# File lib/vendor/okjson.rb, line 335
  def unsubst(u)
    if u < Usurrself || u > Umax || surrogate?(u)
      return Ucharerr, Ucharerr
    end
    u -= Usurrself
    [Usurr1 + ((u>>10)&0x3ff), Usurr2 + (u&0x3ff)]
  end