We can replace the function foo below by an equivalent one-line C function. Which one?  

uint32_t foo(uint32_t a, uint32_t b) { 

    uint32_t r=0; 

    for (int i=0; i<32; i++) { 

        r = r | ((((a >> i) & 1) != ((b >> i) & 1)) << i); 

    } 

    return r; 

}