code: function bnCompareTo(a) {
    var this_array = this.array;
    var a_array = a.array;
  
    var r = this.s-a.s;
    if(r != 0) return r;
    var i = this.t;
    r = i-a.t;
    if(r != 0) return r;
    while(--i >= 0) if((r=this_array[i]-a_array[i]) != 0) return r;
    return 0;
  }
docs: (public) return + if this > a, - if this < a, 0 if equal