chd_builder.go
func (h *chdHasher) HashIndexFromKey(b []byte) uint64 {
	return (hasher(b) ^ h.r[0]) % h.buckets
}
func (h *chdHasher) HashIndexFromKey(b []byte) uint64 {
	return (hasher(b) ^ h.r[0]) % h.buckets
}
// Hash index from key.