Function pio_branches 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pio_branches(
    net: *const PioNetwork,
    from: *mut i64,
    to: *mut i64,
    r: *mut f64,
    x: *mut f64,
    b: *mut f64,
    tap: *mut f64,
    shift: *mut f64,
    in_service: *mut u8,
)

Fill the branch tables (each length pio_n_branches). from/to are the 1-based bus ids (the same id space as pio_bus_ids, not dense indices); map them to dense matrix rows with the pio_bus_ids ordering. Any pointer may be NULL to skip.