/*      $OpenBSD: in_cksum.c,v 1.9 2019/04/22 22:47:49 bluhm Exp $      */
/*      $NetBSD: in_cksum.c,v 1.11 1996/04/08 19:55:37 jonathan Exp $   */

/*
 * 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
 */

#include <sys/param.h>
#include <sys/mbuf.h>
#include <sys/systm.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.
 */

#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
in_cksum(struct mbuf *m, int len)
{
        uint16_t *w;
        int sum = 0;
        int mlen = 0;
        int byte_swapped = 0;
        union {
                uint8_t  c[2];
                uint16_t s;
        } s_util;
        union {
                uint16_t s[2];
                uint32_t l;
        } l_util;

        for (;m && len; m = m->m_next) {
                if (m->m_len == 0)
                        continue;
                w = mtod(m, uint16_t *);
                if (mlen == -1) {
                        /*
                         * The first byte of this mbuf is the continuation
                         * of a word spanning between this mbuf and the
                         * last mbuf.
                         *
                         * s_util.c[0] is already saved when scanning previous
                         * mbuf.
                         */
                        s_util.c[1] = *(uint8_t *)w;
                        sum += s_util.s;
                        w = (uint16_t *)((uint8_t *)w + 1);
                        mlen = m->m_len - 1;
                        len--;
                } else
                        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] = *(uint8_t *)w;
                        w = (uint16_t *)((uint8_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)
                        continue;
                REDUCE;
                while ((mlen -= 2) >= 0) {
                        sum += *w++;
                }
                if (byte_swapped) {
                        REDUCE;
                        sum <<= 8;
                        byte_swapped = 0;
                        if (mlen == -1) {
                                s_util.c[1] = *(uint8_t *)w;
                                sum += s_util.s;
                                mlen = 0;
                        } else
                                mlen = -1;
                } else if (mlen == -1)
                        s_util.c[0] = *(uint8_t *)w;
        }
        if (len)
                panic("%s: out of data, len %d", __func__, len);
        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);
}