def getKey(k)
      return nil if k > @nitems || k <= 0
      pos = SIZEOF_BLOCK_HEADER + (SIZEOF_KEY * (k - 1))
      keydata = @data[pos, SIZEOF_KEY]
      data2key(keydata)
    end
def getKey(k)
      return nil if k > @nitems || k <= 0
      pos = SIZEOF_BLOCK_HEADER + (SIZEOF_KEY * (k - 1))
      keydata = @data[pos, SIZEOF_KEY]
      data2key(keydata)
    end
Keys are 1-based