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/*

 * Copyright (c) 1988, 1992, 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.

 *

 *        @(#)in_cksum.c        8.1 (Berkeley) 6/10/93

 * in_cksum.c,v 1.2 1994/08/02 07:48:16 davidg Exp

 */

#include <slirp.h>

/*

 * Checksum routine for Internet Protocol family headers (Portable Version).

 *

 * This routine is very heavily used in the network

 * code and should be modified for each CPU to be as fast as possible.

 * 

 * XXX Since we will never span more than 1 mbuf, we can optimise this

 */

#define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)

#define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}

int cksum(struct mbuf *m, int len)

{

        register u_int16_t *w;

        register int sum = 0;

        register int mlen = 0;

        int byte_swapped = 0;

        union {

                u_int8_t        c[2];

                u_int16_t        s;

        } s_util;

        union {

                u_int16_t s[2];

                u_int32_t l;

        } l_util;

        if (m->m_len == 0)

           goto cont;

        w = mtod(m, u_int16_t *);

        mlen = m->m_len;

        if (len < mlen)

           mlen = len;

        len -= mlen;

        /*

         * Force to even boundary.

         */

        if ((1 & (long) w) && (mlen > 0)) {

                REDUCE;

                sum <<= 8;

                s_util.c[0] = *(u_int8_t *)w;

                w = (u_int16_t *)((int8_t *)w + 1);

                mlen--;

                byte_swapped = 1;

        }

        /*

         * Unroll the loop to make overhead from

         * branches &c small.

         */

        while ((mlen -= 32) >= 0) {

                sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];

                sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];

                sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];

                sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];

                w += 16;

        }

        mlen += 32;

        while ((mlen -= 8) >= 0) {

                sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];

                w += 4;

        }

        mlen += 8;

        if (mlen == 0 && byte_swapped == 0)

           goto cont;

        REDUCE;

        while ((mlen -= 2) >= 0) {

                sum += *w++;

        }

        if (byte_swapped) {

                REDUCE;

                sum <<= 8;

                byte_swapped = 0;

                if (mlen == -1) {

                        s_util.c[1] = *(u_int8_t *)w;

                        sum += s_util.s;

                        mlen = 0;

                } else

                   mlen = -1;

        } else if (mlen == -1)

           s_util.c[0] = *(u_int8_t *)w;

cont:

#ifdef DEBUG

        if (len) {

                DEBUG_ERROR((dfd, "cksum: out of data\n"));

                DEBUG_ERROR((dfd, " len = %d\n", len));

        }

#endif

        if (mlen == -1) {

                /* The last mbuf has odd # of bytes. Follow the

                 standard (the odd byte may be shifted left by 8 bits

                           or not as determined by endian-ness of the machine) */

                s_util.c[1] = 0;

                sum += s_util.s;

        }

        REDUCE;

        return (~sum & 0xffff);

}