-ffast-math is actually something like 15 separate flags, and you can use them individually if you want. 3 of them are "no NaNs," "no infinities," and "no subno

-ffast-math is actually something like 15 separate flags, and you can use them individually if you want. 3 of them are "no NaNs," "no infinities," and "no subnormals." Several of the other flags allow you to treat math as associative or distributive if you want that. The library has some merit, but the goal you've stated here is given to you with 5 compiler flags. The benefit of the library is choosing when these apply.