How to use (n & ~ (n – 1)) In Javascript

Using & and shift operator

Take 2’s complement of the given number as all bits are reverted except the first ‘1’ from right. 2’s complement is negation (~) of the given number + 1 (i.e. ~ n + 1). Do a bit-wise & with original no, this will return number with the required rightmost set bit. Take the log₂ of the number got in step 2, you will get (position – 1), add 1 to it to get the position.

Example: The example below shows how to return the position of the rightmost set bit in JavaScript using (n & ~ (n -1)).

JavaScript

function rightBitPos(n) {
    if (n === 0) {
        return -1;
        // Return -1 for the case where n is 0
    }
    return Math.log2(n & (~(n - 1))) + 1;
}

// Driver code
let n = 20;
console.log(rightBitPos(n));

Output

Time Complexity: O(log₂n), time taken by log₂ function.

Auxiliary Space: O(1)

JavaScript Program to Find the Position of the Rightmost Set Bit

Given a number, the task is to find the position of the rightmost set bit. The indexing is from right to left, where the rightmost bit position starts from 1.

Example:

Input: n = 20
Output: 3
Explanation: Binary Representation of 20 is 10100, hence position of first set bit from right is 3.

Input:  n = 48
Output: 5
Explanation: Binary Representation of 48 is 110000, hence position of first set bit from right is 5.