Function lc_knearest_d2 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn lc_knearest_d2(
    xyz: *const f64,
    n: usize,
    simbox: *const lc_cell,
    k: usize,
    mask: *const c_int,
    cell_hint: f64,
    out_nn: *mut c_int,
    out_d2: *mut f64,
) -> c_int

Like lc_knearest, and write squared distances into out_d2.

out_d2 is caller-owned, length n * k. Unused slots are NaN. out_d2 may be NULL to skip distances (same as lc_knearest).

Safety

Same pointer contract as lc_knearest. out_d2, if non-null, is aligned for double and writable for n * k doubles.