netmask_to_cidr.php

<?php

$netmtocidr = array(
'255.255.255.255' => 32,
'255.255.255.254' => 31,
'255.255.255.252' => 30,
'255.255.255.248' => 29,
'255.255.255.240' => 28,
'255.255.255.224' => 27,
'255.255.255.192' => 26,
'255.255.255.128' => 25,
'255.255.255.0' => 24,
'255.255.254.0' => 23,
'255.255.252.0' => 22,
'255.255.248.0' => 21,
'255.255.240.0' => 20,
'255.255.224.0' => 19,
'255.255.192.0' => 18,
'255.255.128.0' => 17,
'255.255.0.0' => 16,
'255.254.0.0' => 15,
'255.252.0.0' => 14,
'255.248.0.0' => 13,
'255.240.0.0' => 12,
'255.224.0.0' => 11,
'255.192.0.0' => 10,
'255.128.0.0' => 9,
'255.0.0.0' => 8,
'254.0.0.0' => 7,
'252.0.0.0' => 6,
'248.0.0.0' => 5,
'240.0.0.0' => 4,
'224.0.0.0' => 3,
'192.0.0.0' => 2,
'128.0.0.0' => 1
);

echo $netmtocidr['255.255.224.0']; // 19