322 lines
10 KiB
C++
322 lines
10 KiB
C++
/*
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Stockfish, a UCI chess playing engine derived from Glaurung 2.1
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Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
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Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
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Stockfish is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Stockfish is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <algorithm>
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#include <cstring> // For std::memset
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#include "bitboard.h"
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#include "bitcount.h"
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#include "misc.h"
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int SquareDistance[SQUARE_NB][SQUARE_NB];
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Bitboard RookMasks [SQUARE_NB];
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Bitboard RookMagics [SQUARE_NB];
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Bitboard* RookAttacks[SQUARE_NB];
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unsigned RookShifts [SQUARE_NB];
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Bitboard BishopMasks [SQUARE_NB];
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Bitboard BishopMagics [SQUARE_NB];
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Bitboard* BishopAttacks[SQUARE_NB];
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unsigned BishopShifts [SQUARE_NB];
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Bitboard SquareBB[SQUARE_NB];
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Bitboard FileBB[FILE_NB];
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Bitboard RankBB[RANK_NB];
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Bitboard AdjacentFilesBB[FILE_NB];
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Bitboard InFrontBB[COLOR_NB][RANK_NB];
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Bitboard StepAttacksBB[PIECE_NB][SQUARE_NB];
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Bitboard BetweenBB[SQUARE_NB][SQUARE_NB];
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Bitboard LineBB[SQUARE_NB][SQUARE_NB];
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Bitboard DistanceRingBB[SQUARE_NB][8];
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Bitboard ForwardBB[COLOR_NB][SQUARE_NB];
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Bitboard PassedPawnMask[COLOR_NB][SQUARE_NB];
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Bitboard PawnAttackSpan[COLOR_NB][SQUARE_NB];
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Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
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namespace {
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// De Bruijn sequences. See chessprogramming.wikispaces.com/BitScan
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const uint64_t DeBruijn64 = 0x3F79D71B4CB0A89ULL;
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const uint32_t DeBruijn32 = 0x783A9B23;
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int MS1BTable[256]; // To implement software msb()
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Square BSFTable[SQUARE_NB]; // To implement software bitscan
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Bitboard RookTable[0x19000]; // To store rook attacks
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Bitboard BishopTable[0x1480]; // To store bishop attacks
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typedef unsigned (Fn)(Square, Bitboard);
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void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
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Bitboard masks[], unsigned shifts[], Square deltas[], Fn index);
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// bsf_index() returns the index into BSFTable[] to look up the bitscan. Uses
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// Matt Taylor's folding for 32 bit case, extended to 64 bit by Kim Walisch.
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FORCE_INLINE unsigned bsf_index(Bitboard b) {
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b ^= b - 1;
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return Is64Bit ? (b * DeBruijn64) >> 58
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: ((unsigned(b) ^ unsigned(b >> 32)) * DeBruijn32) >> 26;
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}
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}
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#ifndef USE_BSFQ
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/// Software fall-back of lsb() and msb() for CPU lacking hardware support
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Square lsb(Bitboard b) {
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return BSFTable[bsf_index(b)];
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}
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Square msb(Bitboard b) {
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unsigned b32;
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int result = 0;
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if (b > 0xFFFFFFFF)
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{
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b >>= 32;
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result = 32;
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}
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b32 = unsigned(b);
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if (b32 > 0xFFFF)
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{
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b32 >>= 16;
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result += 16;
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}
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if (b32 > 0xFF)
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{
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b32 >>= 8;
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result += 8;
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}
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return Square(result + MS1BTable[b32]);
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}
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#endif // ifndef USE_BSFQ
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/// Bitboards::pretty() returns an ASCII representation of a bitboard suitable
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/// to be printed to standard output. Useful for debugging.
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const std::string Bitboards::pretty(Bitboard b) {
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std::string s = "+---+---+---+---+---+---+---+---+\n";
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for (Rank r = RANK_8; r >= RANK_1; --r)
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{
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for (File f = FILE_A; f <= FILE_H; ++f)
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s.append(b & make_square(f, r) ? "| X " : "| ");
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s.append("|\n+---+---+---+---+---+---+---+---+\n");
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}
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return s;
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}
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/// Bitboards::init() initializes various bitboard tables. It is called at
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/// startup and relies on global objects to be already zero-initialized.
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void Bitboards::init() {
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for (Square s = SQ_A1; s <= SQ_H8; ++s)
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{
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SquareBB[s] = 1ULL << s;
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BSFTable[bsf_index(SquareBB[s])] = s;
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}
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for (Bitboard b = 1; b < 256; ++b)
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MS1BTable[b] = more_than_one(b) ? MS1BTable[b - 1] : lsb(b);
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for (File f = FILE_A; f <= FILE_H; ++f)
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FileBB[f] = f > FILE_A ? FileBB[f - 1] << 1 : FileABB;
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for (Rank r = RANK_1; r <= RANK_8; ++r)
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RankBB[r] = r > RANK_1 ? RankBB[r - 1] << 8 : Rank1BB;
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for (File f = FILE_A; f <= FILE_H; ++f)
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AdjacentFilesBB[f] = (f > FILE_A ? FileBB[f - 1] : 0) | (f < FILE_H ? FileBB[f + 1] : 0);
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for (Rank r = RANK_1; r < RANK_8; ++r)
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InFrontBB[WHITE][r] = ~(InFrontBB[BLACK][r + 1] = InFrontBB[BLACK][r] | RankBB[r]);
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for (Color c = WHITE; c <= BLACK; ++c)
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for (Square s = SQ_A1; s <= SQ_H8; ++s)
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{
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ForwardBB[c][s] = InFrontBB[c][rank_of(s)] & FileBB[file_of(s)];
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PawnAttackSpan[c][s] = InFrontBB[c][rank_of(s)] & AdjacentFilesBB[file_of(s)];
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PassedPawnMask[c][s] = ForwardBB[c][s] | PawnAttackSpan[c][s];
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}
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for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
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for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
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if (s1 != s2)
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{
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SquareDistance[s1][s2] = std::max(distance<File>(s1, s2), distance<Rank>(s1, s2));
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DistanceRingBB[s1][SquareDistance[s1][s2] - 1] |= s2;
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}
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int steps[][9] = { {}, { 7, 9 }, { 17, 15, 10, 6, -6, -10, -15, -17 },
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{}, {}, {}, { 9, 7, -7, -9, 8, 1, -1, -8 } };
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for (Color c = WHITE; c <= BLACK; ++c)
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for (PieceType pt = PAWN; pt <= KING; ++pt)
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for (Square s = SQ_A1; s <= SQ_H8; ++s)
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for (int i = 0; steps[pt][i]; ++i)
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{
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Square to = s + Square(c == WHITE ? steps[pt][i] : -steps[pt][i]);
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if (is_ok(to) && distance(s, to) < 3)
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StepAttacksBB[make_piece(c, pt)][s] |= to;
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}
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Square RookDeltas[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W };
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Square BishopDeltas[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
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init_magics(RookTable, RookAttacks, RookMagics, RookMasks, RookShifts, RookDeltas, magic_index<ROOK>);
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init_magics(BishopTable, BishopAttacks, BishopMagics, BishopMasks, BishopShifts, BishopDeltas, magic_index<BISHOP>);
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for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
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{
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PseudoAttacks[QUEEN][s1] = PseudoAttacks[BISHOP][s1] = attacks_bb<BISHOP>(s1, 0);
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PseudoAttacks[QUEEN][s1] |= PseudoAttacks[ ROOK][s1] = attacks_bb< ROOK>(s1, 0);
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for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
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{
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Piece pc = (PseudoAttacks[BISHOP][s1] & s2) ? W_BISHOP :
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(PseudoAttacks[ROOK][s1] & s2) ? W_ROOK : NO_PIECE;
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if (pc == NO_PIECE)
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continue;
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LineBB[s1][s2] = (attacks_bb(pc, s1, 0) & attacks_bb(pc, s2, 0)) | s1 | s2;
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BetweenBB[s1][s2] = attacks_bb(pc, s1, SquareBB[s2]) & attacks_bb(pc, s2, SquareBB[s1]);
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}
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}
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}
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namespace {
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Bitboard sliding_attack(Square deltas[], Square sq, Bitboard occupied) {
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Bitboard attack = 0;
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for (int i = 0; i < 4; ++i)
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for (Square s = sq + deltas[i];
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is_ok(s) && distance(s, s - deltas[i]) == 1;
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s += deltas[i])
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{
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attack |= s;
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if (occupied & s)
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break;
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}
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return attack;
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}
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// init_magics() computes all rook and bishop attacks at startup. Magic
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// bitboards are used to look up attacks of sliding pieces. As a reference see
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// chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
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// use the so called "fancy" approach.
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void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
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Bitboard masks[], unsigned shifts[], Square deltas[], Fn index) {
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int seeds[][RANK_NB] = { { 8977, 44560, 54343, 38998, 5731, 95205, 104912, 17020 },
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{ 728, 10316, 55013, 32803, 12281, 15100, 16645, 255 } };
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Bitboard occupancy[4096], reference[4096], edges, b;
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int i, size;
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// attacks[s] is a pointer to the beginning of the attacks table for square 's'
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attacks[SQ_A1] = table;
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for (Square s = SQ_A1; s <= SQ_H8; ++s)
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{
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// Board edges are not considered in the relevant occupancies
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edges = ((Rank1BB | Rank8BB) & ~rank_bb(s)) | ((FileABB | FileHBB) & ~file_bb(s));
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// Given a square 's', the mask is the bitboard of sliding attacks from
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// 's' computed on an empty board. The index must be big enough to contain
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// all the attacks for each possible subset of the mask and so is 2 power
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// the number of 1s of the mask. Hence we deduce the size of the shift to
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// apply to the 64 or 32 bits word to get the index.
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masks[s] = sliding_attack(deltas, s, 0) & ~edges;
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shifts[s] = (Is64Bit ? 64 : 32) - popcount<Max15>(masks[s]);
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// Use Carry-Rippler trick to enumerate all subsets of masks[s] and
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// store the corresponding sliding attack bitboard in reference[].
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b = size = 0;
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do {
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occupancy[size] = b;
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reference[size] = sliding_attack(deltas, s, b);
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if (HasPext)
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attacks[s][pext(b, masks[s])] = reference[size];
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size++;
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b = (b - masks[s]) & masks[s];
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} while (b);
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// Set the offset for the table of the next square. We have individual
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// table sizes for each square with "Fancy Magic Bitboards".
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if (s < SQ_H8)
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attacks[s + 1] = attacks[s] + size;
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if (HasPext)
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continue;
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PRNG rng(seeds[Is64Bit][rank_of(s)]);
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// Find a magic for square 's' picking up an (almost) random number
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// until we find the one that passes the verification test.
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do {
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do
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magics[s] = rng.sparse_rand<Bitboard>();
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while (popcount<Max15>((magics[s] * masks[s]) >> 56) < 6);
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std::memset(attacks[s], 0, size * sizeof(Bitboard));
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// A good magic must map every possible occupancy to an index that
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// looks up the correct sliding attack in the attacks[s] database.
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// Note that we build up the database for square 's' as a side
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// effect of verifying the magic.
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for (i = 0; i < size; ++i)
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{
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Bitboard& attack = attacks[s][index(s, occupancy[i])];
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if (attack && attack != reference[i])
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break;
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assert(reference[i]);
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attack = reference[i];
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}
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} while (i < size);
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}
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}
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}
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