code: def _var_uint64_byte_size_no_tag(uint64):
      
      if uint64 > UINT64_MAX:
          raise errors.EncodeError('Value out of range: %d' % uint64)
      bytes = 1
      while uint64 > 0x7f:
          bytes += 1
          uint64 >>= 7
      return bytes
docs: Returns the bytes required to serialize a single varint.
      uint64 must be unsigned.