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run code in 300+ PHP versions simultaneously
<?php $stop = microtime(true) + 1; $i = 0; while(microtime(true) < $stop){ if(++$i % 1000000 == 0){ echo $i / 1000000, "<br/>\n"; } } echo "done.<br/>\n";

preferences:
42.9 ms | 404 KiB | 5 Q