code: func fastHash(a int64, bs ...int64) int64 {
  	buf := make([]byte, 8)
  	hasher := fnv.New64a()
  	w := func(v int64) {
  		binary.LittleEndian.PutUint64(buf, uint64(v))
  		if _, err := hasher.Write(buf); err != nil {
  			panic(err)
  		}
  	}
  	w(a)
  	for _, b := range bs {
  		w(b)
  	}
  	return int64(hasher.Sum64())
  }
docs: // fastHash is a non-cryptographic NxN -> N hash function. It's used to
  // deterministically blend seeds for subjobs.