Efficient random function when I want only 0 or 1

I know you can use rand() % 2 to get a random choice of 0 and 1 in C, but is there something more efficient?

My question is not so much about C specifically but about how random number generators work. If I understand correctly, they do some complicated math on the seed to get an even distribution between 0 and RAND_MAX, but is there a way to do less math if you just need a binary choice?

Thanks