/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
- Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2004-2021 The Stockfish developers (see AUTHORS file)
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
*/
#include <algorithm>
-#include <cstring>
-#include <iostream>
+#include <bitset>
#include "bitboard.h"
-#include "bitcount.h"
#include "misc.h"
-#include "rkiss.h"
-
-CACHE_LINE_ALIGNMENT
-
-Bitboard RMasks[64];
-Bitboard RMagics[64];
-Bitboard* RAttacks[64];
-unsigned RShifts[64];
-
-Bitboard BMasks[64];
-Bitboard BMagics[64];
-Bitboard* BAttacks[64];
-unsigned BShifts[64];
-
-Bitboard SquareBB[64];
-Bitboard FileBB[8];
-Bitboard RankBB[8];
-Bitboard AdjacentFilesBB[8];
-Bitboard ThisAndAdjacentFilesBB[8];
-Bitboard InFrontBB[2][8];
-Bitboard StepAttacksBB[16][64];
-Bitboard BetweenBB[64][64];
-Bitboard DistanceRingsBB[64][8];
-Bitboard ForwardBB[2][64];
-Bitboard PassedPawnMask[2][64];
-Bitboard AttackSpanMask[2][64];
-Bitboard PseudoAttacks[6][64];
-
-int SquareDistance[64][64];
-namespace {
-
- // De Bruijn sequences. See chessprogramming.wikispaces.com/BitScan
- const uint64_t DeBruijn_64 = 0x218A392CD3D5DBFULL;
- const uint32_t DeBruijn_32 = 0x783A9B23;
-
- CACHE_LINE_ALIGNMENT
-
- int MS1BTable[256];
- Square BSFTable[64];
- Bitboard RTable[0x19000]; // Storage space for rook attacks
- Bitboard BTable[0x1480]; // Storage space for bishop attacks
- uint8_t BitCount8Bit[256];
+namespace Stockfish {
- typedef unsigned (Fn)(Square, Bitboard);
+uint8_t PopCnt16[1 << 16];
+uint8_t SquareDistance[SQUARE_NB][SQUARE_NB];
- void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
- Bitboard masks[], unsigned shifts[], Square deltas[], Fn index);
-}
+Bitboard SquareBB[SQUARE_NB];
+Bitboard LineBB[SQUARE_NB][SQUARE_NB];
+Bitboard BetweenBB[SQUARE_NB][SQUARE_NB];
+Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
+Bitboard PawnAttacks[COLOR_NB][SQUARE_NB];
-/// lsb()/msb() finds the least/most significant bit in a nonzero bitboard.
-/// pop_lsb() finds and clears the least significant bit in a nonzero bitboard.
+Magic RookMagics[SQUARE_NB];
+Magic BishopMagics[SQUARE_NB];
-#if !defined(USE_BSFQ)
+namespace {
-FORCE_INLINE unsigned bsf_index(Bitboard b) {
+ Bitboard RookTable[0x19000]; // To store rook attacks
+ Bitboard BishopTable[0x1480]; // To store bishop attacks
- if (Is64Bit)
- return ((b & -b) * DeBruijn_64) >> 58;
+ void init_magics(PieceType pt, Bitboard table[], Magic magics[]);
- // Use Matt Taylor's folding trick for 32 bit systems
- b ^= (b - 1);
- return ((unsigned(b) ^ unsigned(b >> 32)) * DeBruijn_32) >> 26;
}
-Square lsb(Bitboard b) { return BSFTable[bsf_index(b)]; }
+/// safe_destination() returns the bitboard of target square for the given step
+/// from the given square. If the step is off the board, returns empty bitboard.
-Square pop_lsb(Bitboard* b) {
-
- Bitboard bb = *b;
- *b = bb & (bb - 1);
- return BSFTable[bsf_index(bb)];
+inline Bitboard safe_destination(Square s, int step) {
+ Square to = Square(s + step);
+ return is_ok(to) && distance(s, to) <= 2 ? square_bb(to) : Bitboard(0);
}
-Square msb(Bitboard b) {
- unsigned b32;
- int result = 0;
+/// Bitboards::pretty() returns an ASCII representation of a bitboard suitable
+/// to be printed to standard output. Useful for debugging.
- if (b > 0xFFFFFFFF)
- {
- b >>= 32;
- result = 32;
- }
+std::string Bitboards::pretty(Bitboard b) {
- b32 = unsigned(b);
+ std::string s = "+---+---+---+---+---+---+---+---+\n";
- if (b32 > 0xFFFF)
+ for (Rank r = RANK_8; r >= RANK_1; --r)
{
- b32 >>= 16;
- result += 16;
- }
+ for (File f = FILE_A; f <= FILE_H; ++f)
+ s += b & make_square(f, r) ? "| X " : "| ";
- if (b32 > 0xFF)
- {
- b32 >>= 8;
- result += 8;
+ s += "| " + std::to_string(1 + r) + "\n+---+---+---+---+---+---+---+---+\n";
}
+ s += " a b c d e f g h\n";
- return (Square)(result + MS1BTable[b32]);
-}
-
-#endif // !defined(USE_BSFQ)
-
-
-/// Bitboards::print() prints a bitboard in an easily readable format to the
-/// standard output. This is sometimes useful for debugging.
-
-void Bitboards::print(Bitboard b) {
-
- sync_cout;
-
- for (Rank rank = RANK_8; rank >= RANK_1; rank--)
- {
- std::cout << "+---+---+---+---+---+---+---+---+" << '\n';
-
- for (File file = FILE_A; file <= FILE_H; file++)
- std::cout << "| " << (b & (file | rank) ? "X " : " ");
-
- std::cout << "|\n";
- }
- std::cout << "+---+---+---+---+---+---+---+---+" << sync_endl;
+ return s;
}
-/// Bitboards::init() initializes various bitboard arrays. It is called during
-/// program initialization.
+/// 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 (int k = 0, i = 0; i < 8; i++)
- while (k < (2 << i))
- MS1BTable[k++] = i;
-
- for (int i = 0; i < 64; i++)
- BSFTable[bsf_index(1ULL << i)] = Square(i);
-
- for (Bitboard b = 0; b < 256; b++)
- BitCount8Bit[b] = (uint8_t)popcount<Max15>(b);
+ for (unsigned i = 0; i < (1 << 16); ++i)
+ PopCnt16[i] = uint8_t(std::bitset<16>(i).count());
- for (Square s = SQ_A1; s <= SQ_H8; s++)
- SquareBB[s] = 1ULL << s;
+ for (Square s = SQ_A1; s <= SQ_H8; ++s)
+ SquareBB[s] = (1ULL << s);
- FileBB[FILE_A] = FileABB;
- RankBB[RANK_1] = Rank1BB;
+ for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
+ for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
+ SquareDistance[s1][s2] = std::max(distance<File>(s1, s2), distance<Rank>(s1, s2));
- for (int i = 1; i < 8; i++)
- {
- FileBB[i] = FileBB[i - 1] << 1;
- RankBB[i] = RankBB[i - 1] << 8;
- }
+ init_magics(ROOK, RookTable, RookMagics);
+ init_magics(BISHOP, BishopTable, BishopMagics);
- for (File f = FILE_A; f <= FILE_H; f++)
+ for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
{
- AdjacentFilesBB[f] = (f > FILE_A ? FileBB[f - 1] : 0) | (f < FILE_H ? FileBB[f + 1] : 0);
- ThisAndAdjacentFilesBB[f] = FileBB[f] | AdjacentFilesBB[f];
- }
-
- 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)];
- PassedPawnMask[c][s] = InFrontBB[c][rank_of(s)] & ThisAndAdjacentFilesBB[file_of(s)];
- AttackSpanMask[c][s] = InFrontBB[c][rank_of(s)] & AdjacentFilesBB[file_of(s)];
- }
-
- for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
- for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
- SquareDistance[s1][s2] = std::max(file_distance(s1, s2), rank_distance(s1, s2));
-
- for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
- for (int d = 1; d < 8; d++)
- for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
- if (SquareDistance[s1][s2] == d)
- DistanceRingsBB[s1][d - 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 k = 0; steps[pt][k]; k++)
- {
- Square to = s + Square(c == WHITE ? steps[pt][k] : -steps[pt][k]);
+ PawnAttacks[WHITE][s1] = pawn_attacks_bb<WHITE>(square_bb(s1));
+ PawnAttacks[BLACK][s1] = pawn_attacks_bb<BLACK>(square_bb(s1));
- if (is_ok(to) && square_distance(s, to) < 3)
- StepAttacksBB[make_piece(c, pt)][s] |= to;
- }
+ for (int step : {-9, -8, -7, -1, 1, 7, 8, 9} )
+ PseudoAttacks[KING][s1] |= safe_destination(s1, step);
- Square RDeltas[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W };
- Square BDeltas[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
+ for (int step : {-17, -15, -10, -6, 6, 10, 15, 17} )
+ PseudoAttacks[KNIGHT][s1] |= safe_destination(s1, step);
- init_magics(RTable, RAttacks, RMagics, RMasks, RShifts, RDeltas, magic_index<ROOK>);
- init_magics(BTable, BAttacks, BMagics, BMasks, BShifts, BDeltas, magic_index<BISHOP>);
+ PseudoAttacks[QUEEN][s1] = PseudoAttacks[BISHOP][s1] = attacks_bb<BISHOP>(s1, 0);
+ PseudoAttacks[QUEEN][s1] |= PseudoAttacks[ ROOK][s1] = attacks_bb< ROOK>(s1, 0);
- for (Square s = SQ_A1; s <= SQ_H8; s++)
- {
- PseudoAttacks[QUEEN][s] = PseudoAttacks[BISHOP][s] = attacks_bb<BISHOP>(s, 0);
- PseudoAttacks[QUEEN][s] |= PseudoAttacks[ ROOK][s] = attacks_bb< ROOK>(s, 0);
- }
-
- for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
- for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
- if (PseudoAttacks[QUEEN][s1] & s2)
+ for (PieceType pt : { BISHOP, ROOK })
+ for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
{
- Square delta = (s2 - s1) / square_distance(s1, s2);
-
- for (Square s = s1 + delta; s != s2; s += delta)
- BetweenBB[s1][s2] |= s;
+ if (PseudoAttacks[pt][s1] & s2)
+ {
+ LineBB[s1][s2] = (attacks_bb(pt, s1, 0) & attacks_bb(pt, s2, 0)) | s1 | s2;
+ BetweenBB[s1][s2] = (attacks_bb(pt, s1, square_bb(s2)) & attacks_bb(pt, s2, square_bb(s1)));
+ }
+ BetweenBB[s1][s2] |= s2;
}
+ }
}
-
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;
- }
-
+ Bitboard sliding_attack(PieceType pt, Square sq, Bitboard occupied) {
- Bitboard pick_random(RKISS& rk, int booster) {
+ Bitboard attacks = 0;
+ Direction RookDirections[4] = {NORTH, SOUTH, EAST, WEST};
+ Direction BishopDirections[4] = {NORTH_EAST, SOUTH_EAST, SOUTH_WEST, NORTH_WEST};
- // Values s1 and s2 are used to rotate the candidate magic of a
- // quantity known to be the optimal to quickly find the magics.
- int s1 = booster & 63, s2 = (booster >> 6) & 63;
+ for (Direction d : (pt == ROOK ? RookDirections : BishopDirections))
+ {
+ Square s = sq;
+ while (safe_destination(s, d) && !(occupied & s))
+ attacks |= (s += d);
+ }
- Bitboard m = rk.rand<Bitboard>();
- m = (m >> s1) | (m << (64 - s1));
- m &= rk.rand<Bitboard>();
- m = (m >> s2) | (m << (64 - s2));
- return m & rk.rand<Bitboard>();
+ return attacks;
}
// 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.
+ // www.chessprogramming.org/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) {
+ void init_magics(PieceType pt, Bitboard table[], Magic magics[]) {
- int MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 },
- { 1059, 3608, 605, 3234, 3326, 38, 2029, 3043 } };
- RKISS rk;
- Bitboard occupancy[4096], reference[4096], edges, b;
- int i, size, booster;
+ // Optimal PRNG seeds to pick the correct magics in the shortest time
+ int seeds[][RANK_NB] = { { 8977, 44560, 54343, 38998, 5731, 95205, 104912, 17020 },
+ { 728, 10316, 55013, 32803, 12281, 15100, 16645, 255 } };
- // attacks[s] is a pointer to the beginning of the attacks table for square 's'
- attacks[SQ_A1] = table;
+ Bitboard occupancy[4096], reference[4096], edges, b;
+ int epoch[4096] = {}, cnt = 0, size = 0;
- for (Square s = SQ_A1; s <= SQ_H8; s++)
+ 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));
// 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]);
+ Magic& m = magics[s];
+ m.mask = sliding_attack(pt, s, 0) & ~edges;
+ m.shift = (Is64Bit ? 64 : 32) - popcount(m.mask);
+
+ // Set the offset for the attacks table of the square. We have individual
+ // table sizes for each square with "Fancy Magic Bitboards".
+ m.attacks = s == SQ_A1 ? table : magics[s - 1].attacks + size;
// 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);
- b = (b - masks[s]) & masks[s];
+ reference[size] = sliding_attack(pt, s, b);
+
+ if (HasPext)
+ m.attacks[pext(b, m.mask)] = reference[size];
+
+ size++;
+ b = (b - m.mask) & m.mask;
} 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)];
+ PRNG rng(seeds[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] = pick_random(rk, booster);
- while (BitCount8Bit[(magics[s] * masks[s]) >> 56] < 6);
-
- memset(attacks[s], 0, size * sizeof(Bitboard));
+ for (int i = 0; i < size; )
+ {
+ for (m.magic = 0; popcount((m.magic * m.mask) >> 56) < 6; )
+ m.magic = rng.sparse_rand<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++)
+ // effect of verifying the magic. Keep track of the attempt count
+ // and save it in epoch[], little speed-up trick to avoid resetting
+ // m.attacks[] after every failed attempt.
+ for (++cnt, i = 0; i < size; ++i)
{
- Bitboard& attack = attacks[s][index(s, occupancy[i])];
-
- if (attack && attack != reference[i])
+ unsigned idx = m.index(occupancy[i]);
+
+ if (epoch[idx] < cnt)
+ {
+ epoch[idx] = cnt;
+ m.attacks[idx] = reference[i];
+ }
+ else if (m.attacks[idx] != reference[i])
break;
-
- assert(reference[i] != 0);
-
- attack = reference[i];
}
- } while (i != size);
+ }
}
}
}
+
+} // namespace Stockfish