Find nth SET bit in an int

Question

Instead of just the lowest set bit, I want to find the position of the nth lowest set bit. (I\'m NOT talking about value on the nt

Answer 1

v-1 has a zero where v has its least significant "one" bit, while all more significant bits are the same. This leads to the following function:

int ffsn(unsigned int v, int n) {
   for (int i=0; i