linux kernel bisops.h - test_bit函数解析

static inline int
test_bit(int nr, const volatile void * addr)
{
	return (1UL & (((const int *) addr)[nr >> 5] >> (nr & 31))) != 0UL;
}

　　

参数nr  第几位

参数addr  测试数的地址可以为数组

 

#include <stdio.h>


static inline int
test_bit(int nr, const volatile void * addr)
{
    return (1UL & (((const int *) addr)[nr >> 5] >> (nr & 31))) != 0UL;
}


int main()
{
    int a[] = {1, 1, 1};

    for (int i = 0; i < sizeof(a) * 8; ++i)
    {
        printf("%d: %d\n", i, test_bit(i, a));
    }

    return 0;
}

　　输出：

0: 1
1: 0
2: 0
3: 0
4: 0
5: 0
6: 0
7: 0
8: 0
9: 0
10: 0
11: 0
12: 0
13: 0
14: 0
15: 0
16: 0
17: 0
18: 0
19: 0
20: 0
21: 0
22: 0
23: 0
24: 0
25: 0
26: 0
27: 0
28: 0
29: 0
30: 0
31: 0
32: 1
33: 0
34: 0
35: 0
36: 0
37: 0
38: 0
39: 0
40: 0
41: 0
42: 0
43: 0
44: 0
45: 0
46: 0
47: 0
48: 0
49: 0
50: 0
51: 0
52: 0
53: 0
54: 0
55: 0
56: 0
57: 0
58: 0
59: 0
60: 0
61: 0
62: 0
63: 0
64: 1
65: 0
66: 0
67: 0
68: 0
69: 0
70: 0
71: 0
72: 0
73: 0
74: 0
75: 0
76: 0
77: 0
78: 0
79: 0
80: 0
81: 0
82: 0
83: 0
84: 0
85: 0
86: 0
87: 0
88: 0
89: 0
90: 0
91: 0
92: 0
93: 0
94: 0
95: 0