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) & ((1 << n) - 1);
    unsigned int set2 = (x >> p2) & ((1 << n) - 1);
    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(28, 0, 3, 2) << endl;
    return 0;
}

 2. Add two integer

int Add(int x, int y) {
    while (y) {
        int carry = x & y;
        x = x ^ y;
        y = carry << 1;
       // 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) * 8 - 1)));
}

also can use division

4. count bit set in an integer

int countsetbits(int x) {
    int ans = 0;
    while(x) {
        x &= (x-1);
        ans++;
    }
    return ans;
}