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Code Issues Releases Wiki Activity

Remove magics

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root 2015-01-10 12:28:12 +00:00
parent 1e66854938
commit a69619e174
2 changed files with 1 additions and 111 deletions
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110
src/bitboard.cpp
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@ -26,16 +26,6 @@
int SquareDistance[SQUARE_NB][SQUARE_NB];
Bitboard RookMasks [SQUARE_NB];
Bitboard RookMagics [SQUARE_NB];
Bitboard* RookAttacks[SQUARE_NB];
unsigned RookShifts [SQUARE_NB];
Bitboard BishopMasks [SQUARE_NB];
Bitboard BishopMagics [SQUARE_NB];
Bitboard* BishopAttacks[SQUARE_NB];
unsigned BishopShifts [SQUARE_NB];
Bitboard SquareBB[SQUARE_NB];
Bitboard FileBB[FILE_NB];
Bitboard RankBB[RANK_NB];
@ -58,13 +48,9 @@ namespace {
int MS1BTable[256]; // To implement software msb()
Square BSFTable[SQUARE_NB]; // To implement software bitscan
Bitboard RookTable[0x19000]; // To store rook attacks
Bitboard BishopTable[0x1480]; // To store bishop attacks
typedef unsigned (Fn)(Square, Bitboard);
void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
Bitboard masks[], unsigned shifts[], Square deltas[], Fn index);
// bsf_index() returns the index into BSFTable[] to look up the bitscan. Uses
// Matt Taylor's folding for 32 bit case, extended to 64 bit by Kim Walisch.
@ -193,9 +179,6 @@ void Bitboards::init() {
Square RookDeltas[] = { DELTA_N, DELTA_E, DELTA_S, DELTA_W };
Square BishopDeltas[] = { DELTA_NE, DELTA_SE, DELTA_SW, DELTA_NW };
init_magics(RookTable, RookAttacks, RookMagics, RookMasks, RookShifts, RookDeltas, magic_index<ROOK>);
init_magics(BishopTable, BishopAttacks, BishopMagics, BishopMasks, BishopShifts, BishopDeltas, magic_index<BISHOP>);
for (Square s1 = SQ_A1; s1 <= SQ_H8; ++s1)
{
PseudoAttacks[QUEEN][s1] = PseudoAttacks[BISHOP][s1] = attacks_bb<BISHOP>(s1, 0);
@ -215,96 +198,3 @@ void Bitboards::init() {
}
}
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) && distance(s, s - deltas[i]) == 1;
s += deltas[i])
{
attack |= s;
if (occupied & s)
break;
}
return attack;
}
// 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.
void init_magics(Bitboard table[], Bitboard* attacks[], Bitboard magics[],
Bitboard masks[], unsigned shifts[], Square deltas[], Fn index) {
Bitboard occupancy[4096], reference[4096], edges, b;
int i, size;
// attacks[s] is a pointer to the beginning of the attacks table for square 's'
attacks[SQ_A1] = table;
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));
// 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_attack(deltas, s, 0) & ~edges;
shifts[s] = (Is64Bit ? 64 : 32) - popcount<Max15>(masks[s]);
// 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);
size++;
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] + size;
// 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] = 0ULL;
while (popcount<Max15>((magics[s] * masks[s]) >> 56) < 6);
std::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)
{
Bitboard& attack = attacks[s][index(s, occupancy[i])];
if (attack && attack != reference[i])
break;
assert(reference[i]);
attack = reference[i];
}
} while (i < size);
}
}
}

2
src/bitboard.h
View file

@ -244,7 +244,7 @@ inline unsigned magic_index(Square s, Bitboard occupied) {
template<PieceType Pt>
inline Bitboard attacks_bb(Square s, Bitboard occupied) {
return (Pt == ROOK ? RookAttacks : BishopAttacks)[s][magic_index<Pt>(s, occupied)];
return 0ULL;
}
inline Bitboard attacks_bb(Piece pc, Square s, Bitboard occupied) {