1use std::cmp; 2 3fn bits_helper(n: u64, i: u64) -> u64 { 4 if n == 0 { i } else { bits_helper(n / 2, i + 1) } 5} 6 7/// Number of bits needed to represent a number. 8pub fn bits_needed_for(n: u64) -> u64 { 9 cmp::max(bits_helper(n - 1, 0), 1) 10}