位运算技巧

 1 int abs( int x )
 2 {
 3     int y ;
 4     y = x >> 31 ;
 5     return y ? ( ~x + 1) : x;
 6 } 
 7 
 8 //任何数与0异或都保持不变，与-1（0xffffffff）异或都取反
 9 //优化后：
10 int abs( int x )
11 {
12     int y ;
13     y = x >> 31 ;
14     return (x^y)-y ;//or: (x+y)^y
15 }

1 void swap( int x, int y )
2 {
3     x^ = y;
4     y^ = x;
5     x^ = y;   
6 }

1 //奇数返回true，偶数返回false
2 bool isOdd( int x )
3 {
4     if( x & 1)
5         return true;
6     else
7         return false;
8 }

1 int reverseSign( int x )
2 {
3     return ~x + 1;
4 }

 1 //前16位与后16位互换
 2 int main()
 3 {
 4         unsigned int x;
 5 
 6         scanf("%d",&x);
 7         printf("%x\n",x);
 8 
 9         x = (x << 16) | (x >> 16);
10         printf("%x\n",x);
11 }

1 int findOdd(int A[], int n)
2 {
3     int rs;
4     for(int i = 0; i < n; i++){
5         rs ^= A[i];
6     }
7     return rs;
8 }