X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fbitbase.cpp;h=0f274c8aeb82a7d1d7ab0ddf3cfc6833d6f7b570;hp=0599c3c81238d2255583291bc5f3a1ab9a4829ef;hb=d3091971b789b4be4c56fdf608eae33c5c54bbd4;hpb=9a1d5f0f1d8a12a85b198688d4f1d636a146eb7a diff --git a/src/bitbase.cpp b/src/bitbase.cpp index 0599c3c8..0f274c8a 100644 --- a/src/bitbase.cpp +++ b/src/bitbase.cpp @@ -1,7 +1,7 @@ /* Stockfish, a UCI chess playing engine derived from Glaurung 2.1 Copyright (C) 2004-2008 Tord Romstad (Glaurung author) - Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, Tord Romstad + Copyright (C) 2008-2014 Marco Costalba, Joona Kiiski, 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 @@ -25,23 +25,23 @@ namespace { - // The possible pawns squares are 24, the first 4 files and ranks from 2 to 7 - const unsigned IndexMax = 2*24*64*64; // stm * psq * wksq * bksq = 196608 + // 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 // Each uint32_t stores results of 32 positions, one per bit - uint32_t KPKBitbase[IndexMax / 32]; + 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 number of iterations: + // 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 6 - rank (from 6 - RANK_7 to 6 - RANK_2) + // 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) + ((6 - rank_of(psq)) << 15); + return wksq + (bksq << 6) + (us << 12) + (file_of(psq) << 13) + ((RANK_7 - rank_of(psq)) << 15); } enum Result { @@ -55,8 +55,8 @@ namespace { struct KPKPosition { - operator Result() const { return res; } - Result classify_leaf(unsigned idx); + KPKPosition(unsigned idx); + operator Result() const { return result; } Result classify(const std::vector& db) { return us == WHITE ? classify(db) : classify(db); } @@ -65,7 +65,7 @@ namespace { Color us; Square bksq, wksq, psq; - Result res; + Result result; }; } // namespace @@ -83,20 +83,21 @@ bool Bitbases::probe_kpk(Square wksq, Square wpsq, Square bksq, Color us) { void Bitbases::init_kpk() { unsigned idx, repeat = 1; - std::vector db(IndexMax); + std::vector db; + db.reserve(MAX_INDEX); // Initialize db with known win / draw positions - for (idx = 0; idx < IndexMax; idx++) - db[idx].classify_leaf(idx); + for (idx = 0; idx < MAX_INDEX; ++idx) + db.push_back(KPKPosition(idx)); - // Iterate until all positions are classified (15 cycles needed) + // 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 < IndexMax; idx++) - if (db[idx] == UNKNOWN && db[idx].classify(db) != UNKNOWN) - repeat = 1; + for (repeat = idx = 0; idx < MAX_INDEX; ++idx) + repeat |= (db[idx] == UNKNOWN && db[idx].classify(db) != UNKNOWN); // Map 32 results into one KPKBitbase[] entry - for (idx = 0; idx < IndexMax; idx++) + for (idx = 0; idx < MAX_INDEX; ++idx) if (db[idx] == WIN) KPKBitbase[idx / 32] |= 1 << (idx & 0x1F); } @@ -104,34 +105,34 @@ void Bitbases::init_kpk() { namespace { - Result KPKPosition::classify_leaf(unsigned idx) { + KPKPosition::KPKPosition(unsigned idx) { - wksq = Square((idx >> 0) & 0x3F); - bksq = Square((idx >> 6) & 0x3F); - us = Color((idx >> 12) & 0x01); - psq = File((idx >> 13) & 3) | Rank(6 - (idx >> 15)); + wksq = Square((idx >> 0) & 0x3F); + bksq = Square((idx >> 6) & 0x3F); + us = Color ((idx >> 12) & 0x01); + psq = make_square(File((idx >> 13) & 0x3), RANK_7 - Rank((idx >> 15) & 0x7)); + result = UNKNOWN; // Check if two pieces are on the same square or if a king can be captured - if ( wksq == psq || wksq == bksq || bksq == psq - || (StepAttacksBB[KING][wksq] & bksq) + if ( square_distance(wksq, bksq) <= 1 + || wksq == psq + || bksq == psq || (us == WHITE && (StepAttacksBB[PAWN][psq] & bksq))) - return res = INVALID; + result = INVALID; - if (us == WHITE) + else if (us == WHITE) { - // Immediate win if pawn can be promoted without getting captured + // Immediate win if a pawn can be promoted without getting captured if ( rank_of(psq) == RANK_7 && wksq != psq + DELTA_N && ( square_distance(bksq, psq + DELTA_N) > 1 ||(StepAttacksBB[KING][wksq] & (psq + DELTA_N)))) - return res = WIN; + result = WIN; } - // Immediate draw if is stalemate or king captures undefended pawn + // Immediate draw if it is a stalemate or a king captures undefended pawn else if ( !(StepAttacksBB[KING][bksq] & ~(StepAttacksBB[KING][wksq] | StepAttacksBB[PAWN][psq])) || (StepAttacksBB[KING][bksq] & psq & ~StepAttacksBB[KING][wksq])) - return res = DRAW; - - return res = UNKNOWN; + result = DRAW; } template @@ -139,34 +140,36 @@ namespace { // 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 DRAW otherwise the current + // 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 WIN otherwise the current position is - // classified UNKNOWN. + // as WIN, the position is classified as WIN, otherwise the current position is + // classified as UNKNOWN. + + const Color Them = (Us == WHITE ? BLACK : WHITE); Result r = INVALID; Bitboard b = StepAttacksBB[KING][Us == WHITE ? wksq : bksq]; while (b) - r |= Us == WHITE ? db[index(~Us, bksq, pop_lsb(&b), psq)] - : db[index(~Us, pop_lsb(&b), wksq, psq)]; + r |= Us == WHITE ? db[index(Them, bksq, pop_lsb(&b), psq)] + : db[index(Them, pop_lsb(&b), wksq, psq)]; if (Us == WHITE && rank_of(psq) < RANK_7) { Square s = psq + DELTA_N; r |= db[index(BLACK, bksq, wksq, s)]; // Single push - if (rank_of(s) == RANK_3 && s != wksq && s != bksq) + if (rank_of(psq) == RANK_2 && s != wksq && s != bksq) r |= db[index(BLACK, bksq, wksq, s + DELTA_N)]; // Double push } if (Us == WHITE) - return res = r & WIN ? WIN : r & UNKNOWN ? UNKNOWN : DRAW; + return result = r & WIN ? WIN : r & UNKNOWN ? UNKNOWN : DRAW; else - return res = r & DRAW ? DRAW : r & UNKNOWN ? UNKNOWN : WIN; + return result = r & DRAW ? DRAW : r & UNKNOWN ? UNKNOWN : WIN; } } // namespace