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Member "stockfish-11-linux/src/bitboard.cpp" (18 Jan 2020, 7761 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 <algorithm>
   22 #include <bitset>
   23 
   24 #include "bitboard.h"
   25 #include "misc.h"
   26 
   27 uint8_t PopCnt16[1 << 16];
   28 uint8_t SquareDistance[SQUARE_NB][SQUARE_NB];
   29 
   30 Bitboard SquareBB[SQUARE_NB];
   31 Bitboard LineBB[SQUARE_NB][SQUARE_NB];
   32 Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
   33 Bitboard PawnAttacks[COLOR_NB][SQUARE_NB];
   34 
   35 Magic RookMagics[SQUARE_NB];
   36 Magic BishopMagics[SQUARE_NB];
   37 
   38 namespace {
   39 
   40   Bitboard RookTable[0x19000];  // To store rook attacks
   41   Bitboard BishopTable[0x1480]; // To store bishop attacks
   42 
   43   void init_magics(Bitboard table[], Magic magics[], Direction directions[]);
   44 }
   45 
   46 
   47 /// Bitboards::pretty() returns an ASCII representation of a bitboard suitable
   48 /// to be printed to standard output. Useful for debugging.
   49 
   50 const std::string Bitboards::pretty(Bitboard b) {
   51 
   52   std::string s = "+---+---+---+---+---+---+---+---+\n";
   53 
   54   for (Rank r = RANK_8; r >= RANK_1; --r)
   55   {
   56       for (File f = FILE_A; f <= FILE_H; ++f)
   57           s += b & make_square(f, r) ? "| X " : "|   ";
   58 
   59       s += "|\n+---+---+---+---+---+---+---+---+\n";
   60   }
   61 
   62   return s;
   63 }
   64 
   65 
   66 /// Bitboards::init() initializes various bitboard tables. It is called at
   67 /// startup and relies on global objects to be already zero-initialized.
   68 
   69 void Bitboards::init() {
   70 
   71   for (unsigned i = 0; i < (1 << 16); ++i)
   72       PopCnt16[i] = std::bitset<16>(i).count();
   73 
   74   for (Square s = SQ_A1; s <= SQ_H8; ++s)
   75       SquareBB[s] = (1ULL << s);
   76 
   77   for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
   78       for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
   79           SquareDistance[s1][s2] = std::max(distance<File>(s1, s2), distance<Rank>(s1, s2));
   80 
   81   for (Square s = SQ_A1; s <= SQ_H8; ++s)
   82   {
   83       PawnAttacks[WHITE][s] = pawn_attacks_bb<WHITE>(square_bb(s));
   84       PawnAttacks[BLACK][s] = pawn_attacks_bb<BLACK>(square_bb(s));
   85   }
   86 
   87   // Helper returning the target bitboard of a step from a square
   88   auto landing_square_bb = [&](Square s, int step)
   89   {
   90       Square to = Square(s + step);
   91       return is_ok(to) && distance(s, to) <= 2 ? square_bb(to) : Bitboard(0);
   92   };
   93 
   94   for (Square s = SQ_A1; s <= SQ_H8; ++s)
   95   {
   96       for (int step : {-9, -8, -7, -1, 1, 7, 8, 9} )
   97          PseudoAttacks[KING][s] |= landing_square_bb(s, step);
   98 
   99       for (int step : {-17, -15, -10, -6, 6, 10, 15, 17} )
  100          PseudoAttacks[KNIGHT][s] |= landing_square_bb(s, step);
  101   }
  102 
  103   Direction RookDirections[] = { NORTH, EAST, SOUTH, WEST };
  104   Direction BishopDirections[] = { NORTH_EAST, SOUTH_EAST, SOUTH_WEST, NORTH_WEST };
  105 
  106   init_magics(RookTable, RookMagics, RookDirections);
  107   init_magics(BishopTable, BishopMagics, BishopDirections);
  108 
  109   for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
  110   {
  111       PseudoAttacks[QUEEN][s1]  = PseudoAttacks[BISHOP][s1] = attacks_bb<BISHOP>(s1, 0);
  112       PseudoAttacks[QUEEN][s1] |= PseudoAttacks[  ROOK][s1] = attacks_bb<  ROOK>(s1, 0);
  113 
  114       for (PieceType pt : { BISHOP, ROOK })
  115           for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
  116               if (PseudoAttacks[pt][s1] & s2)
  117                   LineBB[s1][s2] = (attacks_bb(pt, s1, 0) & attacks_bb(pt, s2, 0)) | s1 | s2;
  118   }
  119 }
  120 
  121 
  122 namespace {
  123 
  124   Bitboard sliding_attack(Direction directions[], Square sq, Bitboard occupied) {
  125 
  126     Bitboard attack = 0;
  127 
  128     for (int i = 0; i < 4; ++i)
  129         for (Square s = sq + directions[i];
  130              is_ok(s) && distance(s, s - directions[i]) == 1;
  131              s += directions[i])
  132         {
  133             attack |= s;
  134 
  135             if (occupied & s)
  136                 break;
  137         }
  138 
  139     return attack;
  140   }
  141 
  142 
  143   // init_magics() computes all rook and bishop attacks at startup. Magic
  144   // bitboards are used to look up attacks of sliding pieces. As a reference see
  145   // www.chessprogramming.org/Magic_Bitboards. In particular, here we use the so
  146   // called "fancy" approach.
  147 
  148   void init_magics(Bitboard table[], Magic magics[], Direction directions[]) {
  149 
  150     // Optimal PRNG seeds to pick the correct magics in the shortest time
  151     int seeds[][RANK_NB] = { { 8977, 44560, 54343, 38998,  5731, 95205, 104912, 17020 },
  152                              {  728, 10316, 55013, 32803, 12281, 15100,  16645,   255 } };
  153 
  154     Bitboard occupancy[4096], reference[4096], edges, b;
  155     int epoch[4096] = {}, cnt = 0, size = 0;
  156 
  157     for (Square s = SQ_A1; s <= SQ_H8; ++s)
  158     {
  159         // Board edges are not considered in the relevant occupancies
  160         edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
  161 
  162         // Given a square 's', the mask is the bitboard of sliding attacks from
  163         // 's' computed on an empty board. The index must be big enough to contain
  164         // all the attacks for each possible subset of the mask and so is 2 power
  165         // the number of 1s of the mask. Hence we deduce the size of the shift to
  166         // apply to the 64 or 32 bits word to get the index.
  167         Magic& m = magics[s];
  168         m.mask  = sliding_attack(directions, s, 0) & ~edges;
  169         m.shift = (Is64Bit ? 64 : 32) - popcount(m.mask);
  170 
  171         // Set the offset for the attacks table of the square. We have individual
  172         // table sizes for each square with "Fancy Magic Bitboards".
  173         m.attacks = s == SQ_A1 ? table : magics[s - 1].attacks + size;
  174 
  175         // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
  176         // store the corresponding sliding attack bitboard in reference[].
  177         b = size = 0;
  178         do {
  179             occupancy[size] = b;
  180             reference[size] = sliding_attack(directions, s, b);
  181 
  182             if (HasPext)
  183                 m.attacks[pext(b, m.mask)] = reference[size];
  184 
  185             size++;
  186             b = (b - m.mask) & m.mask;
  187         } while (b);
  188 
  189         if (HasPext)
  190             continue;
  191 
  192         PRNG rng(seeds[Is64Bit][rank_of(s)]);
  193 
  194         // Find a magic for square 's' picking up an (almost) random number
  195         // until we find the one that passes the verification test.
  196         for (int i = 0; i < size; )
  197         {
  198             for (m.magic = 0; popcount((m.magic * m.mask) >> 56) < 6; )
  199                 m.magic = rng.sparse_rand<Bitboard>();
  200 
  201             // A good magic must map every possible occupancy to an index that
  202             // looks up the correct sliding attack in the attacks[s] database.
  203             // Note that we build up the database for square 's' as a side
  204             // effect of verifying the magic. Keep track of the attempt count
  205             // and save it in epoch[], little speed-up trick to avoid resetting
  206             // m.attacks[] after every failed attempt.
  207             for (++cnt, i = 0; i < size; ++i)
  208             {
  209                 unsigned idx = m.index(occupancy[i]);
  210 
  211                 if (epoch[idx] < cnt)
  212                 {
  213                     epoch[idx] = cnt;
  214                     m.attacks[idx] = reference[i];
  215                 }
  216                 else if (m.attacks[idx] != reference[i])
  217                     break;
  218             }
  219         }
  220     }
  221   }
  222 }