date and time created 83/05/30 18:37:27 by sam

[unix-history] / usr / src / sys / deprecated / netpup / pup_cksum.c

/*      pup_cksum.c     4.1     83/05/30        */

#include "../h/types.h"
#include "../h/mbuf.h"

/*
* Checksum routine for PUP-I Protocol family (VAX Version).
*/
pup_cksum(m, len)
       register struct mbuf *m;
       register int len;
{
       register u_short *w;
       register int sum = 0;                   /* known to be r8 */
       register int mlen = 0;

       for (;;) {
               /*
                * Each trip around loop adds in
                * words from one mbuf segment.
                */
               w = mtod(m, u_short *);
               if (mlen == -1) {
                       /*
                        * There is a byte left from the last segment;
                        * add it into the checksum. 
                        */
                       sum += *(u_char *)w << 8;
                       asm("rotl $1,r8,r8");
                       w = (u_short *)((char *)w + 1);
                       mlen = m->m_len - 1;
                       len--;
               } else
                       mlen = m->m_len;
               m = m->m_next;
               if (len < mlen)
                       mlen = len;
               len -= mlen;
               while ((mlen -= 2) >= 0) {
                       asm("addw2 (r9)+,r8; rotl $1,r8,r8;");
               }
               if (mlen == -1)
                       sum += *(u_char *)w;
               if (len == 0)
                       break;
               /*
                * Locate the next block with some data.
                * If there is a word split across a boundary we
                * will wrap to the top with mlen == -1 and
                * then add it in shifted appropriately.
                */
               for (;;) {
                       if (m == 0) {
                               printf("pup_cksum: out of data\n");
                               goto done;
                       }
                       if (m->m_len)
                               break;
                       m = m->m_next;
               }
       }
done:
       return (sum);
}