BITS_TO_LONGS宏的作用

[linux-3.0]

BITS_TO_LONGS

定义在：include/linux/bitops.h

#define BITS_PER_BYTE        8

#define BITS_TO_LONGS(nr)    DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))

DIV_ROUND_UP

定义在：include/linux/kernel.h (line 58)

#define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))

其目的就是求一个数是几个long的长度。

例：sizeof(long) = 4;

则

BITS_TO_LONGS(31) = 1

BITS_TO_LONGS(32) = 1

BITS_TO_LONGS(33) = 2

The following is the test code:

[cpp] view plaincopy

1. #include <stdio.h>  
2. #define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))  
3. #define BITS_PER_BYTE           8  
4. #define BITS_TO_LONGS(nr)       DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))  
5.   
6. main()  
7. {  
8.         int j = 32;   
9.         printf("The size of long is %ld\n", sizeof(long));  
10.         printf("The convertion result is %ld\n", BITS_TO_LONGS(j));  
11. }