/*
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
+ Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2015-2020 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 <cassert>
+#include <numeric>
+#include <vector>
+#include <bitset>
#include "bitboard.h"
#include "types.h"
namespace {
+ // 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
+
+ std::bitset<MAX_INDEX> KPKBitbase;
+
+ // A KPK bitbase index is an integer in [0, IndexMax] range
+ //
+ // Information is mapped in a way that minimizes the number of iterations:
+ //
+ // bit 0- 5: white king square (from SQ_A1 to SQ_H8)
+ // bit 6-11: black king square (from SQ_A1 to SQ_H8)
+ // 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 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 {
- RESULT_UNKNOWN,
- RESULT_INVALID,
- RESULT_WIN,
- RESULT_LOSS,
- RESULT_DRAW
+ INVALID = 0,
+ UNKNOWN = 1,
+ DRAW = 2,
+ WIN = 4
};
+ Result& operator|=(Result& r, Result v) { return r = Result(r | v); }
+
struct KPKPosition {
- void from_index(int index);
- bool is_legal() const;
- bool is_immediate_draw() const;
- bool is_immediate_win() const;
- Bitboard wk_attacks() const { return NonSlidingAttacksBB[WK][whiteKingSquare]; }
- Bitboard bk_attacks() const { return NonSlidingAttacksBB[BK][blackKingSquare]; }
- Bitboard pawn_attacks() const { return NonSlidingAttacksBB[WP][pawnSquare]; }
-
- Square whiteKingSquare, blackKingSquare, pawnSquare;
- Color sideToMove;
+ KPKPosition() = default;
+ explicit KPKPosition(unsigned idx);
+ operator Result() const { return result; }
+ Result classify(const std::vector<KPKPosition>& db);
+
+ Color stm;
+ Square ksq[COLOR_NB], psq;
+ Result result;
};
- const int IndexMax = 2 * 24 * 64 * 64;
-
- Result classify_wtm(const KPKPosition& pos, const Result bb[]);
- Result classify_btm(const KPKPosition& pos, const Result bb[]);
- int compute_index(Square wksq, Square bksq, Square psq, Color stm);
-}
+} // namespace
-void generate_kpk_bitbase(uint8_t bitbase[]) {
+bool Bitbases::probe(Square wksq, Square wpsq, Square bksq, Color stm) {
- bool repeat;
- int i, j, b;
- KPKPosition pos;
- Result bb[IndexMax];
+ assert(file_of(wpsq) <= FILE_D);
- // Initialize table
- for (i = 0; i < IndexMax; i++)
- {
- pos.from_index(i);
- bb[i] = !pos.is_legal() ? RESULT_INVALID
- : pos.is_immediate_draw() ? RESULT_DRAW
- : pos.is_immediate_win() ? RESULT_WIN : RESULT_UNKNOWN;
- }
+ return KPKBitbase[index(stm, bksq, wksq, wpsq)];
+}
- // Iterate until all positions are classified (30 cycles needed)
- do {
- repeat = false;
- for (i = 0; i < IndexMax; i++)
- if (bb[i] == RESULT_UNKNOWN)
- {
- pos.from_index(i);
+void Bitbases::init() {
- bb[i] = (pos.sideToMove == WHITE) ? classify_wtm(pos, bb)
- : classify_btm(pos, bb);
- if (bb[i] != RESULT_UNKNOWN)
- repeat = true;
- }
+ std::vector<KPKPosition> db(MAX_INDEX);
+ unsigned idx, repeat = 1;
- } while (repeat);
+ // Initialize db with known win / draw positions
+ for (idx = 0; idx < MAX_INDEX; ++idx)
+ db[idx] = KPKPosition(idx);
- // Compress result and map into supplied bitbase parameter
- for (i = 0; i < 24576; i++)
- {
- b = 0;
- for (j = 0; j < 8; j++)
- if (bb[8*i+j] == RESULT_WIN || bb[8*i+j] == RESULT_LOSS)
- b |= (1 << j);
+ // Iterate through the positions until none of the unknown positions can be
+ // changed to either wins or draws (15 cycles needed).
+ while (repeat)
+ for (repeat = idx = 0; idx < MAX_INDEX; ++idx)
+ repeat |= (db[idx] == UNKNOWN && db[idx].classify(db) != UNKNOWN);
- bitbase[i] = (uint8_t)b;
- }
+ // Fill the bitbase with the decisive results
+ for (idx = 0; idx < MAX_INDEX; ++idx)
+ if (db[idx] == WIN)
+ KPKBitbase.set(idx);
}
namespace {
- int compute_index(Square wksq, Square bksq, Square psq, Color stm) {
-
- int p = int(square_file(psq)) + (int(square_rank(psq)) - 1) * 4;
- int r = int(stm) + 2 * int(bksq) + 128 * int(wksq) + 8192 * p;
-
- assert(r >= 0 && r < IndexMax);
-
- return r;
- }
-
- void KPKPosition::from_index(int index) {
-
- int s = (index / 8192) % 24;
-
- sideToMove = Color(index % 2);
- blackKingSquare = Square((index / 2) % 64);
- whiteKingSquare = Square((index / 128) % 64);
- pawnSquare = make_square(File(s % 4), Rank(s / 4 + 1));
- }
-
- bool KPKPosition::is_legal() const {
-
- if ( whiteKingSquare == pawnSquare
- || whiteKingSquare == blackKingSquare
- || pawnSquare == blackKingSquare)
- return false;
-
- if (sideToMove == WHITE)
- {
- if ( bit_is_set(wk_attacks(), blackKingSquare)
- || bit_is_set(pawn_attacks(), blackKingSquare))
- return false;
- }
- else if (bit_is_set(bk_attacks(), whiteKingSquare))
- return false;
-
- return true;
- }
-
- bool KPKPosition::is_immediate_draw() const {
-
- if (sideToMove == BLACK)
- {
- Bitboard wka = wk_attacks();
- Bitboard bka = bk_attacks();
-
- // Case 1: Stalemate
- if ((bka & ~(wka | pawn_attacks())) == EmptyBoardBB)
- return true;
-
- // Case 2: King can capture pawn
- if (bit_is_set(bka, pawnSquare) && !bit_is_set(wka, pawnSquare))
- return true;
- }
+ KPKPosition::KPKPosition(unsigned idx) {
+
+ ksq[WHITE] = Square((idx >> 0) & 0x3F);
+ ksq[BLACK] = Square((idx >> 6) & 0x3F);
+ 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
+ if ( distance(ksq[WHITE], ksq[BLACK]) <= 1
+ || ksq[WHITE] == psq
+ || ksq[BLACK] == psq
+ || (stm == WHITE && (PawnAttacks[WHITE][psq] & ksq[BLACK])))
+ result = INVALID;
+
+ // Immediate win if a pawn can be promoted without getting captured
+ else if ( stm == WHITE
+ && rank_of(psq) == RANK_7
+ && ksq[stm] != psq + NORTH
+ && ( distance(ksq[~stm], psq + NORTH) > 1
+ || (PseudoAttacks[KING][ksq[stm]] & (psq + NORTH))))
+ result = WIN;
+
+ // Immediate draw if it is a stalemate or a king captures undefended pawn
+ else if ( stm == BLACK
+ && ( !(PseudoAttacks[KING][ksq[stm]] & ~(PseudoAttacks[KING][ksq[~stm]] | PawnAttacks[~stm][psq]))
+ || (PseudoAttacks[KING][ksq[stm]] & psq & ~PseudoAttacks[KING][ksq[~stm]])))
+ result = DRAW;
+
+ // Position will be classified later
else
- {
- // Case 1: Stalemate
- if ( whiteKingSquare == SQ_A8
- && pawnSquare == SQ_A7
- && (blackKingSquare == SQ_C7 || blackKingSquare == SQ_C8))
- return true;
- }
- return false;
+ result = UNKNOWN;
}
- bool KPKPosition::is_immediate_win() const {
-
- // The position is an immediate win if it is white to move and the
- // white pawn can be promoted without getting captured.
- return sideToMove == WHITE
- && square_rank(pawnSquare) == RANK_7
- && ( square_distance(blackKingSquare, pawnSquare + DELTA_N) > 1
- || bit_is_set(wk_attacks(), pawnSquare + DELTA_N));
- }
+ Result KPKPosition::classify(const std::vector<KPKPosition>& db) {
- Result classify_wtm(const KPKPosition& pos, const Result bb[]) {
+ // White to move: If one move leads to a position classified as WIN, the result
+ // of the current position is WIN. If all moves lead to positions classified
+ // as DRAW, the current position is classified as DRAW, otherwise the current
+ // position is classified as UNKNOWN.
+ //
+ // Black to move: If one move leads to a position classified as DRAW, 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 Result Good = (stm == WHITE ? WIN : DRAW);
+ const Result Bad = (stm == WHITE ? DRAW : WIN);
- // If one move leads to a position classified as RESULT_LOSS, the result
- // of the current position is RESULT_WIN. If all moves lead to positions
- // classified as RESULT_DRAW, the current position is classified RESULT_DRAW
- // otherwise the current position is classified as RESULT_UNKNOWN.
+ Result r = INVALID;
+ Bitboard b = PseudoAttacks[KING][ksq[stm]];
- bool unknownFound = false;
- Bitboard b;
- Square s;
- int idx;
-
- // King moves
- b = pos.wk_attacks();
while (b)
- {
- s = pop_1st_bit(&b);
- idx = compute_index(s, pos.blackKingSquare, pos.pawnSquare, BLACK);
-
- switch (bb[idx]) {
-
- case RESULT_LOSS:
- return RESULT_WIN;
-
- case RESULT_UNKNOWN:
- unknownFound = true;
-
- case RESULT_DRAW:
- case RESULT_INVALID:
- break;
-
- default:
- assert(false);
- }
- }
+ r |= stm == WHITE ? db[index(BLACK, ksq[BLACK] , pop_lsb(&b), psq)]
+ : db[index(WHITE, pop_lsb(&b), ksq[WHITE], psq)];
- // Pawn moves
- if (square_rank(pos.pawnSquare) < RANK_7)
+ if (stm == WHITE)
{
- s = pos.pawnSquare + DELTA_N;
- idx = compute_index(pos.whiteKingSquare, pos.blackKingSquare, s, BLACK);
-
- switch (bb[idx]) {
-
- case RESULT_LOSS:
- return RESULT_WIN;
-
- case RESULT_UNKNOWN:
- unknownFound = true;
-
- case RESULT_DRAW:
- case RESULT_INVALID:
- break;
-
- default:
- assert(false);
- }
-
- // Double pawn push
- if ( square_rank(s) == RANK_3
- && s != pos.whiteKingSquare
- && s != pos.blackKingSquare)
- {
- s += DELTA_N;
- idx = compute_index(pos.whiteKingSquare, pos.blackKingSquare, s, BLACK);
-
- switch (bb[idx]) {
-
- case RESULT_LOSS:
- return RESULT_WIN;
+ if (rank_of(psq) < RANK_7) // Single push
+ r |= db[index(BLACK, ksq[BLACK], ksq[WHITE], psq + NORTH)];
- case RESULT_UNKNOWN:
- unknownFound = true;
-
- case RESULT_DRAW:
- case RESULT_INVALID:
- break;
-
- default:
- assert(false);
- }
- }
+ if ( rank_of(psq) == RANK_2 // Double push
+ && psq + NORTH != ksq[WHITE]
+ && psq + NORTH != ksq[BLACK])
+ r |= db[index(BLACK, ksq[BLACK], ksq[WHITE], psq + NORTH + NORTH)];
}
- return unknownFound ? RESULT_UNKNOWN : RESULT_DRAW;
- }
-
-
- Result classify_btm(const KPKPosition& pos, const Result bb[]) {
-
- // If one move leads to a position classified as RESULT_DRAW, the result
- // of the current position is RESULT_DRAW. If all moves lead to positions
- // classified as RESULT_WIN, the current position is classified as
- // RESULT_LOSS. Otherwise, the current position is classified as
- // RESULT_UNKNOWN.
-
- bool unknownFound = false;
- Bitboard b;
- Square s;
- int idx;
-
- // King moves
- b = pos.bk_attacks();
- while (b)
- {
- s = pop_1st_bit(&b);
- idx = compute_index(pos.whiteKingSquare, s, pos.pawnSquare, WHITE);
-
- switch (bb[idx]) {
-
- case RESULT_DRAW:
- return RESULT_DRAW;
- case RESULT_UNKNOWN:
- unknownFound = true;
-
- case RESULT_WIN:
- case RESULT_INVALID:
- break;
-
- default:
- assert(false);
- }
- }
- return unknownFound ? RESULT_UNKNOWN : RESULT_LOSS;
+ return result = r & Good ? Good : r & UNKNOWN ? UNKNOWN : Bad;
}
-}
+} // namespace
projects / stockfish / blobdiff