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85 lines
2.7 KiB
C
85 lines
2.7 KiB
C
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/*-
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* SPDX-License-Identifier: BSD-3-Clause
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*
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* Copyright (c) 1989, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* Mike Muuss.
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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. 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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#include <string.h>
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#include "utils.h"
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/*
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* in_cksum --
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* Checksum routine for Internet Protocol family headers (C Version)
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*/
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u_short
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in_cksum(u_char *addr, int len)
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{
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int nleft, sum;
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u_char *w;
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union {
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u_short us;
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u_char uc[2];
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} last;
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u_short answer;
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nleft = len;
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sum = 0;
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w = addr;
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/*
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* Our algorithm is simple, using a 32 bit accumulator (sum), we add
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* sequential 16 bit words to it, and at the end, fold back all the
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* carry bits from the top 16 bits into the lower 16 bits.
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*/
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while (nleft > 1) {
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u_short data;
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memcpy(&data, w, sizeof(data));
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sum += data;
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w += sizeof(data);
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nleft -= sizeof(data);
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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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last.uc[0] = *w;
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last.uc[1] = 0;
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sum += last.us;
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}
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/* add back carry outs from top 16 bits to low 16 bits */
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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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