/*
 * Copyright (c) 1989, 1990, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Mike Muuss.
 *
 * 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.
 */
/*
UPDATED LICENSE:

July 22, 1999

To All Licensees, Distributors of Any Version of BSD:

As you know, certain of the Berkeley Software Distribution ("BSD") source
code files require that further distributions of products containing all or
portions of the software, acknowledge within their advertising materials
that such products contain software developed by UC Berkeley and its
contributors.

Specifically, the provision reads:

"     * 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."

Effective immediately, licensees and distributors are no longer required to
include the acknowledgement within advertising materials.  Accordingly, the
foregoing paragraph of those BSD Unix files containing it is hereby deleted
in its entirety.

William Hoskins
Director, Office of Technology Licensing
University of California, Berkeley

*/
/*
 * Borrowed from /usr/src/sbin/ping/ping.c
 */

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <arpa/inet.h>

union l_util {
        u_int16_t s[2];
        u_int32_t l;
};
union q_util {
        u_int16_t s[4];
        u_int32_t l[2];
        u_int64_t q;
};   

#define ADDCARRY(x)     if ((x) > 0xffff) (x) -= 0xffff

#define REDUCE16                                                          \
    {                                                                     \
        q_util.q = sum;                                                   \
        l_util.l = q_util.s[0] + q_util.s[1] + q_util.s[2] + q_util.s[3]; \
        sum = l_util.s[0] + l_util.s[1];                                  \
        ADDCARRY(sum);                                                    \
    }


u_short
in_pseudo(u_int32_t a, u_int32_t b, u_int32_t c)
{
        u_int64_t sum;
        union q_util q_util;
        union l_util l_util;
        
        sum = (u_int64_t) a + b + c;
        REDUCE16;
        return (sum);
}

u_short
in_cksum(addr, len)
        u_short *addr;
        int len;
{
        register int nleft = len;
        register u_short *w = addr;
        register int sum = 0;
        union {
                u_short us;
                u_char  uc[2];
        } last;
        u_short answer;

        /*
         * Our algorithm is simple, using a 32 bit accumulator (sum), we add
         * sequential 16 bit words to it, and at the end, fold back all the
         * carry bits from the top 16 bits into the lower 16 bits.
         */
        while (nleft > 1)  {
                sum += *w++;
                nleft -= 2;
        }

        /* mop up an odd byte, if necessary */
        if (nleft == 1) {
                last.uc[0] = *(u_char *)w;
                last.uc[1] = 0;
                sum += last.us;
        }

        /* add back carry outs from top 16 bits to low 16 bits */
        sum = (sum >> 16) + (sum & 0xffff);     /* add hi 16 to low 16 */
        sum += (sum >> 16);                     /* add carry */
        answer = ~sum;                          /* truncate to 16 bits */
        return(answer);
}