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Further touches to magic bitboards code

Browse source 
No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2011-11-01 09:07:23 +01:00
parent ac7339877b
commit 22b9307aba
2 changed files with 52 additions and 50 deletions
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71
src/bitboard.cpp
View file

@ -67,8 +67,8 @@ namespace {
Bitboard RookTable[0x19000]; // Storage space for rook attacks
Bitboard BishopTable[0x1480]; // Storage space for bishop attacks
void init_magic_bitboards(Bitboard* attacks[], Bitboard magics[],
Bitboard masks[], int shifts[], Square deltas[]);
void init_magic_bitboards(PieceType pt, Bitboard* attacks[], Bitboard magics[],
Bitboard masks[], int shifts[]);
}
@ -228,14 +228,8 @@ void init_bitboards() {
set_bit(&StepAttacksBB[make_piece(c, pt)][s], to);
}
Square RDeltas[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W };
Square BDeltas[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
RAttacks[0] = RookTable;
BAttacks[0] = BishopTable;
init_magic_bitboards(RAttacks, RMagics, RMasks, RShifts, RDeltas);
init_magic_bitboards(BAttacks, BMagics, BMasks, BShifts, BDeltas);
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++)
{
@ -248,35 +242,35 @@ void init_bitboards() {
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 delta = (s2 - s1) / square_distance(s1, s2);
Square d = (s2 - s1) / std::max(f, r);
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 deltas[]) {
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++)
{
Square s = sq + deltas[i];
Square s = sq + delta[i];
while (square_is_ok(s) && square_distance(s, s - deltas[i]) == 1)
while (square_is_ok(s) && square_distance(s, s - delta[i]) == 1)
{
set_bit(&attacks, s);
if (bit_is_set(occupied, s))
break;
s += deltas[i];
s += delta[i];
}
}
return attacks;
@ -309,14 +303,17 @@ namespace {
// 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[]) {
void init_magic_bitboards(PieceType pt, Bitboard* attacks[], Bitboard magics[],
Bitboard masks[], int shifts[]) {
const int MagicBoosters[][8] = { { 3191, 2184, 1310, 3618, 2091, 1308, 2452, 3996 },
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;
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++)
{
@ -328,22 +325,22 @@ namespace {
// 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;
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 in reference[].
b = maxKey = 0;
// store the corresponding sliding attacks bitboard in reference[].
b = size = 0;
do {
occupancy[maxKey] = b;
reference[maxKey++] = sliding_attacks(s, b, deltas);
occupancy[size] = b;
reference[size++] = sliding_attacks(pt, s, b);
b = (b - masks[s]) & masks[s];
} 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] + maxKey;
attacks[s + 1] = attacks[s] + size;
booster = MagicBoosters[CpuIs64Bit][rank_of(s)];
@ -351,24 +348,24 @@ namespace {
// until we find the one that passes the verification test.
do {
magics[s] = pick_random(masks[s], rk, booster);
memset(attacks[s], 0, maxKey * sizeof(Bitboard));
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 (key = 0; key < maxKey; key++)
for (i = 0; i < size; i++)
{
index = CpuIs64Bit ? unsigned((occupancy[key] * magics[s]) >> shifts[s])
: unsigned(occupancy[key] * magics[s] ^ (occupancy[key] >> 32) * (magics[s] >> 32)) >> shifts[s];
index = (pt == ROOK ? rook_index(s, occupancy[i])
: bishop_index(s, occupancy[i]));
if (!attacks[s][index])
attacks[s][index] = reference[key];
attacks[s][index] = reference[i];
else if (attacks[s][index] != reference[key])
else if (attacks[s][index] != reference[i])
break;
}
} while (key != maxKey);
} while (i != size);
}
}
}

29
src/bitboard.h
View file

@ -171,30 +171,35 @@ inline Bitboard in_front_bb(Color c, Square s) {
#if defined(IS_64BIT)
inline Bitboard rook_attacks_bb(Square s, Bitboard occ) {
return RAttacks[s][((occ & RMasks[s]) * RMagics[s]) >> RShifts[s]];
FORCE_INLINE unsigned rook_index(Square s, Bitboard occ) {
return unsigned(((occ & RMasks[s]) * RMagics[s]) >> RShifts[s]);
}
inline Bitboard bishop_attacks_bb(Square s, Bitboard occ) {
return BAttacks[s][((occ & BMasks[s]) * BMagics[s]) >> BShifts[s]];
FORCE_INLINE unsigned bishop_index(Square s, Bitboard occ) {
return unsigned(((occ & BMasks[s]) * BMagics[s]) >> BShifts[s]);
}
#else // if !defined(IS_64BIT)
inline Bitboard rook_attacks_bb(Square s, Bitboard occ) {
FORCE_INLINE unsigned rook_index(Square s, Bitboard occ) {
Bitboard b = occ & RMasks[s];
return RAttacks[s]
[unsigned(int(b) * int(RMagics[s]) ^ int(b >> 32) * int(RMagics[s] >> 32)) >> RShifts[s]];
return unsigned(int(b) * int(RMagics[s]) ^ int(b >> 32) * int(RMagics[s] >> 32)) >> RShifts[s];
}
FORCE_INLINE unsigned bishop_index(Square s, Bitboard occ) {
Bitboard b = occ & BMasks[s];
return unsigned(int(b) * int(BMagics[s]) ^ int(b >> 32) * int(BMagics[s] >> 32)) >> BShifts[s];
}
#endif
inline Bitboard rook_attacks_bb(Square s, Bitboard occ) {
return RAttacks[s][rook_index(s, occ)];
}
inline Bitboard bishop_attacks_bb(Square s, Bitboard occ) {
Bitboard b = occ & BMasks[s];
return BAttacks[s]
[unsigned(int(b) * int(BMagics[s]) ^ int(b >> 32) * int(BMagics[s] >> 32)) >> BShifts[s]];
return BAttacks[s][bishop_index(s, occ)];
}
#endif
inline Bitboard queen_attacks_bb(Square s, Bitboard blockers) {
return rook_attacks_bb(s, blockers) | bishop_attacks_bb(s, blockers);
}