Function find_interv_vec 

pub unsafe extern "C" fn find_interv_vec(
    xt: *mut c_double,
    n: *mut c_int,
    x: *mut c_double,
    nx: *mut c_int,
    rightmost_closed: *mut c_int,
    all_inside: *mut c_int,
    indx: *mut c_int,
)