code: func sum64(hash [md5.Size]byte) uint64 {
  	var s uint64
  
  	for i, b := range hash {
  		shift := uint64((md5.Size - i - 1) * 8)
  
  		s |= uint64(b) << shift
  	}
  	return s
  }
docs: // sum64 sums the md5 hash to an uint64.