int sSearcher::RecognizeDraw(sPosition *p)
{
if ( p->pcCount[WHITE][P] == 0 && p->pcCount[BLACK][P] == 0 ) {
if ( p->pieceMat[WHITE] + p->pieceMat[BLACK] < 400 ) {
if ( !IllegalPosition(p) ) return 1;
} // bare kings or Km vs K
if (p->pieceMat[WHITE] < 400
&& p->pieceMat[BLACK] < 400
&& (bbPc(p, WHITE, K) & bbRim) == 0
&& (bbPc(p, BLACK, K) & bbRim) == 0 ) {
if ( !IllegalPosition(p) ) return 1;
} // Km vs Km; just in case we ensure that neither king is on the rim
} // no pawns
if (p->pieceMat[WHITE] == 0 && p->pieceMat[BLACK] == 0) {
if (p->pcCount[WHITE][P] == 1 && p->pcCount[BLACK][P] == 0)
return KPKdraw(p, WHITE); // exactly one white pawn
if (p->pcCount[BLACK][P] == 1 && p->pcCount[WHITE][P] == 0)
return KPKdraw(p, BLACK); // exactly one black pawn
} // pawns only
return 0;
}
int IsDraw(POS *p) {
static const U64 bbRim = { FILE_A_BB | FILE_H_BB | RANK_1_BB | RANK_8_BB };
// Draw by 50 move rule
if (p->rev_moves > 100) return 1;
// Draw by repetition
for (int i = 4; i <= p->rev_moves; i += 2)
if (p->hash_key == p->rep_list[p->head - i])
return 1;
// With no major pieces on the board, we have some heuristic draws to consider
if (p->cnt[WC][Q] + p->cnt[BC][Q] + p->cnt[WC][R] + p->cnt[BC][R] == 0) {
// Draw by insufficient material (bare kings or Km vs K)
if (!Illegal(p)) {
if (p->cnt[WC][P] + p->cnt[BC][P] == 0) {
if (p->cnt[WC][N] + p->cnt[BC][N] + p->cnt[WC][B] + p->cnt[BC][B] <= 1) return 0; // KmK
}
}
// Trivially drawn KPK endgames
if (p->cnt[WC][N] + p->cnt[BC][N] + p->cnt[WC][B] + p->cnt[BC][B] == 0) {
if (p->cnt[WC][P] + p->cnt[BC][P] == 1) {
if (p->cnt[WC][P] == 1 && p->cnt[BC][P] == 0)
return KPKdraw(p, WC); // exactly one white pawn
if (p->cnt[BC][P] == 1 && p->cnt[WC][P] == 0)
return KPKdraw(p, BC); // exactly one black pawn
}
} // pawns only
}
return 0; // default: no draw
}
