def previous(time, base)
      current = time
      until match?(current, base) && current < time
        pot_prev = align(potential_previous(current, base), base)
        pot_prev -= min_step if pot_prev == current

        current = pot_prev
      end

      current
    end
def previous(time, base)
      current = time
      until match?(current, base) && current < time
        pot_prev = align(potential_previous(current, base), base)
        pot_prev -= min_step if pot_prev == current

        current = pot_prev
      end

      current
    end
get previous date matching the rule (not checking limits). Returns next occurrence even if +time+ matches the rule.