#include <cstring>
#include <iostream>
+#include <algorithm>
#include "bitboard.h"
#include "bitcount.h"
// Global bitboards definitions with static storage duration are
// automatically set to zero before enter main().
-Bitboard RMask[64];
-Bitboard RMult[64];
+Bitboard RMasks[64];
+Bitboard RMagics[64];
Bitboard* RAttacks[64];
-int RShift[64];
+int RShifts[64];
-Bitboard BMask[64];
-Bitboard BMult[64];
+Bitboard BMasks[64];
+Bitboard BMagics[64];
Bitboard* BAttacks[64];
-int BShift[64];
+int BShifts[64];
Bitboard SetMaskBB[65];
Bitboard ClearMaskBB[65];
CACHE_LINE_ALIGNMENT
int BSFTable[64];
- Bitboard RAttacksTable[0x19000];
- Bitboard BAttacksTable[0x1480];
+ Bitboard RookTable[0x19000]; // Storage space for rook attacks
+ Bitboard BishopTable[0x1480]; // Storage space for bishop attacks
- void init_sliding_attacks(Bitboard magic[], Bitboard* attack[], Bitboard attTable[],
- Bitboard mask[], int shift[], Square delta[]);
+ void init_magic_bitboards(Bitboard* attacks[], Bitboard magics[],
+ Bitboard masks[], int shifts[], Square deltas[]);
}
for (Square s1 = SQ_A1; s1 <= SQ_H8; s1++)
for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
- SquareDistance[s1][s2] = Max(file_distance(s1, s2), rank_distance(s1, s2));
+ SquareDistance[s1][s2] = std::max(file_distance(s1, s2), rank_distance(s1, s2));
SquaresByColorBB[DARK] = 0xAA55AA55AA55AA55ULL;
SquaresByColorBB[LIGHT] = ~SquaresByColorBB[DARK];
set_bit(&StepAttacksBB[make_piece(c, pt)][s], to);
}
- Square RDelta[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W };
- Square BDelta[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
+ Square RDeltas[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W };
+ Square BDeltas[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
- init_sliding_attacks(BMult, BAttacks, BAttacksTable, BMask, BShift, BDelta);
- init_sliding_attacks(RMult, RAttacks, RAttacksTable, RMask, RShift, RDelta);
+ RAttacks[0] = RookTable;
+ BAttacks[0] = BishopTable;
+
+ init_magic_bitboards(RAttacks, RMagics, RMasks, RShifts, RDeltas);
+ init_magic_bitboards(BAttacks, BMagics, BMasks, BShifts, BDeltas);
for (Square s = SQ_A1; s <= SQ_H8; s++)
{
int f = file_distance(s1, s2);
int r = rank_distance(s1, s2);
- Square d = (s2 - s1) / Max(f, r);
+ Square d = (s2 - s1) / std::max(f, r);
for (Square s3 = s1 + d; s3 != s2; s3 += d)
set_bit(&BetweenBB[s1][s2], s3);
namespace {
- Bitboard sliding_attacks(Square sq, Bitboard occupied, Square delta[]) {
+ Bitboard sliding_attacks(Square sq, Bitboard occupied, Square deltas[]) {
Bitboard attacks = 0;
for (int i = 0; i < 4; i++)
{
- Square s = sq + delta[i];
+ Square s = sq + deltas[i];
- while (square_is_ok(s) && square_distance(s, s - delta[i]) == 1)
+ while (square_is_ok(s) && square_distance(s, s - deltas[i]) == 1)
{
set_bit(&attacks, s);
if (bit_is_set(occupied, s))
break;
- s += delta[i];
+ s += deltas[i];
}
}
return attacks;
}
- Bitboard pick_magic(Bitboard mask, RKISS& rk, int booster) {
+ Bitboard pick_random(Bitboard mask, RKISS& rk, int booster) {
Bitboard magic;
}
}
- void init_sliding_attacks(Bitboard magic[], Bitboard* attack[], Bitboard attTable[],
- Bitboard mask[], int shift[], Square delta[]) {
+
+ // init_magic_bitboards() computes all rook and bishop magics at startup.
+ // Magic bitboards are used to look up attacks of sliding pieces. As reference
+ // see chessprogramming.wikispaces.com/Magic+Bitboards. In particular, here we
+ // use the so called "fancy" approach.
+
+ void init_magic_bitboards(Bitboard* attacks[], Bitboard magics[],
+ Bitboard masks[], int shifts[], Square deltas[]) {
const 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 key, maxKey, index, booster, offset = 0;
+ int key, maxKey, index, booster;
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));
- attack[s] = &attTable[offset];
- mask[s] = sliding_attacks(s, EmptyBoardBB, delta) & ~edges;
- shift[s] = (CpuIs64Bit ? 64 : 32) - count_1s<CNT32_MAX15>(mask[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_attacks(s, EmptyBoardBB, deltas) & ~edges;
+ shifts[s] = (CpuIs64Bit ? 64 : 32) - count_1s<CNT32_MAX15>(masks[s]);
- // Use Carry-Rippler trick to enumerate all subsets of mask[s]
+ // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
+ // store the corresponding sliding attacks in reference[].
b = maxKey = 0;
do {
occupancy[maxKey] = b;
- reference[maxKey++] = sliding_attacks(s, b, delta);
- b = (b - mask[s]) & mask[s];
+ reference[maxKey++] = sliding_attacks(s, b, deltas);
+ b = (b - masks[s]) & masks[s];
} while (b);
- offset += maxKey;
+ // 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] + maxKey;
+
booster = MagicBoosters[CpuIs64Bit][rank_of(s)];
- // Then find a possible magic and the corresponding attacks
+ // Find a magic for square 's' picking up an (almost) random number
+ // until we find the one that passes the verification test.
do {
- magic[s] = pick_magic(mask[s], rk, booster);
- memset(attack[s], 0, maxKey * sizeof(Bitboard));
+ magics[s] = pick_random(masks[s], rk, booster);
+ memset(attacks[s], 0, maxKey * 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 (key = 0; key < maxKey; key++)
{
- index = CpuIs64Bit ? unsigned((occupancy[key] * magic[s]) >> shift[s])
- : unsigned(occupancy[key] * magic[s] ^ (occupancy[key] >> 32) * (magic[s] >> 32)) >> shift[s];
+ index = CpuIs64Bit ? unsigned((occupancy[key] * magics[s]) >> shifts[s])
+ : unsigned(occupancy[key] * magics[s] ^ (occupancy[key] >> 32) * (magics[s] >> 32)) >> shifts[s];
- if (!attack[s][index])
- attack[s][index] = reference[key];
+ if (!attacks[s][index])
+ attacks[s][index] = reference[key];
- else if (attack[s][index] != reference[key])
+ else if (attacks[s][index] != reference[key])
break;
}
} while (key != maxKey);
projects / stockfish / blobdiff