/*

 *  IP checksumming functions.

 *  (c) 2008 Gerd Hoffmann <kraxel@redhat.com>

 *

 *  This program is free software; you can redistribute it and/or modify

 *  it under the terms of the GNU General Public License as published by

 *  the Free Software Foundation; under version 2 of the License.

 *

 *  This program is distributed in the hope that it will be useful,

 *  but WITHOUT ANY WARRANTY; without even the implied warranty of

 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 *  GNU General Public License for more details.

 *

 *  You should have received a copy of the GNU General Public License

 *  along with this program; if not, write to the Free Software

 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 */

#include "hw/hw.h"

#include "net.h"

#define PROTO_TCP  6

#define PROTO_UDP 17

uint32_t net_checksum_add(int len, uint8_t *buf)

{

    uint32_t sum = 0;

    int i;

    for (i = 0; i < len; i++) {

	if (i & 1)

	    sum += (uint32_t)buf[i];

	else

	    sum += (uint32_t)buf[i] << 8;

    }

    return sum;

}

uint16_t net_checksum_finish(uint32_t sum)

{

    while (sum>>16)

	sum = (sum & 0xFFFF)+(sum >> 16);

    return ~sum;

}

uint16_t net_checksum_tcpudp(uint16_t length, uint16_t proto,

                             uint8_t *addrs, uint8_t *buf)

{

    uint32_t sum = 0;

    sum += net_checksum_add(length, buf);         // payload

    sum += net_checksum_add(8, addrs);            // src + dst address

    sum += proto + length;                        // protocol & length

    return net_checksum_finish(sum);

}

void net_checksum_calculate(uint8_t *data, int length)

{

    int hlen, plen, proto, csum_offset;

    uint16_t csum;

    if ((data[14] & 0xf0) != 0x40)

	return; /* not IPv4 */

    hlen  = (data[14] & 0x0f) * 4;

    plen  = (data[16] << 8 | data[17]) - hlen;

    proto = data[23];

    switch (proto) {

    case PROTO_TCP:

	csum_offset = 16;

	break;

    case PROTO_UDP:

	csum_offset = 6;

	break;

    default:

	return;

    }

    if (plen < csum_offset+2)

	return;

    data[14+hlen+csum_offset]   = 0;

    data[14+hlen+csum_offset+1] = 0;

    csum = net_checksum_tcpudp(plen, proto, data+14+12, data+14+hlen);

    data[14+hlen+csum_offset]   = csum >> 8;

    data[14+hlen+csum_offset+1] = csum & 0xff;

}