ones.js

// calculate the number of "ones" on tan integer

function calculate(num) {
    let count = 0;
    do {
        count += num & 1;
        num = num >> 1;
    } while (num);

    return count;
}

function test(num) {
    console.log(`${num} has ${calculate(num)} ones.`)
}

test(0);
test(1);
test(2);
test(3);
test(8);
test(0xf);
test(0xff);