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Better name and document magic botboard stuff

Browse source 
No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2011-06-05 09:04:57 +01:00
parent 2f6142cb9b
commit 3092f0c646
2 changed files with 44 additions and 47 deletions
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85
src/bitboard.cpp
View file

@ -194,7 +194,7 @@ const int RShift[64] = {
CACHE_LINE_ALIGNMENT int BSFTable[64]; CACHE_LINE_ALIGNMENT int BSFTable[64];
void init_sliding_attacks(Bitboard attacks[], Magics m[], const int shift[], void init_sliding_attacks(Bitboard attacks[], Magics m[], const int shift[],
const Bitboard mult[], int deltas[][2]); const Bitboard mult[], Square deltas[]);
} }
@ -351,11 +351,11 @@ void init_bitboards() {
set_bit(&StepAttacksBB[make_piece(c, pt)][s], to); set_bit(&StepAttacksBB[make_piece(c, pt)][s], to);
} }
int rookDeltas[4][2] = { {0,1}, {0 ,-1}, {1, 0}, {-1, 0} }; Square RDeltas[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W };
int bishopDeltas[4][2] = { {1,1}, {-1, 1}, {1,-1}, {-1,-1} }; Square BDeltas[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
init_sliding_attacks(RAttacks, RMagics, RShift, RMult, rookDeltas); init_sliding_attacks(RAttacks, RMagics, RShift, RMult, RDeltas);
init_sliding_attacks(BAttacks, BMagics, BShift, BMult, bishopDeltas); init_sliding_attacks(BAttacks, BMagics, BShift, BMult, BDeltas);
for (Square s = SQ_A1; s <= SQ_H8; s++) for (Square s = SQ_A1; s <= SQ_H8; s++)
{ {
@ -381,70 +381,67 @@ void init_bitboards() {
namespace { namespace {
Bitboard index_to_bitboard(int index, Bitboard mask) { Bitboard submask(Bitboard mask, int key) {
Bitboard result = 0; Bitboard subMask = 0;
int sq, cnt = 0; int bitNum = -1;
while (mask) // Extract an unique submask out of a mask according to the given key
{ for (Square s = SQ_A1; s <= SQ_H8; s++)
sq = pop_1st_bit(&mask); if (bit_is_set(mask, s) && bit_is_set(key, Square(++bitNum)))
set_bit(&subMask, s);
if (index & (1 << cnt++)) return subMask;
result |= (1ULL << sq);
}
return result;
} }
Bitboard sliding_attacks(int sq, Bitboard occupied, int deltas[][2], Bitboard sliding_attacks(Square sq, Bitboard occupied, Square deltas[], bool skipLast) {
int fmin, int fmax, int rmin, int rmax) {
Bitboard attacks = 0; Bitboard attacks = 0;
int dx, dy, f, r;
int rk = sq / 8;
int fl = sq % 8;
for (int i = 0; i < 4; i++) for (int i = 0; i < 4; i++)
{ {
dx = deltas[i][0]; Square s = sq + deltas[i];
dy = deltas[i][1];
f = fl + dx;
r = rk + dy;
while ( (dx == 0 || (f >= fmin && f <= fmax)) while ( square_is_ok(s)
&& (dy == 0 || (r >= rmin && r <= rmax))) && square_distance(s, s - deltas[i]) == 1
&& (!skipLast || !file_distance(s, sq) || (square_file(s) != FILE_A && square_file(s) != FILE_H))
&& (!skipLast || !rank_distance(s, sq) || (square_rank(s) != RANK_1 && square_rank(s) != RANK_8)))
{ {
attacks |= (1ULL << (f + r * 8)); attacks |= 1ULL << s;
if (occupied & (1ULL << (f + r * 8))) if (occupied & (1ULL << s))
break; break;
f += dx; s += deltas[i];
r += dy;
} }
} }
return attacks; return attacks;
} }
void init_sliding_attacks(Bitboard attacks[], Magics m[], const int shift[], void init_sliding_attacks(Bitboard attacks[], Magics m[], const int shift[],
const Bitboard mult[], int deltas[][2]) { const Bitboard mult[], Square deltas[]) {
Bitboard b, v; Bitboard occupancy, index;
int i, j, index; int maxKey, offset = 0;
for (i = index = 0; i < 64; i++) for (Square s = SQ_A1; s <= SQ_H8; s++)
{ {
m[i].index = index; m[s].offset = offset;
m[i].mult = mult[i]; m[s].mult = mult[s];
m[i].shift = shift[i]; m[s].shift = shift[s];
m[i].mask = sliding_attacks(i, 0, deltas, 1, 6, 1, 6); m[s].mask = sliding_attacks(s, EmptyBoardBB, deltas, true);
j = 1 << ((CpuIs64Bit ? 64 : 32) - m[i].shift);
for (int k = 0; k < j; k++) maxKey = 1 << (CpuIs64Bit ? 64 - shift[s] : 32 - shift[s]);
for (int key = 0; key < maxKey; key++)
{ {
b = index_to_bitboard(k, m[i].mask); occupancy = submask(m[s].mask, key);
v = CpuIs64Bit ? b * mult[i] : unsigned(b * mult[i] ^ (b >> 32) * (mult[i] >> 32));
attacks[index + (v >> shift[i])] = sliding_attacks(i, b, deltas, 0, 7, 0, 7); index = CpuIs64Bit ? occupancy * mult[s]
: unsigned(occupancy * mult[s] ^ (occupancy >> 32) * (mult[s] >> 32));
attacks[offset + (index >> shift[s])] = sliding_attacks(s, occupancy, deltas, false);
} }
index += j; offset += maxKey;
} }
} }
} }

6
src/bitboard.h
View file

@ -69,7 +69,7 @@ extern uint8_t BitCount8Bit[256];
struct Magics { struct Magics {
Bitboard mask; Bitboard mask;
uint64_t mult; uint64_t mult;
uint32_t index; uint32_t offset;
uint32_t shift; uint32_t shift;
}; };
@ -189,14 +189,14 @@ inline Bitboard bishop_attacks_bb(Square s, Bitboard occ) {
inline Bitboard rook_attacks_bb(Square s, Bitboard occ) { inline Bitboard rook_attacks_bb(Square s, Bitboard occ) {
const Magics& m = RMagics[s]; const Magics& m = RMagics[s];
Bitboard b = occ & m.mask; Bitboard b = occ & m.mask;
return RAttacks[m.index + return RAttacks[m.offset +
((unsigned(b) * unsigned(m.mult) ^ unsigned(b >> 32) * unsigned(m.mult >> 32)) >> m.shift)]; ((unsigned(b) * unsigned(m.mult) ^ unsigned(b >> 32) * unsigned(m.mult >> 32)) >> m.shift)];
} }
inline Bitboard bishop_attacks_bb(Square s, Bitboard occ) { inline Bitboard bishop_attacks_bb(Square s, Bitboard occ) {
const Magics& m = BMagics[s]; const Magics& m = BMagics[s];
Bitboard b = occ & m.mask; Bitboard b = occ & m.mask;
return BAttacks[m.index + return BAttacks[m.offset +
((unsigned(b) * unsigned(m.mult) ^ unsigned(b >> 32) * unsigned(m.mult >> 32)) >> m.shift)]; ((unsigned(b) * unsigned(m.mult) ^ unsigned(b >> 32) * unsigned(m.mult >> 32)) >> m.shift)];
} }