Function sys_bigint 

pub unsafe extern "C" fn sys_bigint(
    result: *mut [u32; 8],
    op: u32,
    x: *const [u32; 8],
    y: *const [u32; 8],
    modulus: *const [u32; 8],
)

Safety

result, x, y, and modulus must be aligned and dereferenceable.