gistfile1.txt

uin16_t icmp6_checksum(const u_char *src_addr, const u_char *dest_addr, u_char *buff, size_t dlen, uint16_t *target) {
   uint16_t word16;
   uint32_t sum=0;
   size_t i;
   uint16_t pad;

   pad=dlen&1;
   for (i=0;i<16;i=i+2){
     word16 =((src_addr[i]<<8)&0xFF00)+(src_addr[i+1]&0xFF);
     sum += (uint32_t)word16;
   }
   for (i=0;i<16;i=i+2){
     word16 =((dest_addr[i]<<8)&0xFF00)+(dest_addr[i+1]&0xFF);
     sum += (uint32_t)word16;
   }
   sum += ntohl(dlen);
   sum += 0x003A; // ICMPv6
   for (i=0;i<dlen+pad;i=i+2){
     word16 =((buff[i]<<8)&0xff00)+(buff[i+1]&0xff);
     sum += (uint32_t)word16;
   }
   sum = (sum & 0xFFFF)+(sum >> 16);
   (*target) = htons((uint16_t)~sum);
   return *target;
}