internal static void init()
{
var db = new KPKPosition[MAX_INDEX];
uint idx, repeat = 1;
// Initialize db with known win / draw positions
for (idx = 0; idx < MAX_INDEX; ++idx)
{
db[idx] = new KPKPosition(idx);
}
// Iterate through the positions until none of the unknown positions can be
// changed to either wins or draws (15 cycles needed).
while (repeat != 0)
{
for (repeat = idx = 0; idx < MAX_INDEX; ++idx)
{
repeat |= ((db[idx] == Result.UNKNOWN && db[idx].classify(db) != Result.UNKNOWN)) ? 1u : 0;
}
}
// Map 32 results into one KPKBitbase[] entry
for (idx = 0; idx < MAX_INDEX; ++idx)
{
if (db[idx] == Result.WIN)
{
KPKBitbase[idx/32] |= (uint) (1 << (int) (idx & 0x1F));
}
}
}
internal Result classify(ColorT Us, KPKPosition[] db)
{
// White to move: If one move leads to a position classified as WIN, the result
// of the current position is WIN. If all moves lead to positions classified
// as DRAW, the current position is classified as DRAW, otherwise the current
// position is classified as UNKNOWN.
//
// Black to move: If one move leads to a position classified as DRAW, the result
// of the current position is DRAW. If all moves lead to positions classified
// as WIN, the position is classified as WIN, otherwise the current position is
// classified as UNKNOWN.
var Them = (Us == Color.WHITE ? Color.BLACK : Color.WHITE);
var Good = (Us == Color.WHITE ? Result.WIN : Result.DRAW);
var Bad = (Us == Color.WHITE ? Result.DRAW : Result.WIN);
var r = Result.INVALID;
var b = Utils.StepAttacksBB[PieceType.KING, ksq[Us]];
while (b != 0)
{
r |= Us == Color.WHITE
? db[Bitbases.index(Them, ksq[Them], Utils.pop_lsb(ref b), psq)]
: db[Bitbases.index(Them, Utils.pop_lsb(ref b), ksq[Them], psq)];
}
if (Us == Color.WHITE)
{
if (Square.rank_of(psq) < Rank.RANK_7) // Single push
{
r |= db[Bitbases.index(Them, ksq[Them], ksq[Us], psq + Square.DELTA_N)];
}
if (Square.rank_of(psq) == Rank.RANK_2 // Double push
&& psq + Square.DELTA_N != ksq[Us] && psq + Square.DELTA_N != ksq[Them])
{
r |= db[Bitbases.index(Them, ksq[Them], ksq[Us], psq + Square.DELTA_N + Square.DELTA_N)];
}
}
return result = (r & Good) != 0 ? Good : (r & Result.UNKNOWN) != 0 ? Result.UNKNOWN : Bad;
}
internal Result classify(KPKPosition[] db)
{
return us == Color.WHITE ? classify(Color.WHITE, db) : classify(Color.BLACK, db);
}
