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position.cpp
1223 lines (909 loc) · 37.6 KB
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position.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) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
Copyright (C) 2015-2017 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 <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 PSQT {
extern Score psq[PIECE_NB][SQUARE_NB];
}
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");
const 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 };
// min_attacker() is a helper function used by see_ge() to locate the least
// valuable attacker for the side to move, remove the attacker we just found
// from the bitboards and scan for new X-ray attacks behind it.
template<int Pt>
PieceType min_attacker(const Bitboard* bb, Square to, Bitboard stmAttackers,
Bitboard& occupied, Bitboard& attackers) {
Bitboard b = stmAttackers & bb[Pt];
if (!b)
return min_attacker<Pt + 1>(bb, to, stmAttackers, occupied, attackers);
occupied ^= b & ~(b - 1);
if (Pt == PAWN || Pt == BISHOP || Pt == QUEEN)
attackers |= attacks_bb<BISHOP>(to, occupied) & (bb[BISHOP] | bb[QUEEN]);
if (Pt == ROOK || Pt == QUEEN)
attackers |= attacks_bb<ROOK>(to, occupied) & (bb[ROOK] | bb[QUEEN]);
attackers &= occupied; // After X-ray that may add already processed pieces
return (PieceType)Pt;
}
template<>
PieceType min_attacker<KING>(const Bitboard*, Square, Bitboard, Bitboard&, Bitboard&) {
return KING; // No need to update bitboards: it is the last cycle
}
} // 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 << " |\n +---+---+---+---+---+---+---+---+\n";
}
os << "\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;
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;
}
/// 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] = 0;
Bitboard b = cr;
while (b)
{
Key k = Zobrist::castling[1ULL << pop_lsb(&b)];
Zobrist::castling[cr] ^= k ? k : rng.rand<Key>();
}
}
Zobrist::side = rng.rand<Key>();
Zobrist::noPawns = rng.rand<Key>();
}
/// 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. 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));
std::fill_n(&pieceList[0][0], sizeof(pieceList) / sizeof(Square), SQ_NONE);
st = si;
ss >> std::noskipws;
// 1. Piece placement
while ((ss >> token) && !isspace(token))
{
if (isdigit(token))
sq += Square(token - '0'); // Advance the given number of files
else if (token == '/')
sq -= Square(16);
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 no pawn capture is possible
if ( ((ss >> col) && (col >= 'a' && col <= 'h'))
&& ((ss >> row) && (row == '3' || row == '6')))
{
st->epSquare = make_square(File(col - 'a'), Rank(row - '1'));
if ( !(attackers_to(st->epSquare) & pieces(sideToMove, PAWN))
|| !(pieces(~sideToMove, PAWN) & (st->epSquare + pawn_push(~sideToMove))))
st->epSquare = SQ_NONE;
}
else
st->epSquare = SQ_NONE;
// 5-6. Halfmove clock and fullmove number
ss >> std::skipws >> st->rule50 >> gamePly;
// Convert from fullmove starting from 1 to ply 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);
CastlingSide cs = kfrom < rfrom ? KING_SIDE : QUEEN_SIDE;
CastlingRight cr = (c | cs);
st->castlingRights |= cr;
castlingRightsMask[kfrom] |= cr;
castlingRightsMask[rfrom] |= cr;
castlingRookSquare[cr] = rfrom;
Square kto = relative_square(c, cs == KING_SIDE ? SQ_G1 : SQ_C1);
Square rto = relative_square(c, cs == KING_SIDE ? SQ_F1 : SQ_D1);
for (Square s = std::min(rfrom, rto); s <= std::max(rfrom, rto); ++s)
if (s != kfrom && s != rfrom)
castlingPath[cr] |= s;
for (Square s = std::min(kfrom, kto); s <= std::max(kfrom, kto); ++s)
if (s != kfrom && s != rfrom)
castlingPath[cr] |= s;
}
/// 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->pinnersForKing[WHITE]);
si->blockersForKing[BLACK] = slider_blockers(pieces(WHITE), square<KING>(BLACK), si->pinnersForKing[BLACK]);
Square ksq = square<KING>(~sideToMove);
si->checkSquares[PAWN] = attacks_from<PAWN>(ksq, ~sideToMove);
si->checkSquares[KNIGHT] = attacks_from<KNIGHT>(ksq);
si->checkSquares[BISHOP] = attacks_from<BISHOP>(ksq);
si->checkSquares[ROOK] = attacks_from<ROOK>(ksq);
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->psq = SCORE_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];
si->psq += PSQT::psq[pc][s];
}
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 (Bitboard b = pieces(PAWN); b; )
{
Square s = pop_lsb(&b);
si->pawnKey ^= Zobrist::psq[piece_on(s)][s];
}
for (Piece pc : Pieces)
{
if (type_of(pc) != PAWN && type_of(pc) != KING)
si->nonPawnMaterial[color_of(pc)] += pieceCount[pc] * PieceValue[MG][pc];
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 is not playable,
/// indeed is even not guaranteed to be legal.
Position& Position::set(const string& code, Color c, StateInfo* si) {
assert(code.length() > 0 && code.length() < 8);
assert(code[0] == 'K');
string sides[] = { code.substr(code.find('K', 1)), // Weak
code.substr(0, code.find('K', 1)) }; // Strong
std::transform(sides[c].begin(), sides[c].end(), sides[c].begin(), tolower);
string fenStr = sides[0] + char(8 - sides[0].length() + '0') + "/8/8/8/8/8/8/"
+ sides[1] + char(8 - sides[1].length() + '0') + " 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.
const 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 | KING_SIDE))) : 'K');
if (can_castle(WHITE_OOO))
ss << (chess960 ? char('A' + file_of(castling_rook_square(WHITE | QUEEN_SIDE))) : 'Q');
if (can_castle(BLACK_OO))
ss << (chess960 ? char('a' + file_of(castling_rook_square(BLACK | KING_SIDE))) : 'k');
if (can_castle(BLACK_OOO))
ss << (chess960 ? char('a' + file_of(castling_rook_square(BLACK | QUEEN_SIDE))) : 'q');
if (!can_castle(WHITE) && !can_castle(BLACK))
ss << '-';
ss << (ep_square() == SQ_NONE ? " - " : " " + UCI::square(ep_square()) + " ")
<< st->rule50 << " " << 1 + (gamePly - (sideToMove == BLACK)) / 2;
return ss.str();
}
/// Position::game_phase() calculates the game phase interpolating total non-pawn
/// material between endgame and midgame limits.
Phase Position::game_phase() const {
Value npm = st->nonPawnMaterial[WHITE] + st->nonPawnMaterial[BLACK];
npm = std::max(EndgameLimit, std::min(npm, MidgameLimit));
return Phase(((npm - EndgameLimit) * PHASE_MIDGAME) / (MidgameLimit - EndgameLimit));
}
/// 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 result = 0;
pinners = 0;
// Snipers are sliders that attack 's' when a piece is removed
Bitboard snipers = ( (PseudoAttacks[ROOK ][s] & pieces(QUEEN, ROOK))
| (PseudoAttacks[BISHOP][s] & pieces(QUEEN, BISHOP))) & sliders;
while (snipers)
{
Square sniperSq = pop_lsb(&snipers);
Bitboard b = between_bb(s, sniperSq) & pieces();
if (!more_than_one(b))
{
result |= b;
if (b & pieces(color_of(piece_on(s))))
pinners |= sniperSq;
}
}
return result;
}
/// 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 (attacks_from<PAWN>(s, BLACK) & pieces(WHITE, PAWN))
| (attacks_from<PAWN>(s, WHITE) & pieces(BLACK, PAWN))
| (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
| (attacks_bb<ROOK >(s, occupied) & pieces(ROOK, QUEEN))
| (attacks_bb<BISHOP>(s, occupied) & pieces(BISHOP, QUEEN))
| (attacks_from<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);
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) == ENPASSANT)
{
Square ksq = square<KING>(us);
Square to = to_sq(m);
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));
}
// If the moving piece is a king, check whether the destination
// square is attacked by the opponent. Castling moves are checked
// for legality during move generation.
if (type_of(piece_on(from)) == KING)
return type_of(m) == CASTLING || !(attackers_to(to_sq(m)) & 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 !(pinned_pieces(us) & from)
|| aligned(from, to_sq(m), 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
if (type_of(m) != NORMAL)
return MoveList<LEGAL>(*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 (rank_of(to) == relative_rank(us, RANK_8))
return false;
if ( !(attacks_from<PAWN>(from, us) & 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
&& (rank_of(from) == relative_rank(us, RANK_2))
&& empty(to)
&& empty(to - pawn_push(us))))
return false;
}
else if (!(attacks_from(type_of(pc), from) & 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 evasion or a capture of the checking piece
if (!((between_bb(lsb(checkers()), square<KING>(us)) | 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 (st->checkSquares[type_of(piece_on(from))] & to)
return true;
// Is there a discovered check?
if ( (discovered_check_candidates() & 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 ENPASSANT:
{
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));
}
case CASTLING:
{
Square kfrom = from;
Square rfrom = to; // Castling is encoded as 'King captures the rook'
Square kto = relative_square(sideToMove, rfrom > kfrom ? SQ_G1 : SQ_C1);
Square rto = relative_square(sideToMove, rfrom > kfrom ? SQ_F1 : SQ_D1);
return (PseudoAttacks[ROOK][rto] & square<KING>(~sideToMove))
&& (attacks_bb<ROOK>(rto, (pieces() ^ kfrom ^ rfrom) | rto | kto) & square<KING>(~sideToMove));
}
default:
assert(false);
return false;
}
}
/// 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);
++nodes;
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;
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) == ENPASSANT ? 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);
st->psq += PSQT::psq[captured][rto] - PSQT::psq[captured][rfrom];
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) == ENPASSANT)
{
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));
board[capsq] = NO_PIECE; // Not done by remove_piece()
}
st->pawnKey ^= Zobrist::psq[captured][capsq];
}
else
st->nonPawnMaterial[them] -= PieceValue[MG][captured];
// Update board and piece lists
remove_piece(captured, capsq);
// 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]);
// Update incremental scores
st->psq -= PSQT::psq[captured][capsq];
// 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]))
{
int cr = castlingRightsMask[from] | castlingRightsMask[to];
k ^= Zobrist::castling[st->castlingRights & cr];
st->castlingRights &= ~cr;
}
// Move the piece. The tricky Chess960 castling is handled earlier
if (type_of(m) != CASTLING)
move_piece(pc, 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
&& (attacks_from<PAWN>(to - pawn_push(us), us) & pieces(them, PAWN)))
{
st->epSquare = (from + to) / 2;
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(pc, to);
put_piece(promotion, to);
// 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 incremental score
st->psq += PSQT::psq[promotion][to] - PSQT::psq[pc][to];
// Update material
st->nonPawnMaterial[us] += PieceValue[MG][promotion];
}
// Update pawn hash key and prefetch access to pawnsTable
st->pawnKey ^= Zobrist::psq[pc][from] ^ Zobrist::psq[pc][to];
prefetch2(thisThread->pawnsTable[st->pawnKey]);
// Reset rule 50 draw counter
st->rule50 = 0;
}
// Update incremental scores
st->psq += PSQT::psq[pc][to] - PSQT::psq[pc][from];
// 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);
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(pc, 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(pc, to, from); // Put the piece back at the source square
if (st->capturedPiece)
{
Square capsq = to;
if (type_of(m) == ENPASSANT)
{
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);
// Remove both pieces first since squares could overlap in Chess960
remove_piece(make_piece(us, KING), Do ? from : to);
remove_piece(make_piece(us, ROOK), Do ? rfrom : rto);
board[Do ? from : to] = board[Do ? rfrom : rto] = NO_PIECE; // Since remove_piece doesn't do it for us
put_piece(make_piece(us, KING), Do ? to : from);
put_piece(make_piece(us, ROOK), Do ? rto : rfrom);
}
/// Position::do(undo)_null_move() is used to do(undo) 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, sizeof(StateInfo));
newSt.previous = st;
st = &newSt;
if (st->epSquare != SQ_NONE)
{
st->key ^= Zobrist::enpassant[file_of(st->epSquare)];
st->epSquare = SQ_NONE;
}
st->key ^= Zobrist::side;
prefetch(TT.first_entry(st->key));
++st->rule50;
st->pliesFromNull = 0;
sideToMove = ~sideToMove;
set_check_info(st);
assert(pos_is_ok());
}
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];
}