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stockfish/src/position.cpp

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/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2021 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 <algorithm>
#include <cassert>
#include <cstddef> // For offsetof()
#include <cstring> // For std::memset, std::memcmp
#include <iomanip>
#include <sstream>
#include "bitboard.h"
#include "misc.h"
#include "movegen.h"
#include "position.h"
#include "thread.h"
#include "tt.h"
#include "uci.h"
#include "syzygy/tbprobe.h"
using std::string;
namespace Stockfish {
namespace Zobrist {
Key psq[PIECE_NB][SQUARE_NB];
Key enpassant[FILE_NB];
Key castling[CASTLING_RIGHT_NB];
Key side, noPawns;
}
namespace {
const string PieceToChar(" PNBRQK pnbrqk");
constexpr Piece Pieces[] = { W_PAWN, W_KNIGHT, W_BISHOP, W_ROOK, W_QUEEN, W_KING,
B_PAWN, B_KNIGHT, B_BISHOP, B_ROOK, B_QUEEN, B_KING };
} // namespace
/// operator<<(Position) returns an ASCII representation of the position
std::ostream& operator<<(std::ostream& os, const Position& pos) {
os << "\n +---+---+---+---+---+---+---+---+\n";
for (Rank r = RANK_8; r >= RANK_1; --r)
{
for (File f = FILE_A; f <= FILE_H; ++f)
os << " | " << PieceToChar[pos.piece_on(make_square(f, r))];
os << " | " << (1 + r) << "\n +---+---+---+---+---+---+---+---+\n";
}
os << " a b c d e f g h\n"
<< "\nFen: " << pos.fen() << "\nKey: " << std::hex << std::uppercase
<< 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;
ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize);
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;
}
// Marcel van Kervinck's cuckoo algorithm for fast detection of "upcoming repetition"
// situations. Description of the algorithm in the following paper:
// https://marcelk.net/2013-04-06/paper/upcoming-rep-v2.pdf
// First and second hash functions for indexing the cuckoo tables
inline int H1(Key h) { return h & 0x1fff; }
inline int H2(Key h) { return (h >> 16) & 0x1fff; }
// Cuckoo tables with Zobrist hashes of valid reversible moves, and the moves themselves
Key cuckoo[8192];
Move cuckooMove[8192];
/// Position::init() initializes at startup the various arrays used to compute hash keys
void Position::init() {
PRNG rng(1070372);
for (Piece pc : Pieces)
for (Square s = SQ_A1; s <= SQ_H8; ++s)
Zobrist::psq[pc][s] = rng.rand<Key>();
for (File f = FILE_A; f <= FILE_H; ++f)
Zobrist::enpassant[f] = rng.rand<Key>();
for (int cr = NO_CASTLING; cr <= ANY_CASTLING; ++cr)
Zobrist::castling[cr] = rng.rand<Key>();
Zobrist::side = rng.rand<Key>();
Zobrist::noPawns = rng.rand<Key>();
// Prepare the cuckoo tables
std::memset(cuckoo, 0, sizeof(cuckoo));
std::memset(cuckooMove, 0, sizeof(cuckooMove));
int count = 0;
for (Piece pc : Pieces)
for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
for (Square s2 = Square(s1 + 1); s2 <= SQ_H8; ++s2)
if ((type_of(pc) != PAWN) && (attacks_bb(type_of(pc), s1, 0) & s2))
{
Move move = make_move(s1, s2);
Key key = Zobrist::psq[pc][s1] ^ Zobrist::psq[pc][s2] ^ Zobrist::side;
int i = H1(key);
while (true)
{
std::swap(cuckoo[i], key);
std::swap(cuckooMove[i], move);
if (move == MOVE_NONE) // Arrived at empty slot?
break;
i = (i == H1(key)) ? H2(key) : H1(key); // Push victim to alternative slot
}
count++;
}
assert(count == 3668);
}
/// Position::set() initializes the position object with the given FEN string.
/// This function is not very robust - make sure that input FENs are correct,
/// this is assumed to be the responsibility of the GUI.
Position& Position::set(const string& fenStr, bool isChess960, StateInfo* si, Thread* th) {
/*
A FEN string defines a particular position using only the ASCII character set.
A FEN string contains six fields separated by a space. The fields are:
1) Piece placement (from white's perspective). Each rank is described, starting
with rank 8 and ending with rank 1. Within each rank, the contents of each
square are described from file A through file H. Following the Standard
Algebraic Notation (SAN), each piece is identified by a single letter taken
from the standard English names. White pieces are designated using upper-case
letters ("PNBRQK") whilst Black uses lowercase ("pnbrqk"). Blank squares are
noted using digits 1 through 8 (the number of blank squares), and "/"
separates ranks.
2) Active color. "w" means white moves next, "b" means black.
3) Castling availability. If neither side can castle, this is "-". Otherwise,
this has one or more letters: "K" (White can castle kingside), "Q" (White
can castle queenside), "k" (Black can castle kingside), and/or "q" (Black
can castle queenside).
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. Following X-FEN standard, 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
fifty-move rule.
6) Fullmove number. The number of the full move. It starts at 1, and is
incremented after Black's move.
*/
unsigned char col, row, token;
size_t idx;
Square sq = SQ_A8;
std::istringstream ss(fenStr);
std::memset(this, 0, sizeof(Position));
std::memset(si, 0, sizeof(StateInfo));
st = si;
ss >> std::noskipws;
// 1. Piece placement
while ((ss >> token) && !isspace(token))
{
if (isdigit(token))
sq += (token - '0') * EAST; // Advance the given number of files
else if (token == '/')
sq += 2 * SOUTH;
else if ((idx = PieceToChar.find(token)) != string::npos) {
put_piece(Piece(idx), sq);
++sq;
}
}
// 2. Active color
ss >> token;
sideToMove = (token == 'w' ? WHITE : BLACK);
ss >> token;
// 3. Castling availability. Compatible with 3 standards: Normal FEN standard,
// Shredder-FEN that uses the letters of the columns on which the rooks began
// the game instead of KQkq and also X-FEN standard that, in case of Chess960,
// if an inner rook is associated with the castling right, the castling tag is
// replaced by the file letter of the involved rook, as for the Shredder-FEN.
while ((ss >> token) && !isspace(token))
{
Square rsq;
Color c = islower(token) ? BLACK : WHITE;
Piece rook = make_piece(c, ROOK);
token = char(toupper(token));
if (token == 'K')
for (rsq = relative_square(c, SQ_H1); piece_on(rsq) != rook; --rsq) {}
else if (token == 'Q')
for (rsq = relative_square(c, SQ_A1); piece_on(rsq) != rook; ++rsq) {}
else if (token >= 'A' && token <= 'H')
rsq = make_square(File(token - 'A'), relative_rank(c, RANK_1));
else
continue;
set_castling_right(c, rsq);
}
// 4. En passant square.
// Ignore if square is invalid or not on side to move relative rank 6.
bool enpassant = false;
if ( ((ss >> col) && (col >= 'a' && col <= 'h'))
&& ((ss >> row) && (row == (sideToMove == WHITE ? '6' : '3'))))
{
st->epSquare = make_square(File(col - 'a'), Rank(row - '1'));
// En passant square will be considered only if
// a) side to move have a pawn threatening epSquare
// b) there is an enemy pawn in front of epSquare
// c) there is no piece on epSquare or behind epSquare
enpassant = pawn_attacks_bb(~sideToMove, st->epSquare) & pieces(sideToMove, PAWN)
&& (pieces(~sideToMove, PAWN) & (st->epSquare + pawn_push(~sideToMove)))
&& !(pieces() & (st->epSquare | (st->epSquare + pawn_push(sideToMove))));
}
if (!enpassant)
st->epSquare = SQ_NONE;
// 5-6. Halfmove clock and fullmove number
ss >> std::skipws >> st->rule50 >> gamePly;
// Convert from fullmove starting from 1 to gamePly starting from 0,
// handle also common incorrect FEN with fullmove = 0.
gamePly = std::max(2 * (gamePly - 1), 0) + (sideToMove == BLACK);
chess960 = isChess960;
thisThread = th;
set_state(st);
assert(pos_is_ok());
return *this;
}
/// Position::set_castling_right() is a helper function used to set castling
/// rights given the corresponding color and the rook starting square.
void Position::set_castling_right(Color c, Square rfrom) {
Square kfrom = square<KING>(c);
CastlingRights cr = c & (kfrom < rfrom ? KING_SIDE: QUEEN_SIDE);
st->castlingRights |= cr;
castlingRightsMask[kfrom] |= cr;
castlingRightsMask[rfrom] |= cr;
castlingRookSquare[cr] = rfrom;
Square kto = relative_square(c, cr & KING_SIDE ? SQ_G1 : SQ_C1);
Square rto = relative_square(c, cr & KING_SIDE ? SQ_F1 : SQ_D1);
castlingPath[cr] = (between_bb(rfrom, rto) | between_bb(kfrom, kto))
& ~(kfrom | rfrom);
}
/// Position::set_check_info() sets king attacks to detect if a move gives check
void Position::set_check_info(StateInfo* si) const {
si->blockersForKing[WHITE] = slider_blockers(pieces(BLACK), square<KING>(WHITE), si->pinners[BLACK]);
si->blockersForKing[BLACK] = slider_blockers(pieces(WHITE), square<KING>(BLACK), si->pinners[WHITE]);
Square ksq = square<KING>(~sideToMove);
si->checkSquares[PAWN] = pawn_attacks_bb(~sideToMove, ksq);
si->checkSquares[KNIGHT] = attacks_bb<KNIGHT>(ksq);
si->checkSquares[BISHOP] = attacks_bb<BISHOP>(ksq, pieces());
si->checkSquares[ROOK] = attacks_bb<ROOK>(ksq, pieces());
si->checkSquares[QUEEN] = si->checkSquares[BISHOP] | si->checkSquares[ROOK];
si->checkSquares[KING] = 0;
}
/// Position::set_state() computes the hash keys of the position, and other
/// data that once computed is updated incrementally as moves are made.
/// The function is only used when a new position is set up, and to verify
/// the correctness of the StateInfo data when running in debug mode.
void Position::set_state(StateInfo* si) const {
si->key = si->materialKey = 0;
si->pawnKey = Zobrist::noPawns;
si->nonPawnMaterial[WHITE] = si->nonPawnMaterial[BLACK] = VALUE_ZERO;
si->checkersBB = attackers_to(square<KING>(sideToMove)) & pieces(~sideToMove);
set_check_info(si);
for (Bitboard b = pieces(); b; )
{
Square s = pop_lsb(b);
Piece pc = piece_on(s);
si->key ^= Zobrist::psq[pc][s];
if (type_of(pc) == PAWN)
si->pawnKey ^= Zobrist::psq[pc][s];
else if (type_of(pc) != KING)
si->nonPawnMaterial[color_of(pc)] += PieceValue[MG][pc];
}
if (si->epSquare != SQ_NONE)
si->key ^= Zobrist::enpassant[file_of(si->epSquare)];
if (sideToMove == BLACK)
si->key ^= Zobrist::side;
si->key ^= Zobrist::castling[si->castlingRights];
for (Piece pc : Pieces)
for (int cnt = 0; cnt < pieceCount[pc]; ++cnt)
si->materialKey ^= Zobrist::psq[pc][cnt];
}
/// 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& Position::set(const string& code, Color c, StateInfo* si) {
assert(code[0] == 'K');
string sides[] = { code.substr(code.find('K', 1)), // Weak
code.substr(0, std::min(code.find('v'), code.find('K', 1))) }; // Strong
assert(sides[0].length() > 0 && sides[0].length() < 8);
assert(sides[1].length() > 0 && sides[1].length() < 8);
std::transform(sides[c].begin(), sides[c].end(), sides[c].begin(), tolower);
string fenStr = "8/" + sides[0] + char(8 - sides[0].length() + '0') + "/8/8/8/8/"
+ sides[1] + char(8 - sides[1].length() + '0') + "/8 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.
string Position::fen() const {
int emptyCnt;
std::ostringstream ss;
for (Rank r = RANK_8; r >= RANK_1; --r)
{
for (File f = FILE_A; f <= FILE_H; ++f)
{
for (emptyCnt = 0; f <= FILE_H && empty(make_square(f, r)); ++f)
++emptyCnt;
if (emptyCnt)
ss << emptyCnt;
if (f <= FILE_H)
ss << PieceToChar[piece_on(make_square(f, r))];
}
if (r > RANK_1)
ss << '/';
}
ss << (sideToMove == WHITE ? " w " : " b ");
if (can_castle(WHITE_OO))
ss << (chess960 ? char('A' + file_of(castling_rook_square(WHITE_OO ))) : 'K');
if (can_castle(WHITE_OOO))
ss << (chess960 ? char('A' + file_of(castling_rook_square(WHITE_OOO))) : 'Q');
if (can_castle(BLACK_OO))
ss << (chess960 ? char('a' + file_of(castling_rook_square(BLACK_OO ))) : 'k');
if (can_castle(BLACK_OOO))
ss << (chess960 ? char('a' + file_of(castling_rook_square(BLACK_OOO))) : 'q');
if (!can_castle(ANY_CASTLING))
ss << '-';
ss << (ep_square() == SQ_NONE ? " - " : " " + UCI::square(ep_square()) + " ")
<< st->rule50 << " " << 1 + (gamePly - (sideToMove == BLACK)) / 2;
return ss.str();
}
/// Position::slider_blockers() returns a bitboard of all the pieces (both colors)
/// that are blocking attacks on the square 's' from 'sliders'. A piece blocks a
/// slider if removing that piece from the board would result in a position where
/// square 's' is attacked. For example, a king-attack blocking piece can be either
/// a pinned or a discovered check piece, according if its color is the opposite
/// or the same of the color of the slider.
Bitboard Position::slider_blockers(Bitboard sliders, Square s, Bitboard& pinners) const {
Bitboard blockers = 0;
pinners = 0;
// Snipers are sliders that attack 's' when a piece and other snipers are removed
Bitboard snipers = ( (attacks_bb< ROOK>(s) & pieces(QUEEN, ROOK))
| (attacks_bb<BISHOP>(s) & pieces(QUEEN, BISHOP))) & sliders;
Bitboard occupancy = pieces() ^ snipers;
while (snipers)
{
Square sniperSq = pop_lsb(snipers);
Bitboard b = between_bb(s, sniperSq) & occupancy;
if (b && !more_than_one(b))
{
blockers |= b;
if (b & pieces(color_of(piece_on(s))))
pinners |= sniperSq;
}
}
return blockers;
}
/// Position::attackers_to() computes a bitboard of all pieces which attack a
/// given square. Slider attacks use the occupied bitboard to indicate occupancy.
Bitboard Position::attackers_to(Square s, Bitboard occupied) const {
return (pawn_attacks_bb(BLACK, s) & pieces(WHITE, PAWN))
| (pawn_attacks_bb(WHITE, s) & pieces(BLACK, PAWN))
| (attacks_bb<KNIGHT>(s) & pieces(KNIGHT))
| (attacks_bb< ROOK>(s, occupied) & pieces( ROOK, QUEEN))
| (attacks_bb<BISHOP>(s, occupied) & pieces(BISHOP, QUEEN))
| (attacks_bb<KING>(s) & pieces(KING));
}
/// Position::legal() tests whether a pseudo-legal move is legal
bool Position::legal(Move m) const {
assert(is_ok(m));
Color us = sideToMove;
Square from = from_sq(m);
Square to = to_sq(m);
assert(color_of(moved_piece(m)) == us);
assert(piece_on(square<KING>(us)) == make_piece(us, KING));
// En passant captures are a tricky special case. Because they are rather
// uncommon, we do it simply by testing whether the king is attacked after
// the move is made.
if (type_of(m) == EN_PASSANT)
{
Square ksq = square<KING>(us);
Square capsq = to - pawn_push(us);
Bitboard occupied = (pieces() ^ from ^ capsq) | to;
assert(to == ep_square());
assert(moved_piece(m) == make_piece(us, PAWN));
assert(piece_on(capsq) == make_piece(~us, PAWN));
assert(piece_on(to) == NO_PIECE);
return !(attacks_bb< ROOK>(ksq, occupied) & pieces(~us, QUEEN, ROOK))
&& !(attacks_bb<BISHOP>(ksq, occupied) & pieces(~us, QUEEN, BISHOP));
}
// Castling moves generation does not check if the castling path is clear of
// enemy attacks, it is delayed at a later time: now!
if (type_of(m) == CASTLING)
{
// After castling, the rook and king final positions are the same in
// Chess960 as they would be in standard chess.
to = relative_square(us, to > from ? SQ_G1 : SQ_C1);
Direction step = to > from ? WEST : EAST;
for (Square s = to; s != from; s += step)
if (attackers_to(s) & pieces(~us))
return false;
// In case of Chess960, verify if the Rook blocks some checks
// For instance an enemy queen in SQ_A1 when castling rook is in SQ_B1.
return !chess960 || !(blockers_for_king(us) & to_sq(m));
}
// If the moving piece is a king, check whether the destination square is
// attacked by the opponent.
if (type_of(piece_on(from)) == KING)
return !(attackers_to(to, pieces() ^ from) & pieces(~us));
// A non-king move is legal if and only if it is not pinned or it
// is moving along the ray towards or away from the king.
return !(blockers_for_king(us) & from)
|| aligned(from, to, square<KING>(us));
}
/// Position::pseudo_legal() takes a random move and tests whether the move is
/// pseudo legal. It is used to validate moves from TT that can be corrupted
/// due to SMP concurrent access or hash position key aliasing.
bool Position::pseudo_legal(const Move m) const {
Color us = sideToMove;
Square from = from_sq(m);
Square to = to_sq(m);
Piece pc = moved_piece(m);
// Use a slower but simpler function for uncommon cases
// yet we skip the legality check of MoveList<LEGAL>().
if (type_of(m) != NORMAL)
return checkers() ? MoveList< EVASIONS>(*this).contains(m)
: MoveList<NON_EVASIONS>(*this).contains(m);
// Is not a promotion, so promotion piece must be empty
if (promotion_type(m) - KNIGHT != NO_PIECE_TYPE)
return false;
// If the 'from' square is not occupied by a piece belonging to the side to
// move, the move is obviously not legal.
if (pc == NO_PIECE || color_of(pc) != us)
return false;
// The destination square cannot be occupied by a friendly piece
if (pieces(us) & to)
return false;
// Handle the special case of a pawn move
if (type_of(pc) == PAWN)
{
// We have already handled promotion moves, so destination
// cannot be on the 8th/1st rank.
if ((Rank8BB | Rank1BB) & to)
return false;
if ( !(pawn_attacks_bb(us, from) & pieces(~us) & to) // Not a capture
&& !((from + pawn_push(us) == to) && empty(to)) // Not a single push
&& !( (from + 2 * pawn_push(us) == to) // Not a double push
&& (relative_rank(us, from) == RANK_2)
&& empty(to)
&& empty(to - pawn_push(us))))
return false;
}
else if (!(attacks_bb(type_of(pc), from, pieces()) & to))
return false;
// Evasions generator already takes care to avoid some kind of illegal moves
// and legal() relies on this. We therefore have to take care that the same
// kind of moves are filtered out here.
if (checkers())
{
if (type_of(pc) != KING)
{
// Double check? In this case a king move is required
if (more_than_one(checkers()))
return false;
// Our move must be a blocking interposition or a capture of the checking piece
if (!(between_bb(square<KING>(us), lsb(checkers())) & to))
return false;
}
// In case of king moves under check we have to remove king so as to catch
// invalid moves like b1a1 when opposite queen is on c1.
else if (attackers_to(to, pieces() ^ from) & pieces(~us))
return false;
}
return true;
}
/// Position::gives_check() tests whether a pseudo-legal move gives a check
bool Position::gives_check(Move m) const {
assert(is_ok(m));
assert(color_of(moved_piece(m)) == sideToMove);
Square from = from_sq(m);
Square to = to_sq(m);
// Is there a direct check?
if (check_squares(type_of(piece_on(from))) & to)
return true;
// Is there a discovered check?
if ( (blockers_for_king(~sideToMove) & from)
&& !aligned(from, to, square<KING>(~sideToMove)))
return true;
switch (type_of(m))
{
case NORMAL:
return false;
case PROMOTION:
return attacks_bb(promotion_type(m), to, pieces() ^ from) & square<KING>(~sideToMove);
// En passant capture with check? We have already handled the case
// of direct checks and ordinary discovered check, so the only case we
// need to handle is the unusual case of a discovered check through
// the captured pawn.
case EN_PASSANT:
{
Square capsq = make_square(file_of(to), rank_of(from));
Bitboard b = (pieces() ^ from ^ capsq) | to;
return (attacks_bb< ROOK>(square<KING>(~sideToMove), b) & pieces(sideToMove, QUEEN, ROOK))
| (attacks_bb<BISHOP>(square<KING>(~sideToMove), b) & pieces(sideToMove, QUEEN, BISHOP));
}
default: //CASTLING
{
// Castling is encoded as 'king captures the rook'
Square ksq = square<KING>(~sideToMove);
Square rto = relative_square(sideToMove, to > from ? SQ_F1 : SQ_D1);
return (attacks_bb<ROOK>(rto) & ksq)
&& (attacks_bb<ROOK>(rto, pieces() ^ from ^ to) & ksq);
}
}
}
/// Position::do_move() makes a move, and saves all information necessary
/// to a StateInfo object. The move is assumed to be legal. Pseudo-legal
/// moves should be filtered out before this function is called.
void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
assert(is_ok(m));
assert(&newSt != st);
thisThread->nodes.fetch_add(1, std::memory_order_relaxed);
Key k = st->key ^ Zobrist::side;
// Copy some fields of the old state to our new StateInfo object except the
// ones which are going to be recalculated from scratch anyway and then switch
// our state pointer to point to the new (ready to be updated) state.
std::memcpy(&newSt, st, offsetof(StateInfo, key));
newSt.previous = st;
st = &newSt;
// Increment ply counters. In particular, rule50 will be reset to zero later on
// in case of a capture or a pawn move.
++gamePly;
++st->rule50;
++st->pliesFromNull;
// Used by NNUE
st->accumulator.computed[WHITE] = false;
st->accumulator.computed[BLACK] = false;
auto& dp = st->dirtyPiece;
dp.dirty_num = 1;
Color us = sideToMove;
Color them = ~us;
Square from = from_sq(m);
Square to = to_sq(m);
Piece pc = piece_on(from);
Piece captured = type_of(m) == EN_PASSANT ? make_piece(them, PAWN) : piece_on(to);
assert(color_of(pc) == us);
assert(captured == NO_PIECE || color_of(captured) == (type_of(m) != CASTLING ? them : us));
assert(type_of(captured) != KING);
if (type_of(m) == CASTLING)
{
assert(pc == make_piece(us, KING));
assert(captured == make_piece(us, ROOK));
Square rfrom, rto;
do_castling<true>(us, from, to, rfrom, rto);
k ^= Zobrist::psq[captured][rfrom] ^ Zobrist::psq[captured][rto];
captured = NO_PIECE;
}
if (captured)
{
Square capsq = to;
// If the captured piece is a pawn, update pawn hash key, otherwise
// update non-pawn material.
if (type_of(captured) == PAWN)
{
if (type_of(m) == EN_PASSANT)
{
capsq -= pawn_push(us);
assert(pc == make_piece(us, PAWN));
assert(to == st->epSquare);
assert(relative_rank(us, to) == RANK_6);
assert(piece_on(to) == NO_PIECE);
assert(piece_on(capsq) == make_piece(them, PAWN));
}
st->pawnKey ^= Zobrist::psq[captured][capsq];
}
else
st->nonPawnMaterial[them] -= PieceValue[MG][captured];
if (Eval::useNNUE)
{
dp.dirty_num = 2; // 1 piece moved, 1 piece captured
dp.piece[1] = captured;
dp.from[1] = capsq;
dp.to[1] = SQ_NONE;
}
// Update board and piece lists
remove_piece(capsq);
if (type_of(m) == EN_PASSANT)
board[capsq] = NO_PIECE;
// Update material hash key and prefetch access to materialTable
k ^= Zobrist::psq[captured][capsq];
st->materialKey ^= Zobrist::psq[captured][pieceCount[captured]];
prefetch(thisThread->materialTable[st->materialKey]);
// Reset rule 50 counter
st->rule50 = 0;
}
// Update hash key
k ^= Zobrist::psq[pc][from] ^ Zobrist::psq[pc][to];
// Reset en passant square
if (st->epSquare != SQ_NONE)
{
k ^= Zobrist::enpassant[file_of(st->epSquare)];
st->epSquare = SQ_NONE;
}
// Update castling rights if needed
if (st->castlingRights && (castlingRightsMask[from] | castlingRightsMask[to]))
{
k ^= Zobrist::castling[st->castlingRights];
st->castlingRights &= ~(castlingRightsMask[from] | castlingRightsMask[to]);
k ^= Zobrist::castling[st->castlingRights];
}
// Move the piece. The tricky Chess960 castling is handled earlier
if (type_of(m) != CASTLING)
{
if (Eval::useNNUE)
{
dp.piece[0] = pc;
dp.from[0] = from;
dp.to[0] = to;
}
move_piece(from, to);
}
// If the moving piece is a pawn do some special extra work
if (type_of(pc) == PAWN)
{
// Set en passant square if the moved pawn can be captured
if ( (int(to) ^ int(from)) == 16
&& (pawn_attacks_bb(us, to - pawn_push(us)) & pieces(them, PAWN)))
{
st->epSquare = to - pawn_push(us);
k ^= Zobrist::enpassant[file_of(st->epSquare)];
}
else if (type_of(m) == PROMOTION)
{
Piece promotion = make_piece(us, promotion_type(m));
assert(relative_rank(us, to) == RANK_8);
assert(type_of(promotion) >= KNIGHT && type_of(promotion) <= QUEEN);
remove_piece(to);
put_piece(promotion, to);
if (Eval::useNNUE)
{
// Promoting pawn to SQ_NONE, promoted piece from SQ_NONE
dp.to[0] = SQ_NONE;
dp.piece[dp.dirty_num] = promotion;
dp.from[dp.dirty_num] = SQ_NONE;
dp.to[dp.dirty_num] = to;
dp.dirty_num++;
}
// Update hash keys
k ^= Zobrist::psq[pc][to] ^ Zobrist::psq[promotion][to];
st->pawnKey ^= Zobrist::psq[pc][to];
st->materialKey ^= Zobrist::psq[promotion][pieceCount[promotion]-1]
^ Zobrist::psq[pc][pieceCount[pc]];
// Update material
st->nonPawnMaterial[us] += PieceValue[MG][promotion];
}
// Update pawn hash key
st->pawnKey ^= Zobrist::psq[pc][from] ^ Zobrist::psq[pc][to];
// Reset rule 50 draw counter
st->rule50 = 0;
}
// Set capture piece
st->capturedPiece = captured;
// Update the key with the final value
st->key = k;
// Calculate checkers bitboard (if move gives check)
st->checkersBB = givesCheck ? attackers_to(square<KING>(them)) & pieces(us) : 0;
sideToMove = ~sideToMove;
// Update king attacks used for fast check detection
set_check_info(st);
// Calculate the repetition info. It is the ply distance from the previous
// occurrence of the same position, negative in the 3-fold case, or zero
// if the position was not repeated.
st->repetition = 0;
int end = std::min(st->rule50, st->pliesFromNull);
if (end >= 4)
{
StateInfo* stp = st->previous->previous;
for (int i = 4; i <= end; i += 2)
{
stp = stp->previous->previous;
if (stp->key == st->key)
{
st->repetition = stp->repetition ? -i : i;
break;
}
}
}
assert(pos_is_ok());
}
/// Position::undo_move() unmakes a move. When it returns, the position should
/// be restored to exactly the same state as before the move was made.
void Position::undo_move(Move m) {
assert(is_ok(m));
sideToMove = ~sideToMove;
Color us = sideToMove;
Square from = from_sq(m);
Square to = to_sq(m);
Piece pc = piece_on(to);
assert(empty(from) || type_of(m) == CASTLING);
assert(type_of(st->capturedPiece) != KING);
if (type_of(m) == PROMOTION)
{
assert(relative_rank(us, to) == RANK_8);
assert(type_of(pc) == promotion_type(m));
assert(type_of(pc) >= KNIGHT && type_of(pc) <= QUEEN);
remove_piece(to);
pc = make_piece(us, PAWN);
put_piece(pc, to);
}
if (type_of(m) == CASTLING)
{
Square rfrom, rto;
do_castling<false>(us, from, to, rfrom, rto);
}
else
{
move_piece(to, from); // Put the piece back at the source square
if (st->capturedPiece)
{
Square capsq = to;
if (type_of(m) == EN_PASSANT)
{
capsq -= pawn_push(us);
assert(type_of(pc) == PAWN);
assert(to == st->previous->epSquare);
assert(relative_rank(us, to) == RANK_6);
assert(piece_on(capsq) == NO_PIECE);
assert(st->capturedPiece == make_piece(~us, PAWN));
}
put_piece(st->capturedPiece, capsq); // Restore the captured piece
}
}
// Finally point our state pointer back to the previous state
st = st->previous;
--gamePly;
assert(pos_is_ok());
}
/// Position::do_castling() is a helper used to do/undo a castling move. This
/// is a bit tricky in Chess960 where from/to squares can overlap.
template<bool Do>
void Position::do_castling(Color us, Square from, Square& to, Square& rfrom, Square& rto) {
bool kingSide = to > from;
rfrom = to; // Castling is encoded as "king captures friendly rook"
rto = relative_square(us, kingSide ? SQ_F1 : SQ_D1);
to = relative_square(us, kingSide ? SQ_G1 : SQ_C1);
if (Do && Eval::useNNUE)
{
auto& dp = st->dirtyPiece;
dp.piece[0] = make_piece(us, KING);
dp.from[0] = from;
dp.to[0] = to;
dp.piece[1] = make_piece(us, ROOK);
dp.from[1] = rfrom;
dp.to[1] = rto;
dp.dirty_num = 2;
}
// Remove both pieces first since squares could overlap in Chess960
remove_piece(Do ? from : to);
remove_piece(Do ? rfrom : rto);
board[Do ? from : to] = board[Do ? rfrom : rto] = NO_PIECE; // Since remove_piece doesn't do this for us
put_piece(make_piece(us, KING), Do ? to : from);
put_piece(make_piece(us, ROOK), Do ? rto : rfrom);
}
/// Position::do_null_move() is used to do a "null move": it flips
/// the side to move without executing any move on the board.
void Position::do_null_move(StateInfo& newSt) {
assert(!checkers());
assert(&newSt != st);
std::memcpy(&newSt, st, offsetof(StateInfo, accumulator));
newSt.previous = st;
st = &newSt;
st->dirtyPiece.dirty_num = 0;
st->dirtyPiece.piece[0] = NO_PIECE; // Avoid checks in UpdateAccumulator()
st->accumulator.computed[WHITE] = false;
st->accumulator.computed[BLACK] = false;
if (st->epSquare != SQ_NONE)
{
st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
st->epSquare = SQ_NONE;
}
st->key ^= Zobrist::side;
++st->rule50;
prefetch(TT.first_entry(key()));
st->pliesFromNull = 0;
sideToMove = ~sideToMove;
set_check_info(st);
st->repetition = 0;
assert(pos_is_ok());
}
/// Position::undo_null_move() must be used to undo a "null move"
void Position::undo_null_move() {
assert(!checkers());
st = st->previous;
sideToMove = ~sideToMove;
}
/// Position::key_after() computes the new hash key after the given move. Needed
/// for speculative prefetch. It doesn't recognize special moves like castling,
/// en passant and promotions.
Key Position::key_after(Move m) const {
Square from = from_sq(m);
Square to = to_sq(m);
Piece pc = piece_on(from);
Piece captured = piece_on(to);
Key k = st->key ^ Zobrist::side;
if (captured)
k ^= Zobrist::psq[captured][to];
return k ^ Zobrist::psq[pc][to] ^ Zobrist::psq[pc][from];
}
/// Position::see_ge (Static Exchange Evaluation Greater or Equal) tests if the
/// SEE value of move is greater or equal to the given threshold. We'll use an
/// algorithm similar to alpha-beta pruning with a null window.
bool Position::see_ge(Move m, Value threshold) const {
assert(is_ok(m));
// Only deal with normal moves, assume others pass a simple SEE
if (type_of(m) != NORMAL)
return VALUE_ZERO >= threshold;
Square from = from_sq(m), to = to_sq(m);
int swap = PieceValue[MG][piece_on(to)] - threshold;
if (swap < 0)
return false;
swap = PieceValue[MG][piece_on(from)] - swap;
if (swap <= 0)
return true;
assert(color_of(piece_on(from)) == sideToMove);
Bitboard occupied = pieces() ^ from ^ to;
Color stm = sideToMove;
Bitboard attackers = attackers_to(to, occupied);
Bitboard stmAttackers, bb;
int res = 1;
while (true)
{
stm = ~stm;
attackers &= occupied;
// If stm has no more attackers then give up: stm loses
if (!(stmAttackers = attackers & pieces(stm)))
break;
// Don't allow pinned pieces to attack as long as there are
// pinners on their original square.
if (pinners(~stm) & occupied)
stmAttackers &= ~blockers_for_king(stm);
if (!stmAttackers)
break;
res ^= 1;
// Locate and remove the next least valuable attacker, and add to
// the bitboard 'attackers' any X-ray attackers behind it.
if ((bb = stmAttackers & pieces(PAWN)))
{
if ((swap = PawnValueMg - swap) < res)
break;
occupied ^= least_significant_square_bb(bb);
attackers |= attacks_bb<BISHOP>(to, occupied) & pieces(BISHOP, QUEEN);
}
else if ((bb = stmAttackers & pieces(KNIGHT)))
{
if ((swap = KnightValueMg - swap) < res)
break;
occupied ^= least_significant_square_bb(bb);
}
else if ((bb = stmAttackers & pieces(BISHOP)))
{
if ((swap = BishopValueMg - swap) < res)
break;
occupied ^= least_significant_square_bb(bb);
attackers |= attacks_bb<BISHOP>(to, occupied) & pieces(BISHOP, QUEEN);
}
else if ((bb = stmAttackers & pieces(ROOK)))
{
if ((swap = RookValueMg - swap) < res)
break;
occupied ^= least_significant_square_bb(bb);
attackers |= attacks_bb<ROOK>(to, occupied) & pieces(ROOK, QUEEN);
}
else if ((bb = stmAttackers & pieces(QUEEN)))
{
if ((swap = QueenValueMg - swap) < res)
break;
occupied ^= least_significant_square_bb(bb);
attackers |= (attacks_bb<BISHOP>(to, occupied) & pieces(BISHOP, QUEEN))
| (attacks_bb<ROOK >(to, occupied) & pieces(ROOK , QUEEN));
}
else // KING
// If we "capture" with the king but opponent still has attackers,
// reverse the result.
return (attackers & ~pieces(stm)) ? res ^ 1 : res;
}
return bool(res);
}
/// 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(int ply) const {
if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
return true;
// Return a draw score if a position repeats once earlier but strictly
// after the root, or repeats twice before or at the root.
return st->repetition && st->repetition < ply;
}
// Position::has_repeated() tests whether there has been at least one repetition
// of positions since the last capture or pawn move.
bool Position::has_repeated() const {
StateInfo* stc = st;
int end = std::min(st->rule50, st->pliesFromNull);
while (end-- >= 4)
{
if (stc->repetition)
return true;
stc = stc->previous;
}
return false;
}
/// Position::has_game_cycle() tests if the position has a move which draws by repetition,
/// or an earlier position has a move that directly reaches the current position.
bool Position::has_game_cycle(int ply) const {
int j;
int end = std::min(st->rule50, st->pliesFromNull);
if (end < 3)
return false;
Key originalKey = st->key;
StateInfo* stp = st->previous;
for (int i = 3; i <= end; i += 2)
{
stp = stp->previous->previous;
Key moveKey = originalKey ^ stp->key;
if ( (j = H1(moveKey), cuckoo[j] == moveKey)
|| (j = H2(moveKey), cuckoo[j] == moveKey))
{
Move move = cuckooMove[j];
Square s1 = from_sq(move);
Square s2 = to_sq(move);
if (!((between_bb(s1, s2) ^ s2) & pieces()))
{
if (ply > i)
return true;
// For nodes before or at the root, check that the move is a
// repetition rather than a move to the current position.
// In the cuckoo table, both moves Rc1c5 and Rc5c1 are stored in
// the same location, so we have to select which square to check.
if (color_of(piece_on(empty(s1) ? s2 : s1)) != side_to_move())
continue;
// For repetitions before or at the root, require one more
if (stp->repetition)
return true;
}
}
}
return false;
}
/// Position::flip() flips position with the white and black sides reversed. This
/// is only useful for debugging e.g. for finding evaluation symmetry bugs.
void Position::flip() {
string f, token;
std::stringstream ss(fen());
for (Rank r = RANK_8; r >= RANK_1; --r) // Piece placement
{
std::getline(ss, token, r > RANK_1 ? '/' : ' ');
f.insert(0, token + (f.empty() ? " " : "/"));
}
ss >> token; // Active color
f += (token == "w" ? "B " : "W "); // Will be lowercased later
ss >> token; // Castling availability
f += token + " ";
std::transform(f.begin(), f.end(), f.begin(),
[](char c) { return char(islower(c) ? toupper(c) : tolower(c)); });
ss >> token; // En passant square
f += (token == "-" ? token : token.replace(1, 1, token[1] == '3' ? "6" : "3"));
std::getline(ss, token); // Half and full moves
f += token;
set(f, is_chess960(), st, this_thread());
assert(pos_is_ok());
}
/// Position::pos_is_ok() performs some consistency checks for the
/// position object and raises an asserts if something wrong is detected.
/// This is meant to be helpful when debugging.
bool Position::pos_is_ok() const {
constexpr bool Fast = true; // Quick (default) or full check?
if ( (sideToMove != WHITE && sideToMove != BLACK)
|| piece_on(square<KING>(WHITE)) != W_KING
|| piece_on(square<KING>(BLACK)) != B_KING
|| ( ep_square() != SQ_NONE
&& relative_rank(sideToMove, ep_square()) != RANK_6))
assert(0 && "pos_is_ok: Default");
if (Fast)
return true;
if ( pieceCount[W_KING] != 1
|| pieceCount[B_KING] != 1
|| attackers_to(square<KING>(~sideToMove)) & pieces(sideToMove))
assert(0 && "pos_is_ok: Kings");
if ( (pieces(PAWN) & (Rank1BB | Rank8BB))
|| pieceCount[W_PAWN] > 8
|| pieceCount[B_PAWN] > 8)
assert(0 && "pos_is_ok: Pawns");
if ( (pieces(WHITE) & pieces(BLACK))
|| (pieces(WHITE) | pieces(BLACK)) != pieces()
|| popcount(pieces(WHITE)) > 16
|| popcount(pieces(BLACK)) > 16)
assert(0 && "pos_is_ok: Bitboards");
for (PieceType p1 = PAWN; p1 <= KING; ++p1)
for (PieceType p2 = PAWN; p2 <= KING; ++p2)
if (p1 != p2 && (pieces(p1) & pieces(p2)))
assert(0 && "pos_is_ok: Bitboards");
StateInfo si = *st;
ASSERT_ALIGNED(&si, Eval::NNUE::CacheLineSize);
set_state(&si);
if (std::memcmp(&si, st, sizeof(StateInfo)))
assert(0 && "pos_is_ok: State");
for (Piece pc : Pieces)
if ( pieceCount[pc] != popcount(pieces(color_of(pc), type_of(pc)))
|| pieceCount[pc] != std::count(board, board + SQUARE_NB, pc))
assert(0 && "pos_is_ok: Pieces");
for (Color c : { WHITE, BLACK })
for (CastlingRights cr : {c & KING_SIDE, c & QUEEN_SIDE})
{
if (!can_castle(cr))
continue;
if ( piece_on(castlingRookSquare[cr]) != make_piece(c, ROOK)
|| castlingRightsMask[castlingRookSquare[cr]] != cr
|| (castlingRightsMask[square<KING>(c)] & cr) != cr)
assert(0 && "pos_is_ok: Castling");
}
return true;
}
} // namespace Stockfish
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