Crit can either double the damage of what you rolled or roll double the dice. Most tables I played at rolled the usual dice and then doubled their values. I believe the game doubles the values of the dice.
Really? I actually think it does the opposite, I'm not sure but I think I've seen a crit 1 from a (1-1) + (2-1) instead of a (1-1)*2, you just broke me xD