title: NSDate and double precision problem
body: <p>Here is the code </p>
  
  <pre><code>NSDate* d = [NSDate dateWithTimeIntervalSince1970:32.4560];
  double ti = [d timeIntervalSince1970];
  NSLog(@"Interval: %f %f %f %f",ti,32.4560,ti*1000.0,32.4560*1000.0);
  </code></pre>
  
  <p>the output is </p>
  
  <blockquote>
    <p>Interval: 32.456000 32.456000 32455.999970 32456.000000</p>
  </blockquote>
  
  <p>Why NSDate return the value which lose some precisions?</p>