Question

Found the function on “Computer Systems”:

int fun_a(unsigned x){
    int val = 0;
    while(x){
        val ^= x;
        x >>= 1;
    }
    return val & 0x1;
}

it return 1 if x contains odd “1”, return 0 if x contains even “1”.
I know “val & 0x1” check val is odd or even, but I don’t know how it count the bits number on val.

Answer 1

It doesn’t exactly count the bits, but the XOR will flip the low bit in val once for each bit in x. That will make it a 1 if it is flipped an odd number of times.

It also flips a lot of other bits in val, but that is irrelevant as they are masked off in the return statement.