title: generate random 64 bit integer
body: <p>I need your help and please  give me some advice. From programming pearls I know that to generate random 30 bit integer we should write it like this:       </p>
  
  <pre><code>RAND_MAX*rand()+rand()
  </code></pre>
  
  <p>But what could I do for generating not 30, but 64 bit random integer instead? I think that is very inefficient method if I multiply two 30 bit integers and then multiply again 4 bit integer, so what kind of method should I use? 
  I am using now  popcount_1 different method for 64 bit one and I would like to test it on random integers(I am also measuring the time which each one takes to accomplish the task)</p>