#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(PieceType pt, Bitboard* attacks[], Bitboard magics[],
+ Bitboard masks[], int shifts[]);
}
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 };
-
- init_sliding_attacks(BMult, BAttacks, BAttacksTable, BMask, BShift, BDelta);
- init_sliding_attacks(RMult, RAttacks, RAttacksTable, RMask, RShift, RDelta);
+ init_magic_bitboards(ROOK, RAttacks, RMagics, RMasks, RShifts);
+ init_magic_bitboards(BISHOP, BAttacks, BMagics, BMasks, BShifts);
for (Square s = SQ_A1; s <= SQ_H8; s++)
{
for (Square s2 = SQ_A1; s2 <= SQ_H8; s2++)
if (bit_is_set(QueenPseudoAttacks[s1], s2))
{
- int f = file_distance(s1, s2);
- int r = rank_distance(s1, s2);
-
- Square d = (s2 - s1) / Max(f, r);
+ Square delta = (s2 - s1) / square_distance(s1, s2);
- for (Square s3 = s1 + d; s3 != s2; s3 += d)
- set_bit(&BetweenBB[s1][s2], s3);
+ for (Square s = s1 + delta; s != s2; s += delta)
+ set_bit(&BetweenBB[s1][s2], s);
}
}
namespace {
- Bitboard sliding_attacks(Square sq, Bitboard occupied, Square delta[]) {
+ Bitboard sliding_attacks(PieceType pt, Square sq, Bitboard occupied) {
+ Square deltas[][4] = { { DELTA_N, DELTA_E, DELTA_S, DELTA_W },
+ { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW } };
Bitboard attacks = 0;
+ Square* delta = (pt == ROOK ? deltas[0] : deltas[1]);
for (int i = 0; i < 4; 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[]) {
- const int MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 },
- { 1059, 3608, 605, 3234, 3326, 38, 2029, 3043 } };
+ // 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(PieceType pt, Bitboard* attacks[], Bitboard magics[],
+ Bitboard masks[], int shifts[]) {
+
+ 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 i, size, index, booster;
+
+ // attacks[s] is a pointer to the beginning of the attacks table for square 's'
+ attacks[SQ_A1] = (pt == ROOK ? RookTable : BishopTable);
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]);
-
- // Use Carry-Rippler trick to enumerate all subsets of mask[s]
- b = maxKey = 0;
+ // 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(pt, s, EmptyBoardBB) & ~edges;
+ shifts[s] = (CpuIs64Bit ? 64 : 32) - count_1s<CNT32_MAX15>(masks[s]);
+
+ // Use Carry-Rippler trick to enumerate all subsets of masks[s] and
+ // store the corresponding sliding attacks bitboard in reference[].
+ b = size = 0;
do {
- occupancy[maxKey] = b;
- reference[maxKey++] = sliding_attacks(s, b, delta);
- b = (b - mask[s]) & mask[s];
+ occupancy[size] = b;
+ reference[size++] = sliding_attacks(pt, s, b);
+ b = (b - masks[s]) & masks[s];
} while (b);
- offset += maxKey;
- booster = MagicBoosters[CpuIs64Bit][square_rank(s)];
+ // 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;
- // Then find a possible magic and the corresponding attacks
- do {
- magic[s] = pick_magic(mask[s], rk, booster);
- memset(attack[s], 0, maxKey * sizeof(Bitboard));
+ booster = MagicBoosters[CpuIs64Bit][rank_of(s)];
- for (key = 0; key < maxKey; key++)
+ // Find a magic for square 's' picking up an (almost) random number
+ // until we find the one that passes the verification test.
+ do {
+ magics[s] = pick_random(masks[s], rk, booster);
+ 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++)
{
- index = CpuIs64Bit ? unsigned((occupancy[key] * magic[s]) >> shift[s])
- : unsigned(occupancy[key] * magic[s] ^ (occupancy[key] >> 32) * (magic[s] >> 32)) >> shift[s];
+ index = (pt == ROOK ? rook_index(s, occupancy[i])
+ : bishop_index(s, occupancy[i]));
- if (!attack[s][index])
- attack[s][index] = reference[key];
+ if (!attacks[s][index])
+ attacks[s][index] = reference[i];
- else if (attack[s][index] != reference[key])
+ else if (attacks[s][index] != reference[i])
break;
}
- } while (key != maxKey);
+ } while (i != size);
}
}
}
projects / stockfish / blobdiff