BSD 4_3_Net_1 release

[unix-history] / timed / cksum.tahoe.c

/*
* Copyright (c) 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.
*/

#ifndef lint
static char sccsid[] = "@(#)cksum.tahoe.c       2.3 (Berkeley) 6/18/88";
#endif /* not lint */

#include <sys/types.h>

/*
* Checksum routine for Internet Protocol family headers.
*
* This routine is very heavily used in the network
* code and should be modified for each CPU to be as fast as possible.
* 
* This implementation is TAHOE version.
*/

#undef  ADDCARRY
#define ADDCARRY(sum) { \
       if (sum & 0xffff0000) { \
               sum &= 0xffff; \
               sum++; \
       } \
}

in_cksum(addr, len)
       register u_short *addr;
       register int len;
{
       union word {
               char    c[2];
               u_short s;
       } u;
       register int sum = 0;

       while (len > 0) {
               /*
                * add by words.
                */
               while ((len -= 2) >= 0) {
                       if ((int)addr & 0x1) {
                               /* word is not aligned */
                               u.c[0] = *(char *)addr;
                               u.c[1] = *((char *)addr+1);
                               sum += u.s;
                               addr++;
                       } else
                               sum += *addr++;
                       ADDCARRY(sum);
               }
               if (len == -1)
                       /*
                        * Odd number of bytes. 
                        */
                       u.c[0] = *(u_char *)addr;
       }
       if (len == -1) {
               /* The last mbuf has odd # of bytes. Follow the
                  standard (the odd byte is shifted left by 8 bits) */
               u.c[1] = 0;
               sum += u.s;
               ADDCARRY(sum);
       }
       return (~sum & 0xffff);
}