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position.cpp
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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) 2008-2012 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 <cstring>
#include <iostream>
#include <sstream>
#include <algorithm>
#include "bitcount.h"
#include "movegen.h"
#include "position.h"
#include "psqtab.h"
#include "rkiss.h"
#include "thread.h"
#include "tt.h"
using std::string;
using std::cout;
using std::endl;
Key Position::zobrist[2][8][64];
Key Position::zobEp[8];
Key Position::zobCastle[16];
Key Position::zobSideToMove;
Key Position::zobExclusion;
Score Position::pieceSquareTable[16][64];
// Material values arrays, indexed by Piece
const Value PieceValueMidgame[17] = {
VALUE_ZERO,
PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
RookValueMidgame, QueenValueMidgame,
VALUE_ZERO, VALUE_ZERO, VALUE_ZERO,
PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
RookValueMidgame, QueenValueMidgame
};
const Value PieceValueEndgame[17] = {
VALUE_ZERO,
PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
RookValueEndgame, QueenValueEndgame,
VALUE_ZERO, VALUE_ZERO, VALUE_ZERO,
PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
RookValueEndgame, QueenValueEndgame
};
namespace {
// Bonus for having the side to move (modified by Joona Kiiski)
const Score Tempo = make_score(48, 22);
// To convert a Piece to and from a FEN char
const string PieceToChar(" PNBRQK pnbrqk .");
}
/// CheckInfo c'tor
CheckInfo::CheckInfo(const Position& pos) {
Color them = ~pos.side_to_move();
ksq = pos.king_square(them);
pinned = pos.pinned_pieces();
dcCandidates = pos.discovered_check_candidates();
checkSq[PAWN] = pos.attacks_from<PAWN>(ksq, them);
checkSq[KNIGHT] = pos.attacks_from<KNIGHT>(ksq);
checkSq[BISHOP] = pos.attacks_from<BISHOP>(ksq);
checkSq[ROOK] = pos.attacks_from<ROOK>(ksq);
checkSq[QUEEN] = checkSq[BISHOP] | checkSq[ROOK];
checkSq[KING] = 0;
}
/// Position::copy() creates a copy of 'pos'. We want the new born Position
/// object do not depend on any external data so we detach state pointer from
/// the source one.
void Position::copy(const Position& pos, Thread* th) {
memcpy(this, &pos, sizeof(Position));
startState = *st;
st = &startState;
thisThread = th;
nodes = 0;
assert(pos_is_ok());
}
/// Position::from_fen() 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).
void Position::from_fen(const string& fenStr, bool isChess960, 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") while Black take 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 regardless of whether
there is a pawn in position to make an en passant capture.
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.
*/
char col, row, token;
size_t p;
Square sq = SQ_A8;
std::istringstream fen(fenStr);
clear();
fen >> std::noskipws;
// 1. Piece placement
while ((fen >> token) && !isspace(token))
{
if (isdigit(token))
sq += Square(token - '0'); // Advance the given number of files
else if (token == '/')
sq = make_square(FILE_A, rank_of(sq) - Rank(2));
else if ((p = PieceToChar.find(token)) != string::npos)
{
put_piece(Piece(p), sq);
sq++;
}
}
// 2. Active color
fen >> token;
sideToMove = (token == 'w' ? WHITE : BLACK);
fen >> 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 ((fen >> token) && !isspace(token))
{
Square rsq;
Color c = islower(token) ? BLACK : WHITE;
token = char(toupper(token));
if (token == 'K')
for (rsq = relative_square(c, SQ_H1); type_of(piece_on(rsq)) != ROOK; rsq--) {}
else if (token == 'Q')
for (rsq = relative_square(c, SQ_A1); type_of(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_castle_right(c, rsq);
}
// 4. En passant square. Ignore if no pawn capture is possible
if ( ((fen >> col) && (col >= 'a' && col <= 'h'))
&& ((fen >> row) && (row == '3' || row == '6')))
{
st->epSquare = make_square(File(col - 'a'), Rank(row - '1'));
if (!(attackers_to(st->epSquare) & pieces(PAWN, sideToMove)))
st->epSquare = SQ_NONE;
}
// 5-6. Halfmove clock and fullmove number
fen >> std::skipws >> st->rule50 >> startPosPly;
// Convert from fullmove starting from 1 to ply starting from 0,
// handle also common incorrect FEN with fullmove = 0.
startPosPly = std::max(2 * (startPosPly - 1), 0) + int(sideToMove == BLACK);
st->key = compute_key();
st->pawnKey = compute_pawn_key();
st->materialKey = compute_material_key();
st->psqScore = compute_psq_score();
st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
st->checkersBB = attackers_to(king_square(sideToMove)) & pieces(~sideToMove);
chess960 = isChess960;
thisThread = th;
assert(pos_is_ok());
}
/// Position::set_castle_right() is an helper function used to set castling
/// rights given the corresponding color and the rook starting square.
void Position::set_castle_right(Color c, Square rfrom) {
Square kfrom = king_square(c);
bool kingSide = kfrom < rfrom;
int cr = (kingSide ? WHITE_OO : WHITE_OOO) << c;
st->castleRights |= cr;
castleRightsMask[kfrom] |= cr;
castleRightsMask[rfrom] |= cr;
castleRookSquare[cr] = rfrom;
Square kto = relative_square(c, kingSide ? SQ_G1 : SQ_C1);
Square rto = relative_square(c, kingSide ? SQ_F1 : SQ_D1);
for (Square s = std::min(rfrom, rto); s <= std::max(rfrom, rto); s++)
if (s != kfrom && s != rfrom)
castlePath[cr] |= s;
for (Square s = std::min(kfrom, kto); s <= std::max(kfrom, kto); s++)
if (s != kfrom && s != rfrom)
castlePath[cr] |= s;
}
/// Position::to_fen() returns a FEN representation of the position. In case
/// of Chess960 the Shredder-FEN notation is used. Mainly a debugging function.
const string Position::to_fen() const {
std::ostringstream fen;
Square sq;
int emptyCnt;
for (Rank rank = RANK_8; rank >= RANK_1; rank--)
{
emptyCnt = 0;
for (File file = FILE_A; file <= FILE_H; file++)
{
sq = make_square(file, rank);
if (square_empty(sq))
emptyCnt++;
else
{
if (emptyCnt > 0)
{
fen << emptyCnt;
emptyCnt = 0;
}
fen << PieceToChar[piece_on(sq)];
}
}
if (emptyCnt > 0)
fen << emptyCnt;
if (rank > RANK_1)
fen << '/';
}
fen << (sideToMove == WHITE ? " w " : " b ");
if (can_castle(WHITE_OO))
fen << (chess960 ? char(toupper(file_to_char(file_of(castle_rook_square(WHITE_OO))))) : 'K');
if (can_castle(WHITE_OOO))
fen << (chess960 ? char(toupper(file_to_char(file_of(castle_rook_square(WHITE_OOO))))) : 'Q');
if (can_castle(BLACK_OO))
fen << (chess960 ? file_to_char(file_of(castle_rook_square(BLACK_OO))) : 'k');
if (can_castle(BLACK_OOO))
fen << (chess960 ? file_to_char(file_of(castle_rook_square(BLACK_OOO))) : 'q');
if (st->castleRights == CASTLES_NONE)
fen << '-';
fen << (ep_square() == SQ_NONE ? " - " : " " + square_to_string(ep_square()) + " ")
<< st->rule50 << " " << 1 + (startPosPly - int(sideToMove == BLACK)) / 2;
return fen.str();
}
/// Position::print() prints an ASCII representation of the position to
/// the standard output. If a move is given then also the san is printed.
void Position::print(Move move) const {
const char* dottedLine = "\n+---+---+---+---+---+---+---+---+\n";
if (move)
{
Position p(*this, thisThread);
cout << "\nMove is: " << (sideToMove == BLACK ? ".." : "") << move_to_san(p, move);
}
for (Rank rank = RANK_8; rank >= RANK_1; rank--)
{
cout << dottedLine << '|';
for (File file = FILE_A; file <= FILE_H; file++)
{
Square sq = make_square(file, rank);
Piece piece = piece_on(sq);
char c = (color_of(piece) == BLACK ? '=' : ' ');
if (piece == NO_PIECE && !opposite_colors(sq, SQ_A1))
piece++; // Index the dot
cout << c << PieceToChar[piece] << c << '|';
}
}
cout << dottedLine << "Fen is: " << to_fen() << "\nKey is: " << st->key << endl;
}
/// Position:hidden_checkers<>() returns a bitboard of all pinned (against the
/// king) pieces for the given color. Or, when template parameter FindPinned is
/// false, the function return the pieces of the given color candidate for a
/// discovery check against the enemy king.
template<bool FindPinned>
Bitboard Position::hidden_checkers() const {
// Pinned pieces protect our king, dicovery checks attack the enemy king
Bitboard b, result = 0;
Bitboard pinners = pieces(FindPinned ? ~sideToMove : sideToMove);
Square ksq = king_square(FindPinned ? sideToMove : ~sideToMove);
// Pinners are sliders, that give check when candidate pinned is removed
pinners &= (pieces(ROOK, QUEEN) & PseudoAttacks[ROOK][ksq])
| (pieces(BISHOP, QUEEN) & PseudoAttacks[BISHOP][ksq]);
while (pinners)
{
b = squares_between(ksq, pop_1st_bit(&pinners)) & pieces();
if (b && single_bit(b) && (b & pieces(sideToMove)))
result |= b;
}
return result;
}
// Explicit template instantiations
template Bitboard Position::hidden_checkers<true>() const;
template Bitboard Position::hidden_checkers<false>() const;
/// Position::attackers_to() computes a bitboard of all pieces which attack a
/// given square. Slider attacks use occ bitboard as occupancy.
Bitboard Position::attackers_to(Square s, Bitboard occ) const {
return (attacks_from<PAWN>(s, BLACK) & pieces(PAWN, WHITE))
| (attacks_from<PAWN>(s, WHITE) & pieces(PAWN, BLACK))
| (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
| (attacks_bb<ROOK>(s, occ) & pieces(ROOK, QUEEN))
| (attacks_bb<BISHOP>(s, occ) & pieces(BISHOP, QUEEN))
| (attacks_from<KING>(s) & pieces(KING));
}
/// Position::attacks_from() computes a bitboard of all attacks of a given piece
/// put in a given square. Slider attacks use occ bitboard as occupancy.
Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
assert(is_ok(s));
switch (type_of(p))
{
case BISHOP: return attacks_bb<BISHOP>(s, occ);
case ROOK : return attacks_bb<ROOK>(s, occ);
case QUEEN : return attacks_bb<BISHOP>(s, occ) | attacks_bb<ROOK>(s, occ);
default : return StepAttacksBB[p][s];
}
}
/// Position::move_attacks_square() tests whether a move from the current
/// position attacks a given square.
bool Position::move_attacks_square(Move m, Square s) const {
assert(is_ok(m));
assert(is_ok(s));
Bitboard occ, xray;
Square from = from_sq(m);
Square to = to_sq(m);
Piece piece = piece_moved(m);
assert(!square_empty(from));
// Update occupancy as if the piece is moving
occ = pieces() ^ from ^ to;
// The piece moved in 'to' attacks the square 's' ?
if (attacks_from(piece, to, occ) & s)
return true;
// Scan for possible X-ray attackers behind the moved piece
xray = (attacks_bb<ROOK>(s, occ) & pieces(ROOK, QUEEN, color_of(piece)))
|(attacks_bb<BISHOP>(s, occ) & pieces(BISHOP, QUEEN, color_of(piece)));
// Verify attackers are triggered by our move and not already existing
return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
}
/// Position::pl_move_is_legal() tests whether a pseudo-legal move is legal
bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
assert(is_ok(m));
assert(pinned == pinned_pieces());
Color us = sideToMove;
Square from = from_sq(m);
assert(color_of(piece_moved(m)) == us);
assert(piece_on(king_square(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 (is_enpassant(m))
{
Color them = ~us;
Square to = to_sq(m);
Square capsq = to + pawn_push(them);
Square ksq = king_square(us);
Bitboard b = (pieces() ^ from ^ capsq) | to;
assert(to == ep_square());
assert(piece_moved(m) == make_piece(us, PAWN));
assert(piece_on(capsq) == make_piece(them, PAWN));
assert(piece_on(to) == NO_PIECE);
return !(attacks_bb<ROOK>(ksq, b) & pieces(ROOK, QUEEN, them))
&& !(attacks_bb<BISHOP>(ksq, b) & pieces(BISHOP, QUEEN, them));
}
// 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 is_castle(m) || !(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
|| !(pinned & from)
|| squares_aligned(from, to_sq(m), king_square(us));
}
/// Position::move_is_legal() takes a random move and tests whether the move
/// is legal. This version is not very fast and should be used only in non
/// time-critical paths.
bool Position::move_is_legal(const Move m) const {
for (MoveList<MV_LEGAL> ml(*this); !ml.end(); ++ml)
if (ml.move() == m)
return true;
return false;
}
/// Position::is_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::is_pseudo_legal(const Move m) const {
Color us = sideToMove;
Color them = ~sideToMove;
Square from = from_sq(m);
Square to = to_sq(m);
Piece pc = piece_moved(m);
// Use a slower but simpler function for uncommon cases
if (is_special(m))
return move_is_legal(m);
// Is not a promotion, so promotion piece must be empty
if (promotion_type(m) - 2 != 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 (color_of(piece_on(to)) == us)
return false;
// Handle the special case of a pawn move
if (type_of(pc) == PAWN)
{
// Move direction must be compatible with pawn color
int direction = to - from;
if ((us == WHITE) != (direction > 0))
return false;
// We have already handled promotion moves, so destination
// cannot be on the 8/1th rank.
if (rank_of(to) == RANK_8 || rank_of(to) == RANK_1)
return false;
// Proceed according to the square delta between the origin and
// destination squares.
switch (direction)
{
case DELTA_NW:
case DELTA_NE:
case DELTA_SW:
case DELTA_SE:
// Capture. The destination square must be occupied by an enemy
// piece (en passant captures was handled earlier).
if (color_of(piece_on(to)) != them)
return false;
// From and to files must be one file apart, avoids a7h5
if (abs(file_of(from) - file_of(to)) != 1)
return false;
break;
case DELTA_N:
case DELTA_S:
// Pawn push. The destination square must be empty.
if (!square_empty(to))
return false;
break;
case DELTA_NN:
// Double white pawn push. The destination square must be on the fourth
// rank, and both the destination square and the square between the
// source and destination squares must be empty.
if ( rank_of(to) != RANK_4
|| !square_empty(to)
|| !square_empty(from + DELTA_N))
return false;
break;
case DELTA_SS:
// Double black pawn push. The destination square must be on the fifth
// rank, and both the destination square and the square between the
// source and destination squares must be empty.
if ( rank_of(to) != RANK_5
|| !square_empty(to)
|| !square_empty(from + DELTA_S))
return false;
break;
default:
return false;
}
}
else if (!(attacks_from(pc, from) & to))
return false;
// Evasions generator already takes care to avoid some kind of illegal moves
// and pl_move_is_legal() relies on this. So we have to take care that the
// same kind of moves are filtered out here.
if (in_check())
{
if (type_of(pc) != KING)
{
Bitboard b = checkers();
Square checksq = pop_1st_bit(&b);
if (b) // double check ? In this case a king move is required
return false;
// Our move must be a blocking evasion or a capture of the checking piece
if (!((squares_between(checksq, king_square(us)) | checkers()) & to))
return false;
}
// In case of king moves under check we have to remove king so to catch
// as invalid moves like b1a1 when opposite queen is on c1.
else if (attackers_to(to, pieces() ^ from) & pieces(~us))
return false;
}
return true;
}
/// Position::move_gives_check() tests whether a pseudo-legal move gives a check
bool Position::move_gives_check(Move m, const CheckInfo& ci) const {
assert(is_ok(m));
assert(ci.dcCandidates == discovered_check_candidates());
assert(color_of(piece_moved(m)) == sideToMove);
Square from = from_sq(m);
Square to = to_sq(m);
PieceType pt = type_of(piece_on(from));
// Direct check ?
if (ci.checkSq[pt] & to)
return true;
// Discovery check ?
if (ci.dcCandidates && (ci.dcCandidates & from))
{
// For pawn and king moves we need to verify also direction
if ( (pt != PAWN && pt != KING)
|| !squares_aligned(from, to, king_square(~sideToMove)))
return true;
}
// Can we skip the ugly special cases ?
if (!is_special(m))
return false;
Color us = sideToMove;
Square ksq = king_square(~us);
// Promotion with check ?
if (is_promotion(m))
return attacks_from(Piece(promotion_type(m)), to, pieces() ^ from) & ksq;
// En passant capture with check ? We have already handled the case
// of direct checks and ordinary discovered check, the only case we
// need to handle is the unusual case of a discovered check through
// the captured pawn.
if (is_enpassant(m))
{
Square capsq = make_square(file_of(to), rank_of(from));
Bitboard b = (pieces() ^ from ^ capsq) | to;
return (attacks_bb< ROOK>(ksq, b) & pieces( ROOK, QUEEN, us))
| (attacks_bb<BISHOP>(ksq, b) & pieces(BISHOP, QUEEN, us));
}
// Castling with check ?
if (is_castle(m))
{
Square kfrom = from;
Square rfrom = to; // 'King captures the rook' notation
Square kto = relative_square(us, rfrom > kfrom ? SQ_G1 : SQ_C1);
Square rto = relative_square(us, rfrom > kfrom ? SQ_F1 : SQ_D1);
Bitboard b = (pieces() ^ kfrom ^ rfrom) | rto | kto;
return attacks_bb<ROOK>(rto, b) & ksq;
}
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) {
CheckInfo ci(*this);
do_move(m, newSt, ci, move_gives_check(m, ci));
}
void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveIsCheck) {
assert(is_ok(m));
assert(&newSt != st);
nodes++;
Key k = st->key;
// Copy some fields of old state to our new StateInfo object except the ones
// which are recalculated from scratch anyway, then switch our state pointer
// to point to the new, ready to be updated, state.
struct ReducedStateInfo {
Key pawnKey, materialKey;
Value npMaterial[2];
int castleRights, rule50, pliesFromNull;
Score psq_score;
Square epSquare;
};
memcpy(&newSt, st, sizeof(ReducedStateInfo));
newSt.previous = st;
st = &newSt;
// Update side to move
k ^= zobSideToMove;
// Increment the 50 moves rule draw counter. Resetting it to zero in the
// case of a capture or a pawn move is taken care of later.
st->rule50++;
st->pliesFromNull++;
if (is_castle(m))
{
st->key = k;
do_castle_move<true>(m);
return;
}
Color us = sideToMove;
Color them = ~us;
Square from = from_sq(m);
Square to = to_sq(m);
Piece piece = piece_on(from);
PieceType pt = type_of(piece);
PieceType capture = is_enpassant(m) ? PAWN : type_of(piece_on(to));
assert(color_of(piece) == us);
assert(color_of(piece_on(to)) != us);
assert(capture != KING);
if (capture)
{
Square capsq = to;
// If the captured piece is a pawn, update pawn hash key, otherwise
// update non-pawn material.
if (capture == PAWN)
{
if (is_enpassant(m))
{
capsq += pawn_push(them);
assert(pt == 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;
}
st->pawnKey ^= zobrist[them][PAWN][capsq];
}
else
st->npMaterial[them] -= PieceValueMidgame[capture];
// Remove the captured piece
byTypeBB[ALL_PIECES] ^= capsq;
byTypeBB[capture] ^= capsq;
byColorBB[them] ^= capsq;
// Update piece list, move the last piece at index[capsq] position and
// shrink the list.
//
// WARNING: This is a not revresible operation. When we will reinsert the
// captured piece in undo_move() we will put it at the end of the list and
// not in its original place, it means index[] and pieceList[] are not
// guaranteed to be invariant to a do_move() + undo_move() sequence.
Square lastSquare = pieceList[them][capture][--pieceCount[them][capture]];
index[lastSquare] = index[capsq];
pieceList[them][capture][index[lastSquare]] = lastSquare;
pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
// Update hash keys
k ^= zobrist[them][capture][capsq];
st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
// Update incremental scores
st->psqScore -= pieceSquareTable[make_piece(them, capture)][capsq];
// Reset rule 50 counter
st->rule50 = 0;
}
// Update hash key
k ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
// Reset en passant square
if (st->epSquare != SQ_NONE)
{
k ^= zobEp[file_of(st->epSquare)];
st->epSquare = SQ_NONE;
}
// Update castle rights if needed
if (st->castleRights && (castleRightsMask[from] | castleRightsMask[to]))
{
int cr = castleRightsMask[from] | castleRightsMask[to];
k ^= zobCastle[st->castleRights & cr];
st->castleRights &= ~cr;
}
// Prefetch TT access as soon as we know key is updated
prefetch((char*)TT.first_entry(k));
// Move the piece
Bitboard from_to_bb = SquareBB[from] | SquareBB[to];
byTypeBB[ALL_PIECES] ^= from_to_bb;
byTypeBB[pt] ^= from_to_bb;
byColorBB[us] ^= from_to_bb;
board[to] = board[from];
board[from] = NO_PIECE;
// Update piece lists, index[from] is not updated and becomes stale. This
// works as long as index[] is accessed just by known occupied squares.
index[to] = index[from];
pieceList[us][pt][index[to]] = to;
// If the moving piece is a pawn do some special extra work
if (pt == PAWN)
{
// Set en-passant square, only if moved pawn can be captured
if ( (int(to) ^ int(from)) == 16
&& (attacks_from<PAWN>(from + pawn_push(us), us) & pieces(PAWN, them)))
{
st->epSquare = Square((from + to) / 2);
k ^= zobEp[file_of(st->epSquare)];
}
if (is_promotion(m))
{
PieceType promotion = promotion_type(m);
assert(relative_rank(us, to) == RANK_8);
assert(promotion >= KNIGHT && promotion <= QUEEN);
// Replace the pawn with the promoted piece
byTypeBB[PAWN] ^= to;
byTypeBB[promotion] |= to;
board[to] = make_piece(us, promotion);
// Update piece lists, move the last pawn at index[to] position
// and shrink the list. Add a new promotion piece to the list.
Square lastSquare = pieceList[us][PAWN][--pieceCount[us][PAWN]];
index[lastSquare] = index[to];
pieceList[us][PAWN][index[lastSquare]] = lastSquare;
pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
index[to] = pieceCount[us][promotion];
pieceList[us][promotion][index[to]] = to;
// Update hash keys
k ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
st->pawnKey ^= zobrist[us][PAWN][to];
st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]++]
^ zobrist[us][PAWN][pieceCount[us][PAWN]];
// Update incremental score
st->psqScore += pieceSquareTable[make_piece(us, promotion)][to]
- pieceSquareTable[make_piece(us, PAWN)][to];
// Update material
st->npMaterial[us] += PieceValueMidgame[promotion];
}
// Update pawn hash key
st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
// Reset rule 50 draw counter
st->rule50 = 0;
}
// Prefetch pawn and material hash tables
prefetch((char*)thisThread->pawnTable.entries[st->pawnKey]);
prefetch((char*)thisThread->materialTable.entries[st->materialKey]);
// Update incremental scores
st->psqScore += psq_delta(piece, from, to);
// Set capture piece
st->capturedType = capture;
// Update the key with the final value
st->key = k;
// Update checkers bitboard, piece must be already moved
st->checkersBB = 0;
if (moveIsCheck)
{
if (is_special(m))
st->checkersBB = attackers_to(king_square(them)) & pieces(us);
else
{
// Direct checks
if (ci.checkSq[pt] & to)
st->checkersBB |= to;
// Discovery checks
if (ci.dcCandidates && (ci.dcCandidates & from))
{
if (pt != ROOK)
st->checkersBB |= attacks_from<ROOK>(king_square(them)) & pieces(ROOK, QUEEN, us);
if (pt != BISHOP)
st->checkersBB |= attacks_from<BISHOP>(king_square(them)) & pieces(BISHOP, QUEEN, us);
}
}
}
// Finish
sideToMove = ~sideToMove;
st->psqScore += (sideToMove == WHITE ? Tempo : -Tempo);
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;
if (is_castle(m))
{
do_castle_move<false>(m);
return;
}
Color us = sideToMove;
Color them = ~us;
Square from = from_sq(m);
Square to = to_sq(m);
Piece piece = piece_on(to);
PieceType pt = type_of(piece);
PieceType capture = st->capturedType;
assert(square_empty(from));
assert(color_of(piece) == us);
assert(capture != KING);
if (is_promotion(m))
{
PieceType promotion = promotion_type(m);
assert(promotion == pt);
assert(relative_rank(us, to) == RANK_8);
assert(promotion >= KNIGHT && promotion <= QUEEN);
// Replace the promoted piece with the pawn
byTypeBB[promotion] ^= to;
byTypeBB[PAWN] |= to;
board[to] = make_piece(us, PAWN);
// Update piece lists, move the last promoted piece at index[to] position
// and shrink the list. Add a new pawn to the list.
Square lastSquare = pieceList[us][promotion][--pieceCount[us][promotion]];
index[lastSquare] = index[to];
pieceList[us][promotion][index[lastSquare]] = lastSquare;
pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
index[to] = pieceCount[us][PAWN]++;
pieceList[us][PAWN][index[to]] = to;
pt = PAWN;
}
// Put the piece back at the source square
Bitboard from_to_bb = SquareBB[from] | SquareBB[to];
byTypeBB[ALL_PIECES] ^= from_to_bb;