code: func EncodeUvarint(b []byte, v uint64) []byte {
  	var data [binary.MaxVarintLen64]byte
  	n := binary.PutUvarint(data[:], v)
  	return append(b, data[:n]...)
  }
docs: // EncodeUvarint appends the encoded value to slice b and returns the appended slice.
  // Note that the encoded result is not memcomparable.