X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fbitbase.cpp;h=7bc4a65c25900324ecbed98f7db7ab1598d830f2;hp=3426a3182ee703e0919001447a4ed84a241fa0ba;hb=75dfdeac119d0ce71c36ba5ab4f33318f589b158;hpb=d653aeca05bf13b42f57c65ecaa642217166c813 diff --git a/src/bitbase.cpp b/src/bitbase.cpp index 3426a318..7bc4a65c 100644 --- a/src/bitbase.cpp +++ b/src/bitbase.cpp @@ -1,7 +1,8 @@ /* 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 @@ -18,294 +19,156 @@ */ #include +#include +#include #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 + + // Each uint32_t stores results of 32 positions, one per bit + uint32_t KPKBitbase[MAX_INDEX / 32]; + + // 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 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; + KPKPosition() = default; + explicit KPKPosition(unsigned idx); + operator Result() const { return result; } + Result classify(const std::vector& 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; - } + unsigned idx = index(stm, bksq, wksq, wpsq); + return KPKBitbase[idx / 32] & (1 << (idx & 0x1F)); +} - // 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 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; - } + // Map 32 results into one KPKBitbase[] entry + for (idx = 0; idx < MAX_INDEX; ++idx) + if (db[idx] == WIN) + KPKBitbase[idx / 32] |= 1 << (idx & 0x1F); } 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; - - if ( whiteKingSquare == SQ_H8 - && pawnSquare == SQ_H7 - && (blackKingSquare == SQ_F7 || blackKingSquare == SQ_F8)) - 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 - && whiteKingSquare != pawnSquare + DELTA_N - && ( square_distance(blackKingSquare, pawnSquare + DELTA_N) > 1 - || bit_is_set(wk_attacks(), pawnSquare + DELTA_N)); - } + Result KPKPosition::classify(const std::vector& 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