BSD 4_3_Tahoe release

[unix-history] / usr / src / sys / vax / ns_cksum.c

/*
* Copyright (c) 1985, 1986 Regents of the University of California.
* All rights reserved.
*
* Redistribution and use in source and binary forms are permitted
* provided that the above copyright notice and this paragraph are
* duplicated in all such forms and that any documentation,
* advertising materials, and other materials related to such
* distribution and use acknowledge that the software was developed
* by the University of California, Berkeley.  The name of the
* University may not be used to endorse or promote products derived
* from this software without specific prior written permission.
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*
*      @(#)ns_cksum.c  7.3 (Berkeley) 6/29/88
*/

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


/*
* Checksum routine for Network Systems Protocol Packets (VAX Version).
*
* This routine is very heavily used in the network
* code and should be modified for each CPU to be as fast as possible.
*/

u_short
ns_cksum(m, len)
       register struct mbuf *m;
       register int len;
{
       register u_short *w;            /* on vax, known to be r9 */
       register int sum = 0;           /* on vax, known to be r8 */
       register int low = 0;           /* on vax, known to be r7 */
       register int mlen = low;        /* want 0, shuts lint up about low */

       for (;;) {
               /*
                * Each trip around loop adds in
                * word 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.  Don't have to worry
                        * about a carry-out here because we make sure
                        * that high part of (32 bit) sum is small below.
                        */
                       sum += *(u_char *)w << 8;
                       sum += sum;
                       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;
               /*
                * Force to long boundary so we do longword aligned
                * memory operations.  It is too hard to do byte
                * adjustment, do only word adjustment.
                */
               if (((int)w&0x2) && mlen >= 2) {
                       sum += *w++;
                       sum += sum;
                       mlen -= 2;
               }
               /*
                *
                * We can do a 16 bit ones complement sum using
                * 32 bit arithmetic registers for adding,
                * with carries from the low added
                * into the high (by normal carry-chaining)
                * so long as we fold back before 16 carries have occured.
                *
                */
               while ((mlen -= 32) >= 0) {
                       /*asm("bicpsw $1");              clears carry */
#undef ADD
#define ADD asm("movw (r9)+,r7")asm("addl2 r7,r8")asm("addl2 r8,r8")
#define FOLD { asm("ashl $-16,r8,r0")asm(" addw2 r0,r8"); \
                 asm("adwc $0,r8")asm(" movzwl r8,r8"); }
                       FOLD;
                       ADD; ADD; ADD; ADD; ADD; ADD; ADD; ADD;
                       FOLD;
                       ADD; ADD; ADD; ADD; ADD; ADD; ADD; ADD;
               }
               mlen += 32;
               while ((mlen -= 8) >= 0) {
                       /*asm("bicpsw $1");              clears carry */
                       FOLD;
                       ADD; ADD; ADD; ADD;
               }
               mlen += 8;
               /*
                * Now eliminate the possibility of carry-out's by
                * folding back to a 16 bit number (adding high and
                * low parts together.)  Then mop up trailing words
                * and maybe an odd byte.
                */
               FOLD;
               while ((mlen -= 2) >= 0) {
                       ADD;
               }
               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("idpcksum: out of data\n");
                               goto done;
                       }
                       if (m->m_len)
                               break;
                       m = m->m_next;
               }
       }
done:
       /*
        * Add together high and low parts of sum
        * and carry to get cksum.
        * Have to be careful to not drop the last
        * carry here.
        */
       FOLD;
       
       if(sum==0xffff) sum = 0;
       return (sum);
}