void silc_mp_div_2exp_qr(SilcMPInt *q, SilcMPInt *r, SilcMPInt *mp1,
                             SilcUInt32 exp);

    Divide the `mp1' with 2 ** `exp' and save the quotient to `q' and
    the remainder to `r'. This is equivalent to q = mp1 / (2 ^ exp),
    r = mp1 mod (2 ^ exp). If the `q' or `r' is NULL then the operation
    is omitted.