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Annotation of qemu/net/checksum.c, revision 1.1.1.2

1.1       root        1: /*
                      2:  *  IP checksumming functions.
                      3:  *  (c) 2008 Gerd Hoffmann <[email protected]>
                      4:  *
                      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
1.1.1.2 ! root        7:  *  the Free Software Foundation; under version 2 or later of the License.
1.1       root        8:  *
                      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.
                     13:  *
                     14:  *  You should have received a copy of the GNU General Public License
                     15:  *  along with this program; if not, see <http://www.gnu.org/licenses/>.
                     16:  */
                     17: 
                     18: #include "net/checksum.h"
                     19: 
                     20: #define PROTO_TCP  6
                     21: #define PROTO_UDP 17
                     22: 
                     23: uint32_t net_checksum_add(int len, uint8_t *buf)
                     24: {
                     25:     uint32_t sum = 0;
                     26:     int i;
                     27: 
                     28:     for (i = 0; i < len; i++) {
                     29:        if (i & 1)
                     30:            sum += (uint32_t)buf[i];
                     31:        else
                     32:            sum += (uint32_t)buf[i] << 8;
                     33:     }
                     34:     return sum;
                     35: }
                     36: 
                     37: uint16_t net_checksum_finish(uint32_t sum)
                     38: {
                     39:     while (sum>>16)
                     40:        sum = (sum & 0xFFFF)+(sum >> 16);
                     41:     return ~sum;
                     42: }
                     43: 
                     44: uint16_t net_checksum_tcpudp(uint16_t length, uint16_t proto,
                     45:                              uint8_t *addrs, uint8_t *buf)
                     46: {
                     47:     uint32_t sum = 0;
                     48: 
                     49:     sum += net_checksum_add(length, buf);         // payload
                     50:     sum += net_checksum_add(8, addrs);            // src + dst address
                     51:     sum += proto + length;                        // protocol & length
                     52:     return net_checksum_finish(sum);
                     53: }
                     54: 
                     55: void net_checksum_calculate(uint8_t *data, int length)
                     56: {
                     57:     int hlen, plen, proto, csum_offset;
                     58:     uint16_t csum;
                     59: 
                     60:     if ((data[14] & 0xf0) != 0x40)
                     61:        return; /* not IPv4 */
                     62:     hlen  = (data[14] & 0x0f) * 4;
                     63:     plen  = (data[16] << 8 | data[17]) - hlen;
                     64:     proto = data[23];
                     65: 
                     66:     switch (proto) {
                     67:     case PROTO_TCP:
                     68:        csum_offset = 16;
                     69:        break;
                     70:     case PROTO_UDP:
                     71:        csum_offset = 6;
                     72:        break;
                     73:     default:
                     74:        return;
                     75:     }
                     76: 
                     77:     if (plen < csum_offset+2)
                     78:        return;
                     79: 
                     80:     data[14+hlen+csum_offset]   = 0;
                     81:     data[14+hlen+csum_offset+1] = 0;
                     82:     csum = net_checksum_tcpudp(plen, proto, data+14+12, data+14+hlen);
                     83:     data[14+hlen+csum_offset]   = csum >> 8;
                     84:     data[14+hlen+csum_offset+1] = csum & 0xff;
                     85: }

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