struct KPKPosition {
- operator Result() const { return res; }
- Result classify_leaf(unsigned idx);
+ KPKPosition(unsigned idx);
+ operator Result() const { return result; }
Result classify(const std::vector<KPKPosition>& db)
{ return us == WHITE ? classify<WHITE>(db) : classify<BLACK>(db); }
Color us;
Square bksq, wksq, psq;
- Result res;
+ Result result;
};
} // namespace
void Bitbases::init_kpk() {
unsigned idx, repeat = 1;
- std::vector<KPKPosition> db(IndexMax);
+ std::vector<KPKPosition> db;
+ db.reserve(IndexMax);
// Initialize db with known win / draw positions
- for (idx = 0; idx < IndexMax; idx++)
- db[idx].classify_leaf(idx);
+ for (idx = 0; idx < IndexMax; ++idx)
+ db.push_back(KPKPosition(idx));
// Iterate through the positions until no more of the unknown positions can be
// changed to either wins or draws (15 cycles needed).
while (repeat)
- for (repeat = idx = 0; idx < IndexMax; idx++)
- if (db[idx] == UNKNOWN && db[idx].classify(db) != UNKNOWN)
- repeat = 1;
+ for (repeat = idx = 0; idx < IndexMax; ++idx)
+ repeat |= (db[idx] == UNKNOWN && db[idx].classify(db) != UNKNOWN);
// Map 32 results into one KPKBitbase[] entry
- for (idx = 0; idx < IndexMax; idx++)
+ for (idx = 0; idx < IndexMax; ++idx)
if (db[idx] == WIN)
KPKBitbase[idx / 32] |= 1 << (idx & 0x1F);
}
namespace {
- Result KPKPosition::classify_leaf(unsigned idx) {
+ KPKPosition::KPKPosition(unsigned idx) {
wksq = Square((idx >> 0) & 0x3F);
bksq = Square((idx >> 6) & 0x3F);
us = Color ((idx >> 12) & 0x01);
psq = File ((idx >> 13) & 0x03) | Rank(RANK_7 - (idx >> 15));
+ result = UNKNOWN;
// Check if two pieces are on the same square or if a king can be captured
- if ( wksq == psq || wksq == bksq || bksq == psq
- || (StepAttacksBB[KING][wksq] & bksq)
+ if ( square_distance(wksq, bksq) <= 1 || wksq == psq || bksq == psq
|| (us == WHITE && (StepAttacksBB[PAWN][psq] & bksq)))
- return res = INVALID;
+ result = INVALID;
- if (us == WHITE)
+ else if (us == WHITE)
{
// Immediate win if pawn can be promoted without getting captured
if ( rank_of(psq) == RANK_7
&& wksq != psq + DELTA_N
&& ( square_distance(bksq, psq + DELTA_N) > 1
||(StepAttacksBB[KING][wksq] & (psq + DELTA_N))))
- return res = WIN;
+ result = WIN;
}
// Immediate draw if is stalemate or king captures undefended pawn
else if ( !(StepAttacksBB[KING][bksq] & ~(StepAttacksBB[KING][wksq] | StepAttacksBB[PAWN][psq]))
|| (StepAttacksBB[KING][bksq] & psq & ~StepAttacksBB[KING][wksq]))
- return res = DRAW;
-
- return res = UNKNOWN;
+ result = DRAW;
}
template<Color Us>
Square s = psq + DELTA_N;
r |= db[index(BLACK, bksq, wksq, s)]; // Single push
- if (rank_of(s) == RANK_3 && s != wksq && s != bksq)
+ if (rank_of(psq) == RANK_2 && s != wksq && s != bksq)
r |= db[index(BLACK, bksq, wksq, s + DELTA_N)]; // Double push
}
if (Us == WHITE)
- return res = r & WIN ? WIN : r & UNKNOWN ? UNKNOWN : DRAW;
+ return result = r & WIN ? WIN : r & UNKNOWN ? UNKNOWN : DRAW;
else
- return res = r & DRAW ? DRAW : r & UNKNOWN ? UNKNOWN : WIN;
+ return result = r & DRAW ? DRAW : r & UNKNOWN ? UNKNOWN : WIN;
}
} // namespace