Algorithm: bit manipulation

1. 一个数的从右起第p1位和第p2位swap n位

 unsigned int swapBits(unsigned int x, unsigned int p1, unsigned int p2, unsigned int n) {
     unsigned int set1 = (x >> p1) & (( << n) - );
     unsigned int set2 = (x >> p2) & (( << n) - );
     unsigned int xored = set1 ^ set2; //same is 0, different is 1
     xored = (xored << p1) | (xored << p2);
     return x ^ xored;  //anybit ^ 0 = anybit, anybit ^ 1 = !anybit, so same no need to change, different need to be changed
 }
 
 int main()
 {
     cout << swapBits(, , , ) << endl;
     return ;
 }

2. Add two integer

 int Add(int x, int y) {
     while (y) {
         int carry = x & y;
         x = x ^ y;
         y = carry << ;
        // cout << carry << " " << x << " " << y << endl;
     }
     return x;
 }

3. min函数

 int minnum(int x, int y) {
     return y + ((x - y) & ((x - y) >> (sizeof(int) *  - )));
 }

also can use division

4. count bit set in an integer

 int countsetbits(int x) {
     int ans = ;
     while(x) {
         x &= (x-);
         ans++;
     }
     return ans;
 }