4.3BSD - /usr/src/etc/timed/m68000/cksum.c

   1: /*
   2:  * Copyright (c) 1983 Regents of the University of California.
   3:  * All rights reserved.  The Berkeley software License Agreement
   4:  * specifies the terms and conditions for redistribution.
   5:  */
   6: 
   7: #ifndef lint
   8: static char sccsid[] = "@(#)cksum.c	2.1 (Berkeley) 6/6/86";
   9: #endif not lint
  10: 
  11: #include "../globals.h"
  12: #include <protocols/timed.h>
  13: 
  14: /* computes the checksum for ip packets for a Motorola 68000 base computer */
  15: 
  16: in_cksum(w, mlen)
  17:     register u_short *w;
  18:     register int mlen;
  19: {
  20:     register int sum = 0;
  21: 
  22:     if (mlen > 0) {
  23:         if (((int)w & 1) == 0) {
  24:             sum = ocsum(w, mlen>>1);
  25:             w += mlen>>1;
  26:             if (mlen & 1) {
  27:                 sum += *(u_char *)w << 8;
  28:                 mlen = -1;
  29:             }
  30:         } else {
  31:             u_short swsum;
  32: 
  33:             sum = *(u_char *)w << 8;
  34:             mlen--;
  35:             w = (u_short *)(1 + (int)w);
  36:             swsum = ocsum(w, mlen>>1);
  37:             swab((char *)&swsum, (char *)&swsum, sizeof swsum);
  38:             sum += swsum;
  39:             w += mlen>>1;
  40:             if (mlen & 1)
  41:                 sum += *(u_char *)w;
  42:         }
  43:     }
  44:     sum = (sum & 0xFFFF) + (sum >> 16);
  45:     sum = (sum & 0xFFFF) + (sum >> 16);
  46:     sum = (~sum) & 0xFFFF;
  47:     return (sum);
  48: }

Defined functions

Defined variables