docs: function hrtimeDiff(a, b)
  {
  	assertHrtime(a);
  	assertHrtime(b);
  	mod_assert.ok(a[0] > b[0] || (a[0] == b[0] && a[1] >= b[1]),
  	    'negative differences not allowed');
  
  	var rv = [ a[0] - b[0], 0 ];
  
  	if (a[1] >= b[1]) {
  		rv[1] = a[1] - b[1];
  	} else {
  		rv[0]--;
  		rv[1] = 1e9 - (b[1] - a[1]);
  	}
  
  	return (rv);
  }