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SOURCE.ARC
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IPSUBR.C
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1990-07-10
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/* IP header and checksum processing
*/
#include "global.h"
#include "mbuf.h"
#include "internet.h"
#include "timer.h"
#include "netuser.h"
#include "ip.h"
/* Convert IP header in host format to network mbuf */
struct mbuf *
htonip(ip,data)
struct ip *ip;
struct mbuf *data;
{
int16 hdr_len;
struct mbuf *bp;
register char *cp;
int16 checksum;
hdr_len = IPLEN + ip->optlen;
if((bp = pushdown(data,hdr_len)) == NULLBUF){
free_p(data);
return NULLBUF;
}
cp = bp->data;
*cp++ = (IPVERSION << 4) | (hdr_len >> 2);
*cp++ = ip->tos;
cp = put16(cp,ip->length);
cp = put16(cp,ip->id);
cp = put16(cp,ip->fl_offs);
*cp++ = ip->ttl;
*cp++ = ip->protocol;
cp = put16(cp,0); /* Clear checksum */
cp = put32(cp,ip->source);
cp = put32(cp,ip->dest);
if(ip->optlen != 0)
memcpy(cp,ip->options,ip->optlen);
/* Compute checksum and insert into header */
checksum = cksum(NULLHEADER,bp,hdr_len);
put16(&bp->data[10],checksum);
return bp;
}
/* Extract an IP header from mbuf */
int
ntohip(ip,bpp)
struct ip *ip;
struct mbuf **bpp;
{
int16 ihl;
char iphead[20];
if(pullup(bpp,iphead,20) != 20)
return -1;
if((ihl = (iphead[0] & 0xf) << 2) < IPLEN){
/* Bogus packet; header is too short */
return -1;
}
ip->version = (iphead[0] >> 4) & 0xf;
ip->tos = uchar(iphead[1]);
ip->length = get16(iphead + 2);
ip->id = get16(iphead + 4);
ip->fl_offs = get16(iphead + 6);
ip->ttl = uchar(iphead[8]);
ip->protocol = uchar(iphead[9]);
ip->source = get32(iphead + 12);
ip->dest = get32(iphead + 16);
if((ip->optlen = ihl - IPLEN) != 0)
if (pullup(bpp,ip->options,ip->optlen) != ip->optlen)
return -1;
return ip->optlen + IPLEN;
}
/* Perform end-around-carry adjustment */
int16
eac(sum)
register int32 sum; /* Carries in high order 16 bits */
{
register int16 csum;
while((csum = hiword(sum)) != 0)
sum = csum + (sum & 0xffffL);
return (int16) (sum & 0xffffl); /* Chops to 16 bits */
}
/* Checksum a mbuf chain, with optional pseudo-header */
int16
cksum(ph,m,len)
struct pseudo_header *ph;
register struct mbuf *m;
int16 len;
{
register unsigned int cnt, total;
register int32 sum, csum;
register char *up;
int16 csum1;
int swap = 0;
int16 lcsum();
sum = 0l;
/* Sum pseudo-header, if present */
if(ph != NULLHEADER){
sum = hiword(ph->source);
sum += loword(ph->source);
sum += hiword(ph->dest);
sum += loword(ph->dest);
sum += uchar(ph->protocol);
sum += ph->length;
}
/* Now do each mbuf on the chain */
for(total = 0; m != NULLBUF && total < len; m = m->next) {
cnt = min(m->cnt, len - total);
up = (char *)m->data;
csum = 0;
if(((long)up) & 1){
/* Handle odd leading byte */
if(swap)
csum = uchar(*up++);
else
csum = (int16)(uchar(*up++) << 8);
cnt--;
swap = !swap;
}
if(cnt > 1){
/* Have the primitive checksumming routine do most of
* the work. At this point, up is guaranteed to be on
* a short boundary
*/
csum1 = lcsum((unsigned short *)up, cnt >> 1);
if(swap)
csum1 = (csum1 << 8) | (csum1 >> 8);
csum += csum1;
}
/* Handle odd trailing byte */
if(cnt & 1){
if(swap)
csum += uchar(up[--cnt]);
else
csum += (int16)(uchar(up[--cnt]) << 8);
swap = !swap;
}
sum += csum;
total += m->cnt;
}
/* Do final end-around carry, complement and return */
return ~eac(sum) & 0xffff;
}
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