code: function getChangedBits({ state: prevState }, { state: nextState }) {
      let mask = 0
      for (let id in nextState) {
        if (prevState[id] !== nextState[id]) {
          mask |= NAME_BITS[id]
        }
      }
      return mask
    }
docs: calculate changed bits for StoreContext, whose value is { state, actions, register, read }