Subversion Repositories 1g_ethernet_dpi

/*

 *

 * Portable C implementation of the Internet checksum, derived

 * from Braden, Borman, and Partridge's example implementation

 * in RFC 1071.

 *

 */

unsigned short cksum(void * ptr, int count)

{

    unsigned short checksum;

    unsigned short *addr = (unsigned short *)ptr;

    /********** code from rfc1071 **********/

    {

        /* Compute Internet Checksum for "count" bytes

        *         beginning at location "addr".

        */

        long sum = 0;

        while( count > 1 )

        {

            /*  This is the inner loop */

            sum += *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;

   }

    /******** end of RFC 1071 code **********/

    return checksum;

}