--- researchv9/sys/inet/ip_subr.c	2018/04/24 17:21:59	1.1
+++ researchv9/sys/inet/ip_subr.c	2018/04/24 17:29:28	1.1.1.2
@@ -288,6 +288,8 @@ in_cksum(m, len)
 	register u_short *w;
 	register u_long sum = 0;
 	register int mlen = 0;
+	register int odd = 0;	/* set if last block ended on an odd
+				 * numbered byte */
 
 	MCHECK(m);
 	for (; len!=0; m=m->m_next) {
@@ -296,19 +298,14 @@ in_cksum(m, len)
 			break;
 		}
 		w = mtod(m, u_short *);
-		if (mlen == -1) {
-			/* last block ended on an odd numbered byte */
-			sum += *(u_char *)w << 8;
-			w = (u_short *)((char *)w + 1);
-			mlen = BLEN(m) - 1;
-			len--;
-		} else
-			mlen = BLEN(m);
+		mlen = BLEN(m);
 		if (len < mlen)
 			mlen = len;
 		len -= mlen;
 		/* vecadd returns a 16-bit checksum of the block + sum */
-		sum = vecadd(w, mlen, sum);
+		sum = vecadd(w, mlen, sum, odd);
+		if((int)mlen & 1)
+			odd = !odd;
 	}
 	/* return complement of sum */
 	return sum^0xffff;