1c335da8a3
Obtained from: KAME
519 lines
16 KiB
C
519 lines
16 KiB
C
/*
|
|
* Copyright (C) 1999 LSIIT Laboratory.
|
|
* All rights reserved.
|
|
*
|
|
* Redistribution and use in source and binary forms, with or without
|
|
* modification, are permitted provided that the following conditions
|
|
* are met:
|
|
* 1. Redistributions of source code must retain the above copyright
|
|
* notice, this list of conditions and the following disclaimer.
|
|
* 2. Redistributions in binary form must reproduce the above copyright
|
|
* notice, this list of conditions and the following disclaimer in the
|
|
* documentation and/or other materials provided with the distribution.
|
|
* 3. Neither the name of the project nor the names of its contributors
|
|
* may be used to endorse or promote products derived from this software
|
|
* without specific prior written permission.
|
|
*
|
|
* THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
|
|
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
* ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
|
|
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
* SUCH DAMAGE.
|
|
*/
|
|
/*
|
|
* Copyright (C) 1998 WIDE Project.
|
|
* All rights reserved.
|
|
*
|
|
* Redistribution and use in source and binary forms, with or without
|
|
* modification, are permitted provided that the following conditions
|
|
* are met:
|
|
* 1. Redistributions of source code must retain the above copyright
|
|
* notice, this list of conditions and the following disclaimer.
|
|
* 2. Redistributions in binary form must reproduce the above copyright
|
|
* notice, this list of conditions and the following disclaimer in the
|
|
* documentation and/or other materials provided with the distribution.
|
|
* 3. Neither the name of the project nor the names of its contributors
|
|
* may be used to endorse or promote products derived from this software
|
|
* without specific prior written permission.
|
|
*
|
|
* THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
|
|
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
* ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
|
|
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
* SUCH DAMAGE.
|
|
*/
|
|
/*
|
|
* Questions concerning this software should be directed to
|
|
* Mickael Hoerdt (hoerdt@clarinet.u-strasbg.fr) LSIIT Strasbourg.
|
|
*
|
|
*/
|
|
/*
|
|
* This program has been derived from pim6dd.
|
|
* The pim6dd program is covered by the license in the accompanying file
|
|
* named "LICENSE.pim6dd".
|
|
*/
|
|
/*
|
|
* This program has been derived from pimd.
|
|
* The pimd program is covered by the license in the accompanying file
|
|
* named "LICENSE.pimd".
|
|
*
|
|
* $FreeBSD$
|
|
*/
|
|
|
|
#include <sys/param.h>
|
|
#include <sys/types.h>
|
|
#include <sys/socket.h>
|
|
#include <sys/uio.h>
|
|
#include <errno.h>
|
|
#include <netinet/in.h>
|
|
#include <string.h>
|
|
#include <netinet6/ip6_mroute.h>
|
|
#include <netinet6/pim6.h>
|
|
#include <netinet/ip6.h>
|
|
#include <arpa/inet.h>
|
|
#include <stdlib.h>
|
|
#include <syslog.h>
|
|
#include <signal.h>
|
|
#include "mld6.h"
|
|
#include "defs.h"
|
|
#include "kern.h"
|
|
#include "pim6.h"
|
|
#include "pimd.h"
|
|
#include "pim6_proto.h"
|
|
#include "inet6.h"
|
|
#include "debug.h"
|
|
|
|
struct sockaddr_in6 allpim6routers_group;
|
|
int pim6_socket;
|
|
char *pim6_recv_buf;
|
|
char *pim6_send_buf;
|
|
|
|
static struct sockaddr_in6 from;
|
|
static struct iovec sndiovpim[2];
|
|
static struct iovec rcviovpim[2];
|
|
static struct msghdr sndmhpim,
|
|
rcvmhpim;
|
|
static u_char *sndcmsgbufpim = NULL;
|
|
static int sndcmsglen;
|
|
static u_char *rcvcmsgbufpim = NULL;
|
|
static int rcvcmsglen;
|
|
|
|
|
|
/*
|
|
* Local function definitions.
|
|
*/
|
|
static void pim6_read __P((int f, fd_set *rfd));
|
|
static void accept_pim6 __P((int recvlen));
|
|
static int pim6_cksum __P((u_short *, struct in6_addr *,
|
|
struct in6_addr *, int));
|
|
|
|
|
|
|
|
void
|
|
init_pim6()
|
|
{
|
|
struct cmsghdr *cmsgp;
|
|
int on;
|
|
|
|
if ( (pim6_recv_buf = malloc( RECV_BUF_SIZE)) == NULL ||
|
|
(pim6_send_buf = malloc (RECV_BUF_SIZE)) == NULL)
|
|
log(LOG_ERR,errno,"pim6 buffer allocation");
|
|
|
|
IF_DEBUG(DEBUG_KERN)
|
|
log(LOG_DEBUG,0,"%d octets allocated for the emit/recept buffer pim6",RECV_BUF_SIZE);
|
|
|
|
if( (pim6_socket = socket(AF_INET6,SOCK_RAW,IPPROTO_PIM)) < 0 )
|
|
log(LOG_ERR,errno,"pim6_socket");
|
|
|
|
k_set_rcvbuf(pim6_socket,SO_RECV_BUF_SIZE_MAX,SO_RECV_BUF_SIZE_MIN);
|
|
k_set_hlim(pim6_socket,MINHLIM);
|
|
k_set_loop(pim6_socket,FALSE);
|
|
|
|
memset(&allpim6routers_group, 0, sizeof(allpim6routers_group));
|
|
allpim6routers_group.sin6_len = sizeof(allpim6routers_group);
|
|
allpim6routers_group.sin6_family = AF_INET6;
|
|
if (inet_pton(AF_INET6, "ff02::d",
|
|
(void *)&allpim6routers_group.sin6_addr) != 1 )
|
|
log(LOG_ERR, 0, "inet_pton failed for ff02::d");
|
|
memset(&sockaddr6_d, 0, sizeof(sockaddr6_d));
|
|
sockaddr6_d.sin6_len = sizeof(sockaddr6_d);
|
|
sockaddr6_d.sin6_family = AF_INET6;
|
|
if (inet_pton(AF_INET6, "ff00::",
|
|
(void *)&sockaddr6_d.sin6_addr) != 1)
|
|
log(LOG_ERR, 0, "inet_pton failed for ff00::");
|
|
|
|
/* specify to tell receiving interface */
|
|
on = 1;
|
|
#ifdef IPV6_RECVPKTINFO
|
|
if (setsockopt(pim6_socket, IPPROTO_IPV6, IPV6_RECVPKTINFO, &on,
|
|
sizeof(on)) < 0)
|
|
log(LOG_ERR, errno, "setsockopt(IPV6_RECVPKTINFO)");
|
|
#else
|
|
if (setsockopt(pim6_socket, IPPROTO_IPV6, IPV6_PKTINFO, &on,
|
|
sizeof(on)) < 0)
|
|
log(LOG_ERR, errno, "setsockopt(IPV6_PKTINFO)");
|
|
#endif
|
|
|
|
/* initialize msghdr for receiving packets */
|
|
rcviovpim[0].iov_base = (caddr_t) pim6_recv_buf;
|
|
rcviovpim[0].iov_len = RECV_BUF_SIZE;
|
|
rcvmhpim.msg_name = (caddr_t ) &from;
|
|
rcvmhpim.msg_namelen = sizeof (from);
|
|
rcvmhpim.msg_iov = rcviovpim;
|
|
rcvmhpim.msg_iovlen = 1;
|
|
rcvcmsglen = CMSG_SPACE(sizeof(struct in6_pktinfo));
|
|
if (rcvcmsgbufpim == NULL &&
|
|
(rcvcmsgbufpim = malloc(rcvcmsglen)) == NULL)
|
|
log(LOG_ERR, 0, "malloc failed");
|
|
rcvmhpim.msg_control = (caddr_t ) rcvcmsgbufpim;
|
|
rcvmhpim.msg_controllen = rcvcmsglen;
|
|
|
|
sndmhpim.msg_namelen=sizeof(struct sockaddr_in6);
|
|
sndmhpim.msg_iov=sndiovpim;
|
|
sndmhpim.msg_iovlen=1;
|
|
sndcmsglen = CMSG_SPACE(sizeof(struct in6_pktinfo));
|
|
if (sndcmsgbufpim == NULL &&
|
|
(sndcmsgbufpim = malloc(sndcmsglen)) == NULL)
|
|
log(LOG_ERR, 0, "malloc failed");
|
|
sndmhpim.msg_control = (caddr_t)sndcmsgbufpim;
|
|
sndmhpim.msg_controllen = sndcmsglen;
|
|
cmsgp=(struct cmsghdr *)sndcmsgbufpim;
|
|
cmsgp->cmsg_len = CMSG_LEN(sizeof(struct in6_pktinfo));
|
|
cmsgp->cmsg_level = IPPROTO_IPV6;
|
|
cmsgp->cmsg_type = IPV6_PKTINFO;
|
|
|
|
if ( register_input_handler(pim6_socket, pim6_read) <0)
|
|
log(LOG_ERR,0,"Registering pim6 socket");
|
|
|
|
/* Initialize the building Join/Prune messages working area */
|
|
build_jp_message_pool = (build_jp_message_t *)NULL;
|
|
build_jp_message_pool_counter = 0;
|
|
}
|
|
|
|
/* Read a PIM message */
|
|
|
|
static void
|
|
pim6_read(f, rfd)
|
|
int f;
|
|
fd_set *rfd;
|
|
{
|
|
register int pim6_recvlen;
|
|
|
|
#ifdef SYSV
|
|
sigset_t block, oblock;
|
|
#else
|
|
register int omask;
|
|
#endif
|
|
|
|
pim6_recvlen = recvmsg(pim6_socket,&rcvmhpim,0);
|
|
|
|
if (pim6_recvlen < 0) {
|
|
if (errno != EINTR)
|
|
log(LOG_ERR, errno, "PIM6 recvmsg");
|
|
return;
|
|
}
|
|
|
|
#ifdef SYSV
|
|
(void)sigemptyset(&block);
|
|
(void)sigaddset(&block, SIGALRM);
|
|
if (sigprocmask(SIG_BLOCK, &block, &oblock) < 0)
|
|
log(LOG_ERR, errno, "sigprocmask");
|
|
#else
|
|
/* Use of omask taken from main() */
|
|
omask = sigblock(sigmask(SIGALRM));
|
|
#endif /* SYSV */
|
|
|
|
accept_pim6(pim6_recvlen);
|
|
|
|
#ifdef SYSV
|
|
(void)sigprocmask(SIG_SETMASK, &oblock, (sigset_t *)NULL);
|
|
#else
|
|
(void)sigsetmask(omask);
|
|
#endif /* SYSV */
|
|
}
|
|
|
|
static void
|
|
accept_pim6(pimlen)
|
|
int pimlen;
|
|
{
|
|
register struct pim *pim;
|
|
struct sockaddr_in6 dst;
|
|
struct in6_pktinfo *pi=NULL;
|
|
struct sockaddr_in6 *src = (struct sockaddr_in6 *)rcvmhpim.msg_name;
|
|
struct cmsghdr *cm;
|
|
int ifindex=0;
|
|
|
|
/* sanity check */
|
|
if (pimlen < sizeof(pim)) {
|
|
log(LOG_WARNING, 0,
|
|
"data field too short (%u bytes) for PIM header, from %s",
|
|
pimlen, inet6_fmt(&src->sin6_addr));
|
|
return;
|
|
}
|
|
pim = (struct pim *)rcvmhpim.msg_iov[0].iov_base;
|
|
|
|
/* extract vital information via Advanced API */
|
|
for(cm = (struct cmsghdr *)CMSG_FIRSTHDR(&rcvmhpim);
|
|
cm;
|
|
cm =(struct cmsghdr *)CMSG_NXTHDR(&rcvmhpim , cm ))
|
|
{
|
|
|
|
if( cm->cmsg_level == IPPROTO_IPV6 &&
|
|
cm->cmsg_type == IPV6_PKTINFO &&
|
|
cm->cmsg_len == CMSG_LEN(sizeof(struct in6_pktinfo)))
|
|
{
|
|
pi=(struct in6_pktinfo *)(CMSG_DATA(cm));
|
|
dst.sin6_addr=pi->ipi6_addr;
|
|
ifindex = pi->ipi6_ifindex;
|
|
if (IN6_IS_ADDR_LINKLOCAL(&dst.sin6_addr))
|
|
dst.sin6_scope_id = ifindex;
|
|
else
|
|
dst.sin6_scope_id = 0;
|
|
}
|
|
}
|
|
|
|
if(pi==NULL)
|
|
log(LOG_ERR,0,"pim6_socket : unable to get destination packet");
|
|
|
|
if(ifindex==0)
|
|
log(LOG_ERR,0,"pim6_socket : unable to get ifindex");
|
|
|
|
#define NOSUCHDEF
|
|
#ifdef NOSUCHDEF /* TODO: delete. Too noisy */
|
|
IF_DEBUG(DEBUG_PIM_DETAIL) {
|
|
IF_DEBUG(DEBUG_PIM) {
|
|
log(LOG_DEBUG, 0, "Receiving %s from %s",
|
|
packet_kind(IPPROTO_PIM, pim->pim_type, 0),
|
|
inet6_fmt(&src->sin6_addr));
|
|
}
|
|
}
|
|
#endif /* NOSUCHDEF */
|
|
|
|
|
|
/* Check of PIM version is already done in the kernel */
|
|
|
|
/*
|
|
* TODO: check the dest. is ALL_PIM_ROUTERS (if multicast address)
|
|
* is it necessary?
|
|
*/
|
|
/* Checksum verification is done in the kernel. */
|
|
|
|
switch (pim->pim_type) {
|
|
case PIM_HELLO:
|
|
receive_pim6_hello(src, (char *)(pim), pimlen);
|
|
break;
|
|
case PIM_REGISTER:
|
|
receive_pim6_register(src, &dst, (char *)(pim), pimlen);
|
|
break;
|
|
case PIM_REGISTER_STOP:
|
|
receive_pim6_register_stop(src, &dst, (char *)(pim), pimlen);
|
|
break;
|
|
case PIM_JOIN_PRUNE:
|
|
receive_pim6_join_prune(src, &dst, (char *)(pim), pimlen);
|
|
break;
|
|
case PIM_BOOTSTRAP:
|
|
receive_pim6_bootstrap(src, &dst, (char *)(pim), pimlen);
|
|
break;
|
|
case PIM_ASSERT:
|
|
receive_pim6_assert(src, &dst, (char *)(pim), pimlen);
|
|
break;
|
|
case PIM_GRAFT:
|
|
pim6dstat.in_pim6_graft++;
|
|
log(LOG_INFO, 0, "ignore %s from %s",
|
|
packet_kind(IPPROTO_PIM, pim->pim_type, 0),
|
|
inet6_fmt(&src->sin6_addr));
|
|
break;
|
|
case PIM_GRAFT_ACK:
|
|
pim6dstat.in_pim6_graft_ack++;
|
|
log(LOG_INFO, 0, "ignore %s from %s",
|
|
packet_kind(IPPROTO_PIM, pim->pim_type, 0),
|
|
inet6_fmt(&src->sin6_addr));
|
|
break;
|
|
case PIM_CAND_RP_ADV:
|
|
receive_pim6_cand_rp_adv(src, &dst, (char *)(pim), pimlen);
|
|
break;
|
|
default:
|
|
log(LOG_INFO, 0,
|
|
"ignore unknown PIM message code %u from %s",
|
|
pim->pim_type,
|
|
inet6_fmt(&src->sin6_addr));
|
|
break;
|
|
}
|
|
}
|
|
|
|
void
|
|
send_pim6(char *buf, struct sockaddr_in6 *src,
|
|
struct sockaddr_in6 *dst, int type, int datalen)
|
|
{
|
|
struct pim *pim;
|
|
int setloop=0;
|
|
int ifindex=0;
|
|
int sendlen=sizeof(struct pim)+datalen;
|
|
struct cmsghdr *cmsgp;
|
|
struct in6_pktinfo *sndpktinfo;
|
|
|
|
sndiovpim[0].iov_base=(caddr_t)buf;
|
|
sndiovpim[0].iov_len=datalen+sizeof(struct pim);
|
|
cmsgp=(struct cmsghdr *)sndcmsgbufpim;
|
|
sndpktinfo=(struct in6_pktinfo *)CMSG_DATA(cmsgp);
|
|
sndmhpim.msg_name=(caddr_t)dst;
|
|
|
|
pim = (struct pim *)buf;
|
|
pim->pim_type = type;
|
|
pim->pim_ver = PIM_PROTOCOL_VERSION;
|
|
pim->pim_rsv = 0;
|
|
pim->pim_cksum = 0;
|
|
|
|
if(pim->pim_type == PIM_REGISTER)
|
|
{
|
|
sendlen = sizeof(struct pim)+sizeof(pim_register_t);
|
|
|
|
}
|
|
|
|
pim->pim_cksum = pim6_cksum((u_int16 *)pim,
|
|
&src->sin6_addr, &dst->sin6_addr,
|
|
sendlen);
|
|
|
|
if (IN6_IS_ADDR_MULTICAST(&dst->sin6_addr))
|
|
{
|
|
if (!IN6_IS_ADDR_LINKLOCAL(&src->sin6_addr))
|
|
{
|
|
log(LOG_WARNING, 0,
|
|
"trying to send pim multicast packet "
|
|
"with non linklocal src(%s), ignoring",
|
|
inet6_fmt(&src->sin6_addr));
|
|
return;
|
|
}
|
|
sndmhpim.msg_control=NULL;
|
|
sndmhpim.msg_controllen=0;
|
|
ifindex=src->sin6_scope_id;
|
|
|
|
k_set_if(pim6_socket , ifindex);
|
|
if( IN6_ARE_ADDR_EQUAL(&dst->sin6_addr,
|
|
&allnodes_group.sin6_addr) ||
|
|
IN6_ARE_ADDR_EQUAL(&dst->sin6_addr,
|
|
&allrouters_group.sin6_addr) ||
|
|
IN6_ARE_ADDR_EQUAL(&dst->sin6_addr,
|
|
&allpim6routers_group.sin6_addr))
|
|
{
|
|
setloop=1;
|
|
k_set_loop(pim6_socket, TRUE);
|
|
}
|
|
}
|
|
else
|
|
{
|
|
sndmhpim.msg_control = (caddr_t)sndcmsgbufpim;
|
|
sndmhpim.msg_controllen = sndcmsglen;
|
|
sndpktinfo->ipi6_ifindex=src->sin6_scope_id;
|
|
memcpy(&sndpktinfo->ipi6_addr, &src->sin6_addr,
|
|
sizeof(sndpktinfo->ipi6_addr));
|
|
}
|
|
if (sendmsg(pim6_socket, &sndmhpim, 0) < 0) {
|
|
if (errno == ENETDOWN)
|
|
check_vif_state();
|
|
else {
|
|
log(LOG_WARNING, errno, "sendmsg from %s to %s",
|
|
inet6_fmt(&src->sin6_addr),
|
|
inet6_fmt(&dst->sin6_addr));
|
|
}
|
|
}
|
|
|
|
if(setloop)
|
|
k_set_loop(pim6_socket, FALSE);
|
|
|
|
return;
|
|
}
|
|
|
|
/* ============================== */
|
|
|
|
/*
|
|
* Checksum routine for Internet Protocol family headers (Portable Version).
|
|
*
|
|
* This routine is very heavily used in the network
|
|
* code and should be modified for each CPU to be as fast as possible.
|
|
*/
|
|
|
|
#define ADDCARRY(x) (x > 65535 ? x -= 65535 : x)
|
|
#define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
|
|
|
|
static union {
|
|
u_short phs[4];
|
|
struct {
|
|
u_long ph_len;
|
|
u_char ph_zero[3];
|
|
u_char ph_nxt;
|
|
} ph;
|
|
} uph;
|
|
|
|
/*
|
|
* Our algorithm is simple, using a 32 bit accumulator (sum), we add
|
|
* sequential 16 bit words to it, and at the end, fold back all the
|
|
* carry bits from the top 16 bits into the lower 16 bits.
|
|
*/
|
|
int pim6_cksum(u_short *addr, struct in6_addr *src ,struct in6_addr *dst , int len )
|
|
{
|
|
register int nleft = len;
|
|
register u_short *w;
|
|
register int sum = 0;
|
|
u_short answer = 0;
|
|
|
|
/*
|
|
* First create IP6 pseudo header and calculate a summary.
|
|
*/
|
|
w = (u_short *)src;
|
|
uph.ph.ph_len = htonl(len);
|
|
uph.ph.ph_nxt = IPPROTO_PIM;
|
|
|
|
/* IPv6 source address */
|
|
sum += w[0];
|
|
/* XXX: necessary? */
|
|
if (!(IN6_IS_ADDR_LINKLOCAL(src) || IN6_IS_ADDR_MC_LINKLOCAL(src)))
|
|
sum += w[1];
|
|
sum += w[2]; sum += w[3]; sum += w[4]; sum += w[5];
|
|
sum += w[6]; sum += w[7];
|
|
/* IPv6 destination address */
|
|
w = (u_short *)dst;
|
|
sum += w[0];
|
|
/* XXX: necessary? */
|
|
if (!(IN6_IS_ADDR_LINKLOCAL(dst) || IN6_IS_ADDR_MC_LINKLOCAL(dst)))
|
|
sum += w[1];
|
|
sum += w[2]; sum += w[3]; sum += w[4]; sum += w[5];
|
|
sum += w[6]; sum += w[7];
|
|
/* Payload length and upper layer identifier */
|
|
sum += uph.phs[0]; sum += uph.phs[1];
|
|
sum += uph.phs[2]; sum += uph.phs[3];
|
|
|
|
/*
|
|
* Secondly calculate a summary of the first mbuf excluding offset.
|
|
*/
|
|
w = addr;
|
|
while (nleft > 1) {
|
|
sum += *w++;
|
|
nleft -= 2;
|
|
}
|
|
|
|
/* mop up an odd byte, if necessary */
|
|
if (nleft == 1) {
|
|
*(u_char *)(&answer) = *(u_char *)w ;
|
|
sum += answer;
|
|
}
|
|
|
|
/* add back carry outs from top 16 bits to low 16 bits */
|
|
sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */
|
|
sum += (sum >> 16); /* add carry */
|
|
answer = ~sum; /* truncate to 16 bits */
|
|
return(answer);
|
|
}
|