/*
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 "bitboard.h"
#include "types.h"
namespace {
- enum Result {
- RESULT_UNKNOWN,
- RESULT_INVALID,
- RESULT_WIN,
- RESULT_DRAW
- };
-
- struct KPKPosition {
- Result classify_knowns(int index);
- Result classify(int index, Result db[]);
-
- private:
- void from_index(int index);
- Result classify_white(const Result db[]);
- Result classify_black(const Result db[]);
- Bitboard wk_attacks() const { return StepAttacksBB[WK][whiteKingSquare]; }
- Bitboard bk_attacks() const { return StepAttacksBB[BK][blackKingSquare]; }
- Bitboard pawn_attacks() const { return StepAttacksBB[WP][pawnSquare]; }
-
- Square whiteKingSquare, blackKingSquare, pawnSquare;
- Color sideToMove;
- };
-
- // The possible pawns squares are 24, the first 4 files and ranks from 2 to 7
- const int IndexMax = 2 * 24 * 64 * 64; // color * wp_sq * wk_sq * bk_sq = 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[IndexMax / 32];
-
- int compute_index(Square wksq, Square bksq, Square wpsq, Color stm);
-}
-
-
-uint32_t probe_kpk_bitbase(Square wksq, Square wpsq, Square bksq, Color stm) {
-
- int index = compute_index(wksq, bksq, wpsq, stm);
-
- return KPKBitbase[index / 32] & (1 << (index & 31));
-}
-
-
-void kpk_bitbase_init() {
-
- Result db[IndexMax];
- KPKPosition pos;
- int index, bit, repeat = 1;
-
- // Initialize table
- for (index = 0; index < IndexMax; index++)
- db[index] = pos.classify_knowns(index);
-
- // Iterate until all positions are classified (30 cycles needed)
- while (repeat)
- for (repeat = index = 0; index < IndexMax; index++)
- if ( db[index] == RESULT_UNKNOWN
- && pos.classify(index, db) != RESULT_UNKNOWN)
- repeat = 1;
-
- // Map 32 position results into one KPKBitbase[] entry
- for (index = 0; index < IndexMax / 32; index++)
- for (bit = 0; bit < 32; bit++)
- if (db[32 * index + bit] == RESULT_WIN)
- KPKBitbase[index] |= (1 << bit);
-}
-
-
-namespace {
+ uint32_t KPKBitbase[MAX_INDEX / 32];
// A KPK bitbase index is an integer in [0, IndexMax] range
//
- // Information is mapped in this way
+ // Information is mapped in a way that minimizes the number of iterations:
//
- // bit 0: side to move (WHITE or BLACK)
- // bit 1- 6: black king square (from SQ_A1 to SQ_H8)
- // bit 7-12: white king square (from SQ_A1 to SQ_H8)
+ // 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 - 1 (from RANK_2 - 1 to RANK_7 - 1)
-
- int compute_index(Square wksq, Square bksq, Square wpsq, Color stm) {
-
- assert(file_of(wpsq) <= FILE_D);
-
- int p = file_of(wpsq) + 4 * (rank_of(wpsq) - 1);
- int r = stm + 2 * bksq + 128 * wksq + 8192 * p;
-
- assert(r >= 0 && r < IndexMax);
-
- return r;
+ // 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 int(wksq) | (bksq << 6) | (us << 12) | (file_of(psq) << 13) | ((RANK_7 - rank_of(psq)) << 15);
}
- void KPKPosition::from_index(int index) {
-
- int s = index >> 13;
- sideToMove = Color(index & 1);
- blackKingSquare = Square((index >> 1) & 63);
- whiteKingSquare = Square((index >> 7) & 63);
- pawnSquare = make_square(File(s & 3), Rank((s >> 2) + 1));
- }
+ enum Result {
+ INVALID = 0,
+ UNKNOWN = 1,
+ DRAW = 2,
+ WIN = 4
+ };
- Result KPKPosition::classify_knowns(int index) {
+ Result& operator|=(Result& r, Result v) { return r = Result(r | v); }
- from_index(index);
+ struct KPKPosition {
+ 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); }
- // Check if two pieces are on the same square
- if ( whiteKingSquare == pawnSquare
- || whiteKingSquare == blackKingSquare
- || blackKingSquare == pawnSquare)
- return RESULT_INVALID;
+ template<Color Us> Result classify(const std::vector<KPKPosition>& db);
- // Check if a king can be captured
- if ( bit_is_set(wk_attacks(), blackKingSquare)
- || (bit_is_set(pawn_attacks(), blackKingSquare) && sideToMove == WHITE))
- return RESULT_INVALID;
+ Color us;
+ Square ksq[COLOR_NB], psq;
+ Result result;
+ };
- // The position is an immediate win if it is white to move and the
- // white pawn can be promoted without getting captured.
- if ( rank_of(pawnSquare) == RANK_7
- && sideToMove == WHITE
- && whiteKingSquare != pawnSquare + DELTA_N
- && ( square_distance(blackKingSquare, pawnSquare + DELTA_N) > 1
- || bit_is_set(wk_attacks(), pawnSquare + DELTA_N)))
- return RESULT_WIN;
+} // namespace
- // Check for known draw positions
- //
- // Case 1: Stalemate
- if ( sideToMove == BLACK
- && (bk_attacks() & ~(wk_attacks() | pawn_attacks())) == EmptyBoardBB)
- return RESULT_DRAW;
-
- // Case 2: King can capture pawn
- if ( sideToMove == BLACK
- && bit_is_set(bk_attacks(), pawnSquare) && !bit_is_set(wk_attacks(), pawnSquare))
- return RESULT_DRAW;
-
- // Case 3: Black king in front of white pawn
- if ( blackKingSquare == pawnSquare + DELTA_N
- && rank_of(pawnSquare) < RANK_7)
- return RESULT_DRAW;
-
- // Case 4: White king in front of pawn and black has opposition
- if ( whiteKingSquare == pawnSquare + DELTA_N
- && blackKingSquare == pawnSquare + DELTA_N + DELTA_N + DELTA_N
- && rank_of(pawnSquare) < RANK_5
- && sideToMove == WHITE)
- return RESULT_DRAW;
-
- // Case 5: Stalemate with rook pawn
- if ( blackKingSquare == SQ_A8
- && file_of(pawnSquare) == FILE_A)
- return RESULT_DRAW;
-
- return RESULT_UNKNOWN;
- }
- Result KPKPosition::classify(int index, Result db[]) {
+bool Bitbases::probe(Square wksq, Square wpsq, Square bksq, Color us) {
- from_index(index);
- db[index] = (sideToMove == WHITE ? classify_white(db) : classify_black(db));
- return db[index];
- }
+ assert(file_of(wpsq) <= FILE_D);
- Result KPKPosition::classify_white(const Result db[]) {
+ unsigned idx = index(us, bksq, wksq, wpsq);
+ return KPKBitbase[idx / 32] & (1 << (idx & 0x1F));
+}
- // If one move leads to a position classified as RESULT_WIN, 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.
- bool unknownFound = false;
- Bitboard b;
- Square s;
- Result r;
+void Bitbases::init() {
- // King moves
- b = wk_attacks();
- while (b)
- {
- s = pop_1st_bit(&b);
- r = db[compute_index(s, blackKingSquare, pawnSquare, BLACK)];
+ std::vector<KPKPosition> db(MAX_INDEX);
+ unsigned idx, repeat = 1;
- if (r == RESULT_WIN)
- return RESULT_WIN;
+ // Initialize db with known win / draw positions
+ for (idx = 0; idx < MAX_INDEX; ++idx)
+ db[idx] = KPKPosition(idx);
- if (r == RESULT_UNKNOWN)
- unknownFound = true;
- }
-
- // Pawn moves
- if (rank_of(pawnSquare) < RANK_7)
- {
- s = pawnSquare + DELTA_N;
- r = db[compute_index(whiteKingSquare, blackKingSquare, s, BLACK)];
-
- if (r == RESULT_WIN)
- return RESULT_WIN;
+ // 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);
- if (r == RESULT_UNKNOWN)
- unknownFound = true;
+ // Map 32 results into one KPKBitbase[] entry
+ for (idx = 0; idx < MAX_INDEX; ++idx)
+ if (db[idx] == WIN)
+ KPKBitbase[idx / 32] |= 1 << (idx & 0x1F);
+}
- // Double pawn push
- if (rank_of(s) == RANK_3 && r != RESULT_INVALID)
- {
- s += DELTA_N;
- r = db[compute_index(whiteKingSquare, blackKingSquare, s, BLACK)];
- if (r == RESULT_WIN)
- return RESULT_WIN;
+namespace {
- if (r == RESULT_UNKNOWN)
- unknownFound = true;
- }
- }
- return unknownFound ? RESULT_UNKNOWN : RESULT_DRAW;
+ 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(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
+ || (us == WHITE && (PawnAttacks[WHITE][psq] & ksq[BLACK])))
+ result = INVALID;
+
+ // Immediate win if a pawn can be promoted without getting captured
+ else if ( us == WHITE
+ && rank_of(psq) == RANK_7
+ && ksq[us] != psq + NORTH
+ && ( distance(ksq[~us], psq + NORTH) > 1
+ || (PseudoAttacks[KING][ksq[us]] & (psq + NORTH))))
+ result = WIN;
+
+ // Immediate draw if it is a stalemate or a king captures undefended pawn
+ else if ( us == BLACK
+ && ( !(PseudoAttacks[KING][ksq[us]] & ~(PseudoAttacks[KING][ksq[~us]] | PawnAttacks[~us][psq]))
+ || (PseudoAttacks[KING][ksq[us]] & psq & ~PseudoAttacks[KING][ksq[~us]])))
+ result = DRAW;
+
+ // Position will be classified later
+ else
+ result = UNKNOWN;
}
- Result KPKPosition::classify_black(const Result db[]) {
+ template<Color Us>
+ Result KPKPosition::classify(const std::vector<KPKPosition>& db) {
- // 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 position is classified as RESULT_WIN.
- // Otherwise, the current position is classified as RESULT_UNKNOWN.
+ // 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.
+
+ constexpr Color Them = (Us == WHITE ? BLACK : WHITE);
+ constexpr Result Good = (Us == WHITE ? WIN : DRAW);
+ constexpr Result Bad = (Us == WHITE ? DRAW : WIN);
- bool unknownFound = false;
- Bitboard b;
- Square s;
- Result r;
+ Result r = INVALID;
+ Bitboard b = PseudoAttacks[KING][ksq[Us]];
- // King moves
- b = bk_attacks();
while (b)
- {
- s = pop_1st_bit(&b);
- r = db[compute_index(whiteKingSquare, s, pawnSquare, WHITE)];
+ r |= Us == WHITE ? db[index(Them, ksq[Them] , pop_lsb(&b), psq)]
+ : db[index(Them, pop_lsb(&b), ksq[Them] , psq)];
- if (r == RESULT_DRAW)
- return RESULT_DRAW;
+ if (Us == WHITE)
+ {
+ if (rank_of(psq) < RANK_7) // Single push
+ r |= db[index(Them, ksq[Them], ksq[Us], psq + NORTH)];
- if (r == RESULT_UNKNOWN)
- unknownFound = true;
+ if ( rank_of(psq) == RANK_2 // Double push
+ && psq + NORTH != ksq[Us]
+ && psq + NORTH != ksq[Them])
+ r |= db[index(Them, ksq[Them], ksq[Us], psq + NORTH + NORTH)];
}
- return unknownFound ? RESULT_UNKNOWN : RESULT_WIN;
+
+ return result = r & Good ? Good : r & UNKNOWN ? UNKNOWN : Bad;
}
-}
+} // namespace
projects / stockfish / blobdiff