[src/trunk]: src/usr.sbin/mrouted avoid issues with typecast optimization (ta...

[itojun <itojun%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/0ccefd415f6d
branches:  trunk
changeset: 534661:0ccefd415f6d
user:      itojun <itojun%NetBSD.org@localhost>
date:      Thu Aug 01 08:33:14 2002 +0000

description:
avoid issues with typecast optimization (taking advantage of pointer aliasing),
which results in incorrect igmp checksum.
confirmed by taca@netbsd

diffstat:

 usr.sbin/mrouted/inet.c |  16 ++++++++++------
 1 files changed, 10 insertions(+), 6 deletions(-)

diffs (43 lines):

diff -r 5b9149f6602b -r 0ccefd415f6d usr.sbin/mrouted/inet.c
--- a/usr.sbin/mrouted/inet.c   Thu Aug 01 06:26:24 2002 +0000
+++ b/usr.sbin/mrouted/inet.c   Thu Aug 01 08:33:14 2002 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: inet.c,v 1.6 2002/08/01 03:40:34 itojun Exp $  */
+/*     $NetBSD: inet.c,v 1.7 2002/08/01 08:33:14 itojun Exp $  */
 
 /*
  * The mrouted program is covered by the license in the accompanying file
@@ -189,8 +189,11 @@
 {
        int nleft = (int)len;
        u_int16_t *w = addr;
-       u_int16_t answer = 0;
        int32_t sum = 0;
+       union {
+               u_int16_t w;
+               u_int8_t b[2];
+       } answer;
 
        /*
         *  Our algorithm is simple, using a 32 bit accumulator (sum),
@@ -205,8 +208,9 @@
 
        /* mop up an odd byte, if necessary */
        if (nleft == 1) {
-               *(u_char *) (&answer) = *(u_char *)w ;
-               sum += answer;
+               answer.w = 0;
+               answer.b[0] = *(u_char *)w ;
+               sum += answer.w;
        }
 
        /*
@@ -214,6 +218,6 @@
         */
        sum = (sum >> 16) + (sum & 0xffff);     /* add hi 16 to low 16 */
        sum += (sum >> 16);                     /* add carry */
-       answer = ~sum;                          /* truncate to 16 bits */
-       return (answer);
+       answer.w = ~sum;                        /* truncate to 16 bits */
+       return (answer.w);
 }