362 lines
12 KiB
C++
362 lines
12 KiB
C++
/*
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Stockfish, a UCI chess playing engine derived from Glaurung 2.1
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Copyright (C) 2004-2021 The Stockfish developers (see AUTHORS file)
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Stockfish is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Stockfish is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <cassert>
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#include "movegen.h"
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#include "position.h"
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namespace Stockfish {
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namespace {
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template<GenType Type, Direction D>
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ExtMove* make_promotions(ExtMove* moveList, Square to, Square ksq) {
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if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
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{
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*moveList++ = make<PROMOTION>(to - D, to, QUEEN);
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if (attacks_bb<KNIGHT>(to) & ksq)
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*moveList++ = make<PROMOTION>(to - D, to, KNIGHT);
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}
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if (Type == QUIETS || Type == EVASIONS || Type == NON_EVASIONS)
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{
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*moveList++ = make<PROMOTION>(to - D, to, ROOK);
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*moveList++ = make<PROMOTION>(to - D, to, BISHOP);
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if (!(attacks_bb<KNIGHT>(to) & ksq))
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*moveList++ = make<PROMOTION>(to - D, to, KNIGHT);
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}
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return moveList;
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}
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template<Color Us, GenType Type>
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ExtMove* generate_pawn_moves(const Position& pos, ExtMove* moveList, Bitboard target) {
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constexpr Color Them = ~Us;
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constexpr Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
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constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
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constexpr Direction Up = pawn_push(Us);
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constexpr Direction UpRight = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
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constexpr Direction UpLeft = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
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const Square ksq = pos.square<KING>(Them);
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Bitboard emptySquares;
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Bitboard pawnsOn7 = pos.pieces(Us, PAWN) & TRank7BB;
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Bitboard pawnsNotOn7 = pos.pieces(Us, PAWN) & ~TRank7BB;
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Bitboard enemies = (Type == EVASIONS ? pos.checkers():
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Type == CAPTURES ? target : pos.pieces(Them));
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// Single and double pawn pushes, no promotions
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if (Type != CAPTURES)
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{
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emptySquares = (Type == QUIETS || Type == QUIET_CHECKS ? target : ~pos.pieces());
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Bitboard b1 = shift<Up>(pawnsNotOn7) & emptySquares;
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Bitboard b2 = shift<Up>(b1 & TRank3BB) & emptySquares;
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if (Type == EVASIONS) // Consider only blocking squares
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{
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b1 &= target;
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b2 &= target;
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}
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if (Type == QUIET_CHECKS)
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{
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b1 &= pawn_attacks_bb(Them, ksq);
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b2 &= pawn_attacks_bb(Them, ksq);
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// Add pawn pushes which give discovered check. This is possible only
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// if the pawn is not on the same file as the enemy king, because we
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// don't generate captures. Note that a possible discovered check
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// promotion has been already generated amongst the captures.
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Bitboard dcCandidateQuiets = pos.blockers_for_king(Them) & pawnsNotOn7;
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if (dcCandidateQuiets)
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{
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Bitboard dc1 = shift<Up>(dcCandidateQuiets) & emptySquares & ~file_bb(ksq);
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Bitboard dc2 = shift<Up>(dc1 & TRank3BB) & emptySquares;
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b1 |= dc1;
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b2 |= dc2;
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}
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}
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while (b1)
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{
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Square to = pop_lsb(b1);
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*moveList++ = make_move(to - Up, to);
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}
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while (b2)
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{
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Square to = pop_lsb(b2);
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*moveList++ = make_move(to - Up - Up, to);
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}
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}
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// Promotions and underpromotions
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if (pawnsOn7)
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{
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if (Type == CAPTURES)
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emptySquares = ~pos.pieces();
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if (Type == EVASIONS)
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emptySquares &= target;
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Bitboard b1 = shift<UpRight>(pawnsOn7) & enemies;
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Bitboard b2 = shift<UpLeft >(pawnsOn7) & enemies;
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Bitboard b3 = shift<Up >(pawnsOn7) & emptySquares;
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while (b1)
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moveList = make_promotions<Type, UpRight>(moveList, pop_lsb(b1), ksq);
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while (b2)
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moveList = make_promotions<Type, UpLeft >(moveList, pop_lsb(b2), ksq);
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while (b3)
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moveList = make_promotions<Type, Up >(moveList, pop_lsb(b3), ksq);
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}
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// Standard and en passant captures
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if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
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{
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Bitboard b1 = shift<UpRight>(pawnsNotOn7) & enemies;
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Bitboard b2 = shift<UpLeft >(pawnsNotOn7) & enemies;
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while (b1)
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{
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Square to = pop_lsb(b1);
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*moveList++ = make_move(to - UpRight, to);
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}
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while (b2)
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{
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Square to = pop_lsb(b2);
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*moveList++ = make_move(to - UpLeft, to);
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}
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if (pos.ep_square() != SQ_NONE)
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{
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assert(rank_of(pos.ep_square()) == relative_rank(Us, RANK_6));
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// An en passant capture cannot resolve a discovered check
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if (Type == EVASIONS && (target & (pos.ep_square() + Up)))
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return moveList;
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b1 = pawnsNotOn7 & pawn_attacks_bb(Them, pos.ep_square());
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assert(b1);
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while (b1)
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*moveList++ = make<EN_PASSANT>(pop_lsb(b1), pos.ep_square());
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}
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}
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return moveList;
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}
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template<PieceType Pt, bool Checks>
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ExtMove* generate_moves(const Position& pos, ExtMove* moveList, Bitboard piecesToMove, Bitboard target) {
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static_assert(Pt != KING && Pt != PAWN, "Unsupported piece type in generate_moves()");
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Bitboard bb = piecesToMove & pos.pieces(Pt);
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while (bb)
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{
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Square from = pop_lsb(bb);
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Bitboard b = attacks_bb<Pt>(from, pos.pieces()) & target;
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if constexpr (Checks)
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b &= pos.check_squares(Pt);
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while (b)
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*moveList++ = make_move(from, pop_lsb(b));
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}
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return moveList;
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}
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template<Color Us, GenType Type>
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ExtMove* generate_all(const Position& pos, ExtMove* moveList) {
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static_assert(Type != LEGAL, "Unsupported type in generate_all()");
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constexpr bool Checks = Type == QUIET_CHECKS; // Reduce template instantiations
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Bitboard target, piecesToMove = pos.pieces(Us);
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if(Type == QUIET_CHECKS)
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piecesToMove &= ~pos.blockers_for_king(~Us);
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switch (Type)
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{
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case CAPTURES:
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target = pos.pieces(~Us);
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break;
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case QUIETS:
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case QUIET_CHECKS:
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target = ~pos.pieces();
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break;
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case EVASIONS:
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target = between_bb(pos.square<KING>(Us), lsb(pos.checkers()));
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break;
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case NON_EVASIONS:
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target = ~pos.pieces(Us);
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break;
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}
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moveList = generate_pawn_moves<Us, Type>(pos, moveList, target);
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moveList = generate_moves<KNIGHT, Checks>(pos, moveList, piecesToMove, target);
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moveList = generate_moves<BISHOP, Checks>(pos, moveList, piecesToMove, target);
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moveList = generate_moves< ROOK, Checks>(pos, moveList, piecesToMove, target);
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moveList = generate_moves< QUEEN, Checks>(pos, moveList, piecesToMove, target);
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if (Type != QUIET_CHECKS && Type != EVASIONS)
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{
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Square ksq = pos.square<KING>(Us);
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Bitboard b = attacks_bb<KING>(ksq) & target;
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while (b)
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*moveList++ = make_move(ksq, pop_lsb(b));
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if ((Type != CAPTURES) && pos.can_castle(Us & ANY_CASTLING))
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for (CastlingRights cr : { Us & KING_SIDE, Us & QUEEN_SIDE } )
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if (!pos.castling_impeded(cr) && pos.can_castle(cr))
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*moveList++ = make<CASTLING>(ksq, pos.castling_rook_square(cr));
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}
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return moveList;
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}
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} // namespace
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/// <CAPTURES> Generates all pseudo-legal captures plus queen and checking knight promotions
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/// <QUIETS> Generates all pseudo-legal non-captures and underpromotions (except checking knight)
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/// <NON_EVASIONS> Generates all pseudo-legal captures and non-captures
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///
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/// Returns a pointer to the end of the move list.
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template<GenType Type>
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ExtMove* generate(const Position& pos, ExtMove* moveList) {
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static_assert(Type == CAPTURES || Type == QUIETS || Type == NON_EVASIONS, "Unsupported type in generate()");
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assert(!pos.checkers());
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Color us = pos.side_to_move();
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return us == WHITE ? generate_all<WHITE, Type>(pos, moveList)
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: generate_all<BLACK, Type>(pos, moveList);
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}
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// Explicit template instantiations
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template ExtMove* generate<CAPTURES>(const Position&, ExtMove*);
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template ExtMove* generate<QUIETS>(const Position&, ExtMove*);
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template ExtMove* generate<NON_EVASIONS>(const Position&, ExtMove*);
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/// generate<QUIET_CHECKS> generates all pseudo-legal non-captures giving check,
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/// except castling. Returns a pointer to the end of the move list.
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template<>
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ExtMove* generate<QUIET_CHECKS>(const Position& pos, ExtMove* moveList) {
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assert(!pos.checkers());
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Color us = pos.side_to_move();
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Bitboard dc = pos.blockers_for_king(~us) & pos.pieces(us) & ~pos.pieces(PAWN);
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while (dc)
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{
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Square from = pop_lsb(dc);
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PieceType pt = type_of(pos.piece_on(from));
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Bitboard b = attacks_bb(pt, from, pos.pieces()) & ~pos.pieces();
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if (pt == KING)
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b &= ~attacks_bb<QUEEN>(pos.square<KING>(~us));
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while (b)
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*moveList++ = make_move(from, pop_lsb(b));
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}
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return us == WHITE ? generate_all<WHITE, QUIET_CHECKS>(pos, moveList)
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: generate_all<BLACK, QUIET_CHECKS>(pos, moveList);
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}
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/// generate<EVASIONS> generates all pseudo-legal check evasions when the side
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/// to move is in check. Returns a pointer to the end of the move list.
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template<>
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ExtMove* generate<EVASIONS>(const Position& pos, ExtMove* moveList) {
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assert(pos.checkers());
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Color us = pos.side_to_move();
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Square ksq = pos.square<KING>(us);
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Bitboard sliderAttacks = 0;
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Bitboard sliders = pos.checkers() & ~pos.pieces(KNIGHT, PAWN);
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// Find all the squares attacked by slider checkers. We will remove them from
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// the king evasions in order to skip known illegal moves, which avoids any
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// useless legality checks later on.
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while (sliders)
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sliderAttacks |= line_bb(ksq, pop_lsb(sliders)) & ~pos.checkers();
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// Generate evasions for king, capture and non capture moves
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Bitboard b = attacks_bb<KING>(ksq) & ~pos.pieces(us) & ~sliderAttacks;
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while (b)
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*moveList++ = make_move(ksq, pop_lsb(b));
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if (more_than_one(pos.checkers()))
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return moveList; // Double check, only a king move can save the day
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// Generate blocking interpositions or captures of the checking piece
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return us == WHITE ? generate_all<WHITE, EVASIONS>(pos, moveList)
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: generate_all<BLACK, EVASIONS>(pos, moveList);
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}
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/// generate<LEGAL> generates all the legal moves in the given position
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template<>
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ExtMove* generate<LEGAL>(const Position& pos, ExtMove* moveList) {
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Color us = pos.side_to_move();
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Bitboard pinned = pos.blockers_for_king(us) & pos.pieces(us);
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Square ksq = pos.square<KING>(us);
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ExtMove* cur = moveList;
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moveList = pos.checkers() ? generate<EVASIONS >(pos, moveList)
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: generate<NON_EVASIONS>(pos, moveList);
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while (cur != moveList)
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if ( ((pinned && pinned & from_sq(*cur)) || from_sq(*cur) == ksq || type_of(*cur) == EN_PASSANT)
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&& !pos.legal(*cur))
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*cur = (--moveList)->move;
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else
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++cur;
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return moveList;
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}
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} // namespace Stockfish
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