Linux内核中的BITS_TO_LONGS宏的作用

Linux内核中的BITS_TO_LONGS宏的作用

下面BITS_TO_LONGS这个宏定义经常出现在内核中。

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:

#include <stdio.h>  
#define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))  
#define BITS_PER_BYTE           8  
#define BITS_TO_LONGS(nr)       DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))  
  
main()  
{  
        int j = 34;   
        printf("The size of long is %ld\n", sizeof(long));  
        printf("The convertion result is %ld\n", BITS_TO_LONGS(j));  
}