IPv4 Address Bitmap

gistfile1.c

// bitmap of observed IP addresses
static uint64_t *ip_seen = NULL;
static const int IP_SEEN_SIZE = 0x4000000; // == 2^32/64

// check if we've received a response from this address previously
static inline int check_ip(uint32_t ip)
{
	return (ip_seen[ip >> 6] >> (ip & 0x3F)) & 1;
}

// set that we've received a response from the address
static inline void set_ip(uint32_t ip)
{
	ip_seen[ip >> 6] |= (uint64_t)1 << (ip & 0x3F);
}


inline uint32_t ipconv(char *ip) 
{
	struct in_addr a;
	inet_aton(ip, &a);
	return (uint32_t) a.s_addr;

}

int main(void)
{
	ip_seen = calloc(IP_SEEN_SIZE, sizeof(uint64_t));
	assert(ip_seen);
  	for (...) {
    		uint32_t ip = ...
  		if (!check_ip(ip)) {
			set_ip(ip);
			fprintf(out, "%s\n", line);
		}
  	}
}