Doesn’t matter who did the calculations, Extrafire, your assumptions are questionable, to say the least.
You are assuming that Muslim birthrate will continue same as before, without any basis for it. As to Muslims assimilating, some do and some don’t. And what evidence do you have to claim that those who don’t assimilate have the same birthrate as first generation immigrants?
Besides, how do you know that European birthrate will stay at the level that is it now? We are talking of several decades into future, and any assumption you make is going to be questionable.
I think this is the hobby horse of the far right, they like to scare people about stories of Islam, they like to demonize Muslims. While no doubt some Muslims do meet that stereotype, many don’t.
The Muslims we know (admittedly doctors, scientists and other intellectuals) have two or three children at most, their birthrate isn’t really any different from that of White Canadians. Second and third generation usually has a lower birthrate than first generation. Even if they don’t assimilate, there is no evidence to suggest that non assimilation keeps their birthrate high.