Bitwise operation and arrow function return statement

Question

I have a byte, and I want to increment bits left to the first bit by 1 (the context is a small Conway's Game of Life).

Example: 11 is 0000 1011:

1. I want to increment 101
2. 5 + 1 = 6 is 110
3. reset the first bit to initial state
4. the byte is now 0000 1101 which is 13

Questions:

• Is there a way to make addNeighbour proceed as a void method (I couldn't find a way to not return num)?
• Is there a better way to perform addNeighbour operations :

const getBinaryRepresentation = (number) => {
    let str = "";
    for (let i = 7; i >= 0; i--) {
        ((number & (1 << i)) != 0) ? str += "1" : str += "0";
    }
    console.log(str)
}

let num = 5; 
getBinaryRepresentation(num) // 0000 0101
const addNeighbour = (num) => {
    const isAlive = num & 1;
    const neighbours = num >> 1;

    num = (neighbours + 1) << 1;
    if (isAlive === 1) num |= (1 << 0)
    return num;
}
num = addNeighbour(num);
getBinaryRepresentation(num) // 0000 0111

Answer 1

Is there a way to make addNeighbour proceed as a void method (I couldn't find a way to not return num)?

No. If you don't return the result, you cannot assign it back to num. And you cannot pass a reference to the let num (or any other) variable that the function should read from and store into.

Is there a better way to perform addNeighbour operations

Yes. Adding 1 at the second-least significant bit position is just the same as adding 2 at the least signification position. Replace your code with

num += 2;

Put in other terms,

  (((num >> 1) + 1) << 1) | (num & 1)
≡ (((num >> 1) << 1) + (1 << 1)) | (num & 1)
≡ ((num & ~1) + (1 << 1)) | (num & 1)
≡ ((num & ~1) | (num & 1)) + (1 << 1)
≡ num + (1 << 1)