isPowerOfTwoBitwise.js

/**
 * @param {number} number
 * @return {boolean}
 */
export default function isPowerOfTwoBitwise(number) {
  // Don't work with negative numbers.
  if (number < 0) {
    throw new Error('Please provide positive number');
  }

  // 0 and 1 are not powers of two.
  if (number <= 1) {
    return false;
  }

  /*
   * Powers of two in binary look like this:
   * 1: 0001
   * 2: 0010
   * 4: 0100
   * 8: 1000
   *
   * Note that there is always exactly 1 bit set. The only exception is with a signed integer.
   * e.g. An 8-bit signed integer with a value of -128 looks like:
   * 10000000
   *
   * So after checking that the number is greater than zero, we can use a clever little bit
   * hack to test that one and only one bit is set.
   */
  return (number & (number - 1)) === 0;
}