Linux的位图

原创

QtHalcon 2022-06-09 16:37:35 博主文章分类：Linux内核 ©著作权

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可以参考：

重要宏定义：

#define DYNAMIC_MINORS 64 /* like dynamic majors */

#define DECLARE_BITMAP(name,bits) \
  unsigned long name[BITS_TO_LONGS(bits)]
#define BITS_PER_LONG __WORDSIZE
#define BITS_PER_BYTE           8
#define BITS_TO_LONGS(nr)       DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))
#define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))

首先注册一个位图数组：

static DECLARE_BITMAP(misc_minors, DYNAMIC_MINORS);

int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS); //查找第一个为零的bit位

函数：查找第一个为零的bit位

unsigned long find_first_zero_bit(const unsigned long *addr, unsigned long size)
{
  const unsigned long *p = addr;
  unsigned long result = 0;
  unsigned long tmp;

  while (size & ~(BITS_PER_LONG-1)) {
    if (~(tmp = *(p++)))
      goto found;
    result += BITS_PER_LONG;
    size -= BITS_PER_LONG;
  }
  if (!size)
    return result;

  tmp = (*p) | (~0UL << size);
  if (tmp == ~0UL)  /* Are any bits zero? */
    return result + size; /* Nope. */
found:
  return result + ffz(tmp);
}

函数：查找第一个不为零的bit位

unsigned long find_first_bit(const unsigned long *addr, unsigned long size)
{
  const unsigned long *p = addr;
  unsigned long result = 0;
  unsigned long tmp;

  while (size & ~(BITS_PER_LONG-1)) {
    if ((tmp = *(p++)))
      goto found;
    result += BITS_PER_LONG;
    size -= BITS_PER_LONG;
  }
  if (!size)
    return result;

  tmp = (*p) & (~0UL >> (BITS_PER_LONG - size));
  if (tmp == 0UL)   /* Are any bits set? */
    return result + size; /* Nope. */
found:
  return result + __ffs(tmp);
}

函数：设置bit位

static inline void set_bit(int nr, unsigned long *addr)
{
  addr[nr / BITS_PER_LONG] |= 1UL << (nr % BITS_PER_LONG);
}

测试代码：

#include <stdio.h>
#define DYNAMIC_MINORS 64 /* like dynamic majors */

#define DECLARE_BITMAP(name,bits) \
  unsigned long name[BITS_TO_LONGS(bits)]
#define BITS_PER_LONG __WORDSIZE
#define BITS_PER_BYTE           8
#define BITS_TO_LONGS(nr)       DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))
#define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))

static DECLARE_BITMAP(misc_minors, DYNAMIC_MINORS);
int
main(void)
{
  
  printf("数组个数 = %d\n", sizeof(misc_minors) / sizeof(unsigned long));
  printf("long size = %d\n", sizeof(long));
  printf("size = %d\n", DIV_ROUND_UP(64,32));
  printf("size = %d\n", BITS_TO_LONGS(64)); 
}