Concatenation of Consecutive Binary Numbers

//https://leetcode.com/explore/challenge/card/january-leetcoding-challenge-2021/582/week-4-january-22nd-january-28th/3618/
class Solution {
public:
    int concatenatedBinary(int n) {
        const int mod = 1e9 + 7;
        long result = 0;
        int length = 0;
        for(int i = 1; i <= n; ++i) {
            if((i & (i-1)) == 0) {
                length++;
            }
            result = ((result << length) | i) % mod;
        }
        return result;
    }
};