checksum-8位和16位校验和代码示例

// linux 系统编译通过// gcc filename.c -o filename// ./filename#include <stdlib.h>#include <stdio.h>unsigned char ip_hdr_8[] = {    0x45,0x00,    0x00,0x3c,    0x00,0x00,    0x00,0x00,    0x40,0x01,    0x00,0x00,  // checksum    0xc0,0xa8,    0x01,0x25,    0xda,0x3c,    0x06,0x82};unsigned short ip_hdr_16[] = {    0x4500,    0x003c,    0x0000,    0x0000,    0x4001,    0x0000,     // checksum    0xc0a8,    0x0125,    0xda3c,    0x0682};unsigned int checksum_8(unsigned int cksum, void *pBuffer, unsigned int size){    char num = 0;    unsigned char *p = (unsigned char *)pBuffer;    if ((NULL == pBuffer) || (0 == size))    {        return cksum;    }    while (size > 1)    {        cksum += ((unsigned short)p[num] << 8 & 0xff00) | (unsigned short)p[num + 1] & 0x00FF;        size  -= 2;        num   += 2;    }    if (size > 0)    {        cksum += ((unsigned short)p[num] << 8) & 0xFFFF;        num += 1;    }    while (cksum >> 16)    {        cksum = (cksum & 0xFFFF) + (cksum >> 16);    }    return ~cksum;}unsigned short checksum_16(unsigned short *addr,int len){    unsigned short chksum;    unsigned int sum = 0;    while(len > 1)    {        sum += *addr++;        len -= 2;    }    if(len == 1)        sum += *(unsigned char*)addr;    sum = (sum>>16) + (sum & 0xffff);    sum += (sum>>16);    chksum = ~sum;    return (chksum);}void main(){    unsigned short chksum;    printf("--------------------------------------------\n");    chksum = checksum_8(0,ip_hdr_8,sizeof(ip_hdr_8));    printf("checksum_8 = 0x%04x \n",chksum);    ip_hdr_8[10] = chksum >> 8;    ip_hdr_8[11] = chksum & 0xff;    chksum = checksum_8(0,ip_hdr_8,20);    if(chksum)        printf("Checksum_8 is incorrect! \n");    else        printf("Checksum_8 is correct! \n");    printf("--------------------------------------------\n");    chksum = checksum_16(ip_hdr_16,sizeof(ip_hdr_16));    printf("checksum_16 = 0x%04x \n",chksum);    ip_hdr_16[5] = chksum;    chksum = checksum_16(ip_hdr_16,20);    if(chksum)        printf("Checksum 16 is incorrect! \n");    else        printf("Checksum 16 is correct! \n");    printf("--------------------------------------------\n");}