Can someone explain to me how this function works? I understand the drop the lowest set of a bit of x part which is the 5th line but I don't understand the assignment result ^= 1; Shouldn't result be counting 0 and 1 when deciding parity of a word?
short Parity_of_word(unsigned long long x) {
short result = 0;
while(x) {
result ^= 1;
x &= (x-1);
}
return result;
}
result ^= 1;
changes result between 0 and 1, repeatedly. So, the question is: How many time will this be done?
x&=(x-1);
is a hacky way to do "remove the last bit from x". To see it, imagine x is
0101000110
removing one will make it:
0101000101
(all the 0 in the end became 1, and the first 1 became 0). Once you and both values together:
0101000100
Tada, one less 1. So, the while loop will execute just as many times as there are 1s in x. And it will flip result accordingly.