Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
- Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
+ Copyright (C) 2015-2017 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
#include <algorithm>
#include <cassert>
-#include <cstring> // For std::memset, std::memcmp
+#include <cstddef> // For offsetof()
+#include <cstring> // For std::memset, std::memcmp
#include <iomanip>
#include <sstream>
#include "thread.h"
#include "tt.h"
#include "uci.h"
+#include "syzygy/tbprobe.h"
using std::string;
+namespace PSQT {
+ extern Score psq[PIECE_NB][SQUARE_NB];
+}
+
namespace Zobrist {
- Key psq[COLOR_NB][PIECE_TYPE_NB][SQUARE_NB];
+ Key psq[PIECE_NB][SQUARE_NB];
Key enpassant[FILE_NB];
Key castling[CASTLING_RIGHT_NB];
- Key side;
- Key exclusion;
+ Key side, noPawns;
}
-Key Position::exclusion_key() const { return st->key ^ Zobrist::exclusion; }
-
namespace {
const string PieceToChar(" PNBRQK pnbrqk");
-// min_attacker() is a helper function used by see() to locate the least
+const Piece Pieces[] = { W_PAWN, W_KNIGHT, W_BISHOP, W_ROOK, W_QUEEN, W_KING,
+ B_PAWN, B_KNIGHT, B_BISHOP, B_ROOK, B_QUEEN, B_KING };
+
+// min_attacker() is a helper function used by see_ge() to locate the least
// valuable attacker for the side to move, remove the attacker we just found
// from the bitboards and scan for new X-ray attacks behind it.
Bitboard b = stmAttackers & bb[Pt];
if (!b)
- return min_attacker<Pt+1>(bb, to, stmAttackers, occupied, attackers);
+ return min_attacker<Pt + 1>(bb, to, stmAttackers, occupied, attackers);
occupied ^= b & ~(b - 1);
}
os << "\nFen: " << pos.fen() << "\nKey: " << std::hex << std::uppercase
- << std::setfill('0') << std::setw(16) << pos.key() << std::dec << "\nCheckers: ";
+ << std::setfill('0') << std::setw(16) << pos.key()
+ << std::setfill(' ') << std::dec << "\nCheckers: ";
for (Bitboard b = pos.checkers(); b; )
os << UCI::square(pop_lsb(&b)) << " ";
+ if ( int(Tablebases::MaxCardinality) >= popcount(pos.pieces())
+ && !pos.can_castle(ANY_CASTLING))
+ {
+ StateInfo st;
+ Position p;
+ p.set(pos.fen(), pos.is_chess960(), &st, pos.this_thread());
+ Tablebases::ProbeState s1, s2;
+ Tablebases::WDLScore wdl = Tablebases::probe_wdl(p, &s1);
+ int dtz = Tablebases::probe_dtz(p, &s2);
+ os << "\nTablebases WDL: " << std::setw(4) << wdl << " (" << s1 << ")"
+ << "\nTablebases DTZ: " << std::setw(4) << dtz << " (" << s2 << ")";
+ }
+
return os;
}
PRNG rng(1070372);
- for (Color c = WHITE; c <= BLACK; ++c)
- for (PieceType pt = PAWN; pt <= KING; ++pt)
- for (Square s = SQ_A1; s <= SQ_H8; ++s)
- Zobrist::psq[c][pt][s] = rng.rand<Key>();
+ for (Piece pc : Pieces)
+ for (Square s = SQ_A1; s <= SQ_H8; ++s)
+ Zobrist::psq[pc][s] = rng.rand<Key>();
for (File f = FILE_A; f <= FILE_H; ++f)
Zobrist::enpassant[f] = rng.rand<Key>();
}
Zobrist::side = rng.rand<Key>();
- Zobrist::exclusion = rng.rand<Key>();
+ Zobrist::noPawns = rng.rand<Key>();
}
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.
+ is the position "behind" the pawn. This is recorded only if there is a pawn
+ in position to make an en passant capture, and if there really is a pawn
+ that might have advanced two squares.
5) Halfmove clock. This is the number of halfmoves since the last pawn advance
or capture. This is used to determine if a draw can be claimed under the
std::memset(this, 0, sizeof(Position));
std::memset(si, 0, sizeof(StateInfo));
- std::fill_n(&pieceList[0][0][0], sizeof(pieceList) / sizeof(Square), SQ_NONE);
+ std::fill_n(&pieceList[0][0], sizeof(pieceList) / sizeof(Square), SQ_NONE);
st = si;
ss >> std::noskipws;
else if ((idx = PieceToChar.find(token)) != string::npos)
{
- put_piece(color_of(Piece(idx)), type_of(Piece(idx)), sq);
+ put_piece(Piece(idx), sq);
++sq;
}
}
{
st->epSquare = make_square(File(col - 'a'), Rank(row - '1'));
- if (!(attackers_to(st->epSquare) & pieces(sideToMove, PAWN)))
+ if ( !(attackers_to(st->epSquare) & pieces(sideToMove, PAWN))
+ || !(pieces(~sideToMove, PAWN) & (st->epSquare + pawn_push(~sideToMove))))
st->epSquare = SQ_NONE;
}
else
void Position::set_check_info(StateInfo* si) const {
- si->blockersForKing[WHITE] = slider_blockers(pieces(BLACK), square<KING>(WHITE));
- si->blockersForKing[BLACK] = slider_blockers(pieces(WHITE), square<KING>(BLACK));
+ si->blockersForKing[WHITE] = slider_blockers(pieces(BLACK), square<KING>(WHITE), si->pinnersForKing[WHITE]);
+ si->blockersForKing[BLACK] = slider_blockers(pieces(WHITE), square<KING>(BLACK), si->pinnersForKing[BLACK]);
Square ksq = square<KING>(~sideToMove);
void Position::set_state(StateInfo* si) const {
- si->key = si->pawnKey = si->materialKey = 0;
+ si->key = si->materialKey = 0;
+ si->pawnKey = Zobrist::noPawns;
si->nonPawnMaterial[WHITE] = si->nonPawnMaterial[BLACK] = VALUE_ZERO;
si->psq = SCORE_ZERO;
si->checkersBB = attackers_to(square<KING>(sideToMove)) & pieces(~sideToMove);
{
Square s = pop_lsb(&b);
Piece pc = piece_on(s);
- si->key ^= Zobrist::psq[color_of(pc)][type_of(pc)][s];
- si->psq += PSQT::psq[color_of(pc)][type_of(pc)][s];
+ si->key ^= Zobrist::psq[pc][s];
+ si->psq += PSQT::psq[pc][s];
}
if (si->epSquare != SQ_NONE)
for (Bitboard b = pieces(PAWN); b; )
{
Square s = pop_lsb(&b);
- si->pawnKey ^= Zobrist::psq[color_of(piece_on(s))][PAWN][s];
+ si->pawnKey ^= Zobrist::psq[piece_on(s)][s];
}
- for (Color c = WHITE; c <= BLACK; ++c)
- for (PieceType pt = PAWN; pt <= KING; ++pt)
- for (int cnt = 0; cnt < pieceCount[c][pt]; ++cnt)
- si->materialKey ^= Zobrist::psq[c][pt][cnt];
+ for (Piece pc : Pieces)
+ {
+ if (type_of(pc) != PAWN && type_of(pc) != KING)
+ si->nonPawnMaterial[color_of(pc)] += pieceCount[pc] * PieceValue[MG][pc];
+
+ for (int cnt = 0; cnt < pieceCount[pc]; ++cnt)
+ si->materialKey ^= Zobrist::psq[pc][cnt];
+ }
+}
+
+
+/// Position::set() is an overload to initialize the position object with
+/// the given endgame code string like "KBPKN". It is mainly a helper to
+/// get the material key out of an endgame code. Position is not playable,
+/// indeed is even not guaranteed to be legal.
+
+Position& Position::set(const string& code, Color c, StateInfo* si) {
- for (Color c = WHITE; c <= BLACK; ++c)
- for (PieceType pt = KNIGHT; pt <= QUEEN; ++pt)
- si->nonPawnMaterial[c] += pieceCount[c][pt] * PieceValue[MG][pt];
+ assert(code.length() > 0 && code.length() < 8);
+ assert(code[0] == 'K');
+
+ string sides[] = { code.substr(code.find('K', 1)), // Weak
+ code.substr(0, code.find('K', 1)) }; // Strong
+
+ std::transform(sides[c].begin(), sides[c].end(), sides[c].begin(), tolower);
+
+ string fenStr = sides[0] + char(8 - sides[0].length() + '0') + "/8/8/8/8/8/8/"
+ + sides[1] + char(8 - sides[1].length() + '0') + " w - - 0 10";
+
+ return set(fenStr, false, si, nullptr);
}
}
-/// Position::slider_blockers() returns a bitboard of all the pieces (both colors) that
-/// are blocking attacks on the square 's' from 'sliders'. A piece blocks a slider
-/// if removing that piece from the board would result in a position where square 's'
-/// is attacked. For example, a king-attack blocking piece can be either a pinned or
-/// a discovered check piece, according if its color is the opposite or the same of
-/// the color of the slider.
+/// Position::slider_blockers() returns a bitboard of all the pieces (both colors)
+/// that are blocking attacks on the square 's' from 'sliders'. A piece blocks a
+/// slider if removing that piece from the board would result in a position where
+/// square 's' is attacked. For example, a king-attack blocking piece can be either
+/// a pinned or a discovered check piece, according if its color is the opposite
+/// or the same of the color of the slider.
-Bitboard Position::slider_blockers(Bitboard sliders, Square s) const {
+Bitboard Position::slider_blockers(Bitboard sliders, Square s, Bitboard& pinners) const {
- Bitboard b, pinners, result = 0;
+ Bitboard result = 0;
+ pinners = 0;
- // Pinners are sliders that attack 's' when a pinned piece is removed
- pinners = ( (PseudoAttacks[ROOK ][s] & pieces(QUEEN, ROOK))
- | (PseudoAttacks[BISHOP][s] & pieces(QUEEN, BISHOP))) & sliders;
+ // Snipers are sliders that attack 's' when a piece is removed
+ Bitboard snipers = ( (PseudoAttacks[ ROOK][s] & pieces(QUEEN, ROOK))
+ | (PseudoAttacks[BISHOP][s] & pieces(QUEEN, BISHOP))) & sliders;
- while (pinners)
+ while (snipers)
{
- b = between_bb(s, pop_lsb(&pinners)) & pieces();
-
- if (!more_than_one(b))
- result |= b;
+ Square sniperSq = pop_lsb(&snipers);
+ Bitboard b = between_bb(s, sniperSq) & pieces();
+
+ if (!more_than_one(b))
+ {
+ result |= b;
+ if (b & pieces(color_of(piece_on(s))))
+ pinners |= sniperSq;
+ }
}
return result;
}
return (attacks_from<PAWN>(s, BLACK) & pieces(WHITE, PAWN))
| (attacks_from<PAWN>(s, WHITE) & pieces(BLACK, PAWN))
| (attacks_from<KNIGHT>(s) & pieces(KNIGHT))
- | (attacks_bb<ROOK >(s, occupied) & pieces(ROOK, QUEEN))
+ | (attacks_bb< ROOK>(s, occupied) & pieces( ROOK, QUEEN))
| (attacks_bb<BISHOP>(s, occupied) & pieces(BISHOP, QUEEN))
| (attacks_from<KING>(s) & pieces(KING));
}
&& empty(to - pawn_push(us))))
return false;
}
- else if (!(attacks_from(pc, from) & to))
+ else if (!(attacks_from(type_of(pc), from) & to))
return false;
// Evasions generator already takes care to avoid some kind of illegal moves
return false;
case PROMOTION:
- return attacks_bb(Piece(promotion_type(m)), to, pieces() ^ from) & square<KING>(~sideToMove);
+ return attacks_bb(promotion_type(m), to, pieces() ^ from) & square<KING>(~sideToMove);
// En passant capture with check? We have already handled the case
// of direct checks and ordinary discovered check, so the only case we
Color them = ~us;
Square from = from_sq(m);
Square to = to_sq(m);
- PieceType pt = type_of(piece_on(from));
- PieceType captured = type_of(m) == ENPASSANT ? PAWN : type_of(piece_on(to));
+ Piece pc = piece_on(from);
+ Piece captured = type_of(m) == ENPASSANT ? make_piece(them, PAWN) : piece_on(to);
- assert(color_of(piece_on(from)) == us);
- assert(piece_on(to) == NO_PIECE || color_of(piece_on(to)) == (type_of(m) != CASTLING ? them : us));
- assert(captured != KING);
+ assert(color_of(pc) == us);
+ assert(captured == NO_PIECE || color_of(captured) == (type_of(m) != CASTLING ? them : us));
+ assert(type_of(captured) != KING);
if (type_of(m) == CASTLING)
{
- assert(pt == KING);
+ assert(pc == make_piece(us, KING));
+ assert(captured == make_piece(us, ROOK));
Square rfrom, rto;
do_castling<true>(us, from, to, rfrom, rto);
- captured = NO_PIECE_TYPE;
- st->psq += PSQT::psq[us][ROOK][rto] - PSQT::psq[us][ROOK][rfrom];
- k ^= Zobrist::psq[us][ROOK][rfrom] ^ Zobrist::psq[us][ROOK][rto];
+ st->psq += PSQT::psq[captured][rto] - PSQT::psq[captured][rfrom];
+ k ^= Zobrist::psq[captured][rfrom] ^ Zobrist::psq[captured][rto];
+ captured = NO_PIECE;
}
if (captured)
// If the captured piece is a pawn, update pawn hash key, otherwise
// update non-pawn material.
- if (captured == PAWN)
+ if (type_of(captured) == PAWN)
{
if (type_of(m) == ENPASSANT)
{
capsq -= pawn_push(us);
- assert(pt == PAWN);
+ assert(pc == make_piece(us, PAWN));
assert(to == st->epSquare);
assert(relative_rank(us, to) == RANK_6);
assert(piece_on(to) == NO_PIECE);
board[capsq] = NO_PIECE; // Not done by remove_piece()
}
- st->pawnKey ^= Zobrist::psq[them][PAWN][capsq];
+ st->pawnKey ^= Zobrist::psq[captured][capsq];
}
else
st->nonPawnMaterial[them] -= PieceValue[MG][captured];
// Update board and piece lists
- remove_piece(them, captured, capsq);
+ remove_piece(captured, capsq);
// Update material hash key and prefetch access to materialTable
- k ^= Zobrist::psq[them][captured][capsq];
- st->materialKey ^= Zobrist::psq[them][captured][pieceCount[them][captured]];
+ k ^= Zobrist::psq[captured][capsq];
+ st->materialKey ^= Zobrist::psq[captured][pieceCount[captured]];
prefetch(thisThread->materialTable[st->materialKey]);
// Update incremental scores
- st->psq -= PSQT::psq[them][captured][capsq];
+ st->psq -= PSQT::psq[captured][capsq];
// Reset rule 50 counter
st->rule50 = 0;
}
// Update hash key
- k ^= Zobrist::psq[us][pt][from] ^ Zobrist::psq[us][pt][to];
+ k ^= Zobrist::psq[pc][from] ^ Zobrist::psq[pc][to];
// Reset en passant square
if (st->epSquare != SQ_NONE)
// Move the piece. The tricky Chess960 castling is handled earlier
if (type_of(m) != CASTLING)
- move_piece(us, pt, from, to);
+ move_piece(pc, from, to);
// If the moving piece is a pawn do some special extra work
- if (pt == PAWN)
+ if (type_of(pc) == PAWN)
{
// Set en-passant square if the moved pawn can be captured
if ( (int(to) ^ int(from)) == 16
else if (type_of(m) == PROMOTION)
{
- PieceType promotion = promotion_type(m);
+ Piece promotion = make_piece(us, promotion_type(m));
assert(relative_rank(us, to) == RANK_8);
- assert(promotion >= KNIGHT && promotion <= QUEEN);
+ assert(type_of(promotion) >= KNIGHT && type_of(promotion) <= QUEEN);
- remove_piece(us, PAWN, to);
- put_piece(us, promotion, to);
+ remove_piece(pc, to);
+ put_piece(promotion, 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]-1]
- ^ Zobrist::psq[us][PAWN][pieceCount[us][PAWN]];
+ k ^= Zobrist::psq[pc][to] ^ Zobrist::psq[promotion][to];
+ st->pawnKey ^= Zobrist::psq[pc][to];
+ st->materialKey ^= Zobrist::psq[promotion][pieceCount[promotion]-1]
+ ^ Zobrist::psq[pc][pieceCount[pc]];
// Update incremental score
- st->psq += PSQT::psq[us][promotion][to] - PSQT::psq[us][PAWN][to];
+ st->psq += PSQT::psq[promotion][to] - PSQT::psq[pc][to];
// Update material
st->nonPawnMaterial[us] += PieceValue[MG][promotion];
}
// Update pawn hash key and prefetch access to pawnsTable
- st->pawnKey ^= Zobrist::psq[us][PAWN][from] ^ Zobrist::psq[us][PAWN][to];
- prefetch(thisThread->pawnsTable[st->pawnKey]);
+ st->pawnKey ^= Zobrist::psq[pc][from] ^ Zobrist::psq[pc][to];
+ prefetch2(thisThread->pawnsTable[st->pawnKey]);
// Reset rule 50 draw counter
st->rule50 = 0;
}
// Update incremental scores
- st->psq += PSQT::psq[us][pt][to] - PSQT::psq[us][pt][from];
+ st->psq += PSQT::psq[pc][to] - PSQT::psq[pc][from];
// Set capture piece
- st->capturedType = captured;
+ st->capturedPiece = captured;
// Update the key with the final value
st->key = k;
Color us = sideToMove;
Square from = from_sq(m);
Square to = to_sq(m);
- PieceType pt = type_of(piece_on(to));
+ Piece pc = piece_on(to);
assert(empty(from) || type_of(m) == CASTLING);
- assert(st->capturedType != KING);
+ assert(type_of(st->capturedPiece) != KING);
if (type_of(m) == PROMOTION)
{
assert(relative_rank(us, to) == RANK_8);
- assert(pt == promotion_type(m));
- assert(pt >= KNIGHT && pt <= QUEEN);
+ assert(type_of(pc) == promotion_type(m));
+ assert(type_of(pc) >= KNIGHT && type_of(pc) <= QUEEN);
- remove_piece(us, pt, to);
- put_piece(us, PAWN, to);
- pt = PAWN;
+ remove_piece(pc, to);
+ pc = make_piece(us, PAWN);
+ put_piece(pc, to);
}
if (type_of(m) == CASTLING)
}
else
{
- move_piece(us, pt, to, from); // Put the piece back at the source square
+ move_piece(pc, to, from); // Put the piece back at the source square
- if (st->capturedType)
+ if (st->capturedPiece)
{
Square capsq = to;
{
capsq -= pawn_push(us);
- assert(pt == PAWN);
+ assert(type_of(pc) == PAWN);
assert(to == st->previous->epSquare);
assert(relative_rank(us, to) == RANK_6);
assert(piece_on(capsq) == NO_PIECE);
- assert(st->capturedType == PAWN);
+ assert(st->capturedPiece == make_piece(~us, PAWN));
}
- put_piece(~us, st->capturedType, capsq); // Restore the captured piece
+ put_piece(st->capturedPiece, capsq); // Restore the captured piece
}
}
/// Position::do_castling() is a helper used to do/undo a castling move. This
-/// is a bit tricky, especially in Chess960.
+/// is a bit tricky in Chess960 where from/to squares can overlap.
template<bool Do>
void Position::do_castling(Color us, Square from, Square& to, Square& rfrom, Square& rto) {
to = relative_square(us, kingSide ? SQ_G1 : SQ_C1);
// Remove both pieces first since squares could overlap in Chess960
- remove_piece(us, KING, Do ? from : to);
- remove_piece(us, ROOK, Do ? rfrom : rto);
+ remove_piece(make_piece(us, KING), Do ? from : to);
+ remove_piece(make_piece(us, ROOK), Do ? rfrom : rto);
board[Do ? from : to] = board[Do ? rfrom : rto] = NO_PIECE; // Since remove_piece doesn't do it for us
- put_piece(us, KING, Do ? to : from);
- put_piece(us, ROOK, Do ? rto : rfrom);
+ put_piece(make_piece(us, KING), Do ? to : from);
+ put_piece(make_piece(us, ROOK), Do ? rto : rfrom);
}
Key Position::key_after(Move m) const {
- Color us = sideToMove;
Square from = from_sq(m);
Square to = to_sq(m);
- PieceType pt = type_of(piece_on(from));
- PieceType captured = type_of(piece_on(to));
+ Piece pc = piece_on(from);
+ Piece captured = piece_on(to);
Key k = st->key ^ Zobrist::side;
if (captured)
- k ^= Zobrist::psq[~us][captured][to];
+ k ^= Zobrist::psq[captured][to];
- return k ^ Zobrist::psq[us][pt][to] ^ Zobrist::psq[us][pt][from];
+ return k ^ Zobrist::psq[pc][to] ^ Zobrist::psq[pc][from];
}
-/// Position::see() is a static exchange evaluator: It tries to estimate the
-/// material gain or loss resulting from a move.
+/// Position::see_ge (Static Exchange Evaluation Greater or Equal) tests if the
+/// SEE value of move is greater or equal to the given value. We'll use an
+/// algorithm similar to alpha-beta pruning with a null window.
-Value Position::see_sign(Move m) const {
+bool Position::see_ge(Move m, Value v) const {
assert(is_ok(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 (PieceValue[MG][moved_piece(m)] <= PieceValue[MG][piece_on(to_sq(m))])
- return VALUE_KNOWN_WIN;
-
- return see(m);
-}
+ // Castling moves are implemented as king capturing the rook so cannot be
+ // handled correctly. Simply assume the SEE value is VALUE_ZERO that is always
+ // correct unless in the rare case the rook ends up under attack.
+ if (type_of(m) == CASTLING)
+ return VALUE_ZERO >= v;
-Value Position::see(Move m) const {
+ Square from = from_sq(m), to = to_sq(m);
+ PieceType nextVictim = type_of(piece_on(from));
+ Color stm = ~color_of(piece_on(from)); // First consider opponent's move
+ Value balance; // Values of the pieces taken by us minus opponent's ones
+ Bitboard occupied, stmAttackers;
- Square from, to;
- Bitboard occupied, attackers, stmAttackers;
- Value swapList[32];
- int slIndex = 1;
- PieceType captured;
- Color stm;
+ if (type_of(m) == ENPASSANT)
+ {
+ occupied = SquareBB[to - pawn_push(~stm)]; // Remove the captured pawn
+ balance = PieceValue[MG][PAWN];
+ }
+ else
+ {
+ balance = PieceValue[MG][piece_on(to)];
+ occupied = 0;
+ }
- assert(is_ok(m));
+ if (balance < v)
+ return false;
- from = from_sq(m);
- to = to_sq(m);
- swapList[0] = PieceValue[MG][piece_on(to)];
- stm = color_of(piece_on(from));
- occupied = pieces() ^ from;
+ if (nextVictim == KING)
+ return true;
- // Castling moves are implemented as king capturing the rook so cannot
- // be handled correctly. Simply return VALUE_ZERO that is always correct
- // unless in the rare case the rook ends up under attack.
- if (type_of(m) == CASTLING)
- return VALUE_ZERO;
+ balance -= PieceValue[MG][nextVictim];
- if (type_of(m) == ENPASSANT)
- {
- occupied ^= to - pawn_push(stm); // Remove the captured pawn
- swapList[0] = PieceValue[MG][PAWN];
- }
+ if (balance >= v)
+ return true;
- // Find all attackers to the destination square, with the moving piece
- // removed, but possibly an X-ray attacker added behind it.
- attackers = attackers_to(to, occupied) & occupied;
+ bool relativeStm = true; // True if the opponent is to move
+ occupied ^= pieces() ^ from ^ to;
- // If the opponent has no attackers we are finished
- stm = ~stm;
- stmAttackers = attackers & pieces(stm);
- if (!stmAttackers)
- return swapList[0];
+ // Find all attackers to the destination square, with the moving piece removed,
+ // but possibly an X-ray attacker added behind it.
+ Bitboard attackers = attackers_to(to, occupied) & occupied;
- // 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.
- captured = type_of(piece_on(from));
+ while (true)
+ {
+ stmAttackers = attackers & pieces(stm);
- do {
- assert(slIndex < 32);
+ // Don't allow pinned pieces to attack pieces except the king as long all
+ // pinners are on their original square.
+ if (!(st->pinnersForKing[stm] & ~occupied))
+ stmAttackers &= ~st->blockersForKing[stm];
- // Add the new entry to the swap list
- swapList[slIndex] = -swapList[slIndex - 1] + PieceValue[MG][captured];
+ if (!stmAttackers)
+ return relativeStm;
// Locate and remove the next least valuable attacker
- captured = min_attacker<PAWN>(byTypeBB, to, stmAttackers, occupied, attackers);
- stm = ~stm;
- stmAttackers = attackers & pieces(stm);
- ++slIndex;
+ nextVictim = min_attacker<PAWN>(byTypeBB, to, stmAttackers, occupied, attackers);
- } while (stmAttackers && (captured != KING || (--slIndex, false))); // Stop before a king capture
+ if (nextVictim == KING)
+ return relativeStm == bool(attackers & pieces(~stm));
- // 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] = std::min(-swapList[slIndex], swapList[slIndex - 1]);
+ balance += relativeStm ? PieceValue[MG][nextVictim]
+ : -PieceValue[MG][nextVictim];
- return swapList[0];
+ relativeStm = !relativeStm;
+
+ if (relativeStm == (balance >= v))
+ return relativeStm;
+
+ stm = ~stm;
+ }
}
/// Position::is_draw() tests whether the position is drawn by 50-move rule
/// or by repetition. It does not detect stalemates.
-bool Position::is_draw() const {
+bool Position::is_draw(int ply) const {
if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
return true;
- StateInfo* stp = st;
- for (int i = 2, e = std::min(st->rule50, st->pliesFromNull); i <= e; i += 2)
+ int end = std::min(st->rule50, st->pliesFromNull);
+
+ if (end < 4)
+ return false;
+
+ StateInfo* stp = st->previous->previous;
+ int cnt = 0;
+
+ for (int i = 4; i <= end; i += 2)
{
stp = stp->previous->previous;
- if (stp->key == st->key)
- return true; // Draw at first repetition
+ // At root position ply is 1, so return a draw score if a position
+ // repeats once earlier but strictly after the root, or repeats twice
+ // before or at the root.
+ if ( stp->key == st->key
+ && ++cnt + (ply - 1 > i) == 2)
+ return true;
}
return false;
}
if (step == Lists)
- for (Color c = WHITE; c <= BLACK; ++c)
- for (PieceType pt = PAWN; pt <= KING; ++pt)
- {
- if (pieceCount[c][pt] != popcount(pieces(c, pt)))
- return false;
+ for (Piece pc : Pieces)
+ {
+ if (pieceCount[pc] != popcount(pieces(color_of(pc), type_of(pc))))
+ return false;
- for (int i = 0; i < pieceCount[c][pt]; ++i)
- if ( board[pieceList[c][pt][i]] != make_piece(c, pt)
- || index[pieceList[c][pt][i]] != i)
- return false;
- }
+ for (int i = 0; i < pieceCount[pc]; ++i)
+ if (board[pieceList[pc][i]] != pc || index[pieceList[pc][i]] != i)
+ return false;
+ }
if (step == Castling)
for (Color c = WHITE; c <= BLACK; ++c)
projects / stockfish / blobdiff