SQL function to convert an integer into an IP address.  Note: 255 could be
replaced with X'FF'::integer if that makes more sense to you.

CREATE OR REPLACE FUNCTION long_to_ip ( integer ) RETURNS text AS '
	SELECT (($1 >> 24) & 255)::text || \'.\' || 
		(($1 >> 16) & 255)::text || \'.\' || 
		(($1 >> 8) & 255)::text || \'.\' || 
		($1 & 255)::text;
' LANGUAGE SQL
IMMUTABLE
RETURNS NULL ON NULL INPUT;

---------------------------------------------------------------------------

Here's a convenience C function to convert from IPs to integers.  See the
PostgreSQL docs for directions for compiling for your specific platform.  


#include "postgres.h"
#include "fmgr.h"
#include <stdlib.h>
#include <string.h>

PG_FUNCTION_INFO_V1(ip_to_long);

Datum
ip_to_long(PG_FUNCTION_ARGS)
{
    text*   text_ip_in = PG_GETARG_TEXT_P(0);
    int32   longIP = 0;
    int     octets[4] = {0, 0, 0, 0};
    char    textIP[16] = {0,0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,0};
    char*   ipAddress = textIP;
    char*   dot;
    int     octetIdx;
    
    /* put input text into textIP char array */
    memcpy( (void*) textIP, (void*) VARDATA(text_ip_in), 15 );
    
    /* put each class into octets array */
    for( octetIdx = 0; octetIdx < 4; octetIdx++ )
    {
        dot = strchr( ipAddress, '.' );
        if (dot)
        {
            *dot = '\0';
            octets[octetIdx] = atoi(ipAddress);
            ipAddress = dot + 1;
        } else {
            /* dot not found, must be last octet */
            octets[octetIdx] = atoi(ipAddress);
            break;
        }
    }
    
    /* put octets into long IP */
    longIP = (octets[0] & 0xFF) << 24 | 
              (octets[1] & 0xFF) << 16 | 
              (octets[2] & 0xFF) << 8  | 
              (octets[3] & 0xFF);
    
    PG_RETURN_INT32(longIP);
}


Once compiled, put the library in the correct place and create a PostgreSQL
function like this.  Note that you must be logged in as superuser to create the
function.

CREATE OR REPLACE FUNCTION ip_to_long ( text ) RETURNS integer AS 
	'$libdir/ip_to_long'
LANGUAGE C
IMMUTABLE
RETURNS NULL ON NULL INPUT;