Linux的位图

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可以参考：

https://www.cnblogs.com/zpcdbky/p/5825849.html

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));	
}

运行结果：

数组个数 = 2
long size = 4
size = 2
size = 2