请教一下TCP/IP协议报头中是怎样计算校验和的？请详细指教！

caicheng

如果不麻烦请配以c代码！

lzlz

RFC

IPv4 CRC-sum:

unsigned short int check_sum(unsigned char* addr, size_t count)
{
    unsigned short checksum = 0;
    /* Compute Internet Checksum for "count" bytes
     *         beginning at location "addr".
     */
    register long sum = 0;
    while( count > 1 )  {
        /*  This is the inner loop */
        sum += * (unsigned short*) addr++;
        count -= 2;
    }
    /*  Add left-over byte, if any */
    if( count > 0 )
        sum += * (unsigned char *) addr;
    /*  Fold 32-bit sum to 16 bits */
    while (sum>>16)
        sum = (sum & 0xffff) + (sum >> 16);

    checksum = ~sum;

    return checksum;
}

caicheng

谢谢!~~