net/dhcp/udp_sum.c

	udp_sum.c revision 7c478bd95313f5f23a4c958a745db2134aa03244
/*
 * 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.
 */

#pragma ident   "%Z%%M% %I% %E% SMI"

#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);
}