/* Returns the offset within |array[]| of an element equal to |key|,
   or |-1| if |key| is not in |array[]|.
   |array[]| must be an array of |n| |int|s sorted in ascending order. */
int
binary_search (int array[], int n, int key)
{
  int min = 0;
  int max = n - 1;

  while (max >= min)
    {
      int i = (min + max) / 2;
      if (key < array[i])
        max = i - 1;
      else if (key > array[i])
        min = i + 1;
      else
        return i;
    }

  return -1;
}