Simple PHP cache

cache.php

<?php
$cache = json_decode(file_get_contents("cache.json"), true);
function get($url, $max_age=1){
	global $cache;
	$hash = crc32($url);
	if(isset($cache[$hash])){
		if(time() - $cache[$hash] > $max_age)
			return cache_add($url, $hash);
		return file_get_contents("cache/" . $hash . ".txt");
	}else
		return cache_add($url, $hash);
}function cache_add($url, $hash){
	global $cache;
	$data = file_get_contents($url);
	file_put_contents("cache/" . $hash . ".txt", $data);
	$cache[$hash] = time();
	file_put_contents("cache.json", json_encode($cache));
	return $data;
}
?>