If you didn't already know, Between 2nd July and 7th July, it's a Double XP Event on BF3 for Premium members. It shows as additional points at the end of the round.
To put it in to perspective, it's not double xp. It's a percentage or something. Don't know how they work it out but I was on Ziba Tower last night. Total score for round was 5,000 somthing. Additional points was 1,200.
Now, I'm not great at mathematics but even I can see that something doesn't add up.