Verifica Partita Iva

gistfile1.php

<?php
function checkVatIt($vat){
		
	if($vat == '') return false;
	if(strlen($vat) != 11) return false;
	if(!preg_match("/^[0-9]+$/", $vat)) return false;
	
	$vat = str_split($vat);
	$x = 0;
	$y = 0;
	
	$i = 1;
	foreach($vat as $n){
		if($i <= 10){
			if($i % 2 == 0){
				$y += ((2 * $n) > 9)? (2 * $n) - 9: 2 * $n;
			} else {
				$x += $n;
			}
		}
		$i++;
	}
	
	$t = ($x + $y) % 10;
	$control = (10 - $t) % 10;
	
	if( $vat[10] != $control){
		return false;
	}
	return true;
	
}