Algorithm: bit manipulation

1. 一个数的从右起第p1位和第p2位swap n位

 1 unsigned int swapBits(unsigned int x, unsigned int p1, unsigned int p2, unsigned int n) {

 2     unsigned int set1 = (x >> p1) & ((1 << n) - 1);

 3     unsigned int set2 = (x >> p2) & ((1 << n) - 1);

 4     unsigned int xored = set1 ^ set2; //same is 0, different is 1

 5     xored = (xored << p1) | (xored << p2);

 6     return x ^ xored;  //anybit ^ 0 = anybit, anybit ^ 1 = !anybit, so same no need to change, different need to be changed

 7 }

 8 

 9 int main()

10 {

11     cout << swapBits(28, 0, 3, 2) << endl;

12     return 0;

13 }

 2. Add two integer

1 int Add(int x, int y) {

2     while (y) {

3         int carry = x & y;

4         x = x ^ y;

5         y = carry << 1;

6        // cout << carry << " " << x << " " << y << endl;

7     }

8     return x;

9 }

3. min函数

1 int minnum(int x, int y) {

2     return y + ((x - y) & ((x - y) >> (sizeof(int) * 8 - 1)));

3 }

also can use division

4. count bit set in an integer

1 int countsetbits(int x) {

2     int ans = 0;

3     while(x) {

4         x &= (x-1);

5         ans++;

6     }

7     return ans;

8 }