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/*
* 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 or later 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, see <http://www.gnu.org/licenses/>.
*/
#include "net/checksum.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;
}
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