Truncation of nasm function returning value

Question

I'm using a nasm sse function returning a float value in a C program. If I put this value directly in a if condition everything works perfectly but if I save it in a float variable it gets cut to an integer and then converted to a float. For example:

if(dist_cent(T,nearest_q-1,T,q,d) > k){
                        ...
}//if   

dist_cent is my nasm function and this way I get 245.73465 as its value . If I write it like this:

float f = dist_cent(T,nearest_q-1,T,q,d);
if(f > k){
                        ...
}//if   

I get 245.000000 as f value. The returning value of the nasm function is stored at the top of the x87 stack. Is there an explanation and a way to avoid this?