// bit 6-11: black king square (from SQ_A1 to SQ_H8)
// bit 12: side to move (WHITE or BLACK)
// bit 13-14: white pawn file (from FILE_A to FILE_D)
- // bit 15-17: white pawn 6 - rank (from 6 - RANK_7 to 6 - RANK_2)
+ // bit 15-17: white pawn RANK_7 - rank (from RANK_7 - RANK_7 to RANK_7 - RANK_2)
unsigned index(Color us, Square bksq, Square wksq, Square psq) {
- return wksq + (bksq << 6) + (us << 12) + (file_of(psq) << 13) + ((6 - rank_of(psq)) << 15);
+ return wksq + (bksq << 6) + (us << 12) + (file_of(psq) << 13) + ((RANK_7 - rank_of(psq)) << 15);
}
enum Result {
for (idx = 0; idx < IndexMax; idx++)
db[idx].classify_leaf(idx);
- // Iterate until all positions are classified (15 cycles needed)
+ // 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)
Result KPKPosition::classify_leaf(unsigned idx) {
- wksq = Square((idx >> 0) & 0x3F);
- bksq = Square((idx >> 6) & 0x3F);
- us = Color((idx >> 12) & 0x01);
- psq = File((idx >> 13) & 3) | Rank(6 - (idx >> 15));
+ 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));
// Check if two pieces are on the same square or if a king can be captured
if ( wksq == psq || wksq == bksq || bksq == psq
// as WIN, the position is classified WIN otherwise the current position is
// classified UNKNOWN.
+ const Color Them = (Us == WHITE ? BLACK : WHITE);
+
Result r = INVALID;
Bitboard b = StepAttacksBB[KING][Us == WHITE ? wksq : bksq];
while (b)
- r |= Us == WHITE ? db[index(~Us, bksq, pop_lsb(&b), psq)]
- : db[index(~Us, pop_lsb(&b), wksq, psq)];
+ r |= Us == WHITE ? db[index(Them, bksq, pop_lsb(&b), psq)]
+ : db[index(Them, pop_lsb(&b), wksq, psq)];
if (Us == WHITE && rank_of(psq) < RANK_7)
{