def bytearray_to_long(byte_array):
  """
  Converts a byte array to long.

  :param byte_array:
      The byte array.
  :returns:
      Long.
  """
  total = 0
  multiplier = 1
  for count in range(len(byte_array) - 1, -1, -1):
    byte_val = byte_array[count]
    total += multiplier * byte_val
    multiplier *= 256
  return total