Check if a given ip is in a network

ip-in-range.php

<?php

/**
 * Check if a given ip is in a network
 * @param  string $ip    IP to check in IPV4 format eg. 127.0.0.1
 * @param  string $range IP/CIDR netmask eg. 127.0.0.0/24, also 127.0.0.1 is accepted and /32 assumed. Hostnames are accepted, too.
 * @return boolean true if the ip is in this range / false if not.
 */
function ip_in_range( $ip, $range ) {
    if (!preg_match('/^[0-9\.]+$/', $ip)) {
        $ip = gethostbyname($ip);
    }
    if (!preg_match('/^[0-9\.]+(\/[0-9]+)?$/', $range)) {
        $range = gethostbyname($range);
    }
    if ( strpos( $range, '/' ) == false ) {
        $range .= '/32';
    }
    // $range is in IP/CIDR format eg 127.0.0.1/24
    list( $range, $netmask ) = explode( '/', $range, 2 );
    $range_decimal = ip2long( $range );
    $ip_decimal = ip2long( $ip );
    $wildcard_decimal = pow( 2, ( 32 - $netmask ) ) - 1;
    $netmask_decimal = ~ $wildcard_decimal;
    return ( ( $ip_decimal & $netmask_decimal ) == ( $range_decimal & $netmask_decimal ) );
}