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movegen.cpp
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movegen.cpp
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/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, 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"
/// Simple macro to wrap a very common while loop, no facny, no flexibility,
/// hardcoded names 'mlist' and 'from'.
#define SERIALIZE(b) while (b) (*mlist++).move = make_move(from, pop_lsb(&b))
/// Version used for pawns, where the 'from' square is given as a delta from the 'to' square
#define SERIALIZE_PAWNS(b, d) while (b) { Square to = pop_lsb(&b); \
(*mlist++).move = make_move(to - (d), to); }
namespace {
template<CastlingSide Side, bool Checks, bool Chess960>
MoveStack* generate_castle(const Position& pos, MoveStack* mlist, Color us) {
if (pos.castle_impeded(us, Side) || !pos.can_castle(make_castle_right(us, Side)))
return mlist;
// After castling, the rook and king final positions are the same in Chess960
// as they would be in standard chess.
Square kfrom = pos.king_square(us);
Square rfrom = pos.castle_rook_square(us, Side);
Square kto = relative_square(us, Side == KING_SIDE ? SQ_G1 : SQ_C1);
Bitboard enemies = pos.pieces(~us);
assert(!pos.checkers());
const int K = Chess960 ? kto > kfrom ? -1 : 1
: Side == KING_SIDE ? -1 : 1;
for (Square s = kto; s != kfrom; s += (Square)K)
if (pos.attackers_to(s) & enemies)
return mlist;
// 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 && (pos.attackers_to(kto, pos.pieces() ^ rfrom) & enemies))
return mlist;
(*mlist++).move = make<CASTLE>(kfrom, rfrom);
if (Checks && !pos.move_gives_check((mlist - 1)->move, CheckInfo(pos)))
mlist--;
return mlist;
}
template<Square Delta>
inline Bitboard move_pawns(Bitboard p) {
return Delta == DELTA_N ? p << 8
: Delta == DELTA_S ? p >> 8
: Delta == DELTA_NE ? (p & ~FileHBB) << 9
: Delta == DELTA_SE ? (p & ~FileHBB) >> 7
: Delta == DELTA_NW ? (p & ~FileABB) << 7
: Delta == DELTA_SW ? (p & ~FileABB) >> 9 : 0;
}
template<GenType Type, Square Delta>
inline MoveStack* generate_promotions(MoveStack* mlist, Bitboard pawnsOn7,
Bitboard target, const CheckInfo* ci) {
Bitboard b = move_pawns<Delta>(pawnsOn7) & target;
while (b)
{
Square to = pop_lsb(&b);
if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
(*mlist++).move = make<PROMOTION>(to - Delta, to, QUEEN);
if (Type == QUIETS || Type == EVASIONS || Type == NON_EVASIONS)
{
(*mlist++).move = make<PROMOTION>(to - Delta, to, ROOK);
(*mlist++).move = make<PROMOTION>(to - Delta, to, BISHOP);
(*mlist++).move = make<PROMOTION>(to - Delta, to, KNIGHT);
}
// Knight-promotion is the only one that can give a direct check not
// already included in the queen-promotion.
if (Type == QUIET_CHECKS && (StepAttacksBB[W_KNIGHT][to] & ci->ksq))
(*mlist++).move = make<PROMOTION>(to - Delta, to, KNIGHT);
else
(void)ci; // Silence a warning under MSVC
}
return mlist;
}
template<Color Us, GenType Type>
MoveStack* generate_pawn_moves(const Position& pos, MoveStack* mlist,
Bitboard target, const CheckInfo* ci) {
// Compute our parametrized parameters at compile time, named according to
// the point of view of white side.
const Color Them = (Us == WHITE ? BLACK : WHITE);
const Bitboard TRank8BB = (Us == WHITE ? Rank8BB : Rank1BB);
const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
const Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
const Square UP = (Us == WHITE ? DELTA_N : DELTA_S);
const Square RIGHT = (Us == WHITE ? DELTA_NE : DELTA_SW);
const Square LEFT = (Us == WHITE ? DELTA_NW : DELTA_SE);
Bitboard b1, b2, dc1, dc2, 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());
b1 = move_pawns<UP>(pawnsNotOn7) & emptySquares;
b2 = move_pawns<UP>(b1 & TRank3BB) & emptySquares;
if (Type == EVASIONS) // Consider only blocking squares
{
b1 &= target;
b2 &= target;
}
if (Type == QUIET_CHECKS)
{
b1 &= pos.attacks_from<PAWN>(ci->ksq, Them);
b2 &= pos.attacks_from<PAWN>(ci->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 among captures.
if (pawnsNotOn7 & ci->dcCandidates)
{
dc1 = move_pawns<UP>(pawnsNotOn7 & ci->dcCandidates) & emptySquares & ~file_bb(ci->ksq);
dc2 = move_pawns<UP>(dc1 & TRank3BB) & emptySquares;
b1 |= dc1;
b2 |= dc2;
}
}
SERIALIZE_PAWNS(b1, UP);
SERIALIZE_PAWNS(b2, UP + UP);
}
// Promotions and underpromotions
if (pawnsOn7 && (Type != EVASIONS || (target & TRank8BB)))
{
if (Type == CAPTURES)
emptySquares = ~pos.pieces();
if (Type == EVASIONS)
emptySquares &= target;
mlist = generate_promotions<Type, RIGHT>(mlist, pawnsOn7, enemies, ci);
mlist = generate_promotions<Type, LEFT>(mlist, pawnsOn7, enemies, ci);
mlist = generate_promotions<Type, UP>(mlist, pawnsOn7, emptySquares, ci);
}
// Standard and en-passant captures
if (Type == CAPTURES || Type == EVASIONS || Type == NON_EVASIONS)
{
b1 = move_pawns<RIGHT>(pawnsNotOn7) & enemies;
b2 = move_pawns<LEFT >(pawnsNotOn7) & enemies;
SERIALIZE_PAWNS(b1, RIGHT);
SERIALIZE_PAWNS(b2, LEFT);
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 mlist;
b1 = pawnsNotOn7 & pos.attacks_from<PAWN>(pos.ep_square(), Them);
assert(b1);
while (b1)
(*mlist++).move = make<ENPASSANT>(pop_lsb(&b1), pos.ep_square());
}
}
return mlist;
}
template<PieceType Pt, bool Checks> FORCE_INLINE
MoveStack* generate_moves(const Position& pos, MoveStack* mlist, Color us,
Bitboard target, const CheckInfo* ci) {
assert(Pt != KING && Pt != PAWN);
const Square* pl = pos.piece_list(us, Pt);
for (Square from = *pl; from != SQ_NONE; from = *++pl)
{
if (Checks)
{
if ( (Pt == BISHOP || Pt == ROOK || Pt == QUEEN)
&& !(PseudoAttacks[Pt][from] & target & ci->checkSq[Pt]))
continue;
if (ci->dcCandidates && (ci->dcCandidates & from))
continue;
}
Bitboard b = pos.attacks_from<Pt>(from) & target;
if (Checks)
b &= ci->checkSq[Pt];
SERIALIZE(b);
}
return mlist;
}
template<GenType Type> FORCE_INLINE
MoveStack* generate_all(const Position& pos, MoveStack* mlist, Color us,
Bitboard target, const CheckInfo* ci = NULL) {
const bool Checks = Type == QUIET_CHECKS;
mlist = (us == WHITE ? generate_pawn_moves<WHITE, Type>(pos, mlist, target, ci)
: generate_pawn_moves<BLACK, Type>(pos, mlist, target, ci));
mlist = generate_moves<KNIGHT, Checks>(pos, mlist, us, target, ci);
mlist = generate_moves<BISHOP, Checks>(pos, mlist, us, target, ci);
mlist = generate_moves<ROOK, Checks>(pos, mlist, us, target, ci);
mlist = generate_moves<QUEEN, Checks>(pos, mlist, us, target, ci);
if (Type != QUIET_CHECKS && Type != EVASIONS)
{
Square from = pos.king_square(us);
Bitboard b = pos.attacks_from<KING>(from) & target;
SERIALIZE(b);
}
if (Type != CAPTURES && Type != EVASIONS && pos.can_castle(us))
{
if (pos.is_chess960())
{
mlist = generate_castle<KING_SIDE, Checks, true>(pos, mlist, us);
mlist = generate_castle<QUEEN_SIDE, Checks, true>(pos, mlist, us);
}
else
{
mlist = generate_castle<KING_SIDE, Checks, false>(pos, mlist, us);
mlist = generate_castle<QUEEN_SIDE, Checks, false>(pos, mlist, us);
}
}
return mlist;
}
} // 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>
MoveStack* generate(const Position& pos, MoveStack* mlist) {
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 generate_all<Type>(pos, mlist, us, target);
}
// Explicit template instantiations
template MoveStack* generate<CAPTURES>(const Position&, MoveStack*);
template MoveStack* generate<QUIETS>(const Position&, MoveStack*);
template MoveStack* generate<NON_EVASIONS>(const Position&, MoveStack*);
/// 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<>
MoveStack* generate<QUIET_CHECKS>(const Position& pos, MoveStack* mlist) {
assert(!pos.checkers());
CheckInfo ci(pos);
Bitboard dc = ci.dcCandidates;
while (dc)
{
Square from = pop_lsb(&dc);
PieceType pt = type_of(pos.piece_on(from));
if (pt == PAWN)
continue; // Will be generated togheter with direct checks
Bitboard b = pos.attacks_from(Piece(pt), from) & ~pos.pieces();
if (pt == KING)
b &= ~PseudoAttacks[QUEEN][ci.ksq];
SERIALIZE(b);
}
return generate_all<QUIET_CHECKS>(pos, mlist, pos.side_to_move(), ~pos.pieces(), &ci);
}
/// 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<>
MoveStack* generate<EVASIONS>(const Position& pos, MoveStack* mlist) {
assert(pos.checkers());
Square from, checksq;
int checkersCnt = 0;
Color us = pos.side_to_move();
Square ksq = pos.king_square(us);
Bitboard sliderAttacks = 0;
Bitboard b = pos.checkers();
assert(pos.checkers());
// Find squares attacked by slider checkers, we will remove them from the king
// evasions so to skip known illegal moves avoiding useless legality check later.
do
{
checkersCnt++;
checksq = pop_lsb(&b);
assert(color_of(pos.piece_on(checksq)) == ~us);
switch (type_of(pos.piece_on(checksq)))
{
case BISHOP: sliderAttacks |= PseudoAttacks[BISHOP][checksq]; break;
case ROOK: sliderAttacks |= PseudoAttacks[ROOK][checksq]; break;
case QUEEN:
// If queen and king are far or not on a diagonal line we can safely
// remove all the squares attacked in the other direction becuase are
// not reachable by the king anyway.
if (between_bb(ksq, checksq) || !(PseudoAttacks[BISHOP][checksq] & ksq))
sliderAttacks |= PseudoAttacks[QUEEN][checksq];
// Otherwise we need to use real rook attacks to check if king is safe
// to move in the other direction. For example: king in B2, queen in A1
// a knight in B1, and we can safely move to C1.
else
sliderAttacks |= PseudoAttacks[BISHOP][checksq] | pos.attacks_from<ROOK>(checksq);
default:
break;
}
} while (b);
// Generate evasions for king, capture and non capture moves
b = pos.attacks_from<KING>(ksq) & ~pos.pieces(us) & ~sliderAttacks;
from = ksq;
SERIALIZE(b);
if (checkersCnt > 1)
return mlist; // Double check, only a king move can save the day
// Generate blocking evasions or captures of the checking piece
Bitboard target = between_bb(checksq, ksq) | pos.checkers();
return generate_all<EVASIONS>(pos, mlist, us, target);
}
/// generate<LEGAL> generates all the legal moves in the given position
template<>
MoveStack* generate<LEGAL>(const Position& pos, MoveStack* mlist) {
MoveStack *end, *cur = mlist;
Bitboard pinned = pos.pinned_pieces();
Square ksq = pos.king_square(pos.side_to_move());
end = pos.checkers() ? generate<EVASIONS>(pos, mlist)
: generate<NON_EVASIONS>(pos, mlist);
while (cur != end)
if ( (pinned || from_sq(cur->move) == ksq || type_of(cur->move) == ENPASSANT)
&& !pos.pl_move_is_legal(cur->move, pinned))
cur->move = (--end)->move;
else
cur++;
return end;
}