code: public long readRawVarint64() throws IOException
      {
          int shift = 0;
          long result = 0;
          while (shift < 64)
          {
              final byte b = readRawByte();
              result |= (long) (b & 0x7F) << shift;
              if ((b & 0x80) == 0)
              {
                  return result;
              }
              shift += 7;
          }
          throw ProtobufException.malformedVarint();
      }
docs: Read a raw Varint from the stream.