[ixp1200] Ip checksum?

[Øyvind Hvamstad]

Not sure if the attachment was sucessfully applied. Here the test case
is inline:

#include <stdio.h>

unsigned short checksum(unsigned short *addr, unsigned int count) 
{
        unsigned long sum = 0;
        while( count > 1 )  {
                sum += *(unsigned short *)addr++;
                count -= 2;
        }
        
        if( count > 0 )
                sum += *(unsigned char *)addr;
        
        while (sum>>16)
                sum = (sum & 0xffff) + (sum >> 16);
        
        return ~sum;
}

unsigned short incr(unsigned short oldsum,
                    unsigned short *old,
                    unsigned short new)
{
        unsigned short sum;
        sum = ~(~oldsum + ~(*old) + new);
        *old = new;
        return sum;
}

int main()
{
        unsigned short hdr[4], csum, oldsum, sum;
        unsigned long dst_ip = 0xc3a91201, src_ip = 0xc3a91203;

        hdr[0] = 0xc0a8;
        hdr[1] = 0x4301;
        hdr[2] = 0xc0a8;
        hdr[3] = 0x4303;        

        oldsum = checksum((unsigned short *)&hdr, sizeof(hdr));

        sum = incr(oldsum, &hdr[0], (dst_ip >> 16));

        printf("Incremental checksum:\t\t%hx\n", sum);
        printf("Header checksum after change:\t%hx\n",
               (csum = checksum((unsigned short *)&hdr, sizeof(hdr))));
        printf("Difference (incr - calc):\t%d\n", sum - csum);

        oldsum = sum;
        sum = incr(oldsum, &hdr[1], (unsigned short)dst_ip);

        printf("Incremental checksum:\t\t%hx\n", sum);
        printf("Header checksum after change:\t%hx\n",
               (csum = checksum((unsigned short *)&hdr, sizeof(hdr))));
        printf("Difference (incr - calc):\t%d\n", sum - csum);

        oldsum = sum;
        sum = incr(oldsum, &hdr[2], (unsigned short)(src_ip >> 16));

        printf("Incremental checksum:\t\t%hx\n", sum);
        printf("Header checksum after change:\t%hx\n",
               (csum = checksum((unsigned short *)&hdr, sizeof(hdr))));
        printf("Difference (incr - calc):\t%d\n", sum - csum);

        oldsum = sum;
        sum = incr(oldsum, &hdr[3], (unsigned short)src_ip);

        printf("Incremental checksum:\t\t%hx\n", sum);
        printf("Header checksum after change:\t%hx\n",
               (csum = checksum((unsigned short *)&hdr, sizeof(hdr))));
        printf("Difference (incr - calc):\t%d\n", sum - csum);

        return 0;
}
-- 
Øyvind Hvamstad <oyvindh at ifi.uio.no>