/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (c) 1996-2001 by Sun Microsystems, Inc.
 * All rights reserved.
 */

#include <sys/types.h>
#include <strings.h>
#include <netinet/in.h>
#include "v4_sum_impl.h"

/*
 * RFC 768 pseudo header. Used in calculating UDP checksums.
 */
struct pseudo_udp {
        struct in_addr  src;
        struct in_addr  dst;
        uint8_t         notused;        /* always zero */
        uint8_t         proto;          /* protocol used */
        uint16_t        len;            /* UDP len */
};

/*
 * One's complement checksum of pseudo header, udp header, and data.
 * Must be MT SAFE.
 */
uint16_t
udp_chksum(struct udphdr *udph, const struct in_addr *src,
    const struct in_addr *dst, uint8_t proto)
{
        struct pseudo_udp       ck;
        uint16_t                *end_pseudo_hdr = (uint16_t *)(&ck + 1);
        uint16_t                *sp = (uint16_t *)&ck;
        uint_t                  sum = 0;
        uint16_t                cnt;

        /*
         * Start on the pseudo header. Note that pseudo_udp already takes
         * acount for the udphdr...
         */

        bzero(&ck, sizeof (ck));

        /* struct copies */
        ck.src   = *src;
        ck.dst   = *dst;
        ck.len   = udph->uh_ulen;
        ck.proto = proto;

        /*
         * If the packet is an odd length, zero the pad byte for checksum
         * purposes [doesn't hurt data]
         */

        cnt = ntohs(ck.len) + sizeof (ck);
        if (cnt & 1) {
                ((caddr_t)udph)[ntohs(udph->uh_ulen)] = '\0';
                cnt++;  /* make even */
        }

        for (cnt >>= 1; cnt != 0; cnt--) {

                sum += *sp++;
                if (sum >= BIT_WRAP) {
                        /* Wrap carries into low bit */
                        sum -= BIT_WRAP;
                        sum++;
                }

                /*
                 * If we've finished checking the pseudo-header, move
                 * onto the udp header and data.
                 */

                if (sp == end_pseudo_hdr)
                        sp = (uint16_t *)udph;
        }

        return (~sum == 0 ? ~0 : ~sum);
}