code: func RegisterHash(h Hash, f func() hash.Hash) {
  	if h >= maxHash {
  		panic("crypto: RegisterHash of unknown hash function")
  	}
  	hashes[h] = f
  }
docs: // RegisterHash registers a function that returns a new instance of the given
  // hash function. This is intended to be called from the init function in
  // packages that implement hash functions.