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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) 2004-2024 The Stockfish developers (see AUTHORS file)
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 "movegen.h"
#include <cassert>
#include <initializer_list>
#include "bitboard.h"
#include "position.h"
namespace Stockfish {
namespace {
template<GenType Type, Direction D, bool Enemy>
ExtMove* make_promotions(ExtMove* moveList, [[maybe_unused]] Square to) {
constexpr bool all = Type == EVASIONS || Type == NON_EVASIONS;
if constexpr (Type == CAPTURES || all)
*moveList++ = Move::make<PROMOTION>(to - D, to, QUEEN);
if constexpr ((Type == CAPTURES && Enemy) || (Type == QUIETS && !Enemy) || all)
{
*moveList++ = Move::make<PROMOTION>(to - D, to, ROOK);
*moveList++ = Move::make<PROMOTION>(to - D, to, BISHOP);
*moveList++ = Move::make<PROMOTION>(to - D, to, KNIGHT);
}
return moveList;
}
template<Color Us, GenType Type>
ExtMove* generate_pawn_moves(const Position& pos, ExtMove* moveList, Bitboard target) {
constexpr Color Them = ~Us;
constexpr Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
constexpr Bitboard TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
constexpr Direction Up = pawn_push(Us);
constexpr Direction UpRight = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);
constexpr Direction UpLeft = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);
const Bitboard emptySquares = ~pos.pieces();
const Bitboard enemies = Type == EVASIONS ? pos.checkers() : pos.pieces(Them);
Bitboard pawnsOn7 = pos.pieces(Us, PAWN) & TRank7BB;
Bitboard pawnsNotOn7 = pos.pieces(Us, PAWN) & ~TRank7BB;
// Single and double pawn pushes, no promotions
if constexpr (Type != CAPTURES)
{
Bitboard b1 = shift<Up>(pawnsNotOn7) & emptySquares;
Bitboard b2 = shift<Up>(b1 & TRank3BB) & emptySquares;
if constexpr (Type == EVASIONS) // Consider only blocking squares
{
b1 &= target;
b2 &= target;
}
if constexpr (Type == QUIET_CHECKS)
{
// To make a quiet check, you either make a direct check by pushing a pawn
// or push a blocker pawn that is not on the same file as the enemy king.
// Discovered check promotion has been already generated amongst the captures.
Square ksq = pos.square<KING>(Them);
Bitboard dcCandidatePawns = pos.blockers_for_king(Them) & ~file_bb(ksq);
b1 &= pawn_attacks_bb(Them, ksq) | shift<Up>(dcCandidatePawns);
b2 &= pawn_attacks_bb(Them, ksq) | shift<Up + Up>(dcCandidatePawns);
}
while (b1)
{
Square to = pop_lsb(b1);
*moveList++ = Move(to - Up, to);
}
while (b2)
{
Square to = pop_lsb(b2);
*moveList++ = Move(to - Up - Up, to);
}
}
// Promotions and underpromotions
if (pawnsOn7)
{
Bitboard b1 = shift<UpRight>(pawnsOn7) & enemies;
Bitboard b2 = shift<UpLeft>(pawnsOn7) & enemies;
Bitboard b3 = shift<Up>(pawnsOn7) & emptySquares;
if constexpr (Type == EVASIONS)
b3 &= target;
while (b1)
moveList = make_promotions<Type, UpRight, true>(moveList, pop_lsb(b1));
while (b2)
moveList = make_promotions<Type, UpLeft, true>(moveList, pop_lsb(b2));
while (b3)
moveList = make_promotions<Type, Up, false>(moveList, pop_lsb(b3));
}
// Standard and en passant captures
if constexpr (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++ = Move(to - UpRight, to);
}
while (b2)
{
Square to = pop_lsb(b2);
*moveList++ = 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 cannot resolve a discovered check
if (Type == EVASIONS && (target & (pos.ep_square() + Up)))
return moveList;
b1 = pawnsNotOn7 & pawn_attacks_bb(Them, pos.ep_square());
assert(b1);
while (b1)
*moveList++ = Move::make<EN_PASSANT>(pop_lsb(b1), pos.ep_square());
}
}
return moveList;
}
template<Color Us, PieceType Pt, bool Checks>
ExtMove* generate_moves(const Position& pos, ExtMove* moveList, Bitboard target) {
static_assert(Pt != KING && Pt != PAWN, "Unsupported piece type in generate_moves()");
Bitboard bb = pos.pieces(Us, Pt);
while (bb)
{
Square from = pop_lsb(bb);
Bitboard b = attacks_bb<Pt>(from, pos.pieces()) & target;
// To check, you either move freely a blocker or make a direct check.
if (Checks && (Pt == QUEEN || !(pos.blockers_for_king(~Us) & from)))
b &= pos.check_squares(Pt);
while (b)
*moveList++ = Move(from, pop_lsb(b));
}
return moveList;
}
template<Color Us, GenType Type>
ExtMove* generate_all(const Position& pos, ExtMove* moveList) {
static_assert(Type != LEGAL, "Unsupported type in generate_all()");
constexpr bool Checks = Type == QUIET_CHECKS; // Reduce template instantiations
const Square ksq = pos.square<KING>(Us);
Bitboard target;
// Skip generating non-king moves when in double check
if (Type != EVASIONS || !more_than_one(pos.checkers()))
{
target = Type == EVASIONS ? between_bb(ksq, lsb(pos.checkers()))
: Type == NON_EVASIONS ? ~pos.pieces(Us)
: Type == CAPTURES ? pos.pieces(~Us)
: ~pos.pieces(); // QUIETS || QUIET_CHECKS
moveList = generate_pawn_moves<Us, Type>(pos, moveList, target);
moveList = generate_moves<Us, KNIGHT, Checks>(pos, moveList, target);
moveList = generate_moves<Us, BISHOP, Checks>(pos, moveList, target);
moveList = generate_moves<Us, ROOK, Checks>(pos, moveList, target);
moveList = generate_moves<Us, QUEEN, Checks>(pos, moveList, target);
}
if (!Checks || pos.blockers_for_king(~Us) & ksq)
{
Bitboard b = attacks_bb<KING>(ksq) & (Type == EVASIONS ? ~pos.pieces(Us) : target);
if (Checks)
b &= ~attacks_bb<QUEEN>(pos.square<KING>(~Us));
while (b)
*moveList++ = Move(ksq, pop_lsb(b));
if ((Type == QUIETS || Type == NON_EVASIONS) && pos.can_castle(Us & ANY_CASTLING))
for (CastlingRights cr : {Us & KING_SIDE, Us & QUEEN_SIDE})
if (!pos.castling_impeded(cr) && pos.can_castle(cr))
*moveList++ = Move::make<CASTLING>(ksq, pos.castling_rook_square(cr));
}
return moveList;
}
} // namespace
// <CAPTURES> Generates all pseudo-legal captures plus queen promotions
// <QUIETS> Generates all pseudo-legal non-captures and underpromotions
// <EVASIONS> Generates all pseudo-legal check evasions
// <NON_EVASIONS> Generates all pseudo-legal captures and non-captures
// <QUIET_CHECKS> Generates all pseudo-legal non-captures giving check,
// except castling and promotions
//
// Returns a pointer to the end of the move list.
template<GenType Type>
ExtMove* generate(const Position& pos, ExtMove* moveList) {
static_assert(Type != LEGAL, "Unsupported type in generate()");
assert((Type == EVASIONS) == bool(pos.checkers()));
Color us = pos.side_to_move();
return us == WHITE ? generate_all<WHITE, Type>(pos, moveList)
: generate_all<BLACK, Type>(pos, moveList);
}
// Explicit template instantiations
template ExtMove* generate<CAPTURES>(const Position&, ExtMove*);
template ExtMove* generate<QUIETS>(const Position&, ExtMove*);
template ExtMove* generate<EVASIONS>(const Position&, ExtMove*);
template ExtMove* generate<QUIET_CHECKS>(const Position&, ExtMove*);
template ExtMove* generate<NON_EVASIONS>(const Position&, ExtMove*);
// 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 & cur->from_sq()) || cur->from_sq() == ksq || cur->type_of() == EN_PASSANT)
&& !pos.legal(*cur))
*cur = *(--moveList);
else
++cur;
return moveList;
}
} // namespace Stockfish