static int roundUpToPowerOfTwo(int v) {
  v--;
  v |= v >> 1;
  v |= v >> 2;
  v |= v >> 4;
  v |= v >> 8;
  v |= v >> 16;
  ret v+1;
}

static long roundUpToPowerOfTwo(long v) {
  long i = Long.highestOneBit(v);
  ret v > i ? i << 1 : i;
}