xref: /csrg-svn/sys/netiso/iso_chksum.c (revision 37469)

/***********************************************************
		Copyright IBM Corporation 1987

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******************************************************************/

/*
 * ARGO Project, Computer Sciences Dept., University of Wisconsin - Madison
 */
/*
 * $Header: iso_chksum.c,v 4.7 88/07/29 15:31:26 nhall Exp $
 * $Source: /usr/argo/sys/netiso/RCS/iso_chksum.c,v $
 *
 * ISO CHECKSUM
 *
 * The checksum generation and check routines are here.
 * The checksum is 2 bytes such that the sum of all the bytes b(i) == 0
 * and the sum of i * b(i) == 0.
 * The whole thing is complicated by the fact that the data are in mbuf
 * chains.
 * Furthermore, there is the possibility of wraparound in the running
 * sums after adding up 4102 octets.  In order to avoid doing a mod
 * operation after EACH add, we have restricted this implementation to
 * negotiating a maximum of 4096-octets per TPDU (for the transport layer).
 * The routine iso_check_csum doesn't need to know where the checksum
 * octets are.
 * The routine iso_gen_csum takes a pointer to an mbuf chain (logically
 * a chunk of data), an offset into the chunk at which the 2 octets are to
 * be stuffed, and the length of the chunk.  The 2 octets have to be
 * logically adjacent, but may be physically located in separate mbufs.
 */

#ifdef ISO
#ifndef lint
static char *rcsid = "$Header: iso_chksum.c,v 4.7 88/07/29 15:31:26 nhall Exp $";
#endif

#include "argo_debug.h"
#include "param.h"
#include "mbuf.h"
#endif ISO

#ifndef MNULL
#define MNULL (struct mbuf *)0
#endif MNULL

/*
 * FUNCTION:	iso_check_csum
 *
 * PURPOSE:		To check the checksum of the packet in the mbuf chain (m).
 * 				The total length of the packet is (len).
 * 				Called from tp_input() and clnp_intr()
 *
 * RETURNS:		 TRUE (something non-zero) if there is a checksum error,
 * 			 	 FALSE if there was NO checksum error.
 *
 * SIDE EFFECTS:  none
 *
 * NOTES:		 It might be possible to gain something by optimizing
 *               this routine (unrolling loops, etc). But it is such
 *				 a horrible thing to fiddle with anyway, it probably
 *				 isn't worth it.
 */
int
iso_check_csum(m, len)
	struct mbuf *m;
	int len;
{
	register u_char *p = mtod(m, u_char *);
	register u_long c0=0, c1=0;
	register int i=0;
	int cum = 0; /* cumulative length */
	int l;

	l = len;
	len = MIN(m->m_len, len);
	i = 0;

	IFDEBUG(D_CHKSUM)
		printf("iso_check_csum: m x%x, l x%x, m->m_len x%x\n", m, l, m->m_len);
	ENDDEBUG

	while( i<l ) {
		cum += len;
		while (i<cum) {
			c0 = c0 + *(p++);
			c1 += c0;
			i++;
		}
		if(i < l) {
			m = m->m_next;
			IFDEBUG(D_CHKSUM)
				printf("iso_check_csum: new mbuf\n");
				if(l-i < m->m_len)
					printf(
					"bad mbuf chain in check csum l 0x%x i 0x%x m_data 0x%x",
						l,i,m->m_data);
			ENDDEBUG
			ASSERT( m != MNULL);
			len = MIN( m->m_len, l-i);
			p = mtod(m, u_char *);
		}
	}
	if ( ((int)c0 % 255) || ((int)c1 % 255) ) {
		IFDEBUG(D_CHKSUM)
			printf("BAD iso_check_csum l 0x%x cum 0x%x len 0x%x, i 0x%x",
				l, cum, len, i);
		ENDDEBUG
		return ((int)c0 % 255)<<8 | ((int)c1 % 255);
	}
	return 0;
}

/*
 * FUNCTION:	iso_gen_csum
 *
 * PURPOSE:		To generate the checksum of the packet in the mbuf chain (m).
 * 				The first of the 2 (logically) adjacent checksum bytes
 *				(x and y) go at offset (n).
 * 				(n) is an offset relative to the beginning of the data,
 *				not the beginning of the mbuf.
 * 				(l) is the length of the total mbuf chain's data.
 * 				Called from tp_emit(), tp_error_emit()
 *				clnp_emit_er(), clnp_forward(), clnp_output().
 *
 * RETURNS:		Rien
 *
 * SIDE EFFECTS: Puts the 2 checksum bytes into the packet.
 *
 * NOTES:		Ditto the note for iso_check_csum().
 */

void
iso_gen_csum(m,n,l)
	struct mbuf *m;
	int n; /* offset of 2 checksum bytes */
	int l;
{
	register u_char *p = mtod(m, u_char *);
	register int c0=0, c1=0;
	register int i=0;
	int loc = n++, len=0; /* n is position, loc is offset */
	u_char *xloc;
	u_char *yloc;
	int cum=0;	/* cum == cumulative length */

	IFDEBUG(D_CHKSUM)
		printf("enter gen csum m 0x%x n 0x%x l 0x%x\n",m, n-1 ,l );
	ENDDEBUG

	while(i < l) {
		len = MIN(m->m_len, CLBYTES);
		/* RAH: don't cksum more than l bytes */
		len = MIN(len, l);

		cum +=len;
		p = mtod(m, u_char *);

		if(loc>=0) {
			if (loc < len) {
				xloc = loc + mtod(m, u_char *);
				IFDEBUG(D_CHKSUM)
					printf("1: zeroing xloc 0x%x loc 0x%x\n",xloc, loc );
				ENDDEBUG
				*xloc = (u_char)0;
				if (loc+1 < len) {
					/* both xloc and yloc are in same mbuf */
					yloc = 1  + xloc;
					IFDEBUG(D_CHKSUM)
						printf("2: zeroing yloc 0x%x loc 0x%x\n",yloc, loc );
					ENDDEBUG
					*yloc = (u_char)0;
				} else {
					/* crosses boundary of mbufs */
					yloc = mtod(m->m_next, u_char *);
					IFDEBUG(D_CHKSUM)
						printf("3: zeroing yloc 0x%x \n",yloc );
					ENDDEBUG
					*yloc = (u_char)0;
				}
			}
			loc -= len;
		}

		while(i < cum) {
			c0 = (c0 + *p);
			c1 += c0 ;
			i++;
			p++;
		}
		m = m->m_next;
	}
	IFDEBUG(D_CHKSUM)
		printf("gen csum final xloc 0x%x yloc 0x%x\n",xloc, yloc );
	ENDDEBUG

	c1 = (((c0 * (l-n))-c1)%255) ;
	*xloc = (u_char) ((c1 < 0)? c1+255 : c1);

	c1 = (-(int)(c1+c0))%255;
	*yloc = (u_char) (c1 < 0? c1 + 255 : c1);

	IFDEBUG(D_CHKSUM)
		printf("gen csum end \n");
	ENDDEBUG
}

struct mbuf  *
m_append(head, m)
	struct mbuf *head, *m;
{
	register struct mbuf *n;

	if (m == 0)
		return head;
	if (head == 0)
		return m;
	n = head;
	while (n->m_next)
		n = n->m_next;
	n->m_next = m;
	return head;
}
/*
 * FUNCTION:	m_datalen
 *
 * PURPOSE:		returns length of the mbuf chain.
 * 				used all over the iso code.
 *
 * RETURNS:		integer
 *
 * SIDE EFFECTS: none
 *
 * NOTES:
 */

int
m_datalen (morig)
	struct mbuf *morig;
{
	int	s = splimp();
	register struct mbuf *n=morig;
	register int datalen = 0;

	if( morig == (struct mbuf *)0)
		return 0;
	for(;;) {
		datalen += n->m_len;
		if (n->m_next == (struct mbuf *)0 ) {
			break;
		}
		n = n->m_next;
	}
	splx(s);
	return datalen;
}

int
m_compress(in, out)
	register struct mbuf *in, **out;
{
	register 	int datalen = 0;
	int	s = splimp();

	if( in->m_next == MNULL ) {
		*out = in;
		IFDEBUG(D_REQUEST)
			printf("m_compress returning 0x%x: A\n", in->m_len);
		ENDDEBUG
		splx(s);
		return in->m_len;
	}
	MGET((*out), M_DONTWAIT, MT_DATA);
	if((*out) == MNULL) {
		*out = in;
		IFDEBUG(D_REQUEST)
			printf("m_compress returning -1: B\n");
		ENDDEBUG
		splx(s);
		return -1;
	}
	(*out)->m_len = 0;
	(*out)->m_act = MNULL;

	while (in) {
		IFDEBUG(D_REQUEST)
			printf("m_compress in 0x%x *out 0x%x\n", in, *out);
			printf("m_compress in: len 0x%x, off 0x%x\n", in->m_len, in->m_data);
			printf("m_compress *out: len 0x%x, off 0x%x\n", (*out)->m_len,
				(*out)->m_data);
		ENDDEBUG
		if (in->m_flags & M_EXT) {
			ASSERT(in->m_len == 0);
		}
		if ( in->m_len == 0) {
			in = in->m_next;
			continue;
		}
		if (((*out)->m_flags & M_EXT) == 0) {
			int len;

			len = M_TRAILINGSPACE(*out);
			len = MIN(len, in->m_len);
			datalen += len;

			IFDEBUG(D_REQUEST)
				printf("m_compress copying len %d\n", len);
			ENDDEBUG
			bcopy(mtod(in, caddr_t), mtod((*out), caddr_t) + (*out)->m_len,
						(unsigned)len);

			(*out)->m_len += len;
			in->m_len -= len;
			continue;
		} else {
			/* (*out) is full */
			if(( (*out)->m_next = m_get(M_DONTWAIT, MT_DATA) ) == MNULL) {
				m_freem(*out);
				*out = in;
				IFDEBUG(D_REQUEST)
					printf("m_compress returning -1: B\n");
				ENDDEBUG
				splx(s);
				return -1;
			}
			(*out)->m_len = 0;
			(*out)->m_act = MNULL;
			*out = (*out)->m_next;
		}
	}
	m_freem(in);
	IFDEBUG(D_REQUEST)
		printf("m_compress returning 0x%x: A\n", datalen);
	ENDDEBUG
	splx(s);
	return datalen;
}