ipx_cksum.c revision 132779 
1/*
2 * Copyright (c) 1995, Mike Mitchell
3 * Copyright (c) 1982, 1992, 1993
4 *	The Regents of the University of California.  All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 *    notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 *    notice, this list of conditions and the following disclaimer in the
13 *    documentation and/or other materials provided with the distribution.
14 * 3. All advertising materials mentioning features or use of this software
15 *    must display the following acknowledgement:
16 *	This product includes software developed by the University of
17 *	California, Berkeley and its contributors.
18 * 4. Neither the name of the University nor the names of its contributors
19 *    may be used to endorse or promote products derived from this software
20 *    without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 *
34 *	@(#)ipx_cksum.c
35 */
36
37#include <sys/cdefs.h>
38__FBSDID("$FreeBSD: head/sys/netipx/ipx_cksum.c 132779 2004-07-28 06:58:23Z kan $");
39
40#include <sys/param.h>
41#include <sys/mbuf.h>
42#include <sys/libkern.h>
43
44#include <netipx/ipx.h>
45#include <netipx/ipx_var.h>
46
47
48#define SUMADV	sum += *w++
49
50u_short
51ipx_cksum(struct mbuf *m, int len) {
52	u_int32_t sum = 0;
53	u_char *w;
54	u_char oldtc;
55	int mlen, words;
56	struct ipx *ipx;
57	union {
58		u_char	b[2];
59		u_short	w;
60	} buf;
61
62	ipx = mtod(m, struct ipx*);
63	oldtc = ipx->ipx_tc;
64	ipx->ipx_tc = 0;
65	w = (u_char *)&ipx->ipx_len;
66	len -= 2;
67	mlen = 2;
68
69	for(;;) {
70		mlen = imin(m->m_len - mlen, len);
71		words = mlen / 2;
72		len -= mlen & ~1;
73		while (words >= 16) {
74			SUMADV;	SUMADV;	SUMADV;	SUMADV;
75			SUMADV;	SUMADV;	SUMADV;	SUMADV;
76			SUMADV;	SUMADV;	SUMADV;	SUMADV;
77			SUMADV;	SUMADV;	SUMADV;	SUMADV;
78			words -= 16;
79		}
80		while (words--)
81			SUMADV;
82		if (len == 0)
83			break;
84		mlen &= 1;
85		if (mlen) {
86			buf.b[0] = *w;
87			if (--len == 0) {
88				buf.b[1] = 0;
89				sum += buf.w;
90				break;
91			}
92		}
93		m = m->m_next;
94		if (m == NULL)
95			break;
96		w = mtod(m, u_char *);
97		if (mlen) {
98			buf.b[1] = *w;
99			sum += buf.w;
100			w++;
101			if (--len == 0)
102				break;
103		}
104	}
105
106	ipx->ipx_tc = oldtc;
107
108	sum = (sum & 0xffff) + (sum >> 16);
109	if (sum >= 0x10000)
110		sum++;
111	if (sum)
112		sum = ~sum;
113	return (sum);
114}
115