/* $Id: cksum.c 76553 2019-01-01 01:45:53Z vboxsync $ */
/** @file
 * NAT - IP checksum generation.
 */

/*
 * Copyright (C) 2006-2019 Oracle Corporation
 *
 * This file is part of VirtualBox Open Source Edition (OSE), as
 * available from http://www.virtualbox.org. This file is free software;
 * you can redistribute it and/or modify it under the terms of the GNU
 * General Public License (GPL) as published by the Free Software
 * Foundation, in version 2 as it comes in the "COPYING" file of the
 * VirtualBox OSE distribution. VirtualBox OSE is distributed in the
 * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
 */

/*
 * This code is based on:
 *
 * 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)
        Log(("cksum: out of data: 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);
}