This should add up to the total number of values summed in a given context.
In a hadoop job for example this should not be an issue.
Possibly in the context of a forever running storm job there should be a way to reset the stats every fixed period of time?
I can add a reset method to enable this.
It would still take a very long time to overflow. 
If I make v a Long and total a double it would become practically impossible to overflow.