code: func WriteFloat64(buf io.Writer, v float64) (n int, err error) {
  	bits := math.Float64bits(v)
  	bits = bits ^ (-(bits >> 63) | (1 << 63))
  	data := make([]byte, 8)
  	binary.BigEndian.PutUint64(data, bits)
  	return buf.Write(data)
  }
docs: // WriteFloat64 writes a memcmp-sortable float to buf. It returns the number
  // of bytes written (8, unless an error occurs), and any write error
  // encountered.