code: function divInt_(x, n) {
    var i, r=0, s;
    for (i=x.length-1; i>=0; i--) {
      s=r*radix+x[i];
      x[i]=Math.floor(s/n);
      r=s%n;
    }
    return r;
  }
docs: do x=floor(x/n) for bigInt x and integer n, and return the remainder