about enumeration's range
the range of an enumeration holds all the enumeration's enumerator values rounded up to the nearest larger binary power minus 1.the range goes down to 0 if the smallest enumerator is non-negative and to the nearest lesser negative binary power if the smallest enumerator is negative.
以上是Bjarne Stroustrup的The C++ Programming Language第77页关于枚举变量范围的阐述,我不怎么理解这个什么"binary power"?