@YongGopher If you want a unique identifier that can fit within a 64-bit integer, you can’t use UUIDs. The problem is that a UUID is too large to fit within an integer no matter what kind of manipulation you do. It’d be the same as trying to fit two liters of water in to a one liter bottle, it’s not physically possible.
If you want a unique ID, you could try generating random uint64 numbers and using those. That would grant you, at most, 18,446,744,073,709,551,615 unique values. Whereas the 128-bit random value has approximately 340,282,366,920,938,463,463,374,607,431,768,211,455 values. The chances of a collision are dramatically less.