<?php                                                                            
$cache = [];                                                                     
$max = pow(2, 16); // 50% chance of collision after 2^16 tries                   
 
for ($i = 1; $i < $max; $i++) {                                                  
    $n = rand();                                                                 
    $hashsum = crc32($n);                                                        
 
    if (isset($cache[$hashsum])) {                                               
        print "Collision: crc32($n) == crc32({$cache[$hashsum]}) == $hashsum\n"; 
    } else {                                                                     
        $cache[$hashsum] = $n;                                                   
    }                                                                            
}             

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