#include <stdio.h>
#include <stdlib.h>
//IP路由查找的“最长匹配原则”
//目的IP:192.168.25.13
/* 路由表：
    8.35.15.0/24
    137.45.2.0/24
    192.168.0.0/16
    192.168.25.0/24
 匹配结果应该为：192.168.25.0/24
*/
typedef struct {
    int ip[4];
    int mask;
} IpRouter;

unsigned int arrayIpToUint(int iparray[])
{
    unsigned int res = 0;
    res = (iparray[0] << 24) + (iparray[1] << 16) +(iparray[2] << 8) + iparray[3];
    return res;
}
int matchIpROuter(char* ip, char* router)
{
    int ipArray[4] = {0};
    IpRouter ipr = {0};
    sscanf(ip, "%d.%d.%d.%d", ipArray, ipArray+1, ipArray+2, ipArray+3);
    sscanf(router, "%d.%d.%d.%d/%d", &(ipr.ip[0]), &(ipr.ip[1]),
     &(ipr.ip[2]), &(ipr.ip[3]), &(ipr.mask));  
    
    unsigned int src = arrayIpToUint(ipArray);
    unsigned int dst = arrayIpToUint(ipr.ip);
    unsigned int bit = 0xFFFFFF00;
    int mask = -1;
    unsigned int offset = 32 - ipr.mask;
    if ((src >> offset) == (dst >> offset)) {
        mask = ipr.mask;
    }

    return mask;
}

int main() {
    char ip[] = "192.168.25.13";
    char router[] = "192.168.25.0/24";
    int mask = matchIpROuter(ip, router);
    return mask;
}