code: func (b *Filter) Touch(d []byte) bool {
  	n := len(b.items)
  	h := hash(b.key0, b.key1, d)
  	i := h % uint64(n)
  	return b.touch(&b.items[i])
  }
docs: // Touch finds the token bucket for d, takes a token out of it and reports if
  // there are still tokens left in the bucket.