-- in - IP address in decimal format with dots. Ex: '127.0.0.1'
-- out - biginteger, that represents IP address.
create function ip2num(ip varchar) returns bigint as $$
declare 
  w text; 
  x text;
  y text;
  z text; 
  l   integer;
  cp  integer;
  cp2 integer; 
begin

  l := char_length(ip);
  if l > 15 then 
    return null;
  end if;  
  if l < 7 then 
    return null;
  end if;
  
  -- 192.168.1.1

  cp  := 1; 
  cp2 := position('.' in ip); -- 4
  l   := cp2 - cp; -- 3
  w   := substring(ip from cp for l); -- '192'

  cp  := cp2 + 1; -- 5
  cp2 := cp  + position('.' in substring(ip from cp)) - 1; -- 8
  l   := cp2 - cp; -- 8-5=3
  x   := substring(ip from cp for l); -- 168
  
  cp  := cp2 + 1; 
  cp2 := cp  + position('.' in substring(ip from cp)) - 1; 
  l   := cp2 - cp; 
  y   := substring(ip from cp for l); 

  z   := substring(ip from cp2 + 1);

  return 16777216 * cast(w as bigint) + 
            65536 * cast(x as bigint) + 
              256 * cast(y as bigint) + 
                    cast(z as bigint);
end;
$$ language plpgsql immutable;