/*
 * 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. 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/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 SLIRPmbuf, 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 SLIRPmbuf *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 & (off_t)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 SLIRP_DEBUG
        if (len) {
                DEBUG_ERROR((dfd, "cksum: out of data\n"));
                DEBUG_ERROR((dfd, " len = %d\n", len));
        }
#endif
        if (mlen == -1) {
                /* The last SLIRPmbuf 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);
}
