利于&操作求模

 const unsigned int n; // 要求模的值 const unsigned int s; const unsigned int d = 1U << s; // So d will be one of: 1, 2, 4, 8, 16, 32, ... unsigned int m; // m will be n % d m = n & (d - 1);

 

例如：

      n =  15;

      d =  4;

      n%4 = n & ((1U << 2) -1) = 3;