[Discuss-gnuradio] question about dvb_bch_bb_impl.cc

[Tiankun Hu]

I found dvb_bch_bb_impl.cc use shift register to implement BCH encode, 
but it seems different with my knowledge.
If I remember right, after shift the register, we should add the info 
bit to register's LSB

dvb_bch_bb_impl.cc:526~535
              b = (temp ^ (shift[5] & 1));
              reg_6_shift(shift);
              if (b) {
                shift[0] ^= m_poly_n_12[0];
                shift[1] ^= m_poly_n_12[1];
                shift[2] ^= m_poly_n_12[2];
                shift[3] ^= m_poly_n_12[3];
                shift[4] ^= m_poly_n_12[4];
                shift[5] ^= m_poly_n_12[5];
              }

should be like this ===========>
              b = shift[5] & 1; // use register's MSB to decide whether 
need to XOR poly
              reg_6_shift(shift);
	      shift[0] = shift[0] ^ (temp<<31);//  add the info bit to 
register's LSB
              if (b) {
                shift[0] ^= m_poly_n_12[0];
                shift[1] ^= m_poly_n_12[1];
                shift[2] ^= m_poly_n_12[2];
                shift[3] ^= m_poly_n_12[3];
                shift[4] ^= m_poly_n_12[4];
                shift[5] ^= m_poly_n_12[5];
              }