code: func (f fnv64a) Sum64(key string) uint64 {
  	var hash uint64 = offset64
  	for i := 0; i < len(key); i++ {
  		hash ^= uint64(key[i])
  		hash *= prime64
  	}
  
  	return hash
  }
docs: // Sum64 gets the string and returns its uint64 hash value.