CREATE OR REPLACE FUNCTION ip_num(ipaddress IN VARCHAR2) RETURN NUMBER AS  ipnum NUMBER := 0;  pos1  NUMBER := 0;  pos2  NUMBER := 0;BEGIN  FOR i IN 1 .. 3 LOOP    pos2  := to_number(instr(ipaddress, '.', 1, i));    ipnum := ipnum + to_number(substr(ipaddress, pos1 + 1, pos2 - pos1 - 1)) *             power(2, 8 * (4 - i));    pos1  := pos2;  END LOOP;  ipnum := ipnum + to_number(substr(ipaddress, pos1 + 1));  RETURN ipnum;exception  when others then    return null;END;/