static int intArrayBinarySearchWithComparator(int[] a, IntComparator comparator, int key) {
  ret intArrayBinarySearchWithComparator(a, 0, a.length, comparator, key);
}

static int intArrayBinarySearchWithComparator(int[] a, int fromIndex, int toIndex, IntComparator comparator, int key) {
  int low = fromIndex;
  int high = toIndex - 1;

  while (low <= high) {
    int mid = (low + high) >>> 1;
    int midVal = a[mid];

    int cmp = comparator.compare(midVal, key);
    if (cmp < 0)
        low = mid + 1;
    else if (cmp > 0)
        high = mid - 1;
    else
        ret mid; // key found
  }
  ret -(low + 1);  // key not found.
}