fn main() {
let p = 0xffff_ffff_0000_0001_u64;
assert_eq!(p & 1, 1);
let old = p.checked_add(1).unwrap() / 2;
let new = p.div_ceil(2);
assert_eq!(old, 9_223_372_034_707_292_161);
assert_eq!(old, new);
println!("p={p}; old_half={old}; div_ceil_half={new}");
}