udpcksum.c,v

关于UDP方面的东西。。看不懂就算了。不适合基础者。

head	1.2;
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	dls:1.2; strict;
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1.2
date	97.09.21.19.30.32;	author dls;	state Dist;
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next	1.1;

1.1
date	94.07.17.19.25.14;	author dls;	state Old;
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1.2
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@pre-3e code
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@/* udpcksum.c - udpcksum */

#include <conf.h>
#include <kernel.h>
#include <network.h>

/*------------------------------------------------------------------------
 *  udpcksum -  compute a UDP pseudo-header checksum
 *------------------------------------------------------------------------
 */
unsigned short udpcksum(pep, len)
struct ep	*pep;
int		len;
{
	struct	ip	*pip = (struct ip *)pep->ep_data;
	struct	udp	*pudp = (struct udp *)pip->ip_data;
	unsigned	short	*sptr;
	unsigned	long ucksum;
	int		i;

	ucksum = 0;

	sptr = (unsigned short *) &pip->ip_src;
	/* 2*IP_ALEN octets = IP_ALEN shorts... */
	/* they are in net order.		*/
	for (i=0; i<IP_ALEN; ++i)
		ucksum += *sptr++;
	sptr = (unsigned short *)pudp;
	ucksum += hs2net(IPT_UDP + len);
	if (len % 2) {
		((char *)pudp)[len] = 0;	/* pad */
		len += 1;	/* for the following division */
	}
	len >>= 1;	/* convert to length in shorts */

	for (i=0; i<len; ++i)
		ucksum += *sptr++;
	ucksum = (ucksum >> 16) + (ucksum & 0xffff);
	ucksum += (ucksum >> 16);

	return (short)(~ucksum & 0xffff);
}
@


1.1
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@Initial revision
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#define	UDP_ALEN	IP_ALEN		/* length of src+dst, in shorts	*/

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unsigned short udpcksum(pip)
struct	ip	*pip;
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	unsigned	short	*psh;
	unsigned	long	sum;
	short		len = net2hs(pudp->u_len);
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	sum = 0;

	psh = (unsigned short *) pip->ip_src;
	for (i=0; i<UDP_ALEN; ++i)
		sum += *psh++;
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	psh = (unsigned short *)pudp;
	sum += hs2net(pip->ip_proto + len);
	if (len & 0x1) {
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	len /= 2;	/* convert to length in shorts */
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		sum += *psh++;
	sum = (sum >> 16) + (sum & 0xffff);
	sum += (sum >> 16);
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	return (short)(~sum & 0xffff);
@