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avoid issues with typecast optimization (taking advantage of pointer aliasing), 

which results in incorrect igmp checksum.
confirmed by taca@netbsd
This commit is contained in:
itojun 2002-08-01 08:33:14 +00:00
parent bff41c67e3
commit a297f25294
1 changed files with 10 additions and 6 deletions
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16
usr.sbin/mrouted/inet.c
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@ -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 @@ inet_cksum(u_int16_t *addr, u_int len)
{
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 @@ inet_cksum(u_int16_t *addr, u_int len)
/* 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 @@ inet_cksum(u_int16_t *addr, u_int len)
*/
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);
}