in_cksum.c revision 50477 
1/*
2 * Copyright (c) 1988, 1992, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 * 3. All advertising materials mentioning features or use of this software
14 *    must display the following acknowledgement:
15 *	This product includes software developed by the University of
16 *	California, Berkeley and its contributors.
17 * 4. Neither the name of the University nor the names of its contributors
18 *    may be used to endorse or promote products derived from this software
19 *    without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 *
33 *	@(#)in_cksum.c	8.1 (Berkeley) 6/10/93
34 * $FreeBSD: head/sys/netinet/in_cksum.c 50477 1999-08-28 01:08:13Z peter $
35 */
36
37#include <sys/param.h>
38#include <sys/mbuf.h>
39
40/*
41 * Checksum routine for Internet Protocol family headers (Portable Version).
42 *
43 * This routine is very heavily used in the network
44 * code and should be modified for each CPU to be as fast as possible.
45 */
46
47#define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
48#define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
49
50int
51in_cksum(m, len)
52	register struct mbuf *m;
53	register int len;
54{
55	register u_short *w;
56	register int sum = 0;
57	register int mlen = 0;
58	int byte_swapped = 0;
59
60	union {
61		char	c[2];
62		u_short	s;
63	} s_util;
64	union {
65		u_short s[2];
66		long	l;
67	} l_util;
68
69	for (;m && len; m = m->m_next) {
70		if (m->m_len == 0)
71			continue;
72		w = mtod(m, u_short *);
73		if (mlen == -1) {
74			/*
75			 * The first byte of this mbuf is the continuation
76			 * of a word spanning between this mbuf and the
77			 * last mbuf.
78			 *
79			 * s_util.c[0] is already saved when scanning previous
80			 * mbuf.
81			 */
82			s_util.c[1] = *(char *)w;
83			sum += s_util.s;
84			w = (u_short *)((char *)w + 1);
85			mlen = m->m_len - 1;
86			len--;
87		} else
88			mlen = m->m_len;
89		if (len < mlen)
90			mlen = len;
91		len -= mlen;
92		/*
93		 * Force to even boundary.
94		 */
95		if ((1 & (int) w) && (mlen > 0)) {
96			REDUCE;
97			sum <<= 8;
98			s_util.c[0] = *(u_char *)w;
99			w = (u_short *)((char *)w + 1);
100			mlen--;
101			byte_swapped = 1;
102		}
103		/*
104		 * Unroll the loop to make overhead from
105		 * branches &c small.
106		 */
107		while ((mlen -= 32) >= 0) {
108			sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
109			sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
110			sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
111			sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
112			w += 16;
113		}
114		mlen += 32;
115		while ((mlen -= 8) >= 0) {
116			sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
117			w += 4;
118		}
119		mlen += 8;
120		if (mlen == 0 && byte_swapped == 0)
121			continue;
122		REDUCE;
123		while ((mlen -= 2) >= 0) {
124			sum += *w++;
125		}
126		if (byte_swapped) {
127			REDUCE;
128			sum <<= 8;
129			byte_swapped = 0;
130			if (mlen == -1) {
131				s_util.c[1] = *(char *)w;
132				sum += s_util.s;
133				mlen = 0;
134			} else
135				mlen = -1;
136		} else if (mlen == -1)
137			s_util.c[0] = *(char *)w;
138	}
139	if (len)
140		printf("cksum: out of data\n");
141	if (mlen == -1) {
142		/* The last mbuf has odd # of bytes. Follow the
143		   standard (the odd byte may be shifted left by 8 bits
144		   or not as determined by endian-ness of the machine) */
145		s_util.c[1] = 0;
146		sum += s_util.s;
147	}
148	REDUCE;
149	return (~sum & 0xffff);
150}
151