var result = prefixMask
        var shift = 0
        while (true) {
          val b = readByte()
          if (b and 0x80 != 0) { // Equivalent to (b >= 128) since b is in [0..255].
            result += b and 0x7f shl shift
            shift += 7
          } else {
            result += b shl shift // Last byte.
            break
          }
        }
        return result