摘自《编程珠玑》一书第1章习题：

1:  #define BITSPERWORD 32

2:  #define SHIFT 5

3:  #define MASK 0x1F

4:  #define N 10000000

5:  int a[1 + N/BITSPERWORD];

6:   

7:  void set(int i){

8:      a[i >> SHIFT] |= (1 << (i & MASK));

9:  }

10:   

11:  void clr(int i){

12:      a[i >> SHIFT] &= ~(1 << (i & MASK));

13:  }

14:   

15:  int test(int i){

16:      return     a[i >> SHIFT] & (1 << (i & MASK));

17:  }

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