# File lib/active_support/json/backends/okjson.rb, line 374
    def subst(u1, u2)
      if Usurr1 <= u1 && u1 < Usurr2 && Usurr2 <= u2 && u2 < Usurr3
        return ((u1-Usurr1)<<10) | (u2-Usurr2) + Usurrself
      end
      return Ucharerr
    end