36 lines
732 B
C
36 lines
732 B
C
#include "packet.h"
|
|
|
|
// shamelessly copied from:
|
|
// http://www.roman10.net/how-to-calculate-iptcpudp-checksumpart-2-implementation/
|
|
unsigned short compute_checksum(unsigned short *addr, unsigned int count) {
|
|
|
|
unsigned long sum = 0;
|
|
|
|
while (count > 1) {
|
|
sum += * addr++;
|
|
count -= 2;
|
|
}
|
|
|
|
//if any bytes left, pad the bytes and add
|
|
if(count > 0) {
|
|
sum += ((*addr)&htons(0xFF00));
|
|
}
|
|
|
|
//Fold sum to 16 bits: add carrier to result
|
|
while (sum>>16) {
|
|
sum = (sum & 0xffff) + (sum >> 16);
|
|
}
|
|
|
|
//one's complement
|
|
sum = ~sum;
|
|
|
|
return ((unsigned short)sum);
|
|
|
|
}
|
|
|
|
void compute_ip_checksum(struct iphdr* pkt)
|
|
{
|
|
pkt->check = 0x0000;
|
|
pkt->check = compute_checksum( (unsigned short*) pkt, pkt->ihl * 4 );
|
|
}
|