From the BF3 Forum:
If you are wondering how exactly your Double XP scores get calculated this weekend, here it is.
So, imagine you have just finished a round with 2 kills and 3 deaths. Your total score on the scoreboard is an amazing 200 points and you finally start feeling like a pro. The whole round, you played as an Engineer. What you will see right after the scoreboard switches to the End of Round screen is that your Engineer symbol will flash, adding a total of 400 points to your engineer kit. This is your original 200 points multiplied by 2.
After your normal points have been doubled on the Engineer kit, it is now time for the game to count your ribbon score. You have received the Squad Rush Ribbon and the MVP 2 Ribbon. The Squad Rush Ribbon adds 200 points in itself and the MVP Ribbon adds 400 points in its original value.
You will first see these points added in their original values. They will then get doubled as “ADDITIONAL POINTS” (600 new points). Your sum total for this round would then be (200x2)+(200+400)x2=1600 points instead of the 800 you would have received on a normal weekend. Easy!
So in short, the scoring would look like this:
Original End of Round Score: 200
Engineer Score: 400 (200 original points + 200 for Double XP)
Squad Rush Ribbon: 200
MVP Ribbon: 400
Additional Score: 600 (Your ribbon score once more)
I wish my grass was Emo, then it would cut itself!