psq = SCORE_ZERO; si->checkersBB = attackers_to(square(sideToMove)) & pieces(~sideToMove); @@ -357,6 +376,28 @@ void Position::set_state(StateInfo* si) const { } +/// Position::set() is an overload to initialize the position object with +/// the given endgame code string like "KBPKN". It is mainly a helper to +/// get the material key out of an endgame code. Position is not playable, +/// indeed is even not guaranteed to be legal. + +Position& Position::set(const string& code, Color c, StateInfo* si) { + + 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 fenStr = 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 set(fenStr, false, si, nullptr); +} + + /// Position::fen() returns a FEN representation of the position. In case of /// Chess960 the Shredder-FEN notation is used. This is mainly a debugging function. @@ -955,121 +996,112 @@ Key Position::key_after(Move m) const { } -/// Position::see() is a static exchange evaluator: It tries to estimate the -/// material gain or loss resulting from a move. - -Value Position::see_sign(Move m) const { - - assert(is_ok(m)); - - // Early return if SEE cannot be negative because captured piece value - // is not less then capturing one. Note that king moves always return - // here because king midgame value is set to 0. - if (PieceValue[MG][moved_piece(m)] <= PieceValue[MG][piece_on(to_sq(m))]) - return VALUE_KNOWN_WIN; - - return see(m); -} +/// Position::see_ge (Static Exchange Evaluation Greater or Equal) tests if the +/// SEE value of move is greater or equal to the given value. We'll use an +/// algorithm similar to alpha-beta pruning with a null window. -Value Position::see(Move m) const { - - Square from, to; - Bitboard occupied, attackers, stmAttackers; - Value swapList[32]; - int slIndex = 1; - PieceType nextVictim; - Color stm; +bool Position::see_ge(Move m, Value v) const { assert(is_ok(m)); - from = from_sq(m); - to = to_sq(m); - swapList[0] = PieceValue[MG][piece_on(to)]; - stm = color_of(piece_on(from)); - occupied = pieces() ^ from; - - // Castling moves are implemented as king capturing the rook so cannot - // be handled correctly. Simply return VALUE_ZERO that is always correct - // unless in the rare case the rook ends up under attack. + // Castling moves are implemented as king capturing the rook so cannot be + // handled correctly. Simply assume the SEE value is VALUE_ZERO that is always + // correct unless in the rare case the rook ends up under attack. if (type_of(m) == CASTLING) - return VALUE_ZERO; + return VALUE_ZERO >= v; + + Square from = from_sq(m), to = to_sq(m); + PieceType nextVictim = type_of(piece_on(from)); + Color stm = ~color_of(piece_on(from)); // First consider opponent's move + Value balance; // Values of the pieces taken by us minus opponent's ones + Bitboard occupied, stmAttackers; if (type_of(m) == ENPASSANT) { - occupied ^= to - pawn_push(stm); // Remove the captured pawn - swapList[0] = PieceValue[MG][PAWN]; + occupied = SquareBB[to - pawn_push(~stm)]; // Remove the captured pawn + balance = PieceValue[MG][PAWN]; } + else + { + balance = PieceValue[MG][piece_on(to)]; + occupied = 0; + } + + if (balance < v) + return false; - // Find all attackers to the destination square, with the moving piece - // removed, but possibly an X-ray attacker added behind it. - attackers = attackers_to(to, occupied) & occupied; + if (nextVictim == KING) + return true; - // If the opponent has no attackers we are finished - stm = ~stm; - stmAttackers = attackers & pieces(stm); - occupied ^= to; // For the case when captured piece is a pinner + balance -= PieceValue[MG][nextVictim]; - // Don't allow pinned pieces to attack pieces except the king as long all - // pinners are on their original square. When a pinner moves to the - // exchange-square or get captured on it, we fall back to standard SEE behaviour. - if ( (stmAttackers & pinned_pieces(stm)) - && (st->pinnersForKing[stm] & occupied) == st->pinnersForKing[stm]) - stmAttackers &= ~pinned_pieces(stm); + if (balance >= v) + return true; - if (!stmAttackers) - return swapList[0]; + bool relativeStm = true; // True if the opponent is to move + occupied ^= pieces() ^ from ^ to; - // The destination square is defended, which makes things rather more - // difficult to compute. We proceed by building up a "swap list" containing - // the material gain or loss at each stop in a sequence of captures to the - // destination square, where the sides alternately capture, and always - // capture with the least valuable piece. After each capture, we look for - // new X-ray attacks from behind the capturing piece. - nextVictim = type_of(piece_on(from)); + // Find all attackers to the destination square, with the moving piece removed, + // but possibly an X-ray attacker added behind it. + Bitboard attackers = attackers_to(to, occupied) & occupied; - do { - assert(slIndex < 32); + while (true) + { + stmAttackers = attackers & pieces(stm); - // Add the new entry to the swap list - swapList[slIndex] = -swapList[slIndex - 1] + PieceValue[MG][nextVictim]; + // Don't allow pinned pieces to attack pieces except the king as long all + // pinners are on their original square. + if (!(st->pinnersForKing[stm] & ~occupied)) + stmAttackers &= ~st->blockersForKing[stm]; + + if (!stmAttackers) + return relativeStm; // Locate and remove the next least valuable attacker nextVictim = min_attacker(byTypeBB, to, stmAttackers, occupied, attackers); - stm = ~stm; - stmAttackers = attackers & pieces(stm); - if ( nextVictim != KING - && (stmAttackers & pinned_pieces(stm)) - && (st->pinnersForKing[stm] & occupied) == st->pinnersForKing[stm]) - stmAttackers &= ~pinned_pieces(stm); - ++slIndex; + if (nextVictim == KING) + return relativeStm == bool(attackers & pieces(~stm)); - } while (stmAttackers && (nextVictim != KING || (--slIndex, false))); // Stop before a king capture + balance += relativeStm ? PieceValue[MG][nextVictim] + : -PieceValue[MG][nextVictim]; - // Having built the swap list, we negamax through it to find the best - // achievable score from the point of view of the side to move. - while (--slIndex) - swapList[slIndex - 1] = std::min(-swapList[slIndex], swapList[slIndex - 1]); + relativeStm = !relativeStm; - return swapList[0]; + if (relativeStm == (balance >= v)) + return relativeStm; + + stm = ~stm; + } } /// Position::is_draw() tests whether the position is drawn by 50-move rule /// or by repetition. It does not detect stalemates. -bool Position::is_draw() const { +bool Position::is_draw(int ply) const { if (st->rule50 > 99 && (!checkers() || MoveList(*this).size())) return true; - StateInfo* stp = st; - for (int i = 2, e = std::min(st->rule50, st->pliesFromNull); i <= e; i += 2) + int end = std::min(st->rule50, st->pliesFromNull); + + if (end < 4) + return false; + + StateInfo* stp = st->previous->previous; + int cnt = 0; + + for (int i = 4; i <= end; i += 2) { stp = stp->previous->previous; - if (stp->key == st->key) - return true; // Draw at first repetition + // At root position ply is 1, so return a draw score if a position + // repeats once earlier but after or at the root, or repeats twice + // strictly before the root. + if ( stp->key == st->key + && ++cnt + (ply - i > 0) == 2) + return true; } return false;