/*

Stockfish, a UCI chess playing engine derived from Glaurung 2.1

Copyright (C) 2004-2008 Tord Romstad (Glaurung author)

Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, Tord Romstad

Stockfish is free software: you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation, either version 3 of the License, or

(at your option) any later version.

Stockfish is distributed in the hope that it will be useful,

but WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

GNU General Public License for more details.

You should have received a copy of the GNU General Public License

along with this program. If not, see <http://www.gnu.org/licenses/>.

*/

#include <cassert>

#include <cstring>

#include <iomanip>

#include <iostream>

#include <sstream>

#include <algorithm>

#include "bitcount.h"

#include "movegen.h"

#include "notation.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;

static const string PieceToChar(" PNBRQK pnbrqk");

CACHE_LINE_ALIGNMENT

Score pieceSquareTable[PIECE_NB][SQUARE_NB];

Value PieceValue[PHASE_NB][PIECE_NB] = {

{ VALUE_ZERO, PawnValueMg, KnightValueMg, BishopValueMg, RookValueMg, QueenValueMg },

{ VALUE_ZERO, PawnValueEg, KnightValueEg, BishopValueEg, RookValueEg, QueenValueEg } };

namespace Zobrist {

Key psq[COLOR_NB][PIECE_TYPE_NB][SQUARE_NB];

Key enpassant[FILE_NB];

Key castle[CASTLE_RIGHT_NB];

Key side;

Key exclusion;

/// init() initializes at startup the various arrays used to compute hash keys

/// and the piece square tables. The latter is a two-step operation: First, the

/// white halves of the tables are copied from PSQT[] tables. Second, the black

/// halves of the tables are initialized by flipping and changing the sign of

/// the white scores.

void init() {

RKISS rk;

for (Color c = WHITE; c <= BLACK; c++)

for (PieceType pt = PAWN; pt <= KING; pt++)

for (Square s = SQ_A1; s <= SQ_H8; s++)

psq[c][pt][s] = rk.rand<Key>();

for (File f = FILE_A; f <= FILE_H; f++)

enpassant[f] = rk.rand<Key>();

for (int cr = CASTLES_NONE; cr <= ALL_CASTLES; cr++)

{

Bitboard b = cr;

while (b)

{

Key k = castle[1ULL << pop_lsb(&b)];

castle[cr] ^= k ? k : rk.rand<Key>();

}

}

side = rk.rand<Key>();

exclusion = rk.rand<Key>();

for (PieceType pt = PAWN; pt <= KING; pt++)

{

PieceValue[MG][make_piece(BLACK, pt)] = PieceValue[MG][pt];

PieceValue[EG][make_piece(BLACK, pt)] = PieceValue[EG][pt];

Score v = make_score(PieceValue[MG][pt], PieceValue[EG][pt]);

for (Square s = SQ_A1; s <= SQ_H8; s++)

{

pieceSquareTable[make_piece(WHITE, pt)][ s] = (v + PSQT[pt][s]);

pieceSquareTable[make_piece(BLACK, pt)][~s] = -(v + PSQT[pt][s]);

}

}

}

} // namespace Zobrist

namespace {

/// next_attacker() is an helper function used by see() to locate the least

/// valuable attacker for the side to move, remove the attacker we just found

/// from the 'occupied' bitboard and scan for new X-ray attacks behind it.

template<int Pt> FORCE_INLINE

PieceType next_attacker(const Bitboard* bb, const Square& to, const Bitboard& stmAttackers,

Bitboard& occupied, Bitboard& attackers) {

if (stmAttackers & bb[Pt])

{

Bitboard b = stmAttackers & bb[Pt];

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]);

return (PieceType)Pt;

}

return next_attacker<Pt+1>(bb, to, stmAttackers, occupied, attackers);

}

template<> FORCE_INLINE

PieceType next_attacker<KING>(const Bitboard*, const Square&, const Bitboard&, Bitboard&, Bitboard&) {

return KING; // No need to update bitboards, it is the last cycle

}

} // namespace

/// 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::operator=() 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.

Position& Position::operator=(const Position& pos) {

memcpy(this, &pos, sizeof(Position));

startState = *st;

st = &startState;

nodes = 0;

assert(pos_is_ok());

return *this;

}

/// 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.

void Position::set(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 ss(fenStr);

clear();

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 ((p = PieceToChar.find(token)) != string::npos)

{

put_piece(Piece(p), 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;

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 = 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 ( ((ss >> col) && (col >= 'a' && col <= 'h'))

&& ((ss >> row) && (row == '3' || row == '6')))

{

st->epSquare = File(col - 'a') | Rank(row - '1');

if (!(attackers_to(st->epSquare) & pieces(sideToMove, PAWN)))

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) + 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);

CastlingSide cs = kfrom < rfrom ? KING_SIDE : QUEEN_SIDE;

CastleRight cr = make_castle_right(c, cs);

st->castleRights |= cr;

castleRightsMask[kfrom] |= cr;

castleRightsMask[rfrom] |= cr;

castleRookSquare[c][cs] = 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)

castlePath[c][cs] |= s;

for (Square s = std::min(kfrom, kto); s <= std::max(kfrom, kto); s++)

if (s != kfrom && s != rfrom)

castlePath[c][cs] |= s;

}

/// Position::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::fen() const {

std::ostringstream ss;

for (Rank rank = RANK_8; rank >= RANK_1; rank--)

{

for (File file = FILE_A; file <= FILE_H; file++)

{

Square sq = file | rank;

if (is_empty(sq))

{

int emptyCnt = 1;

for ( ; file < FILE_H && is_empty(sq++); file++)

emptyCnt++;

ss << emptyCnt;

}

else

ss << PieceToChar[piece_on(sq)];

}

if (rank > RANK_1)

ss << '/';

}

ss << (sideToMove == WHITE ? " w " : " b ");

if (can_castle(WHITE_OO))

ss << (chess960 ? file_to_char(file_of(castle_rook_square(WHITE, KING_SIDE)), false) : 'K');

if (can_castle(WHITE_OOO))

ss << (chess960 ? file_to_char(file_of(castle_rook_square(WHITE, QUEEN_SIDE)), false) : 'Q');

if (can_castle(BLACK_OO))

ss << (chess960 ? file_to_char(file_of(castle_rook_square(BLACK, KING_SIDE)), true) : 'k');

if (can_castle(BLACK_OOO))

ss << (chess960 ? file_to_char(file_of(castle_rook_square(BLACK, QUEEN_SIDE)), true) : 'q');

if (st->castleRights == CASTLES_NONE)

ss << '-';

ss << (ep_square() == SQ_NONE ? " - " : " " + square_to_string(ep_square()) + " ")

<< st->rule50 << " " << 1 + (gamePly - int(sideToMove == BLACK)) / 2;

return ss.str();

}

/// Position::pretty() returns an ASCII representation of the position to be

/// printed to the standard output together with the move's san notation.

const string Position::pretty(Move move) const {

const string dottedLine = "\n+---+---+---+---+---+---+---+---+";

const string twoRows = dottedLine + "\n| | . | | . | | . | | . |"

+ dottedLine + "\n| . | | . | | . | | . | |";

string brd = twoRows + twoRows + twoRows + twoRows + dottedLine;

std::ostringstream ss;

if (move)

ss << "\nMove: " << (sideToMove == BLACK ? ".." : "")

<< move_to_san(*const_cast<Position*>(this), move);

for (Square sq = SQ_A1; sq <= SQ_H8; sq++)

if (piece_on(sq) != NO_PIECE)

brd[513 - 68*rank_of(sq) + 4*file_of(sq)] = PieceToChar[piece_on(sq)];

ss << brd << "\nFen: " << fen() << "\nKey: " << std::hex << std::uppercase

<< std::setfill('0') << std::setw(16) << st->key << "\nCheckers: ";

for (Bitboard b = checkers(); b; )

ss << square_to_string(pop_lsb(&b)) << " ";

ss << "\nLegal moves: ";

for (MoveList<LEGAL> ml(*this); !ml.end(); ++ml)

ss << move_to_san(*const_cast<Position*>(this), ml.move()) << " ";

return ss.str();

}

/// 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 = between_bb(ksq, pop_lsb(&pinners)) & pieces();

if (b && !more_than_one(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(WHITE, PAWN))

| (attacks_from<PAWN>(s, WHITE) & pieces(BLACK, PAWN))

| (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::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 (type_of(m) == ENPASSANT)

{

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(them, QUEEN, ROOK))

&& !(attacks_bb<BISHOP>(ksq, b) & pieces(them, 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) == CASTLE || !(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::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;

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 (type_of(m) != NORMAL)

return MoveList<LEGAL>(*this).contains(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 (piece_on(to) != NO_PIECE && 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 (piece_on(to) == NO_PIECE || color_of(piece_on(to)) != ~us)

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 (!is_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

|| !is_empty(to)

|| !is_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

|| !is_empty(to)

|| !is_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 (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()), 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 (type_of(m) == NORMAL)

return false;

Color us = sideToMove;

Square ksq = king_square(~us);

switch (type_of(m))

{

case PROMOTION:

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.

case ENPASSANT:

{

Square capsq = file_of(to) | rank_of(from);

Bitboard b = (pieces() ^ from ^ capsq) | to;

return (attacks_bb< ROOK>(ksq, b) & pieces(us, QUEEN, ROOK))

| (attacks_bb<BISHOP>(ksq, b) & pieces(us, QUEEN, BISHOP));

}

case CASTLE:

{

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;

}

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) {

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 going to be recalculated from scratch anyway, then switch our state

// pointer to point to the new, ready to be updated, state.

memcpy(&newSt, st, StateCopySize64 * sizeof(uint64_t));

newSt.previous = st;

st = &newSt;

// Update side to move

k ^= Zobrist::side;

// Increment ply counters.In particular rule50 will be later reset it to zero

// 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 piece = piece_on(from);

PieceType pt = type_of(piece);

PieceType capture = type_of(m) == ENPASSANT ? PAWN : type_of(piece_on(to));

assert(color_of(piece) == us);

assert(piece_on(to) == NO_PIECE || color_of(piece_on(to)) == them || type_of(m) == CASTLE);

assert(capture != KING);

if (type_of(m) == CASTLE)

{

assert(piece == make_piece(us, KING));

bool kingSide = to > from;

Square rfrom = to; // Castle is encoded as "king captures friendly rook"

Square rto = relative_square(us, kingSide ? SQ_F1 : SQ_D1);

to = relative_square(us, kingSide ? SQ_G1 : SQ_C1);

capture = NO_PIECE_TYPE;

do_castle(from, to, rfrom, rto);

st->psqScore += psq_delta(make_piece(us, ROOK), rfrom, rto);

k ^= Zobrist::psq[us][ROOK][rfrom] ^ Zobrist::psq[us][ROOK][rto];

}

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 (type_of(m) == ENPASSANT)

{

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::psq[them][PAWN][capsq];

}

else

st->npMaterial[them] -= PieceValue[MG][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 reversible 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 material hash key and prefetch access to materialTable

k ^= Zobrist::psq[them][capture][capsq];

st->materialKey ^= Zobrist::psq[them][capture][pieceCount[them][capture]];

prefetch((char*)thisThread->materialTable[st->materialKey]);

// Update incremental scores

st->psqScore -= pieceSquareTable[make_piece(them, capture)][capsq];

// Reset rule 50 counter

st->rule50 = 0;

}

// Update hash key

k ^= Zobrist::psq[us][pt][from] ^ Zobrist::psq[us][pt][to];

// Reset en passant square

if (st->epSquare != SQ_NONE)

{

k ^= Zobrist::enpassant[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 ^= Zobrist::castle[st->castleRights & cr];

st->castleRights &= ~cr;

}

// Prefetch TT access as soon as we know the new hash key

prefetch((char*)TT.first_entry(k));

// Move the piece. The tricky Chess960 castle is handled earlier

if (type_of(m) != CASTLE)

{

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[from] = NO_PIECE;

board[to] = 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(them, PAWN)))

{

st->epSquare = Square((from + to) / 2);

k ^= Zobrist::enpassant[file_of(st->epSquare)];

}

if (type_of(m) == PROMOTION)

{

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::psq[us][PAWN][to] ^ Zobrist::psq[us][promotion][to];

st->pawnKey ^= Zobrist::psq[us][PAWN][to];

st->materialKey ^= Zobrist::psq[us][promotion][pieceCount[us][promotion]++]

^ Zobrist::psq[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] += PieceValue[MG][promotion];

}

// Update pawn hash key and prefetch access to pawnsTable

st->pawnKey ^= Zobrist::psq[us][PAWN][from] ^ Zobrist::psq[us][PAWN][to];

prefetch((char*)thisThread->pawnsTable[st->pawnKey]);

// Reset rule 50 draw counter

st->rule50 = 0;

}

// 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 (type_of(m) != NORMAL)

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(us, QUEEN, ROOK);

if (pt != BISHOP)

st->checkersBB |= attacks_from<BISHOP>(king_square(them)) & pieces(us, QUEEN, BISHOP);

}

}

}

sideToMove = ~sideToMove;

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;

Color them = ~us;

Square from = from_sq(m);

Square to = to_sq(m);

PieceType pt = type_of(piece_on(to));

PieceType capture = st->capturedType;

assert(is_empty(from) || type_of(m) == CASTLE);

assert(capture != KING);

if (type_of(m) == PROMOTION)

{

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;