function msb32(x) {
  x |= (x >> 1);
  x |= (x >> 2);
  x |= (x >> 4);
  x |= (x >> 8);
  x |= (x >> 16);

  return (x & ~(x >> 1));
}
Takes a 32 bits integer and returns its MSB using SWAR strategy.

@param  {number} x - Target number.
@return {number}