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/*-
* SPDX-License-Identifier: BSD-3-Clause
*
* Copyright (c) 1985, 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. 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.
*/
#ifndef lint
#if 0
static char sccsid[] = "@(#)cksum.c 8.1 (Berkeley) 6/6/93";
#endif
static const char rcsid[] =
"$FreeBSD$";
#endif /* not lint */
#include <sys/types.h>
/*
* I N _ C K S U M
*
* Checksum routine for Internet Protocol family headers (C Version)
*
* There is no profit in a specialized version of the checksum
* function for any machine where int's are 32 bits and shorts are 16.
*
* All timed packets are smaller than 32K shorts, so there is no need to
* worry about carries except at the end.
*/
int
in_cksum(u_short *addr, int len)
{
register int nleft = len;
register u_short *w = addr;
register u_short answer;
register int sum = 0;
/*
* Our algorithm is simple, using a 32 bit accumulator (sum),
* we add sequential 16 bit words to it, and at the end, fold
* back all the carry bits from the top 16 bits into the lower
* 16 bits.
*/
while( nleft > 1 ) {
sum += *w++;
nleft -= 2;
}
/* mop up an odd byte, if necessary */
if( nleft == 1 )
sum += (*(u_char *)w) << 8;
/*
* add back carry outs from top 16 bits to low 16 bits
*/
sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */
sum += (sum >> 16); /* add carry */
answer = ~sum; /* truncate to 16 bits */
return (answer);
}
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