int a = 12;

int set_bit = n ^ (n&(n-1));

int pos = n ^ (n&(n-1));

x & -x
// or
x & (~x + 1)

x &= x - 1
// or
x -= x & -x  // rhs is rightmost set bit

x:                     leading bits  1  all 0
~x:           reversed leading bits  0  all 1
~x + 1 or -x: reversed leading bits  1  all 0
x & -x:                       all 0  1  all 0

// example for get rightmost set bit
x:             01110000
~x:            10001111
-x or ~x + 1:  10010000
x & -x:        00010000

// example for unset rightmost set bit
x:             01110000
x-1:           01101111
x & (x-1):     01100000

#include <limits.h>

int last_set_pos(int a) {
  for (int i = 0; i < sizeof a * CHAR_BIT; ++i) {
    if (a & (0x1 << i)) return i;
  }
  return -1; // a == 0
}

int rightMostSet(int a){
      if (!a) return -1;  //means there isn't any 1-bit
      int i=0;
      while(a&1==0){
        i++;
        a>>1;
      }
      return i;
    }