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/*
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 * Copyright (c) 1988, 1992, 1993
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 *        The Regents of the University of California.  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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 *        @(#)in_cksum.c        8.1 (Berkeley) 6/10/93
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 * in_cksum.c,v 1.2 1994/08/02 07:48:16 davidg Exp
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 */
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#include <slirp.h>
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/*
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 * Checksum routine for Internet Protocol family headers (Portable Version).
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 *
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 * This routine is very heavily used in the network
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 * code and should be modified for each CPU to be as fast as possible.
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 *
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 * XXX Since we will never span more than 1 mbuf, we can optimise this
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 */
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#define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
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#define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
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int cksum(struct mbuf *m, int len)
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{
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        register u_int16_t *w;
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        register int sum = 0;
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        register int mlen = 0;
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        int byte_swapped = 0;
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        union {
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                u_int8_t        c[2];
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                u_int16_t        s;
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        } s_util;
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        union {
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                u_int16_t s[2];
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                u_int32_t l;
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        } l_util;
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        if (m->m_len == 0)
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           goto cont;
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        w = mtod(m, u_int16_t *);
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        mlen = m->m_len;
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        if (len < mlen)
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           mlen = len;
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        len -= mlen;
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        /*
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         * Force to even boundary.
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         */
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        if ((1 & (long) w) && (mlen > 0)) {
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                REDUCE;
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                sum <<= 8;
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                s_util.c[0] = *(u_int8_t *)w;
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                w = (u_int16_t *)((int8_t *)w + 1);
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                mlen--;
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                byte_swapped = 1;
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        }
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        /*
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         * Unroll the loop to make overhead from
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         * branches &c small.
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         */
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        while ((mlen -= 32) >= 0) {
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                sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
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                sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
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                sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
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                sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
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                w += 16;
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        }
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        mlen += 32;
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        while ((mlen -= 8) >= 0) {
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                sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
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                w += 4;
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        }
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        mlen += 8;
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        if (mlen == 0 && byte_swapped == 0)
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           goto cont;
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        REDUCE;
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        while ((mlen -= 2) >= 0) {
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                sum += *w++;
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        }
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        if (byte_swapped) {
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                REDUCE;
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                sum <<= 8;
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                byte_swapped = 0;
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                if (mlen == -1) {
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                        s_util.c[1] = *(u_int8_t *)w;
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                        sum += s_util.s;
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                        mlen = 0;
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                } else
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                   mlen = -1;
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        } else if (mlen == -1)
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           s_util.c[0] = *(u_int8_t *)w;
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cont:
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#ifdef DEBUG
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        if (len) {
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                DEBUG_ERROR((dfd, "cksum: out of data\n"));
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                DEBUG_ERROR((dfd, " len = %d\n", len));
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        }
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#endif
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        if (mlen == -1) {
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                /* The last mbuf has odd # of bytes. Follow the
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                 standard (the odd byte may be shifted left by 8 bits
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                           or not as determined by endian-ness of the machine) */
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                s_util.c[1] = 0;
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                sum += s_util.s;
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        }
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        REDUCE;
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        return (~sum & 0xffff);
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}