/*
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) 2015-2019 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
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Stockfish is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <cassert>
#include "movegen.h"
#include "position.h"
namespace {
template<Color Us, CastlingSide Cs, bool Checks, bool Chess960>
ExtMove* generate_castling(const Position& pos, ExtMove* moveList) {
constexpr CastlingRight Cr = Us | Cs;
constexpr bool KingSide = (Cr == WHITE_OO || Cr == BLACK_OO);
if (pos.castling_impeded(Cr) || !pos.can_castle(Cr))
return moveList;
// After castling, the rook and king final positions are the same in Chess960
// as they would be in standard chess.
Square kfrom = pos.square<KING>(Us);
Square rfrom = pos.castling_rook_square(Cr);
Square kto = relative_square(Us, KingSide ? SQ_G1 : SQ_C1);
Bitboard enemies = pos.pieces(~Us);
assert(!pos.checkers());
const Direction step = Chess960 ? kto > kfrom ? WEST : EAST
: KingSide ? WEST : EAST;
for (Square s = kto; s != kfrom; s += step)
if (pos.attackers_to(s) & enemies)
return moveList;
// Because we generate only legal castling moves we need to verify that
// when moving the castling rook we do not discover some hidden checker.
// For instance an enemy queen in SQ_A1 when castling rook is in SQ_B1.
if (Chess960 && (attacks_bb<ROOK>(kto, pos.pieces() ^ rfrom) & pos.pieces(~Us, ROOK, QUEEN)))
return moveList;
Move m = make<CASTLING>(kfrom, rfrom);
if (Checks && !pos.gives_check(m))
return moveList;
*moveList++ = m;
return moveList;
}
template<GenType Type, Direction D>
ExtMove* make_promotions(ExtMove* moveList, Square to, Square ksq) {
if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
*moveList++ = make<PROMOTION>(to - D, to, QUEEN);
if (Type == QUIETS || Type == EVASIONS || Type == NON_EVASIONS)
{
*moveList++ = make<PROMOTION>(to - D, to, ROOK);
*moveList++ = make<PROMOTION>(to - D, to, BISHOP);
*moveList++ = make<PROMOTION>(to - D, to, KNIGHT);
}
// Knight promotion is the only promotion that can give a direct check
// that's not already included in the queen promotion.
if (Type == QUIET_CHECKS && (PseudoAttacks[KNIGHT][to] & ksq))
*moveList++ = make<PROMOTION>(to - D, to, KNIGHT);
else
(void)ksq; // Silence a warning under MSVC
return moveList;
}
template<Color Us, GenType Type>
ExtMove* generate_pawn_moves(const Position& pos, ExtMove* moveList, Bitboard target) {
// Compute our parametrized parameters at compile time, named according to
// the point of view of white side.
constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
constexpr Bitboard TRank8BB = (Us == WHITE ? Rank8BB : Rank1BB);
constexpr Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
constexpr Direction Up = (Us == WHITE ? NORTH : SOUTH);
constexpr Direction UpRight = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
constexpr Direction UpLeft = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
Bitboard emptySquares;
Bitboard pawnsOn7 = pos.pieces(Us, PAWN) & TRank7BB;
Bitboard pawnsNotOn7 = pos.pieces(Us, PAWN) & ~TRank7BB;
Bitboard enemies = (Type == EVASIONS ? pos.pieces(Them) & target:
Type == CAPTURES ? target : pos.pieces(Them));
// Single and double pawn pushes, no promotions
if (Type != CAPTURES)
{
emptySquares = (Type == QUIETS || Type == QUIET_CHECKS ? target : ~pos.pieces());
Bitboard b1 = shift<Up>(pawnsNotOn7) & emptySquares;
Bitboard b2 = shift<Up>(b1 & TRank3BB) & emptySquares;
if (Type == EVASIONS) // Consider only blocking squares
{
b1 &= target;
b2 &= target;
}
if (Type == QUIET_CHECKS)
{
Square ksq = pos.square<KING>(Them);
b1 &= pos.attacks_from<PAWN>(ksq, Them);
b2 &= pos.attacks_from<PAWN>(ksq, Them);
// Add pawn pushes which give discovered check. This is possible only
// if the pawn is not on the same file as the enemy king, because we
// don't generate captures. Note that a possible discovery check
// promotion has been already generated amongst the captures.
Bitboard dcCandidates = pos.blockers_for_king(Them);
if (pawnsNotOn7 & dcCandidates)
{
Bitboard dc1 = shift<Up>(pawnsNotOn7 & dcCandidates) & emptySquares & ~file_bb(ksq);
Bitboard dc2 = shift<Up>(dc1 & TRank3BB) & emptySquares;
b1 |= dc1;
b2 |= dc2;
}
}
while (b1)
{
Square to = pop_lsb(&b1);
*moveList++ = make_move(to - Up, to);
}
while (b2)
{
Square to = pop_lsb(&b2);
*moveList++ = make_move(to - Up - Up, to);
}
}
// Promotions and underpromotions
if (pawnsOn7 && (Type != EVASIONS || (target & TRank8BB)))
{
if (Type == CAPTURES)
emptySquares = ~pos.pieces();
if (Type == EVASIONS)
emptySquares &= target;
Bitboard b1 = shift<UpRight>(pawnsOn7) & enemies;
Bitboard b2 = shift<UpLeft >(pawnsOn7) & enemies;
Bitboard b3 = shift<Up >(pawnsOn7) & emptySquares;
Square ksq = pos.square<KING>(Them);
while (b1)
moveList = make_promotions<Type, UpRight>(moveList, pop_lsb(&b1), ksq);
while (b2)
moveList = make_promotions<Type, UpLeft >(moveList, pop_lsb(&b2), ksq);
while (b3)
moveList = make_promotions<Type, Up >(moveList, pop_lsb(&b3), ksq);
}
// Standard and en-passant captures
if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
{
Bitboard b1 = shift<UpRight>(pawnsNotOn7) & enemies;
Bitboard b2 = shift<UpLeft >(pawnsNotOn7) & enemies;
while (b1)
{
Square to = pop_lsb(&b1);
*moveList++ = make_move(to - UpRight, to);
}
while (b2)
{
Square to = pop_lsb(&b2);
*moveList++ = make_move(to - UpLeft, to);
}
if (pos.ep_square() != SQ_NONE)
{
assert(rank_of(pos.ep_square()) == relative_rank(Us, RANK_6));
// An en passant capture can be an evasion only if the checking piece
// is the double pushed pawn and so is in the target. Otherwise this
// is a discovery check and we are forced to do otherwise.
if (Type == EVASIONS && !(target & (pos.ep_square() - Up)))
return moveList;
b1 = pawnsNotOn7 & pos.attacks_from<PAWN>(pos.ep_square(), Them);
assert(b1);
while (b1)
*moveList++ = make<ENPASSANT>(pop_lsb(&b1), pos.ep_square());
}
}
return moveList;
}
template<PieceType Pt, bool Checks>
ExtMove* generate_moves(const Position& pos, ExtMove* moveList, Color us,
Bitboard target) {
assert(Pt != KING && Pt != PAWN);
const Square* pl = pos.squares<Pt>(us);
for (Square from = *pl; from != SQ_NONE; from = *++pl)
{
if (Checks)
{
if ( (Pt == BISHOP || Pt == ROOK || Pt == QUEEN)
&& !(PseudoAttacks[Pt][from] & target & pos.check_squares(Pt)))
continue;
if (pos.blockers_for_king(~us) & from)
continue;
}
Bitboard b = pos.attacks_from<Pt>(from) & target;
if (Checks)
b &= pos.check_squares(Pt);
while (b)
*moveList++ = make_move(from, pop_lsb(&b));
}
return moveList;
}
template<Color Us, GenType Type>
ExtMove* generate_all(const Position& pos, ExtMove* moveList, Bitboard target) {
constexpr bool Checks = Type == QUIET_CHECKS;
moveList = generate_pawn_moves<Us, Type>(pos, moveList, target);
moveList = generate_moves<KNIGHT, Checks>(pos, moveList, Us, target);
moveList = generate_moves<BISHOP, Checks>(pos, moveList, Us, target);
moveList = generate_moves< ROOK, Checks>(pos, moveList, Us, target);
moveList = generate_moves< QUEEN, Checks>(pos, moveList, Us, target);
if (Type != QUIET_CHECKS && Type != EVASIONS)
{
Square ksq = pos.square<KING>(Us);
Bitboard b = pos.attacks_from<KING>(ksq) & target;
while (b)
*moveList++ = make_move(ksq, pop_lsb(&b));
}
if (Type != CAPTURES && Type != EVASIONS && pos.can_castle(Us))
{
if (pos.is_chess960())
{
moveList = generate_castling<Us, KING_SIDE, Checks, true>(pos, moveList);
moveList = generate_castling<Us, QUEEN_SIDE, Checks, true>(pos, moveList);
}
else
{
moveList = generate_castling<Us, KING_SIDE, Checks, false>(pos, moveList);
moveList = generate_castling<Us, QUEEN_SIDE, Checks, false>(pos, moveList);
}
}
return moveList;
}
} // namespace
/// generate<CAPTURES> generates all pseudo-legal captures and queen
/// promotions. Returns a pointer to the end of the move list.
///
/// generate<QUIETS> generates all pseudo-legal non-captures and
/// underpromotions. Returns a pointer to the end of the move list.
///
/// generate<NON_EVASIONS> generates all pseudo-legal captures and
/// non-captures. Returns a pointer to the end of the move list.
template<GenType Type>
ExtMove* generate(const Position& pos, ExtMove* moveList) {
assert(Type == CAPTURES || Type == QUIETS || Type == NON_EVASIONS);
assert(!pos.checkers());
Color us = pos.side_to_move();
Bitboard target = Type == CAPTURES ? pos.pieces(~us)
: Type == QUIETS ? ~pos.pieces()
: Type == NON_EVASIONS ? ~pos.pieces(us) : 0;
return us == WHITE ? generate_all<WHITE, Type>(pos, moveList, target)
: generate_all<BLACK, Type>(pos, moveList, target);
}
// Explicit template instantiations
template ExtMove* generate<CAPTURES>(const Position&, ExtMove*);
template ExtMove* generate<QUIETS>(const Position&, ExtMove*);
template ExtMove* generate<NON_EVASIONS>(const Position&, ExtMove*);
/// generate<QUIET_CHECKS> generates all pseudo-legal non-captures and knight
/// underpromotions that give check. Returns a pointer to the end of the move list.
template<>
ExtMove* generate<QUIET_CHECKS>(const Position& pos, ExtMove* moveList) {
assert(!pos.checkers());
Color us = pos.side_to_move();
Bitboard dc = pos.blockers_for_king(~us) & pos.pieces(us);
while (dc)
{
Square from = pop_lsb(&dc);
PieceType pt = type_of(pos.piece_on(from));
if (pt == PAWN)
continue; // Will be generated together with direct checks
Bitboard b = pos.attacks_from(pt, from) & ~pos.pieces();
if (pt == KING)
b &= ~PseudoAttacks[QUEEN][pos.square<KING>(~us)];
while (b)
*moveList++ = make_move(from, pop_lsb(&b));
}
return us == WHITE ? generate_all<WHITE, QUIET_CHECKS>(pos, moveList, ~pos.pieces())
: generate_all<BLACK, QUIET_CHECKS>(pos, moveList, ~pos.pieces());
}
/// generate<EVASIONS> generates all pseudo-legal check evasions when the side
/// to move is in check. Returns a pointer to the end of the move list.
template<>
ExtMove* generate<EVASIONS>(const Position& pos, ExtMove* moveList) {
assert(pos.checkers());
Color us = pos.side_to_move();
Square ksq = pos.square<KING>(us);
Bitboard sliderAttacks = 0;
Bitboard sliders = pos.checkers() & ~pos.pieces(KNIGHT, PAWN);
// Find all the squares attacked by slider checkers. We will remove them from
// the king evasions in order to skip known illegal moves, which avoids any
// useless legality checks later on.
while (sliders)
{
Square checksq = pop_lsb(&sliders);
sliderAttacks |= LineBB[checksq][ksq] ^ checksq;
}
// Generate evasions for king, capture and non capture moves
Bitboard b = pos.attacks_from<KING>(ksq) & ~pos.pieces(us) & ~sliderAttacks;
while (b)
*moveList++ = make_move(ksq, pop_lsb(&b));
if (more_than_one(pos.checkers()))
return moveList; // Double check, only a king move can save the day
// Generate blocking evasions or captures of the checking piece
Square checksq = lsb(pos.checkers());
Bitboard target = between_bb(checksq, ksq) | checksq;
return us == WHITE ? generate_all<WHITE, EVASIONS>(pos, moveList, target)
: generate_all<BLACK, EVASIONS>(pos, moveList, target);
}
/// generate<LEGAL> generates all the legal moves in the given position
template<>
ExtMove* generate<LEGAL>(const Position& pos, ExtMove* moveList) {
Color us = pos.side_to_move();
Bitboard pinned = pos.blockers_for_king(us) & pos.pieces(us);
Square ksq = pos.square<KING>(us);
ExtMove* cur = moveList;
moveList = pos.checkers() ? generate<EVASIONS >(pos, moveList)
: generate<NON_EVASIONS>(pos, moveList);
while (cur != moveList)
if ( (pinned || from_sq(*cur) == ksq || type_of(*cur) == ENPASSANT)
&& !pos.legal(*cur))
*cur = (--moveList)->move;
else
++cur;
return moveList;
}