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,
    cap: usize,
) -> usize

Write the branch table as parallel arrays, each up to cap entries, and return the total branch count. A branch is any two-terminal series element lines and transformers alike (a transformer has tap != 0). from/to are 1-based bus IDS (the pio_bus_ids id space, not dense indices); map them to dense matrix rows with the pio_bus_ids ordering. Any output pointer may be NULL to skip that column; all NULL is the count query.