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;

BITS_TO_LONGS(31) = 1

BITS_TO_LONGS(32) = 1

BITS_TO_LONGS(33) = 2


The following is the test code:

[cpp] view plain copy
  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));  

你可能感兴趣的:(BITS_TO_LONGS宏的作用)