/*
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) 2004-2023 The Stockfish developers (see AUTHORS file)
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
-#include <algorithm>
#include <cassert>
-#include <numeric>
#include <vector>
+#include <bitset>
#include "bitboard.h"
#include "types.h"
+namespace Stockfish {
+
namespace {
- // There are 24 possible pawn squares: the first 4 files and ranks from 2 to 7
- const unsigned MAX_INDEX = 2*24*64*64; // stm * psq * wksq * bksq = 196608
+ // There are 24 possible pawn squares: files A to D and ranks from 2 to 7.
+ // Positions with the pawn on files E to H will be mirrored before probing.
+ constexpr unsigned MAX_INDEX = 2*24*64*64; // stm * psq * wksq * bksq = 196608
- // Each uint32_t stores results of 32 positions, one per bit
- uint32_t KPKBitbase[MAX_INDEX / 32];
+ std::bitset<MAX_INDEX> KPKBitbase;
// A KPK bitbase index is an integer in [0, IndexMax] range
//
// bit 12: side to move (WHITE or BLACK)
// bit 13-14: white pawn file (from FILE_A to FILE_D)
// bit 15-17: white pawn RANK_7 - rank (from RANK_7 - RANK_7 to RANK_7 - RANK_2)
- unsigned index(Color us, Square bksq, Square wksq, Square psq) {
- return wksq | (bksq << 6) | (us << 12) | (file_of(psq) << 13) | ((RANK_7 - rank_of(psq)) << 15);
+ unsigned index(Color stm, Square bksq, Square wksq, Square psq) {
+ return int(wksq) | (bksq << 6) | (stm << 12) | (file_of(psq) << 13) | ((RANK_7 - rank_of(psq)) << 15);
}
enum Result {
KPKPosition() = default;
explicit KPKPosition(unsigned idx);
operator Result() const { return result; }
- Result classify(const std::vector<KPKPosition>& db)
- { return us == WHITE ? classify<WHITE>(db) : classify<BLACK>(db); }
-
- template<Color Us> Result classify(const std::vector<KPKPosition>& db);
+ Result classify(const std::vector<KPKPosition>& db);
- Color us;
+ Color stm;
Square ksq[COLOR_NB], psq;
Result result;
};
} // namespace
-
-bool Bitbases::probe(Square wksq, Square wpsq, Square bksq, Color us) {
+bool Bitbases::probe(Square wksq, Square wpsq, Square bksq, Color stm) {
assert(file_of(wpsq) <= FILE_D);
- unsigned idx = index(us, bksq, wksq, wpsq);
- return KPKBitbase[idx / 32] & (1 << (idx & 0x1F));
+ return KPKBitbase[index(stm, bksq, wksq, wpsq)];
}
for (repeat = idx = 0; idx < MAX_INDEX; ++idx)
repeat |= (db[idx] == UNKNOWN && db[idx].classify(db) != UNKNOWN);
- // Map 32 results into one KPKBitbase[] entry
+ // Fill the bitbase with the decisive results
for (idx = 0; idx < MAX_INDEX; ++idx)
if (db[idx] == WIN)
- KPKBitbase[idx / 32] |= 1 << (idx & 0x1F);
+ KPKBitbase.set(idx);
}
-
namespace {
KPKPosition::KPKPosition(unsigned idx) {
ksq[WHITE] = Square((idx >> 0) & 0x3F);
ksq[BLACK] = Square((idx >> 6) & 0x3F);
- us = Color ((idx >> 12) & 0x01);
- psq = make_square(File((idx >> 13) & 0x3), RANK_7 - Rank((idx >> 15) & 0x7));
+ stm = Color ((idx >> 12) & 0x01);
+ psq = make_square(File((idx >> 13) & 0x3), Rank(RANK_7 - ((idx >> 15) & 0x7)));
- // Check if two pieces are on the same square or if a king can be captured
+ // Invalid if two pieces are on the same square or if a king can be captured
if ( distance(ksq[WHITE], ksq[BLACK]) <= 1
|| ksq[WHITE] == psq
|| ksq[BLACK] == psq
- || (us == WHITE && (StepAttacksBB[PAWN][psq] & ksq[BLACK])))
+ || (stm == WHITE && (pawn_attacks_bb(WHITE, psq) & ksq[BLACK])))
result = INVALID;
- // Immediate win if a pawn can be promoted without getting captured
- else if ( us == WHITE
+ // Win if the pawn can be promoted without getting captured
+ else if ( stm == WHITE
&& rank_of(psq) == RANK_7
- && ksq[us] != psq + DELTA_N
- && ( distance(ksq[~us], psq + DELTA_N) > 1
- || (StepAttacksBB[KING][ksq[us]] & (psq + DELTA_N))))
+ && ksq[WHITE] != psq + NORTH
+ && ( distance(ksq[BLACK], psq + NORTH) > 1
+ || (distance(ksq[WHITE], psq + NORTH) == 1)))
result = WIN;
- // Immediate draw if it is a stalemate or a king captures undefended pawn
- else if ( us == BLACK
- && ( !(StepAttacksBB[KING][ksq[us]] & ~(StepAttacksBB[KING][ksq[~us]] | StepAttacksBB[PAWN][psq]))
- || (StepAttacksBB[KING][ksq[us]] & psq & ~StepAttacksBB[KING][ksq[~us]])))
+ // Draw if it is stalemate or the black king can capture the pawn
+ else if ( stm == BLACK
+ && ( !(attacks_bb<KING>(ksq[BLACK]) & ~(attacks_bb<KING>(ksq[WHITE]) | pawn_attacks_bb(WHITE, psq)))
+ || (attacks_bb<KING>(ksq[BLACK]) & ~attacks_bb<KING>(ksq[WHITE]) & psq)))
result = DRAW;
// Position will be classified later
result = UNKNOWN;
}
- template<Color Us>
Result KPKPosition::classify(const std::vector<KPKPosition>& db) {
// White to move: If one move leads to a position classified as WIN, the result
// of the current position is DRAW. If all moves lead to positions classified
// as WIN, the position is classified as WIN, otherwise the current position is
// classified as UNKNOWN.
-
- const Color Them = (Us == WHITE ? BLACK : WHITE);
- const Result Good = (Us == WHITE ? WIN : DRAW);
- const Result Bad = (Us == WHITE ? DRAW : WIN);
+ const Result Good = (stm == WHITE ? WIN : DRAW);
+ const Result Bad = (stm == WHITE ? DRAW : WIN);
Result r = INVALID;
- Bitboard b = StepAttacksBB[KING][ksq[Us]];
+ Bitboard b = attacks_bb<KING>(ksq[stm]);
while (b)
- r |= Us == WHITE ? db[index(Them, ksq[Them] , pop_lsb(&b), psq)]
- : db[index(Them, pop_lsb(&b), ksq[Them] , psq)];
+ r |= stm == WHITE ? db[index(BLACK, ksq[BLACK], pop_lsb(b), psq)]
+ : db[index(WHITE, pop_lsb(b), ksq[WHITE], psq)];
- if (Us == WHITE)
+ if (stm == WHITE)
{
if (rank_of(psq) < RANK_7) // Single push
- r |= db[index(Them, ksq[Them], ksq[Us], psq + DELTA_N)];
+ r |= db[index(BLACK, ksq[BLACK], ksq[WHITE], psq + NORTH)];
if ( rank_of(psq) == RANK_2 // Double push
- && psq + DELTA_N != ksq[Us]
- && psq + DELTA_N != ksq[Them])
- r |= db[index(Them, ksq[Them], ksq[Us], psq + DELTA_N + DELTA_N)];
+ && psq + NORTH != ksq[WHITE]
+ && psq + NORTH != ksq[BLACK])
+ r |= db[index(BLACK, ksq[BLACK], ksq[WHITE], psq + NORTH + NORTH)];
}
return result = r & Good ? Good : r & UNKNOWN ? UNKNOWN : Bad;
}
} // namespace
+
+} // namespace Stockfish