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344 lines
11 KiB
C++
344 lines
11 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) 2008-2013 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>
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#include <iostream>
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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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#include "rkiss.h"
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CACHE_LINE_ALIGNMENT
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Bitboard RMasks[SQUARE_NB];
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Bitboard RMagics[SQUARE_NB];
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Bitboard* RAttacks[SQUARE_NB];
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unsigned RShifts[SQUARE_NB];
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Bitboard BMasks[SQUARE_NB];
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Bitboard BMagics[SQUARE_NB];
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Bitboard* BAttacks[SQUARE_NB];
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unsigned BShifts[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 DistanceRingsBB[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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int SquareDistance[SQUARE_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 DeBruijn_64 = 0x3F79D71B4CB0A89ULL;
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const uint32_t DeBruijn_32 = 0x783A9B23;
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CACHE_LINE_ALIGNMENT
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int MS1BTable[256];
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Square BSFTable[SQUARE_NB];
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Bitboard RTable[0x19000]; // Storage space for rook attacks
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Bitboard BTable[0x1480]; // Storage space for 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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FORCE_INLINE unsigned bsf_index(Bitboard b) {
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// Matt Taylor's folding for 32 bit systems, extended to 64 bits by Kim Walisch
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b ^= (b - 1);
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return Is64Bit ? (b * DeBruijn_64) >> 58
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: ((unsigned(b) ^ unsigned(b >> 32)) * DeBruijn_32) >> 26;
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}
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}
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/// lsb()/msb() finds the least/most significant bit in a nonzero bitboard.
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/// pop_lsb() finds and clears the least significant bit in a nonzero bitboard.
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#ifndef USE_BSFQ
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Square lsb(Bitboard b) { return BSFTable[bsf_index(b)]; }
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Square pop_lsb(Bitboard* b) {
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Bitboard bb = *b;
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*b = bb & (bb - 1);
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return BSFTable[bsf_index(bb)];
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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::print() prints a bitboard in an easily readable format to the
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/// standard output. This is sometimes useful for debugging.
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void Bitboards::print(Bitboard b) {
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sync_cout;
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for (Rank rank = RANK_8; rank >= RANK_1; --rank)
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{
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std::cout << "+---+---+---+---+---+---+---+---+" << '\n';
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for (File file = FILE_A; file <= FILE_H; ++file)
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std::cout << "| " << (b & (file | rank) ? "X " : " ");
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std::cout << "|\n";
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}
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std::cout << "+---+---+---+---+---+---+---+---+" << sync_endl;
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}
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/// Bitboards::init() initializes various bitboard arrays. It is called during
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/// program initialization.
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void Bitboards::init() {
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for (int k = 0, i = 0; i < 8; ++i)
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while (k < (2 << i))
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MS1BTable[k++] = i;
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for (int i = 0; i < 64; ++i)
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BSFTable[bsf_index(1ULL << i)] = Square(i);
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for (Square s = SQ_A1; s <= SQ_H8; ++s)
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SquareBB[s] = 1ULL << s;
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FileBB[FILE_A] = FileABB;
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RankBB[RANK_1] = Rank1BB;
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for (int i = 1; i < 8; ++i)
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{
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FileBB[i] = FileBB[i - 1] << 1;
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RankBB[i] = RankBB[i - 1] << 8;
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}
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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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{
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SquareDistance[s1][s2] = std::max(file_distance(s1, s2), rank_distance(s1, s2));
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if (s1 != s2)
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DistanceRingsBB[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 k = 0; steps[pt][k]; ++k)
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{
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Square to = s + Square(c == WHITE ? steps[pt][k] : -steps[pt][k]);
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if (is_ok(to) && square_distance(s, to) < 3)
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StepAttacksBB[make_piece(c, pt)][s] |= to;
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}
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Square RDeltas[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W };
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Square BDeltas[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
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init_magics(RTable, RAttacks, RMagics, RMasks, RShifts, RDeltas, magic_index<ROOK>);
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init_magics(BTable, BAttacks, BMagics, BMasks, BShifts, BDeltas, magic_index<BISHOP>);
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for (Square s = SQ_A1; s <= SQ_H8; ++s)
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{
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PseudoAttacks[QUEEN][s] = PseudoAttacks[BISHOP][s] = attacks_bb<BISHOP>(s, 0);
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PseudoAttacks[QUEEN][s] |= PseudoAttacks[ ROOK][s] = attacks_bb< ROOK>(s, 0);
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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 (PseudoAttacks[QUEEN][s1] & s2)
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{
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Square delta = (s2 - s1) / square_distance(s1, s2);
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for (Square s = s1 + delta; s != s2; s += delta)
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BetweenBB[s1][s2] |= s;
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PieceType pt = (PseudoAttacks[BISHOP][s1] & s2) ? BISHOP : ROOK;
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LineBB[s1][s2] = (PseudoAttacks[pt][s1] & PseudoAttacks[pt][s2]) | s1 | s2;
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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) && square_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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Bitboard pick_random(RKISS& rk, int booster) {
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// Values s1 and s2 are used to rotate the candidate magic of a
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// quantity known to be the optimal to quickly find the magics.
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int s1 = booster & 63, s2 = (booster >> 6) & 63;
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Bitboard m = rk.rand<Bitboard>();
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m = (m >> s1) | (m << (64 - s1));
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m &= rk.rand<Bitboard>();
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m = (m >> s2) | (m << (64 - s2));
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return m & rk.rand<Bitboard>();
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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 MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 },
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{ 1059, 3608, 605, 3234, 3326, 38, 2029, 3043 } };
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RKISS rk;
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Bitboard occupancy[4096], reference[4096], edges, b;
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int i, size, booster;
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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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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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booster = MagicBoosters[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 magics[s] = pick_random(rk, booster);
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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] != 0);
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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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