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Member "stockfish-11-linux/src/bitbase.cpp" (18 Jan 2020, 6308 Bytes) of package /linux/privat/stockfish-11-linux.zip:


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    1 /*
    2   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
    3   Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
    4   Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
    5   Copyright (C) 2015-2020 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
    6 
    7   Stockfish is free software: you can redistribute it and/or modify
    8   it under the terms of the GNU General Public License as published by
    9   the Free Software Foundation, either version 3 of the License, or
   10   (at your option) any later version.
   11 
   12   Stockfish is distributed in the hope that it will be useful,
   13   but WITHOUT ANY WARRANTY; without even the implied warranty of
   14   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   15   GNU General Public License for more details.
   16 
   17   You should have received a copy of the GNU General Public License
   18   along with this program.  If not, see <http://www.gnu.org/licenses/>.
   19 */
   20 
   21 #include <cassert>
   22 #include <numeric>
   23 #include <vector>
   24 
   25 #include "bitboard.h"
   26 #include "types.h"
   27 
   28 namespace {
   29 
   30   // There are 24 possible pawn squares: files A to D and ranks from 2 to 7.
   31   // Positions with the pawn on files E to H will be mirrored before probing.
   32   constexpr unsigned MAX_INDEX = 2*24*64*64; // stm * psq * wksq * bksq = 196608
   33 
   34   // Each uint32_t stores results of 32 positions, one per bit
   35   uint32_t KPKBitbase[MAX_INDEX / 32];
   36 
   37   // A KPK bitbase index is an integer in [0, IndexMax] range
   38   //
   39   // Information is mapped in a way that minimizes the number of iterations:
   40   //
   41   // bit  0- 5: white king square (from SQ_A1 to SQ_H8)
   42   // bit  6-11: black king square (from SQ_A1 to SQ_H8)
   43   // bit    12: side to move (WHITE or BLACK)
   44   // bit 13-14: white pawn file (from FILE_A to FILE_D)
   45   // bit 15-17: white pawn RANK_7 - rank (from RANK_7 - RANK_7 to RANK_7 - RANK_2)
   46   unsigned index(Color us, Square bksq, Square wksq, Square psq) {
   47     return int(wksq) | (bksq << 6) | (us << 12) | (file_of(psq) << 13) | ((RANK_7 - rank_of(psq)) << 15);
   48   }
   49 
   50   enum Result {
   51     INVALID = 0,
   52     UNKNOWN = 1,
   53     DRAW    = 2,
   54     WIN     = 4
   55   };
   56 
   57   Result& operator|=(Result& r, Result v) { return r = Result(r | v); }
   58 
   59   struct KPKPosition {
   60     KPKPosition() = default;
   61     explicit KPKPosition(unsigned idx);
   62     operator Result() const { return result; }
   63     Result classify(const std::vector<KPKPosition>& db)
   64     { return us == WHITE ? classify<WHITE>(db) : classify<BLACK>(db); }
   65 
   66     template<Color Us> Result classify(const std::vector<KPKPosition>& db);
   67 
   68     Color us;
   69     Square ksq[COLOR_NB], psq;
   70     Result result;
   71   };
   72 
   73 } // namespace
   74 
   75 
   76 bool Bitbases::probe(Square wksq, Square wpsq, Square bksq, Color us) {
   77 
   78   assert(file_of(wpsq) <= FILE_D);
   79 
   80   unsigned idx = index(us, bksq, wksq, wpsq);
   81   return KPKBitbase[idx / 32] & (1 << (idx & 0x1F));
   82 }
   83 
   84 
   85 void Bitbases::init() {
   86 
   87   std::vector<KPKPosition> db(MAX_INDEX);
   88   unsigned idx, repeat = 1;
   89 
   90   // Initialize db with known win / draw positions
   91   for (idx = 0; idx < MAX_INDEX; ++idx)
   92       db[idx] = KPKPosition(idx);
   93 
   94   // Iterate through the positions until none of the unknown positions can be
   95   // changed to either wins or draws (15 cycles needed).
   96   while (repeat)
   97       for (repeat = idx = 0; idx < MAX_INDEX; ++idx)
   98           repeat |= (db[idx] == UNKNOWN && db[idx].classify(db) != UNKNOWN);
   99 
  100   // Map 32 results into one KPKBitbase[] entry
  101   for (idx = 0; idx < MAX_INDEX; ++idx)
  102       if (db[idx] == WIN)
  103           KPKBitbase[idx / 32] |= 1 << (idx & 0x1F);
  104 }
  105 
  106 
  107 namespace {
  108 
  109   KPKPosition::KPKPosition(unsigned idx) {
  110 
  111     ksq[WHITE] = Square((idx >>  0) & 0x3F);
  112     ksq[BLACK] = Square((idx >>  6) & 0x3F);
  113     us         = Color ((idx >> 12) & 0x01);
  114     psq        = make_square(File((idx >> 13) & 0x3), Rank(RANK_7 - ((idx >> 15) & 0x7)));
  115 
  116     // Check if two pieces are on the same square or if a king can be captured
  117     if (   distance(ksq[WHITE], ksq[BLACK]) <= 1
  118         || ksq[WHITE] == psq
  119         || ksq[BLACK] == psq
  120         || (us == WHITE && (PawnAttacks[WHITE][psq] & ksq[BLACK])))
  121         result = INVALID;
  122 
  123     // Immediate win if a pawn can be promoted without getting captured
  124     else if (   us == WHITE
  125              && rank_of(psq) == RANK_7
  126              && ksq[us] != psq + NORTH
  127              && (    distance(ksq[~us], psq + NORTH) > 1
  128                  || (PseudoAttacks[KING][ksq[us]] & (psq + NORTH))))
  129         result = WIN;
  130 
  131     // Immediate draw if it is a stalemate or a king captures undefended pawn
  132     else if (   us == BLACK
  133              && (  !(PseudoAttacks[KING][ksq[us]] & ~(PseudoAttacks[KING][ksq[~us]] | PawnAttacks[~us][psq]))
  134                  || (PseudoAttacks[KING][ksq[us]] & psq & ~PseudoAttacks[KING][ksq[~us]])))
  135         result = DRAW;
  136 
  137     // Position will be classified later
  138     else
  139         result = UNKNOWN;
  140   }
  141 
  142   template<Color Us>
  143   Result KPKPosition::classify(const std::vector<KPKPosition>& db) {
  144 
  145     // White to move: If one move leads to a position classified as WIN, the result
  146     // of the current position is WIN. If all moves lead to positions classified
  147     // as DRAW, the current position is classified as DRAW, otherwise the current
  148     // position is classified as UNKNOWN.
  149     //
  150     // Black to move: If one move leads to a position classified as DRAW, the result
  151     // of the current position is DRAW. If all moves lead to positions classified
  152     // as WIN, the position is classified as WIN, otherwise the current position is
  153     // classified as UNKNOWN.
  154 
  155     constexpr Color  Them = (Us == WHITE ? BLACK : WHITE);
  156     constexpr Result Good = (Us == WHITE ? WIN   : DRAW);
  157     constexpr Result Bad  = (Us == WHITE ? DRAW  : WIN);
  158 
  159     Result r = INVALID;
  160     Bitboard b = PseudoAttacks[KING][ksq[Us]];
  161 
  162     while (b)
  163         r |= Us == WHITE ? db[index(Them, ksq[Them]  , pop_lsb(&b), psq)]
  164                          : db[index(Them, pop_lsb(&b), ksq[Them]  , psq)];
  165 
  166     if (Us == WHITE)
  167     {
  168         if (rank_of(psq) < RANK_7)      // Single push
  169             r |= db[index(Them, ksq[Them], ksq[Us], psq + NORTH)];
  170 
  171         if (   rank_of(psq) == RANK_2   // Double push
  172             && psq + NORTH != ksq[Us]
  173             && psq + NORTH != ksq[Them])
  174             r |= db[index(Them, ksq[Them], ksq[Us], psq + NORTH + NORTH)];
  175     }
  176 
  177     return result = r & Good  ? Good  : r & UNKNOWN ? UNKNOWN : Bad;
  178   }
  179 
  180 } // namespace