var value = 0
    val groupOffset = i
    while (i < limit) {
      val c = input[i]
      if (c < '0' || c > '9') break
      if (value == 0 && groupOffset != i) return false // Reject unnecessary leading '0's.
      value = value * 10 + c.code - '0'.code
      if (value > 255) return false // Value out of range.
      i++
    }
    val groupLength = i - groupOffset