Removed calls to fminf and fmaxf in the critical sections of the code.

Is there any reason not to do this ? I have replaced calls to `fminf` and `fmaxf` by ternary operators. That leads to massive speed-ups. 

According to vTune, we were spending large amounts of time inside these functions. 

Is there any reason to use them over what I have done ? Any special behaviour of the functions that we would need in some cases ?

See merge request !219