text: /*
    Stockfish, a UCI chess playing engine derived from Glaurung 2.1
    Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
    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
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.
  
    Stockfish is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
  
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
  
  #include <algorithm>
  #include <cstring> // For memset
  
  #include "bitboard.h"
  #include "bitcount.h"
  #include "rkiss.h"
  
  CACHE_LINE_ALIGNMENT
  
  Bitboard RMasks[SQUARE_NB];
  Bitboard RMagics[SQUARE_NB];
  Bitboard* RAttacks[SQUARE_NB];
  unsigned RShifts[SQUARE_NB];
  
  Bitboard BMasks[SQUARE_NB];
  Bitboard BMagics[SQUARE_NB];
  Bitboard* BAttacks[SQUARE_NB];
  unsigned BShifts[SQUARE_NB];
  
  Bitboard SquareBB[SQUARE_NB];
  Bitboard FileBB[FILE_NB];
  Bitboard RankBB[RANK_NB];
  Bitboard AdjacentFilesBB[FILE_NB];
  Bitboard InFrontBB[COLOR_NB][RANK_NB];
  Bitboard StepAttacksBB[PIECE_NB][SQUARE_NB];
  Bitboard BetweenBB[SQUARE_NB][SQUARE_NB];
  Bitboard LineBB[SQUARE_NB][SQUARE_NB];
  Bitboard DistanceRingsBB[SQUARE_NB][8];
  Bitboard ForwardBB[COLOR_NB][SQUARE_NB];
  Bitboard PassedPawnMask[COLOR_NB][SQUARE_NB];
  Bitboard PawnAttackSpan[COLOR_NB][SQUARE_NB];
  Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
  
  int SquareDistance[SQUARE_NB][SQUARE_NB];
  
  namespace {
  
    // De Bruijn sequences. See chessprogramming.wikispaces.com/BitScan
    const uint64_t DeBruijn_64 = 0x3F79D71B4CB0A89ULL;
    const uint32_t DeBruijn_32 = 0x783A9B23;
  
    CACHE_LINE_ALIGNMENT
  
    int MS1BTable[256];
    Square BSFTable[SQUARE_NB];
    Bitboard RTable[0x19000]; // Storage space for rook attacks
    Bitboard BTable[0x1480];  // Storage space for bishop attacks
  
    typedef unsigned (Fn)(Square, Bitboard);
  
    void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
                     Bitboard masks[], unsigned shifts[], Square deltas[], Fn index);
  
    FORCE_INLINE unsigned bsf_index(Bitboard b) {
  
      // Matt Taylor's folding for 32 bit systems, extended to 64 bits by Kim Walisch
      b ^= (b - 1);
      return Is64Bit ? (b * DeBruijn_64) >> 58
                     : ((unsigned(b) ^ unsigned(b >> 32)) * DeBruijn_32) >> 26;
    }
  }
  
  /// lsb()/msb() finds the least/most significant bit in a non-zero bitboard.
  /// pop_lsb() finds and clears the least significant bit in a non-zero bitboard.
  
  #ifndef USE_BSFQ
  
  Square lsb(Bitboard b) { return BSFTable[bsf_index(b)]; }
  
  Square pop_lsb(Bitboard* b) {
  
    Bitboard bb = *b;
    *b = bb & (bb - 1);
    return BSFTable[bsf_index(bb)];
  }
  
  Square msb(Bitboard b) {
  
    unsigned b32;
    int result = 0;
  
    if (b > 0xFFFFFFFF)
    {
        b >>= 32;
        result = 32;
    }
  
    b32 = unsigned(b);
  
    if (b32 > 0xFFFF)
    {
        b32 >>= 16;
        result += 16;
    }
  
    if (b32 > 0xFF)
    {
        b32 >>= 8;
        result += 8;
    }
  
    return Square(result + MS1BTable[b32]);
  }
  
  #endif // ifndef USE_BSFQ
  
  
  /// Bitboards::pretty() returns an ASCII representation of a bitboard to be
  /// printed to standard output. This is sometimes useful for debugging.
  
  const std::string Bitboards::pretty(Bitboard b) {
  
    std::string s = "+---+---+---+---+---+---+---+---+\n";
  
    for (Rank r = RANK_8; r >= RANK_1; --r)
    {
        for (File f = FILE_A; f <= FILE_H; ++f)
            s.append(b & make_square(f, r) ? "| X " : "|   ");
  
        s.append("|\n+---+---+---+---+---+---+---+---+\n");
    }
  
    return s;
  }
  
  
  /// Bitboards::init() initializes various bitboard tables. It is called at
  /// startup and relies on global objects to be already zero-initialized.
  
  void Bitboards::init() {
  
    for (Square s = SQ_A1; s <= SQ_H8; ++s)
        BSFTable[bsf_index(SquareBB[s] = 1ULL << s)] = s;
  
    for (Bitboard b = 1; b < 256; ++b)
        MS1BTable[b] = more_than_one(b) ? MS1BTable[b - 1] : lsb(b);
  
    for (File f = FILE_A; f <= FILE_H; ++f)
        FileBB[f] = f > FILE_A ? FileBB[f - 1] << 1 : FileABB;
  
    for (Rank r = RANK_1; r <= RANK_8; ++r)
        RankBB[r] = r > RANK_1 ? RankBB[r - 1] << 8 : Rank1BB;
  
    for (File f = FILE_A; f <= FILE_H; ++f)
        AdjacentFilesBB[f] = (f > FILE_A ? FileBB[f - 1] : 0) | (f < FILE_H ? FileBB[f + 1] : 0);
  
    for (Rank r = RANK_1; r < RANK_8; ++r)
        InFrontBB[WHITE][r] = ~(InFrontBB[BLACK][r + 1] = InFrontBB[BLACK][r] | RankBB[r]);
  
    for (Color c = WHITE; c <= BLACK; ++c)
        for (Square s = SQ_A1; s <= SQ_H8; ++s)
        {
            ForwardBB[c][s]      = InFrontBB[c][rank_of(s)] & FileBB[file_of(s)];
            PawnAttackSpan[c][s] = InFrontBB[c][rank_of(s)] & AdjacentFilesBB[file_of(s)];
            PassedPawnMask[c][s] = ForwardBB[c][s] | PawnAttackSpan[c][s];
        }
  
    for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
        for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
            if (s1 != s2)
            {
                SquareDistance[s1][s2] = std::max(file_distance(s1, s2), rank_distance(s1, s2));
                DistanceRingsBB[s1][SquareDistance[s1][s2] - 1] |= s2;
            }
  
    int steps[][9] = { {}, { 7, 9 }, { 17, 15, 10, 6, -6, -10, -15, -17 },
                       {}, {}, {}, { 9, 7, -7, -9, 8, 1, -1, -8 } };
  
    for (Color c = WHITE; c <= BLACK; ++c)
        for (PieceType pt = PAWN; pt <= KING; ++pt)
            for (Square s = SQ_A1; s <= SQ_H8; ++s)
                for (int i = 0; steps[pt][i]; ++i)
                {
                    Square to = s + Square(c == WHITE ? steps[pt][i] : -steps[pt][i]);
  
                    if (is_ok(to) && square_distance(s, to) < 3)
                        StepAttacksBB[make_piece(c, pt)][s] |= to;
                }
  
    Square RDeltas[] = { DELTA_N,  DELTA_E,  DELTA_S,  DELTA_W  };
    Square BDeltas[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
  
    init_magics(RTable, RAttacks, RMagics, RMasks, RShifts, RDeltas, magic_index<ROOK>);
    init_magics(BTable, BAttacks, BMagics, BMasks, BShifts, BDeltas, magic_index<BISHOP>);
  
    for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
    {
        PseudoAttacks[QUEEN][s1]  = PseudoAttacks[BISHOP][s1] = attacks_bb<BISHOP>(s1, 0);
        PseudoAttacks[QUEEN][s1] |= PseudoAttacks[  ROOK][s1] = attacks_bb<  ROOK>(s1, 0);
  
        for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
        {
            Piece pc = (PseudoAttacks[BISHOP][s1] & s2) ? W_BISHOP :
                       (PseudoAttacks[ROOK][s1]   & s2) ? W_ROOK   : NO_PIECE;
  
            if (pc == NO_PIECE)
                continue;
  
            LineBB[s1][s2] = (attacks_bb(pc, s1, 0) & attacks_bb(pc, s2, 0)) | s1 | s2;
            BetweenBB[s1][s2] = attacks_bb(pc, s1, SquareBB[s2]) & attacks_bb(pc, s2, SquareBB[s1]);
        }
    }
  }
  
  
  namespace {
  
    Bitboard sliding_attack(Square deltas[], Square sq, Bitboard occupied) {
  
      Bitboard attack = 0;
  
      for (int i = 0; i < 4; ++i)
          for (Square s = sq + deltas[i];
               is_ok(s) && square_distance(s, s - deltas[i]) == 1;
               s += deltas[i])
          {
              attack |= s;
  
              if (occupied & s)
                  break;
          }
  
      return attack;
    }
  
  
    // init_magics() computes all rook and bishop attacks at startup. Magic
    // bitboards are used to look up attacks of sliding pieces. As a reference see
    // chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
    // use the so called "fancy" approach.
  
    void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
                     Bitboard masks[], unsigned shifts[], Square deltas[], Fn index) {
  
      int MagicBoosters[][8] = { {  969, 1976, 2850,  542, 2069, 2852, 1708,  164 },
                                 { 3101,  552, 3555,  926,  834,   26, 2131, 1117 } };
  
      RKISS rk;
      Bitboard occupancy[4096], reference[4096], edges, b;
      int i, size, booster;
  
      // attacks[s] is a pointer to the beginning of the attacks table for square 's'
      attacks[SQ_A1] = table;
  
      for (Square s = SQ_A1; s <= SQ_H8; ++s)
      {
          // Board edges are not considered in the relevant occupancies
          edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
  
          // Given a square 's', the mask is the bitboard of sliding attacks from
          // 's' computed on an empty board. The index must be big enough to contain
          // all the attacks for each possible subset of the mask and so is 2 power
          // the number of 1s of the mask. Hence we deduce the size of the shift to
          // apply to the 64 or 32 bits word to get the index.
          masks[s]  = sliding_attack(deltas, s, 0) & ~edges;
          shifts[s] = (Is64Bit ? 64 : 32) - popcount<Max15>(masks[s]);
  
          // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
          // store the corresponding sliding attack bitboard in reference[].
          b = size = 0;
          do {
              occupancy[size] = b;
              reference[size] = sliding_attack(deltas, s, b);
  
              if (HasPext)
                  attacks[s][_pext_u64(b, masks[s])] = reference[size];
  
              size++;
              b = (b - masks[s]) & masks[s];
          } while (b);
  
          // Set the offset for the table of the next square. We have individual
          // table sizes for each square with "Fancy Magic Bitboards".
          if (s < SQ_H8)
              attacks[s + 1] = attacks[s] + size;
  
          if (HasPext)
              continue;
  
          booster = MagicBoosters[Is64Bit][rank_of(s)];
  
          // Find a magic for square 's' picking up an (almost) random number
          // until we find the one that passes the verification test.
          do {
              do magics[s] = rk.magic_rand<Bitboard>(booster);
              while (popcount<Max15>((magics[s] * masks[s]) >> 56) < 6);
  
              std::memset(attacks[s], 0, size * sizeof(Bitboard));
  
              // A good magic must map every possible occupancy to an index that
              // looks up the correct sliding attack in the attacks[s] database.
              // Note that we build up the database for square 's' as a side
              // effect of verifying the magic.
              for (i = 0; i < size; ++i)
              {
                  Bitboard& attack = attacks[s][index(s, occupancy[i])];
  
                  if (attack && attack != reference[i])
                      break;
  
                  assert(reference[i]);
  
                  attack = reference[i];
              }
          } while (i < size);
      }
    }
  }
  