in_cksum.c revision 331643 
1/*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1988, 1992, 1993
5 *	The Regents of the University of California.  All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 * 4. Neither the name of the University nor the names of its contributors
16 *    may be used to endorse or promote products derived from this software
17 *    without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * SUCH DAMAGE.
30 *
31 *	@(#)in_cksum.c	8.1 (Berkeley) 6/10/93
32 */
33
34#include <sys/cdefs.h>
35__FBSDID("$FreeBSD: stable/11/sys/netinet/in_cksum.c 331643 2018-03-27 18:52:27Z dim $");
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(struct mbuf *m, int len)
52{
53	u_short *w;
54	int sum = 0;
55	int mlen = 0;
56	int byte_swapped = 0;
57
58	union {
59		char	c[2];
60		u_short	s;
61	} s_util;
62	union {
63		u_short s[2];
64		long	l;
65	} l_util;
66
67	for (;m && len; m = m->m_next) {
68		if (m->m_len == 0)
69			continue;
70		w = mtod(m, u_short *);
71		if (mlen == -1) {
72			/*
73			 * The first byte of this mbuf is the continuation
74			 * of a word spanning between this mbuf and the
75			 * last mbuf.
76			 *
77			 * s_util.c[0] is already saved when scanning previous
78			 * mbuf.
79			 */
80			s_util.c[1] = *(char *)w;
81			sum += s_util.s;
82			w = (u_short *)((char *)w + 1);
83			mlen = m->m_len - 1;
84			len--;
85		} else
86			mlen = m->m_len;
87		if (len < mlen)
88			mlen = len;
89		len -= mlen;
90		/*
91		 * Force to even boundary.
92		 */
93		if ((1 & (uintptr_t) w) && (mlen > 0)) {
94			REDUCE;
95			sum <<= 8;
96			s_util.c[0] = *(u_char *)w;
97			w = (u_short *)((char *)w + 1);
98			mlen--;
99			byte_swapped = 1;
100		}
101		/*
102		 * Unroll the loop to make overhead from
103		 * branches &c small.
104		 */
105		while ((mlen -= 32) >= 0) {
106			sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
107			sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
108			sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
109			sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
110			w += 16;
111		}
112		mlen += 32;
113		while ((mlen -= 8) >= 0) {
114			sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
115			w += 4;
116		}
117		mlen += 8;
118		if (mlen == 0 && byte_swapped == 0)
119			continue;
120		REDUCE;
121		while ((mlen -= 2) >= 0) {
122			sum += *w++;
123		}
124		if (byte_swapped) {
125			REDUCE;
126			sum <<= 8;
127			byte_swapped = 0;
128			if (mlen == -1) {
129				s_util.c[1] = *(char *)w;
130				sum += s_util.s;
131				mlen = 0;
132			} else
133				mlen = -1;
134		} else if (mlen == -1)
135			s_util.c[0] = *(char *)w;
136	}
137	if (len)
138		printf("cksum: out of data\n");
139	if (mlen == -1) {
140		/* The last mbuf has odd # of bytes. Follow the
141		   standard (the odd byte may be shifted left by 8 bits
142		   or not as determined by endian-ness of the machine) */
143		s_util.c[1] = 0;
144		sum += s_util.s;
145	}
146	REDUCE;
147	return (~sum & 0xffff);
148}
149