86 lines
3.0 KiB
C
86 lines
3.0 KiB
C
/*-
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* Copyright (c) 1985, 1993 The Regents of the University of California.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#ifndef lint
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static char sccsid[] = "@(#)cksum.c 5.2 (Berkeley) 5/11/93";
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#endif /* not lint */
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#ifdef sgi
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#ident "$Revision: 1.5 $"
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#endif
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#include <sys/types.h>
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/*
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* I N _ C K S U M
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*
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* Checksum routine for Internet Protocol family headers (C Version)
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*
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* There is no profit in a specialized version of the checksum
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* function for any machine where int's are 32 bits and shorts are 16.
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*
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* All timed packets are smaller than 32K shorts, so there is no need to
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* worry about carries except at the end.
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*/
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int
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in_cksum(u_short *addr, int len)
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{
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register int nleft = len;
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register u_short *w = addr;
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register u_short answer;
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register int sum = 0;
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/*
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* Our algorithm is simple, using a 32 bit accumulator (sum),
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* we add sequential 16 bit words to it, and at the end, fold
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* back all the carry bits from the top 16 bits into the lower
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* 16 bits.
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*/
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while( nleft > 1 ) {
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sum += *w++;
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nleft -= 2;
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}
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/* mop up an odd byte, if necessary */
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if( nleft == 1 )
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sum += (*(u_char *)w) << 8;
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/*
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* add back carry outs from top 16 bits to low 16 bits
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*/
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sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */
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sum += (sum >> 16); /* add carry */
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answer = ~sum; /* truncate to 16 bits */
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return (answer);
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}
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