IPv4掩碼與掩碼位數的轉換

1. 根據掩碼獲取掩碼的位數

int mask2len(unsigned int mask)
{
    /*eg: 255.255.255.0   255.0.255.255.0*/
    int bit=0,len=0;

    while( ~mask & (1ULL<<bit))
        bit++;
    len = 32 - bit;

    if(~mask >> bit){
        printf("mask is not standerd, get mask length error\n");
        return -1;
    }
    printf("mask:%8.8x    len=%d\n", mask, len);
    return len;
}

2. 根據掩碼位數獲取驗碼

int len2mask(int len, unsigned int *mask)
{
    unsigned int maskwild = 0;

    if(len<0 || len>32)
        return -1;

    int hostbits=32-len;
    while(hostbits--){
        maskwild=(maskwild << 1) + 1;
    }
    maskwild=~maskwild;
    if(mask){
        *mask = maskwild;
    }
    printf("mask len is %d, and mask is %8.8x\n", len, maskwild);
  
#if 0
    struct in_addr ip;
    ip.s_addr=htonl(maskwild);
    printf("mask len is %d, and mask is %s\n", len, inet_ntoa(ip));
#endif
    return 0;
}

3. 測試結果

void main(int argc, char *argv[])
{
	len2mask(9, NULL);
	len2mask(15, NULL);
	len2mask(24, NULL);
	len2mask(28, NULL);
	len2mask(30, NULL);
	len2mask(32, NULL);
	len2mask(34, NULL);

	mask2len(0x80000000);
	mask2len(0xffff0000);
	mask2len(0xfffff000);
	mask2len(0xffffff00);
	mask2len(0xfffffff0);
	mask2len(0xfffffffc);
	
	mask2len(0x12345678);
}

編譯後運行，結果如下：

root@ubantu:/mnt/hgfs/em嵌入式學習記錄/schedule調度器# ./demo.out 
mask len is 9, and mask is ff800000
mask len is 15, and mask is fffe0000
mask len is 24, and mask is ffffff00
mask len is 28, and mask is fffffff0
mask len is 30, and mask is fffffffc
mask len is 32, and mask is ffffffff
mask:80000000    len=1
mask:ffff0000    len=16
mask:fffff000    len=20
mask:ffffff00    len=24
mask:fffffff0    len=28
mask:fffffffc    len=30
mask is not standerd, get mask length error
root@ubantu:/mnt/hgfs/em嵌入式學習記錄/schedule調度器#