BSD 4_3 release

[unix-history] / usr / src / etc / timed / vax / cksum.c

/*
* Copyright (c) 1983 Regents of the University of California.
* All rights reserved.  The Berkeley software License Agreement
* specifies the terms and conditions for redistribution.
*/

#ifndef lint
static char sccsid[] = "@(#)cksum.c     1.2 (Berkeley) 9/18/85";
#endif not lint

#include <sys/types.h>

#define ADD     asm("adwc (r9)+,r8;");

/* computes the checksum for ip packets for the VAX */

in_cksum(addr, len)
u_short *addr;
int len;
{
       register int nleft = len;       /* on vax, (user mode), r11 */
#ifndef lint
       register int xxx;               /* on vax, (user mode), r10 */
#endif not lint
       register u_short *w = addr;     /* on vax, known to be r9 */
       register int sum = 0;           /* on vax, known to be r8 */

       if (((int)w&0x2) && nleft >= 2) {
               sum += *w++;
               nleft -= 2;
       }
       while ((nleft -= 32) >= 0) {
               asm("clrl r0");         /* clears carry */
               ADD; ADD; ADD; ADD; ADD; ADD; ADD; ADD;
               asm("adwc $0,r8");
       }
       nleft += 32;
       while ((nleft -= 8) >= 0) {
               asm("clrl r0");
               ADD; ADD;
               asm("adwc $0,r8");
       }
       nleft += 8;
       { asm("ashl $-16,r8,r0; addw2 r0,r8");
         asm("adwc $0,r8; movzwl r8,r8"); }
       while ((nleft -= 2) >= 0) {
               asm("movzwl (r9)+,r0; addl2 r0,r8");
       }
       if (nleft == -1) {
               sum += *(u_char *)w;
       }

       { asm("ashl $-16,r8,r0; addw2 r0,r8; adwc $0,r8");
         asm("mcoml r8,r8; movzwl r8,r8"); }
       return (sum);
}