reference
http://java.sun.com/javase/6/docs/api/java/util/Random.html#nextInt(int)

do {
      bits = next(31);
      val = bits % n;
  } while (bits - val + (n-1) < 0);

big problem

bits>=0
n>0
n<=bits
therefore
0<=bits%n<bits
therefore bits-bits%n > 0
therefore bits-bits%n+n-1 > 0
therefore bits-bits+n-1<0 is always false?

So how can this loop ever iterate more than once as the documentation
says it can.