Hash collision benchmark

hash_collisions.php

#!/usr/bin/env php
<?php

//
// Benchmark of adding items to associative array with hash collisions.
//

// generate all permutations of $substrings with $count number of concatenations
function do_generate_strings(array $substrings, array &$strings, $prefix, $count) {
	if ($count == 1) {
		foreach ($substrings as $s) {
			$strings[] = "$prefix$s";
		}
		return;
	}

	foreach ($substrings as $s) {
		do_generate_strings($substrings, $strings, "$prefix$s", $count - 1);
	}
}

function generate_strings($count) {
	$strings = array();
	$colliding_substrings = array('ar', 'bQ', 'c0');
	do_generate_strings($colliding_substrings, $strings, '', $count);
	return $strings;
}

$strings = generate_strings(10);

echo "n, duriation (s), memory\n";
for ($n = 0; $n <= count($strings); $n += 1000) {
	$mem_start = memory_get_usage();
	$time_start = microtime(true);

	$params = array();
	for ($i = 0; $i < $n; $i++) {
		$params[$strings[$i]] = '';
	}

	$time_end = microtime(true);
	$mem_end = memory_get_usage();
	$time = $time_end - $time_start;
	$mem = $mem_end - $mem_start;
	echo "$n, $time, $mem\n";
}

?>