2 * IP checksumming functions.
3 * (c) 2008 Gerd Hoffmann <kraxel@redhat.com>
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; under version 2 of the License.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301 USA
25 uint32_t net_checksum_add(int len, uint8_t *buf)
30 for (i = 0; i < len; i++) {
32 sum += (uint32_t)buf[i];
34 sum += (uint32_t)buf[i] << 8;
39 uint16_t net_checksum_finish(uint32_t sum)
42 sum = (sum & 0xFFFF)+(sum >> 16);
46 uint16_t net_checksum_tcpudp(uint16_t length, uint16_t proto,
47 uint8_t *addrs, uint8_t *buf)
51 sum += net_checksum_add(length, buf); // payload
52 sum += net_checksum_add(8, addrs); // src + dst address
53 sum += proto + length; // protocol & length
54 return net_checksum_finish(sum);
57 void net_checksum_calculate(uint8_t *data, int length)
59 int hlen, plen, proto, csum_offset;
62 if ((data[14] & 0xf0) != 0x40)
63 return; /* not IPv4 */
64 hlen = (data[14] & 0x0f) * 4;
65 plen = (data[16] << 8 | data[17]) - hlen;
79 if (plen < csum_offset+2)
82 data[14+hlen+csum_offset] = 0;
83 data[14+hlen+csum_offset+1] = 0;
84 csum = net_checksum_tcpudp(plen, proto, data+14+12, data+14+hlen);
85 data[14+hlen+csum_offset] = csum >> 8;
86 data[14+hlen+csum_offset+1] = csum & 0xff;