Source to i386/i386/in_cksum.c
/*-
* Copyright (c) 1990, 1993
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* from tahoe: in_cksum.c 1.2 86/01/05
* @(#)in_cksum.c 8.1 (Berkeley) 6/11/93
*/
#include <sys/param.h>
#include <sys/mbuf.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
/*
* Checksum routine for Internet Protocol family headers.
*
* This routine is very heavily used in the network
* code and should be modified for each CPU to be as fast as possible.
*
* This implementation is 386 version.
*/
#undef ADDCARRY
#define ADDCARRY(sum) { \
if (sum & 0xffff0000) { \
sum &= 0xffff; \
sum++; \
} \
}
in_cksum(m, len)
register struct mbuf *m;
register int len;
{
union word {
char c[2];
u_short s;
} u;
register u_short *w;
register int sum = 0;
register int mlen = 0;
for (;m && len; m = m->m_next) {
if (m->m_len == 0)
continue;
w = mtod(m, u_short *);
if (mlen == -1) {
/*
* The first byte of this mbuf is the continuation
* of a word spanning between this mbuf and the
* last mbuf.
*/
/* u.c[0] is already saved when scanning previous
* mbuf.
*/
u.c[1] = *(u_char *)w;
sum += u.s;
ADDCARRY(sum);
w = (u_short *)((char *)w + 1);
mlen = m->m_len - 1;
len--;
} else
mlen = m->m_len;
if (len < mlen)
mlen = len;
len -= mlen;
/*
* add by words.
*/
while ((mlen -= 2) >= 0) {
if ((int)w & 0x1) {
/* word is not aligned */
u.c[0] = *(char *)w;
u.c[1] = *((char *)w+1);
sum += u.s;
w++;
} else
sum += *w++;
ADDCARRY(sum);
}
if (mlen == -1)
/*
* This mbuf has odd number of bytes.
* There could be a word split betwen
* this mbuf and the next mbuf.
* Save the last byte (to prepend to next mbuf).
*/
u.c[0] = *(u_char *)w;
}
if (len)
printf("cksum: out of data\n");
if (mlen == -1) {
/* The last mbuf has odd # of bytes. Follow the
standard (the odd byte is shifted left by 8 bits) */
u.c[1] = 0;
sum += u.s;
ADDCARRY(sum);
}
return (~sum & 0xffff);
}