+template<>
+ScaleFactor Endgame<KRPKB>::operator()(const Position& pos) const {
+
+ assert(verify_material(pos, strongSide, RookValueMg, 1));
+ assert(verify_material(pos, weakSide, BishopValueMg, 0));
+
+ // Test for a rook pawn
+ if (pos.pieces(PAWN) & (FileABB | FileHBB))
+ {
+ Square ksq = pos.king_square(weakSide);
+ Square bsq = pos.list<BISHOP>(weakSide)[0];
+ Square psq = pos.list<PAWN>(strongSide)[0];
+ Rank rk = relative_rank(strongSide, psq);
+ Square push = pawn_push(strongSide);
+
+ // If the pawn is on the 5th rank and the pawn (currently) is on
+ // the same color square as the bishop then there is a chance of
+ // a fortress. Depending on the king position give a moderate
+ // reduction or a stronger one if the defending king is near the
+ // corner but not trapped there.
+ if (rk == RANK_5 && !opposite_colors(bsq, psq))
+ {
+ int d = square_distance(psq + 3 * push, ksq);
+
+ if (d <= 2 && !(d == 0 && ksq == pos.king_square(strongSide) + 2 * push))
+ return ScaleFactor(24);
+ else
+ return ScaleFactor(48);
+ }
+
+ // When the pawn has moved to the 6th rank we can be fairly sure
+ // it's drawn if the bishop attacks the square in front of the
+ // pawn from a reasonable distance and the defending king is near
+ // the corner
+ if ( rk == RANK_6
+ && square_distance(psq + 2 * push, ksq) <= 1
+ && (PseudoAttacks[BISHOP][bsq] & (psq + push))
+ && file_distance(bsq, psq) >= 2)
+ return ScaleFactor(8);
+ }