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droidfish/DroidFish/jni/stockfish/position.cpp
Peter Osterlund 252789e186 Moved DroidFish project to trunk/
2011-11-12 19:44:06 +00:00

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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) 2008-2010 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 <fstream>
#include <map>
#include <iostream>
#include <sstream>
#include "bitcount.h"
#include "movegen.h"
#include "position.h"
#include "psqtab.h"
#include "rkiss.h"
#include "thread.h"
#include "tt.h"
#include "ucioption.h"
using std::string;
using std::cout;
using std::endl;
Key Position::zobrist[2][8][64];
Key Position::zobEp[64];
Key Position::zobCastle[16];
Key Position::zobSideToMove;
Key Position::zobExclusion;
Score Position::PieceSquareTable[16][64];
// Material values arrays, indexed by Piece
const Value Position::PieceValueMidgame[17] = {
VALUE_ZERO,
PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
RookValueMidgame, QueenValueMidgame, VALUE_ZERO,
VALUE_ZERO, VALUE_ZERO,
PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
RookValueMidgame, QueenValueMidgame
};
const Value Position::PieceValueEndgame[17] = {
VALUE_ZERO,
PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
RookValueEndgame, QueenValueEndgame, VALUE_ZERO,
VALUE_ZERO, VALUE_ZERO,
PawnValueEndgame, KnightValueEndgame, BishopValueEndgame,
RookValueEndgame, QueenValueEndgame
};
// Material values array used by SEE, indexed by PieceType
const Value Position::seeValues[] = {
VALUE_ZERO,
PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10
};
namespace {
// Bonus for having the side to move (modified by Joona Kiiski)
const Score TempoValue = make_score(48, 22);
struct PieceLetters : public std::map<char, Piece> {
PieceLetters() {
operator[]('K') = WK; operator[]('k') = BK;
operator[]('Q') = WQ; operator[]('q') = BQ;
operator[]('R') = WR; operator[]('r') = BR;
operator[]('B') = WB; operator[]('b') = BB;
operator[]('N') = WN; operator[]('n') = BN;
operator[]('P') = WP; operator[]('p') = BP;
operator[](' ') = PIECE_NONE;
operator[]('.') = PIECE_NONE_DARK_SQ;
}
char from_piece(Piece p) const {
std::map<char, Piece>::const_iterator it;
for (it = begin(); it != end(); ++it)
if (it->second == p)
return it->first;
assert(false);
return 0;
}
};
PieceLetters pieceLetters;
}
/// CheckInfo c'tor
CheckInfo::CheckInfo(const Position& pos) {
Color us = pos.side_to_move();
Color them = opposite_color(us);
ksq = pos.king_square(them);
dcCandidates = pos.discovered_check_candidates(us);
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] = EmptyBoardBB;
}
/// Position c'tors. Here we always create a copy of the original position
/// or the FEN string, 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(const Position& pos, int th) {
memcpy(this, &pos, sizeof(Position));
detach(); // Always detach() in copy c'tor to avoid surprises
threadID = th;
nodes = 0;
}
Position::Position(const string& fen, bool isChess960, int th) {
from_fen(fen, isChess960);
threadID = th;
}
/// Position::detach() copies the content of the current state and castling
/// masks inside the position itself. This is needed when the st pointee could
/// become stale, as example because the caller is about to going out of scope.
void Position::detach() {
startState = *st;
st = &startState;
st->previous = NULL; // as a safe guard
}
/// 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& fen, bool isChess960) {
/*
A FEN string defines a particular position using only the ASCII character set.
A FEN string contains six fields. The separator between fields is 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 "/" separate 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 token;
int hmc, fmn;
std::istringstream ss(fen);
Square sq = SQ_A8;
clear();
// 1. Piece placement field
while (ss.get(token) && token != ' ')
{
if (pieceLetters.find(token) != pieceLetters.end())
{
put_piece(pieceLetters[token], sq);
sq++;
}
else if (isdigit(token))
sq += Square(token - '0'); // Skip the given number of files
else if (token == '/')
sq -= SQ_A3; // Jump back of 2 rows
else
goto incorrect_fen;
}
// 2. Active color
if (!ss.get(token) || (token != 'w' && token != 'b'))
goto incorrect_fen;
sideToMove = (token == 'w' ? WHITE : BLACK);
if (!ss.get(token) || token != ' ')
goto incorrect_fen;
// 3. Castling availability
while (ss.get(token) && token != ' ')
if (!set_castling_rights(token))
goto incorrect_fen;
// 4. En passant square
char col, row;
if ( (ss.get(col) && (col >= 'a' && col <= 'h'))
&& (ss.get(row) && (row == '3' || row == '6')))
{
st->epSquare = make_square(file_from_char(col), rank_from_char(row));
// Ignore if no capture is possible
Color them = opposite_color(sideToMove);
if (!(attacks_from<PAWN>(st->epSquare, them) & pieces(PAWN, sideToMove)))
st->epSquare = SQ_NONE;
}
// 5. Halfmove clock
if (ss >> hmc)
st->rule50 = hmc;
// 6. Fullmove number
if (ss >> fmn)
startPosPlyCounter = (fmn - 1) * 2 + int(sideToMove == BLACK);
// Various initialisations
castleRightsMask[make_square(initialKFile, RANK_1)] ^= WHITE_OO | WHITE_OOO;
castleRightsMask[make_square(initialKFile, RANK_8)] ^= BLACK_OO | BLACK_OOO;
castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
chess960 = isChess960;
find_checkers();
st->key = compute_key();
st->pawnKey = compute_pawn_key();
st->materialKey = compute_material_key();
st->value = compute_value();
st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
return;
incorrect_fen:
cout << "Error in FEN string: " << fen << endl;
}
/// Position::set_castling_rights() sets castling parameters castling avaiability.
/// This function is 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 traditional castling tag will be replaced
/// by the file letter of the involved rook as for the Shredder-FEN.
bool Position::set_castling_rights(char token) {
Color c = token >= 'a' ? BLACK : WHITE;
Square sqA = (c == WHITE ? SQ_A1 : SQ_A8);
Square sqH = (c == WHITE ? SQ_H1 : SQ_H8);
Piece rook = (c == WHITE ? WR : BR);
initialKFile = square_file(king_square(c));
token = char(toupper(token));
if (token == 'K')
{
for (Square sq = sqH; sq >= sqA; sq--)
if (piece_on(sq) == rook)
{
do_allow_oo(c);
initialKRFile = square_file(sq);
break;
}
}
else if (token == 'Q')
{
for (Square sq = sqA; sq <= sqH; sq++)
if (piece_on(sq) == rook)
{
do_allow_ooo(c);
initialQRFile = square_file(sq);
break;
}
}
else if (token >= 'A' && token <= 'H')
{
File rookFile = File(token - 'A') + FILE_A;
if (rookFile < initialKFile)
{
do_allow_ooo(c);
initialQRFile = rookFile;
}
else
{
do_allow_oo(c);
initialKRFile = rookFile;
}
}
else
return token == '-';
return true;
}
/// 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 {
string fen;
Square sq;
char emptyCnt = '0';
for (Rank rank = RANK_8; rank >= RANK_1; rank--, fen += '/')
{
for (File file = FILE_A; file <= FILE_H; file++)
{
sq = make_square(file, rank);
if (square_is_occupied(sq))
{
if (emptyCnt != '0')
{
fen += emptyCnt;
emptyCnt = '0';
}
fen += pieceLetters.from_piece(piece_on(sq));
} else
emptyCnt++;
}
if (emptyCnt != '0')
{
fen += emptyCnt;
emptyCnt = '0';
}
}
fen += (sideToMove == WHITE ? " w " : " b ");
if (st->castleRights != CASTLES_NONE)
{
if (can_castle_kingside(WHITE))
fen += chess960 ? char(toupper(file_to_char(initialKRFile))) : 'K';
if (can_castle_queenside(WHITE))
fen += chess960 ? char(toupper(file_to_char(initialQRFile))) : 'Q';
if (can_castle_kingside(BLACK))
fen += chess960 ? file_to_char(initialKRFile) : 'k';
if (can_castle_queenside(BLACK))
fen += chess960 ? file_to_char(initialQRFile) : 'q';
} else
fen += '-';
fen += (ep_square() == SQ_NONE ? " -" : " " + square_to_string(ep_square()));
return fen;
}
/// 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, thread());
string dd = (color_of_piece_on(move_from(move)) == BLACK ? ".." : "");
cout << "\nMove is: " << dd << 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);
if (piece == PIECE_NONE && square_color(sq) == DARK)
piece = PIECE_NONE_DARK_SQ;
char c = (color_of_piece_on(sq) == BLACK ? '=' : ' ');
cout << c << pieceLetters.from_piece(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 and for the given pinner type. Or, when
/// template parameter FindPinned is false, the pieces of the given color
/// candidate for a discovery check against the enemy king.
/// Bitboard checkersBB must be already updated when looking for pinners.
template<bool FindPinned>
Bitboard Position::hidden_checkers(Color c) const {
Bitboard result = EmptyBoardBB;
Bitboard pinners = pieces_of_color(FindPinned ? opposite_color(c) : c);
// Pinned pieces protect our king, dicovery checks attack
// the enemy king.
Square ksq = king_square(FindPinned ? c : opposite_color(c));
// Pinners are sliders, not checkers, that give check when candidate pinned is removed
pinners &= (pieces(ROOK, QUEEN) & RookPseudoAttacks[ksq]) | (pieces(BISHOP, QUEEN) & BishopPseudoAttacks[ksq]);
if (FindPinned && pinners)
pinners &= ~st->checkersBB;
while (pinners)
{
Square s = pop_1st_bit(&pinners);
Bitboard b = squares_between(s, ksq) & occupied_squares();
assert(b);
if ( !(b & (b - 1)) // Only one bit set?
&& (b & pieces_of_color(c))) // Is an our piece?
result |= b;
}
return result;
}
/// Position:pinned_pieces() returns a bitboard of all pinned (against the
/// king) pieces for the given color. Note that checkersBB bitboard must
/// be already updated.
Bitboard Position::pinned_pieces(Color c) const {
return hidden_checkers<true>(c);
}
/// Position:discovered_check_candidates() returns a bitboard containing all
/// pieces for the given side which are candidates for giving a discovered
/// check. Contrary to pinned_pieces() here there is no need of checkersBB
/// to be already updated.
Bitboard Position::discovered_check_candidates(Color c) const {
return hidden_checkers<false>(c);
}
/// Position::attackers_to() computes a bitboard containing all pieces which
/// attacks a given square.
Bitboard Position::attackers_to(Square s) 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_from<ROOK>(s) & pieces(ROOK, QUEEN))
| (attacks_from<BISHOP>(s) & 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.
Bitboard Position::attacks_from(Piece p, Square s) const {
assert(square_is_ok(s));
switch (p)
{
case WB: case BB: return attacks_from<BISHOP>(s);
case WR: case BR: return attacks_from<ROOK>(s);
case WQ: case BQ: return attacks_from<QUEEN>(s);
default: return StepAttacksBB[p][s];
}
}
Bitboard Position::attacks_from(Piece p, Square s, Bitboard occ) {
assert(square_is_ok(s));
switch (p)
{
case WB: case BB: return bishop_attacks_bb(s, occ);
case WR: case BR: return rook_attacks_bb(s, occ);
case WQ: case BQ: return bishop_attacks_bb(s, occ) | rook_attacks_bb(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(move_is_ok(m));
assert(square_is_ok(s));
Bitboard occ, xray;
Square f = move_from(m), t = move_to(m);
assert(square_is_occupied(f));
if (bit_is_set(attacks_from(piece_on(f), t), s))
return true;
// Move the piece and scan for X-ray attacks behind it
occ = occupied_squares();
do_move_bb(&occ, make_move_bb(f, t));
xray = ( (rook_attacks_bb(s, occ) & pieces(ROOK, QUEEN))
|(bishop_attacks_bb(s, occ) & pieces(BISHOP, QUEEN)))
& pieces_of_color(color_of_piece_on(f));
// If we have attacks we need to verify that are caused by our move
// and are not already existent ones.
return xray && (xray ^ (xray & attacks_from<QUEEN>(s)));
}
/// Position::find_checkers() computes the checkersBB bitboard, which
/// contains a nonzero bit for each checking piece (0, 1 or 2). It
/// currently works by calling Position::attackers_to, which is probably
/// inefficient. Consider rewriting this function to use the last move
/// played, like in non-bitboard versions of Glaurung.
void Position::find_checkers() {
Color us = side_to_move();
st->checkersBB = attackers_to(king_square(us)) & pieces_of_color(opposite_color(us));
}
/// 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());
assert(move_is_ok(m));
assert(pinned == pinned_pieces(side_to_move()));
// Castling moves are checked for legality during move generation.
if (move_is_castle(m))
return true;
// 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 (move_is_ep(m))
{
Color us = side_to_move();
Color them = opposite_color(us);
Square from = move_from(m);
Square to = move_to(m);
Square capsq = make_square(square_file(to), square_rank(from));
Square ksq = king_square(us);
Bitboard b = occupied_squares();
assert(to == ep_square());
assert(piece_on(from) == make_piece(us, PAWN));
assert(piece_on(capsq) == make_piece(them, PAWN));
assert(piece_on(to) == PIECE_NONE);
clear_bit(&b, from);
clear_bit(&b, capsq);
set_bit(&b, to);
return !(rook_attacks_bb(ksq, b) & pieces(ROOK, QUEEN, them))
&& !(bishop_attacks_bb(ksq, b) & pieces(BISHOP, QUEEN, them));
}
Color us = side_to_move();
Square from = move_from(m);
assert(color_of_piece_on(from) == us);
assert(piece_on(king_square(us)) == make_piece(us, KING));
// 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(move_to(m)) & pieces_of_color(opposite_color(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
|| !bit_is_set(pinned, from)
|| squares_aligned(from, move_to(m), king_square(us));
}
/// Position::pl_move_is_evasion() tests whether a pseudo-legal move is a legal evasion
bool Position::pl_move_is_evasion(Move m, Bitboard pinned) const
{
assert(in_check());
Color us = side_to_move();
Square from = move_from(m);
Square to = move_to(m);
// King moves and en-passant captures are verified in pl_move_is_legal()
if (type_of_piece_on(from) == KING || move_is_ep(m))
return pl_move_is_legal(m, pinned);
Bitboard target = checkers();
Square checksq = pop_1st_bit(&target);
if (target) // double check ?
return false;
// Our move must be a blocking evasion or a capture of the checking piece
target = squares_between(checksq, king_square(us)) | checkers();
return bit_is_set(target, to) && pl_move_is_legal(m, pinned);
}
/// Position::move_is_legal() takes a position and a (not necessarily pseudo-legal)
/// 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 {
MoveStack mlist[MAX_MOVES];
MoveStack *cur, *last = generate<MV_PSEUDO_LEGAL>(*this, mlist);
for (cur = mlist; cur != last; cur++)
if (cur->move == m)
return pl_move_is_legal(m, pinned_pieces(sideToMove));
return false;
}
/// Fast version of Position::move_is_legal() that takes a position a move and
/// a bitboard of pinned pieces as input, and tests whether the move is legal.
bool Position::move_is_legal(const Move m, Bitboard pinned) const {
assert(is_ok());
assert(pinned == pinned_pieces(sideToMove));
Color us = sideToMove;
Color them = opposite_color(sideToMove);
Square from = move_from(m);
Square to = move_to(m);
Piece pc = piece_on(from);
// Use a slower but simpler function for uncommon cases
if (move_is_special(m))
return move_is_legal(m);
// If the from square is not occupied by a piece belonging to the side to
// move, the move is obviously not legal.
if (color_of_piece(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_piece(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 (square_rank(to) == RANK_8 || square_rank(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;
break;
case DELTA_N:
case DELTA_S:
// Pawn push. The destination square must be empty.
if (!square_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 ( square_rank(to) != RANK_4
|| !square_is_empty(to)
|| !square_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 ( square_rank(to) != RANK_5
|| !square_is_empty(to)
|| !square_is_empty(from + DELTA_S))
return false;
break;
default:
return false;
}
}
else if (!bit_is_set(attacks_from(pc, from), to))
return false;
// The move is pseudo-legal, check if it is also legal
return in_check() ? pl_move_is_evasion(m, pinned) : pl_move_is_legal(m, pinned);
}
/// Position::move_gives_check() tests whether a pseudo-legal move is a check
bool Position::move_gives_check(Move m) const {
return move_gives_check(m, CheckInfo(*this));
}
bool Position::move_gives_check(Move m, const CheckInfo& ci) const {
assert(is_ok());
assert(move_is_ok(m));
assert(ci.dcCandidates == discovered_check_candidates(side_to_move()));
assert(color_of_piece_on(move_from(m)) == side_to_move());
assert(piece_on(ci.ksq) == make_piece(opposite_color(side_to_move()), KING));
Square from = move_from(m);
Square to = move_to(m);
PieceType pt = type_of_piece_on(from);
// Direct check ?
if (bit_is_set(ci.checkSq[pt], to))
return true;
// Discovery check ?
if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
{
// For pawn and king moves we need to verify also direction
if ( (pt != PAWN && pt != KING)
|| !squares_aligned(from, to, ci.ksq))
return true;
}
// Can we skip the ugly special cases ?
if (!move_is_special(m))
return false;
Color us = side_to_move();
Bitboard b = occupied_squares();
// Promotion with check ?
if (move_is_promotion(m))
{
clear_bit(&b, from);
switch (move_promotion_piece(m))
{
case KNIGHT:
return bit_is_set(attacks_from<KNIGHT>(to), ci.ksq);
case BISHOP:
return bit_is_set(bishop_attacks_bb(to, b), ci.ksq);
case ROOK:
return bit_is_set(rook_attacks_bb(to, b), ci.ksq);
case QUEEN:
return bit_is_set(queen_attacks_bb(to, b), ci.ksq);
default:
assert(false);
}
}
// 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 (move_is_ep(m))
{
Square capsq = make_square(square_file(to), square_rank(from));
clear_bit(&b, from);
clear_bit(&b, capsq);
set_bit(&b, to);
return (rook_attacks_bb(ci.ksq, b) & pieces(ROOK, QUEEN, us))
||(bishop_attacks_bb(ci.ksq, b) & pieces(BISHOP, QUEEN, us));
}
// Castling with check ?
if (move_is_castle(m))
{
Square kfrom, kto, rfrom, rto;
kfrom = from;
rfrom = to;
if (rfrom > kfrom)
{
kto = relative_square(us, SQ_G1);
rto = relative_square(us, SQ_F1);
} else {
kto = relative_square(us, SQ_C1);
rto = relative_square(us, SQ_D1);
}
clear_bit(&b, kfrom);
clear_bit(&b, rfrom);
set_bit(&b, rto);
set_bit(&b, kto);
return bit_is_set(rook_attacks_bb(rto, b), ci.ksq);
}
return false;
}
/// Position::do_setup_move() makes a permanent move on the board. It should
/// be used when setting up a position on board. You can't undo the move.
void Position::do_setup_move(Move m) {
StateInfo newSt;
do_move(m, newSt);
// Reset "game ply" in case we made a non-reversible move.
// "game ply" is used for repetition detection.
if (st->rule50 == 0)
st->gamePly = 0;
// Update the number of plies played from the starting position
startPosPlyCounter++;
// Our StateInfo newSt is about going out of scope so copy
// its content before it disappears.
detach();
}
/// 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());
assert(move_is_ok(m));
assert(&newSt != st);
nodes++;
Key key = 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;
int castleRights, rule50, gamePly, pliesFromNull;
Square epSquare;
Score value;
Value npMaterial[2];
};
memcpy(&newSt, st, sizeof(ReducedStateInfo));
newSt.previous = st;
st = &newSt;
// Save the current key to the history[] array, in order to be able to
// detect repetition draws.
history[st->gamePly++] = key;
// Update side to move
key ^= zobSideToMove;
// Increment the 50 moves rule draw counter. Resetting it to zero in the
// case of non-reversible moves is taken care of later.
st->rule50++;
st->pliesFromNull++;
if (move_is_castle(m))
{
st->key = key;
do_castle_move(m);
return;
}
Color us = side_to_move();
Color them = opposite_color(us);
Square from = move_from(m);
Square to = move_to(m);
bool ep = move_is_ep(m);
bool pm = move_is_promotion(m);
Piece piece = piece_on(from);
PieceType pt = type_of_piece(piece);
PieceType capture = ep ? PAWN : type_of_piece_on(to);
assert(color_of_piece_on(from) == us);
assert(color_of_piece_on(to) == them || square_is_empty(to));
assert(!(ep || pm) || piece == make_piece(us, PAWN));
assert(!pm || relative_rank(us, to) == RANK_8);
if (capture)
do_capture_move(key, capture, them, to, ep);
// Update hash key
key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
// Reset en passant square
if (st->epSquare != SQ_NONE)
{
key ^= zobEp[st->epSquare];
st->epSquare = SQ_NONE;
}
// Update castle rights, try to shortcut a common case
int cm = castleRightsMask[from] & castleRightsMask[to];
if (cm != ALL_CASTLES && ((cm & st->castleRights) != st->castleRights))
{
key ^= zobCastle[st->castleRights];
st->castleRights &= castleRightsMask[from];
st->castleRights &= castleRightsMask[to];
key ^= zobCastle[st->castleRights];
}
// Prefetch TT access as soon as we know key is updated
prefetch((char*)TT.first_entry(key));
// Move the piece
Bitboard move_bb = make_move_bb(from, to);
do_move_bb(&(byColorBB[us]), move_bb);
do_move_bb(&(byTypeBB[pt]), move_bb);
do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
board[to] = board[from];
board[from] = PIECE_NONE;
// Update piece lists, note that 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 was a pawn do some special extra work
if (pt == PAWN)
{
// Reset rule 50 draw counter
st->rule50 = 0;
// Update pawn hash key and prefetch in L1/L2 cache
st->pawnKey ^= zobrist[us][PAWN][from] ^ zobrist[us][PAWN][to];
// Set en passant square, only if moved pawn can be captured
if ((to ^ from) == 16)
{
if (attacks_from<PAWN>(from + (us == WHITE ? DELTA_N : DELTA_S), us) & pieces(PAWN, them))
{
st->epSquare = Square((int(from) + int(to)) / 2);
key ^= zobEp[st->epSquare];
}
}
if (pm) // promotion ?
{
PieceType promotion = move_promotion_piece(m);
assert(promotion >= KNIGHT && promotion <= QUEEN);
// Insert promoted piece instead of pawn
clear_bit(&(byTypeBB[PAWN]), to);
set_bit(&(byTypeBB[promotion]), to);
board[to] = make_piece(us, promotion);
// Update piece counts
pieceCount[us][promotion]++;
pieceCount[us][PAWN]--;
// Update material key
st->materialKey ^= zobrist[us][PAWN][pieceCount[us][PAWN]];
st->materialKey ^= zobrist[us][promotion][pieceCount[us][promotion]-1];
// Update piece lists, move the last pawn at index[to] position
// and shrink the list. Add a new promotion piece to the list.
Square lastPawnSquare = pieceList[us][PAWN][pieceCount[us][PAWN]];
index[lastPawnSquare] = index[to];
pieceList[us][PAWN][index[lastPawnSquare]] = lastPawnSquare;
pieceList[us][PAWN][pieceCount[us][PAWN]] = SQ_NONE;
index[to] = pieceCount[us][promotion] - 1;
pieceList[us][promotion][index[to]] = to;
// Partially revert hash keys update
key ^= zobrist[us][PAWN][to] ^ zobrist[us][promotion][to];
st->pawnKey ^= zobrist[us][PAWN][to];
// Partially revert and update incremental scores
st->value -= pst(us, PAWN, to);
st->value += pst(us, promotion, to);
// Update material
st->npMaterial[us] += PieceValueMidgame[promotion];
}
}
// Prefetch pawn and material hash tables
Threads[threadID].pawnTable.prefetch(st->pawnKey);
Threads[threadID].materialTable.prefetch(st->materialKey);
// Update incremental scores
st->value += pst_delta(piece, from, to);
// Set capture piece
st->capturedType = capture;
// Update the key with the final value
st->key = key;
// Update checkers bitboard, piece must be already moved
st->checkersBB = EmptyBoardBB;
if (moveIsCheck)
{
if (ep | pm)
st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
else
{
// Direct checks
if (bit_is_set(ci.checkSq[pt], to))
st->checkersBB = SetMaskBB[to];
// Discovery checks
if (ci.dcCandidates && bit_is_set(ci.dcCandidates, from))
{
if (pt != ROOK)
st->checkersBB |= (attacks_from<ROOK>(ci.ksq) & pieces(ROOK, QUEEN, us));
if (pt != BISHOP)
st->checkersBB |= (attacks_from<BISHOP>(ci.ksq) & pieces(BISHOP, QUEEN, us));
}
}
}
// Finish
sideToMove = opposite_color(sideToMove);
st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
assert(is_ok());
}
/// Position::do_capture_move() is a private method used to update captured
/// piece info. It is called from the main Position::do_move function.
void Position::do_capture_move(Key& key, PieceType capture, Color them, Square to, bool ep) {
assert(capture != KING);
Square capsq = to;
// If the captured piece was a pawn, update pawn hash key,
// otherwise update non-pawn material.
if (capture == PAWN)
{
if (ep) // en passant ?
{
capsq = (them == BLACK)? (to - DELTA_N) : (to - DELTA_S);
assert(to == st->epSquare);
assert(relative_rank(opposite_color(them), to) == RANK_6);
assert(piece_on(to) == PIECE_NONE);
assert(piece_on(capsq) == make_piece(them, PAWN));
board[capsq] = PIECE_NONE;
}
st->pawnKey ^= zobrist[them][PAWN][capsq];
}
else
st->npMaterial[them] -= PieceValueMidgame[capture];
// Remove captured piece
clear_bit(&(byColorBB[them]), capsq);
clear_bit(&(byTypeBB[capture]), capsq);
clear_bit(&(byTypeBB[0]), capsq);
// Update hash key
key ^= zobrist[them][capture][capsq];
// Update incremental scores
st->value -= pst(them, capture, capsq);
// Update piece count
pieceCount[them][capture]--;
// Update material hash key
st->materialKey ^= zobrist[them][capture][pieceCount[them][capture]];
// Update piece list, move the last piece at index[capsq] position
//
// WARNING: This is a not perfectly 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 lastPieceSquare = pieceList[them][capture][pieceCount[them][capture]];
index[lastPieceSquare] = index[capsq];
pieceList[them][capture][index[lastPieceSquare]] = lastPieceSquare;
pieceList[them][capture][pieceCount[them][capture]] = SQ_NONE;
// Reset rule 50 counter
st->rule50 = 0;
}
/// Position::do_castle_move() is a private method used to make a castling
/// move. It is called from the main Position::do_move function. Note that
/// castling moves are encoded as "king captures friendly rook" moves, for
/// instance white short castling in a non-Chess960 game is encoded as e1h1.
void Position::do_castle_move(Move m) {
assert(move_is_ok(m));
assert(move_is_castle(m));
Color us = side_to_move();
Color them = opposite_color(us);
// Reset capture field
st->capturedType = PIECE_TYPE_NONE;
// Find source squares for king and rook
Square kfrom = move_from(m);
Square rfrom = move_to(m); // HACK: See comment at beginning of function
Square kto, rto;
assert(piece_on(kfrom) == make_piece(us, KING));
assert(piece_on(rfrom) == make_piece(us, ROOK));
// Find destination squares for king and rook
if (rfrom > kfrom) // O-O
{
kto = relative_square(us, SQ_G1);
rto = relative_square(us, SQ_F1);
} else { // O-O-O
kto = relative_square(us, SQ_C1);
rto = relative_square(us, SQ_D1);
}
// Remove pieces from source squares:
clear_bit(&(byColorBB[us]), kfrom);
clear_bit(&(byTypeBB[KING]), kfrom);
clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
clear_bit(&(byColorBB[us]), rfrom);
clear_bit(&(byTypeBB[ROOK]), rfrom);
clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
// Put pieces on destination squares:
set_bit(&(byColorBB[us]), kto);
set_bit(&(byTypeBB[KING]), kto);
set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
set_bit(&(byColorBB[us]), rto);
set_bit(&(byTypeBB[ROOK]), rto);
set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
// Update board array
Piece king = make_piece(us, KING);
Piece rook = make_piece(us, ROOK);
board[kfrom] = board[rfrom] = PIECE_NONE;
board[kto] = king;
board[rto] = rook;
// Update piece lists
pieceList[us][KING][index[kfrom]] = kto;
pieceList[us][ROOK][index[rfrom]] = rto;
int tmp = index[rfrom]; // In Chess960 could be rto == kfrom
index[kto] = index[kfrom];
index[rto] = tmp;
// Update incremental scores
st->value += pst_delta(king, kfrom, kto);
st->value += pst_delta(rook, rfrom, rto);
// Update hash key
st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
st->key ^= zobrist[us][ROOK][rfrom] ^ zobrist[us][ROOK][rto];
// Clear en passant square
if (st->epSquare != SQ_NONE)
{
st->key ^= zobEp[st->epSquare];
st->epSquare = SQ_NONE;
}
// Update castling rights
st->key ^= zobCastle[st->castleRights];
st->castleRights &= castleRightsMask[kfrom];
st->key ^= zobCastle[st->castleRights];
// Reset rule 50 counter
st->rule50 = 0;
// Update checkers BB
st->checkersBB = attackers_to(king_square(them)) & pieces_of_color(us);
// Finish
sideToMove = opposite_color(sideToMove);
st->value += (sideToMove == WHITE ? TempoValue : -TempoValue);
assert(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());
assert(move_is_ok(m));
sideToMove = opposite_color(sideToMove);
if (move_is_castle(m))
{
undo_castle_move(m);
return;
}
Color us = side_to_move();
Color them = opposite_color(us);
Square from = move_from(m);
Square to = move_to(m);
bool ep = move_is_ep(m);
bool pm = move_is_promotion(m);
PieceType pt = type_of_piece_on(to);
assert(square_is_empty(from));
assert(color_of_piece_on(to) == us);
assert(!pm || relative_rank(us, to) == RANK_8);
assert(!ep || to == st->previous->epSquare);
assert(!ep || relative_rank(us, to) == RANK_6);
assert(!ep || piece_on(to) == make_piece(us, PAWN));
if (pm) // promotion ?
{
PieceType promotion = move_promotion_piece(m);
pt = PAWN;
assert(promotion >= KNIGHT && promotion <= QUEEN);
assert(piece_on(to) == make_piece(us, promotion));
// Replace promoted piece with a pawn
clear_bit(&(byTypeBB[promotion]), to);
set_bit(&(byTypeBB[PAWN]), to);
// Update piece counts
pieceCount[us][promotion]--;
pieceCount[us][PAWN]++;
// Update piece list replacing promotion piece with a pawn
Square lastPromotionSquare = pieceList[us][promotion][pieceCount[us][promotion]];
index[lastPromotionSquare] = index[to];
pieceList[us][promotion][index[lastPromotionSquare]] = lastPromotionSquare;
pieceList[us][promotion][pieceCount[us][promotion]] = SQ_NONE;
index[to] = pieceCount[us][PAWN] - 1;
pieceList[us][PAWN][index[to]] = to;
}
// Put the piece back at the source square
Bitboard move_bb = make_move_bb(to, from);
do_move_bb(&(byColorBB[us]), move_bb);
do_move_bb(&(byTypeBB[pt]), move_bb);
do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
board[from] = make_piece(us, pt);
board[to] = PIECE_NONE;
// Update piece list
index[from] = index[to];
pieceList[us][pt][index[from]] = from;
if (st->capturedType)
{
Square capsq = to;
if (ep)
capsq = (us == WHITE)? (to - DELTA_N) : (to - DELTA_S);
assert(st->capturedType != KING);
assert(!ep || square_is_empty(capsq));
// Restore the captured piece
set_bit(&(byColorBB[them]), capsq);
set_bit(&(byTypeBB[st->capturedType]), capsq);
set_bit(&(byTypeBB[0]), capsq);
board[capsq] = make_piece(them, st->capturedType);
// Update piece count
pieceCount[them][st->capturedType]++;
// Update piece list, add a new captured piece in capsq square
index[capsq] = pieceCount[them][st->capturedType] - 1;
pieceList[them][st->capturedType][index[capsq]] = capsq;
}
// Finally point our state pointer back to the previous state
st = st->previous;
assert(is_ok());
}
/// Position::undo_castle_move() is a private method used to unmake a castling
/// move. It is called from the main Position::undo_move function. Note that
/// castling moves are encoded as "king captures friendly rook" moves, for
/// instance white short castling in a non-Chess960 game is encoded as e1h1.
void Position::undo_castle_move(Move m) {
assert(move_is_ok(m));
assert(move_is_castle(m));
// When we have arrived here, some work has already been done by
// Position::undo_move. In particular, the side to move has been switched,
// so the code below is correct.
Color us = side_to_move();
// Find source squares for king and rook
Square kfrom = move_from(m);
Square rfrom = move_to(m); // HACK: See comment at beginning of function
Square kto, rto;
// Find destination squares for king and rook
if (rfrom > kfrom) // O-O
{
kto = relative_square(us, SQ_G1);
rto = relative_square(us, SQ_F1);
} else { // O-O-O
kto = relative_square(us, SQ_C1);
rto = relative_square(us, SQ_D1);
}
assert(piece_on(kto) == make_piece(us, KING));
assert(piece_on(rto) == make_piece(us, ROOK));
// Remove pieces from destination squares:
clear_bit(&(byColorBB[us]), kto);
clear_bit(&(byTypeBB[KING]), kto);
clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
clear_bit(&(byColorBB[us]), rto);
clear_bit(&(byTypeBB[ROOK]), rto);
clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
// Put pieces on source squares:
set_bit(&(byColorBB[us]), kfrom);
set_bit(&(byTypeBB[KING]), kfrom);
set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
set_bit(&(byColorBB[us]), rfrom);
set_bit(&(byTypeBB[ROOK]), rfrom);
set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
// Update board
board[rto] = board[kto] = PIECE_NONE;
board[rfrom] = make_piece(us, ROOK);
board[kfrom] = make_piece(us, KING);
// Update piece lists
pieceList[us][KING][index[kto]] = kfrom;
pieceList[us][ROOK][index[rto]] = rfrom;
int tmp = index[rto]; // In Chess960 could be rto == kfrom
index[kfrom] = index[kto];
index[rfrom] = tmp;
// Finally point our state pointer back to the previous state
st = st->previous;
assert(is_ok());
}
/// Position::do_null_move makes() a "null move": It switches the side to move
/// and updates the hash key without executing any move on the board.
void Position::do_null_move(StateInfo& backupSt) {
assert(is_ok());
assert(!in_check());
// Back up the information necessary to undo the null move to the supplied
// StateInfo object.
// Note that differently from normal case here backupSt is actually used as
// a backup storage not as a new state to be used.
backupSt.key = st->key;
backupSt.epSquare = st->epSquare;
backupSt.value = st->value;
backupSt.previous = st->previous;
backupSt.pliesFromNull = st->pliesFromNull;
st->previous = &backupSt;
// Save the current key to the history[] array, in order to be able to
// detect repetition draws.
history[st->gamePly++] = st->key;
// Update the necessary information
if (st->epSquare != SQ_NONE)
st->key ^= zobEp[st->epSquare];
st->key ^= zobSideToMove;
prefetch((char*)TT.first_entry(st->key));
sideToMove = opposite_color(sideToMove);
st->epSquare = SQ_NONE;
st->rule50++;
st->pliesFromNull = 0;
st->value += (sideToMove == WHITE) ? TempoValue : -TempoValue;
}
/// Position::undo_null_move() unmakes a "null move".
void Position::undo_null_move() {
assert(is_ok());
assert(!in_check());
// Restore information from the our backup StateInfo object
StateInfo* backupSt = st->previous;
st->key = backupSt->key;
st->epSquare = backupSt->epSquare;
st->value = backupSt->value;
st->previous = backupSt->previous;
st->pliesFromNull = backupSt->pliesFromNull;
// Update the necessary information
sideToMove = opposite_color(sideToMove);
st->rule50--;
st->gamePly--;
}
/// Position::see() is a static exchange evaluator: It tries to estimate the
/// material gain or loss resulting from a move. There are three versions of
/// this function: One which takes a destination square as input, one takes a
/// move, and one which takes a 'from' and a 'to' square. The function does
/// not yet understand promotions captures.
int Position::see(Move m) const {
assert(move_is_ok(m));
return see(move_from(m), move_to(m));
}
int Position::see_sign(Move m) const {
assert(move_is_ok(m));
Square from = move_from(m);
Square to = move_to(m);
// Early return if SEE cannot be negative because captured piece value
// is not less then capturing one. Note that king moves always return
// here because king midgame value is set to 0.
if (midgame_value_of_piece_on(to) >= midgame_value_of_piece_on(from))
return 1;
return see(from, to);
}
int Position::see(Square from, Square to) const {
Bitboard occupied, attackers, stmAttackers, b;
int swapList[32], slIndex = 1;
PieceType capturedType, pt;
Color stm;
assert(square_is_ok(from));
assert(square_is_ok(to));
capturedType = type_of_piece_on(to);
// King cannot be recaptured
if (capturedType == KING)
return seeValues[capturedType];
occupied = occupied_squares();
// Handle en passant moves
if (st->epSquare == to && type_of_piece_on(from) == PAWN)
{
Square capQq = (side_to_move() == WHITE ? to - DELTA_N : to - DELTA_S);
assert(capturedType == PIECE_TYPE_NONE);
assert(type_of_piece_on(capQq) == PAWN);
// Remove the captured pawn
clear_bit(&occupied, capQq);
capturedType = PAWN;
}
// Find all attackers to the destination square, with the moving piece
// removed, but possibly an X-ray attacker added behind it.
clear_bit(&occupied, from);
attackers = (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
| (bishop_attacks_bb(to, occupied)& pieces(BISHOP, QUEEN))
| (attacks_from<KNIGHT>(to) & pieces(KNIGHT))
| (attacks_from<KING>(to) & pieces(KING))
| (attacks_from<PAWN>(to, WHITE) & pieces(PAWN, BLACK))
| (attacks_from<PAWN>(to, BLACK) & pieces(PAWN, WHITE));
// If the opponent has no attackers we are finished
stm = opposite_color(color_of_piece_on(from));
stmAttackers = attackers & pieces_of_color(stm);
if (!stmAttackers)
return seeValues[capturedType];
// The destination square is defended, which makes things rather more
// difficult to compute. We proceed by building up a "swap list" containing
// the material gain or loss at each stop in a sequence of captures to the
// destination square, where the sides alternately capture, and always
// capture with the least valuable piece. After each capture, we look for
// new X-ray attacks from behind the capturing piece.
swapList[0] = seeValues[capturedType];
capturedType = type_of_piece_on(from);
do {
// Locate the least valuable attacker for the side to move. The loop
// below looks like it is potentially infinite, but it isn't. We know
// that the side to move still has at least one attacker left.
for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
assert(pt < KING);
// Remove the attacker we just found from the 'occupied' bitboard,
// and scan for new X-ray attacks behind the attacker.
b = stmAttackers & pieces(pt);
occupied ^= (b & (~b + 1));
attackers |= (rook_attacks_bb(to, occupied) & pieces(ROOK, QUEEN))
| (bishop_attacks_bb(to, occupied) & pieces(BISHOP, QUEEN));
attackers &= occupied; // Cut out pieces we've already done
// Add the new entry to the swap list
assert(slIndex < 32);
swapList[slIndex] = -swapList[slIndex - 1] + seeValues[capturedType];
slIndex++;
// Remember the value of the capturing piece, and change the side to
// move before beginning the next iteration.
capturedType = pt;
stm = opposite_color(stm);
stmAttackers = attackers & pieces_of_color(stm);
// Stop before processing a king capture
if (capturedType == KING && stmAttackers)
{
assert(slIndex < 32);
swapList[slIndex++] = QueenValueMidgame*10;
break;
}
} while (stmAttackers);
// Having built the swap list, we negamax through it to find the best
// achievable score from the point of view of the side to move.
while (--slIndex)
swapList[slIndex-1] = Min(-swapList[slIndex], swapList[slIndex-1]);
return swapList[0];
}
/// Position::clear() erases the position object to a pristine state, with an
/// empty board, white to move, and no castling rights.
void Position::clear() {
st = &startState;
memset(st, 0, sizeof(StateInfo));
st->epSquare = SQ_NONE;
startPosPlyCounter = 0;
nodes = 0;
memset(byColorBB, 0, sizeof(Bitboard) * 2);
memset(byTypeBB, 0, sizeof(Bitboard) * 8);
memset(pieceCount, 0, sizeof(int) * 2 * 8);
memset(index, 0, sizeof(int) * 64);
for (int i = 0; i < 64; i++)
board[i] = PIECE_NONE;
for (int i = 0; i < 8; i++)
for (int j = 0; j < 16; j++)
pieceList[0][i][j] = pieceList[1][i][j] = SQ_NONE;
for (Square sq = SQ_A1; sq <= SQ_H8; sq++)
castleRightsMask[sq] = ALL_CASTLES;
sideToMove = WHITE;
initialKFile = FILE_E;
initialKRFile = FILE_H;
initialQRFile = FILE_A;
}
/// Position::put_piece() puts a piece on the given square of the board,
/// updating the board array, pieces list, bitboards, and piece counts.
void Position::put_piece(Piece p, Square s) {
Color c = color_of_piece(p);
PieceType pt = type_of_piece(p);
board[s] = p;
index[s] = pieceCount[c][pt]++;
pieceList[c][pt][index[s]] = s;
set_bit(&(byTypeBB[pt]), s);
set_bit(&(byColorBB[c]), s);
set_bit(&(byTypeBB[0]), s); // HACK: byTypeBB[0] contains all occupied squares.
}
/// Position::compute_key() computes the hash key of the position. The hash
/// key is usually updated incrementally as moves are made and unmade, the
/// compute_key() function is only used when a new position is set up, and
/// to verify the correctness of the hash key when running in debug mode.
Key Position::compute_key() const {
Key result = zobCastle[st->castleRights];
for (Square s = SQ_A1; s <= SQ_H8; s++)
if (square_is_occupied(s))
result ^= zobrist[color_of_piece_on(s)][type_of_piece_on(s)][s];
if (ep_square() != SQ_NONE)
result ^= zobEp[ep_square()];
if (side_to_move() == BLACK)
result ^= zobSideToMove;
return result;
}
/// Position::compute_pawn_key() computes the hash key of the position. The
/// hash key is usually updated incrementally as moves are made and unmade,
/// the compute_pawn_key() function is only used when a new position is set
/// up, and to verify the correctness of the pawn hash key when running in
/// debug mode.
Key Position::compute_pawn_key() const {
Bitboard b;
Key result = 0;
for (Color c = WHITE; c <= BLACK; c++)
{
b = pieces(PAWN, c);
while (b)
result ^= zobrist[c][PAWN][pop_1st_bit(&b)];
}
return result;
}
/// Position::compute_material_key() computes the hash key of the position.
/// The hash key is usually updated incrementally as moves are made and unmade,
/// the compute_material_key() function is only used when a new position is set
/// up, and to verify the correctness of the material hash key when running in
/// debug mode.
Key Position::compute_material_key() const {
int count;
Key result = 0;
for (Color c = WHITE; c <= BLACK; c++)
for (PieceType pt = PAWN; pt <= QUEEN; pt++)
{
count = piece_count(c, pt);
for (int i = 0; i < count; i++)
result ^= zobrist[c][pt][i];
}
return result;
}
/// Position::compute_value() compute the incremental scores for the middle
/// game and the endgame. These functions are used to initialize the incremental
/// scores when a new position is set up, and to verify that the scores are correctly
/// updated by do_move and undo_move when the program is running in debug mode.
Score Position::compute_value() const {
Bitboard b;
Score result = SCORE_ZERO;
for (Color c = WHITE; c <= BLACK; c++)
for (PieceType pt = PAWN; pt <= KING; pt++)
{
b = pieces(pt, c);
while (b)
result += pst(c, pt, pop_1st_bit(&b));
}
result += (side_to_move() == WHITE ? TempoValue / 2 : -TempoValue / 2);
return result;
}
/// Position::compute_non_pawn_material() computes the total non-pawn middle
/// game material value for the given side. Material values are updated
/// incrementally during the search, this function is only used while
/// initializing a new Position object.
Value Position::compute_non_pawn_material(Color c) const {
Value result = VALUE_ZERO;
for (PieceType pt = KNIGHT; pt <= QUEEN; pt++)
result += piece_count(c, pt) * PieceValueMidgame[pt];
return result;
}
/// Position::is_draw() tests whether the position is drawn by material,
/// repetition, or the 50 moves rule. It does not detect stalemates, this
/// must be done by the search.
bool Position::is_draw() const {
// Draw by material?
if ( !pieces(PAWN)
&& (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMidgame))
return true;
// Draw by the 50 moves rule?
if (st->rule50 > 99 && !is_mate())
return true;
// Draw by repetition?
for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
if (history[st->gamePly - i] == st->key)
return true;
return false;
}
/// Position::is_mate() returns true or false depending on whether the
/// side to move is checkmated.
bool Position::is_mate() const {
MoveStack moves[MAX_MOVES];
return in_check() && generate<MV_LEGAL>(*this, moves) == moves;
}
/// Position::init_zobrist() is a static member function which initializes at
/// startup the various arrays used to compute hash keys.
void Position::init_zobrist() {
int i,j, k;
RKISS rk;
for (i = 0; i < 2; i++) for (j = 0; j < 8; j++) for (k = 0; k < 64; k++)
zobrist[i][j][k] = rk.rand<Key>();
for (i = 0; i < 64; i++)
zobEp[i] = rk.rand<Key>();
for (i = 0; i < 16; i++)
zobCastle[i] = rk.rand<Key>();
zobSideToMove = rk.rand<Key>();
zobExclusion = rk.rand<Key>();
}
/// Position::init_piece_square_tables() initializes the piece square tables.
/// This is a two-step operation: First, the white halves of the tables are
/// copied from the MgPST[][] and EgPST[][] arrays. Second, the black halves
/// of the tables are initialized by mirroring and changing the sign of the
/// corresponding white scores.
void Position::init_piece_square_tables() {
for (Square s = SQ_A1; s <= SQ_H8; s++)
for (Piece p = WP; p <= WK; p++)
PieceSquareTable[p][s] = make_score(MgPST[p][s], EgPST[p][s]);
for (Square s = SQ_A1; s <= SQ_H8; s++)
for (Piece p = BP; p <= BK; p++)
PieceSquareTable[p][s] = -PieceSquareTable[p-8][flip_square(s)];
}
/// Position::flip() flips position with the white and black sides reversed. This
/// is only useful for debugging especially for finding evaluation symmetry bugs.
void Position::flip() {
assert(is_ok());
// Make a copy of current position before to start changing
const Position pos(*this, threadID);
clear();
threadID = pos.thread();
// Board
for (Square s = SQ_A1; s <= SQ_H8; s++)
if (!pos.square_is_empty(s))
put_piece(Piece(pos.piece_on(s) ^ 8), flip_square(s));
// Side to move
sideToMove = opposite_color(pos.side_to_move());
// Castling rights
if (pos.can_castle_kingside(WHITE)) do_allow_oo(BLACK);
if (pos.can_castle_queenside(WHITE)) do_allow_ooo(BLACK);
if (pos.can_castle_kingside(BLACK)) do_allow_oo(WHITE);
if (pos.can_castle_queenside(BLACK)) do_allow_ooo(WHITE);
initialKFile = pos.initialKFile;
initialKRFile = pos.initialKRFile;
initialQRFile = pos.initialQRFile;
castleRightsMask[make_square(initialKFile, RANK_1)] ^= (WHITE_OO | WHITE_OOO);
castleRightsMask[make_square(initialKFile, RANK_8)] ^= (BLACK_OO | BLACK_OOO);
castleRightsMask[make_square(initialKRFile, RANK_1)] ^= WHITE_OO;
castleRightsMask[make_square(initialKRFile, RANK_8)] ^= BLACK_OO;
castleRightsMask[make_square(initialQRFile, RANK_1)] ^= WHITE_OOO;
castleRightsMask[make_square(initialQRFile, RANK_8)] ^= BLACK_OOO;
// En passant square
if (pos.st->epSquare != SQ_NONE)
st->epSquare = flip_square(pos.st->epSquare);
// Checkers
find_checkers();
// Hash keys
st->key = compute_key();
st->pawnKey = compute_pawn_key();
st->materialKey = compute_material_key();
// Incremental scores
st->value = compute_value();
// Material
st->npMaterial[WHITE] = compute_non_pawn_material(WHITE);
st->npMaterial[BLACK] = compute_non_pawn_material(BLACK);
assert(is_ok());
}
/// Position::is_ok() performs some consitency checks for the position object.
/// This is meant to be helpful when debugging.
bool Position::is_ok(int* failedStep) const {
// What features of the position should be verified?
const bool debugAll = false;
const bool debugBitboards = debugAll || false;
const bool debugKingCount = debugAll || false;
const bool debugKingCapture = debugAll || false;
const bool debugCheckerCount = debugAll || false;
const bool debugKey = debugAll || false;
const bool debugMaterialKey = debugAll || false;
const bool debugPawnKey = debugAll || false;
const bool debugIncrementalEval = debugAll || false;
const bool debugNonPawnMaterial = debugAll || false;
const bool debugPieceCounts = debugAll || false;
const bool debugPieceList = debugAll || false;
const bool debugCastleSquares = debugAll || false;
if (failedStep) *failedStep = 1;
// Side to move OK?
if (!color_is_ok(side_to_move()))
return false;
// Are the king squares in the position correct?
if (failedStep) (*failedStep)++;
if (piece_on(king_square(WHITE)) != WK)
return false;
if (failedStep) (*failedStep)++;
if (piece_on(king_square(BLACK)) != BK)
return false;
// Castle files OK?
if (failedStep) (*failedStep)++;
if (!file_is_ok(initialKRFile))
return false;
if (!file_is_ok(initialQRFile))
return false;
// Do both sides have exactly one king?
if (failedStep) (*failedStep)++;
if (debugKingCount)
{
int kingCount[2] = {0, 0};
for (Square s = SQ_A1; s <= SQ_H8; s++)
if (type_of_piece_on(s) == KING)
kingCount[color_of_piece_on(s)]++;
if (kingCount[0] != 1 || kingCount[1] != 1)
return false;
}
// Can the side to move capture the opponent's king?
if (failedStep) (*failedStep)++;
if (debugKingCapture)
{
Color us = side_to_move();
Color them = opposite_color(us);
Square ksq = king_square(them);
if (attackers_to(ksq) & pieces_of_color(us))
return false;
}
// Is there more than 2 checkers?
if (failedStep) (*failedStep)++;
if (debugCheckerCount && count_1s<CNT32>(st->checkersBB) > 2)
return false;
// Bitboards OK?
if (failedStep) (*failedStep)++;
if (debugBitboards)
{
// The intersection of the white and black pieces must be empty
if ((pieces_of_color(WHITE) & pieces_of_color(BLACK)) != EmptyBoardBB)
return false;
// The union of the white and black pieces must be equal to all
// occupied squares
if ((pieces_of_color(WHITE) | pieces_of_color(BLACK)) != occupied_squares())
return false;
// Separate piece type bitboards must have empty intersections
for (PieceType p1 = PAWN; p1 <= KING; p1++)
for (PieceType p2 = PAWN; p2 <= KING; p2++)
if (p1 != p2 && (pieces(p1) & pieces(p2)))
return false;
}
// En passant square OK?
if (failedStep) (*failedStep)++;
if (ep_square() != SQ_NONE)
{
// The en passant square must be on rank 6, from the point of view of the
// side to move.
if (relative_rank(side_to_move(), ep_square()) != RANK_6)
return false;
}
// Hash key OK?
if (failedStep) (*failedStep)++;
if (debugKey && st->key != compute_key())
return false;
// Pawn hash key OK?
if (failedStep) (*failedStep)++;
if (debugPawnKey && st->pawnKey != compute_pawn_key())
return false;
// Material hash key OK?
if (failedStep) (*failedStep)++;
if (debugMaterialKey && st->materialKey != compute_material_key())
return false;
// Incremental eval OK?
if (failedStep) (*failedStep)++;
if (debugIncrementalEval && st->value != compute_value())
return false;
// Non-pawn material OK?
if (failedStep) (*failedStep)++;
if (debugNonPawnMaterial)
{
if (st->npMaterial[WHITE] != compute_non_pawn_material(WHITE))
return false;
if (st->npMaterial[BLACK] != compute_non_pawn_material(BLACK))
return false;
}
// Piece counts OK?
if (failedStep) (*failedStep)++;
if (debugPieceCounts)
for (Color c = WHITE; c <= BLACK; c++)
for (PieceType pt = PAWN; pt <= KING; pt++)
if (pieceCount[c][pt] != count_1s<CNT32>(pieces(pt, c)))
return false;
if (failedStep) (*failedStep)++;
if (debugPieceList)
for (Color c = WHITE; c <= BLACK; c++)
for (PieceType pt = PAWN; pt <= KING; pt++)
for (int i = 0; i < pieceCount[c][pt]; i++)
{
if (piece_on(piece_list(c, pt, i)) != make_piece(c, pt))
return false;
if (index[piece_list(c, pt, i)] != i)
return false;
}
if (failedStep) (*failedStep)++;
if (debugCastleSquares)
{
for (Color c = WHITE; c <= BLACK; c++)
{
if (can_castle_kingside(c) && piece_on(initial_kr_square(c)) != make_piece(c, ROOK))
return false;
if (can_castle_queenside(c) && piece_on(initial_qr_square(c)) != make_piece(c, ROOK))
return false;
}
if (castleRightsMask[initial_kr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OO))
return false;
if (castleRightsMask[initial_qr_square(WHITE)] != (ALL_CASTLES ^ WHITE_OOO))
return false;
if (castleRightsMask[initial_kr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OO))
return false;
if (castleRightsMask[initial_qr_square(BLACK)] != (ALL_CASTLES ^ BLACK_OOO))
return false;
}
if (failedStep) *failedStep = 0;
return true;
}
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