void sEvaluator::EvalPawnCenter(sPosition *p, int side)
{
int oppo = Opp(side);
if (bbPc(p, side, P) & RelSqBb(D4,side) ) {
// defend central pawns (pawns side by side evaluated as "phalanx")
if (bbPc(p, side, P) & RelSqBb(E3,side) ) pawnScoreMg[side] += centDefense;
if (bbPc(p, side, P) & RelSqBb(C3,side) ) pawnScoreMg[side] += centDefense;
}
if (bbPc(p, side, P) & RelSqBb(E4,side) ) {
if ( bbPc(p, side, P) & RelSqBb(D3,side) ) pawnScoreMg[side] += centDefense;
}
}
int GetDrawFactor(POS *p, int sd)
{
int op = Opp(sd);
// Case 1: KPK with edge pawn (else KBPK recognizer would break)
if (PcMatNone(p, sd)
&& PcMatNone(p, op)
&& p->cnt[sd][P] == 1 // TODO: all pawns of a stronger side on a rim
&& p->cnt[op][P] == 0) { // TODO: accept pawns for a weaker side
if (p->Pawns(sd) & FILE_H_BB
&& p->Kings(op) & bbKingBlockH[sd]) return 0;
if (p->Pawns(sd) & FILE_A_BB
&& p->Kings(op) & bbKingBlockA[sd]) return 0;
}
// Case 2: KBPK(P) draws with edge pawn and wrong bishop
if (PcMatB(p, sd)
&& PcMatNone(p, op)
&& p->cnt[sd][P] == 1) { // TODO: all pawns of a stronger side on a rim
if (p->Pawns(sd) & FILE_H_BB
&& NotOnBishColor(p, sd, REL_SQ(H8, sd))
&& p->Kings(op) & bbKingBlockH[sd]) return 0;
if (p->Pawns(sd) & FILE_A_BB
&& NotOnBishColor(p, sd, REL_SQ(A8, sd))
&& p->Kings(op) & bbKingBlockA[sd]) return 0;
}
// Case 3: KBP vs Km
// drawn when defending king stands on pawn's path and can't be driven out
// by a bishop (must be dealt with before opposite bishops ending)
if (PcMatB(p, sd)
&& PcMat1Minor(p, op)
&& p->cnt[sd][P] == 1
&& p->cnt[op][P] == 0
&& (SqBb(p->king_sq[op]) & BB.GetFrontSpan(p->Pawns(sd), sd))
&& NotOnBishColor(p, sd, p->king_sq[op]) )
return 0;
// Case 4: Bishops of opposite color
if (PcMatB(p, sd) && PcMatB(p, op) && DifferentBishops(p)) {
// 4a: single bishop cannot win without pawns
if (p->cnt[sd][P] == 0) return 0;
// 4b: different bishops with a single pawn on the own half of the board
if (p->cnt[sd][P] == 1
&& p->cnt[op][P] == 0) {
if (bbHomeZone[sd] & p->Pawns(sd)) return 0;
// TODO: 4c: distant bishop controls a square on pawn's path
}
// 4d: halve the score for pure BOC endings
return 32;
}
if (p->cnt[sd][P] == 0) {
// Case 5: low and almost equal material with no pawns
if (p->cnt[op][P] == 0) {
if (PcMatRm(p, sd) && PcMatRm(p, op)) return 8;
if (PcMatR (p, sd) && PcMatR (p, op)) return 8;
if (PcMatQ (p, sd) && PcMatQ (p, op)) return 8;
if (PcMat2Minors(p, sd) && PcMatR(p, op)) return 8;
}
// Case 6: two knights
if (PcMatNN(p, sd)) {
if (p->cnt[op][P] == 0) return 0;
else return 4;
}
// Case 7: K(m) vs K(m) or Km vs Kp(p)
if (p->cnt[sd][Q] + p->cnt[sd][R] == 0 && p->cnt[sd][B] + p->cnt[sd][N] < 2 )
return 0;
// Case 8: KR vs Km(p)
if (PcMatR(p, sd) && PcMat1Minor(p, op) ) return 16;
// Case 9: KRm vs KR(p)
if (p->cnt[sd][R] == 1 && p->cnt[sd][Q] == 0 && p->cnt[sd][B] + p->cnt[sd][N] == 1
&& PcMatR(p, op) ) return 16;
// Case 10: KQm vs KQ(p)
if (p->cnt[sd][Q] == 1 && p->cnt[sd][R] == 0 && p->cnt[sd][B] + p->cnt[sd][N] == 1
&& PcMatQ(p, op) ) return 32;
// Case 11: Kmm vs KB(p)
if (PcMat2Minors(p,sd) && PcMatB(p, op) ) return 16;
// Case 12: KBN vs Km(p)
if (PcMatBN(p, sd) && PcMat1Minor(p, op) ) return 16;
// Case 13: KRR vs KRm(p)
if (PcMatRR(p, sd) && PcMatRm(p, op)) return 16;
// Case 14: KRRm vs KRR(p)
if (p->cnt[sd][R] == 2 && p->cnt[sd][Q] == 0 && p->cnt[sd][B] + p->cnt[sd][N] == 1
&& PcMatRR(p, op)) return 16;
}
// Case 15: KRP vs KR
if (PcMatR(p, sd) && PcMatR(p, op) && p->cnt[sd][P] == 1 && p->cnt[op][P] == 0) {
// 15a: good defensive position with a king on pawn's path increases drawing chances
if ((SqBb(p->king_sq[op]) & BB.GetFrontSpan(p->Pawns(sd), sd)))
return 32; // 1/2
// 15b: draw code for rook endgame with edge pawn
if ((RelSqBb(A7, sd) & p->Pawns(sd))
&& ( RelSqBb(A8, sd) & p->Rooks(sd))
&& ( FILE_A_BB & p->Rooks(op))
&& ((RelSqBb(H7, sd) & p->Kings(op)) || (RelSqBb(G7, sd) & p->Kings(op)))
) return 0; // dead draw
if ((RelSqBb(H7, sd) & p->Pawns(sd))
&& ( RelSqBb(H8, sd) & p->Rooks(sd))
&& ( FILE_H_BB & p->Rooks(op))
&& ((RelSqBb(A7, sd) & p->Kings(op)) || (RelSqBb(B7, sd) & p->Kings(op)))
) return 0; // dead draw
}
return 64;
}
